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16 pages, 1721 KiB

Open AccessArticle

Location Planning for Dynamic Wireless Charging Systems for Electric Airport Passenger Buses

by Stefan Helber^1,*

, Justine Broihan¹

, Young Jae Jang²

, Peter Hecker³

and Thomas Feuerle³

¹ Department of Production Management, Leibniz Universitat Hannover, 30167 Hannover, Germany

² Department of Industrial and Systems Engineering, Korea Advanced Institute of Science and Technology, 305-701 Daejeoen, Korea

³ Institute of Flight Guidance, Technische Universitat Braunschweig, 38118 Braunschweig, Germany

Energies 2018, 11(2), 258; https://doi.org/10.3390/en11020258 - 23 Jan 2018

Cited by 38 | Viewed by 7355

Abstract

The majority of the ground vehicles operating on the airside parts of commercial airports are currently powered by diesel engines. These include vehicles such as apron buses, fuel trucks, and aircraft tractors. Hence, these vehicles contribute to the overall CO

_{2}

emissions of [...] Read more.

The majority of the ground vehicles operating on the airside parts of commercial airports are currently powered by diesel engines. These include vehicles such as apron buses, fuel trucks, and aircraft tractors. Hence, these vehicles contribute to the overall CO

_{2}

emissions of the aviation transport system and thus negatively influence its environmental footprint. To reduce this damaging environmental impact, these vehicles could potentially be electrified with on-board batteries as their energy sources. However, the conductive charging of such vehicles via stationary cable connections is rather time-consuming. A dynamic wireless charging system to supply public transportation passenger buses with electric energy while in motion has recently been installed on the Korea Advanced Institute of Science and Technology (KAIST) campus and in the Korean city of Gumi. In this paper, we study configuration problems related to the use of this technology to make airport operations more environmentally sustainable. We concentrate on the power supply for apron buses and analyze the location planning problems related to the distribution of the required power supply and the wireless charging units in the apron road system. To this end, we develop a formal optimization model and discuss the first numerical results. Full article

(This article belongs to the Special Issue Towards a Transformation to Sustainable Aviation Systems)

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19 pages, 4524 KiB

Open AccessArticle

Dynamic Simulation of an Absorption Cooling System with Different Working Mixtures

by Jesús Cerezo^1,*

, Rosenberg J. Romero¹

, Jonathan Ibarra¹

, Antonio Rodríguez¹

, Gisela Montero²

and Alexis Acuña²

¹ Centro de Investigación en Ingeniería y Ciencias Aplicadas, Universidad Autónoma del Estado de Morelos, Av. Universidad 1001, Cuernavaca 62209, Morelos, Mexico

² Universidad Autónoma de Baja California, Blvd. Benito Juárez y Calle de la Normal S/N, Insurgentes Este, Mexicali 21280, Baja California, Mexico

Energies 2018, 11(2), 259; https://doi.org/10.3390/en11020259 - 23 Jan 2018

Cited by 17 | Viewed by 5695

Abstract

High consumption of electricity represents an economic and social problem in warm places, caused by the massive use of cooling machines. Absorption systems are a sustainable method for air conditioning applications. However, environmental conditions should be analyzed to avoid crystallization problems of the [...] Read more.

High consumption of electricity represents an economic and social problem in warm places, caused by the massive use of cooling machines. Absorption systems are a sustainable method for air conditioning applications. However, environmental conditions should be analyzed to avoid crystallization problems of the working mixture. This article presents a thermal analysis of a solar absorption cooling system in dynamic conditions using NH₃-H₂O, H₂O-LiBr, NH₃-NaSCN, NH₃-LiNO₃, and H₂O-LiCl working mixtures using Equation Engineering Solver (EES) and TRaNsient SYstem Simulation (TRNSYS) software. A solar collector area of 42.5 m² was selected to carry out the thermal analysis. The results showed that H₂O-LiCl obtained the maximum solar (0.67) and minimum heating (0.33) fraction. However, it obtained the maximum lost heat fraction (0.12), in spite of obtaining the best coefficient of performance (COP) among the other working mixtures, due mainly to a crystallization problem. The gain fraction (GF) parameter was used to select the adequate solar collector number for each working mixture. NH₃-LiNO₃ and NH₃-H₂O obtained the highest GF (up 6), and both obtained the maximum solar (0.91) and minimum heating (0.09) fraction, respectively, using 88.8 and 100.4 m² of solar collector area, respectively. Full article

(This article belongs to the Section L: Energy Sources)

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13 pages, 12604 KiB

Open AccessArticle

Numerical Assessment of the Influences of Gas Pressure on Coal Burst Liability

by Haochen Zhao and Rennie B. Kaunda^*

Department of Mining Engineering, Colorado School of Mines, Golden, CO 80401, USA

Energies 2018, 11(2), 260; https://doi.org/10.3390/en11020260 - 23 Jan 2018

Cited by 12 | Viewed by 3322

Abstract

When coal mines exploit deep seams with high-gas content, risks are encountered due to the additional high likelihood of rock bursting potential problems. The bursts of coal pillars usually lead to severe fatalities, injuries, and destruction of property, including impeding access to active [...] Read more.

When coal mines exploit deep seams with high-gas content, risks are encountered due to the additional high likelihood of rock bursting potential problems. The bursts of coal pillars usually lead to severe fatalities, injuries, and destruction of property, including impeding access to active mine workings underground. The danger exists given that conditions in the already highly brittle coal material can be exacerbated by high stress and high gas pressure conditions. It is thus critical to develop methods that improve current understanding about bursting liability, and techniques to forecast or prevent coal bursting in underground coal mines. This study uses field data from a deep coal mine, and numerical modeling to investigate the effects of gas pressure and mechanical compressive stresses on coal bursting liability in high gas content coal seams. The bursting energy index is adopted to determine the coal bursting liability under high gas pressure conditions. The adopted methodology uses a two-staged approach comprising investigating the influence of gas pressure on the bursting liability of coal pillar, and the influence of the gas pressure on the resulting pillar failure mode. Based on numerical simulations of coal pillars, correlations are observed between the magnitudes of gas pressures and the bursting energy index. Irrespective of pillar size, failure time is shortest when the gas pressure achieves a threshold value between 50 kPa to 70 kPa. At 50 kPa, the value of the BEI increases by 50% going from the 4 m pillar to the 6 m pillar. The value of the BEI increases by 43% going from the 6 m high pillar to the 8 m high pillar at 50 kPa. When pillars fail there is a degree of stress relief leading to a reduction in bursting liability. The results suggest that before 50 kPa, pillar failure is largely due to mechanical loading. After 50 kPa, pillar failure is largely due to excessive gas pressures. Full article

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16 pages, 3655 KiB

Open AccessArticle

Novel Detection Method for Consecutive DC Commutation Failure Based on Daubechies Wavelet with 2nd-Order Vanishing Moments

by Tao Lin¹, Ziyu Guo^1,*, Liyong Wang², Rusi Chen¹ and Ruyu Bi¹

¹ School of Electrical Engineering, Wuhan University, Wuhan 430072, China

² State Grid Beijing Electric Power Company, Beijing 100031, China

Energies 2018, 11(2), 261; https://doi.org/10.3390/en11020261 - 23 Jan 2018

Cited by 7 | Viewed by 3204

Abstract

Accurate detection and effective control strategy of commutation failure (CF) of high voltage direct current (HVDC) are of great significance for keeping the safe and stable operations of the hybrid power grid. At first, a novel detection method for consecutive CF is proposed. [...] Read more.

Accurate detection and effective control strategy of commutation failure (CF) of high voltage direct current (HVDC) are of great significance for keeping the safe and stable operations of the hybrid power grid. At first, a novel detection method for consecutive CF is proposed. Concretely, the 2nd and higher orders’ derivative values of direct current are summarized as the core to judge CF by analyzing the physical characteristics of the direct current waveform of the converter station in CF. Then, the Daubechies wavelet coefficient that can represent the 2nd and higher order derivative values of direct current is derived. Once the wavelet coefficients of the sampling points are detected to exceed the threshold, the occurrence of CF is confirmed. Furthermore, by instantly increasing advanced firing angle β in the inverter side, an additional emergency control strategy to prevent subsequent CF is proposed. Eventually, with simulations of the benchmark model, the effectiveness and superiorities of the proposed detection method and additional control strategy in accuracy and rapidity are verified. Full article

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16 pages, 2353 KiB

Open AccessArticle

Improving Performance for Full-Bridge Inverter of Wind Energy Conversion System Using a Fast and Efficient Control Technique

by En-Chih Chang

Department of Electrical Engineering, I-Shou University, No.1, Sec. 1, Syuecheng Rd., Dashu District, Kaohsiung 84001, Taiwan

Energies 2018, 11(2), 262; https://doi.org/10.3390/en11020262 - 23 Jan 2018

Cited by 3 | Viewed by 5284

Abstract

This paper proposes a fast and efficient control technique with application to a full-bridge inverter of a wind energy conversion system that is capable of yielding better performance in transience and steady state. The presented control technique is made up of a finite-time [...] Read more.

This paper proposes a fast and efficient control technique with application to a full-bridge inverter of a wind energy conversion system that is capable of yielding better performance in transience and steady state. The presented control technique is made up of a finite-time convergent SMGL (sliding-mode guidance law) and a Fourier nonlinear grey Bernoulli model (FNGBM). The finite-time convergent SMGL provides a faster convergence rate of system states, as well as a singularity-free solution. However, in case the overestimation/underestimation of the uncertain system boundary occurs, the chatter/steady-state error may exist in finite-time convergent SMGL and then causes serious harmonic distortion at the full-bridge inverter output. An efficient calculational FNGBM is integrated into the finite-time convergent SMGL, thus overcoming chatter/steady-state error problems if the estimated value of the uncertain system boundary cannot be satisfied. Simulation results indicate that the proposed control technique leads to low total harmonic distortion under nonlinear loading and fast dynamic response under transient loading. Experimental results from a full-bridge inverter prototype are given to confirm the simulation results and the mathematical analyses. Because the proposed full-bridge inverter offers significant advantages over the classical finite-time convergent sliding-mode controlled full-bridge inverter in terms of convergent speed, calculational efficiency, and harmonic distortion removal, this paper will be a feasible reference for wind energy systems or other renewable energy systems in future research; for example, for photovoltaic systems and fuel cell systems. Full article

(This article belongs to the Special Issue Wind Generators Modelling and Control)

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16 pages, 2964 KiB

Open AccessArticle

Comparative Study of Electric Energy Storages and Thermal Energy Auxiliaries for Improving Wind Power Integration in the Cogeneration System

by Yanjuan Yu

, Hongkun Chen^* and Lei Chen

School of Electrical Engineering, Wuhan University, Wuhan 430072, China

Energies 2018, 11(2), 263; https://doi.org/10.3390/en11020263 - 23 Jan 2018

Cited by 23 | Viewed by 4479

Abstract

In regards to the cogeneration system in Northern China, mainly supported by combined heat and power (CHP) plants, it usually offers limited operation flexibility due to the joint production of electric and thermal power. For that large-scale wind farms included in the cogeneration [...] Read more.

In regards to the cogeneration system in Northern China, mainly supported by combined heat and power (CHP) plants, it usually offers limited operation flexibility due to the joint production of electric and thermal power. For that large-scale wind farms included in the cogeneration system, a large amount of wind energy may have to be wasted. To solve this issue, the utilization of the electric energy storages and the thermal energy auxiliaries are recommended, including pumped hydro storage (PHS), compressed air energy storage (CAES), hydrogen-based energy storage (HES), heat storage (HS), electric boilers (EB), and heat pumps (HP). This paper proposes a general evaluation method to compare the performance of these six different approaches for promoting wind power integration. In consideration of saving coal consumption, reducing CO₂ emissions, and increasing investment cost, the comprehensive benefit is defined as the evaluation index. Specifically, a wind-thermal conflicting expression (WTCE) is put forward to simplify the formulation of the comprehensive benefit. Further, according to the cogeneration system of the West Inner Mongolia (WIM) power grid, a test system is modelled to perform the comparison of the six different approaches. The results show that introducing the electric energy storages and the thermal energy auxiliaries can both contribute to facilitating wind power integration, and the HP can provide the best comprehensive benefit. Full article

(This article belongs to the Special Issue Energy Production Systems)

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16 pages, 6331 KiB

Open AccessArticle

Simplified Analytic Approach of Pole-to-Pole Faults in MMC-HVDC for AC System Backup Protection Setting Calculation

by Tongkun Lan

, Yinhong Li^*, Xianzhong Duan and Jia Zhu

State Key Laboratory of Advanced Electromagnetic Engineering and Technology, Hubei Electric Power Security and High Efficiency Key Laboratory, School of Electrical and Electronic Engineering, Huazhong University of Science and Technology, Wuhan 430074, China

Energies 2018, 11(2), 264; https://doi.org/10.3390/en11020264 - 23 Jan 2018

Cited by 10 | Viewed by 3808

Abstract

AC (alternating current) system backup protection setting calculation is an important basis for ensuring the safe operation of power grids. With the increasing integration of modular multilevel converter based high voltage direct current (MMC-HVDC) into power grids, it has been a big challenge [...] Read more.

AC (alternating current) system backup protection setting calculation is an important basis for ensuring the safe operation of power grids. With the increasing integration of modular multilevel converter based high voltage direct current (MMC-HVDC) into power grids, it has been a big challenge for the AC system backup protection setting calculation, as the MMC-HVDC lacks the fault self-clearance capability under pole-to-pole faults. This paper focused on the pole-to-pole faults analysis for the AC system backup protection setting calculation. The principles of pole-to-pole faults analysis were discussed first according to the standard of the AC system protection setting calculation. Then, the influence of fault resistance on the fault process was investigated. A simplified analytic approach of pole-to-pole faults in MMC-HVDC for the AC system backup protection setting calculation was proposed. In the proposed approach, the derived expressions of fundamental frequency current are applicable under arbitrary fault resistance. The accuracy of the proposed approach was demonstrated by PSCAD/EMTDC (Power Systems Computer-Aided Design/Electromagnetic Transients including DC) simulations. Full article

(This article belongs to the Section F: Electrical Engineering)

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13 pages, 4881 KiB

Open AccessArticle

Characterization of Storage Sizing for an Off-Grid House in the US and the Netherlands

by Diego Fernando Quintero Pulido^1,*, Gerwin Hoogsteen¹, Marnix V. Ten Kortenaar², Johann L. Hurink¹

, Robert E. Hebner³ and Gerard J. M. Smit¹

¹ Faculty of Electrical Engineering Mathematics Computer Science, University of Twente, P.O. Box 217, 7500 AE Enschede, The Netherlands

² Dr Ten B.V., Rondweg 11M/N, 8091 XA Wezep, The Netherlands

³ The Center for Electromechanics, The University of Texas at Austin, 10100 Burnet Rd, EME 133, Austin, TX 78758, USA

Energies 2018, 11(2), 265; https://doi.org/10.3390/en11020265 - 23 Jan 2018

Cited by 14 | Viewed by 13162

Abstract

This work uses experimental data to estimate the size of storage needed for an isolated off-grid household in two different regions (Austin, Texas, US, and Nunspeet, NL). In our study, an off-grid house is considered to be supplied with 100% renewable energy during [...] Read more.

This work uses experimental data to estimate the size of storage needed for an isolated off-grid household in two different regions (Austin, Texas, US, and Nunspeet, NL). In our study, an off-grid house is considered to be supplied with 100% renewable energy during the summer period, in which cooling demand is neglected, and a solar photovoltaic (PV) system and batteries are the main electrical energy providers. Based on results achieved with the DEMkit simulation package we can conclude that, in both cases, using a solar PV system and a Sea-Salt battery would have been sufficient to provide the necessary electricity without showing a blackout during the summer of 2016. The Austin household needs a solar PV system of 38 kWp and storage of 452 kWh; in the case of Nunspeet, a solar PV system of 11.5 kWp and storage of 90 kWh is sufficient. Furthermore, using the DEMkit model, it is possible to determine an optimal value for the size of storage to half of the initial battery capacity (226 kWh for Austin and 45 kWh for Nunspeet) and still be able to provide enough power to cover the load demand of the households during the summer. In a second part, data of the solar PV system and load from Austin for one specific week was used to create data of a ‘typical’ but downscaled day. This day was used to determine the fluctuation of electricity for a real Sea-Salt battery for the considered off-grid scenario in Austin. The downscaling of the data was needed in order to have load values that fit to the size of the real battery. The tests show that the Sea-Salt battery under real electricity fluctuations is possibly adequate for off-grid scenarios. Full article

(This article belongs to the Special Issue Selected Papers from International Workshop of Energy-Open)

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13 pages, 4580 KiB

Open AccessArticle

Series-Connected High Frequency Converters in a DC Microgrid System for DC Light Rail Transit

by Bor-Ren Lin

Department of Electrical Engineering, National Yunlin University of Science and Technology, Yunlin 640, Taiwan

Energies 2018, 11(2), 266; https://doi.org/10.3390/en11020266 - 23 Jan 2018

Cited by 5 | Viewed by 4490

Abstract

This paper studies and presents a series-connected high frequency DC/DC converter connected to a DC microgrid system to provide auxiliary power for lighting, control and communication in a DC light rail vehicle. Three converters with low voltage and current stresses of power devices [...] Read more.

This paper studies and presents a series-connected high frequency DC/DC converter connected to a DC microgrid system to provide auxiliary power for lighting, control and communication in a DC light rail vehicle. Three converters with low voltage and current stresses of power devices are series-connected with single transformers to convert a high voltage input to a low voltage output for a DC light rail vehicle. Thus, Metal-Oxide-Semiconductor Field-Effect Transistors (MOSFETs) with a low voltage rating and a turn-on resistance are adopted in the proposed circuit topology in order to decrease power losses on power switches and copper losses on transformer windings. A duty cycle control with an asymmetric pulse-width modulation is adopted to control the output voltage at the desired voltage level. It is also adopted to reduce switching losses on MOSFETs due to the resonant behavior from a leakage inductor of an isolated transformer and output capacitor of MOSFETs at the turn-on instant. The feasibility and effectiveness of the proposed circuit have been verified by a laboratory prototype with a 760 V input and a 24 V/60 A output. Full article

(This article belongs to the Special Issue Power Electronics in DC-Microgrid Systems)

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18 pages, 2158 KiB

Open AccessArticle

The Design of High Efficiency Crossflow Hydro Turbines: A Review and Extension

by Ram Adhikari^† and David Wood^*,†

¹ Department of Mechanical and Manufacturing Engineering, University of Calgary, 2500 University Drive NW, Calgary, AB T2N 1N4, Canada

^† These authors contributed equally to this work.

Energies 2018, 11(2), 267; https://doi.org/10.3390/en11020267 - 23 Jan 2018

Cited by 60 | Viewed by 17027

Abstract

Efficiency is a critical consideration in the design of hydro turbines. The crossflow turbine is the cheapest and easiest hydro turbine to manufacture and so is commonly used in remote power systems for developing countries. A longstanding problem for practical crossflow turbines is [...] Read more.

Efficiency is a critical consideration in the design of hydro turbines. The crossflow turbine is the cheapest and easiest hydro turbine to manufacture and so is commonly used in remote power systems for developing countries. A longstanding problem for practical crossflow turbines is their lower maximum efficiency compared to their more advanced counterparts, such as Pelton and Francis turbines. This paper reviews the experimental and computational studies relevant to the design of high efficiency crossflow turbines. We concentrate on the studies that have contributed to designs with efficiencies in the range of 88–90%. Many recent studies have been conducted on turbines of low maximum efficiency, which we believe is due to misunderstanding of design principles for achieving high efficiencies. We synthesize the key results of experimental and computational fluid dynamics studies to highlight the key fundamental design principles for achieving efficiencies of about 90%, as well as future research and development areas to further improve the maximum efficiency. The main finding of this review is that the total conversion of head into kinetic energy in the nozzle and the matching of nozzle and runner designs are the two main design requirements for the design of high efficiency turbines. Full article

(This article belongs to the Section L: Energy Sources)

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16 pages, 4119 KiB

Open AccessArticle

A Novel Concept for Three-Phase Cascaded Multilevel Inverter Topologies

by Md Mubashwar Hasan^*

, A. Abu-Siada

, Syed M. Islam and S. M. Muyeen

Department of Electrical and Computer Engineering, Curtin University, Perth, WA 6102, Australia

Energies 2018, 11(2), 268; https://doi.org/10.3390/en11020268 - 23 Jan 2018

Cited by 9 | Viewed by 4832

Abstract

One of the key challenges in multilevel inverters (MLIs) design is to reduce the number of components used in the implementation while maximising the number of output voltage levels. This paper proposes a new concept that facilitates a device count reduction technique of [...] Read more.

One of the key challenges in multilevel inverters (MLIs) design is to reduce the number of components used in the implementation while maximising the number of output voltage levels. This paper proposes a new concept that facilitates a device count reduction technique of existing cascaded MLIs. Moreover, the proposed concept can be utilised to extend existing single phase cascaded MLI topologies to three-phase structure without tripling the number of semiconductor components and input dc-supplies as per the current practice. The new generalized concept involves two stages; namely, cascaded stage and phase generator stage. The phase generator stage is a combination of a conventional three-phase two level inverter and three bi-directional switches while the cascaded stage can employ any existing cascaded topology. A laboratory prototype model is built and extensive experimental analyses are conducted to validate the feasibility of the proposed cascaded MLI concept. Full article

(This article belongs to the Section F: Electrical Engineering)

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14 pages, 5048 KiB

Open AccessArticle

An Investigation on the Efficiency Correction Method of the Turbocharger at Low Speed

by Jin Eun Chung^1,*, Jae Woo Chung², Nam Ho Kim², Sang Woon Lee²

and Gi Yong Kim³

¹ Department of Mechanical Engineering, Korea University of Technology and Education, Chungnam 31253, Korea

² Green Car Power System R & D Division, Korea Automotive Technology Institute, Chungnam 31214, Korea

³ R & D Center, Keyyang precision Co. LTD, Gyeongsangbuk 39537, Korea

Energies 2018, 11(2), 269; https://doi.org/10.3390/en11020269 - 23 Jan 2018

Cited by 8 | Viewed by 3814

Abstract

The heat transfer in the turbocharger occurs due to the temperature difference between the exhaust gas and intake air, coolant, and oil. This heat transfer causes the efficiency of the compressor and turbine to be distorted, which is known to be exacerbated during [...] Read more.

The heat transfer in the turbocharger occurs due to the temperature difference between the exhaust gas and intake air, coolant, and oil. This heat transfer causes the efficiency of the compressor and turbine to be distorted, which is known to be exacerbated during low rotational speeds. Thus, this study proposes a method to mitigate the distortion of the test result data caused by heat transfer in the turbocharger. With this method, the representative compressor temperature is defined and the heat transfer rate of the compressor is calculated by considering the effect of the oil and turbine inlet temperatures at low rotation speeds, when the cold and the hot gas test are simultaneously performed. The correction of compressor efficiency, depending on the turbine inlet temperature, was performed through both hot and cold gas tests and the results showed a maximum of 16% error prior to correction and a maximum of 3% error after the correction. In addition, it shows that it is possible to correct the efficiency distortion of the turbocharger by heat transfer by correcting to the combined turbine efficiency based on the corrected compressor efficiency. Full article

(This article belongs to the Section I: Energy Fundamentals and Conversion)

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21 pages, 12748 KiB

Open AccessArticle

Study on the Potential of Rice Straws as a Supplementary Fuel in Very Small Power Plants in Thailand

by Penwadee Cheewaphongphan^1,2,3, Agapol Junpen^1,2,*

, Orachorn Kamnoet^1,2 and Savitri Garivait^1,2

¹ The Joint Graduate School of Energy and Environment (JGSEE), King Mongkut’s University of Technology Thonburi (KMUTT), Bangkok 10140, Thailand

² Center of Excellence on Energy Technology and Environment (CEE-PERDO), Ministry of Education, Bangkok 10140, Thailand

³ National Institute for Environmental Studies (NIES), 16-2 Onogawa, Tsukuba, Ibaraki 305-8506, Japan

Energies 2018, 11(2), 270; https://doi.org/10.3390/en11020270 - 23 Jan 2018

Cited by 33 | Viewed by 7452

Abstract

Agricultural residue is a major raw material for renewable energy production, particularly heat production, in Thailand. Meanwhile, the process-based residue, such as bagasse, rice husk, wood residue, palm fiber, palm shell, and saw dust, is used as a fuel for energy production in [...] Read more.

Agricultural residue is a major raw material for renewable energy production, particularly heat production, in Thailand. Meanwhile, the process-based residue, such as bagasse, rice husk, wood residue, palm fiber, palm shell, and saw dust, is used as a fuel for energy production in the agro-industry. Hence, this study is intended to assess the net potential and capacity of alternative agricultural residues, specifically rice straws, to serve as the supplementary fuel for very small power plants (VSPPs) in Thailand. According to the results obtained during the crop season of 2015/2016, approximately 26 Mt of rice straws were generated upon the harvesting process. The net potential of rice straws, including those that were burned and those that were left in the fields, was only about 15% or 3.85 Mt, which could be used for heat and electricity production at 1331 kilotons of oil equivalent (ktoe) or 457 MWe. As agro-residues vary by seasonality, the peak season of rice straws was in November, where approximately 1.64 Mt (43%) were generated, followed by December, at 1.32 Mt (34%). On the basis of the results, rice straw has the potential to serve as a fuel supply for VSPPs at 14.2%, 21.6%, 26.3%, and 29.0% for the radii of compilation at 24, 36, 48 km and 60 km, respectively. Full article

(This article belongs to the Section L: Energy Sources)

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16 pages, 4922 KiB

Open AccessArticle

New Method for Shallow and Deep Trap Distribution Analysis in Oil Impregnated Insulation Paper Based on the Space Charge Detrapping

by Jian Hao^1,*

, Runhao Zou¹, Ruijin Liao¹, Lijun Yang¹ and Qiang Liao²

¹ The State Key Laboratory of Power Transmission Equipment & System Security and New Technology, Chongqing University, Chongqing 400044, China

² College of Power Engineering, Chongqing University, Chongqing 400044, China

Energies 2018, 11(2), 271; https://doi.org/10.3390/en11020271 - 23 Jan 2018

Cited by 30 | Viewed by 4465

Abstract

Space charge has close relation with the trap distribution in the insulation material. The phenomenon of charges trapping and detrapping has attracted significant attention in recent years. Space charge and trap parameters are effective parameters for assessing the ageing condition of the insulation [...] Read more.

Space charge has close relation with the trap distribution in the insulation material. The phenomenon of charges trapping and detrapping has attracted significant attention in recent years. Space charge and trap parameters are effective parameters for assessing the ageing condition of the insulation material qualitatively. In this paper, a new method for calculating trap distribution based on the double exponential fitting analysis of charge decay process and its application on characterizing the trap distribution of oil impregnated insulation paper was investigated. When compared with the common first order exponential fitting analysis method, the improved dual-level trap method could obtain the energy level range and density of both shallow traps and deep traps, simultaneously. Space charge decay process analysis of the insulation paper immersed with new oil and aged oil shows that the improved trap distribution calculation method can distinguish the physical defects and chemical defects. The trap density shows an increasing trend with the oil ageing, especially for the deep traps mainly related to chemical defects. The greater the energy could be filled by the traps, the larger amount of charges could be trapped, especially under higher electric field strength. The deep trap energy level and trap density could be used to characterize ageing. When one evaluates the ageing condition of oil-paper insulation using trap distribution parameters, the influence of oil performance should not be ignored. Full article

(This article belongs to the Section F: Electrical Engineering)

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26 pages, 20838 KiB

Open AccessArticle

Lost Gas Mechanism and Quantitative Characterization during Injection and Production of Water-Flooded Sandstone Underground Gas Storage

by Jinkai Wang^1,*, Hengyi Liu¹, Jinliang Zhang^1,2 and Jun Xie¹

¹ College of Earth Science and Engineering, Shandong University of Science and Technology, Qingdao 266590, China

² College of Resources Science and Technology, Beijing Normal University, Beijing 100875, China

Energies 2018, 11(2), 272; https://doi.org/10.3390/en11020272 - 23 Jan 2018

Cited by 19 | Viewed by 4520

Abstract

A gas–water two-phase fluid is present in a reservoir before a water-flooded sandstone gas reservoir is rebuilt. Therefore, in the process of injection and production of the rebuilt underground gas storage, the injected gas is easily blocked by the water in the pores, [...] Read more.

A gas–water two-phase fluid is present in a reservoir before a water-flooded sandstone gas reservoir is rebuilt. Therefore, in the process of injection and production of the rebuilt underground gas storage, the injected gas is easily blocked by the water in the pores, and the efficiency is low, resulting in a significant loss of gas. The study completely utilizes the geological data and dynamic operation monitoring data of a water-flooded sandstone underground gas storage and clarifies the rule of the gas–water three-phase seepage in a high-intensity injection–production process. Moreover, the main control factors of the low efficiency of this type of underground gas storage are clarified. The lost gas generated in the injection–production process is described from two aspects: microcosmic experiment and macroscopic law analysis. The type, mechanism, and occurrence state of the loss gas are clearly defined, its main type is “water trapped gas”, it formed when the gas rushing into the water area under high pressure and surrounded by water, and its occurrence of this kind of lost gas is mainly sporadic or continuous free gas. A gas–water two-phase mathematical model that can simulate the high-intensity injection–production process is set up according to the experimental result, this model is used to simulate the operation process of the Ban 876 underground gas storage. Based on the simulation results, the gas–water macroscopic movement rule and macroscopic accumulation mode of the lost gas are defined, and then the collection area of the lost gas is predicted and quantitatively described. The calculation results show that the lost gas in one cycle is about 775 × 10⁴ m³, which are mainly concentrated in the inner of the gas-water transition zone. According to the numerical simulation result, six new wells have been designed to develop its internal lost gas, they all have good predictions, can increase the working gas volume of 3000 × 10⁴ m³ and reduce the single cycle lost gas by 50%, which is only 326 × 10⁴ m³. This provides guidance for the expansion and exploitation of the same type of water-flooded sandstone underground gas storage. Full article

(This article belongs to the Section L: Energy Sources)

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11 pages, 6280 KiB

Open AccessArticle

Experimental Research on the Injection Rate of DME and Diesel Fuel in Common Rail Injection System by Using Bosch and Zeuch Methods

by Seemoon Yang¹ and Changhee Lee^2,*

¹ Leaders in Industry-University Cooperation (LINC) of Chosun University, 309 Pilmun-daero, Dong-gu, Gwangju 61452, Korea

² Department of Mechanical and Automotive Engineering, Songwon University, Songarm-ro, Gwangju 61756, Korea

Energies 2018, 11(2), 273; https://doi.org/10.3390/en11020273 - 23 Jan 2018

Cited by 8 | Viewed by 5405

Abstract

This study investigates a preliminary injection characterization of the injection rate and the injection quantity behavior in a high-pressure common rail injection system used in a heavy-duty engine. The injection rate meter and the injection quantity meter used in the test meter measuring [...] Read more.

This study investigates a preliminary injection characterization of the injection rate and the injection quantity behavior in a high-pressure common rail injection system used in a heavy-duty engine. The injection rate meter and the injection quantity meter used in the test meter measuring systems were jointly connected under the Zeuch method measurement principles at a constant volume chamber and under the Bosch method measurement principles at a long pipe flow. The trade-off trend for the injection rate and the injection quantity was observed according to the injection pressure. As expected, fuel injection with pilot injection affected the spray quantity and the injection evolution of subsequent fuel injection without pilot injection in dimethyl ether and diesel fuel. The pressure variations in the initial injection duration (2000–6000 µs) of the main and pilot injections for diesel and DME were similar. However, after 7000 µs, the pressure of DME increased more rapidly compared to that of diesel. This finding was the result of the rapid density changes caused by the nature of compressive fluid. Therefore, the DME supply pump was expected to require a higher drive energy by approximately 20% compared to that of the diesel supply pump. Full article

(This article belongs to the Section I: Energy Fundamentals and Conversion)

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28 pages, 12559 KiB

Open AccessArticle

Development of Automotive Permanent Magnet Alternator with Fully Controlled AC/DC Converter

by Tareq S. El-Hasan

Electrical Engineering Department, Zarqa University, Zqrqa 13132, Jordan

Energies 2018, 11(2), 274; https://doi.org/10.3390/en11020274 - 24 Jan 2018

Cited by 8 | Viewed by 9525

Abstract

This paper proposes the design of a three-phase axial flux permanent magnet alternator (AFPMA) that is characterized with an air-cored stator and two-rotor (ACSTR) configuration. The AFPMA is harnessed with fully controlled AC/DC converter using six bridge Insulated Gate Bipolar Transistor (IGBTs) capable [...] Read more.

This paper proposes the design of a three-phase axial flux permanent magnet alternator (AFPMA) that is characterized with an air-cored stator and two-rotor (ACSTR) configuration. The AFPMA is harnessed with fully controlled AC/DC converter using six bridge Insulated Gate Bipolar Transistor (IGBTs) capable to deliver a constant DC output power as an attempt to replace the Lundell alternator for automotive applications. First, the design methodology and analysis of the AFPMA is introduced. The most effective parameters, such as rotor diameter, magnet thickness, number of turns, and winding thickness are determined. A smart digital control which facilitates the comparison between the magnitudes of the three-phase input signals instead of finding the zero crossing points is developed. Moreover, custom design comparators are specially designed and developed to generate adaptive signals that are fed into an Arduino Uno microcontroller. Accordingly, the Arduino generates the timely precise pulses that are necessary to maintain the appropriate triggering of the IGBTs. This technique allows the IGBTs to conduct in an adaptive manner to overcome the problem of asymmetrical voltage outputs from the AFPM alternator. The system is also capable of handling the variation in the speed of the AFPMA via the rigor code in Arduino that detects the change in the supply frequency and voltages in a real time process. The system is first analyzed via simulations using MATLAB/Simulink and then experimentally validated at certain speed and loading conditions. The preliminary tests results indicate that such system is capable to provide an efficient solution to satisfy automotive electric power demands. Full article

(This article belongs to the Special Issue Emerging Power Electronics Technologies for Power Systems and Machine Drives)

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17 pages, 3747 KiB

Open AccessArticle

Economic, Energetic, and Environmental Performance of a Solar Powered Organic Rankine Cycle with Electric Energy Storage in Different Commercial Buildings

by Emily Spayde, Pedro J. Mago^* and Rogelio Luck

Department Mechanical Engineering, Mississippi State University, Starkville, MS 39762, USA

Energies 2018, 11(2), 276; https://doi.org/10.3390/en11020276 - 24 Jan 2018

Cited by 14 | Viewed by 3805

Abstract

This paper presents an analysis to determine the economic, energetic, and environmental benefits that could be obtained from the implementation of a combined solar-power organic Rankine cycle (ORC) with electric energy storage (EES) to supply electricity to several commercial buildings including a large [...] Read more.

This paper presents an analysis to determine the economic, energetic, and environmental benefits that could be obtained from the implementation of a combined solar-power organic Rankine cycle (ORC) with electric energy storage (EES) to supply electricity to several commercial buildings including a large office, a small office, and a full service restaurant. The operational strategy for the ORC-EES system consists in the ORC charging the EES when the irradiation level is sufficient to generate power, and the EES providing electricity to the building when there is not irradiation (i.e., during night time). Electricity is purchased from the utility grid unless it is provided by the EES. The potential of the proposed system to reduce primary energy consumption (PEC), carbon dioxide emission (CDE), and cost was evaluated. Furthermore, the available capital cost for a variable payback period for the ORC-EES system was determined for each of the evaluated buildings. The effect of the number of solar collectors on the performance of the ORC-EES is also studied. Results indicate that the proposed ORC-EES system is able to satisfy 11%, 13%, and 18% of the electrical demand for the large office, the small office and the restaurant, respectively. Full article

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17 pages, 3153 KiB

Open AccessArticle

District Heating Expansion Potential with Low-Temperature and End-Use Heat Savings

by Steffen Nielsen^1,*

and Lars Grundahl²

¹ Department of Development and Planning, Aalborg University, Rendsburggade 14, DK-9000 Aalborg, Denmark

² Department of Development and Planning, Aalborg University, A. C. Meyers Vænge 15, DK-2450 København SV, Denmark

Energies 2018, 11(2), 277; https://doi.org/10.3390/en11020277 - 24 Jan 2018

Cited by 12 | Viewed by 3441

Abstract

District heating has the potential to play a key role in the transition towards a renewable energy system. However, the development towards reduced heat demands threatens the feasibility of district heating. Despite this challenge, opportunity exists in the form of fourth generation district [...] Read more.

District heating has the potential to play a key role in the transition towards a renewable energy system. However, the development towards reduced heat demands threatens the feasibility of district heating. Despite this challenge, opportunity exists in the form of fourth generation district heating, which operates at lower temperatures and enables better renewable integration. This article investigates this challenge by examining the district heating potential within three scenarios: The first is a reference scenario with current heat demand and temperatures, the second includes heat demand savings and the third includes reduced grid temperatures in addition to heat savings. To examine the scenarios, two models are developed. The first is a heat atlas model, in which heat demands are mapped on an address level. The second model assesses district heating expansion potentials based on economic costs. The models are applied using an example case of The Northern Region of Denmark. The article concludes that the district heating potential is highest in the reference scenario. When heat savings are introduced, district heating expansions, in most cases, will not be feasible. Introducing low-temperature district heating modestly increases the feasible expansion potential. This general conclusion is highly dependent on the specific system examined. Full article

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26 pages, 9060 KiB

Open AccessArticle

Design and Performance Evaluation of an Axial Inflow Turbocharger Turbine

by Anna Minasyan¹, Jordan Bradshaw¹

and Apostolos Pesyridis^1,2,*

¹ Centre for Advanced Powertrain and Fuels Research (CAPF), Department of Mechanical, Aerospace and Civil Engineering, Brunel University London, Uxbridge UB8 3PH, UK

² Metapulsion Engineering Limited, Northwood, Middlesex HA6 2NP, UK

Energies 2018, 11(2), 278; https://doi.org/10.3390/en11020278 - 24 Jan 2018

Cited by 9 | Viewed by 6510

Abstract

This paper is focussed on the development of an axial inflow turbocharger turbine as a viable alternative to a baseline radial turbine for certain applications. Additionally a variable geometry turbine (VGT) technology is incorporated into the axial-inflow turbine to additionally benefit both efficiency [...] Read more.

This paper is focussed on the development of an axial inflow turbocharger turbine as a viable alternative to a baseline radial turbine for certain applications. Additionally a variable geometry turbine (VGT) technology is incorporated into the axial-inflow turbine to additionally benefit both efficiency and performance. The developed turbine was compared to the baseline in terms of engine performance, fuel consumption and emissions. The design and optimisation of the inlet casing, stator and rotor blades for axial inflow turbine were developed through CFD simulation. Then a VGT system was further developed, equipped with pivoting stator blades. Necessary data at various flow conditions were collected for engine modelling to test the engine performance achieved by the integration of the axial turbine, which achieved a maximum 86.2% isentropic efficiency at 102,000 rpm. The paper further focussed on the design and optimization of a volute for axial inflow turbine. Various initial designs were tested using CFD simulations and the chosen configuration was optimised further to improve overall stage efficiency, which reached 81.2%. Engine model simulations demonstrated that engine power and torque are significantly increased through the application of the proposed variable geometry axial turbocharger turbine. Full article

(This article belongs to the Special Issue Recent Advances in Internal Combustion Engines Operation and Emissions)

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15 pages, 13461 KiB

Open AccessArticle

Study on a Battery Thermal Management System Based on a Thermoelectric Effect

by Chuan-Wei Zhang, Ke-Jun Xu^*, Lin-Yang Li, Man-Zhi Yang, Huai-Bin Gao and Shang-Rui Chen

College of Mechanical Engineering, Xi’an University of Science and Technology, Xi’an 710054, China

Energies 2018, 11(2), 279; https://doi.org/10.3390/en11020279 - 24 Jan 2018

Cited by 43 | Viewed by 8954

Abstract

As is known to all, a battery pack is significantly important for electric vehicles. However, its performance is easily affected by temperature. In order to address this problem, an enhanced battery thermal management system is proposed, which includes two parts: a modified cooling [...] Read more.

As is known to all, a battery pack is significantly important for electric vehicles. However, its performance is easily affected by temperature. In order to address this problem, an enhanced battery thermal management system is proposed, which includes two parts: a modified cooling structure and a control unit. In this paper, more attention has been paid to the structure part. According to the heat generation mechanism of a battery and a thermoelectric chip, a simplified heat generation model for a single cell and a special cooling model were created in ANSYS 17.0. The effects of inlet velocity on the performance of different heat exchanger structures were studied. The results show that the U loop structure is more reasonable and the flow field distribution is the most uniform at the inlet velocity of 1.0 m/s. Then, on the basis of the above heat exchanger and the liquid flow velocity, the cooling effect of the improved battery temperature adjustment structure and the traditional liquid temperature regulating structure were analyzed. It can be seen that the liquid cooling structure combined with thermoelectric cooling demonstrates a better performance. With respect to the control system, the corresponding hardware and software were also developed. In general, the design process for this enhanced battery thermal management system can provide a wealth of guidelines for solving similar problems. The H commutation circuit, matrix switch circuit, temperature measurement circuit, and wireless communication modules were designed in the control system and the temperature control strategy was also developed. Full article

(This article belongs to the Special Issue The International Symposium on Electric Vehicles (ISEV2017))

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19 pages, 6093 KiB

Open AccessArticle

Numerical Investigation on the Heat Extraction Capacity of Dual Horizontal Wells in Enhanced Geothermal Systems Based on the 3-D THM Model

by Zhixue Sun^1,2,*, Ying Xin¹, Jun Yao¹, Kai Zhang^1,*, Li Zhuang³, Xuchen Zhu¹, Tong Wang¹ and Chuanyin Jiang¹

¹ School of Petroleum Engineering, China University of Petroleum (East China), Qingdao 266580, China

² Evaluation and Detection Technology Laboratory of Marine Mineral Resources, Qingdao National Laboratory for Marine Science and Technology, Qingdao 266100, China

³ Geotechnical Engineering Research Institute, Korea Institute of Civil Engineering and Building Technology, 283, Goyang-daero, Ilsanseo-gu, Goyang-si, Gyeonggi-do 10223, Korea

Energies 2018, 11(2), 280; https://doi.org/10.3390/en11020280 - 24 Jan 2018

Cited by 40 | Viewed by 5588

Abstract

The Enhanced Geothermal System (EGS) constructs an artificial thermal reservoir by hydraulic fracturing to extract heat economically from hot dry rock. As the core element of the EGS heat recovery process, mass and heat transfer of working fluid mainly occurs in fractures. Since [...] Read more.

The Enhanced Geothermal System (EGS) constructs an artificial thermal reservoir by hydraulic fracturing to extract heat economically from hot dry rock. As the core element of the EGS heat recovery process, mass and heat transfer of working fluid mainly occurs in fractures. Since the direction of the natural and induced fractures are generally perpendicular to the minimum principal stress in the formation, as an effective stimulation approach, horizontal well production could increase the contact area with the thermal reservoir significantly. In this paper, the thermal reservoir is developed by a dual horizontal well system and treated as a fractured porous medium composed of matrix rock and discrete fracture network. Using the local thermal non-equilibrium theory, a coupled THM mathematical model and an ideal 3D numerical model are established for the EGS heat extraction process. EGS heat extraction capacity is evaluated in the light of thermal recovery lifespan, average outlet temperature, heat production, electricity generation, energy efficiency and thermal recovery rate. The results show that with certain reservoir and production parameters, the heat production, electricity generation and thermal recovery lifespan can achieve the commercial goal of the dual horizontal well system, but the energy efficiency and overall thermal recovery rate are still at low levels. At last, this paper puts forward a series of optimizations to improve the heat extraction capacity, including production conditions and thermal reservoir construction design. Full article

(This article belongs to the Special Issue Geothermal Heating and Cooling)

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12 pages, 4684 KiB

Open AccessArticle

Fabrication of Cost-Effective Dye-Sensitized Solar Cells Using Sheet-Like CoS₂ Films and Phthaloylchitosan-Based Gel-Polymer Electrolyte

by Saradh Prasad^1,2

, Devaraj Durairaj^1,*, Mohamad Saleh AlSalhi^2,3,*

, Jayaraman Theerthagiri⁴, Prabhakarn Arunachalam⁵

and Govindarajan Durai⁴

¹ Department of Electrical and Electronics Engineering, School of Electronics and Electrical Technology (SEET), Kalasalingam Academy of Research and Education (KARE), Krishnankoil, Virudhunagar 626126, Tamil Nadu, India

² Research Chair on Laser Diagnosis of Cancers, Department of Physics and Astronomy, College of Science, King Saud University, 11451 Riyadh, Saudi Arabia

³ Department of Physics and Astronomy, College of Science, King Saud University, 11451 Riyadh, Saudi Arabia

⁴ Centre of Excellence for Energy Research, Sathyabama Institute of Science and Technology, Chennai 600119, India

⁵ Electrochemistry Research Group, Chemistry Department, College of Science, King Saud University, 11451 Riyadh, Saudi Arabia

Energies 2018, 11(2), 281; https://doi.org/10.3390/en11020281 - 24 Jan 2018

Cited by 13 | Viewed by 5244

Abstract

Platinum-free counter electrodes (CE) were developed for use in efficient and cost-effective energy conversion devices, such as dye-sensitized solar cells (DSSCs). Electrochemical deposition of CoS₂ on fluorine-doped tin oxide (FTO) formed a hierarchical sheet-like structured CoS₂ thin film. This film was [...] Read more.

Platinum-free counter electrodes (CE) were developed for use in efficient and cost-effective energy conversion devices, such as dye-sensitized solar cells (DSSCs). Electrochemical deposition of CoS₂ on fluorine-doped tin oxide (FTO) formed a hierarchical sheet-like structured CoS₂ thin film. This film was engaged as a cost-effective platinum-free and high-efficiency CE for DSSCs. High stability was achieved using a phthaloychitosan-based gel-polymer electrolyte as the redox electrolyte. The electrocatalytic performance of the sheet-like CoS₂ film was analyzed by electrochemical impedance spectroscopy and cyclic voltammetry. The film displayed improved electrocatalytic behavior that can be credited to a low charge-transfer resistance at the CE/electrolyte boundary and improved exchange between triiodide and iodide ions. The fabricated DSSCs with a phthaloychitosan-based gel-polymer electrolyte and sheet-like CoS₂ CE had a power conversion efficiency (PCE, η) of 7.29% with a fill factor (FF) of 0.64, J_sc of 17.51 mA/cm², and a V_oc of 0.65 V, which was analogous to that of Pt CE (η = 7.82%). The high PCE of the sheet-like CoS₂ CE arises from the enhanced FF and J_sc, which can be attributed to the abundant active electrocatalytic sites and enhanced interfacial charge-transfer by the well-organized surface structure. Full article

(This article belongs to the Section L: Energy Sources)

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16 pages, 4606 KiB

Open AccessFeature PaperArticle

Speed Synchronous Control of Multiple Permanent Magnet Synchronous Motors Based on an Improved Cross-Coupling Structure

by Wei Chen^*

, Jiaojiao Liang

and Tingna Shi

School of Electrical and Information Engineering, Tianjin University, Tianjin 300072, China

Energies 2018, 11(2), 282; https://doi.org/10.3390/en11020282 - 24 Jan 2018

Cited by 27 | Viewed by 5016

Abstract

Regarding the shortcomings of the cross-coupling control structure during the start-up of a multi-motor with load—namely, a large synchronization error and a long start-up time—this paper proposes a fuzzy self-adjusting cross-coupling control structure. This structure combines a fuzzy self-adjusting filter and an advanced [...] Read more.

Regarding the shortcomings of the cross-coupling control structure during the start-up of a multi-motor with load—namely, a large synchronization error and a long start-up time—this paper proposes a fuzzy self-adjusting cross-coupling control structure. This structure combines a fuzzy self-adjusting filter and an advanced synchronization compensator. The fuzzy self-adjusting filter adjusts the “softened speed”, a newly established concept, so that each motor follows the trajectory of the softened speed during start-up, thus effectively reducing the synchronization error of the starting process. The advanced synchronization compensator is added to shorten the adjusting time of the motors. In addition, this paper analyzes the synchronization performance of the structure when the steady state is interrupted by a sudden step of load. Finally, this paper establishes an experimental platform for a synchronous speed control system for a permanent magnet synchronous motor, and verifies the effectiveness of the proposed structure and the correctness of the theoretical analysis through performing experiments. Full article

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20 pages, 2967 KiB

Open AccessArticle

Lithium-Ion Battery Online Rapid State-of-Power Estimation under Multiple Constraints

by Shun Xiang¹

, Guangdi Hu^1,*, Ruisen Huang², Feng Guo¹ and Pengkai Zhou¹

¹ School of Mechanical Engineering, Southwest Jiaotong University, Chengdu 610031, China

² School of Mechanical Engineering, Pusan National University, Busan 46241, Korea

Energies 2018, 11(2), 283; https://doi.org/10.3390/en11020283 - 24 Jan 2018

Cited by 25 | Viewed by 4412

Abstract

The paper aims to realize a rapid online estimation of the state-of-power (SOP) with multiple constraints of a lithium-ion battery. Firstly, based on the improved first-order resistance-capacitance (RC) model with one-state hysteresis, a linear state-space battery model is built; then, using the dual [...] Read more.

The paper aims to realize a rapid online estimation of the state-of-power (SOP) with multiple constraints of a lithium-ion battery. Firstly, based on the improved first-order resistance-capacitance (RC) model with one-state hysteresis, a linear state-space battery model is built; then, using the dual extended Kalman filtering (DEKF) method, the battery parameters and states, including open-circuit voltage (OCV), are estimated. Secondly, by employing the estimated OCV as the observed value to build the second dual Kalman filters, the battery SOC is estimated. Thirdly, a novel rapid-calculating peak power/SOP method with multiple constraints is proposed in which, according to the bisection judgment method, the battery’s peak state is determined; then, one or two instantaneous peak powers are used to determine the peak power during

T

seconds. In addition, in the battery operating process, the actual constraint that the battery is under is analyzed specifically. Finally, three simplified versions of the Federal Urban Driving Schedule (SFUDS) with inserted pulse experiments are conducted to verify the effectiveness and accuracy of the proposed online SOP estimation method. Full article

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13 pages, 3471 KiB

Open AccessArticle

Stand-Alone Photovoltaic System Assessment in Warmer Urban Areas in Mexico

by Alberto-Jesus Perea-Moreno^1,*

, Quetzalcoatl Hernandez-Escobedo²

, Javier Garrido² and Joel Donaldo Verdugo-Diaz²

¹ Departamento de Física Aplicada, Universidad de Córdoba, CEIA3, Campus de Rabanales, 14071 Córdoba, Spain

² Faculty of Engineering, Campus Coatzacoalcos, University of Veracruz, Veracruz 96535, Mexico

Energies 2018, 11(2), 284; https://doi.org/10.3390/en11020284 - 24 Jan 2018

Cited by 16 | Viewed by 4226

Abstract

The aim of this study is to examine the possibility of using a stand-alone photovoltaic system (SAPVS) for electricity generation in urban areas in Southern Mexico. In Mexico, an urban area is defined as an area where more than 2500 inhabitants live. Due [...] Read more.

The aim of this study is to examine the possibility of using a stand-alone photovoltaic system (SAPVS) for electricity generation in urban areas in Southern Mexico. In Mexico, an urban area is defined as an area where more than 2500 inhabitants live. Due to constant migration from the countryside to the cities, the number of inhabitants of urban localities has been increasing. Global horizontal irradiation (GHI) data were recorded every 10 min during 2014–2016 in Coatzacoalcos in the state of Veracruz located on 18°08′09″ N and 94°27′48″ W. In this study, batteries represented 77% of the total cost, 12 PV panels of 310 W could export 5.41 MWh to the grid, and an inverter with an integrated controller and charger was selected, which decreased the initial cost. The city of Coatzacoalcos was chosen because the average annual temperature is 28°, with an average relative humidity of 75% and an average irradiance of 5.3 kWh/m²/day. An emission factor 0.505 tCO₂/MWh of greenhouse gases (GHG) were obtained, based on the power system, the reduction of net annual GHG would be 11 tCO₂ and a financial revenue of 36.951 × 10³ $/tCO₂ would be obtained. Financial parameters such as a 36.3% Internal Rate Return (IRR) and 3.4 years payback show the financial viability of this investment. SAPVSs in urban areas in Mexico could be a benefit as long as housing has a high consumption of electricity. Full article

(This article belongs to the Special Issue Urban Generation of Renewable Energy and Energy Saving in Cities)

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16 pages, 4791 KiB

Open AccessArticle

Analytical Determination of Energy Release in a Coal Mass

by Chengguo Zhang, Faham Tahmasebinia^*

, Ismet Canbulat, Onur Vardar and Serkan Saydam

School of Mining Engineering, University of New South Wales, Sydney, NSW 2052, Australia

Energies 2018, 11(2), 285; https://doi.org/10.3390/en11020285 - 24 Jan 2018

Cited by 8 | Viewed by 3400

Abstract

In underground mining, it is not currently feasible to forecast a coal burst incident. A coal burst usually includes suddenly abrupt energy release in line with the significant deformed shape in a coal mass as well as coal ejection. The major source of [...] Read more.

In underground mining, it is not currently feasible to forecast a coal burst incident. A coal burst usually includes suddenly abrupt energy release in line with the significant deformed shape in a coal mass as well as coal ejection. The major source of the released energy is the energy stored in the coal. The effect of geological characteristics in the coal on the possible released energy due to material and joint damping is classified as a current silent issue. Therefore, innovative research is needed to understand the influence of coal’s joint and cleat characters (directions and densities) on the possible energy release and/or dissipation. A simple and novel analytical solution is developed in this paper to calculate the amount of released energy due to varying joint density. A broad validation is conducted by comparing the outcomes of the developed analytical model with the results of a three-dimensional numerical simulation using the commercial discrete element package 3DEC. An appropriate agreement has been observed between the results from the numerical modelling and the suggested closed form solution. The paper derives a novel analytical solution to calculate the amount of released energy in coal with different joint densities. Full article

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15 pages, 1391 KiB

Open AccessArticle

Numerical Simulation of Fluid Flow through Fractal-Based Discrete Fractured Network

by Wendong Wang^1,*

, Yuliang Su¹, Bin Yuan^2,*, Kai Wang³

and Xiaopeng Cao⁴

¹ School of Petroleum Engineering, China University of Petroleum (East China), Qingdao 266580, China

² Department of Geoscience, University of Calgary, Calgary, AB T2N1N4, Canada

³ Mewbourne School of Petroleum and Geological Engineering, University of Oklahoma, Norman, OK 73019, USA

⁴ Shengli Oil Field Exploration and Development Research Institute, Dongying 257000, China

Energies 2018, 11(2), 286; https://doi.org/10.3390/en11020286 - 24 Jan 2018

Cited by 31 | Viewed by 5155

Abstract

Abstract: In recent years, multi-stage hydraulic fracturing technologies have greatly facilitated the development of unconventional oil and gas resources. However, a quantitative description of the “complexity” of the fracture network created by the hydraulic fracturing is confronted with many unsolved challenges. Given [...] Read more.

Abstract: In recent years, multi-stage hydraulic fracturing technologies have greatly facilitated the development of unconventional oil and gas resources. However, a quantitative description of the “complexity” of the fracture network created by the hydraulic fracturing is confronted with many unsolved challenges. Given the multiple scales and heterogeneity of the fracture system, this study proposes a “bifurcated fractal” model to quantitatively describe the distribution of induced hydraulic fracture networks. The construction theory is employed to generate hierarchical fracture patterns as a scaled numerical model. With the implementation of discrete fractal-fracture network modeling (DFFN), fluid flow characteristics in bifurcated fractal fracture networks are characterized. The effects of bifurcated fracture length, bifurcated tendency, and number of bifurcation stages are examined. A field example of the fractured horizontal well is introduced to calibrate the accuracy of the flow model. The proposed model can provide a more realistic representation of complex fracture networks around a fractured horizontal well, and offer the way to quantify the “complexity” of the fracture network in shale reservoirs. The simulation results indicate that the geometry of the bifurcated fractal fracture network model has a significant impact on production performance in the tight reservoir, and enhancing connectivity of each bifurcate fracture is the key to improve the stimulation performance. In practice, this work provides a novel and efficient workflow for complex fracture characterization and production prediction in naturally-fractured reservoirs of multi-stage fractured horizontal wells. Full article

(This article belongs to the Special Issue Flow and Transport Properties of Unconventional Reservoirs)

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18 pages, 2955 KiB

Open AccessArticle

Application of H_∞ Robust Control on a Scaled Offshore Oil and Gas De-Oiling Facility

by Petar Durdevic^* and Zhenyu Yang

Department of Energy Technology, Aalborg University, Esbjerg Campus, Niels Bohrs Vej 8, 6700 Esbjerg, Denmark

Energies 2018, 11(2), 287; https://doi.org/10.3390/en11020287 - 24 Jan 2018

Cited by 28 | Viewed by 4112

Abstract

The offshore de-oiling process is a vital part of current oil recovery, as it separates the profitable oil from water and ensures that the discharged water contains as little of the polluting oil as possible. With the passage of time, there is an [...] Read more.

The offshore de-oiling process is a vital part of current oil recovery, as it separates the profitable oil from water and ensures that the discharged water contains as little of the polluting oil as possible. With the passage of time, there is an increase in the water fraction in reservoirs that adds to the strain put on these facilities, and thus larger quantities of oil are being discharged into the oceans, which has in many studies been linked to negative effects on marine life. In many cases, such installations are controlled using non-cooperative single objective controllers which are inefficient in handling fluctuating inflows or complicated operating conditions. This work introduces a model-based robust H

_{\infty}

control solution that handles the entire de-oiling system and improves the system’s robustness towards fluctuating flow thereby improving the oil recovery and reducing the environmental impacts of the discharge. The robust H

_{\infty}

control solution was compared to a benchmark Proportional-Integral-Derivative (PID) control solution and evaluated through simulation and experiments performed on a pilot plant. This study found that the robust H

_{\infty}

control solution greatly improved the performance of the de-oiling process. Full article

(This article belongs to the Section L: Energy Sources)

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17 pages, 6594 KiB

Open AccessArticle

Mechanism and Prevention of a Chock Support Failure in the Longwall Top-Coal Caving Faces: A Case Study in Datong Coalfield, China

by Zhu Li¹, Jialin Xu^1,2,*, Shengchao Yu¹

, Jinfeng Ju³ and Jingmin Xu⁴

¹ School of Mines, China University of Mining and Technology, Xuzhou 221116, China

² State Key Laboratory of Coal Resource and Safe Mining, China University of Mining and Technology, Xuzhou 221116, China

³ IoT Perception Mine Research Center, China University of Mining and Technology, Xuzhou 221008, China

⁴ Department of Civil Engineering, Faculty of Engineering, University of Nottingham, University Park, Nottingham NG7 2RD, UK

Energies 2018, 11(2), 288; https://doi.org/10.3390/en11020288 - 24 Jan 2018

Cited by 36 | Viewed by 4851

Abstract

Longwall chock support failures seriously restrain the safety and high-efficiency of mining of extra thick coal seams, as well as causing a great waste of coal resources. During longwall top-coal caving (LTCC), the influential effect of the properties and the movement regulation of [...] Read more.

Longwall chock support failures seriously restrain the safety and high-efficiency of mining of extra thick coal seams, as well as causing a great waste of coal resources. During longwall top-coal caving (LTCC), the influential effect of the properties and the movement regulation of top-coal on strata behavior cannot be ignored, since the top-coal is the medium through which the load of the overlying strata is transferred to the chock supports. Taking Datong coalfield as an example, the mechanism of a chock support failure in the LTCC face was investigated. Research findings indicated that the hard top-coal and insufficient chock support capacity were primary reasons for chock support failure accidents. On account of the field-measured results, a new method to determine support capacity was proposed, which fully took the impact of the top-coal strength into consideration. The calculation revealed that the required support capacity had exceeded the existing production maximum, at about 22,000 KN. Since it was unrealistic to simply increase chock support capacity, other approaches, according to the theoretical analysis, were proposed, such as lowering the integrity and strength of the top-coal, and upgrading its crushing effect to weaken the support load effectively during the weighting period, which reduces the likelihood of chock support accidents occurring. Based on this, hydraulic fracturing for hard top-coal and optimization of the caving process (chock supports raised up and down repeatedly by manual operation before moving forward) were presented. The proposed solutions were successfully applied in LTCC-west8101 for subsequent mining and achieved substantial benefits. The above research provides valuable references and ideas for the control of strata behavior to ensure safe and highly efficient mining in extremely thick and hard coal seams with the LTCC method. Full article

(This article belongs to the Section L: Energy Sources)

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22 pages, 5283 KiB

Open AccessArticle

Impact of Climate Change on Combined Solar and Run-of-River Power in Northern Italy

by Baptiste François^1,2,3,*

, Benoit Hingray¹, Marco Borga², Davide Zoccatelli⁴, Casey Brown³ and Jean-Dominique Creutin¹

¹ Université de Grenoble-Alpes, CNRS, IGE, F-38000 Grenoble, France

² Department of Land, Environment, Agriculture and Forestry, University of Padova, IT-35020 Padova, Italy

³ Department of Civil and Environmental Engineering, University of Massachusetts Amherst, Amherst, MA 01003-9303, USA

⁴ Department of Geography, Hebrew University of Jerusalem, Jerusalem 9190401, Israel

Energies 2018, 11(2), 290; https://doi.org/10.3390/en11020290 - 25 Jan 2018

Cited by 35 | Viewed by 5190

Abstract

Moving towards energy systems with high variable renewable energy shares requires a good understanding of the impacts of climate change on the energy penetration. To do so, most prior impact studies have considered climate projections available from Global Circulation Models (GCMs). Other studies [...] Read more.

Moving towards energy systems with high variable renewable energy shares requires a good understanding of the impacts of climate change on the energy penetration. To do so, most prior impact studies have considered climate projections available from Global Circulation Models (GCMs). Other studies apply sensitivity analyses on the climate variables that drive the system behavior to inform how much the system changes due to climate change. In the present work, we apply the Decision Scaling approach, a framework merging these two approaches, for analyzing a renewables-only scenario for the electric system of Northern Italy where the main renewable sources are solar and hydropower. Decision Scaling explores the system sensibility to a range of future plausible climate states. GCM projections are considered to estimate probabilities of the future climate states. We focus on the likely future energy mix within the region (25% of solar photovoltaic and 75% of hydropower). We also carry out a sensitivity analysis according to the storage capacity. The results show that run-of-the river power generation from this Alpine area is expected to increase although the average inflow decreases under climate change. They also show that the penetration rate is expected to increase for systems with storage capacity less than one month of average load and inversely for higher storage capacity. Full article

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18 pages, 3728 KiB

Open AccessArticle

Solar Ray Tracing Analysis to Determine Energy Availability in a CPC Designed for Use as a Residential Water Heater

by Miguel Terrón-Hernández¹

, Manuel I. Peña-Cruz², Jose G. Carrillo^1,*

, Ulises Diego-Ayala³

and Vicente Flores⁴

¹ Renewable Energy Department, Centro de Investigación Científica de Yucatán, Mérida 97200, Mexico

² Conacyt—Centro de Investigaciones en Óptica, Unidad de Aguascalientes, Prol. Constitución 607, Reserva Loma Bonita, Aguascalientes 20200, Mexico

³ Arian International Projects, c/Baldiri Reixach, 4, 08028 Barcelona, Spain

⁴ Metal-Mechanical Department, Instituto Tecnológico Nacional de México, Campus Apizaco, Av. Instituto Tecnológico S/N, Apizaco 90300, Mexico

Energies 2018, 11(2), 291; https://doi.org/10.3390/en11020291 - 25 Jan 2018

Cited by 18 | Viewed by 5608

Abstract

Compound parabolic concentrators are relevant systems used in solar thermal technology. With adequate tailoring, they can be used as an efficient and low-cost alternative in residential water heating applications. This work presents a simulation study using a ray tracing analysis. With this technique, [...] Read more.

Compound parabolic concentrators are relevant systems used in solar thermal technology. With adequate tailoring, they can be used as an efficient and low-cost alternative in residential water heating applications. This work presents a simulation study using a ray tracing analysis. With this technique, we simulate the interaction between solar rays and solar concentrator to quantify the amount of energy that impinges on the receiver at a particular time. Energy availability is evaluated in a comparison of two configurations throughout the year: static setup at 21° and multi-position setup; tilted with respect to the horizontal, depending on three seasonal positions: 0° for summer, 16° for spring/autumn, and 32° for winter, with the aim to evaluate the amount of available energy in each season. The fact that a tracking system can be dispensed with also represents an economical option for the proposed application. The results showed that at 21°, the proposed solar Compound Parabolic Concentrator (CPC) works satisfactorily; however, by carrying out the selected angular adjustments, the overall energy availability increased by 22%, resulting in a more efficient option. The most effective design was also built and analyzed outdoors. The obtained thermal efficiency was of ~43%. The optical design and its evaluation developed herein proved to be a valuable tool for prototype design and performance evaluation. Full article

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29 pages, 8042 KiB

Open AccessArticle

Data Analytics Techniques for Performance Prediction of Steamflooding in Naturally Fractured Carbonate Reservoirs

by Ali Shafiei^1,*

, Mohammad Ali Ahmadi²

, Maurice B. Dusseault³, Ali Elkamel^4,5, Sohrab Zendehboudi²

and Ioannis Chatzis⁶

¹ Department of Petroleum Engineering, School of Mining and Geosciences, Nazarbayev University, Astana 010000, Kazakhstan

² Faculty of Engineering & Applied Science, Memorial University, St. John’s, NL A1B3X7, Canada

³ Department of Earth and Environmental Sciences, University of Waterloo, Waterloo, ON N2L 3G2, Canada

⁴ Department of Chemical Engineering, University of Waterloo, Waterloo, ON N2L 3G2, Canada

⁵ Department of Chemical Engineering, The Petroleum Institute, Khalifa University, Abu Dhabi 51900, UAE

⁶ Department of Petroleum Engineering, College of Engineering and Petroleum, Kuwait University, Kuwait City 10002, Kuwait

Energies 2018, 11(2), 292; https://doi.org/10.3390/en11020292 - 26 Jan 2018

Cited by 4 | Viewed by 4907

Abstract

Thermal oil recovery techniques, including steam processes, account for more than 80% of the current global heavy oil, extra heavy oil, and bitumen production. Evaluation of Naturally Fractured Carbonate Reservoirs (NFCRs) for thermal heavy oil recovery using field pilot tests and exhaustive numerical [...] Read more.

Thermal oil recovery techniques, including steam processes, account for more than 80% of the current global heavy oil, extra heavy oil, and bitumen production. Evaluation of Naturally Fractured Carbonate Reservoirs (NFCRs) for thermal heavy oil recovery using field pilot tests and exhaustive numerical and analytical modeling is expensive, complex, and personnel-intensive. Robust statistical models have not yet been proposed to predict cumulative steam to oil ratio (CSOR) and recovery factor (RF) during steamflooding in NFCRs as strong process performance indicators. In this paper, new statistical based techniques were developed using multivariable regression analysis for quick estimation of CSOR and RF in NFCRs subjected to steamflooding. The proposed data based models include vital parameters such as in situ fluid and reservoir properties. The data used are taken from experimental studies and rare field trials of vertical well steamflooding pilots in heavy oil NFCRs reported in the literature. The models show an average error of <6% for the worst cases and contain fewer empirical constants compared with existing correlations developed originally for oil sands. The interactions between the parameters were considered indicating that the initial oil saturation and oil viscosity are the most important predictive factors. The proposed models were successfully predicted CSOR and RF for two heavy oil NFCRs. Results of this study can be used for feasibility assessment of steamflooding in NFCRs Full article

(This article belongs to the Section L: Energy Sources)

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20 pages, 2738 KiB

Open AccessFeature PaperArticle

Technoeconomic and Policy Drivers of Project Performance for Bioenergy Alternatives Using Biomass from Beetle-Killed Trees

by Robert M. Campbell^1,*, Nathaniel M. Anderson², Daren E. Daugaard³ and Helen T. Naughton¹

¹ Department of Economics, University of Montana, Liberal Arts Room 407, 32 Campus Dr., Missoula, MT 59812, USA

² U.S. Forest Service, Rocky Mountain Research Station, 800 East Beckwith, Missoula, MT 59801, USA

³ Cool Planet Energy Systems, 6400 South Fiddlers Green Circle, Greenwood Village, CO 80111, USA

Energies 2018, 11(2), 293; https://doi.org/10.3390/en11020293 - 26 Jan 2018

Cited by 20 | Viewed by 5002

Abstract

As a result of widespread mortality from beetle infestation in the forests of the western United States, there are substantial stocks of biomass suitable as a feedstock for energy production. This study explored the financial viability of four production pathway scenarios for the [...] Read more.

As a result of widespread mortality from beetle infestation in the forests of the western United States, there are substantial stocks of biomass suitable as a feedstock for energy production. This study explored the financial viability of four production pathway scenarios for the conversion of beetle-killed pine to bioenergy and bioproducts in the Rocky Mountains. Monte Carlo simulation using data obtained from planned and existing projects was used to account for uncertainty in key technoeconomic variables and to provide distributions of project net present value (NPV), as well as for sensitivity analysis of key economic and production variables. Over a 20-year project period, results for base case scenarios reveal mean NPV ranging from a low of −$8.3 million for electric power production to a high of $76.0 million for liquid biofuel with a biochar co-product. However, under simulation, all scenarios had conditions resulting in both positive and negative NPV. NPV ranged from −$74.5 million to $51.4 million for electric power, and from −$21.6 million to $246.3 million for liquid biofuels. The potential effects of economic trends and public policies that aim to promote renewable energy and biomass utilization are discussed for each production pathway. Because the factors that most strongly affect financial viability differ across projects, the likely effects of particular types of policies are also shown to vary substantially. Full article

(This article belongs to the Collection Bioenergy and Biofuel)

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13 pages, 14433 KiB

Open AccessArticle

Organic Soiling: The Role of Pollen in PV Module Performance Degradation

by Ricardo Conceição^1,2

, Hugo G. Silva^1,2,*

, José Mirão³

and Manuel Collares-Pereira^1,2

¹ Renewable Energies Chair, University of Evora, 7002-554 Evora, Portugal

² Institute of Earth Sciences, University of Evora, 7000-671 Evora, Portugal

³ Hercules Laboratory, University of Evora, 7000-089 Evora, Portugal

Energies 2018, 11(2), 294; https://doi.org/10.3390/en11020294 - 26 Jan 2018

Cited by 43 | Viewed by 4874

Abstract

Soiling is a problem for solar energy harvesting technologies, such as in photovoltaic modules technologies. This paper describes not only one complete year of Soiling Ratioindex and rates measured in a rural environment of Southern Europe, but also focuses on the seasonal variation [...] Read more.

Soiling is a problem for solar energy harvesting technologies, such as in photovoltaic modules technologies. This paper describes not only one complete year of Soiling Ratioindex and rates measured in a rural environment of Southern Europe, but also focuses on the seasonal variation of the type of soiling, mainly spring and summer. The Soiling Ratio index is calculated based on the maximum power output and short circuit current of two photovoltaic (PV) panels, along with Scanning Electron Microscopy and Energy Dispersive X-Ray of glass samples to provide visual and chemical inspection of the type of soiling. Mass accumulation on glass samples mounted on a “glass tree” was weekly measured with a microbalance and related with the Soiling Ratio metrics. Soiling rates were calculated to infer the degree of soiling for each season and the respective comparison made. Results show a soiling rate of 4.1%/month in April (spring), 1.9%/month in July (summer) and 1.6%/month in September (fall). Rain (the main natural cleaning agent of the photovoltaic modules) as well as aerosol optical depth (proxy for atmospheric particle concentration) were correlated with the Soiling Ratio. In-depth analysis on the type of organic soiling was performed. Full article

(This article belongs to the Special Issue PV System Design and Performance)

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21 pages, 9564 KiB

Open AccessFeature PaperArticle

Analysis of the Effect of Vehicle, Driving and Road Parameters on the Transient Performance and Emissions of a Turbocharged Truck

by Evangelos G. Giakoumis^*

and George Triantafillou

Internal Combustion Engines Laboratory, School of Mechanical Engineering, National Technical University of Athens, 15780 Athens, Greece

Energies 2018, 11(2), 295; https://doi.org/10.3390/en11020295 - 27 Jan 2018

Cited by 13 | Viewed by 4924

Abstract

In this paper, a fundamental analysis of the effects of various influential parameters on the performance and emissions of a turbocharged truck operating under transient conditions is presented. The results derive from a detailed vehicle model that comprises two parts. The first is [...] Read more.

In this paper, a fundamental analysis of the effects of various influential parameters on the performance and emissions of a turbocharged truck operating under transient conditions is presented. The results derive from a detailed vehicle model that comprises two parts. The first is an engine performance and emissions module that follows a mapping approach, with experimentally derived correction coefficients employed to account for transient discrepancies; this is then coupled to a comprehensive vehicle model that takes into account various vehicle operation attributes such as gearbox, tires, tire slip, etc. Soot, as well as nitrogen monoxide, are the examined engine-out pollutants, together with fuel consumption and carbon dioxide. The parameters examined are vehicular (mass and gearbox), driving (driver ‘aggressiveness’ and gear-shift profile) and road (type and grade). From the range of values investigated, the most critical parameters for the emission of NO and soot are vehicle mass, driving ‘aggressiveness’ and the exact gear-change profile. Vehicle mass, driving ‘aggressiveness’ and road-grade were identified as the most influential parameters for the emission of CO₂. A notable statistical correlation was established between pollutant emissions (NO, soot) and vehicle mass or road-tire friction, as well as between fueling/CO₂ and vehicle mass, road-tire friction and road grade. It is believed that the results obtained shed light into the effect of critical operating parameters on the engine-out emissions of a truck/bus, underlining at the same time the peculiarities of transient operating conditions. Full article

(This article belongs to the Special Issue Recent Advances in Internal Combustion Engines Operation and Emissions)

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12 pages, 616 KiB

Open AccessArticle

Generalized Dynamical Modeling of Multiple Photovoltaic Units in a Grid-Connected System for Analyzing Dynamic Interactions

by Tahsin Fahima Orchi, Md Apel Mahmud^*

and Amanullah Maung Than Oo

Electrical Power & Energy Systems Research Laboratory (EPESRL), School of Engineering, Deakin University, Geelong, VIC 3216, Australia

Energies 2018, 11(2), 296; https://doi.org/10.3390/en11020296 - 27 Jan 2018

Cited by 11 | Viewed by 3555

Abstract

This paper aims to develop the generalized dynamical model of multiple photovoltaic (PV) units connected to the grid along with the dynamic interaction analysis among different PV units. The dynamical models of multiple PV units are developed by considering three different configurations through [...] Read more.

This paper aims to develop the generalized dynamical model of multiple photovoltaic (PV) units connected to the grid along with the dynamic interaction analysis among different PV units. The dynamical models of multiple PV units are developed by considering three different configurations through which these PV units are connected to the grid. These configurations include: (a) the direct connection of multiple PV units to the grid; (b) the connection of multiple PV units to the grid through a point of common coupling (PCC); and (c) the connection of PV units without a PCC. The proposed modeling framework provides meaningful insights for analyzing dynamic interaction analysis where these interactions from other PV units are expressed in terms of voltages and line impedances rather than the dynamics of currents. The dynamic interactions among different PV units for all these configurations are analyzed using both analytical and simulation studies. Simulations are carried out on an IEEE 15-bus test system and dynamic interactions are analyzed from the total harmonic distortions (THDs) in the current responses of different PV units. Both analytical and simulation studies clearly indicate that the effects of dynamic interactions are prominent with the increase in PV units. Full article

(This article belongs to the Section L: Energy Sources)

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24 pages, 5366 KiB

Open AccessArticle

Numerical Study of the Effect of Winglets on the Performance of a Straight Blade Darrieus Water Turbine

by Santiago Laín^1,*, Manuel A. Taborda¹ and Omar D. López²

¹ Modelling, Analysis and Simulation of Environmental and Industrial Processes (PAI+) Research Group, Universidad Autónoma de Occidente, Calle 25 No 115-85, Cali, Colombia

² Computational Mechanics Research Group, Universidad de los Andes, Carrera 1Este No 19A-40, Bogotá, Colombia

Energies 2018, 11(2), 297; https://doi.org/10.3390/en11020297 - 28 Jan 2018

Cited by 29 | Viewed by 5098

Abstract

This study deals with the three-dimensional unsteady numerical simulation of the flow around a cross-flow vertical-axis water turbine (CFWT) of the Darrieus type. The influence of turbine design on its hydrodynamic characteristics and performance is investigated by means of a time-accurate Reynolds Averaged [...] Read more.

This study deals with the three-dimensional unsteady numerical simulation of the flow around a cross-flow vertical-axis water turbine (CFWT) of the Darrieus type. The influence of turbine design on its hydrodynamic characteristics and performance is investigated by means of a time-accurate Reynolds Averaged Navier Stokes (RANS) commercial solver. The flow unsteadiness is described using a transient rotor-stator model in connection with a sliding interface. A classical Darrieus straight blade turbine, based on the NACA0025 airfoil, has been modified adding winglets (symmetric and asymmetric designs) to the blades’ tips with the objective of reducing the strength of the detached trailing vortices. The turbulent features of the flow have been modelled by using different turbulence models (k-ε Renormalization Group, standard Shear Stress Transport, transition Shear Stress Transport and Reynolds Stress Model). As a result, the predicted hydrodynamic performance of the turbine including winglets increases, independently of the employed turbulence model, being the improvement higher when a symmetric winglet design is considered. Moreover, visualization of skin friction lines pattern and their connection with vorticity isosurfaces, illustrating the flow detachment in the three blade configurations, has been carried out. Finally, a short discussion about the intermittency behavior along a turbine revolution is presented. Full article

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13 pages, 5343 KiB

Open AccessArticle

Investigation into Window Insulation Retrofitting of Existing Buildings Using Thin and Translucent Frame-Structure Vacuum Insulation Panels

by Zhang Yang^*

, Takao Katsura, Masahiro Aihara, Makoto Nakamura and Katsunori Nagano

Division of Human Environmental Systems, Graduate School of Engineering, Hokkaido University, N13-W8, Kita-ku, Sapporo 060-8628, Japan

Energies 2018, 11(2), 298; https://doi.org/10.3390/en11020298 - 28 Jan 2018

Cited by 5 | Viewed by 5043

Abstract

Insulation performance in older buildings is usually poor, so retrofitting the insulation in these buildings would reduce the energy required for heating, resulting in cost and energy savings. Windows account for a significant amount of the heat loss, therefore, we have developed vacuum [...] Read more.

Insulation performance in older buildings is usually poor, so retrofitting the insulation in these buildings would reduce the energy required for heating, resulting in cost and energy savings. Windows account for a significant amount of the heat loss, therefore, we have developed vacuum layer type vacuum insulation panels (VIPs) with a frame structure that is also slim and lightweight. The developed VIPs are inexpensive and easy to install, as well as being slim and translucent, so retrofitting the window insulation of existing buildings can be easily performed. In this paper, we propose a frame covering with a low emissivity film and a gas barrier envelope coating, with a focus on a reasonable design method. Firstly, a structural model was created to evaluate the safety and specifications of the frame using element mechanical analysis. Next, a finite element model (FEM) was created to predict the insulation performance. Subsequently, experimental validation was completed and the insulation performance was evaluated with the measured thermal conductivity by a guarded hot plate (GHP) apparatus. Finally, case studies were used to evaluate the insulation performance under different conditions. The optimum design included a reasonable frame-structure to hold the vacuum layer with a high insulation thermal conductivity performance of approximately 0.0049 W/(m·K). Full article

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13 pages, 1749 KiB

Open AccessArticle

Biodiesel from Hydrolyzed Waste Cooking Oil Using a S-ZrO₂/SBA-15 Super Acid Catalyst under Sub-Critical Conditions

by Muhammad Nobi Hossain, Md Sufi Ullah Siddik Bhuyan, Abul Hasnat Md Ashraful Alam and Yong Chan Seo^*

Department of Environmental Engineering, Sangji University, 83 Sangjidae-gil, Wonju-si, Gangwon-do 26339, Korea

Energies 2018, 11(2), 299; https://doi.org/10.3390/en11020299 - 29 Jan 2018

Cited by 35 | Viewed by 6376

Abstract

Due to rapid changes in food habits, a substantial amount of waste fat and used oils are generated each year. Due to strong policies, the disposal of this material into nearby sewers causes ecological and environmental problems in many parts of the world. [...] Read more.

Due to rapid changes in food habits, a substantial amount of waste fat and used oils are generated each year. Due to strong policies, the disposal of this material into nearby sewers causes ecological and environmental problems in many parts of the world. For efficient management, waste cooking oil, a less expensive, alternative and promising feedstock, can be used as a raw material for producing biofuel. In the present study, we produced a biodiesel from hydrolyzed waste cooking oil with a subcritical methanol process using a synthesized solid super acid catalyst, a sulfated zirconium oxide supported on Santa Barbara Amorphous silica (S-ZrO₂/SBA-15). The characterization of the synthesized catalyst was carried out using scanning electron microscopy (SEM), X-ray diffraction (XRD), and the Brunauer-Emmett-Teller (BET) method. The catalytic effect on biodiesel production was examined by varying the parameters: temperatures of 120 to 200 °C, 5–20 min times, oil-to-methanol mole ratios between 1:5 to 1:20, and catalyst loadings of 1–2.5%. The maximum biodiesel yield was 96.383%, obtained under optimum reaction conditions of 140 °C, 10 min, and a 1:10 oil-to-methanol molar ratio with a 2.0% catalyst loading. We successfully reused the catalyst five times without regeneration with a 90% efficiency. The fuel properties were found to be within the limits set by the biodiesel standard. Full article

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17 pages, 2447 KiB

Open AccessArticle

Bayesian Based Diagnostic Model for Condition Based Maintenance of Offshore Wind Farms

by Masoud Asgarpour^1,2,* and John Dalsgaard Sørensen¹

¹ Department of Civil Engineering, Aalborg University, DK-9220 Aalborg, Denmark

² Vattenfall, Business Area Wind, Analytics & Asset Integrity Management, Hoekenrode 8, 1102 BR Amsterdam, The Netherlands

Energies 2018, 11(2), 300; https://doi.org/10.3390/en11020300 - 29 Jan 2018

Cited by 23 | Viewed by 5567

Abstract

Operation and maintenance costs are a major contributor to the Levelized Cost of Energy for electricity produced by offshore wind and can be significantly reduced if existing corrective actions are performed as efficiently as possible and if future corrective actions are avoided by [...] Read more.

Operation and maintenance costs are a major contributor to the Levelized Cost of Energy for electricity produced by offshore wind and can be significantly reduced if existing corrective actions are performed as efficiently as possible and if future corrective actions are avoided by performing sufficient preventive actions. This paper presents an applied and generic diagnostic model for fault detection and condition based maintenance of offshore wind components. The diagnostic model is based on two probabilistic matrices; first, a confidence matrix, representing the probability of detection using each fault detection method, and second, a diagnosis matrix, representing the individual outcome of each fault detection method. Once the confidence and diagnosis matrices of a component are defined, the individual diagnoses of each fault detection method are combined into a final verdict on the fault state of that component. Furthermore, this paper introduces a Bayesian updating model based on observations collected by inspections to decrease the uncertainty of initial confidence matrix. The framework and implementation of the presented diagnostic model are further explained within a case study for a wind turbine component based on vibration, temperature, and oil particle fault detection methods. The last part of the paper will have a discussion of the case study results and present conclusions. Full article

(This article belongs to the Section F: Electrical Engineering)

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30 pages, 2505 KiB

Open AccessArticle

Control Scheme of a Concentration Photovoltaic Plant with a Hybrid Energy Storage System Connected to the Grid

by Pedro Roncero-Sánchez^1,*

, Alfonso Parreño Torres²

and Javier Vázquez¹

¹ School of Industrial Engineering, University of Castilla-La Mancha, Campus Universitario S/N, 13071 Ciudad Real, Spain

² Institute of Industrial Development, Castilla-La Mancha Science and Technology Park, Paseo de la Innovación 1, 02006 Albacete, Spain

Energies 2018, 11(2), 301; https://doi.org/10.3390/en11020301 - 30 Jan 2018

Cited by 13 | Viewed by 4205

Abstract

In the last few decades, renewable energy sources (RESs) have been integrated into the electrical grid in order to curb the deficiency of energy owing to, among other factors, the depletion of fossil fuels and the increasing awareness of climate change. However, the [...] Read more.

In the last few decades, renewable energy sources (RESs) have been integrated into the electrical grid in order to curb the deficiency of energy owing to, among other factors, the depletion of fossil fuels and the increasing awareness of climate change. However, the stochastic nature of these sources, along with changes in levels of energy consumption, signifies that attention now needs to be paid for energy storage systems (ESSs). One of the most promising RESs is concentration photovoltaic (CPV) energy, owing to the high efficiency obtained and its sustainability regarding environmental issues. However, as CPV systems work only with direct solar radiation, they require ESSs in order to smooth the variations in the energy generated. This paper deals with the integration into the grid of a CPV plant that employs a hybrid ESS (HESS) based on ultracapacitors and batteries. The HESS allows the complete system to inject a constant active power level into the grid and thus flatten the profile of the energy generated. This goal is achieved by using a power electronic topology based on various DC–DC converters and a DC–AC converter, both of which share the same DC link. The control system is tailored in order to decouple the active-power and the reactive-power injections. Simulation results obtained using PSCAD/EMTDC (Power System Computer Aided Design/Electromagnetic Transient Direct Current) show the resulting performance of a 200 kW CPV plant with a hybrid ESS. Full article

(This article belongs to the Section F: Electrical Engineering)

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9 pages, 985 KiB

Open AccessFeature PaperArticle

Optimization of the Transesterification of Waste Cooking Oil with Mg-Al Hydrotalcite Using Response Surface Methodology

by Laureano Costarrosa¹, David Eduardo Leiva-Candia¹, Antonio José Cubero-Atienza²

, Juan José Ruiz¹ and M. Pilar Dorado^1,*

¹ Department of Physical Chemistry and Applied Thermodynamics, EPS, Edificio Leonardo da Vinci, Campus de Rabanales, Universidad de Córdoba, Campus de Excelencia Agroalimentario ceiA3, 14014 Córdoba, Spain

² Department of Rural Engineering, EPS, Edificio Leonardo da Vinci, Campus de Rabanales, Universidad de Córdoba, Campus de Excelencia Agroalimentario ceiA3, 14014 Córdoba, Spain

Energies 2018, 11(2), 302; https://doi.org/10.3390/en11020302 - 30 Jan 2018

Cited by 23 | Viewed by 4335

Abstract

Nowadays, biodiesel has become a very promising alternative to fossil diesel fuel, regarding environmental concerns and fuel resource depletion. Biodiesel is usually produced through homogeneous or heterogeneous transesterification of different fatty raw materials. Although main research has been carried out with homogenous catalysts, [...] Read more.

Nowadays, biodiesel has become a very promising alternative to fossil diesel fuel, regarding environmental concerns and fuel resource depletion. Biodiesel is usually produced through homogeneous or heterogeneous transesterification of different fatty raw materials. Although main research has been carried out with homogenous catalysts, heterogeneous catalysts may be of interest due to ease of recovery and recycling, as well as readiness for continuous processing. In this work, calcined Mg-Al hydrotalcite (HT) was used for the heterogeneous transesterification of waste cooking oil. Three reaction parameters, namely, reaction time, amount of catalyst, and methanol-to-oil molar ratio, were optimized by means of Response Surface Methodology (RSM) at constant temperature (65 °C), using a Box-Behnken design. Optimal fatty acid methyl ester (FAME) content (86.23% w/w FAME/sample) was predicted by the model with an R-squared value of 98.45%, using 3.39 g of HT (8.5% w/w oil) and an 8:1 methanol-oil molar ratio, for a duration of 3.12 h. It was observed that calcination of HT, while avoiding the previous washing step, allowed the presence of chemical species that enhanced the effect of the catalyst. It can be concluded from this field trial that calcined and nonwashed Mg-Al hydrotalcite may be considered an effective basic catalyst for the production of biodiesel from waste cooking oil. Also, RSM proved to be a useful tool for predicting biodiesel yield. Full article

(This article belongs to the Special Issue Urban Generation of Renewable Energy and Energy Saving in Cities)

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12 pages, 1017 KiB

Open AccessArticle

A Generic Approach to Analyze the Impact of a Future Aircraft Design on the Boarding Process

by Bekir Yildiz¹

, Peter Förster¹, Thomas Feuerle¹, Peter Hecker^1,*

, Stefan Bugow²

and Stefan Helber²

¹ Institute of Flight Guidance, Technische Universität Braunschweig, 38118 Braunschweig, Germany

² Institute of Production Management, Leibniz Universität Hannover, 30167 Hannover, Germany

Energies 2018, 11(2), 303; https://doi.org/10.3390/en11020303 - 30 Jan 2018

Cited by 8 | Viewed by 8418

Abstract

The turnaround process constitutes an important part of the air transportation system. Airports often represent bottlenecks in air traffic management (ATM), thus operations related to the preparation of the aircraft for the next flight leg have to be executed smoothly and in a [...] Read more.

The turnaround process constitutes an important part of the air transportation system. Airports often represent bottlenecks in air traffic management (ATM), thus operations related to the preparation of the aircraft for the next flight leg have to be executed smoothly and in a timely manner. The ATM significantly depends on a reliable turnaround process. Future paradigm changes with respect to airplane energy sources, aircraft design or propulsion concepts will also influence the airport layout. As a consequence, operational processes associated with the turnaround will be affected. Airlines aim for efficient and timely turnaround operations that are correlated with higher profits. This case study discusses an approach to investigate a new aircraft design with respect to the implications on the turnaround. The boarding process, as part of the turnaround, serves as an example to evaluate the consequences of new design concepts. This study is part of an interdisciplinary research to investigate future energy, propulsion and designs concepts and their implications on the whole ATM system. Due to these new concepts, several processes of the turnaround will be affected. For example, new energy storage concepts will influence the fueling process on the aircraft itself or might lead to a new infrastructure at the airport. This paper aims to evaluate the applied methodology in the case of a new boarding process, due to a new aircraft design, by means of a generic example. An agent-based boarding simulation is applied to assess passenger behavior during boarding, particularly with regard to cabin layout and seat configuration. The results of the generic boarding simulation are integrated into a simplified, deterministic and generic simulation of the turnaround process. This was done to assess the proposed framework for future investigations which on the one hand address the ATM system holistically and on the other, incorporate additional or adapted processes of the turnaround. Full article

(This article belongs to the Special Issue Towards a Transformation to Sustainable Aviation Systems)

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25 pages, 16036 KiB

Open AccessFeature PaperArticle

Brazilian Tensile Strength of Anisotropic Rocks: Review and New Insights

by Tianshou Ma^1,2,*

, Nian Peng¹, Zhu Zhu³, Qianbing Zhang⁴, Chunhe Yang² and Jian Zhao⁴

¹ State Key Laboratory of Oil & Gas Reservoir Geology and Exploitation, Southwest Petroleum University, Chengdu 610500, China

² State Key Laboratory of Geomechanics and Geotechnical Engineering, Institute of Rock and Soil Mechanics, Chinese Academy of Sciences, Wuhan 430071, China

³ College of Management and Science, Chengdu University of Technology, Chengdu 610059, China

⁴ Department of Civil Engineering, Monash University, Melbourne, VIC 3800, Australia

Energies 2018, 11(2), 304; https://doi.org/10.3390/en11020304 - 30 Jan 2018

Cited by 89 | Viewed by 11207

Abstract

Strength anisotropy is one of the most distinct features of anisotropic rocks, and it also normally reveals strong anisotropy in Brazilian test Strength (“BtS”). Theoretical research on the “BtS” of anisotropic rocks is seldom performed, and in particular some significant factors, such as [...] Read more.

Strength anisotropy is one of the most distinct features of anisotropic rocks, and it also normally reveals strong anisotropy in Brazilian test Strength (“BtS”). Theoretical research on the “BtS” of anisotropic rocks is seldom performed, and in particular some significant factors, such as the anisotropic tensile strength of anisotropic rocks, the initial Brazilian disc fracture points, and the stress distribution on the Brazilian disc, are often ignored. The aim of the present paper is to review the state of the art in the experimental studies on the “BtS” of anisotropic rocks since the pioneering work was introduced in 1964, and to propose a novel theoretical method to underpin the failure mechanisms and predict the “BtS” of anisotropic rocks under Brazilian test conditions. The experimental data of Longmaxi Shale-I and Jixi Coal were utilized to verify the proposed method. The results show the predicted “BtS” results show strong agreement with experimental data, the maximum error is only ~6.55% for Longmaxi Shale-I and ~7.50% for Jixi Coal, and the simulated failure patterns of the Longmaxi Shale-I are also consistent with the test results. For the Longmaxi Shale-I, the Brazilian disc experiences tensile failure of the intact rock when 0° ≤ β_w ≤ 24°, shear failure along the weakness planes when 24° ≤ β_w ≤ 76°, and tensile failure along the weakness planes when 76° ≤ β_w ≤ 90°. For the Jixi Coal, the Brazilian disc experiences tensile failure when 0° ≤ β_w ≤ 23° or 76° ≤ β_w ≤ 90°, shear failure along the butt cleats when 23° ≤ β_w ≤ 32°, and shear failure along the face cleats when 32° ≤ β_w ≤ 76°. The proposed method can not only be used to predict the “BtS” and underpin the failure mechanisms of anisotropic rocks containing a single group of weakness planes, but can also be generalized for fractured rocks containing multi-groups of weakness planes. Full article

(This article belongs to the Special Issue Unconventional Natural Gas (UNG) Recoveries 2018)

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24 pages, 9278 KiB

Open AccessArticle

The PurdueTracer: An Energy-Efficient Human-Powered Hydraulic Bicycle with Flexible Operation and Software Aids

by Gianluca Marinaro^1,*

, Zhuangying Xu², Zhengpu Chen³, Chenxi Li³

, Yizhou Mao² and Andrea Vacca^2,3,4

¹ Department of Industrial Engineering, University Federico II, 80100 Naples, Italy

² School of Mechanical Engineering, Purdue University, West Lafayette, IN 47906, USA

³ Department of Agricultural and Biological Engineering, Purdue University, West Lafayette, IN 47906, USA

⁴ Maha Fluid Power Research Center, Purdue University, West Lafayette, IN 47906, USA

Energies 2018, 11(2), 305; https://doi.org/10.3390/en11020305 - 31 Jan 2018

Cited by 4 | Viewed by 9440

Abstract

Hydrostatic transmissions (HT) are widely applied to heavy-duty mobile applications because of the advantages of layout flexibility, power to weight ratio, and ease of control. Though applications of fluid power in light-duty vehicles face challenges, including the unavailability of off-the-shelf components suitable to [...] Read more.

Hydrostatic transmissions (HT) are widely applied to heavy-duty mobile applications because of the advantages of layout flexibility, power to weight ratio, and ease of control. Though applications of fluid power in light-duty vehicles face challenges, including the unavailability of off-the-shelf components suitable to the power scale, there are potential advantages for HTs in human-powered vehicles, such as bicycles, the most important one being the energy-saving advantage achievable through regenerative braking in a hybrid HT. This paper describes an innovative design for a hydraulic hybrid bicycle, i.e., the PurdueTracer. The PurdueTracer is an energy-efficient human-powered hydraulic bicycle with flexible operation and software aids. An open-circuit hydraulic hybrid transmission allows PurdueTracer to operate in four modes: Pedaling, Charging, Boost, and Regeneration, to satisfy users’ need for different riding occasions. An aluminum chassis that also functions as a system reservoir was customized for the PurdueTracer to optimize the durability, riding comfort, and space for components. The selection of the hydraulic components was performed by creating a model of the bicycle in AMESim simulation software and conducting a numerical optimization based on the model. The electronic system equipped users with informative feedback showing the bicycle performance, intuitive execution of functions, and comprehensive guidance for operation. This paper describes the design approach and the main results of the PurdueTracer, which also won the 2017 National Fluid Power Association Fluid Power Vehicle Challenge. This championship serves to prove the excellence of this vehicle in terms of effectiveness, efficiency, durability, and novelty. Full article

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22 pages, 4221 KiB

Open AccessArticle

Dynamic Performance Evaluation of Photovoltaic Power Plant by Stochastic Hybrid Fault Tree Automaton Model

by Ferdinando Chiacchio^1,*

, Fabio Famoso²

, Diego D’Urso¹, Sebastian Brusca³

, Jose Ignacio Aizpurua⁴

and Luca Cedola⁵

¹ Department of Electrical, Electronical and Computer Engineering, University of Catania, Viale Andrea Doria 6, 95025 Catania, Italy

² Department of Civil Engineering and Architecture, University of Catania, Viale Andrea Doria 6, 95025 Catania, Italy

³ Department of Engineering, University of Messina, Contrada Di Dio, 98166 Messina, Italy

⁴ Institute for Energy and Environment—Electronic and Electrical Engineering Department, University of Strathclyde, Technology and Innovation Centre, Level 4, 99 George Street, Glasgow G11RD, UK

⁵ Department of Mechanical and Aerospace Engineering, University of Rome, Via Eudossiana 18, 00184 Roma, Italy

Energies 2018, 11(2), 306; https://doi.org/10.3390/en11020306 - 31 Jan 2018

Cited by 34 | Viewed by 4508

Abstract

The contribution of renewable energies to the reduction of the impact of fossil fuels sources and especially energy supply in remote areas has occupied a role more and more important during last decades. The estimation of renewable power plants performances by means of [...] Read more.

The contribution of renewable energies to the reduction of the impact of fossil fuels sources and especially energy supply in remote areas has occupied a role more and more important during last decades. The estimation of renewable power plants performances by means of deterministic models is usually limited by the innate variability of the energy resources. The accuracy of energy production forecasting results may be inadequate. An accurate feasibility analysis requires taking into account the randomness of the primary resource operations and the effect of component failures in the energy production process. This paper treats a novel approach to the estimation of energy production in a real photovoltaic power plant by means of dynamic reliability analysis based on Stochastic Hybrid Fault Tree Automaton (SHyFTA). The comparison between real data, deterministic model and SHyFTA model confirm how the latter better estimate energy production than deterministic model. Full article

(This article belongs to the Section F: Electrical Engineering)

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14 pages, 7734 KiB

Open AccessArticle

A New ZVS Tuning Method for Double-Sided LCC Compensated Wireless Power Transfer System

by Sizhao Lu, Xiaoting Deng, Wenbin Shu, Xiaochao Wei and Siqi Li^*

Faculty of Electric Power Engineering, Kunming University of Science of Technology, Kunming 650500, China

Energies 2018, 11(2), 307; https://doi.org/10.3390/en11020307 - 1 Feb 2018

Cited by 14 | Viewed by 6034

Abstract

This paper presents a new zero voltage switching (ZVS) tuning method for the double-sided inductor/capacitor/capacitor (LCC) compensated wireless power transfer (WPT) system. An additional capacitor is added in the secondary side of the double-sided LCC compensation network in order to tune the network [...] Read more.

This paper presents a new zero voltage switching (ZVS) tuning method for the double-sided inductor/capacitor/capacitor (LCC) compensated wireless power transfer (WPT) system. An additional capacitor is added in the secondary side of the double-sided LCC compensation network in order to tune the network to realize ZVS operation for the primary-side switches. With the proposed tuning method, the turn off current of the primary-side switches at the low input voltage range can be reduced compared with the previous ZVS tuning method. Consequently, the efficiency of the WPT at the low input voltage range is improved. Moreover, the relationship between the input voltage and the output power is more linear than that of the previous ZVS tuning method. In addition, the proposed method has a lower start-up voltage. The analysis and validity of the proposed tuning method are verified by simulation and experimental results. A WPT system with up to 3.5 kW output power is built, and 95.9% overall peak efficiency is achieved. Full article

(This article belongs to the Special Issue Wireless Power Transfer and Energy Harvesting Technologies)

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16 pages, 1727 KiB

Open AccessFeature PaperArticle

Adaptive Protection System for Microgrids Based on a Robust Optimization Strategy

by Oscar Núñez-Mata^1,2,*, Rodrigo Palma-Behnke¹, Felipe Valencia¹

, Patricio Mendoza-Araya¹

and Guillermo Jiménez-Estévez¹

¹ Energy Center, Department of Electrical Engineering, Faculty of Mathematical and Physical Sciences, University of Chile, 8370451 Santiago, Chile

² Electric Power and Energy Research Laboratory (EPER-Lab), School of Electrical Engineering, University of Costa Rica, 11501 San José, Costa Rica

Energies 2018, 11(2), 308; https://doi.org/10.3390/en11020308 - 1 Feb 2018

Cited by 31 | Viewed by 6310

Abstract

The development of a proper protection system is essential for the secure and reliable operation of microgrids. In this paper, a novel adaptive protection system for microgrids is presented. The protection scheme is based on a protective device that includes two directional elements [...] Read more.

The development of a proper protection system is essential for the secure and reliable operation of microgrids. In this paper, a novel adaptive protection system for microgrids is presented. The protection scheme is based on a protective device that includes two directional elements which are operating in an interleaved manner, namely overcurrent and undervoltage elements. The proposed protection scheme can be implemented in microprocessor-based relays. To define the settings of the protective device, a robust programming approach was proposed considering a finite set of fault scenarios. The scenarios are generated based on the predictions about the available energy and the demand. For each decision step, a robust optimization problem is solved online, which is based on forecasting with a confidence band to represent the uncertainty. The system is tested and compared using real data sets from an existing microgrid in northern Chile. To assess the performance of the proposed protection system, fault scenarios not considered in the optimization were taken into account. The results obtained show that the proposed protective device is able to manage those failure scenarios, as well as those included in the tuning of the settings. Practical considerations are also discussed. Full article

(This article belongs to the Section F: Electrical Engineering)

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19 pages, 21678 KiB

Open AccessArticle

Hot-Swappable Modular Converter System Control for Heterogeneous Batteries and ESS

by Dae-Seak Cha¹, Jung-Sik Choi¹, Seung-Yeol Oh¹, Hyun-Jin Ahn² and Young-Cheol Lim^2,*

¹ Korea Electronics Technology Institute 226, Cheomdangwagi-ro, Buk-gu, Gwangju 61011, Korea

² Department of Electrical Engineering, Chonnam National University, Gwangju 61186, Korea

Energies 2018, 11(2), 309; https://doi.org/10.3390/en11020309 - 1 Feb 2018

Cited by 4 | Viewed by 4328

Abstract

This study proposes a modular bidirectional converter system for hot-swappable energy storage systems (ESSs). The proposed modular converter has a four-leg interleaved structure, and therefore it can reduce input current ripples and is suitable for secondary cells. Moreover, if any of the legs [...] Read more.

This study proposes a modular bidirectional converter system for hot-swappable energy storage systems (ESSs). The proposed modular converter has a four-leg interleaved structure, and therefore it can reduce input current ripples and is suitable for secondary cells. Moreover, if any of the legs fails, hot-swap is available through phase control inside the converter. The modular converter uses an independently controllable battery as an input power source, allowing the charge and discharge control according to each stated of charge (SOC). The output voltage of the converter circumvents the module in the event of a high-voltage output control and a fault (exchange due to battery life, repair of converter) through the cascade-type bypass, thereby enabling continuous operation. The hot-swap operation of the proposed modular ESS converter system and the charge and discharge control algorithm according to battery SOC are verified by experiment. Full article

(This article belongs to the Section D: Energy Storage and Application)

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19 pages, 3220 KiB

Open AccessArticle

Direct Probabilistic Load Flow in Radial Distribution Systems Including Wind Farms: An Approach Based on Data Clustering

by Arman Oshnoei¹, Rahmat Khezri^2,*, Mehrdad Tarafdar Hagh³, Kuaanan Techato⁴

, SM Muyeen⁵ and Omid Sadeghian³

¹ Faculty of Electrical and Computer Engineering, Shahid Beheshti University, Tehran 1983969411, Iran

² Department of Electrical and Computer Engineering, University of Kurdistan, Sanandaj, Kurdistan 6617715177, Iran

³ Faculty of Electrical and Computer Engineering, University of Tabriz, Tabriz 5166616471, Iran

⁴ Faculty of Environmental Management, Prince of Songkla University, Songkhla 90110, Thailand

⁵ Department of Electrical and Computer Engineering, Curtin University, Perth, WA 6845, Australia

Energies 2018, 11(2), 310; https://doi.org/10.3390/en11020310 - 1 Feb 2018

Cited by 23 | Viewed by 4395

Abstract

The ongoing study aims to establish a direct probabilistic load flow (PLF) for the analysis of wind integrated radial distribution systems. Because of the stochastic output power of wind farms, it is very important to find a method which can reduce the calculation [...] Read more.

The ongoing study aims to establish a direct probabilistic load flow (PLF) for the analysis of wind integrated radial distribution systems. Because of the stochastic output power of wind farms, it is very important to find a method which can reduce the calculation burden significantly, without having compromising the accuracy of results. In the proposed approach, a K-means based data clustering algorithm is employed, in which all data points are bunched into desired clusters. In this regard, probable agents are selected to run the PLF algorithm. The clustered data are used to employ the Monte Carlo simulation (MCS) method. In this paper, the analysis is performed in terms of simulation run-time. Also, this research follows a two-fold aim. In the first stage, the superiority of data clustering-based MCS over the unsorted data MCS is demonstrated properly. Moreover, the impact of data clustering-based MCS and unsorted data-based MCS is investigated using an indirect probabilistic forward/backward sweep (PFBS) method. Thus, in the second stage, the simulation run-time comparison is carried out rigorously between the proposed direct PLF and the indirect PFBS method to examine the computational burden effects. Simulation results are exhibited on the IEEE 33-bus and 69-bus radial distribution systems. Full article

(This article belongs to the Section F: Electrical Engineering)

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26 pages, 8796 KiB

Open AccessArticle

Natural Fractures Characterization and In Situ Stresses Inference in a Carbonate Reservoir—An Integrated Approach

by Ali Shafiei^1,*

, Maurice B. Dusseault², Ehsan Kosari³ and Morteza N. Taleghani⁴

¹ Department of Petroleum Engineering, School of Mining and Geosciences, Nazarbayev University, Astana 010000, Kazakhstan

² Department of Earth & Environmental Sciences, University of Waterloo, Waterloo, ON N2L 3G1, Canada

³ Research Institute for Earth Sciences, Geological Survey of Iran, P.O. Box 13185-1494 Tehran, Iran

⁴ National Iranian Offshore Oil Company (IOOC), P.O. Box 13185-1494 Tehran, Iran

Energies 2018, 11(2), 312; https://doi.org/10.3390/en11020312 - 1 Feb 2018

Cited by 15 | Viewed by 6106

Abstract

In this paper, we characterized the natural fracture systems and inferred the state of in situ stress field through an integrated study in a very complex and heterogeneous fractured carbonate reservoir. Relative magnitudes and orientations of the in-situ principal stresses in a naturally [...] Read more.

In this paper, we characterized the natural fracture systems and inferred the state of in situ stress field through an integrated study in a very complex and heterogeneous fractured carbonate reservoir. Relative magnitudes and orientations of the in-situ principal stresses in a naturally fractured carbonate heavy oil field were estimated with a combination of available data (World Stress Map, geological and geotectonic evidence, outcrop studies) and techniques (core analysis, borehole image logs and Side View Seismic Location). The estimates made here using various tools and data including routine core analysis and image logs are confirmatory to estimates made by the World Stress Map and geotectonic facts. NE-SW and NW-SE found to be the dominant orientations for maximum and minimum horizontal stresses in the study area. In addition, three dominant orientations were identified for vertical and sub-vertical fractures atop the crestal region of the anticlinal structure. Image logs found useful in recognition and delineation of natural fractures. The results implemented in a real field development and proved practical in optimal well placement, drilling and production practices. Such integrated studies can be instrumental in any E&P projects and related projects such as geological CO₂ sequestration site characterization. Full article

(This article belongs to the Section L: Energy Sources)

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21 pages, 6106 KiB

Open AccessArticle

Analysis of Point-of-Use Energy Return on Investment and Net Energy Yields from China’s Conventional Fossil Fuels

by Jingxuan Feng

, Lianyong Feng^* and Jianliang Wang

School of Business Administration, China University of Petroleum (Beijing), Beijing 102249, China

Energies 2018, 11(2), 313; https://doi.org/10.3390/en11020313 - 1 Feb 2018

Cited by 8 | Viewed by 4795

Abstract

There is a strong correlation between net energy yield (NEY) and energy return on investment (EROI). Although a few studies have researched the EROI at the extraction level in China, none have calculated the EROI at the point of use (EROI_POU). [...] Read more.

There is a strong correlation between net energy yield (NEY) and energy return on investment (EROI). Although a few studies have researched the EROI at the extraction level in China, none have calculated the EROI at the point of use (EROI_POU). EROI_POU includes the entire energy conversion chain from extraction to point of use. To more comprehensively measure changes in the EROI_POU for China’s conventional fossil fuels, a “bottom-up” model to calculate EROI_POU was improved by extending the conventional calculation boundary from the wellhead to the point of use. To predict trends in the EROI_POU of fossil fuels in China, a dynamic function of the EROI was then used to projections future EROI_POU in this study. Results of this paper show that the EROI_POU of both coal (range of value: 14:1–9.2:1), oil (range of value: 8:1–3.5:1) and natural gas (range of value: 6.5:1–3.5:1) display downward trends during the next 15 years. Based on the results, the trends in the EROI_POU of China’s conventional fossil fuels will rapidly decrease in the future indicating that it is more difficult to obtain NEY from China’s conventional fossil fuels. Full article

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19 pages, 1646 KiB

Open AccessArticle

Economic Optimal HVAC Design for Hybrid GEOTABS Buildings and CO₂ Emissions Analysis

by Damien Picard^1,* and Lieve Helsen^1,2

¹ Department of Mechanical Engineering, University of Leuven (KU Leuven), Celestijnenlaan 300-box 2421, 3001 Leuven, Belgium

² EnergyVille, Thor Park 8310, 3600 Genk, Belgium

Energies 2018, 11(2), 314; https://doi.org/10.3390/en11020314 - 1 Feb 2018

Cited by 9 | Viewed by 5295

Abstract

In the early design phase of a building, the task of the Heating, Ventilation and Air Conditioning (HVAC) engineer is to propose an appropriate HVAC system for a given building. This system should provide thermal comfort to the building occupants at all time, [...] Read more.

In the early design phase of a building, the task of the Heating, Ventilation and Air Conditioning (HVAC) engineer is to propose an appropriate HVAC system for a given building. This system should provide thermal comfort to the building occupants at all time, meet the building owner’s specific requirements, and have minimal investment, running, maintenance and replacement costs (i.e., the total cost) and energy use or environmental impact. Calculating these different aspects is highly time-consuming and the HVAC engineer will therefore only be able to compare a (very) limited number of alternatives leading to suboptimal designs. This study presents therefore a Python tool that automates the generation of all possible scenarios for given thermal power profiles and energy load and a given database of HVAC components. The tool sizes each scenario properly, computes its present total cost (PC) and the total CO

_{2}

emissions associated with the building energy use. Finally, the different scenarios can be searched and classified to pick the most appropriate scenario. The tool uses static calculations based on standards, manufacturer data and basic assumptions similar to those made by engineers in the early design phase. The current version of the tool is further focused on hybrid GEOTABS building, which combines a GEOthermal heat pump with a Thermally Activated System (TABS). It should further be noted that the tool optimizes the HVAC system but not the building envelope, while, ideally, both should be simultaneously optimized. Full article

(This article belongs to the Special Issue Geothermal Heating and Cooling)

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21 pages, 3711 KiB

Open AccessArticle

Thermodynamic Performance Assessment of a Novel Micro-CCHP System Based on a Low Temperature PEMFC Power Unit and a Half-Effect Li/Br Absorption Chiller

by Raffaello Cozzolino

Department of Engineering, Niccolò Cusano University, via Don Carlo Gnocchi 3, 00166 Rome, Italy

Energies 2018, 11(2), 315; https://doi.org/10.3390/en11020315 - 1 Feb 2018

Cited by 38 | Viewed by 5625

Abstract

The aim of this work has been to evaluate the energetic feasibility and the performances of a novel residential micro-Combined Cooling, Heating and Power (CCHP) system, based on low temperature proton exchange membrane fuel cell (PEMFC) power unit and half effect lithium bromide [...] Read more.

The aim of this work has been to evaluate the energetic feasibility and the performances of a novel residential micro-Combined Cooling, Heating and Power (CCHP) system, based on low temperature proton exchange membrane fuel cell (PEMFC) power unit and half effect lithium bromide absorption chiller. This integrated system has been designed to produce both electric, thermal and cooling power by recovering heat from the fuel cell power unit cooling system. The analysis has been conducted by using numerical simulations: the PEMFC power unit and the absorption chiller have been modeled by means of one-dimensional and thermochemical models, respectively, and by means of available experimental and literature reference data, has been performed the validation. The performance parameters such as: the energy utilization factor (EUF), the exergy utilization factor (ExUF) and the trigeneration primary energy saving (TPES), have been used to analyzed the performances of the system. The numerical results showed a good performance in terms of energy and ExUF, in the whole operating field of the trigeneration system. Furthermore, the highest ExUF values are obtained for the minimum evaporator temperature (4 °C) and minimum condenser temperature (27 °C) of the absorption chiller. The calculated values of TPES for the CCHP mode, ranges from −0.07 to 0.19, thus, the system has good performance in a wide operating range, but the better performance can be achieved at lower loads. Full article

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19 pages, 3680 KiB

Open AccessArticle

Cyber-Attacks on Smart Meters in Household Nanogrid: Modeling, Simulation and Analysis

by Denise Tellbach^1,2 and Yan-Fu Li^1,*

¹ Department of Industrial Engineering, Tsinghua University, 100084 Beijing, China

² Faculty of Mechanical Engineering, RWTH Aachen University, 52062 Aachen, Germany

Energies 2018, 11(2), 316; https://doi.org/10.3390/en11020316 - 2 Feb 2018

Cited by 23 | Viewed by 5326

Abstract

The subject of cyber-security and therefore cyber-attacks on smart grid (SG) has become subject of many publications in the last years, emphasizing its importance in research, as well as in practice. One especially vulnerable part of SG are smart meters (SMs). The major [...] Read more.

The subject of cyber-security and therefore cyber-attacks on smart grid (SG) has become subject of many publications in the last years, emphasizing its importance in research, as well as in practice. One especially vulnerable part of SG are smart meters (SMs). The major contribution of simulating a variety of cyber-attacks on SMs that have not been done in previous studies is the identification and quantification of the possible impacts on the security of SG. In this study, a simulation model of a nanogrid, including a complete household with an SM, was developed. Different cyber-attacks were injected into the SM to simulate their effects on household nanogrid. The analysis of the impacts of different cyber-attacks showed that the effects of cyber-attacks can be sorted into various categories. Integrity and confidentiality attacks cause monetary effects on the grid. While, availability attacks have monetary effects on the grid as well, they are mainly aimed at compromising the SM communication by either delaying or stopping it completely. Full article

(This article belongs to the Section F: Electrical Engineering)

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14 pages, 5632 KiB

Open AccessArticle

Design and Optimization of a Brushless Wound-Rotor Vernier Machine

by Qasim Ali, Asif Hussain, Noman Baloch and Byung Il Kwon^*

Department of Electronic Systems Engineering, Hanyang University, Ansan 15588, Korea

Energies 2018, 11(2), 317; https://doi.org/10.3390/en11020317 - 2 Feb 2018

Cited by 11 | Viewed by 4645

Abstract

In this paper, a permanent magnet (PM)-less, brushless, wound-rotor vernier machine (BL-WRVM) is proposed for variable speed applications such as electric vehicles and washing machines. The wound rotor is excited through an already existing brushless topology, which requires a dual inverter configuration to [...] Read more.

In this paper, a permanent magnet (PM)-less, brushless, wound-rotor vernier machine (BL-WRVM) is proposed for variable speed applications such as electric vehicles and washing machines. The wound rotor is excited through an already existing brushless topology, which requires a dual inverter configuration to generate an additional subharmonic component in the stator magnetomotive force (MMF). Different from permanent magnet vernier machines (PMVMs), the proposed BL-WRVM provides easy regulation of the rotor flux for variable speed operation. A 24-slot, 4-pole stator, and 44-pole outer rotor were designed, and 2D finite element analysis (FEA) was carried out to determine the performance of the proposed machine. To improve the performance of the proposed machine, optimization of the rotor and stator winding turns was done. The optimized model was further analyzed for wide-speed operation, and its performance was then compared with that of an equivalent permanent magnet vernier machine (PMVM). The proposed machine has the advantage of low cost due to its PM-less structure and is suitable for variable speed applications. Full article

(This article belongs to the Section I: Energy Fundamentals and Conversion)

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12 pages, 3517 KiB

Open AccessArticle

Icing Condition Assessment of In-Service Glass Insulators Based on Graphical Shed Spacing and Graphical Shed Overhang

by Yanpeng Hao¹, Jie Wei¹, Xiaolan Jiang¹, Lin Yang^1,*, Licheng Li¹, Junke Wang², Hao Li² and Ruihai Li²

¹ School of Electric Power, South China University of Technology, Guangzhou 510640, China

² Electric Power Research Institute, China Southern Power Grid, Guangzhou 510080, China

Energies 2018, 11(2), 318; https://doi.org/10.3390/en11020318 - 2 Feb 2018

Cited by 27 | Viewed by 4096

Abstract

Icing on transmission lines might lead to ice flashovers of insulators, collapse of towers, tripping faults of transmission lines, and other accidents. Shed spacing and shed overhang of insulators are clues for evaluating the probability of ice flashover. This paper researches image-processing methods [...] Read more.

Icing on transmission lines might lead to ice flashovers of insulators, collapse of towers, tripping faults of transmission lines, and other accidents. Shed spacing and shed overhang of insulators are clues for evaluating the probability of ice flashover. This paper researches image-processing methods for the natural icing of in-service glass insulators. Calculation methods of graphical shed spacing and graphical shed overhang are proposed via recognizing the convexity defects of the contours of an icing insulator string based on the GrabCut segmentation algorithm. The experiments are carried out with image data from our climatic chamber and the China Southern Power Grid Disaster (Icing) Warning System of Transmission Lines. The results show that the graphical shed overhang of insulators show evident change due to icing. This method can recognize the most serious icing conditions where the insulator sheds are completely bridged. Also, it can detect bridging positions including the left side, right side, or both sides of the insulator strings in the images. Full article

(This article belongs to the Special Issue Emerging Power Electronics Technologies for Power Systems and Machine Drives)

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14 pages, 4668 KiB

Open AccessArticle

Experimental Study on Improvement of Performance by Wave Form Cathode Channels in a PEM Fuel Cell

by Sun-Joon Byun¹

, Zhen Huan Wang², Jun Son², Dong-Kurl Kwak³ and Young-Chul Kwon^2,*

¹ SFR NSSS System Design Division, Korea Atomic Energy Research Institute, 111 Daedeok-daero 989 Beon-gil, Yuseong-gu, Daejeon 34057, Korea

² Department of Mechanical Engineering, Sunmoon University, 221-70 Sunmoon-ro, Tangjeong-myeon, Asan-si, Chungcheongnam-do 31460, Korea

³ Graduate School of Disaster Prevention, Kangwon National University, 346 Joongang-ro, Samcheck-si, Gangwon-do 25913, Korea

Energies 2018, 11(2), 319; https://doi.org/10.3390/en11020319 - 2 Feb 2018

Cited by 17 | Viewed by 4393

Abstract

We propose a wave-like design on the surface of cathode channels (wave form cathode channels) to improve oxidant delivery to gas diffusion layers (GDLs). We performed experiments using proton-exchange membrane fuel cells (PEMFCs) combined with wave form surface design on cathodes. We varied [...] Read more.

We propose a wave-like design on the surface of cathode channels (wave form cathode channels) to improve oxidant delivery to gas diffusion layers (GDLs). We performed experiments using proton-exchange membrane fuel cells (PEMFCs) combined with wave form surface design on cathodes. We varied the factors of the distance between wave-bumps (the adhesive distance, AD), and the size of the wave-bumps (the expansion ratio, ER). The ADs are three, four, and five times the size of the half-circle bump’s radius, and the ERs are two-thirds, one-half, and one-third of the channel’s height. We evaluated the performances of the fuel cells, and compared the current-voltage (I-V) relations. For comparison, we prepared PEMFCs with conventional flat-surfaced oxygen channels. Our aim in this work is to identify fuel cell operation by modifying the surface design of channels, and ultimately to find the optimal design of cathode channels that will maximize fuel cell performance. Full article

(This article belongs to the Special Issue Polymer Electrolyte Membrane Fuel Cells 2017)

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19 pages, 4258 KiB

Open AccessFeature PaperArticle

An Investigation of Parallel Post-Laminar Flow through Coarse Granular Porous Media with the Wilkins Equation

by Ashes Banerjee^1,*

, Srinivas Pasupuleti¹, Mritunjay Kumar Singh² and G.N. Pradeep Kumar³

¹ Departmentof Civil Engineering, Indian Institute of Technology (Indian School of Mines), Dhanbad 826004, Jharkhand, India

² Department of Applied Mathematics, Indian Institute of Technology (Indian School of Mines), Dhanbad 826004, Jharkhand, India

³ Department of Civil Engineering, SVU College of Engineering, Sri Venkateswara University, Tirupati 517502, Andhra Pradesh, India

Energies 2018, 11(2), 320; https://doi.org/10.3390/en11020320 - 2 Feb 2018

Cited by 11 | Viewed by 4537

Abstract

Behaviour of flow resistance with velocity is still undefined for post-laminar flow through coarse granular media. This can cause considerable errors during flow measurements in situations like rock fill dams, water filters, pumping wells, oil and gas exploration, and so on. Keeping the [...] Read more.

Behaviour of flow resistance with velocity is still undefined for post-laminar flow through coarse granular media. This can cause considerable errors during flow measurements in situations like rock fill dams, water filters, pumping wells, oil and gas exploration, and so on. Keeping the non-deviating nature of Wilkins coefficients with the hydraulic radius of media in mind, the present study further explores their behaviour to independently varying media size and porosity, subjected to parallel post-laminar flow through granular media. Furthermore, an attempt is made to simulate the post-laminar flow conditions with the help of a Computational Fluid Dynamic (CFD) Model in ANSYS FLUENT, since conducting large-scale experiments are often costly and time-consuming. The model output and the experimental results are found to be in good agreement. Percentage deviations between the experimental and numerical results are found to be in the considerable range. Furthermore, the simulation results are statistically validated with the experimental results using the standard ‘Z-test’. The output from the model advocates the importance and applicability of CFD modelling in understanding post-laminar flow through granular media. Full article

(This article belongs to the Special Issue Emerging Advances in Petrophysics: Porous Media Characterization and Modeling of Multiphase Flow)

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33 pages, 4468 KiB

Open AccessArticle

A Novel Hybrid Strategy Using Three-Phase Feature Extraction and a Weighted Regularized Extreme Learning Machine for Multi-Step Ahead Wind Speed Prediction

by Jujie Wang^1,*, Yanfeng Wang^2,* and Yaning Li³

¹ Climate and Weather Disasters Collaborative Innovation Center, School of Management Science and Engineering, Nanjing University of Information Science and Technology, Nanjing 210044, China

² Gansu Weather Modification Office, Lanzhou 730020, China

³ College of Mathematics and Statistics, Nanjing University of Information Science and Technology, Nanjing 210044, China

Energies 2018, 11(2), 321; https://doi.org/10.3390/en11020321 - 2 Feb 2018

Cited by 26 | Viewed by 3907

Abstract

With the growing penetration of wind power into electric grids, improving wind speed prediction accuracy has become particularly valuable for the exploitation of wind power. In this paper, a novel hybrid strategy based on a three-phase signal decomposition (TPSD) technique, feature extraction (FE) [...] Read more.

With the growing penetration of wind power into electric grids, improving wind speed prediction accuracy has become particularly valuable for the exploitation of wind power. In this paper, a novel hybrid strategy based on a three-phase signal decomposition (TPSD) technique, feature extraction (FE) and weighted regularized extreme learning machine (WRELM) is developed for multi-step ahead wind speed prediction. The TPSD including seasonal separation algorithm (SSA), fast ensemble empirical mode decomposition (FEEMD) and variational mode decomposition (VMD) is proposed for the first time to handle the complex and irregular natures of wind speed comprehensively. The FE process is used to capture the useful features of wind speed fluctuations and determine the optimal inputs for a prediction model. The WRELM is employed as a basic predictor for building the prediction model by these selected features. Four real wind speed prediction cases are utilized to evaluate the proposed model, and experimental results verify the effectiveness of the proposed model compared with the benchmark models. Full article

(This article belongs to the Section A: Sustainable Energy)

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14 pages, 3132 KiB

Open AccessArticle

Two-Stage Battery Energy Storage System (BESS) in AC Microgrids with Balanced State-of-Charge and Guaranteed Small-Signal Stability

by Bing Xie¹, Yiqi Liu², Yanchao Ji^1,* and Jianze Wang¹

¹ School of Electrical Engineering and Automation, Harbin Institute of Technology, Harbin 150001, China

² College of Mechanical and Electrical Engineering, Northeast Forestry University, Harbin 150040, China

Energies 2018, 11(2), 322; https://doi.org/10.3390/en11020322 - 2 Feb 2018

Cited by 16 | Viewed by 4961

Abstract

In this paper, a two-stage battery energy storage system (BESS) is implemented to enhance the operation condition of conventional battery storage systems in a microgrid. Particularly, the designed BESS is composed of two stages, i.e., Stage I: integration of dispersed energy storage units [...] Read more.

In this paper, a two-stage battery energy storage system (BESS) is implemented to enhance the operation condition of conventional battery storage systems in a microgrid. Particularly, the designed BESS is composed of two stages, i.e., Stage I: integration of dispersed energy storage units (ESUs) using parallel DC/DC converters, and Stage II: aggregated ESUs in grid-connected operation. Different from a conventional BESS consisting of a battery management system (BMS) and power conditioning system (PCS), the developed two-stage architecture enables additional operation and control flexibility in balancing the state-of-charge (SoC) of each ESU and ensures the guaranteed small-signal stability, especially in extremely weak grid conditions. The above benefits are achieved by separating the control functions between the two stages. In Stage I, a localized power sharing scheme based on the SoC of each particular ESU is developed to manage the SoC and avoid over-charge or over-discharge issues; on the other hand, in Stage II, an additional virtual impedance loop is implemented in the grid-interactive DC/AC inverters to enhance the stability margin with multiple parallel-connected inverters integrating at the point of common coupling (PCC) simultaneously. A simulation model based on MATLAB/Simulink is established, and simulation results verify the effectiveness of the proposed BESS architecture and the corresponding control diagram. Full article

(This article belongs to the Section D: Energy Storage and Application)

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24 pages, 4557 KiB

Open AccessArticle

Design, Evaluation and Implementation of an Islanding Detection Method for a Micro-grid

by Taiying Zheng¹, Huan Yang^1,*, Rongxiang Zhao¹, Yong Cheol Kang² and Vladimir Terzija³

¹ College of Electrical Engineering, Zhejiang University, Hangzhou 310027, China

² Department of Energy IT, Gachon University, Seoul 13120, Korea

³ Department of Electrical and Electronic Engineering, University of Manchester, Manchester M13 9PL, UK

Energies 2018, 11(2), 323; https://doi.org/10.3390/en11020323 - 2 Feb 2018

Cited by 30 | Viewed by 3315

Abstract

Correct and fast detection of a micro-grid (MG) islanding is essential to the MG since operation, control, and protection of the MG depend on its operating mode i.e., an interconnected mode or islanding mode. This study describes the design, evaluation and implementation of [...] Read more.

Correct and fast detection of a micro-grid (MG) islanding is essential to the MG since operation, control, and protection of the MG depend on its operating mode i.e., an interconnected mode or islanding mode. This study describes the design, evaluation and implementation of an islanding detection method for an MG, which includes a natural gas-fired generator, a doubly fed induction generator type wind generator, a photovoltaic generator, and some associated local loads. The proposed method is based on the instantaneous active and reactive powers at the point of common coupling (PCC) of the MG. During the islanding mode, the instantaneous active and reactive powers at the PCC are constants, which depend on the voltage of the PCC and the impedance of the dedicated line. The performance of the proposed method is verified under various scenarios including islanding conditions for the different outputs of the MG, and fault conditions by varying the position, type, inception angle and resistance of the fault, using the PSCAD/EMTDC simulator. This paper also concludes by implementing proposed method into a TMS320C6701 digital signal processor. The results indicate that the proposed method successfully detects islanding for the MG in islanding conditions, and remains stable in fault conditions. Full article

(This article belongs to the Section F: Electrical Engineering)

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14 pages, 3935 KiB

Open AccessArticle

Analysis of the Scavenging Process of a Two-Stroke Free-Piston Engine Based on the Selection of Scavenging Ports or Valves

by Boru Jia^1,2,*

, Yaodong Wang¹, Andrew Smallbone¹ and Anthony Paul Roskilly¹

¹ Sir Joseph Swan Centre for Energy Research, Newcastle University, Newcastle upon Tyne NE1 7RU, UK

² School of Mechanical Engineering, Beijing Institute of Technology, Beijing 100081, China

Energies 2018, 11(2), 324; https://doi.org/10.3390/en11020324 - 2 Feb 2018

Cited by 14 | Viewed by 6021

Abstract

The free-piston engine generator (FPEG) is a linear energy conversion device with the objective of utilisation within a hybrid-electric automotive vehicle power system. In this research, the piston dynamic characteristics of an FPEG is compared with that of a conventional engine (CE) of [...] Read more.

The free-piston engine generator (FPEG) is a linear energy conversion device with the objective of utilisation within a hybrid-electric automotive vehicle power system. In this research, the piston dynamic characteristics of an FPEG is compared with that of a conventional engine (CE) of the same size, and the difference in the valve timing is compared for both port scavenging type and valve scavenging type, with the exhaust valve closing timing is selected as the parameter. A zero-dimensional simulation model is developed in Ricardo WAVE software (2016.1), with the piston dynamics obtained from the simulation model in Matlab/SIMULINK (R2017a). For the CE and FEPG using scavenging ports, in order to improve its power output to the same level as that of a CE, the inlet gas pressure is suggested to be improved to above 1.2 bar, approximately 0.2 bar higher than that used for a CE. If a CE cylinder with exhaust valves is adopted or referred to during the development of an FPEG prototype, the exhaust valve is suggested to be closed earlier to improve its power output, and a higher intake pressure is also suggested if its output power is expected to be the same or higher than that of a CE. Full article

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16 pages, 7371 KiB

Open AccessArticle

Application-Oriented Optimal Shift Schedule Extraction for a Dual-Motor Electric Bus with Automated Manual Transmission

by Mingjie Zhao¹, Junhui Shi², Cheng Lin^1,* and Junzhi Zhang²

¹ National Engineering Laboratory for Electric Vehicles, School of Mechanical Engineering, Beijing Institute of Technology, Beijing 100081, China

² State Key Laboratory of Automotive Safety and Energy, Tsinghua University, Beijing 100084, China

Energies 2018, 11(2), 325; https://doi.org/10.3390/en11020325 - 2 Feb 2018

Cited by 30 | Viewed by 6163

Abstract

The conventional battery electric buses (BEBs) have limited potential to optimize the energy consumption and reach a better dynamic performance. A practical dual-motor equipped with 4-speed Automated Manual Transmission (AMT) propulsion system is proposed, which can eliminate the traction interruption in conventional AMT. [...] Read more.

The conventional battery electric buses (BEBs) have limited potential to optimize the energy consumption and reach a better dynamic performance. A practical dual-motor equipped with 4-speed Automated Manual Transmission (AMT) propulsion system is proposed, which can eliminate the traction interruption in conventional AMT. A discrete model of the dual-motor-AMT electric bus (DMAEB) is built and used to optimize the gear shift schedule. Dynamic programming (DP) algorithm is applied to find the optimal results where the efficiency and shift time of each gear are considered to handle the application problem of global optimization. A rational penalty factor and a proper shift time delay based on bench test results are set to reduce the shift frequency by 82.5% in Chinese-World Transient Vehicle Cycle (C-WTVC). Two perspectives of applicable shift rule extraction methods, i.e., the classification method based on optimal operating points and clustering method based on optimal shifting points, are explored and compared. Eventually, the hardware-in-the-loop (HIL) simulation results demonstrate that the proposed structure and extracted shift schedule can realize a significant improvement in reducing energy loss by 20.13% compared to traditional empirical strategies. Full article

(This article belongs to the Special Issue The International Symposium on Electric Vehicles (ISEV2017))

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17 pages, 10323 KiB

Open AccessArticle

A Seasonal Model Using Optimized Multi-Layer Neural Networks to Forecast Power Output of PV Plants

by Yang Hu¹

, Weiwei Lian², Yutong Han², Songyuan Dai^2,3,4 and Honglu Zhu^2,3,4,*

¹ The School of Control and Computer Engineering, North China Electric Power University, Changping District, Beijing 102206, China

² The School of Renewable Energy, North China Electric Power University, Changping District, Beijing 102206, China

³ The State Key Laboratory of Alternate Electrical Power System with Renewable Energy Sources, North China Electric Power University, Changping District, Beijing 102206, China

⁴ The Beijing Key Laboratory of New and Renewable Energy, North China Electric Power University, Changping District, Beijing 102206, China

Energies 2018, 11(2), 326; https://doi.org/10.3390/en11020326 - 2 Feb 2018

Cited by 36 | Viewed by 4187

Abstract

With the continuous increase of grid-connected photovoltaic (PV) installed capacity and the urgent demand of synergetic utilization with the other power generation forms, the high-precision prediction of PV power generation is increasingly important for the optimal scheduling and safe operation of the grid. [...] Read more.

With the continuous increase of grid-connected photovoltaic (PV) installed capacity and the urgent demand of synergetic utilization with the other power generation forms, the high-precision prediction of PV power generation is increasingly important for the optimal scheduling and safe operation of the grid. In order to improve the power prediction accuracy, using the response characteristics of PV array under different environmental conditions, a data driven multi-model power prediction method for PV power generation is proposed, based on the seasonal meteorological features. Firstly, through the analysis of PV power characteristics in typical seasons and seasonal distribution of the weather factors, such as solar irradiance and ambient temperature, the influences of different weather factors on PV power prediction are studied. Then, according to the meteorology characteristics of Beijing, different seasons can be divided. The historical data corresponding to different seasons are acquired and then the seasonal PV power forecasting models are established based on optimized multi-layer back propagation neural network (BPNN), realizing the multi-model prediction of PV power. Finally, effectiveness of the seasonal PV power forecasting method is compared and validated. The performance analysis of the neural network forecasting model under typical seasonal conditions shows that the multi-model forecasting method based on seasonal characteristics of PV power generation is better than that of single power forecasting model for the whole year. The results show that the proposed method can effectively improve the power forecasting accuracy of PV power. Full article

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12 pages, 7065 KiB

Open AccessArticle

Electrical Trees and Their Growth in Silicone Rubber at Various Voltage Frequencies

by Yunxiao Zhang¹, Yuanxiang Zhou^1,*, Ling Zhang^1,2, Zhongliu Zhou¹ and Qiong Nie³

¹ State Key Lab of Electrical Power System, Department of Electrical Engineering, Tsinghua University, Beijing 100084, China

² State Key Laboratory of Electrical Insulation and Power Equipment, Xi’an Jiaotong University, Xi’an 710049, Shaanxi, China

³ AC Project Construction Branch, State Grid Corporation of China, Beijing 100052, China

Energies 2018, 11(2), 327; https://doi.org/10.3390/en11020327 - 2 Feb 2018

Cited by 15 | Viewed by 4578

Abstract

The insulation property at high voltage frequencies has become a tough challenge with the rapid development of high-voltage and high-frequency power electronics. In this paper, the electrical treeing behavior of silicone rubber (SIR) is examined and determined at various voltage frequencies, ranging from [...] Read more.

The insulation property at high voltage frequencies has become a tough challenge with the rapid development of high-voltage and high-frequency power electronics. In this paper, the electrical treeing behavior of silicone rubber (SIR) is examined and determined at various voltage frequencies, ranging from 50 Hz to 130 kHz. The results show that the initiation voltage of electrical trees decreased by 27.9% monotonically, and they became denser when the voltage frequency increased. A bubble-shaped deterioration phenomenon was observed when the voltage frequency exceeded 100 kHz. We analyze the typical treeing growth pattern at 50 Hz (including pine-like treeing growth and bush-like treeing growth) and the bubble-growing pattern at 130 kHz. Bubbles grew exponentially within several seconds. Moreover, bubble cavities were detected in electrical tree channels at 50 Hz. Combined with the bubble-growing characteristics at 130 kHz, a potential growing model for electrical trees and bubbles in SIR is proposed to explain the growing patterns at various voltage frequencies. Full article

(This article belongs to the Section F: Electrical Engineering)

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11 pages, 3650 KiB

Open AccessArticle

Efficient Polymer Solar Cells with Alcohol-Soluble Zirconium(IV) Isopropoxide Cathode Buffer Layer

by Zhen Luo¹, Bo Yang¹, Yiming Bai¹

, Tasawar Hayat^2,3, Ahmed Alsaedi³

and Zhan’ao Tan^1,*

¹ State Key Laboratory of Alternate Electrical Power System with Renewable Energy Sources, North China Electric Power University, Beijing 102206, China

² Department of Mathematics, Quiad-I-Azam University, Islamabad 44000, Pakistan

³ NAAM Research Group, Faculty of Science, King Abdulaziz University, Jeddah 21589, Saudi Arabia

Energies 2018, 11(2), 328; https://doi.org/10.3390/en11020328 - 2 Feb 2018

Cited by 6 | Viewed by 3744

Abstract

Interfacial materials are essential to the performance and stability of polymer solar cells (PSCs). Herein, solution-processed zirconium(IV) isopropoxide (Zr[OCH(CH₃)₂]₄, ZrIPO) has been employed as an efficient cathode buffer layer between the Al cathode and photoactive layer. The [...] Read more.

Interfacial materials are essential to the performance and stability of polymer solar cells (PSCs). Herein, solution-processed zirconium(IV) isopropoxide (Zr[OCH(CH₃)₂]₄, ZrIPO) has been employed as an efficient cathode buffer layer between the Al cathode and photoactive layer. The ZrIPO buffer layer is prepared simply via spin-coating its isopropanol solution on the photoactive layer at room temperature without any post-treatment. When using ZrIPO/Al instead of the traditionally used Ca/Al cathode in PSCs, the short-circuit current density (J_sc) is significantly improved and the series resistance of the device is decreased. The power conversion efficiency (PCE) of the P3HT:PCBM-based device with ZrIPO buffer layer reaches 4.47% under the illumination of AM1.5G, 100 mW/cm². A better performance with PCE of 8.07% is achieved when a low bandgap polymer PBDTBDD is selected as donor material. The results indicate that ZrIPO is a promising electron collection material as a substitute of the traditional low-work-function cathode for high performance PSCs. Full article

(This article belongs to the Section I: Energy Fundamentals and Conversion)

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16 pages, 3504 KiB

Open AccessArticle

A Study of Nonlinear Elasticity Effects on Permeability of Stress Sensitive Shale Rocks Using an Improved Coupled Flow and Geomechanics Model: A Case Study of the Longmaxi Shale in China

by Chenji Wei¹, Liangang Wang², Baozhu Li¹, Lihui Xiong¹, Shuangshuang Liu¹, Jie Zheng¹, Suming Hu³ and Hongqing Song^4,*

¹ Research Institute of Petroleum Exploration and Development, PetroChina, Beijing 100083, China

² PetroChina Exploration & Production Company, Beijing 100032, China

³ Natural Gas Division, Tarim Oilfield Company, CNPC, Xinjiang 841000, China

⁴ School of Civil and Resource Engineering, University of Science and Technology Beijing, Beijing 100083, China

Energies 2018, 11(2), 329; https://doi.org/10.3390/en11020329 - 2 Feb 2018

Cited by 17 | Viewed by 3923

Abstract

Gas transport in shale gas reservoirs is largely affected by rock properties such as permeability. These properties are often sensitive to the in-situ stress state changes. Accurate modeling of shale gas transport in shale reservoir rocks considering the stress sensitive effects on rock [...] Read more.

Gas transport in shale gas reservoirs is largely affected by rock properties such as permeability. These properties are often sensitive to the in-situ stress state changes. Accurate modeling of shale gas transport in shale reservoir rocks considering the stress sensitive effects on rock petrophysical properties is important for successful shale gas extraction. Nonlinear elasticity in stress sensitive reservoir rocks depicts the nonlinear stress-strain relationship, yet it is not thoroughly studied in previous reservoir modeling works. In this study, an improved coupled flow and geomechanics model that considers nonlinear elasticity is proposed. The model is based on finite element methods, and the nonlinear elasticity in the model is validated with experimental data on shale samples selected from the Longmaxi Formation in Sichuan Basin China. Numerical results indicate that, in stress sensitive shale rocks, nonlinear elasticity affects shale permeability, shale porosity, and distributions of effective stress and pore pressure. Elastic modulus change is dependent on not only in-situ stress state but also stress history path. Without considering nonlinear elasticity, the modeling of shale rock permeability in Longmaxi Formation can overestimate permeability values by 1.6 to 53 times. Full article

(This article belongs to the Section L: Energy Sources)

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15 pages, 2104 KiB

Open AccessArticle

Design and CFD Simulations of a Vortex-Induced Piezoelectric Energy Converter (VIPEC) for Underwater Environment

by Xinyu An^1,*, Baowei Song¹, Wenlong Tian¹ and Congcong Ma²

¹ School of Marine Science and Technology, Northwestern Polytechnical University, Xi’an 710072, China

² Laboratoire Roberval, Université de Technologie de Compiègne, Compiègne 60200, France

Energies 2018, 11(2), 330; https://doi.org/10.3390/en11020330 - 2 Feb 2018

Cited by 31 | Viewed by 5393

Abstract

A novel vortex-induced piezoelectric energy converter (VIPEC) is presented in this paper to harvest ocean kinetic energy in the underwater environment. The converter consists of a circular cylinder, a pivoted plate attached to the tail of the cylinder, several piezoelectric patches and a [...] Read more.

A novel vortex-induced piezoelectric energy converter (VIPEC) is presented in this paper to harvest ocean kinetic energy in the underwater environment. The converter consists of a circular cylinder, a pivoted plate attached to the tail of the cylinder, several piezoelectric patches and a storage circuit. Vortex-induced pressure difference acts on the plate and drives the plate to squeeze piezo patches to convert fluid dynamic energy into electric energy. The output voltage is derived from the piezoelectric constitutive equation with fluid forces. In order to evaluate the performance of the VIPEC, two-dimensional computational fluid dynamics (CFD) simulations based on the Reynolds averaged Navier–Stokes (RANS) equation and the shear stress transport (SST) k-

ω

turbulence model are conducted. The CFD method is firstly verified for different grid resolutions and time steps, and then validated using simulation and experimental data. The influences of the plate length and flow velocity on the wake structure, the driving force and the performance of the VIPEC are investigated. The results reveal that different parameters reach their peaks at different plate lengths, and the converter has a maximal output voltage of

2.3

mV in a specified condition and the maximal power density reaches 0.035

μ

W/m

^{3}

with a resistance load of 10 M

Ω

. The influence of the simulated subcritical Reynolds number on the driving force is not noticeable. The simulation results also demonstrate the feasibility of this device. Full article

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13 pages, 2522 KiB

Open AccessArticle

Determination of Particle Size and Distribution through Image-Based Macroscopic Analysis of the Structure of Biomass Briquettes

by Veronika Chaloupková¹, Tatiana Ivanova^1,*

, Ondřej Ekrt², Abraham Kabutey³ and David Herák³

¹ Department of Sustainable Technologies, Faculty of Tropical AgriSciences, Czech University of Life Sciences Prague, Kamýcká 129, 165 21 Prague 6 - Suchdol, Czech Republic

² Department of Physics and Measurements, Faculty of Chemical Engineering, University of Chemistry and Technology Prague, Technická 5, 166 28 Prague 6 - Dejvice, Czech Republic

³ Department of Mechanical Engineering, Faculty of Engineering, Czech University of Life Sciences Prague, Kamýcká 129, 165 21 Prague 6 - Suchdol, Czech Republic

Energies 2018, 11(2), 331; https://doi.org/10.3390/en11020331 - 2 Feb 2018

Cited by 40 | Viewed by 5908

Abstract

Via image-based macroscopic, analysis of a briquettes’ surface structure, particle size, and distribution was determined to better understand the behavioural pattern of input material during agglomeration in the pressing chamber of a briquetting machine. The briquettes, made of miscanthus, industrial hemp and pine [...] Read more.

Via image-based macroscopic, analysis of a briquettes’ surface structure, particle size, and distribution was determined to better understand the behavioural pattern of input material during agglomeration in the pressing chamber of a briquetting machine. The briquettes, made of miscanthus, industrial hemp and pine sawdust were produced by a hydraulic piston press. Their structure was visualized by a stereomicroscope equipped with a digital camera and software for image analysis and data measurements. In total, 90 images of surface structure were obtained and quantitatively analysed. Using Nikon Instruments Software (NIS)-Elements software, the length and area of 900 particles were measured and statistically tested to compare the size of the particles at different surface locations. Results showed statistically significant differences in particles’ size distribution: larger particles were generally on the front side of briquettes and vice versa, smaller particles were on the rear side. As well, larger particles were centred in the middle of cross sections and the smaller particles were centred on the bottom of the briquette. Full article

(This article belongs to the Section L: Energy Sources)

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12 pages, 2259 KiB

Open AccessArticle

Influence of Conductive and Semi-Conductive Nanoparticles on the Dielectric Response of Natural Ester-Based Nanofluid Insulation

by M. Z. H. Makmud^1,2,*

, H. A. Illias^1,*

, C. Y. Chee³ and M. S. Sarjadi²

¹ UM High Voltage Laboratory (UMHVL), Department of Electrical Engineering, Faculty of Engineering, University of Malaya, 50603 Kuala Lumpur, Malaysia

² Complex of Science and Technology, Faculty of Science and Natural Resources, Universiti Malaysia Sabah, 88400 Kota Kinabalu, Malaysia

³ Department of Chemical Engineering, Faculty of Engineering, University of Malaya, 50603 Kuala Lumpur, Malaysia

Energies 2018, 11(2), 333; https://doi.org/10.3390/en11020333 - 2 Feb 2018

Cited by 64 | Viewed by 4670

Abstract

Nowadays, studies of alternative liquid insulation in high voltage apparatus have become increasingly important due to higher concerns regarding safety, sustainable resources and environmentally friendly issues. To fulfil this demand, natural ester has been extensively studied and it can become a potential product [...] Read more.

Nowadays, studies of alternative liquid insulation in high voltage apparatus have become increasingly important due to higher concerns regarding safety, sustainable resources and environmentally friendly issues. To fulfil this demand, natural ester has been extensively studied and it can become a potential product to replace mineral oil in power transformers. In addition, the incorporation of nanoparticles has been remarkable in producing improved characteristics of insulating oil. Although much extensive research has been carried out, there is no general agreement on the influence on the dielectric response of base oil due to the addition of different amounts and conductivity types of nanoparticle concentrations. Therefore, in this work, a natural ester-based nanofluid was prepared by a two-step method using iron oxide (Fe₂O₃) and titanium dioxide (TiO₂) as the conductive and semi-conductive nanoparticles, respectively. The concentration amount of each nanoparticle types was varied at 0.01, 0.1 and 1.0 g/L. The nanofluid samples were characterised by visual inspection, morphology and the dynamic light scattering (DLS) method before the dielectric response measurement was carried out for frequency-dependent spectroscopy (FDS), current-voltage (I-V), and dielectric breakdown (BD) strength. The results show that the dielectric spectra and I-V curves of nanofluid-based iron oxide increases with the increase of iron oxide nanoparticle loading, while for titanium dioxide, it exhibits a decreasing response. The dielectric BD strength is enhanced for both types of nanoparticles at 0.01 g/L concentration. However, the increasing amount of nanoparticles at 0.1 and 1.0 g/L led to a contrary dielectric BD response. Thus, the results indicate that the augmentation of conductive nanoparticles in the suspension can lead to overlapping mechanisms. Consequently, this reduces the BD strength compared to pristine materials during electron injection in high electric fields. Full article

(This article belongs to the Section F: Electrical Engineering)

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21 pages, 7575 KiB

Open AccessArticle

Multifunctional Composites for Future Energy Storage in Aerospace Structures

by Till Julian Adam^1,*, Guangyue Liao¹, Jan Petersen¹, Sebastian Geier¹

, Benedikt Finke², Peter Wierach¹, Arno Kwade²

and Martin Wiedemann¹

¹ German Aerospace Center (DLR e. V.), Institute of Composite Structures and Adaptive Systems, Lilienthalplatz 7, 38108 Braunschweig, Germany

² Technische Universität Braunschweig, Institute for Particle Technology, Volkmaroder Str. 5, 38104 Braunschweig, Germany

Energies 2018, 11(2), 335; https://doi.org/10.3390/en11020335 - 2 Feb 2018

Cited by 109 | Viewed by 11002

Abstract

Multifunctionalization of fiber-reinforced composites, especially by adding energy storage capabilities, is a promising approach to realize lightweight structural energy storages for future transport vehicles. Compared to conventional energy storage systems, energy density can be increased by reducing parasitic masses of non-energy-storing components and [...] Read more.

Multifunctionalization of fiber-reinforced composites, especially by adding energy storage capabilities, is a promising approach to realize lightweight structural energy storages for future transport vehicles. Compared to conventional energy storage systems, energy density can be increased by reducing parasitic masses of non-energy-storing components and by benefitting from the composite meso- and microarchitectures. In this paper, the most relevant existing approaches towards multifunctional energy storages are reviewed and subdivided into five groups by distinguishing their degree of integration and their scale of multifunctionalization. By introducing a modified range equation for battery-powered electric aircrafts, possible range extensions enabled by multifunctionalization are estimated. Furthermore, general and aerospace specific potentials of multifunctional energy storages are discussed. Representing an intermediate degree of structural integration, experimental results for a multifunctional energy-storing glass fiber-reinforced composite based on the ceramic electrolyte Li_1.4Al_0.4Ti_1.6(PO₄)₃ are presented. Cyclic voltammetry tests are used to characterize the double-layer behavior combined with galvanostatic charge–discharge measurements for capacitance calculation. The capacitance is observed to be unchanged after 1500 charge–discharge cycles revealing a promising potential for future applications. Furthermore, the mechanical properties are assessed by means of four-point bending and tensile tests. Additionally, the influence of mechanical loads on the electrical properties is also investigated, demonstrating the storage stability of the composites. Full article

(This article belongs to the Special Issue Towards a Transformation to Sustainable Aviation Systems)

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15 pages, 2665 KiB

Open AccessArticle

Analysis of Combustion Process in Industrial Gas Engine with Prechamber-Based Ignition System

by Rafał Ślefarski^1,*, Michał Gołębiewski¹, Paweł Czyżewski¹, Przemysław Grzymisławski¹ and Jacek Wawrzyniak²

¹ Poznan University of Technology, Piotrowo 3 Str., Chair of Thermal Engineering, 60-965 Poznan, Poland

² Polish Oil & Gas Company, Branch KRIO Odolanow, Krotoszynska 148, 63-430 Odolanow, Poland

Energies 2018, 11(2), 336; https://doi.org/10.3390/en11020336 - 2 Feb 2018

Cited by 11 | Viewed by 5190

Abstract

Application of a pre-combustion chamber (PCC) ignition system is one of the methods to improve combustion stability and reduce toxic compounds emission, especially NO_x. Using PCC allows the operation of the engine at lean combustion conditions or the utilization of low [...] Read more.

Application of a pre-combustion chamber (PCC) ignition system is one of the methods to improve combustion stability and reduce toxic compounds emission, especially NO_x. Using PCC allows the operation of the engine at lean combustion conditions or the utilization of low calorific gaseous fuels such as syngas or biogas. The paper presents the results of an experimental study of the combustion process in two stroke, large bore, stationary gas engine GMVH 12 equipped with two spark plugs (2-SP) and a PCC ignition system. The experimental research has been performed during the normal operation of the engine in an industrial compression station. It was observed that application of PCC provides less cycle-to-cycle combustion variation (more than 10%) and nitric oxide and carbon monoxide emissions decreased to 60% and 26% respectively. The total hydrocarbon (THC) emission rate is 25% higher for the engine equipped with PCC, which results in roughly two percent engine efficiency decrease. Another important criterion of engine retrofitting was the PCC location in the engine head. The experimental results show that improvement of engine operating parameters was recorded only for a configuration with one port offset by 45° from the axis of the main chamber. The study of the ignition delay angle and equivalence ratio in PCC did not demonstrate explicit influence on engine performance. Full article

(This article belongs to the Section I: Energy Fundamentals and Conversion)

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13 pages, 2472 KiB

Open AccessArticle

NOx and SO₂ Emissions during Co-Combustion of RDF and Anthracite in the Environment of Precalciner

by Xiaolin Chen^1,2, Junlin Xie^1,3, Shuxia Mei^1,2,* and Feng He^1,2

¹ State Key Laboratory of Silicate Materials for Architectures, Wuhan University of Technology, Wuhan 430070, China

² School of Materials Science and Engineering, Wuhan University of Technology, Wuhan 430070, China

³ Research and Test Center of Materials, Wuhan University of Technology, Wuhan 430070, China

Energies 2018, 11(2), 337; https://doi.org/10.3390/en11020337 - 2 Feb 2018

Cited by 12 | Viewed by 4199

Abstract

Based on the temperature and O₂ concentration in the cement precalciner, co-combustion of anthracite and Refuse Derived Fuel (RDF) were investigated using a thermogravimetric analyzer (TGA) and a double furnaces reactor. Both the TGA and double furnaces reactor results indicated that the [...] Read more.

Based on the temperature and O₂ concentration in the cement precalciner, co-combustion of anthracite and Refuse Derived Fuel (RDF) were investigated using a thermogravimetric analyzer (TGA) and a double furnaces reactor. Both the TGA and double furnaces reactor results indicated that the co-combustion characteristics were the linear additive effect in the devolatilization stage, while it was the synergistic effect in the char combustion stage. During co-combustion, at 900 °C, NOx released rapidly during the devolatilization stage, but in the char combustion stage the NOx formation were inhibited; at 800 °C, a large amount of CO formed, which could reduce the NOx. In general, at 900 °C and 800 °C, the application of co-combustion could lower the NOx emission yield and lower the NOx conversion. By combining the combustion characteristics with the XRD results, it was indicated that during co-combustion, at 800 °C, the SO₂ formation reaction was inhibited, and the SO₂ yield and conversion were quite low. Full article

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18 pages, 2340 KiB

Open AccessArticle

Device Performance Improvement of Recycling Double-Pass Cross-Corrugated Solar Air Collectors

by Chii-Dong Ho^*, Hsuan Chang, Ching-Fang Hsiao and Chien-Chang Huang

Energy and Opto-Electronic Materials Research Center, Department of Chemical and Materials Engineering, Tamkang University, Tamsui, New Taipei 251, Taiwan

Energies 2018, 11(2), 338; https://doi.org/10.3390/en11020338 - 2 Feb 2018

Cited by 20 | Viewed by 3352

Abstract

The device performance of cross-corrugated double-pass solar air heaters under external recycle conditions was investigated experimentally and theoretically, and solved numerically using the Newton method. Comparisons were made and represented graphically among three different configurations of the single-pass, flat-plate double-pass and cross-corrugated double-pass [...] Read more.

The device performance of cross-corrugated double-pass solar air heaters under external recycle conditions was investigated experimentally and theoretically, and solved numerically using the Newton method. Comparisons were made and represented graphically among three different configurations of the single-pass, flat-plate double-pass and cross-corrugated double-pass devices. Air flowing simultaneously over the wavelike corrugated absorbing plate and in-between both wavelike cross-corrugated absorbing and transverse bottom plates was conducted under double-pass operations. A considerable heat-transfer efficiency enhancement is obtained employing such a recycling double pass device with welding cross-corrugated absorbing plates, instead of using the flat-plate device. An effective thermal performance was achieved because the heat transfer area is doubled and the turbulent intensity is enhanced as well. The power consumption increment owing to the reduction in the cross-sectional area was taken into account associated with the heat-transfer efficiency enhancement for comparisons in determining the optimal design on an economic consideration for the recycling cross-corrugated double-pass device. Full article

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16 pages, 2539 KiB

Open AccessArticle

Influence of Reservoir Stimulation on Marine Gas Hydrate Conversion Efficiency in Different Accumulation Conditions

by Lin Yang^1,2,3,4, Chen Chen^1,2,3,4,*, Rui Jia^1,2,3,4,*, Youhong Sun^1,2,3,4, Wei Guo^1,2,3,4, Dongbin Pan^1,2,3,4, Xitong Li^1,2,3,4 and Yong Chen^1,2,3,4

¹ Engineering College, Jilin University, Changchun 130026, China

² State Key Laboratory of Superhard Materials, Changchun 130012, China

³ Key Laboratory of Drilling and Exploitation Technology in Complex Conditions, Ministry of Land and Resources, Changchun 130026, China

⁴ National Geophysical Exploration Equipment Engineering Research Center, Jilin University, Changchun 130026, China

Energies 2018, 11(2), 339; https://doi.org/10.3390/en11020339 - 2 Feb 2018

Cited by 39 | Viewed by 3917

Abstract

In this paper, we used a method of combining reservoir stimulation technique (RST) with depressurization to investigate the conversion efficiency of marine natural gas hydrate (NGH) reservoirs in the Shenhu area, on the northern slope of the South China Sea, which differ in [...] Read more.

In this paper, we used a method of combining reservoir stimulation technique (RST) with depressurization to investigate the conversion efficiency of marine natural gas hydrate (NGH) reservoirs in the Shenhu area, on the northern slope of the South China Sea, which differ in intrinsic permeability and initial NGH saturation conditions. We also analyzed the influence of the variable-stimulation effect on marine NGH conversion efficiency in different accumulation conditions, providing a reference scheme for improving the NGH conversion efficiency in the Shenhu area. In this work, we performed calculations for the variations in CH₄ production rate and cumulative volume of CH₄ in different initial NGH saturation, intrinsic permeability, and stimulation effect conditions. Variance analysis and range analysis methods were used to analyze the significance of these key factors and their interaction. Furthermore, we investigated the sensitivity of stimulation effect on NGH conversion efficiency. The simulation results showed that the stimulation effect has a significant influence on NGH conversion efficiency, and the influence of interaction between these three factors was not obvious. Possibly most importantly, we clarified that the sparsely fractured networks (N = 3) had a better effect for higher NGH conversion efficiency under higher saturation conditions. For lower permeability cases, the influence between sparsely (N = 3) and densely (N = 5) fractured networks were similar. Full article

(This article belongs to the Section I: Energy Fundamentals and Conversion)

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12 pages, 9671 KiB

Open AccessArticle

Multi-Saliency Aggregation-Based Approach for Insulator Flashover Fault Detection Using Aerial Images

by Yongjie Zhai¹, Haiyan Cheng¹, Rui Chen¹, Qiang Yang^2,*

and Xiaoxia Li²

¹ Department of Automation, North China Electric Power University, Baoding 071003, China

² College of Electrical Engineering, Zhejiang University, Hangzhou 310027, China

Energies 2018, 11(2), 340; https://doi.org/10.3390/en11020340 - 2 Feb 2018

Cited by 33 | Viewed by 3663

Abstract

Accurate and timely detection of insulator flashover on power transmission lines is of paramount importance to power utilities. Most available solutions mainly focus on the exploitation of the flashover mechanism or the discharge area detection, rather than the identification of a damaged area [...] Read more.

Accurate and timely detection of insulator flashover on power transmission lines is of paramount importance to power utilities. Most available solutions mainly focus on the exploitation of the flashover mechanism or the discharge area detection, rather than the identification of a damaged area due to flashovers using captured aerial images. To this end, this paper proposes a multi-saliency aggregation-based porcelain insulator flashover fault detection approach. The target area of the insulator is determined using the Faster-Pixelwise Image Saliency by Aggregating (F-PISA) algorithm based on the color and structural features. The color model can be established based on the color feature of the damaged areas on the insulator surface, and hence the damaged area can be identified. Based on the information obtained above, the contour information can be extracted. With the preceding process, the fault location can be confirmed with a good accuracy. The performance of the proposed detection approach is assessed through a comparative study with other available solutions. The numerical result demonstrates that the suggested solution can detect the insulator flashover with improved performance in terms of the average detection rate and average efficient detection rate. Additional analysis is carried out to evaluate its robustness and real-time performance, which confirms its deployment feasibility in practice. Full article

(This article belongs to the Section F: Electrical Engineering)

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18 pages, 2065 KiB

Open AccessArticle

Fuzzy Stochastic Unit Commitment Model with Wind Power and Demand Response under Conditional Value-At-Risk Assessment

by Jiafu Yin^*

and Dongmei Zhao

School of Electrical and Electronic Engineering, North China Electric Power University, Beijing 102206, China

Energies 2018, 11(2), 341; https://doi.org/10.3390/en11020341 - 2 Feb 2018

Cited by 10 | Viewed by 3335

Abstract

With the increasing penetration of wind power and demand response integrated into the grid, the combined uncertainties from wind power and demand response have been a challenging concern for system operators. It is necessary to develop an approach to accommodate the combined uncertainties [...] Read more.

With the increasing penetration of wind power and demand response integrated into the grid, the combined uncertainties from wind power and demand response have been a challenging concern for system operators. It is necessary to develop an approach to accommodate the combined uncertainties in the source side and load side. In this paper, the fuzzy stochastic conditional value-at-risk criterions are proposed as the risk measure of the combination of both wind power uncertainty and demand response uncertainty. To improve the computational tractability without sacrificing the accuracy, the fuzzy stochastic chance-constrained goal programming is proposed to transfer the fuzzy stochastic conditional value-at-risk to a deterministic equivalent. The operational risk of forecast error under fuzzy stochastic conditional value-at-risk assessment is represented by the shortage of reserve resource, which can be further divided into the load-shedding risk and the wind curtailment risk. To identify different priority levels for the different objective functions, the three-stage day-ahead unit commitment model is proposed through preemptive goal programming, in which the reliability requirement has the priority over the economic operation. Finally, a case simulation is performed on the IEEE 39-bus system to verify the effectiveness and efficiency of the proposed model. Full article

(This article belongs to the Section F: Electrical Engineering)

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19 pages, 8141 KiB

Open AccessArticle

Investigation of Unsteady Flow Interactions in a Transonic High Pressure Turbine Using Nonlinear Harmonic Method

by Muhammad Afzaal Asghar¹, Yangwei Liu^1,2,*

, Jiahuan Cui^3,4 and Lipeng Lu^1,2,*

¹ National Key Laboratory of Science and Technology on Aero-Engine Aero-Thermodynamics, School of Energy and Power Engineering, Beihang University, Beijing 100191, China

² Collaborative Innovation Center of Advanced Aero-Engine, Beihang University, Beijing 100191, China

³ Department of Engineering, University of Cambridge, Cambridge CB2 1PZ, UK

⁴ School of Aeronautics and Astronautics, and ZJU-UIUC Institute, Zhejiang University, Zhejiang 310027, China

Energies 2018, 11(2), 342; https://doi.org/10.3390/en11020342 - 2 Feb 2018

Cited by 6 | Viewed by 3697

Abstract

The performance of a transonic high pressure turbine is mainly influenced by the unsteady interactions associated with the passing blades. In this paper, the unsteady flow interactions in a transonic turbine have been numerically investigated using the nonlinear harmonic (NLH) method in comparison [...] Read more.

The performance of a transonic high pressure turbine is mainly influenced by the unsteady interactions associated with the passing blades. In this paper, the unsteady flow interactions in a transonic turbine have been numerically investigated using the nonlinear harmonic (NLH) method in comparison with the steady and unsteady Reynolds-averaged Navier–Stokes (RANS). The comparison shows that the NLH method using three harmonics could capture the main unsteady flow interactions efficiently with about seven times smaller computational cost than the unsteady RANS, resulting in a more accurate time-averaged flow than for steady RANS. However, the continuity of the flow variables across the rotor-stator interface has shown some discrepancies compared with the unsteady RANS, which can be further satisfied by increasing the numbers of harmonics. The unsteady interactions are analyzed in detail; the results show that the wake and trailing edge shock from the upstream stator are the major sources of unsteadiness in the downstream rotor passage. The stator trailing edge shock impinges on the suction side of the passing rotor blades and generates pressure waves. These pressure waves are periodically reflected back to trigger the stator wake shedding. These waves are strong enough to travel through the rotor passage, and eventually affect the flow at the rotor’s trailing edge. The stator wakes are chopped by the downstream rotor, and travel through the rotor passage. This significantly enhances the unsteadiness of the flow near the rotor trailing edge. Lastly, the deterministic stresses and enthalpy distributions extracted from the NLH method have revealed that the effects of the unsteadiness are relatively weaker in the axial direction. Furthermore, the deterministic correlations analysis has shown that, some empirical deterministic correlations models based on the decay concept of compressors are not suitable for turbines. Full article

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25 pages, 8037 KiB

Open AccessArticle

Challenges and Opportunities of Very Light High-Performance Electric Drives for Aviation

by Markus Henke^1,*, Gerrit Narjes²

, Jan Hoffmann¹, Constantin Wohlers², Stefan Urbanek²

, Christian Heister¹

, Jörn Steinbrink², Wolf-Rüdiger Canders¹ and Bernd Ponick²

¹ Institut für Elektrische Maschinen, Antriebe und Bahnen, Technische Universität Braunschweig, 38106 Braunschweig, Germany

² Institut für Antriebssysteme und Leistungselektronik, Leibniz Universität Hannover, 30167 Hannover, Germany

Energies 2018, 11(2), 344; https://doi.org/10.3390/en11020344 - 2 Feb 2018

Cited by 72 | Viewed by 11030

Abstract

The demand for alternative fueling methods to reduce the need for fossil fuels is not limited to the electrification of ground vehicles. More-electric and all-electric aircraft pose challenges, with extensive requirements in terms of power density, efficiency, safety, and environmental sustainability. This paper [...] Read more.

The demand for alternative fueling methods to reduce the need for fossil fuels is not limited to the electrification of ground vehicles. More-electric and all-electric aircraft pose challenges, with extensive requirements in terms of power density, efficiency, safety, and environmental sustainability. This paper focuses on electrical machines and their components, especially for high-power applications like the main propulsion. The electrical machine is evaluated from different aspects, followed by a closer look at the components and materials to determine the suitability of the current standard materials and advanced technologies. Furthermore, the mechanical and thermal aspects are reviewed, including new and innovative concepts for the cooling of windings and for the use of additive manufacturing. Aircraft have special demands regarding weight and installation space. Following recent developments and looking ahead to the future, the need and the possibilities for light and efficient electrical machines are addressed. All of the approaches and developments presented lead to a better understanding of the challenges to be expected and highlight the upcoming opportunities in electrical machine design for the use of electric motors and generators in future aircraft. Several prototypes of electrical machines for smaller aircraft already exist, such as the electric drive of the Siemens powered Extra 330LE. The focus of this paper is to provide an overview of current technical possibilities and technical interrelations of high performance electric drives for aviation. A 1 MW drive is exemplified to present the possibilities for future drives for airplanes carrying a larger number of passengers. All presented techniques can also be applied to other drive power classes. Full article

(This article belongs to the Special Issue Towards a Transformation to Sustainable Aviation Systems)

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21 pages, 6682 KiB

Open AccessFeature PaperArticle

Impact of Heat Pump-Driven Liquid Desiccant Dehumidification on the Energy Performance of an Evaporative Cooling-Assisted Air Conditioning System

by Jang-Hoon Shin, Joon-Young Park, Min-Suk Jo and Jae-Weon Jeong^*

Department of Architectural Engineering, College of Engineering, Hanyang University, 222 Wangsimni-Ro, Seongdong-Gu, Seoul 04763, Korea

Energies 2018, 11(2), 345; https://doi.org/10.3390/en11020345 - 2 Feb 2018

Cited by 21 | Viewed by 6484

Abstract

The main objective of this research is to investigate the energy performance enhancement obtained by applying a heat pump to a liquid desiccant and indirect and direct evaporative cooling-assisted 100% outdoor air system (LD-IDECOAS). In conventional LD-IDECOAS operation, the boiler providing regeneration heat [...] Read more.

The main objective of this research is to investigate the energy performance enhancement obtained by applying a heat pump to a liquid desiccant and indirect and direct evaporative cooling-assisted 100% outdoor air system (LD-IDECOAS). In conventional LD-IDECOAS operation, the boiler providing regeneration heat to the weak desiccant solution consumes most of the energy. In order to reduce the regeneration energy consumption in the LD-IDECOAS, a heat pump-integrated LD-IDECOAS (HPLD-IDECOAS) is suggested in this research. The heat pump reclaims waste heat from the absorber side of the system, and delivers the reclaimed heat to the regenerator side. Detailed energy simulations for both the LD-IDECOAS and HPLD-IDECOAS were conducted to analyze the energy saving potentiality of the proposed system over the conventional LD-IDECOAS. In both systems, it was assumed that a packed-bed type liquid desiccant unit with an aqueous solution of lithium chloride (LiCl) was used. In the proposed system, a heat pump with R-134a refrigerant was adopted. The results show that the proposed system was able to provide a 33% reduction in annual primary energy consumption compared with the conventional LD-IDECOAS. This significantly enhanced energy performance was mainly obtained through an 83% reduction in the gas energy consumed for regeneration of the desiccant solution in the proposed system by applying the heat pump. Full article

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20 pages, 1869 KiB

Open AccessArticle

Electricity Market Design in Croatia within the European Electricity Market—Recommendations for Further Development

by Mateo Beus^1,*, Ivan Pavić¹, Ivona Štritof², Tomislav Capuder¹ and Hrvoje Pandžić¹

¹ Faculty of Electrical Engineering and Computing University of Zagreb, Unska 3, 10000 Zagreb, Croatia

² Croatian Power Utility (Hrvatska Elektroprivreda d.d.), Ulica grada Vukovara, 10000 Zagreb, Croatia

Energies 2018, 11(2), 346; https://doi.org/10.3390/en11020346 - 2 Feb 2018

Cited by 18 | Viewed by 9124

Abstract

One of the most important objectives of the European Union is the creation of an Internal Electricity Market (IEM) in Europe. Various national electricity market designs represent one of the major obstacles to the creation of IEM and it is necessary to coordinate [...] Read more.

One of the most important objectives of the European Union is the creation of an Internal Electricity Market (IEM) in Europe. Various national electricity market designs represent one of the major obstacles to the creation of IEM and it is necessary to coordinate national market designs among Member States in order to achieve that. Therefore, this paper gives a comprehensive overview of the electricity market design according to laws related to the electricity sector that are in force in Croatia. Additionally, the paper identifies key obstacles that hamper the development of a well-functioning electricity market in Croatia towards its further integration into the IEM. Since Croatian Power Exchange (CROPEX) is not coupled with any other power exchange, special attention was given to necessary prerequisites for market coupling with the Slovenian Power Exchange (BSP SouthPool) and with the Hungarian Power Exchange (HUPX). Full article

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17 pages, 1538 KiB

Open AccessArticle

On the Application of Joint-Domain Dictionary Mapping for Multiple Power Disturbance Assessment

by Delong Cai¹

, Kaicheng Li^1,*, Shunfan He², Yuanzheng Li³ and Yi Luo¹

¹ State Key Laboratory of Advanced Electromagnetic Engineering and Technology, School of Electrical and Electronics Engineering, Huazhong University of Science and Technology, Wuhan 430074, China

² School of Computer Science, South-Central University for Nationalities, Wuhan 430074, China

³ School of Automation, Ministry of Education Key Laboratory of Image Processing and Intelligence Control, Huazhong University of Science and Technology, Wuhan 430074, China

Energies 2018, 11(2), 347; https://doi.org/10.3390/en11020347 - 2 Feb 2018

Cited by 4 | Viewed by 2729

Abstract

This paper proposes a joint-domain dictionary mapping method to obtain high assessment accuracy of multiple power disturbances. Firstly, in order to achieve resolutions in both the time and frequency domains, a joint-domain dictionary is proposed which consists of a discrete Hartley base and [...] Read more.

This paper proposes a joint-domain dictionary mapping method to obtain high assessment accuracy of multiple power disturbances. Firstly, in order to achieve resolutions in both the time and frequency domains, a joint-domain dictionary is proposed which consists of a discrete Hartley base and an identity matrix. Due to the low correlation between the discrete Hartley base and the identity matrix, the joint-domain dictionary mapping can separately capture the approximations of the sinusoidal components and transients. Since the mapping coefficients contain the physical quantities, the eigenvalues of each component can be effectively estimated. A quantified eigenvalue classifier was designed for identifying power disturbances using the estimated eigenvalues. The proposed method was compared with several advanced methods through simulated power disturbances under different noise conditions, and actual data from the Institute of Electrical and Electronics Engineers Power and Energy Society database. The results reveal that the joint-domain dictionary mapping technique shows good performance on parameter estimation and recognition precision, even dealing with complicated multiple power disturbances. Full article

(This article belongs to the Section F: Electrical Engineering)

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22 pages, 5312 KiB

Open AccessArticle

Study of the Energy Conversion Process in the Electro-Hydrostatic Drive of a Vehicle

by Wiesław Grzesikiewicz, Lech Knap^*, Michał Makowski and Janusz Pokorski

Faculty of Automotive and Construction Machinery Engineering, Warsaw University of Technology, Narbutta 84, 02-524 Warsaw, Poland

Energies 2018, 11(2), 348; https://doi.org/10.3390/en11020348 - 2 Feb 2018

Cited by 3 | Viewed by 4827

Abstract

In the paper, we describe a study of an electro-hydrostatic hybrid drive of a utility van intended for city traffic. In this hybrid drive, the electric drive is periodically accompanied by hydrostatic drive, especially during acceleration and regenerative braking of the vehicle. We [...] Read more.

In the paper, we describe a study of an electro-hydrostatic hybrid drive of a utility van intended for city traffic. In this hybrid drive, the electric drive is periodically accompanied by hydrostatic drive, especially during acceleration and regenerative braking of the vehicle. We present a mathematical model of the hybrid drive as a set of dynamics and regulation equations of the van traveling at a given speed. On this basis, we construct a computer program which we use to simulate the processes of energy conversion in the electro-hydrostatic drive. The main goal of the numerical simulation is to assess the possibility of reducing energy intensity of the electric drive through such a support of the hydrostatic drive. The obtained results indicate that it is possible to reduce the load on elements of the electric system and, therefore, improve energy conversion. Full article

(This article belongs to the Collection Electric and Hybrid Vehicles Collection)

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22 pages, 7367 KiB

Open AccessArticle

Common Grounded H-Type Bidirectional DC-DC Converter with a Wide Voltage Conversion Ratio for a Hybrid Energy Storage System

by Huakun Bi, Ping Wang^*

and Zhishuang Wang

School of Electrical and Information Engineering, Tianjin University, Tianjin 300072, China

Energies 2018, 11(2), 349; https://doi.org/10.3390/en11020349 - 2 Feb 2018

Cited by 9 | Viewed by 4486

Abstract

Hybrid energy storage systems (HESS) play an important role in maintaining the power balance of a direct current (DC) micro-grid. A HESS is mainly composed of high power density super-capacitors (SCs) and high energy density batteries. According to the operational requirements of an [...] Read more.

Hybrid energy storage systems (HESS) play an important role in maintaining the power balance of a direct current (DC) micro-grid. A HESS is mainly composed of high power density super-capacitors (SCs) and high energy density batteries. According to the operational requirements of an SC, a bidirectional DC-DC converter with the characteristics of a good dynamic response and a wide voltage conversion ratio is needed to interface the SC and a high-voltage DC bus. In this paper, a novel common grounded H-type bidirectional converter characterized by a good dynamic response, a low inductor current ripple, and a wide voltage conversion ratio is proposed. In addition, it can avoid the narrow pulse of pulse width modulation (PWM) voltage waveforms when a high voltage conversion ratio is achieved. All of these features are beneficial to the operation of the SC connected to a DC bus. The operating principle and characteristics of the proposed converter are presented in this paper. A 320 W prototype with a wide voltage conversion ranging from 3.3 to 8 in step-up mode and 1/8 to 1/3 in step-down mode has been constructed to validate the feasibility and effectiveness of the proposed converter. Full article

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19 pages, 9074 KiB

Open AccessArticle

Continuous Steering Stability Control Based on an Energy-Saving Torque Distribution Algorithm for a Four in-Wheel-Motor Independent-Drive Electric Vehicle

by Li Zhai^1,2,*

, Rufei Hou^1,2, Tianmin Sun³ and Steven Kavuma^1,2

¹ National Engineering Laboratory for Electric Vehicles, Beijing Institute of Technology, Beijing 100081, China

² Co-Innovation Center of Electric Vehicles in Beijing, Beijing Institute of Technology, Beijing 100081, China

³ BAIC BJEV Inc., Beijing 100021, China

Energies 2018, 11(2), 350; https://doi.org/10.3390/en11020350 - 2 Feb 2018

Cited by 54 | Viewed by 7279

Abstract

In this paper, a continuous steering stability controller based on an energy-saving torque distribution algorithm is proposed for a four in-wheel-motor independent-drive electric vehicle (4MIDEV) to improve the energy consumption efficiency while maintaining the stability in steering maneuvers. The controller is designed as [...] Read more.

In this paper, a continuous steering stability controller based on an energy-saving torque distribution algorithm is proposed for a four in-wheel-motor independent-drive electric vehicle (4MIDEV) to improve the energy consumption efficiency while maintaining the stability in steering maneuvers. The controller is designed as a hierarchical structure, including the reference model level, the upper-level controller, and the lower-level controller. The upper-level controller adopts the direct yaw moment control (DYC), which is designed to work continuously during the steering maneuver to better ensure steering stability in extreme situations, rather than working only after the vehicle is judged to be unstable. An adaptive two-hierarchy energy-saving torque distribution algorithm is developed in the lower-level controller with the friction ellipse constraint as a basis for judging whether the algorithm needs to be switched, so as to achieve a more stable and energy-efficient steering operation. The proposed stability controller was validated in a co-simulation of CarSim and Matlab/Simulink. The simulation results under different steering maneuvers indicate that the proposed controller, compared with the conventional servo controller and the ordinary continuous controller, can reduce energy consumption up to 23.68% and improve the vehicle steering stability. Full article

(This article belongs to the Collection Electric and Hybrid Vehicles Collection)

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14 pages, 3258 KiB

Open AccessArticle

Effect of Nitrogen/Oxygen Substances on the Pyrolysis of Alkane-Rich Gases to Acetylene by Thermal Plasma

by Wei Huang, Junkui Jin, Guangdong Wen, Qiwei Yang^*

, Baogen Su^* and Qilong Ren

Key Laboratory of Biomass Chemical Engineering, College of Chemical and Biological Engineering, Zhejiang University, Hangzhou 310027, China

Energies 2018, 11(2), 351; https://doi.org/10.3390/en11020351 - 2 Feb 2018

Cited by 5 | Viewed by 3941

Abstract

It is important to convert alkane-rich gases, such as coke oven gas, to value-added chemicals rather than direct emission or combustion. Abundant nitrogen/oxygen substances are present in the actual alkane-rich gases. However, the research about how they influence the conversion in the pyrolysis [...] Read more.

It is important to convert alkane-rich gases, such as coke oven gas, to value-added chemicals rather than direct emission or combustion. Abundant nitrogen/oxygen substances are present in the actual alkane-rich gases. However, the research about how they influence the conversion in the pyrolysis process is missing. In this work, a systematic investigation on the effect of various nitrogen/oxygen-containing substances, including N₂, CO, and CO₂,on the pyrolysis of CH₄ to C₂H₂ was performed by a self-made 50 kW rotating arc thermal plasma reactor, and the pyrolysis of a simulated coke oven gas as a model of alkane-rich mixing gas was conducted as well. It was found that the presence of N₂ and CO₂ was not conducive to the main reaction of alkane pyrolysis for C₂H₂, while CO, as a stable equilibrium product, had little effect on the cracking reaction. Consequently, it is suggested that a pretreatment process of removing N₂ and CO₂ should be present before pyrolysis. Both input power and feed rate had considerable effect on the pyrolysis of the simulated coke oven gas, and a C₂H₂ selectivity of 91.2% and a yield of 68.3% could be obtained at an input power of 17.9 kW. Full article

(This article belongs to the Section I: Energy Fundamentals and Conversion)

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15 pages, 5752 KiB

Open AccessArticle

Wireless Power Transfer Technology Applied to an Autonomous Electric UAV with a Small Secondary Coil

by Tommaso Campi^*

, Silvano Cruciani

and Mauro Feliziani

Department of Industrial and Information Engineering and Economics, University of L’Aquila, 67100 L’Aquila, Italy

Energies 2018, 11(2), 352; https://doi.org/10.3390/en11020352 - 2 Feb 2018

Cited by 113 | Viewed by 7933

Abstract

This study deals with the design and the optimization of a wireless power transfer (WPT) charging system based on magnetic resonant coupling applied to an electric vertical take-off and landing Unmanned Aerial Vehicle (UAV). In this study, a procedure for primary and secondary [...] Read more.

This study deals with the design and the optimization of a wireless power transfer (WPT) charging system based on magnetic resonant coupling applied to an electric vertical take-off and landing Unmanned Aerial Vehicle (UAV). In this study, a procedure for primary and secondary coil design is proposed. The primary circuit in the ground station consists of an array of coils in order to mitigate the negative effects on the coupling factor produced by the possible misalignment between the coils due to an imperfect landing. Key aspects for the design of the secondary coil onboard the UAV are the lightness and compactness of the WPT system components. A demonstrative prototype of the WPT system is applied to a commercial drone. The WPT electrical performances are calculated and measured. Finally, an automatic battery recharge station is built where the drone can autonomously land, recharge the battery and take off to continue its flight mission. Full article

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19 pages, 3838 KiB

Open AccessArticle

Hydro-Thermal-Wind Generation Scheduling Considering Economic and Environmental Factors Using Heuristic Algorithms

by Suresh K. Damodaran^1,*

and T. K. Sunil Kumar²

¹ Department of Electrical Engineering, Government Engineering College, Trichur 680009, India

² Department of Electrical Engineering, National Institute of Technology Calicut, Kerala 673601, India

Energies 2018, 11(2), 353; https://doi.org/10.3390/en11020353 - 2 Feb 2018

Cited by 39 | Viewed by 3892

Abstract

Hydro-thermal-wind generation scheduling (HTWGS) with economic and environmental factors is a multi-objective complex nonlinear power system optimization problem with many equality and inequality constraints. The objective of the problem is to generate an hour-by-hour optimum schedule of hydro-thermal-wind power plants to attain the [...] Read more.

Hydro-thermal-wind generation scheduling (HTWGS) with economic and environmental factors is a multi-objective complex nonlinear power system optimization problem with many equality and inequality constraints. The objective of the problem is to generate an hour-by-hour optimum schedule of hydro-thermal-wind power plants to attain the least emission of pollutants from thermal plants and a reduced generation cost of thermal and wind plants for a 24-h period, satisfying the system constraints. The paper presents a detailed framework of the HTWGS problem and proposes a modified particle swarm optimization (MPSO) algorithm for evolving a solution. The competency of selected heuristic algorithms, representing different heuristic groups, viz. the binary coded genetic algorithm (BCGA), particle swarm optimization (PSO), improved harmony search (IHS), and JAYA algorithm, for searching for an optimal solution to HTWGS considering economic and environmental factors was investigated in a trial system consisting of a multi-stream cascaded system with four reservoirs, three thermal plants, and two wind plants. Appropriate mathematical models were used for representing the water discharge, generation cost, and pollutant emission of respective power plants incorporated in the system. Statistical analysis was performed to check the consistency and reliability of the proposed algorithm. The simulation results indicated that the proposed MPSO algorithm provided a better solution to the problem of HTWGS, with a reduced generation cost and the least emission, when compared with the other heuristic algorithms considered. Full article

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18 pages, 4081 KiB

Open AccessArticle

Co-Planning of Demand Response and Distributed Generators in an Active Distribution Network

by Yi Yu^1,2

, Xishan Wen¹, Jian Zhao^2,3,*, Zhao Xu² and Jiayong Li²

¹ School of Electrical Engineering, Wuhan University, Wuhan 430072, China

² Department of Electrical Engineering, The Hong Kong Polytechnic University, Hong Kong, China

³ Department of Electrical Power Engineering, Shanghai University of Electric Power, Shanghai 200090, China

Energies 2018, 11(2), 354; https://doi.org/10.3390/en11020354 - 2 Feb 2018

Cited by 11 | Viewed by 3949

Abstract

The integration of renewables is fast-growing, in light of smart grid technology development. As a result, the uncertain nature of renewables and load demand poses significant technical challenges to distribution network (DN) daily operation. To alleviate such issues, price-sensitive demand response and distributed [...] Read more.

The integration of renewables is fast-growing, in light of smart grid technology development. As a result, the uncertain nature of renewables and load demand poses significant technical challenges to distribution network (DN) daily operation. To alleviate such issues, price-sensitive demand response and distributed generators can be coordinated to accommodate the renewable energy. However, the investment cost for demand response facilities, i.e., load control switch and advanced metering infrastructure, cannot be ignored, especially when the responsive demand is large. In this paper, an optimal coordinated investment for distributed generator and demand response facilities is proposed, based on a linearized, price-elastic demand response model. To hedge against the uncertainties of renewables and load demand, a two-stage robust investment scheme is proposed, where the investment decisions are optimized in the first stage, and the demand response participation with the coordination of distributed generators is adjusted in the second stage. Simulations on the modified IEEE 33-node and 123-node DN demonstrate the effectiveness of the proposed model. Full article

(This article belongs to the Special Issue Solar Energy Harvesting, Storage and Utilization)

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27 pages, 20788 KiB

Open AccessArticle

Improved Finite-Control-Set Model Predictive Control for Cascaded H-Bridge Inverters

by Roh Chan and Sangshin Kwak^*

School of Electrical and Electronics Engineering, Chung-Ang University, Seoul 06974, Korea

Energies 2018, 11(2), 355; https://doi.org/10.3390/en11020355 - 2 Feb 2018

Cited by 13 | Viewed by 4809

Abstract

In multilevel cascaded H-bridge (CHB) inverters, the number of voltage vectors generated by the inverter quickly increases with increasing voltage level. However, because the sampling period is short, it is difficult to consider all the vectors as the voltage level increases. This paper [...] Read more.

In multilevel cascaded H-bridge (CHB) inverters, the number of voltage vectors generated by the inverter quickly increases with increasing voltage level. However, because the sampling period is short, it is difficult to consider all the vectors as the voltage level increases. This paper proposes a model predictive control algorithm with reduced computational complexity and fast dynamic response for CHB inverters. The proposed method presents a robust approach to interpret a next step as a steady or transient state by comparing an optimal voltage vector at a present step and a reference voltage vector at the next step. During steady state, only an optimal vector at a present step and its adjacent vectors are considered as a candidate-vector subset. On the other hand, this paper defines a new candidate vector subset for the transient state, which consists of more vectors than those in the subset used for the steady state for fast dynamic speed; however, the vectors are less than all the possible vectors generated by the CHB inverter, for calculation simplicity. In conclusion, the proposed method can reduce the computational complexity without significantly deteriorating the dynamic responses. Full article

(This article belongs to the Special Issue Emerging Power Electronics Technologies for Power Systems and Machine Drives)

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19 pages, 5404 KiB

Open AccessArticle

Comparative Study of Different Methods for Estimating Weibull Parameters: A Case Study on Jeju Island, South Korea

by Dongbum Kang¹, Kyungnam Ko^2,* and Jongchul Huh³

¹ Multidisciplinary Graduate School Program for Wind Energy, Graduate School, Jeju National University, 102 Jejudaehakro, Jeju 63243, Korea

² Faculty of Wind Energy Engineering, Graduate School, Jeju National University, 102 Jejudaehakro, Jeju 63243, Korea

³ Department of Mechanical Engineering, College of Engineering, Jeju National University, 102 Jejudaehakro, Jeju 63243, Korea

Energies 2018, 11(2), 356; https://doi.org/10.3390/en11020356 - 3 Feb 2018

Cited by 72 | Viewed by 5409

Abstract

On Jeju Island, South Korea, an investigation was conducted to determine the best method for estimating Weibull parameters. Six methods commonly used in many fields of the wind energy industry were reviewed: the empirical, moment, graphical, energy pattern factor, maximum likelihood, and modified [...] Read more.

On Jeju Island, South Korea, an investigation was conducted to determine the best method for estimating Weibull parameters. Six methods commonly used in many fields of the wind energy industry were reviewed: the empirical, moment, graphical, energy pattern factor, maximum likelihood, and modified maximum likelihood methods. In order to improve the reliability of a research result, five-year actual wind speed data taken from nine sites with various topographical conditions were used for the estimation. Furthermore, the effect of various topographical conditions on the accuracy of the methods was analyzed and 10 bin interval types were applied to determine the most appropriate bin interval based on their performances. Weibull distributions that were estimated using these methods were compared with the observed wind speed distribution. Then the accuracy of each method was evaluated using four accuracy tests. The results showed that of the six methods, the moment method had the best performance regardless of topographical conditions, while the graphical method performed the worst. Additionally, topographical conditions did not affect the accuracy ranking of the methods for estimating the Weibull parameters, while an increase of terrain complexity resulted in an increase of discrepancy between the estimated Weibull distribution and the frequency of the observed wind speed data. In addition, the choice in bin interval greatly affected the accuracy of the graphical method while it did not depend on the accuracy of the modified maximum likelihood method. Full article

(This article belongs to the Section L: Energy Sources)

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11 pages, 2750 KiB

Open AccessArticle

Step-Up Partial Power DC-DC Converters for Two-Stage PV Systems with Interleaved Current Performance

by Jaime Wladimir Zapata^*,†

, Samir Kouro^†, Gonzalo Carrasco^† and Hugues Renaudineau^†

¹ Electronics Engineering Department, Universidad Tecnica Federico Santa Maria, Valparaiso 2390123, Chile

^† These authors contributed equally to this work.

Energies 2018, 11(2), 357; https://doi.org/10.3390/en11020357 - 3 Feb 2018

Cited by 29 | Viewed by 5641

Abstract

This work presents a partial power converter allowing us to obtain, with a single DC-DC converter, the same feature as the classical interleaved operation of two converters. More precisely, the proposed topology performs similarly as the input-parallel output-series (IPOS) configuration reducing the current [...] Read more.

This work presents a partial power converter allowing us to obtain, with a single DC-DC converter, the same feature as the classical interleaved operation of two converters. More precisely, the proposed topology performs similarly as the input-parallel output-series (IPOS) configuration reducing the current ripple at the input of the system and dividing the individual converters power rating, compared to a single converter. The proposed topology consists of a partial DC-DC converter processing only a fraction of the total power, thus allowing high efficiency. Experimental results are provided to validate the proposed converter topology with a Flyback-based 100 W test bench with a transformer turns ratio

n_{1} = n_{2}

. Experimental results show high performances reducing the input current ripple around

30 %

, further increasing the conversion efficiency. Full article

(This article belongs to the Special Issue Emerging Power Electronics Technologies for Power Systems and Machine Drives)

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20 pages, 2869 KiB

Open AccessArticle

A Prediction Mechanism of Energy Consumption in Residential Buildings Using Hidden Markov Model

by Israr Ullah¹

, Rashid Ahmad² and DoHyeun Kim^1,*

¹ Computer Engineering Department, Jeju National University, Jeju-si 63243, Korea

² Computer Science Department, COMSATS Institute of Information Technology, Attock Campus 43600, Pakistan

Energies 2018, 11(2), 358; https://doi.org/10.3390/en11020358 - 3 Feb 2018

Cited by 76 | Viewed by 7998

Abstract

Internet of Things (IoT) is considered as one of the future disruptive technologies, which has the potential to bring positive change in human lifestyle and uplift living standards. Many IoT-based applications have been designed in various fields, e.g., security, health, education, manufacturing, transportation, [...] Read more.

Internet of Things (IoT) is considered as one of the future disruptive technologies, which has the potential to bring positive change in human lifestyle and uplift living standards. Many IoT-based applications have been designed in various fields, e.g., security, health, education, manufacturing, transportation, etc. IoT has transformed conventional homes into Smart homes. By attaching small IoT devices to various appliances, we cannot only monitor but also control indoor environment as per user demand. Intelligent IoT devices can also be used for optimal energy utilization by operating the associated equipment only when it is needed. In this paper, we have proposed a Hidden Markov Model based algorithm to predict energy consumption in Korean residential buildings using data collected through smart meters. We have used energy consumption data collected from four multi-storied buildings located in Seoul, South Korea for model validation and results analysis. Proposed model prediction results are compared with three well-known prediction algorithms i.e., Support Vector Machine (SVM), Artificial Neural Network (ANN) and Classification and Regression Trees (CART). Comparative analysis shows that our proposed model achieves

2.96 %

better than ANN results in terms of root mean square error metric,

6.09 %

better than SVM and

9.03 %

better than CART results. To further establish and validate prediction results of our proposed model, we have performed temporal granularity analysis. For this purpose, we have evaluated our proposed model for hourly, daily and weekly data aggregation. Prediction accuracy in terms of root mean square error metric for hourly, daily and weekly data is 2.62, 1.54 and 0.46, respectively. This shows that our model prediction accuracy improves for coarse grain data. Higher prediction accuracy gives us confidence to further explore its application in building control systems for achieving better energy efficiency. Full article

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14 pages, 2845 KiB

Open AccessArticle

Power Management of Islanded Self-Excited Induction Generator Reinforced by Energy Storage Systems

by Nachat N. Nasser^*

and Mohamed E. A. Farrag

School of Engineering and Built Environment, Glasgow Caledonian University, 70 Cowcaddens Rd., Glasgow G4 0BA, UK

Energies 2018, 11(2), 359; https://doi.org/10.3390/en11020359 - 3 Feb 2018

Cited by 1 | Viewed by 4240

Abstract

Self-Excited Induction Generators (SEIGs), e.g., Small-Scale Embedded wind generation, are increasingly used in electricity distribution networks. The operational stability of stand-alone SEIG is constrained by the local load conditions: stability can be achieved by maintaining the load’s active and reactive power at optimal [...] Read more.

Self-Excited Induction Generators (SEIGs), e.g., Small-Scale Embedded wind generation, are increasingly used in electricity distribution networks. The operational stability of stand-alone SEIG is constrained by the local load conditions: stability can be achieved by maintaining the load’s active and reactive power at optimal values. Changes in power demand are dependent on customers’ requirements, and any deviation from the pre-calculated optimum setting will affect a machine’s operating voltage and frequency. This paper presents an investigation of the operation of the SEIG in islanding mode of operation under different load conditions, with the aid of batteries as an energy storage source. In this research a current-controlled voltage-source converter is proposed to regulate the power exchange between a direct current (DC) energy storage source and an alternating current (AC) grid, the converter’s controller is driven by any variation between machine capability and load demand. In order to prolong the system stability when the battery reaches its operation constraints, it is recommended that an ancillary generator and a dummy local load be embedded in the system. The results show the robustness and operability of the proposed system in the islanding mode of the SEIG under different load conditions. Full article

(This article belongs to the Section F: Electrical Engineering)

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17 pages, 12226 KiB

Open AccessArticle

Determining the U-Value of Façades Using the Thermometric Method: Potentials and Limitations

by David Bienvenido-Huertas^1,*

, Roberto Rodríguez-Álvaro²

, Juan José Moyano¹

, Fernando Rico¹

and David Marín¹

¹ Department of Graphical Expression and Building Engineering, University of Seville, 41012 Seville, Spain

² Department of Civil Engineering, Universidade da Coruña, 15071 A Coruña, Spain

Energies 2018, 11(2), 360; https://doi.org/10.3390/en11020360 - 3 Feb 2018

Cited by 73 | Viewed by 6956

Abstract

The thermal transmittance of building envelopes determines to a large extent the energy demand of buildings. Thus, there is a keen interest in having methods which can precisely evaluate thermal transmittance. From a scientific point of view, this study analyses the viability of [...] Read more.

The thermal transmittance of building envelopes determines to a large extent the energy demand of buildings. Thus, there is a keen interest in having methods which can precisely evaluate thermal transmittance. From a scientific point of view, this study analyses the viability of the application of the thermometric method (THM), one of the most used methods in Spain. For this purpose, the test method has been improved by determining the adequate test conditions, the selection and installation of equipment, data acquisition and post-processing, and the estimation of uncertainty. We analyse eight case studies in a Mediterranean climate (Csa) to determine the potentials and limitations of the method. The results show that the values obtained through THM are valid under winter environmental conditions with relative uncertainties between 6% and 13%, while difficulties to perform the test in optimal conditions, and therefore to obtain valid results in warmer seasons, are detected. In this regard, the case studies which obtained a greater number of observations by performing the filtrate conditions were able to obtain representative results. Furthermore, there are significant differences depending on the kind of equipment and probes used during the experimental campaign. Finally, in warm climate regions a data filtrate can be considered for observations of a temperature difference higher than 5 °C, obtaining valid results for the case studies, although the rise in the thermal gradient can guarantee a greater stability of data. Full article

(This article belongs to the Special Issue Building Energy Use: Modeling and Analysis)

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16 pages, 9824 KiB

Open AccessArticle

Comparison of Positive Streamers in Liquid Dielectrics with and without Nanoparticles Simulated with Finite-Element Software

by Juan Velasco^1,†, Ricardo Frascella^1,†, Ricardo Albarracín^1,*

, Juan Carlos Burgos², Ming Dong³, Ming Ren³ and Li Yang³

¹ Departamento de Ingeniería Eléctrica, Electrónica, Automática y Física Aplicada, Escuela Técnica Superior de Ingeniería y Diseño Industrial (ETSIDI), Universidad Politécnica de Madrid (UPM), Ronda de Valencia 3, 28012 Madrid, Spain

² Electrical Engineering Department, Universidad Carlos III de Madrid, Avda. de la Universidad 30, 28911 Leganés, Madrid, Spain

³ State Key Laboratory of Electrical Insulation for Power Equipment, Xi’an Jiaotong University, Xi’an 710049, China

^† These authors contributed equally to this work.

Energies 2018, 11(2), 361; https://doi.org/10.3390/en11020361 - 3 Feb 2018

Cited by 28 | Viewed by 8801

Abstract

In this paper, a comparison of positive streamer diffusion propagation is carried out in three configurations of oil transformers: mineral transformer oil, mineral oil with solid dielectric barriers, and a nanofluid. The results have been solved using a finite-element method with a two-dimensional [...] Read more.

In this paper, a comparison of positive streamer diffusion propagation is carried out in three configurations of oil transformers: mineral transformer oil, mineral oil with solid dielectric barriers, and a nanofluid. The results have been solved using a finite-element method with a two-dimensional (2D) axi-symmetric space dimension selected. Additionally, previous results from other research has been reviewed to compare the results obtained. As expected, it is confirmed that the nanoparticles improve the dielectric properties of the mineral oil. In addition, it is observed that the dielectric solid blocks the propagation of the streamer when it is submerged with a horizontal orientation, thus perpendicular to the applied electric field. The computer used, with four cores (each 3.4 GHz) and 16 GB of RAM, was not sufficient for performing the simulations of the models with great precision. However, with these first models, the tendency of the dielectric behavior of the oil was obtained for the three cases in which the streamer was acting through the transformer oil. The simulation of these models, in the future, in a supercomputer with a high performance in terms of RAM memory may allow us to predict, as an example, the best concentration of nanoparticles to retard the streamer inception. Finally, other dielectric issues will be predicted using these models, such as to analyze the advantages and drawbacks of the presence of dielectrics inside the oil transformer. Full article

(This article belongs to the Special Issue Engineering Dielectric Liquid Applications)

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19 pages, 582 KiB

Open AccessArticle

Simulation-Optimization Framework for Synthesis and Design of Natural Gas Downstream Utilization Networks

by Saad A. Al-Sobhi^1,2, Ali Elkamel^1,3, Fatih S. Erenay^4,* and Munawar A. Shaik^3,5

¹ Department of Chemical Engineering, University of Waterloo, Waterloo, ON N2L 3G1, Canada

² Department of Chemical Engineering, Qatar University, Doha 2713, Qatar

³ Department of Chemical Engineering, The Petroleum Institute, Khalifa University of Science & Technology, Abu Dhabi 2533, UAE

⁴ Department of Management Sciences, University of Waterloo, Waterloo, ON N2L 3G1, Canada

⁵ Department of Chemical Engineering, Indian Institute of Technology Delhi, Hauz Khas, New Delhi 110016, India

Energies 2018, 11(2), 362; https://doi.org/10.3390/en11020362 - 3 Feb 2018

Cited by 14 | Viewed by 4551

Abstract

Many potential diversification and conversion options are available for utilization of natural gas resources, and several design configurations and technology choices exist for conversion of natural gas to value-added products. Therefore, a detailed mathematical model is desirable for selection of optimal configuration and [...] Read more.

Many potential diversification and conversion options are available for utilization of natural gas resources, and several design configurations and technology choices exist for conversion of natural gas to value-added products. Therefore, a detailed mathematical model is desirable for selection of optimal configuration and operating mode among the various options available. In this study, we present a simulation-optimization framework for the optimal selection of economic and environmentally sustainable pathways for natural gas downstream utilization networks by optimizing process design and operational decisions. The main processes (e.g., LNG, GTL, and methanol production), along with different design alternatives in terms of flow-sheeting for each main processing unit (namely syngas preparation, liquefaction, N₂ rejection, hydrogen, FT synthesis, methanol synthesis, FT upgrade, and methanol upgrade units), are used for superstructure development. These processes are simulated using ASPEN Plus V7.3 to determine the yields of different processing units under various operating modes. The model has been applied to maximize total profit of the natural gas utilization system with penalties for environmental impact, represented by CO_2eq emission obtained using ASPEN Plus for each flowsheet configuration and operating mode options. The performance of the proposed modeling framework is demonstrated using a case study. Full article

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23 pages, 9313 KiB

Open AccessArticle

Impact of Energy Losses Due to Failures on Photovoltaic Plant Energy Balance

by Isidoro Lillo-Bravo^1,*

, Pablo González-Martínez¹

, Miguel Larrañeta²

and José Guasumba-Codena³

¹ Department of Energy Engineering, Universidad de Sevilla, Camino de los Descubrimientos s/n, 41092 Seville, Spain

² Andalusian Association for Research and Industrial Cooperation (AICIA), Camino de los Descubrimientos s/n, 41092 Sevilla, Spain

³ Renewable Energy Laboratory, Universidad de las Fuerzas Armadas, 171103 Sangolquí, Ecuador

Energies 2018, 11(2), 363; https://doi.org/10.3390/en11020363 - 3 Feb 2018

Cited by 53 | Viewed by 6447

Abstract

Photovoltaic (PV) plant failures have a significant influence on PV plant security, reliability, and energy balance. Energy losses produced by a PV plant are due to two large causes: failures and inefficiencies. Knowing the relative influence of energy losses due to failures and [...] Read more.

Photovoltaic (PV) plant failures have a significant influence on PV plant security, reliability, and energy balance. Energy losses produced by a PV plant are due to two large causes: failures and inefficiencies. Knowing the relative influence of energy losses due to failures and energy losses due to inefficiencies on the PV plant energy balance contribute to the optimization of its design, commissioning, and maintenance tasks. This paper estimates the failure rates, grouped by components, and the relative impact of the failures on the PV plant energy balance through real operation and maintenance follow-up data of 15 PV plants in Spain and Italy for 15 months. Results show that the influence of failures in energy losses of all analysed PV plants is low, reaching a maximum value of 0.96% of the net energy yield. Solar field energy losses only represent 4.26% of all failure energy losses. On the other hand, energy losses due to inefficiencies have represented between 22.34% and 27.58% of the net energy yield. Full article

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12 pages, 4327 KiB

Open AccessFeature PaperArticle

Fourier Transform Infrared (FTIR) Spectroscopy Analysis of Transformer Paper in Mineral Oil-Paper Composite Insulation under Accelerated Thermal Aging

by Abi Munajad^*

, Cahyo Subroto

and Suwarno

School of Electrical Engineering and Informatics, Institut Teknologi Bandung, Bandung 40132, Indonesia

Energies 2018, 11(2), 364; https://doi.org/10.3390/en11020364 - 4 Feb 2018

Cited by 194 | Viewed by 21101

Abstract

Mineral oil is the most popular insulating liquid for high voltage transformers due to its function as a cooling liquid and an electrical insulator. Kraft paper has been widely used as transformer solid insulation for a long time already. The degradation process of [...] Read more.

Mineral oil is the most popular insulating liquid for high voltage transformers due to its function as a cooling liquid and an electrical insulator. Kraft paper has been widely used as transformer solid insulation for a long time already. The degradation process of transformer paper due to thermal aging in mineral oil can change the physical and chemical structure of the cellulose paper. Fourier transform infrared (FTIR) spectroscopy analysis was used to identify changes in the chemical structure of transformer paper aged in mineral oil. FTIR results show that the intensity of the peak absorbance of the O–H functional group decreased with aging but the intensity of the peak absorbance of the C–H and C=O functional groups increased with aging. Changes in the chemical structure of the cellulose paper during thermal aging in mineral oil can be analyzed by an oxidation process of the cellulose paper and the reaction process between the carboxylic acids in the mineral oil and the hydroxyl groups on the cellulose. The correlation between the functional groups and the average number of chain scissions of transformer paper gives initial information that the transformer paper performance can be identified by using a spectroscopic technique as a non-destructive diagnostic technique. Full article

(This article belongs to the Section F: Electrical Engineering)

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22 pages, 7520 KiB

Open AccessArticle

Applying Petroleum the Pressure Buildup Well Test Procedure on Thermal Response Test—A Novel Method for Analyzing Temperature Recovery Period

by Tomislav Kurevija^*

, Kristina Strpić and Sonja Koščak-Kolin

Faculty of Mining, Geology and Petroleum Engineering, University of Zagreb, 10000 Zagreb, Croatia

Energies 2018, 11(2), 366; https://doi.org/10.3390/en11020366 - 4 Feb 2018

Cited by 14 | Viewed by 7389

Abstract

The theory of Thermal Response Testing (TRT) is a well-known part of the sizing process of the geothermal exchange system. Multiple parameters influence the accuracy of effective ground thermal conductivity measurement; like testing time, variable power, climate interferences, groundwater effect, etc. To improve [...] Read more.

The theory of Thermal Response Testing (TRT) is a well-known part of the sizing process of the geothermal exchange system. Multiple parameters influence the accuracy of effective ground thermal conductivity measurement; like testing time, variable power, climate interferences, groundwater effect, etc. To improve the accuracy of the TRT, we introduced a procedure to additionally analyze falloff temperature decline after the power test. The method is based on a premise of analogy between TRT and petroleum well testing, since the origin of both procedures lies in the diffusivity equation with solutions for heat conduction or pressure analysis during radial flow. Applying pressure build-up test interpretation techniques to borehole heat exchanger testing, greater accuracy could be achieved since ground conductivity could be obtained from this period. Analysis was conducted on a coaxial exchanger with five different power steps, and with both direct and reverse flow regimes. Each test was set with 96 h of classical TRT, followed by 96 h of temperature decline, making for almost 2000 h of cumulative borehole testing. Results showed that the ground conductivity value could vary by as much as 25%, depending on test time, seasonal period and power fluctuations, while the thermal conductivity obtained from the falloff period provided more stable values, with only a 10% value variation. Full article

(This article belongs to the Special Issue Geothermal Heating and Cooling)

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15 pages, 388 KiB

Open AccessArticle

A Load Flow Analysis for AC/DC Hybrid Distribution Network Incorporated with Distributed Energy Resources for Different Grid Scenarios

by Muhammad Omer Khan, Saeed Zaman Jamali,

, Chul-Ho Noh, Gi-Hyeon Gwon and Chul-Hwan Kim^*

College of Information and Communication Engineering, Sungkyunkwan University, Suwon 440-746, Korea

Energies 2018, 11(2), 367; https://doi.org/10.3390/en11020367 - 4 Feb 2018

Cited by 27 | Viewed by 6635

Abstract

With the recent developments in power electronics technologies, increased deployment of distributed energy resources (DER) with DC output type at distribution voltage levels and significant increase in the number of sensitive AC and DC loads integrated in distribution network have enforced the traditional [...] Read more.

With the recent developments in power electronics technologies, increased deployment of distributed energy resources (DER) with DC output type at distribution voltage levels and significant increase in the number of sensitive AC and DC loads integrated in distribution network have enforced the traditional power network in the continuous renovation process. In this paper, the load flow solution of hybrid AC/DC distribution networks with the multi-terminal configuration is studied. The impact of voltage source converter (VSC) losses and AC and DC line losses in the presence of DER in the distribution system are assessed. The motivation of this analysis is to consider an increase in the number of converter stations which might result in non-negligible converter losses and the presence of various DER within the network imposing different network scenarios. The proposed schemes are simulated on two modified IEEE 33 bus hybrid AC/DC distribution network test system equipped with VSC-MTDC and the results are presented. Obtained results show that by considering the network losses and the converter losses with large number of converters within the network could lead to very different load flow solution and power transfer between networks, especially considering the AC or DC bus dominated network. Full article

(This article belongs to the Section F: Electrical Engineering)

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21 pages, 4337 KiB

Open AccessArticle

Hydropower Impacts on Electrical System Production Costs in the Southwest United States

by Dominique M. Bain^1,*

and Thomas L. Acker²

¹ School of Earth Sciences and Environmental Sustainability, Northern Arizona University, Flagstaff, AZ 86011, USA

² Mechanical Engineering, Northern Arizona University, Flagstaff, AZ 86011, USA

Energies 2018, 11(2), 368; https://doi.org/10.3390/en11020368 - 4 Feb 2018

Cited by 19 | Viewed by 8183

Abstract

The Colorado River is an important natural resource for the Southwestern United States. Predicted climate change impacts include increased temperature, decreased rainfall and increased probability of drought in this region. Given the large amount of hydropower on the Colorado River and its importance [...] Read more.

The Colorado River is an important natural resource for the Southwestern United States. Predicted climate change impacts include increased temperature, decreased rainfall and increased probability of drought in this region. Given the large amount of hydropower on the Colorado River and its importance to the bulk electricity system, this purpose of this study was to quantify the value hydropower in operating the electrical system, and examined changes in hydropower value and electricity costs under different possible future drought conditions and regional generation scenarios. The goal was to better understand how these scenarios affect operating costs of the bulk electrical system, as well as the value of the hydropower produced, and proposed a method for doing so. The calculated value of the hydroelectric power was nearly double the mean locational marginal price in the study area, about $73 to $75 for most scenarios, demonstrating a high value of the hydropower. In general, it was found that reduced water availability increased operating costs, and increased the value of the hydropower. A calculated value factor showed that when less hydroelectric power is available, the hydropower is more valuable. Furthermore, the value factor showed that the value of hydro increases with the addition of solar or the retirement of thermal generating resources. Full article

(This article belongs to the Special Issue Hydropower 2017)

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12 pages, 1766 KiB

Open AccessArticle

Improving the Energy Efficiency of Direct Formate Fuel Cells with a Pd/C-CeO₂ Anode Catalyst and Anion Exchange Ionomer in the Catalyst Layer

by Hamish Andrew Miller^1,*, Jacopo Ruggeri^1,2, Andrea Marchionni¹

, Marco Bellini¹, Maria Vincenza Pagliaro¹, Carlo Bartoli¹

, Andrea Pucci²

, Elisa Passaglia³

and Francesco Vizza^1,*

¹ Istituto di Chimica dei Composti Organometallici (CNR-ICCOM), Via Madonna del Piano 10, 50019 Sesto Fiorentino, Firenze, Italy

² Department of Chemistry and Industrial Chemistry, University of Pisa, Via Moruzzi 13, 56124 Pisa, Italy

³ Istituto di Chimica dei Composti Organometallici (CNR-ICCOM), Area della Ricerca, Via G. Moruzzi 1, 56124 Pisa, Italy

Energies 2018, 11(2), 369; https://doi.org/10.3390/en11020369 - 5 Feb 2018

Cited by 38 | Viewed by 6960

Abstract

This article describes the development of a high power density Direct Formate Fuel Cell (DFFC) fed with potassium formate (KCOOH). The membrane electrode assembly (MEA) contains no platinum metal. The cathode catalyst is FeCo/C combined with a commercial anion exchange membrane (AEM). To [...] Read more.

This article describes the development of a high power density Direct Formate Fuel Cell (DFFC) fed with potassium formate (KCOOH). The membrane electrode assembly (MEA) contains no platinum metal. The cathode catalyst is FeCo/C combined with a commercial anion exchange membrane (AEM). To enhance the power output and energy efficiency we have employed a nanostructured Pd/C-CeO₂ anode catalyst. The activity for the formate oxidation reaction (FOR) is enhanced when compared to a Pd/C catalyst with the same Pd loading. Fuel cell tests at 60 °C show a peak power density of almost 250 mW cm⁻². The discharge energy (14 kJ), faradic efficiency (89%) and energy efficiency (46%) were determined for a single fuel charge (30 mL of 4 M KCOOH and 4 M KOH). Energy analysis demonstrates that removal of the expensive KOH electrolyte is essential for the future development of these devices. To compensate we apply for the first time a polymeric ionomer in the catalyst layer of the anode electrode. A homopolymer is synthesized by the radical polymerization of vinyl benzene chloride followed by amination with 1,4-diazabicyclo[2.2.2]octane (DABCO). The energy delivered, energy efficiency and fuel consumption efficiency of DFFCs fed with 4 M KCOOH are doubled with the use of the ionomer. Full article

(This article belongs to the Special Issue Direct Alcohol Fuel Cells 2018)

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13 pages, 4980 KiB

Open AccessArticle

A Duty Cycle Space Vector Modulation Strategy for a Three-to-Five Phase Direct Matrix Converter

by Rutian Wang^1,*

, Xue Wang¹

, Chuang Liu¹ and Xiwen Gao²

¹ School of Electrical Engineering, Northeast Electric Power University, Jilin 132012, China

² Jilin Electric Power Survey Design Limited Company, Jilin 132000, China

Energies 2018, 11(2), 370; https://doi.org/10.3390/en11020370 - 5 Feb 2018

Cited by 2 | Viewed by 4133

Abstract

The duty cycle space vector (DCSV) modulation strategy is of universal significance, and the method can be utilized for different modulation approaches. In this paper, the vectors of input voltages and currents are equivalently represented by a complex two-dimensional space vector, and the [...] Read more.

The duty cycle space vector (DCSV) modulation strategy is of universal significance, and the method can be utilized for different modulation approaches. In this paper, the vectors of input voltages and currents are equivalently represented by a complex two-dimensional space vector, and the vectors of output voltages and currents are equivalently represented by two two-dimensional space vectors. Then, input–output relationships in both the d1-q1 space and the d3-q3 space are obtained. Because the desired output voltages are only mapped onto a reference voltage space vector in the d1-q1 space, the reference in the d3-q3 space is regarded as zero, in order to reduce harmonics of output voltages to the greatest extent. Then, the duty cycle space vector modulation strategy of the three-to-five phase direct matrix converter (DMC) is deduced. Considering the influence of the zero vector on system performance, the duty cycles are decomposed and recomposed to obtain the space vector pulse width modulation (SVPWM) strategy based on the duty cycle space vector. Finally, the accuracy and feasibility of the theory are verified through experiments. Full article

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18 pages, 8862 KiB

Open AccessArticle

Impact of Demand Side Response on a Commercial Retail Refrigeration System

by Ibrahim M. Saleh^*,†

, Andrey Postnikov^*,†, Corneliu Arsene, Argyrios C. Zolotas

, Chris Bingham, Ronald Bickerton and Simon Pearson^*

¹ School of Engineering, University of Lincoln, Brayford Pool, Lincoln LN6 7TS, UK

^† These authors contributed equally to this work.

Energies 2018, 11(2), 371; https://doi.org/10.3390/en11020371 - 5 Feb 2018

Cited by 13 | Viewed by 4521

Abstract

The UK National Grid has placed increased emphasis on the development of Demand Side Response (DSR) tariff mechanisms to manage load at peak times. Refrigeration systems, along with HVAC, are estimated to consume 14% of the UK’s electricity and could have a significant [...] Read more.

The UK National Grid has placed increased emphasis on the development of Demand Side Response (DSR) tariff mechanisms to manage load at peak times. Refrigeration systems, along with HVAC, are estimated to consume 14% of the UK’s electricity and could have a significant role for DSR application. However, characterized by relatively low individual electrical loads and massive asset numbers, multiple low power refrigerators need aggregation for inclusion in these tariffs. In this paper, the impact of the Demand Side Response (DSR) control mechanisms on food retailing refrigeration systems is investigated. The experiments are conducted in a test-rig built to resemble a typical small supermarket store. The paper demonstrates how the temperature and pressure profiles of the system, the active power and the drawn current of the compressors are affected following a rapid shut down and subsequent return to normal operation as a response to a DSR event. Moreover, risks and challenges associated with primary and secondary Firm Frequency Response (FFR) mechanisms, where the load is rapidly shed at high speed in response to changes in grid frequency, is considered. For instance, measurements are included that show a significant increase in peak inrush currents of approx. 30% when the system returns to normal operation at the end of a DSR event. Consideration of how high inrush currents after a DSR event can produce voltage fluctuations of the supply and we assess risks to the local power supply system. Full article

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14 pages, 929 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Development of Easily Accessible Electricity Consumption Model Using Open Data and GA-SVR

by Seunghyeon Wang¹

, Hyeonyong Hae² and Juhyung Kim^3,*

¹ Institute for Environmental Design and Engineering, Bartlett, University College London, 14 Upper Woburn Place, London WC1H 0NN, UK

² Department of Economics, Hansung University, 116 Samseongyoro-16Gil, Seongbuk-Gu, Seoul 02876, Korea

³ Department of Architectural Engineering, Hanyang University, 222 Wangsimni-Ro, Seungdong-Gu, Seoul 133791, Korea

Energies 2018, 11(2), 373; https://doi.org/10.3390/en11020373 - 5 Feb 2018

Cited by 17 | Viewed by 5956

Abstract

In many countries, DR (Demand Response) has been developed for which customers are motivated to save electricity by themselves during peak time to prevent grand-scale blackouts. One of the common methods in DR, is CPP (Critical Peak Pricing). Predicting energy consumption is recognized [...] Read more.

In many countries, DR (Demand Response) has been developed for which customers are motivated to save electricity by themselves during peak time to prevent grand-scale blackouts. One of the common methods in DR, is CPP (Critical Peak Pricing). Predicting energy consumption is recognized as one of the tool for dealing with CPP. There are a variety of studies in developing the model of energy consumption, which is based on energy simulation, data-driven model or metamodelling. However, it is difficult for general users to use these models due to requirement of various sensing data and expertise. And it also takes long time to simulate the models. These limitations can be an obstacle for achieving CPP’s purpose that encourages general users to manage their energy usage by themselves. As an alternative, this research suggests to use open data and GA (Genetic Algorithm)–SVR (Support Vector Regression). The model is applied to a hospital in Korea and 34,636 data sets (1 year) are collected while 31,756 (11 months) sets are used for training and 2880 sets (1 month) are used for validation. As a result, the performance of proposed model is 14.17% in CV (RMSE), which satisfies the Korea Energy Agency’s and ASHRAE (American Society of Heating, Refrigerating and Air-Conditioning Engineers) error allowance range of ±30%, and ±20% respectively. Full article

(This article belongs to the Special Issue Building Energy Use: Modeling and Analysis)

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16 pages, 989 KiB

Open AccessArticle

Stationary-Frame Modeling of VSC Based on Current-Balancing Driven Internal Voltage Motion for Current Control Timescale Dynamic Analysis

by Yabing Yan, Xiaoming Yuan^* and Jiabing Hu

State Key Laboratory of Advanced Electromagnetic Engineering Technology, Huazhong University of Science and Technology, Wuhan 430074, China

Energies 2018, 11(2), 374; https://doi.org/10.3390/en11020374 - 6 Feb 2018

Cited by 14 | Viewed by 4090

Abstract

High-frequency oscillations caused by voltage source converters (VSCs) are constantly emerging in power systems with the increasing penetration of renewable energies. VSC models in current control timescale play a pivotal role in the analysis of these oscillation issues. Conventional VSC models show few [...] Read more.

High-frequency oscillations caused by voltage source converters (VSCs) are constantly emerging in power systems with the increasing penetration of renewable energies. VSC models in current control timescale play a pivotal role in the analysis of these oscillation issues. Conventional VSC models show few physical mechanisms of VSC dynamics during system oscillations. Hence, this paper proposes a VSC model from the viewpoint of its internal voltage (namely, VSC output voltage), which is driven by current balancing between the current reference and the feedback in a stationary frame. The proposed model can be used to study VSC dynamic characteristics in an intuitionistic physical way. Based on the proposed model, it is found that VSC current reference in a stationary frame varies with internal voltage dynamic due to the essence of active and reactive current control in a current control timescale. Additionally, in a stationary frame, the dynamic relation between internal voltage and error current embodies a generalized integrating characteristic with adaptable center frequency determined by a phase-locked loop, which guarantees the zero steady state error of VSC current control. Comparisons of simulations between the proposed model and a switch-based model validates the effectiveness of the proposed model. Full article

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15 pages, 393 KiB

Open AccessArticle

Analysis and Design of Fuel Cell Systems for Aviation

by Thomas Kadyk^1,*

, Christopher Winnefeld², Richard Hanke-Rauschenbach² and Ulrike Krewer¹

¹ Institute of Energy and Process System Engineering, TU Braunschweig, Franz-Liszt Str. 35, 38106 Braunschweig, Germany

² Institute of Electric Power Systems, Gottfried Wilhelm Leibniz Universität Hannover, Welfengarten 1, 30167 Hannover, Germany

Energies 2018, 11(2), 375; https://doi.org/10.3390/en11020375 - 6 Feb 2018

Cited by 102 | Viewed by 15301

Abstract

In this paper, the design of fuel cells for the main energy supply of passenger transportation aircraft is discussed. Using a physical model of a fuel cell, general design considerations are derived. Considering different possible design objectives, the trade-off between power density and [...] Read more.

In this paper, the design of fuel cells for the main energy supply of passenger transportation aircraft is discussed. Using a physical model of a fuel cell, general design considerations are derived. Considering different possible design objectives, the trade-off between power density and efficiency is discussed. A universal cost–benefit curve is derived to aid the design process. A weight factor

w_{P}

is introduced, which allows incorporating technical (e.g., system mass and efficiency) as well as non-technical design objectives (e.g., operating cost, emission goals, social acceptance or technology affinity, political factors). The optimal fuel cell design is not determined by the characteristics of the fuel cell alone, but also by the characteristics of the other system components. The fuel cell needs to be designed in the context of the whole energy system. This is demonstrated by combining the fuel cell model with simple and detailed design models of a liquid hydrogen tank. The presented methodology and models allows assessing the potential of fuel cell systems for mass reduction of future passenger aircraft. Full article

(This article belongs to the Special Issue Towards a Transformation to Sustainable Aviation Systems)

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12 pages, 1076 KiB

Open AccessArticle

Changes in Lignin Chemistry of Switchgrass due to Delignification by Sodium Hydroxide Pretreatment

by Woochul Jung¹, Dhanalekshmi Savithri², Ratna Sharma-Shivappa¹ and Praveen Kolar^1,*

¹ Biological and Agricultural Engineering, Campus Box 7625, North Carolina State University, Raleigh, NC 27695-7625, USA

² Department of Forest Biomaterials, Campus Box 8001, North Carolina State University, Raleigh, NC 27695-8001, USA

Energies 2018, 11(2), 376; https://doi.org/10.3390/en11020376 - 6 Feb 2018

Cited by 33 | Viewed by 4306

Abstract

Switchgrass was pretreated with sodium hydroxide (NaOH) at various concentrations and pretreatment times to investigate how delignification caused by NaOH affects its lignin chemistry. NaOH resulted in significant delignification ranging from 44.0 to 84.6% depending on pretreatment intensity. While there was no significant [...] Read more.

Switchgrass was pretreated with sodium hydroxide (NaOH) at various concentrations and pretreatment times to investigate how delignification caused by NaOH affects its lignin chemistry. NaOH resulted in significant delignification ranging from 44.0 to 84.6% depending on pretreatment intensity. While there was no significant glucan loss due to NaOH pretreatment, higher NaOH concentrations removed xylan by up to 28.3%. Nitrobenzene oxidation (NBO) was used to study changes in lignin chemistry, and indicated that at higher NaOH concentrations, the amount of 4-hydroxygenzaldehyde (Hy) degraded from p-hydroxyphenyl propanol (H) lignin units was significantly reduced (p < 0.05). However, amounts of syringic (SA) and vanillic (VA) acids generated from syringyl (S) and guaiacyl (G) degradation were greater at higher NaOH concentration. S/G ratio (=0.62 raw switchgrass) did not significantly (p > 0.05) change with 15 min pretreatment, but it increased to 0.75 and 0.72, respectively, with 30 and 60 min pretreatments (p < 0.05). Increase in NaOH concentration did not significantly (p > 0.05) change S/G ratio, but H/G ratio (=0.48 raw switchgrass) decreased significantly to 0.14 regardless of pretreatment times. Overall, the H unit was found to be more susceptible to NaOH than S and G unit monolignols. Though changes in lignin chemistry due to NaOH concentration were observed, their impact on cellulolytic enzyme action during hydrolysis could not be fully understood. Further studies on lignin isolation may help to determine how these changes in lignin chemistry by NaOH impact cellulolytic enzymes. Full article

(This article belongs to the Section L: Energy Sources)

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17 pages, 26288 KiB

Open AccessArticle

A Wavelet-Based Optimization Method for Biofuel Production

by Maurizio Carlini¹

, Sonia Castellucci^1,*

, Guomin Sun², Jinsong Leng², Carlo Cattani¹

and Alessandro Cardarelli¹

¹ Engineering School, DEIM, University of Tuscia, 01100 Viterbo, Italy

² School of Mathematical Sciences, University of Electronic Science and Technology of China, Chengdu 611731, China

Energies 2018, 11(2), 377; https://doi.org/10.3390/en11020377 - 6 Feb 2018

Cited by 1 | Viewed by 3354

Abstract

On a global scale many countries are still heavily dependent on crude oil to produce energy and fuel for transport, with a resulting increase of atmospheric pollution. A possible solution to obviate this problem is to find eco-sustainable energy sources. A potential choice [...] Read more.

On a global scale many countries are still heavily dependent on crude oil to produce energy and fuel for transport, with a resulting increase of atmospheric pollution. A possible solution to obviate this problem is to find eco-sustainable energy sources. A potential choice could be the use of biodiesel as fuel. The work presented aims to characterise the transesterification reaction of waste peanut frying oil using colour analysis and wavelet analysis. The biodiesel production, with the complete absence of mucilages, was evaluated through a suitable set of energy wavelet coefficients and scalograms. The physical characteristics of the biodiesel are influenced by mucilages. In particular the viscosity, that is a fundamental parameter for the correct use of the biodiesel, might be compromised. The presence of contaminants in the samples can often be missed by visual analysis. The low and high frequency wavelet analysis, by investigating the energy change of wavelet coefficient, provided a valid characterisation of the quality of the samples, related to the absence of mucilages, which is consistent with the experimental results. The proposed method of this work represents a preliminary analysis, before the subsequent chemical physical analysis, that can be develop during the production phases of the biodiesel in order to optimise the process, avoiding the presence of impurities in suspension in the final product. Full article

(This article belongs to the Section L: Energy Sources)

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24 pages, 12641 KiB

Open AccessArticle

Development of a Cooperative Braking System for Front-Wheel Drive Electric Vehicles

by Di Zhao

, Liang Chu^*, Nan Xu, Chengwei Sun and Yanwu Xu

State Key Laboratory of Automotive Simulation and Control, Jilin University, Changchun 130022, China

Energies 2018, 11(2), 378; https://doi.org/10.3390/en11020378 - 6 Feb 2018

Cited by 37 | Viewed by 11103

Abstract

Most electric vehicles adopt cooperative braking systems that can blend friction braking torque with regenerative braking torque to achieve higher energy efficiency while maintaining a certain braking performance and driving safety. This paper presented a new cooperative regenerative braking system that contained a [...] Read more.

Most electric vehicles adopt cooperative braking systems that can blend friction braking torque with regenerative braking torque to achieve higher energy efficiency while maintaining a certain braking performance and driving safety. This paper presented a new cooperative regenerative braking system that contained a fully-decoupled hydraulic braking mechanism based on a modified electric stability control system. The pressure control algorithm and brake force distribution strategy were also discussed. Dynamic models of a front wheel drive electric car equipped with this system and a simulation platform with a driver model and driving cycles were established. Tests to evaluate the braking performance and energy regeneration were simulated and analyzed on this platform and the simulation results showed the feasibility and effectiveness of this system. Full article

(This article belongs to the Special Issue Methods to Improve Energy Use in Road Vehicles)

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17 pages, 5694 KiB

Open AccessArticle

On Reducing the Shaft Torque Ripple of Small-to-Medium-Scale Wind Energy Conversion Systems Using Multi-Pulse Autotransformer Rectifier

by Jie Chen¹

and Jiawei Chen^2,*

¹ College of Automation Engineering, Nanjing University of Aeronautics and Astronautics, Nanjing 211106, China

² College of Automation, Chongqing University, Chongqing 400044, China

Energies 2018, 11(2), 379; https://doi.org/10.3390/en11020379 - 6 Feb 2018

Cited by 16 | Viewed by 4407

Abstract

In a small-to-medium-scale wind energy conversion system (WECS), diode rectifiers rather than pulse-width modulated (PWM) rectifiers are widely adopted due to the features of high reliability and low cost. However, large current harmonics are induced in the generator phase current by commutations of [...] Read more.

In a small-to-medium-scale wind energy conversion system (WECS), diode rectifiers rather than pulse-width modulated (PWM) rectifiers are widely adopted due to the features of high reliability and low cost. However, large current harmonics are induced in the generator phase current by commutations of diode rectifier, eventually causing large torque ripple on the drive-train of the WECS and making it more likely to be fatigue breakdown. In this paper, a 12-pulse autotransformer rectifier unit (ATRU) with reduced volume and weight is proposed for WECS application. By analyzing the characteristics of the input current and output voltage of the ATRU within the entire operation range of WECS, the method to properly design its parameters is proposed. A 1.2 kW direct-drive WECS demonstration platform using ATRU is built in the lab. A modified sensorless overall power control strategy is adopted to control the WECS. Experimental tests are carried out and the results not only validate the feasibility of implementing ATRU in WECS applications, but also prove its high torque ripple reduction ability. Full article

(This article belongs to the Section A: Sustainable Energy)

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20 pages, 363 KiB

Open AccessArticle

Bayesian Energy Measurement and Verification Analysis

by Herman Carstens^1,*

, Xiaohua Xia¹ and Sarma Yadavalli²

¹ Centre for New Energy Systems, University of Pretoria, Pretoria 0002, South Africa

² Department of Industrial and Systems Engineering, University of Pretoria, Pretoria 0002, South Africa

Energies 2018, 11(2), 380; https://doi.org/10.3390/en11020380 - 6 Feb 2018

Cited by 22 | Viewed by 4525

Abstract

Energy Measurement and Verification (M&V) aims to make inferences about the savings achieved in energy projects, given the data and other information at hand. Traditionally, a frequentist approach has been used to quantify these savings and their associated uncertainties. We demonstrate that the [...] Read more.

Energy Measurement and Verification (M&V) aims to make inferences about the savings achieved in energy projects, given the data and other information at hand. Traditionally, a frequentist approach has been used to quantify these savings and their associated uncertainties. We demonstrate that the Bayesian paradigm is an intuitive, coherent, and powerful alternative framework within which M&V can be done. Its advantages and limitations are discussed, and two examples from the industry-standard International Performance Measurement and Verification Protocol (IPMVP) are solved using the framework. Bayesian analysis is shown to describe the problem more thoroughly and yield richer information and uncertainty quantification results than the standard methods while not sacrificing model simplicity. We also show that Bayesian methods can be more robust to outliers. Bayesian alternatives to standard M&V methods are listed, and examples from literature are cited. Full article

(This article belongs to the Special Issue Bayesian Building Energy Modeling)

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15 pages, 875 KiB

Open AccessArticle

Robust Allocation of Reserve Policies for a Multiple-Cell Based Power System

by Junjie Hu¹

, Tian Lan^2,*, Kai Heussen³

, Mattia Marinelli³

, Alexander Prostejovsky³

and Xianzhang Lei²

¹ State Key Laboratory of Alternate Electrical Power Systems with Renewable Energy Sources, North China Electric Power University, Beijing 102206, China

² Global Energy Interconnection Research Institute Europe GmbH, 10117 Berlin, Germany

³ Center for Electrical Power and Energy, DK2800 Lyngby, Denmark

Energies 2018, 11(2), 381; https://doi.org/10.3390/en11020381 - 7 Feb 2018

Cited by 5 | Viewed by 3750

Abstract

This paper applies a robust optimization technique for coordinating reserve allocations in multiple-cell based power systems. The linear decision rules (LDR)-based policies were implemented to achieve the reserve robustness, and consist of a nominal power schedule with a series of linear modifications. The [...] Read more.

This paper applies a robust optimization technique for coordinating reserve allocations in multiple-cell based power systems. The linear decision rules (LDR)-based policies were implemented to achieve the reserve robustness, and consist of a nominal power schedule with a series of linear modifications. The LDR method can effectively adapt the participation factors of reserve providers to respond to system imbalance signals. The policies considered the covariance of historic system imbalance signals to reduce the overall reserve cost. When applying this method to the cell-based power system for a certain horizon, the influence of different time resolutions on policy-making is also investigated, which presents guidance for its practical application. The main results illustrate that: (a) the LDR-based method shows better performance, by producing smaller reserve costs compared to the costs given by a reference method; and (b) the cost index decreases with increased time intervals, however, longer intervals might result in insufficient reserves, due to low time resolution. On the other hand, shorter time intervals require heavy computational time. Thus, it is important to choose a proper time interval in real time operation to make a trade off. Full article

(This article belongs to the Special Issue Methods and Concepts for Designing and Validating Smart Grid Systems)

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13 pages, 3422 KiB

Open AccessArticle

Effect of Surface Thermal Resistance on the Simulation Accuracy of the Condensation Risk Assessment for a High-Performance Window

by So Young Koo, Sihyun Park, Jin-Hee Song and Seung-Yeong Song^*

Department of Architectural Engineering, Ewha Womans University, 52 Ewhayeodae-gil, Seodaemun-gu, Seoul 03760, Korea

Energies 2018, 11(2), 382; https://doi.org/10.3390/en11020382 - 7 Feb 2018

Cited by 12 | Viewed by 3955

Abstract

The accuracy of condensation risk assessment depends on the accuracy of the measured or calculated temperatures. The existing 2D simulation method provides sufficiently accurate results for evaluating average performance values, such as U-values. However, the accuracy of predicting the temperatures in the local [...] Read more.

The accuracy of condensation risk assessment depends on the accuracy of the measured or calculated temperatures. The existing 2D simulation method provides sufficiently accurate results for evaluating average performance values, such as U-values. However, the accuracy of predicting the temperatures in the local areas such as the edge-of-glazing and the frame has been questioned. This study analyzes the effect of the surface thermal resistance on the accuracy of the condensation risk assessment for high-performance windows. Experiments and three-dimensional simulations were performed for a triple-glazed window. The differences in results between the basic experimental test and the simulations with several different applied boundary conditions were analyzed. The results show that, in the simulations, a small change in the surface thermal resistance has no significant effect on the accuracy of the condensation risk assessment of the center-of-glazing or the frame. However, for the edge-of-glazing, the accuracy of predicting the condensation risk was significantly improved by using the increased local surface thermal resistance with the simulation. By employing the reduced radiation and convection at the edges or junctions between two surfaces, the error between the measured and calculated temperature factors can be reduced to less than 3%. Full article

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21 pages, 10782 KiB

Open AccessArticle

A Structural Design Concept for a Multi-Shell Blended Wing Body with Laminar Flow Control

by Majeed Bishara^1,*

, Peter Horst², Hinesh Madhusoodanan³, Martin Brod³, Benedikt Daum³

and Raimund Rolfes³

¹ Aeronautics Research Center Niedersachsen (NFL), TU Braunschweig, Hermann-Blenk-Straße 42, 38108 Braunschweig, Germany

² Institute of Aircraft Design and Lightweight Structures, TU Braunschweig, Hermann-Blenk-Straße 35, 38108 Braunschweig, Germany

³ Institute of Structural Analysis, Leibniz University of Hannover, Appelstraße 9A, 30167 Hannover, Germany

Energies 2018, 11(2), 383; https://doi.org/10.3390/en11020383 - 7 Feb 2018

Cited by 21 | Viewed by 7867

Abstract

Static and fatigue analyses are presented for a new blended wing body (BWB) fuselage concept considering laminar flow control (LFC) by boundary layer suction in order to reduce the aerodynamic drag. BWB aircraft design concepts profit from a structurally beneficial distribution of lift [...] Read more.

Static and fatigue analyses are presented for a new blended wing body (BWB) fuselage concept considering laminar flow control (LFC) by boundary layer suction in order to reduce the aerodynamic drag. BWB aircraft design concepts profit from a structurally beneficial distribution of lift and weight and allow a better utilization of interior space over conventional layouts. A structurally efficient design concept for the pressurized BWB cabin is a vaulted layout that is, however, aerodynamically disadvantageous. A suitable remedy is a multi-shell design concept with a separate outer skin. The synergetic combination of such a multi-shell BWB fuselage with a LFC via perforation of the outer skin to attain a drag reduction appears promising. In this work, two relevant structural design aspects are considered. First, a numerical model for a ribbed double-shell design of a fuselage segment is analyzed. Second, fatigue aspects of the perforation in the outer skin are investigated. A design making use of controlled fiber orientation is proposed for the perforated skin. The fatigue behavior is compared to perforation methods with conventional fiber topologies and to configurations without perforations. Full article

(This article belongs to the Special Issue Towards a Transformation to Sustainable Aviation Systems)

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25 pages, 1223 KiB

Open AccessArticle

Efficient Power Scheduling in Smart Homes Using Hybrid Grey Wolf Differential Evolution Optimization Technique with Real Time and Critical Peak Pricing Schemes

by Muqaddas Naz¹, Zafar Iqbal²

, Nadeem Javaid^1,*

, Zahoor Ali Khan³

, Wadood Abdul⁴

, Ahmad Almogren⁴

and Atif Alamri⁴

¹ COMSATS Institute of Information Technology, Islamabad 44000, Pakistan

² PMAS, Arid Agriculture University, Rawalpindi 46000, Pakistan

³ CIS, Higher Colleges of Technology, Fujairah 4114, UAE

⁴ Research Chair of Pervasive and Mobile Computing, College of Computer and Information Sciences, King Saud University, Riyadh 11633, Saudi Arabia

Energies 2018, 11(2), 384; https://doi.org/10.3390/en11020384 - 7 Feb 2018

Cited by 65 | Viewed by 6673

Abstract

With the emergence of automated environments, energy demand by consumers is increasing rapidly. More than 80% of total electricity is being consumed in the residential sector. This brings a challenging task of maintaining the balance between demand and generation of electric power. In [...] Read more.

With the emergence of automated environments, energy demand by consumers is increasing rapidly. More than 80% of total electricity is being consumed in the residential sector. This brings a challenging task of maintaining the balance between demand and generation of electric power. In order to meet such challenges, a traditional grid is renovated by integrating two-way communication between the consumer and generation unit. To reduce electricity cost and peak load demand, demand side management (DSM) is modeled as an optimization problem, and the solution is obtained by applying meta-heuristic techniques with different pricing schemes. In this paper, an optimization technique, the hybrid gray wolf differential evolution (HGWDE), is proposed by merging enhanced differential evolution (EDE) and gray wolf optimization (GWO) scheme using real-time pricing (RTP) and critical peak pricing (CPP). Load shifting is performed from on-peak hours to off-peak hours depending on the electricity cost defined by the utility. However, there is a trade-off between user comfort and cost. To validate the performance of the proposed algorithm, simulations have been carried out in MATLAB. Results illustrate that using RTP, the peak to average ratio (PAR) is reduced to 53.02%, 29.02% and 26.55%, while the electricity bill is reduced to 12.81%, 12.012% and 12.95%, respectively, for the 15-, 30- and 60-min operational time interval (OTI). On the other hand, the PAR and electricity bill are reduced to 47.27%, 22.91%, 22% and 13.04%, 12%, 11.11% using the CPP tariff. Full article

(This article belongs to the Special Issue Building Energy Use: Modeling and Analysis)

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17 pages, 10081 KiB

Open AccessArticle

The Effects of NaCl Concentration and Confining Pressure on Mechanical and Acoustic Behaviors of Brine-Saturated Sandstone

by Yan-Hua Huang^1,2, Sheng-Qi Yang^1,*

, Matthew R. Hall² and Yuan-Chao Zhang¹

¹ State Key Laboratory for Geomechanics and Deep Underground Engineering, School of Mechanics and Civil Engineering, China University of Mining and Technology, Xuzhou 221116, China

² GeoEnergy Research Centre, Faculty of Engineering, University of Nottingham, University Park, Nottingham NG7 2RD, UK

Energies 2018, 11(2), 385; https://doi.org/10.3390/en11020385 - 7 Feb 2018

Cited by 43 | Viewed by 5336

Abstract

To better understand the mechanical behavior of rock with brine saturation, conventional triaxial experiments were carried out on sandstone for a range of confining pressures (0–60 MPa) and NaCl concentrations (0–30%). As the confining pressure and NaCl concentration increased, the triaxial compressive strength, [...] Read more.

To better understand the mechanical behavior of rock with brine saturation, conventional triaxial experiments were carried out on sandstone for a range of confining pressures (0–60 MPa) and NaCl concentrations (0–30%). As the confining pressure and NaCl concentration increased, the triaxial compressive strength, crack damage threshold, Young’s modulus, cohesion, and internal friction angle all increased. Real-time ultrasonic wave and acoustic emission (AE) techniques were used to obtain the relationship between acoustic behavior and stress level during the whole triaxial compression process. During the whole deformation process, the evolution of P-wave velocity and accumulated AE count could be divided into four phases. The microstructural characteristics of brine-saturated sandstone, before and after loading, indicated that the strength enhancement mechanism may be attributed to an increase in inter-particle friction resulting from salt crystallisation around the points of contact. The angle of friction increased by more than 86% at maximum NaCl concentration compared to that for distilled water. The NaCl deposition in the pore space resulted in nonlinear strength increases for the brine-saturated sandstone specimens with increasing salinity. The present study is expected to improve the knowledge of the strength and failure mechanisms of sedimentary rock in deep saline aquifers. Full article

(This article belongs to the Special Issue Geothermal Energy: Utilization and Technology 2018)

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16 pages, 4963 KiB

Open AccessArticle

Detailed Theoretical Characterization of a Transcritical CO₂ Direct Expansion Ground Source Heat Pump Water Heater

by Parham Eslami-Nejad^*, Messaoud Badache, Arash Bastani and Zine Aidoun

CanmetENERGY, Natural Resources Canada, 1615 Lionel-Boulet, Case Postale 4800, Varennes, QC J3X 1S6, Canada

Energies 2018, 11(2), 387; https://doi.org/10.3390/en11020387 - 7 Feb 2018

Cited by 13 | Viewed by 4328

Abstract

A new avenue in modern heat pump technology is related to the use of natural refrigerants such as carbon dioxide (CO₂). The use of CO₂ in direct expansion ground source heat pumps (DX-GSHP) has also gained significant interest as it [...] Read more.

A new avenue in modern heat pump technology is related to the use of natural refrigerants such as carbon dioxide (CO₂). The use of CO₂ in direct expansion ground source heat pumps (DX-GSHP) has also gained significant interest as it offers opportunities for cost reduction of the ground loop, albeit some challenges remain in their development, design and use. To address these challenges and to characterize CO₂-DX-GSHP performance for water heating applications, a detailed theoretical model and a fully-instrumented test apparatus was developed and built at CanmetENERGY Research Laboratory. The theoretical model was validated against a set of experimental results and adopted to investigate the performance of the system over a wide operating range. Validation results showed that the model predicts the experimental results within the measurement uncertainty. A detailed system performance analysis was also performed using the theoretical model to understand the system behavior and explore the actions required for performance improvement in future installations. The results of the analysis showed that improper design and control of some components, such as the gas cooler and ground heat exchanger can degrade the system performance by up to 25%, and the heat pump heating capacity by 7.5%. Full article

(This article belongs to the Special Issue Geothermal Heating and Cooling)

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19 pages, 30108 KiB

Open AccessArticle

Determination of the Structural Characteristics of Microalgal Cells Walls under the Influence of Turbulent Mixing Energy in Open Raceway Ponds

by Haider Ali¹

, Taqi Ahmad Cheema² and Cheol Woo Park^1,*

¹ School of Mechanical Engineering, Kyungpook National University, Daegu 41566, Korea

² Department of Mechanical Engineering, GIK Institute of Engineering Sciences and Technology, Topi 23460, Pakistan

Energies 2018, 11(2), 388; https://doi.org/10.3390/en11020388 - 7 Feb 2018

Cited by 7 | Viewed by 5755

Abstract

Turbulent flow mixing is essential in optimizing microalgal cultivation in raceway ponds. Microalgal cells are however highly sensitive to hydrodynamic stresses produced by turbulent mixing because of their small size. The mechanical properties (wall deformation and von Misses stress) of the microalgal cell [...] Read more.

Turbulent flow mixing is essential in optimizing microalgal cultivation in raceway ponds. Microalgal cells are however highly sensitive to hydrodynamic stresses produced by turbulent mixing because of their small size. The mechanical properties (wall deformation and von Misses stress) of the microalgal cell wall structure under the influence of turbulent mixing are yet to be explored. High turbulence magnitudes damage microalgal cell walls by adversely affecting their mechanical properties which consequently destroy the microalgal cells and reduce the biofuel production. Therefore, such a study is required to improve the biofuel productivity of microalgal cells before their cell wall damage in raceway pond. This study developed a novel fluid–structure interaction (FSI)-based numerical model to investigate the effects of turbulent mixing on the cell wall damage of microalgal cells in raceway ponds. The study investigated microalgal cell wall damage at four different locations in a raceway pond in consideration of the effects of pond’s hydrodynamic and geometric properties. An experiment was conducted with a laboratory-scale raceway pond to compare and validate the numerical results by using time-dependent water velocities. Microalgal cell wall shear stress, cell wall deformation, and von Misses stress in the raceway pond were investigated by considering the effects of aspect ratios, water depths, and paddle wheel rotational speeds. Results showed that the proposed numerical model can be used as a prerequisite method for the selection of appropriate turbulent mixing. Microalgal cell wall damage is high in shallow and narrow raceway ponds with high paddle rotational speeds. Full article

(This article belongs to the Section I: Energy Fundamentals and Conversion)

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20 pages, 3095 KiB

Open AccessArticle

A Hierarchical Optimal Operation Strategy of Hybrid Energy Storage System in Distribution Networks with High Photovoltaic Penetration

by Jian Chen^1,*

, Jiaqi Li¹, Yicheng Zhang²

, Guannan Bao³, Xiaohui Ge⁴ and Peng Li⁴

¹ Key Laboratory of Power System Intelligent Dispatch and Control of Ministry of Education, Shandong University, Jinan 250061, China

² School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore 639798, Singapore

³ State Grid Shandong Electric Power Dispatching & Control Center, Jinan 250001, China

⁴ Electric Power Research Institute of State Grid Zhejiang Electric Power Co., LTD., Hangzhou 310014, China

Energies 2018, 11(2), 389; https://doi.org/10.3390/en11020389 - 7 Feb 2018

Cited by 19 | Viewed by 4234

Abstract

In this paper, a hierarchical optimal operation strategy for a hybrid energy storage system (HESS) is proposed, which is suitable to be utilized in distribution networks (DNs) with high photovoltaic (PV) penetration to achieve PV power smoothing, voltage regulation and price arbitrage. Firstly, [...] Read more.

In this paper, a hierarchical optimal operation strategy for a hybrid energy storage system (HESS) is proposed, which is suitable to be utilized in distribution networks (DNs) with high photovoltaic (PV) penetration to achieve PV power smoothing, voltage regulation and price arbitrage. Firstly, a fuzzy-logic based variable step-size control strategy for an ultracapacitor (UC) with the improvement of the lifetime of UC and tracking performance is adopted to smooth PV power fluctuations. The impact of PV forecasting errors is eliminated by adjusting the UC power in real time. Secondly, a coordinated control strategy, which includes centralized and local controls, is proposed for lithium-ion batteries. The centralized control is structured to determine the optimal battery unit for voltage regulation or price arbitrage according to lithium-ion battery performance indices. A modified lithium-ion battery aging model with better accuracy is proposed and the coupling relationship between the lifetime and the effective capacity is also considered. Additionally, the local control of the selected lithium-ion battery unit determines the charging/discharging power. A case study is used to validate the operation strategy and the results show that the lifetime equilibrium among different lithium-ion battery units can be achieved using the proposed strategy. Full article

(This article belongs to the Section D: Energy Storage and Application)

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13 pages, 5713 KiB

Open AccessArticle

Harmonic Spectrum of Output Voltage for Space Vector Pulse Width Modulated Ultra Sparse Matrix Converter

by Tingna Shi^*

, Lingling Wu, Yan Yan and Changliang Xia

School of Electrical and Information Engineering, Tianjin University, Tianjin 300072, China

Energies 2018, 11(2), 390; https://doi.org/10.3390/en11020390 - 8 Feb 2018

Cited by 7 | Viewed by 4432

Abstract

In a matrix converter, the frequencies of output voltage harmonics are related to the frequencies of input, output, and carrier signals, which are independent of each other. This nature may cause an inaccurate harmonic spectrum when using conventional analytical methods, such as fast [...] Read more.

In a matrix converter, the frequencies of output voltage harmonics are related to the frequencies of input, output, and carrier signals, which are independent of each other. This nature may cause an inaccurate harmonic spectrum when using conventional analytical methods, such as fast Fourier transform (FFT) and the double Fourier analysis. Based on triple Fourier series, this paper proposes a method to pinpoint harmonic components of output voltages of an ultra sparse matrix converter (USMC) under space vector pulse width modulation (SVPWM) strategy. Amplitudes and frequencies of harmonic components are determined precisely for the first time, and the distribution pattern of harmonics can be observed directly from the analytical results. The conclusions drawn in this paper may contribute to the analysis of harmonic characteristics and serve as a reference for the harmonic suppression of USMC. Besides, the proposed method is also applicable to other types of matrix converters. Full article

(This article belongs to the Section I: Energy Fundamentals and Conversion)

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12 pages, 4882 KiB

Open AccessArticle

Miscible CO₂ Flooding for EOR in the Presence of Natural Gas Components in Displacing and Displaced Fluids

by Aly A Hamouda^* and Sidra Chughtai

Department of Energy and Petroleum Engineering, University of Stavanger, 4036 Stavanger, Norway

Energies 2018, 11(2), 391; https://doi.org/10.3390/en11020391 - 8 Feb 2018

Cited by 14 | Viewed by 4765

Abstract

Carbon dioxide (CO₂) flooding is a complicated process as it involves phase behavior. The objective of this work was to understand the mass transfer mechanisms during flooding with CO₂ and CO₂/C1/C3 (CO₂/HC) based on experimental and [...] Read more.

Carbon dioxide (CO₂) flooding is a complicated process as it involves phase behavior. The objective of this work was to understand the mass transfer mechanisms during flooding with CO₂ and CO₂/C1/C3 (CO₂/HC) based on experimental and simulated composition changes. Three model oil compositions were used (n-C10, n-C10/C1, and n-C10/C1/C3). For a comparison, crude oil from a North Sea field was included. The second part of the investigation was to compare the effect of the combined light components (C1/C3) with CO₂ as a displacing fluid on enhanced oil recovery (EOR). Equation of State EOS SRK–Peneloux was used for the simulations to predict composition changes. The highest recovery was obtained from model oil (n-C10) displaced with CO₂ compared to model oil containing light components with the highest recovery recorded from model oil/C1 (live oil A) compared to model oil/C1/C3 at all of the tested temperatures. The presence of light components (C1/C3) in the injected CO₂ at miscible conditions increased the oil recovery for crude oil compared to flooding only with CO₂. Transverse dispersion of CO₂ helps in eliminating/reducing the effect of viscous instabilities by shortening fingering travel/widening the fingers. The collected samples contained water, although the flooding was done on dry sandstone cores. Possible mechanisms are discussed in a later section. Full article

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23 pages, 2732 KiB

Open AccessArticle

A Study on Electrofuels in Aviation

by Andreas Goldmann¹

, Waldemar Sauter², Marcel Oettinger³

, Tim Kluge³, Uwe Schröder², Joerg R. Seume³, Jens Friedrichs⁴ and Friedrich Dinkelacker^1,*

¹ Institute of Technical Combustion, Leibniz Universität Hannover, Welfengarten 1A, 30167 Hannover, Germany

² Institute of Environmental and Sustainable Chemistry, TU-Braunschweig, Hagenring 30, 38106 Braunschweig, Germany

³ Institute of Turbomachinery and Fluid Dynamics, Leibniz Universität Hannover, Appelstraße 9, 30167 Hannover, Germany

⁴ Institute of Jet propulsion and Turbomachinery, TU-Braunschweig, Hermann-Blenk-Strasse 37, 38108 Braunschweig, Germany

Energies 2018, 11(2), 392; https://doi.org/10.3390/en11020392 - 8 Feb 2018

Cited by 104 | Viewed by 15659

Abstract

With the growth of aviation traffic and the demand for emission reduction, alternative fuels like the so-called electrofuels could comprise a sustainable solution. Electrofuels are understood as those that use renewable energy for fuel synthesis and that are carbon-neutral with respect to greenhouse [...] Read more.

With the growth of aviation traffic and the demand for emission reduction, alternative fuels like the so-called electrofuels could comprise a sustainable solution. Electrofuels are understood as those that use renewable energy for fuel synthesis and that are carbon-neutral with respect to greenhouse gas emission. In this study, five potential electrofuels are discussed with respect to the potential application as aviation fuels, being n-octane, methanol, methane, hydrogen and ammonia, and compared to conventional Jet A-1 fuel. Three important aspects are illuminated. Firstly, the synthesis process of the electrofuel is described with its technological paths, its energy efficiency and the maturity or research need of the production. Secondly, the physico-chemical properties are compared with respect to specific energy, energy density, as well as those properties relevant to the combustion of the fuels, i.e., autoignition delay time, adiabatic flame temperature, laminar flame speed and extinction strain rate. Results show that the physical and combustion properties significantly differ from jet fuel, except for n-octane. The results describe how the different electrofuels perform with respect to important aspects such as fuel and air mass flow rates. In addition, the results help determine mixture properties of the exhaust gas for each electrofuel. Thirdly, a turbine configuration is investigated at a constant operating point to further analyze the drop-in potential of electrofuels in aircraft engines. It is found that electrofuels can generally substitute conventional kerosene-based fuels, but have some downsides in the form of higher structural loads and potentially lower efficiencies. Finally, a preliminary comparative evaluation matrix is developed. It contains specifically those fields for the different proposed electrofuels where special challenges and problematic points are seen that need more research for potential application. Synthetically-produced n-octane is seen as a potential candidate for a future electrofuel where even a drop-in capability is given. For the other fuels, more issues need further research to allow the application as electrofuels in aviation. Specifically interesting could be the combination of hydrogen with ammonia in the far future; however, the research is just at the beginning stage. Full article

(This article belongs to the Special Issue Towards a Transformation to Sustainable Aviation Systems)

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17 pages, 3442 KiB

Open AccessArticle

An Improved Rate-Transient Analysis Model of Multi-Fractured Horizontal Wells with Non-Uniform Hydraulic Fracture Properties

by Youwei He¹

, Shiqing Cheng^1,*, Zhenhua Rui², Jiazheng Qin¹

, Liang Fu³, Jianguo Shi³, Yang Wang¹, Dingyi Li¹, Shirish Patil⁴, Haiyang Yu¹ and Jun Lu^5,6,*

¹ State Key Laboratory of Petroleum Resources and Prospecting, China University of Petroleum, Beijing 102249, China

² Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139, USA

³ No. 4 Oil Production Plant, Changqing Oil Field, PetroChina, Yinchuan 750001, China

⁴ Department of Petroleum Engineering, King Fahd University of Petroleum and Minerals, Dhahran 31261, Saudi Arabia

⁵ College of Petroleum Engineering, Xi’an Shiyou University, Xi’an 710065, China

⁶ McDougall School of Petroleum Engineering, The University of Tulsa, Tulsa, OK 74104, USA

Energies 2018, 11(2), 393; https://doi.org/10.3390/en11020393 - 8 Feb 2018

Cited by 63 | Viewed by 5719

Abstract

Although technical advances in hydraulically fracturing and drilling enable commercial production from tight reservoirs, oil/gas recovery remains at a low level. Due to the technical and economic limitations of well-testing operations in tight reservoirs, rate-transient analysis (RTA) has become a more attractive option. [...] Read more.

Although technical advances in hydraulically fracturing and drilling enable commercial production from tight reservoirs, oil/gas recovery remains at a low level. Due to the technical and economic limitations of well-testing operations in tight reservoirs, rate-transient analysis (RTA) has become a more attractive option. However, current RTA models hardly consider the effect of the non-uniform production on rate decline behaviors. In fact, PLT results demonstrate that production profile is non-uniform. To fill this gap, this paper presents an improved RTA model of multi-fractured horizontal wells (MFHWs) to investigate the effects of non-uniform properties of hydraulic fractures (production of fractures, fracture half-length, number of fractures, fracture conductivity, and vertical permeability) on rate transient behaviors through the diagnostic type curves. Results indicate obvious differences on the rate decline curves among the type curves of uniform properties of fractures (UPF) and non-uniform properties of fractures (NPF). The use of dimensionless production integral derivative curve magnifies the differences so that we can diagnose the phenomenon of non-uniform production. Therefore, it’s significant to incorporate the effects of NPF into the RDA models of MFHWs, and the model proposed in this paper enables us to better evaluate well performance based on long-term production data. Full article

(This article belongs to the Section L: Energy Sources)

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12 pages, 2532 KiB

Open AccessArticle

Improving Vegetable Oil Properties by Transforming Fatty Acid Chain Length in Jatropha Oil and Coconut Oil Blends

by Wahyudi^1,2,*

, I.N.G. Wardana¹, Agung Widodo¹ and Widya Wijayanti¹

¹ Department of Mechanical Engineering, Faculty of Engineering, Brawijaya University, Jl. M.T. Haryono No. 167, Malang 65145, Indonesia

² Department of Mechanical Engineering, Faculty of Engineering, Universitas Muhammadiyah Yogyakarta, Jl. Lingkar Selatan Tamantirto, Yogyakarta 55183, Indonesia

Energies 2018, 11(2), 394; https://doi.org/10.3390/en11020394 - 8 Feb 2018

Cited by 47 | Viewed by 8542

Abstract

Efforts to improve the physical and chemical properties of vegetable oils as diesel fuels such as viscosity and calorific value are indispensable with the depletion of fossil oil reserves. Jatropha oil with long chain fatty acids and high degree of unsaturation is mixed [...] Read more.

Efforts to improve the physical and chemical properties of vegetable oils as diesel fuels such as viscosity and calorific value are indispensable with the depletion of fossil oil reserves. Jatropha oil with long chain fatty acids and high degree of unsaturation is mixed with short chain saturated fatty acid coconut oil in various compositions. The mixture was heated and stirred for 30 min at 90 °C. This mixing leads to a decrease in viscosity which allows for the breaking of the bond. The fatty acid molecule structure undergoes transformation that changes the degree of unsaturation and the average length of the carbon chain. Consequently, the kinematic viscosity and flash point of the mixture decreases while its calorific value increases. Full article

(This article belongs to the Collection Bioenergy and Biofuel)

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12 pages, 5015 KiB

Open AccessArticle

Smart Building: Use of the Artificial Neural Network Approach for Indoor Temperature Forecasting

by Nivine Attoue¹, Isam Shahrour^1,2,*

and Rafic Younes³

¹ Laboratory of Civil Engineering and Geo-Environment, Lille University, 59650 Villeneuve d’Ascq, France

² School of Civil Engineering, Tongji University, Shanghai 200092, China

³ Modeling Center, Lebanese University, Hadath 99000, Lebanon

Energies 2018, 11(2), 395; https://doi.org/10.3390/en11020395 - 8 Feb 2018

Cited by 116 | Viewed by 7867

Abstract

The smart building concept aims to use smart technology to reduce energy consumption, as well as to improve comfort conditions and users’ satisfaction. It is based on the use of smart sensors and software to follow both outdoor and indoor conditions for the [...] Read more.

The smart building concept aims to use smart technology to reduce energy consumption, as well as to improve comfort conditions and users’ satisfaction. It is based on the use of smart sensors and software to follow both outdoor and indoor conditions for the control of comfort, and security devices for the optimization of energy consumption. This paper presents a data-based model for indoor temperature forecasting, which could be used for the optimization of energy device use. The model is based on an artificial neural network (ANN), which is validated on data recorded in an old building. The novelty of this work consists of the methodology proposed for the development of a simplified model for indoor temperature forecasting. This methodology is based on the selection of pertinent input parameters after a relevance analysis of a large set of input parameters, including solar radiation outdoor temperature history, outdoor humidity, indoor facade temperature, and humidity. It shows that an ANN-based model using outdoor and facade temperature sensors provides good forecasting of indoor temperatures. This model can be easily used in the optimal regulation of buildings’ energy devices. Full article

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23 pages, 8186 KiB

Open AccessEditor’s ChoiceArticle

Dynamic Analysis of a Hybrid Energy Storage System (H-ESS) Coupled to a Photovoltaic (PV) Plant

by Linda Barelli^1,*

, Gianni Bidini¹

, Fabio Bonucci², Luca Castellini³

, Simone Castellini⁴, Andrea Ottaviano¹

, Dario Pelosi¹

and Alberto Zuccari⁵

¹ Department of Engineering, University of Perugia, Via G. Duranti 1/A4, 06125 Perugia, Italy

² VGA Srl, Via dell’Innovazione SNC, 06053 Deruta, Italy

³ Umbra Cuscinetti SpA, Via V. Baldiccini 1, 06034 Foligno, Italy

⁴ ERA Electronic Systems Srl, Via G. Benucci 206, 06135 Perugia, Italy

⁵ QFP Srl, Via Gullotti 31, 06049 Spoleto, Italy

Energies 2018, 11(2), 396; https://doi.org/10.3390/en11020396 - 8 Feb 2018

Cited by 64 | Viewed by 7162

Abstract

Nowadays energy storage is strongly needed to allow grid safety and stability due to the wide penetration of renewable plants. Mainly economic and technological issues impede a relevant integration of conventional storage devices in the energy system. In this scenario, the hybridization of [...] Read more.

Nowadays energy storage is strongly needed to allow grid safety and stability due to the wide penetration of renewable plants. Mainly economic and technological issues impede a relevant integration of conventional storage devices in the energy system. In this scenario, the hybridization of different storage technologies can be a techno-economic solution useful to overcome these issues and promote their diffusion. Hybridization allows multi-operation modes of the Energy Storage System (ESS), merging the positive features of base-technologies and extending their application ranges. This paper provides a dynamic analysis of a hybrid energy storage system (H-ESS) consisting of a flywheel and a battery pack coupled to a photovoltaic generation plant and a residential load up to 20 kW. A dynamic model of the overall micro-grid (MG) was developed implementing the H-ESS preliminary sizing and a suitable management algorithm. The instantaneous behavior of each component was evaluated. A brief summary of the MG performance at different weather and load conditions was provided together with a characterization of the impact of power fluctuations on the battery current and on the power exchange with the grid. Full article

(This article belongs to the Section D: Energy Storage and Application)

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14 pages, 6940 KiB

Open AccessArticle

AC-Chopper-Based Inrush Current Suppressor in a Wind Power Generation System with Squirrel-Cage Induction Machines

by Sho Shibata^1,†, Hiroaki Yamada^1,*, Toshihiko Tanaka^1,† and Masayuki Okamoto^2,†

¹ Graduate School of Science and Engineering, Yamaguchi University, 2-16-1, Tokiwadai Ube City 755-8611, Japan

² Department of Electrical Engineering, National Institute of Technology, Ube College, 2-14-1, Tokiwadai Ube City 755-8555, Japan

^† These authors contributed equally to this work.

Energies 2018, 11(2), 397; https://doi.org/10.3390/en11020397 - 8 Feb 2018

Cited by 1 | Viewed by 3933

Abstract

This paper proposes the inrush current suppressor using an AC chopper in a large-capacity wind power generation system (WPGS) with two squirrel-cage induction machines (SCIMs), which are switched over depending on the wind speed. The input side of the AC chopper is connected [...] Read more.

This paper proposes the inrush current suppressor using an AC chopper in a large-capacity wind power generation system (WPGS) with two squirrel-cage induction machines (SCIMs), which are switched over depending on the wind speed. The input side of the AC chopper is connected to the source in parallel. The output side of the AC chopper is connected in series with the SCIM through matching transformers. In the proposed inrush current suppressor, the output voltage of the AC chopper is the same as the receiving-end voltage before connecting the SCIM. By gradually decreasing the output voltage of the AC chopper, the applied voltage of the SCIM is gradually increased without the inrush current. The basic principle of the proposed inrush current suppressor is discussed in detail. A computer simulation is implemented to confirm the validity and practicability of the proposed inrush current suppressor using a power system computer-aided design/electromagnetic transients including DC (PSCAD/EMTDC). Simulation results demonstrate that the proposed inrush current suppressor can suppress the inrush current. Full article

(This article belongs to the Section F: Electrical Engineering)

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26 pages, 6182 KiB

Open AccessArticle

Assessment of the Joint Development Potential of Wave and Wind Energy in the South China Sea

by Yong Wan^1,2,*, Chenqing Fan², Yongshou Dai¹, Ligang Li¹, Weifeng Sun¹, Peng Zhou¹ and Xiaojun Qu¹

¹ College of Information and Control Engineering, China University of Petroleum, No. 66, Changjiangxi Road, Huangdao District, Qingdao 266580, China

² The First Institute of Oceanography, State Oceanic Administration, No. 6, Xianxialing Road, Qingdao 266061, China

Energies 2018, 11(2), 398; https://doi.org/10.3390/en11020398 - 8 Feb 2018

Cited by 53 | Viewed by 7210

Abstract

The South China Sea is a major shipping hub between the West Pacific and Indian Oceans. In this region, the demand for energy is enormous, both for residents’ daily lives and for economic development. Wave energy and wind energy are two major clean [...] Read more.

The South China Sea is a major shipping hub between the West Pacific and Indian Oceans. In this region, the demand for energy is enormous, both for residents’ daily lives and for economic development. Wave energy and wind energy are two major clean and low-cost ocean sources of renewable energy. The reasonable development and utilization of these energy sources can provide a stable energy supply for coastal cities and remote islands of China. Before wave energy and wind energy development, however, we must assess the potential of each of these sources. Based on high-resolution and high-accuracy wave field data and wind field data obtained by ERA-Interim reanalysis for the recent 38-year period from 1979–2016, the joint development potential of wave energy and wind energy was assessed in detail for offshore and nearshore areas in the South China Sea. Based on potential installed capacity, the results revealed three promising areas for the joint development of nearshore wave energy and wind energy, including the Taiwan Strait, Luzon Strait and the sea southeast of the Indo-China Peninsula. For these three dominant areas (key stations), the directionality of wave energy and wind energy propagation were good in various seasons; the dominant wave conditions and the dominant wind conditions were the same, which is advantageous for the joint development of wave and wind energy. Existing well-known wave energy converters (WECs) are not suitable for wave energy development in the areas of interest. Therefore, we must consider the distributions of wave conditions and develop more suitable WECs for these areas. The economic and environmental benefits of the joint development of wave and wind energy are high in these promising areas. The results described in this paper can provide references for the joint development of wave and wind energy in the South China Sea. Full article

(This article belongs to the Section L: Energy Sources)

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12 pages, 3034 KiB

Open AccessArticle

Anti-Agglomerator of Tetra-n-Butyl Ammonium Bromide Hydrate and Its Effect on Hydrate-Based CO₂ Capture

by Rong Li^1,2,3, Xiao-Sen Li^1,2,4, Zhao-Yang Chen^1,2,4,*

, Yu Zhang^1,2,4, Chun-Gang Xu^1,2,4

and Zhi-Ming Xia^1,2,4

¹ Guangzhou Institute of Energy Conversion, Chinese Academy of Sciences, Guangzhou 510640, China

² Key Laboratory of Gas Hydrate, CAS and Guangzhou Center for Gas Hydrate Research, CAS, Guangzhou 510640, China

³ Nano Sciences and Technology Institute, University of Science and Technology of China, Suzhou 215123, China

⁴ Guangdong Key Laboratory of New and Renewable Energy Research and Development, Guangzhou 510640, China

Energies 2018, 11(2), 399; https://doi.org/10.3390/en11020399 - 8 Feb 2018

Cited by 14 | Viewed by 4621

Abstract

Tetra-n-butyl ammonium bromide (TBAB) was widely used in the research fields of cold storage and CO₂ hydrate separation due to its high phase change latent heat and thermodynamic promotion for hydrate formation. Agglomeration always occurred in the process of TBAB hydrate generation, [...] Read more.

Tetra-n-butyl ammonium bromide (TBAB) was widely used in the research fields of cold storage and CO₂ hydrate separation due to its high phase change latent heat and thermodynamic promotion for hydrate formation. Agglomeration always occurred in the process of TBAB hydrate generation, which led to the blockage in the pipeline and the separation apparatus. In this work, we screened out a kind of anti-agglomerant that can effectively solve the problem of TBAB hydrate agglomeration. The anti-agglomerant (AA) is composed of 90% cocamidopropyl dimethylamine and 10% glycerol, which can keep TBAB hydrate of 19.3–29.0 wt. % in a stable state of slurry over 72 h. The microscopic observation of the morphology of the TBAB hydrate particles showed that the addition of AA can greatly reduce the size of the TBAB hydrate particles. CO₂ gas separation experiments found that the addition of AA led to great improvement on gas storage capacity, CO₂ split fraction and separation factor, due to the increasing of contact area between gas phase and hydrate particles. The CO₂ split fraction and separation factor with AA addition reached up to 70.3% and 42.8%, respectively. Full article

(This article belongs to the Special Issue Carbon Capture and Storage)

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17 pages, 5403 KiB

Open AccessArticle

On the Performance Optimization of Two-Level Three-Phase Grid-Feeding Voltage-Source Inverters

by Issam A. Smadi^*

, Saher Albatran

and Hamzeh J. Ahmad

Department of Electrical Engineering, Faculty of Engineering, Jordan University of Science and Technology, Irbid 22110, Jordan

Energies 2018, 11(2), 400; https://doi.org/10.3390/en11020400 - 9 Feb 2018

Cited by 6 | Viewed by 3958

Abstract

The performance optimization of the two-level, three-phase, grid-feeding, voltage-source inverter (VSI) is studied in this paper, which adopts an online adaptive switching frequency algorithm (OASF). A new degree of freedom has been added to the employed OASF algorithm for optimal selection of the [...] Read more.

The performance optimization of the two-level, three-phase, grid-feeding, voltage-source inverter (VSI) is studied in this paper, which adopts an online adaptive switching frequency algorithm (OASF). A new degree of freedom has been added to the employed OASF algorithm for optimal selection of the weighting factor and overall system optimization design. Toward that end, a full mathematical formulation, including the impact of the coupling inductor and the controller response time, is presented. At first, the weighting factor is selected to favor the switching losses, and the controller gains are optimized by minimizing the integral time-weighted absolute error (ITAE) of the output active and reactive power. Different loading and ambient temperature conditions are considered to validate the optimized controller and its fast response through online field programmable gate array (FPGA)-in-the-loop. Then, the weighting factor is optimally selected to reduce the cost of the L-filter and the heat-sink. An optimization problem to minimize the cost design at the worst case of loading condition for grid-feeding VSI is formulated. The results from this optimization problem are the filter inductance, the thermal resistance of the heat-sink, and the optimal switching frequency with the optimal weighting factor. The VSI test-bed using the optimized parameters is used to verify the proposed work experimentally. Adopting the OASF algorithm that employs the optimal weighting factor for grid-feeding VSI, the percentages of the reductions in the slope of the steady state junction temperature profile compared to fixed frequencies of 10 kHz, 14.434 kHz, and 20 kHz are about 6%, 30%, and 18%, respectively. Full article

(This article belongs to the Special Issue Emerging Power Electronics Technologies for Power Systems and Machine Drives)

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15 pages, 5269 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

A Traveling-Wave-Based Fault Location Scheme for MMC-Based Multi-Terminal DC Grids

by Shuo Zhang

, Guibin Zou^*

, Qiang Huang

and Houlei Gao

Key Laboratory of Power System Intelligent Dispatch and Control of Ministry of Education, Shandong University, Jinan 250000, China

Energies 2018, 11(2), 401; https://doi.org/10.3390/en11020401 - 9 Feb 2018

Cited by 25 | Viewed by 4670

Abstract

This paper presents a novel fault location scheme of DC line in modular multilevel converter (MMC)-based multi-terminal DC (MTDC) grids. Considering the low-inertia characteristics and the meshed topology, the scheme, based on traveling-wave principle, is divided into three steps, namely, faulty pole identification, [...] Read more.

This paper presents a novel fault location scheme of DC line in modular multilevel converter (MMC)-based multi-terminal DC (MTDC) grids. Considering the low-inertia characteristics and the meshed topology, the scheme, based on traveling-wave principle, is divided into three steps, namely, faulty pole identification, faulty segment determination and fault-distance calculation. With accurate amplitude, polarities and arrival times of the first arrival current traveling waves (FACTWs) collected from time-synchronized measurements taken just at the converter stations, the proposed scheme can correctly determine the faulty pole, the faulty segment and the precise fault location. The continuous wavelet transform (CWT) is deployed to extract the required features of the input signals at the DC lines. Since the scheme merely needs the features of FACTWs, the practical difficulties of detecting subsequent traveling waves are avoided. A four-terminal MMC-based high voltage direct current (HVDC) grid was built in PSCAD/EMTDC software to evaluate the performance of the fault-location scheme. Simulation results for different cases demonstrate that the proposed fault-location scheme has high accuracy, good adaptability and reliability. Furthermore, the algorithm can be used for a MMC-MTDC grid with any number of meshes. Full article

(This article belongs to the Section F: Electrical Engineering)

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15 pages, 450 KiB

Open AccessArticle

Improving Control Efficiency of Dynamic Street Lighting by Utilizing the Dual Graph Grammar Concept

by Igor Wojnicki^*

and Leszek Kotulski

Department of Applied Computer Science, AGH University of Science and Technology, Al. Mickiewicza 30, 30-059 Kraków, Poland

Energies 2018, 11(2), 402; https://doi.org/10.3390/en11020402 - 9 Feb 2018

Cited by 24 | Viewed by 4905

Abstract

The paper introduces a definition of dual graph grammar. It enables two graphs to share information in a synchronized way. A smart city example application, which is an outdoor lighting control system utilizing the dual graph grammar, is also demonstrated. The [...] Read more.

The paper introduces a definition of dual graph grammar. It enables two graphs to share information in a synchronized way. A smart city example application, which is an outdoor lighting control system utilizing the dual graph grammar, is also demonstrated. The system controls dimming of street lights which is based on traffic intensity. Each luminaire’s light level is adjusted individually to comply with the lighting norms to ensure safety. Benefits of applying the dual graph grammar are twofold. First, it increases expressive power of the mathematical model that the system uses. It becomes possible to take into account complex geographical distribution of sensors and logical dependencies among them. Second, it increases the system’s efficiency by reducing the problem size during run-time. Experimental results show a reduction of the computation time by a factor of 2.8. The approach has been verified in practice. Full article

(This article belongs to the Collection Smart Grid)

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12 pages, 4454 KiB

Open AccessArticle

Power Generation Targets from Hot Composite Curves

by Omar Al-Ani^*

and Patrick Linke

Department of Chemical Engineering, Texas A&M University at Qatar, P.O. Box 23874, Education City, 77874 Doha, Qatar

Energies 2018, 11(2), 403; https://doi.org/10.3390/en11020403 - 9 Feb 2018

Cited by 2 | Viewed by 2927

Abstract

The paper proposes a simple systematic procedure to target thermodynamic power generation limits from a set of heat source streams. The procedure takes the form of an algebraic targeting approach commonly applied in process heat integration. It allows the designer to quickly determine [...] Read more.

The paper proposes a simple systematic procedure to target thermodynamic power generation limits from a set of heat source streams. The procedure takes the form of an algebraic targeting approach commonly applied in process heat integration. It allows the designer to quickly determine the maximum amount of power that can theoretically be generated from the available heat in thermodynamic cycles. The paper describes the procedure and is applicability in the context of common data availability for heat source streams in the form of a Composite Curve or Total Site Profile (hot composite curves) commonly developed in heat integration. The application of the procedure is illustrated with examples. Full article

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11 pages, 3190 KiB

Open AccessArticle

Deacetylation Followed by Fractionation of Yellow Poplar Sawdust for the Production of Toxicity-Reduced Hemicellulosic Sugar for Ethanol Fermentation

by Seong Ju Kim¹, Tae Hyun Kim²

and Kyeong Keun Oh^3,4,*

¹ Department of Biomolecular and Chemical Engineering, Hankyong National University, Anseong, Gyeonggi-do 17579, Korea

² Department of Materials Science and Chemical Engineering, Hanyang University, Ansan, Gyeonggi-do 15588, Korea

³ Department of Chemical Engineering, Dankook University, Yongin, Gyeonggi-do 16890, Korea

⁴ R&D Center, SugarEn Co., Ltd., Yongin, Gyeonggi-do 16890, Korea

Energies 2018, 11(2), 404; https://doi.org/10.3390/en11020404 - 9 Feb 2018

Cited by 13 | Viewed by 3640

Abstract

In order to produce bioethanol from yellow poplar sawdust without detoxification, deacetylation (mild alkali treatment) was performed with aqueous ammonia solution. To select the optimal conditions, deacetylation was carried out under different conditions: NH₄OH loading (2–10% (w/v)) and a solid-to-liquid ratio [...] Read more.

In order to produce bioethanol from yellow poplar sawdust without detoxification, deacetylation (mild alkali treatment) was performed with aqueous ammonia solution. To select the optimal conditions, deacetylation was carried out under different conditions: NH₄OH loading (2–10% (w/v)) and a solid-to-liquid ratio of 1:4–1:10 at 121 °C for 60 min. In order to assess the effectiveness of deacetylation, fractionation of deacetylated yellow poplar sawdust was performed using dilute acid (H₂SO₄, 0.5–2.0% (w/v)) at a reaction temperature of 130–150 °C for 10–80 min. The toxicity-reduced hemicellulosic hydrolyzates that were obtained through a two-step treatment at optimized conditions were fermented using Pichia stipitis for ethanol production, without any further detoxification. The maximum ethanol production was 4.84 g/L, corresponding to a theoretical ethanol yield of 82.52%, which is comparable to those of intentionally made hydrolyzates as controls. Full article

(This article belongs to the Section A: Sustainable Energy)

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14 pages, 5497 KiB

Open AccessArticle

Performance Analysis of Multiple Wave Energy Converters Placed on a Floating Platform in the Frequency Domain

by Hyebin Lee¹

, Sunny Kumar Poguluri²

and Yoon Hyeok Bae^2,*

¹ Multidisciplinary Graduate School Program for Wind Energy, Jeju National University, Jeju 63243, Korea

² Department of Ocean System Engineering, Jeju National University, Jeju 63243, Korea

Energies 2018, 11(2), 406; https://doi.org/10.3390/en11020406 - 9 Feb 2018

Cited by 70 | Viewed by 7421

Abstract

Wind-wave hybrid power generation systems have the potential to become a significant source of affordable renewable energy. However, their strong interactions with both wind- and wave-induced forces raise a number of technical challenges for modelling. The present study undertakes a numerical investigation on [...] Read more.

Wind-wave hybrid power generation systems have the potential to become a significant source of affordable renewable energy. However, their strong interactions with both wind- and wave-induced forces raise a number of technical challenges for modelling. The present study undertakes a numerical investigation on multi-body hydrodynamic interaction between a wind-wave hybrid floating platform and multiple wave energy converters (WECs) in a frequency domain. In addition to the exact responses of the platform and the WECs, the power take-off (PTO) mechanism was taken into account for analysis. The coupled hydrodynamic coefficients and wave exciting forces were obtained from WAMIT, the 3D diffraction/radiation solver based on the boundary element method. The overall performance of the multiple WECs is presented and compared with the performance of a single isolated WEC. The analysis showed significant differences in the dynamic responses of the WECs when the multi-body interaction was considered. In addition, the PTO damping effect made a considerable difference to the responses of the WECs. However, the platform response was only minimally affected by PTO damping. With regard to energy capture, the interaction effect of the designed multiple WEC array layout is evaluated. The WEC array configuration showed both constructive and destructive effects in accordance with the incident wave frequency and direction. Full article

(This article belongs to the Section I: Energy Fundamentals and Conversion)

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16 pages, 4401 KiB

Open AccessArticle

Development of a Data-Driven Predictive Model of Supply Air Temperature in an Air-Handling Unit for Conserving Energy

by Goopyo Hong¹ and Byungseon Sean Kim^2,*

¹ SH Urban Research Center, Seoul Housing & Communities Corporation, 621, Gaepo-ro, Gangnam-gu, Seoul 06336, Korea

² Department of Architectural Engineering, Yonsei University, 50 Yonsei Street, Seodaemun-gu, Seoul 03722, Korea

Energies 2018, 11(2), 407; https://doi.org/10.3390/en11020407 - 9 Feb 2018

Cited by 10 | Viewed by 6978

Abstract

The purpose of this study was to develop a data-driven predictive model that can predict the supply air temperature (SAT) in an air-handling unit (AHU) by using a neural network. A case study was selected, and AHU operational data from December 2015 to [...] Read more.

The purpose of this study was to develop a data-driven predictive model that can predict the supply air temperature (SAT) in an air-handling unit (AHU) by using a neural network. A case study was selected, and AHU operational data from December 2015 to November 2016 was collected. A data-driven predictive model was generated through an evolving process that consisted of an initial model, an optimal model, and an adaptive model. In order to develop the optimal model, input variables, the number of neurons and hidden layers, and the period of the training data set were considered. Since AHU data changes over time, an adaptive model, which has the ability to actively cope with constantly changing data, was developed. This adaptive model determined the model with the lowest mean square error (MSE) of the 91 models, which had two hidden layers and sets up a 12-hour test set at every prediction. The adaptive model used recently collected data as training data and utilized the sliding window technique rather than the accumulative data method. Furthermore, additional testing was performed to validate the adaptive model using AHU data from another building. The final adaptive model predicts SAT to a root mean square error (RMSE) of less than 0.6 °C. Full article

(This article belongs to the Special Issue Control and Nonlinear Dynamics on Energy Conversion Systems)

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22 pages, 5171 KiB

Open AccessArticle

A Mixed WLS Power System State Estimation Method Integrating a Wide-Area Measurement System and SCADA Technology

by Tao Jin^* and Xueyu Shen

Department of Electrical Engineering, Fuzhou University, Fuzhou 350116, China

Energies 2018, 11(2), 408; https://doi.org/10.3390/en11020408 - 9 Feb 2018

Cited by 15 | Viewed by 3986

Abstract

To address the issue that the phasor measurement units (PMUs) of wide area measurement system (WAMS) are not sufficient for static state estimation in most existing power systems, this paper proposes a mixed power system weighted least squares (WLS) state estimation method integrating [...] Read more.

To address the issue that the phasor measurement units (PMUs) of wide area measurement system (WAMS) are not sufficient for static state estimation in most existing power systems, this paper proposes a mixed power system weighted least squares (WLS) state estimation method integrating a wide-area measurement system and supervisory control and data acquisition (SCADA) technology. The hybrid calculation model is established by incorporating phasor measurements (including the node voltage phasors and branch current phasors) and the results of the traditional state estimator in a post-processing estimator. The performance assessment is discussed through setting up mathematical models of the distribution network. Based on PMU placement optimization and bias analysis, the effectiveness of the proposed method was proved to be accurate and reliable by simulations of different cases. Furthermore, emulating calculation shows this method greatly improves the accuracy and stability of the state estimation solution, compared with the traditional WLS state estimation. Full article

(This article belongs to the Section F: Electrical Engineering)

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11 pages, 382 KiB

Open AccessFeature PaperArticle

The EU ETS and Dynamic Allocation in Phase IV—An Ex-Ante Assessment

by Vicki Duscha

Fraunhofer Institute for Systems and Innovation Research, Breslauer Strasse 48, 76139 Karlsruhe, Germany

Energies 2018, 11(2), 409; https://doi.org/10.3390/en11020409 - 9 Feb 2018

Cited by 2 | Viewed by 3959

Abstract

Fear of lowering firms’ competitiveness and carbon leakage is the reason for large amounts of allowances in the European Union’s Emissions Trading System (EU ETS) still being allocated for free. At the same time, unadjusted free allocation of allowances in times of economic [...] Read more.

Fear of lowering firms’ competitiveness and carbon leakage is the reason for large amounts of allowances in the European Union’s Emissions Trading System (EU ETS) still being allocated for free. At the same time, unadjusted free allocation of allowances in times of economic recession is partly responsible for the large surplus of allowances that has cumulated in the EU ETS and that is lowering prices in the market. For Phase IV, the introduction of dynamic allocation has been proposed to react to significant changes in production, to prevent the accumulation of further surplus on the one hand and to protect installations from severe underallocation on the other. A reserve of about 400 million allowances is planned for that purpose. This paper analyses the demand for certificates from this reserve under different assumptions on production development as well as different design options for Phase IV. The analysis builds on freely available allocation data from Phase III along with projections of production trends from different time periods in the past. In most of the scenarios, the 400 million allowances are sufficient to fulfil demand for allowances from dynamic allocation until at least the second half of Phase IV (often even for the whole of Phase IV). Even though certain aspects analysed are now not fully compatible with the agreed-upon Phase IV revision, the analysis indicates that the amount of allowances foreseen for dynamic allocation is sufficient for Phase IV. In particular the threshold value of 10% that was introduced in the legislation will ensure that the demand of allowances is likely well below the demand found in the different scenarios in this analysis that neglects this threshold value. Full article

(This article belongs to the Special Issue Lessons from the Evaluation of Existing Emission Trading Schemes)

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14 pages, 3682 KiB

Open AccessArticle

Integration of Photovoltaic Plants and Supercapacitors in Tramway Power Systems

by Flavio Ciccarelli¹

, Luigi Pio Di Noia² and Renato Rizzo^2,*

¹ University of Naples Federico II, 80125 Naples, Italy

² Department of Electrical Engineering and Information Technologies, University of Naples Federico II, 80125 Naples, Italy

Energies 2018, 11(2), 410; https://doi.org/10.3390/en11020410 - 9 Feb 2018

Cited by 33 | Viewed by 4752

Abstract

The growing interest in the use of energy storage systems to improve the performance of tramways has prompted the development of control techniques and optimal storage devices, displacement, and sizing to obtain the maximum profit and reduce the total installation cost. Recently, the [...] Read more.

The growing interest in the use of energy storage systems to improve the performance of tramways has prompted the development of control techniques and optimal storage devices, displacement, and sizing to obtain the maximum profit and reduce the total installation cost. Recently, the rapid diffusion of renewable energy generation from photovoltaic panels has also created a large interest in coupling renewable energy and storage units. This study analyzed the integration of a photovoltaic power plant, supercapacitor energy storage system, and railway power system. Random optimization was used to verify the feasibility of this integration in a real tramway electric system operating in the city of Naples, and the benefits and total cost of this integration were evaluated. Full article

(This article belongs to the Section F: Electrical Engineering)

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17 pages, 6369 KiB

Open AccessArticle

A Control Approach and Supplementary Controllers for a Stand-Alone System with Predominance of Wind Generation

by Tiago Lukasievicz^*

, Ricardo Oliveira and César Torrico

Electrical Engineering Department, Federal University of Technology, Pato Branco 85503-390, Paraná, Brazil

Energies 2018, 11(2), 411; https://doi.org/10.3390/en11020411 - 10 Feb 2018

Cited by 13 | Viewed by 3228

Abstract

This paper proposes a control approach and supplementary controllers for the operation of a hybrid stand-alone system composed of a wind generation unit and a conventional generation unit based on synchronous generator (CGU). The proposed controllers allow the islanded or isolated operation of [...] Read more.

This paper proposes a control approach and supplementary controllers for the operation of a hybrid stand-alone system composed of a wind generation unit and a conventional generation unit based on synchronous generator (CGU). The proposed controllers allow the islanded or isolated operation of small power systems with predominance of wind generation. As an advantage and a paradigm shift, the DC-link voltage of the wind unit is controlled by means of a conventional synchronous generator connected to the AC grid of the system. Two supplementary controllers, added to a diesel generator (DIG) and to a DC dump load (DL), are proposed to control the DC-link voltage. The wind generation unit operates in V-f control mode and the DIG operates in PQ control mode, which allows the stand-alone system to operate either in wind-diesel (WD) mode or in wind-only (WO) mode. The strong influence of the wind turbine speed variations in the DC-link voltage is mitigated by a low-pass filter added to the speed control loop of the wind turbine. The proposed control approach does not require the use battery bank and ultra-capacitor to control the DC-link voltage in wind generation units based on fully rated converter. Full article

(This article belongs to the Section F: Electrical Engineering)

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23 pages, 5445 KiB

Open AccessArticle

Modelling the Effect of Driving Events on Electrical Vehicle Energy Consumption Using Inertial Sensors in Smartphones

by David Jiménez^1,*

, Sara Hernández², Jesús Fraile-Ardanuy³

, Javier Serrano¹, Rubén Fernández²

and Federico Álvarez¹

¹ Grupo de Aplicación de Telecomunicaciones Visuales (GATV), IPTC, Universidad Politécnica de Madrid, 28040 Madrid, Spain

² Grupo de Aplicaciones de Procesado de Señales (GAPS), IPTC, Universidad Politécnica de Madrid, 28040 Madrid, Spain

³ Grupo de Sistemas Dinámicos, Aprendizaje y Control (SISDAC), IPTC, Universidad Politécnica de Madrid, 28040 Madrid, Spain

Energies 2018, 11(2), 412; https://doi.org/10.3390/en11020412 - 10 Feb 2018

Cited by 36 | Viewed by 7249

Abstract

Air pollution and climate change are some of the main problems that humankind is currently facing. The electrification of the transport sector will help to reduce these problems, but one of the major barriers for the massive adoption of electric vehicles is their [...] Read more.

Air pollution and climate change are some of the main problems that humankind is currently facing. The electrification of the transport sector will help to reduce these problems, but one of the major barriers for the massive adoption of electric vehicles is their limited range. The energy consumption in these vehicles is affected, among other variables, by the driving behavior, making range a value that must be personalized to each driver and each type of electric vehicle. In this paper we offer a way to estimate a personalized energy consumption model by the use of the vehicle dynamics and the driving events detected by the use of the smartphone inertial sensors, allowing an easy and non-intrusive manner to predict the correct range for each user. This paper proposes, for the classification of events, a deep neural network (Long-Short Time Memory) which has been trained with more than 22,000 car trips, and the application to improve the consumption model taking into account the driver behavior captured across different trips, allowing a personalized prediction. Results and validation in real cases show that errors in the predicted consumption values are halved when abrupt events are considered in the model. Full article

(This article belongs to the Special Issue Methods to Improve Energy Use in Road Vehicles)

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13 pages, 4653 KiB

Open AccessArticle

Frequency-Controlled Current-Fed Resonant Converter with No Input Ripple Current

by Bor-Ren Lin^*

and Guan-Hong Lin

Department of Electrical Engineering, National Yunlin University of Science and Technology, Yunlin 640, Taiwan

Energies 2018, 11(2), 413; https://doi.org/10.3390/en11020413 - 11 Feb 2018

Cited by 3 | Viewed by 3443

Abstract

This paper studies a frequency-controlled current-fed resonant circuit. The adopted direct current (DC)-to-DC converter contains two boost circuits and a resonant circuit on the primary side. First, two boost circuits are connected in parallel to achieve voltage step-up and reduce input ripple current [...] Read more.

This paper studies a frequency-controlled current-fed resonant circuit. The adopted direct current (DC)-to-DC converter contains two boost circuits and a resonant circuit on the primary side. First, two boost circuits are connected in parallel to achieve voltage step-up and reduce input ripple current by using interleaved pulse-width modulation. Therefore, the size and current rating of boost inductors are decreased in the proposed converter. Second, the boost voltage is connected to the resonant circuit to realize the mechanism of the zero-voltage switching of all active switches and zero-current switching of all diodes. Two boost circuits and a resonant circuit use the same power devices in order to lessen the switch counts. The voltage doubler topology is adopted on the secondary side (high-voltage side). Therefore, the voltage rating of diodes on the high-voltage side is clamped at output voltage. The feasibility of the studied circuit is confirmed by the experimental tests with a 1 kW prototype circuit. Full article

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19 pages, 8108 KiB

Open AccessArticle

An Analysis for the Influences of Fracture Network System on Multi-Stage Fractured Horizontal Well Productivity in Shale Gas Reservoirs

by Deliang Zhang^1,2,*, Yu Dai¹, Xinhua Ma¹, Liehui Zhang², Bing Zhong¹, Jianfa Wu¹ and Zhengwu Tao³

¹ PetroChina Southwest Oil & Gas Field Company, Chengdu 610000, Sichuan, China

² Petroleum Engineering College, Southwest Petroleum University, Chengdu 610500, Sichuan, China

³ PetroChina Tarim Oilfield Company, Korla 841000, Xinjiang, China

Energies 2018, 11(2), 414; https://doi.org/10.3390/en11020414 - 11 Feb 2018

Cited by 20 | Viewed by 4762

Abstract

This paper presents two representative models to analyze the flow dynamic of multi-scale porous medium in hydraulic fractured horizontal shale gas wells. In this work, considering the characteristic mechanisms (multi-scale porous space, desorption and diffusion), flow equations in shale are established. After that, [...] Read more.

This paper presents two representative models to analyze the flow dynamic of multi-scale porous medium in hydraulic fractured horizontal shale gas wells. In this work, considering the characteristic mechanisms (multi-scale porous space, desorption and diffusion), flow equations in shale are established. After that, two representative models (discrete fracture model and dual-porosity model) are tailored to our issues. Solved by the control-volume finite element method (CVFEM), influences of fracture network system on productivity in shale reservoirs are analyzed in detail. Based on the analysis, the effects can be summarized as follow: at the beginning of production, high conductivity fracture network means more free gas could be produced; at the later part of production, high conductive fracture network can form a large low pressure region, which can not only stimulate the desorption of adsorbed gas, but also reduce the flow resistance to the well. Finally, the sensitivities of characteristic parameters in shale are discussed. Full article

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17 pages, 1382 KiB

Open AccessArticle

CAES Systems Integrated into a Gas-Steam Combined Plant: Design Point Performance Assessment

by Coriolano Salvini

Department of Engineering, ROMA TRE University, via della Vasca Navale 79, 00146 Rome, Italy

Energies 2018, 11(2), 415; https://doi.org/10.3390/en11020415 - 11 Feb 2018

Cited by 18 | Viewed by 5601

Abstract

In the present paper, the performance of an energy storage concept based on the integration of a compressed air energy storage (CAES) system into a gas–steam combined cycle (GSCC) plant is investigated. CAES systems featured by different design specifications have been coupled with [...] Read more.

In the present paper, the performance of an energy storage concept based on the integration of a compressed air energy storage (CAES) system into a gas–steam combined cycle (GSCC) plant is investigated. CAES systems featured by different design specifications have been coupled with a commercially available small size GSCC plant. Storage efficiencies up to 65% have been evaluated for CAES design power output ranging from 5 to 10 MW. A techno-economic analysis aimed at assessing plant performance and investment costs has been performed. Despite the relatively high investment costs and the storage efficiency being less than those featuring alternative storage approaches, the proposed system may be considered of interest due to the long-life duration and the established technologies available for the key plant components. Full article

(This article belongs to the Special Issue Selected Papers from ICEER 2017: 2017 the 4th International Conference on Energy and Environment Research)

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14 pages, 3049 KiB

Open AccessArticle

Study on the Hazard Limitation of Hybrid Circuit Breaker Actuator Operation

by Piotr Jankowski^* and Janusz Mindykowski

Department of Marine Electrical Power Engineering, Gdynia Maritime University Poland, 81-225 Gdynia, Poland

Energies 2018, 11(2), 416; https://doi.org/10.3390/en11020416 - 11 Feb 2018

Cited by 4 | Viewed by 3576

Abstract

The paper deals with a key issue, how to limit the hazard and assure reliability, safety and repeatability of operation of selected critical devices protecting electrical power systems. The main research is focused on the incorrect operation of hybrid switches caused by random [...] Read more.

The paper deals with a key issue, how to limit the hazard and assure reliability, safety and repeatability of operation of selected critical devices protecting electrical power systems. The main research is focused on the incorrect operation of hybrid switches caused by random disturbances of the thyristor gate signals in the electrodynamic drive coil power supply circuit. Firstly, a pilot experiment on the operation of hybrid circuit breaker actuators under random disturbance conditions was carried out and the results are presented. Next, an in-depth operation analysis, based on experimental and simulation research, according to setting conditions of the circuit breaker actuator parameters such as capacitance, voltage and switching time was performed. A simulation study with the use of a field–circumferential model in the Ansys Maxwell program of electrodynamic propulsion of rectilinear motion, which enables energy transfer from the capacitor bank to the actuator coil power supply at selected time intervals, was executed. The study analysed the impact of the discontinuity of energy transfer on the dynamic properties of the actuator and some recommendations for designers and users on how to limit this hazard are formulated. Full article

(This article belongs to the Section F: Electrical Engineering)

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19 pages, 1518 KiB

Open AccessArticle

Derivation and Application of a New Transmission Loss Formula for Power System Economic Dispatch

by Wei-Tzer Huang^1,*

, Kai-Chao Yao^1,*, Ming-Ku Chen¹, Feng-Ying Wang¹, Cang-Hui Zhu¹, Yung-Ruei Chang², Yih-Der Lee² and Yuan-Hsiang Ho²

¹ Department of Industrial Education and Technology, National Changhua University of Education, No. 2, Shida Rd., Changhua 500, Taiwan

² The Institute of Nuclear Energy Research, 1000 Wenhua Rd., Jiaan Village, Longtan Dist., Taoyuan City 325, Taiwan

Energies 2018, 11(2), 417; https://doi.org/10.3390/en11020417 - 11 Feb 2018

Cited by 17 | Viewed by 7603

Abstract

The expression and calculation of transmission loss (TL) play key roles for solving the power system economic dispatch (ED) problem. ED including TL must compute the total TL and incremental transmission loss (ITL) by executing power flow equations. However, solving the power flow [...] Read more.

The expression and calculation of transmission loss (TL) play key roles for solving the power system economic dispatch (ED) problem. ED including TL must compute the total TL and incremental transmission loss (ITL) by executing power flow equations. However, solving the power flow equations is time-consuming and may result in divergence by the iteration procedure. This approach is unsuitable for real-time ED in practical power systems. To avoid solving nonlinear power flow equations, most power companies continue to adopt the TL formula in ED. Traditional loss formulas are composed of network parameters and in terms of the generator’s real power outputs. These formulas are derived by several assumptions, but these basic assumptions sacrifice accuracy. In this study, a new expression for the loss formula is proposed to improve the shortcomings of traditional loss formulas. The coefficients in the new loss formula can be obtained by recording the power losses according to varying real and reactive power outputs without any assumptions. The simultaneous equations of the second-order expansion of the Taylor series are then established. Finally, the corresponding coefficients can be calculated by solving the simultaneous equations. These new coefficients can be used in optimal real and reactive power dispatch problems. The proposed approach is tested by IEEE 14-bus and 30-bus systems, and the results are compared with those obtained from the traditional B coefficient method and the load flow method. The numerical results show that the proposed new loss formula for ED can hold high accuracy for different loading conditions and is very suitable for real-time applications. Full article

(This article belongs to the Section F: Electrical Engineering)

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15 pages, 7917 KiB

Open AccessArticle

Prediction of Thermal Environment in a Large Space Using Artificial Neural Network

by Hyun-Jung Yoon¹, Dong-Seok Lee¹

, Hyun Cho² and Jae-Hun Jo^1,3,*

¹ Department of Architectural Engineering, Inha University, Incheon 22212, Korea

² Research & Engineering Division, R&D Center, Posco E&C, Incheon 21985, Korea

³ Center for Korean Studies, University of California, Berkeley, CA 94704, USA

Energies 2018, 11(2), 418; https://doi.org/10.3390/en11020418 - 11 Feb 2018

Cited by 11 | Viewed by 3483

Abstract

Since the thermal environment of large space buildings such as stadiums can vary depending on the location of the stands, it is important to divide them into different zones and evaluate their thermal environment separately. The thermal environment can be evaluated using physical [...] Read more.

Since the thermal environment of large space buildings such as stadiums can vary depending on the location of the stands, it is important to divide them into different zones and evaluate their thermal environment separately. The thermal environment can be evaluated using physical values measured with the sensors, but the occupant density of the stadium stands is high, which limits the locations available to install the sensors. As a method to resolve the limitations of installing the sensors, we propose a method to predict the thermal environment of each zone in a large space. We set six key thermal factors affecting the thermal environment in a large space to be predicted factors (indoor air temperature, mean radiant temperature, and clothing) and the fixed factors (air velocity, metabolic rate, and relative humidity). Using artificial neural network (ANN) models and the outdoor air temperature and the surface temperature of the interior walls around the stands as input data, we developed a method to predict the three thermal factors. Learning and verification datasets were established using STAR CCM+ (2016.10, Siemens PLM software, Plano, TX, USA). An analysis of each model’s prediction results showed that the prediction accuracy increased with the number of learning data points. The thermal environment evaluation process developed in this study can be used to control heating, ventilation, and air conditioning (HVAC) facilities in each zone in a large space building with sufficient learning by ANN models at the building testing or the evaluation stage. Full article

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14 pages, 4029 KiB

Open AccessArticle

Evaluation of the Optimal Connection of Power Transformers in the Substations of a Hospital

by Carlos Javier Renedo^*

, Agustín Santisteban, Félix Ortiz

, Cristian Olmo and Alfredo Ortiz

Electrical and Energy Engineering Department, University of Cantabria, 39005 Santander, Spain

Energies 2018, 11(2), 419; https://doi.org/10.3390/en11020419 - 11 Feb 2018

Cited by 3 | Viewed by 3635

Abstract

Transformers are installed in power distribution systems to perform changes in supply voltage. Large consumers often have several transformers installed in parallel to ensure continuity of supply in the event of failure. These machines can achieve very high efficiency, but their efficiency is [...] Read more.

Transformers are installed in power distribution systems to perform changes in supply voltage. Large consumers often have several transformers installed in parallel to ensure continuity of supply in the event of failure. These machines can achieve very high efficiency, but their efficiency is not constant since it depends on the power demanded at each time. Therefore, the level of efficiency that correspond to the operation of a specific transformer depends on two factors: machine technical characteristics and electrical load. In this work, the authors have proposed a methodology which shows the optimal number of transformers to be connected at each period in the substations of a large Spanish hospital, in order to achieve the maximum seasonal efficiency of these machines. The results of the energy saving are determined with respect to the current situation, in which all the transformers are permanently connected. On the other hand, the European Union has established a new regulation that sets the minimum energy efficiency requirements for new power transformers. This efficiency improvement is proposed to be applied gradually in two stages, a first limit came into force in 2015, while a more restrictive approach will appear in the year 2021. This work has also studied the potential energy savings that would occur when the substations of the hospital have more efficient transformers complying with the new European Regulation 548/2014. Full article

(This article belongs to the Section F: Electrical Engineering)

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21 pages, 17137 KiB

Open AccessArticle

Coordination of Heat Pumps, Electric Vehicles and AGC for Efficient LFC in a Smart Hybrid Power System via SCA-Based Optimized FOPID Controllers

by Rahmat Khezri¹, Arman Oshnoei², Mehrdad Tarafdar Hagh^3,4 and SM Muyeen^5,*

¹ Department of Electrical and Computer Engineering, University of Kurdistan, Sanandaj 6617715177, Iran

² Faculty of Electrical and Computer Engineering, Shahid Beheshti University, Tehran 1983969411, Iran

³ Faculty of Electrical and Computer Engineering Department, University of Tabriz, Tabriz 5166616471, Iran

⁴ Engineering Faculty, Near East University, Nicosia 99138, Cyprus

⁵ Department of Electrical and Computer Engineering, Curtin University, Perth, WA 6845, Australia

Energies 2018, 11(2), 420; https://doi.org/10.3390/en11020420 - 12 Feb 2018

Cited by 57 | Viewed by 5453

Abstract

Due to the high price of fossil fuels, the increased carbon footprint in conventional generation units and the intermittent functionality of renewable units, alternative sources must contribute to the load frequency control (LFC) of the power system. To tackle the challenge, dealing with [...] Read more.

Due to the high price of fossil fuels, the increased carbon footprint in conventional generation units and the intermittent functionality of renewable units, alternative sources must contribute to the load frequency control (LFC) of the power system. To tackle the challenge, dealing with controllable loads, the ongoing study aims at efficient LFC in smart hybrid power systems. To achieve this goal, heat pumps (HPs) and electric vehicles (EVs) are selected as the most effective controllable loads to contribute to the LFC issue. In this regard, the EVs can be controlled in a bidirectional manner as known charging and discharging states under a smart structure. In addition, regarding the HPs, the power consumption is controllable. As the main task, this paper proposes a fractional order proportional integral differential (FOPID) controller for coordinated control of power consumption in HPs, the discharging state in EVs and automatic generation control (AGC). The parameters of the FOPID controllers are optimized simultaneously by the sine cosine algorithm (SCA), which is a new method for optimization problems. In the sequel, four scenarios, including step and random load changes, aggregated intermittent generated power from wind turbines, a random load change scenario and a sensitivity analysis scenario, are selected to demonstrate the efficiency of the proposed SCA-based FOPID controllers in a hybrid two-area power system. Full article

(This article belongs to the Section F: Electrical Engineering)

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19 pages, 5271 KiB

Open AccessArticle

Research on an Electric Vehicle Owner-Friendly Charging Strategy Using Photovoltaic Generation at Office Sites in Major Chinese Cities

by Su Su¹, Yong Hu^1,*, Tiantian Yang^1,*, Shidan Wang², Ziqi Liu³, Xiangxiang Wei^4,*, Mingchao Xia⁵

, Yutaka Ota⁶ and Koji Yamashita^7,*

¹ National Active Distribution Network Technology Research Center, Beijing Jiaotong University, Beijing 100044, China

² Haidian Electric Power Supply Company of State Grid Beijing Electric Power Company, Beijing 100044, China

³ Inner Mongolia Electric Power Research Institute, Hohhot 010020, Inner Mongolia, China

⁴ Liuzhou Power Supply Bureau, Guangxi Power Grid Co., Ltd., Liuzhou 545000, Guangxi, China

⁵ School of Electrical Engineering, Beijing Jiaotong University, Beijing 100044, China

⁶ Department of Electrical and Electronic Engineering, Faculty of Engineering, Tokyo City University, Tokyo 163-8001, Japan

⁷ Department of Electrical and Computer Engineering, Michigan Technological University, Houghton, MI 49931, USA

Energies 2018, 11(2), 421; https://doi.org/10.3390/en11020421 - 12 Feb 2018

Cited by 7 | Viewed by 4388

Abstract

Electric vehicles (EV) and photovoltaic (PV) generation are widely recognized around the world. Most EV owners in the major Chinese cities are forced to charge their EV batteries at the workplace during the daytime due to the limited space near their homes, which [...] Read more.

Electric vehicles (EV) and photovoltaic (PV) generation are widely recognized around the world. Most EV owners in the major Chinese cities are forced to charge their EV batteries at the workplace during the daytime due to the limited space near their homes, which will increase the peak load during the daytime. On the other hand, the PV output is most likely to have a peak at around noon, which means, PVs could have a potential capability to compensate the EV charging load. An EV owner-friendly charging strategy based on PV utilization which alleviates both the EV charging constraints and the negative impact of the EV charging load on the grid is proposed. The PV utilization for compensating the unconstrained EV charging load is maximized to derive the maximum number of EVs with unconstrained charging. If the actual number of EVs exceeds the maximum number, a portion of EVs have to be charged only from the grid. Then, the line loss is introduced as the optimization objective in which the charging states are regulated. The case study shows that the proposed strategy can successfully increase the number of EVs with unconstrained charging, and reduce the peak-to-peak of the load curve. Full article

(This article belongs to the Special Issue Energy Management in Vehicle–Grid–Traffic Nexus)

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16 pages, 5041 KiB

Open AccessArticle

Risk Assessment of Power System Considering Frequency Dynamics and Cascading Process

by Chao Luo, Jun Yang^*,† and Yuanzhang Sun

¹ School of Electrical Engineering, Wuhan University, Wuhan 430072, China

^† Current address: No. 8 South Street of East Lake, Wuhan 430072, China.

Energies 2018, 11(2), 422; https://doi.org/10.3390/en11020422 - 12 Feb 2018

Cited by 10 | Viewed by 3646

Abstract

Frequency security is vital to the safety of power systems and has been scrutinized for many years. The conventional frequency security analysis only checks whether the frequency after anticipated initial failures can remain in the normal range based on some aggregated models, but [...] Read more.

Frequency security is vital to the safety of power systems and has been scrutinized for many years. The conventional frequency security analysis only checks whether the frequency after anticipated initial failures can remain in the normal range based on some aggregated models, but the influence of potential cascading failures has not been considered yet. This is not enough, especially when the modern power system suffers the increasing threat of cascading failures. Therefore, this paper proposes a novel frequency simulation model considering the influence of cascading failure to reveal the security level of power systems comprehensively. The proposed model is based on a platform on which the frequency dynamics and the power flow distributions can be calculated jointly. Moreover, simulation models of protection devices and some supervisory operation-control schemes are also taken into account. Case studies validate the effectiveness of the proposed model on the IEEE 39-bus system. Moreover, the results of some further probabilistic simulations under different operation parameters are obtained, which show the great significance of improving the frequency regulation performance to cope with challenges of blackouts. Full article

(This article belongs to the Section F: Electrical Engineering)

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15 pages, 2295 KiB

Open AccessArticle

An Improved Energy Management Strategy for Hybrid Energy Storage System in Light Rail Vehicles

by Long Cheng^*

, Wei Wang, Shaoyuan Wei, Hongtao Lin and Zhidong Jia

National Active Distribution Network Technology Research Center, Beijing Jiaotong University, Beijing 100044, China

Energies 2018, 11(2), 423; https://doi.org/10.3390/en11020423 - 12 Feb 2018

Cited by 27 | Viewed by 4959

Abstract

A single-objective optimization energy management strategy (EMS) for an onboard hybrid energy storage system (HESS) for light rail (LR) vehicles is proposed. The HESS uses batteries and supercapacitors (SCs). The main objective of the proposed optimization is to reduce the battery and SC [...] Read more.

A single-objective optimization energy management strategy (EMS) for an onboard hybrid energy storage system (HESS) for light rail (LR) vehicles is proposed. The HESS uses batteries and supercapacitors (SCs). The main objective of the proposed optimization is to reduce the battery and SC losses while maintaining the SC state of charge (SOC) within specific limits based on the distance between consecutive LR stations. To do this, a series of optimized SOC limits is used to prevent the SC from becoming exhausted prematurely instead of the standard SC SOC penalty term in the cost function. Meanwhile, a rule-based EMS (RB-EMS) is used to give the SCs charging priority over the batteries when the vehicle is braking. Moreover, a simplified method for the optimization is proposed to reduce the computational burden. Simulation and experimental results for the proposed EMS and a standard SC SOC penalty-based cost function optimization are provided to evaluate losses. As a result, it is shown that the proposed EMS, compared with standard SC SOC penalty-based cost function optimization, decreases losses and prevents the SOC from reach the discharging limits. Full article

(This article belongs to the Section D: Energy Storage and Application)

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13 pages, 5835 KiB

Open AccessArticle

The Design of a Permanent Magnet In-Wheel Motor with Dual-Stator and Dual-Field-Excitation Used in Electric Vehicles

by Peng Gao^*, Yuxi Gu and Xiaoyuan Wang

School of Electrical and Information Engineering, Tianjin University, No. 92 Weijin Road, Tianjin 300072, China

Energies 2018, 11(2), 424; https://doi.org/10.3390/en11020424 - 12 Feb 2018

Cited by 23 | Viewed by 7566

Abstract

The in-wheel motor has received more attention owing to its simple structure, high transmission efficiency, flexible control, and easy integration design. It is difficult to achieve high performance with conventional motors due to their dimensions and structure. This paper presents a new dual-stator [...] Read more.

The in-wheel motor has received more attention owing to its simple structure, high transmission efficiency, flexible control, and easy integration design. It is difficult to achieve high performance with conventional motors due to their dimensions and structure. This paper presents a new dual-stator and dual-field-excitation permanent-magnet in-wheel motor (DDPMIM) that is based on the structure of the conventional in-wheel motor and the structure of both the radial and axial magnetic field motor. The finite element analysis (FEA) model of the DDPMIM is established and compared with that of the conventional in-wheel motor. The results show that the DDPMIM achieves a higher output torque at low speeds and that the flux-weakening control strategy is not needed in the full speed range. Full article

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15 pages, 3786 KiB

Open AccessArticle

Short-Circuit Current Analysis for DFIG Wind Farm Considering the Action of a Crowbar

by Yan Hong Yuan

and Feng Wu^*

College of Energy and Electrical Engineering, Hohai University, Nanjing 211100, China

Energies 2018, 11(2), 425; https://doi.org/10.3390/en11020425 - 12 Feb 2018

Cited by 22 | Viewed by 6259

Abstract

With the increasing capacity of wind farms integrated into the power grid, the short-circuit current analysis for wind farms becomes more and more important. Since the wind turbine is usually integrated into the power grid via power electronic devices, the “crowbar” is installed [...] Read more.

With the increasing capacity of wind farms integrated into the power grid, the short-circuit current analysis for wind farms becomes more and more important. Since the wind turbine is usually integrated into the power grid via power electronic devices, the “crowbar” is installed in the wind turbine to protect the power electronic devices and to improve the fault ride through capability. The impact of the crowbar has to be considered during the short-circuit current analysis for the wind farm. In order to fully analyze the short-circuit current characteristics of a wind farm, the short-circuit currents for a doubly-fed induction generator (DFIG) wind turbine under symmetrical and asymmetrical faults considering the crowbar action characteristic are derived firstly. Then the action situation of the crowbar of a DFIG wind turbine is studied and the action area curve is obtained. Taking the crowbar action, or not, as the grouping criterion, wind turbines in the wind farm are divided into two groups, and the wind farm is aggregated into two equivalent wind turbines. Using the equivalent model, the short-circuit current of a wind farm can be calculated accurately. Finally, simulations are performed in MATLAB/Simulink which is the commercial math software produced by the MathWorks company in Natick, Massachusetts, the United States to verify the proposed short-circuit current calculation method for the DFIG wind farm. Full article

(This article belongs to the Section F: Electrical Engineering)

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13 pages, 1914 KiB

Open AccessArticle

Data Mining and Neural Networks Based Self-Adaptive Protection Strategies for Distribution Systems with DGs and FCLs

by Wen-Jun Tang and Hong-Tzer Yang^*

Department of Electrical Engineering, National Cheng Kung University, East Dist., Tainan City 701, Taiwan

Energies 2018, 11(2), 426; https://doi.org/10.3390/en11020426 - 13 Feb 2018

Cited by 23 | Viewed by 3883

Abstract

In light of the development of renewable energy and concerns over environmental protection, distributed generations (DGs) have become a trend in distribution systems. In addition, fault current limiters (FCLs) may be installed in such systems to prevent the short-circuit current from exceeding the [...] Read more.

In light of the development of renewable energy and concerns over environmental protection, distributed generations (DGs) have become a trend in distribution systems. In addition, fault current limiters (FCLs) may be installed in such systems to prevent the short-circuit current from exceeding the capacity of the power apparatus. However, DGs and FCLs can lead to problems, the most critical of which is miscoordination in protection system. This paper proposes overcurrent protection strategies for distribution systems with DGs and FCLs. Through the proposed approach, relays with communication ability can determine their own operating states with the help of an operation setting decision tree and topology-adaptive neural network model based on data processed through continuous wavelet transform. The performance and effectiveness of the proposed protection strategies are verified by the simulation results obtained from various system topologies with or without DGs, FCLs, and load variations. Full article

(This article belongs to the Special Issue 17TH International Conference on Environment and Electrical Engineering)

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19 pages, 6293 KiB

Open AccessArticle

Research on Hydraulic Technology for Seam Permeability Enhancement in Underground Coal Mines in China

by Liang Cheng^1,*

, Zhaolong Ge^1,2,*, Binwei Xia^1,2, Qian Li^1,2, Jiren Tang^1,2, Yugang Cheng^1,2,* and Shaojie Zuo^1,2

¹ State Key Laboratory of Coal Mine Disaster Dynamics and Control, Chongqing University, Chongqing 400044, China

² College of Resources and Environmental Science, Chongqing University, Chongqing 400030, China

Energies 2018, 11(2), 427; https://doi.org/10.3390/en11020427 - 13 Feb 2018

Cited by 40 | Viewed by 4331

Abstract

Coalbed methane (gas) is a high quality and clean resource, but it also causes disasters in coal mines in China. The low permeability of coal seams is the main reason that developing coalbed methane (CBM) as an energy resource is difficult, so increasing [...] Read more.

Coalbed methane (gas) is a high quality and clean resource, but it also causes disasters in coal mines in China. The low permeability of coal seams is the main reason that developing coalbed methane (CBM) as an energy resource is difficult, so increasing coal seam permeability is the key to CBM development in China. In this paper, the principal techniques for seam permeability enhancement are presented. The paper focuses on hydraulic technology for seam permeability enhancement (HTSPE), which is considered an economic and highly efficient technology for seam permeability enhancement. The process of HTSPE development is reviewed and the current status of the theories behind HTSPE and the technology and equipment for its use are summarized. The goal is to identify the gaps in HTSPE research and the problems in its implementation. In the future, integration and diversification of the technologies along with on-board intelligence and miniaturization may be the trends for the equipment. Finally, it is shown that tree-shaped borehole fracturing can be used to develop CBM in underground coal mines. This study could be used as a valuable example for other coal deposits being mined under similar geological conditions. Full article

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11 pages, 3651 KiB

Open AccessArticle

Experimental Enrichment of Low-Concentration Ventilation Air Methane in Free Diffusion Conditions

by Wen Wang^1,2,*

, Heng Wang¹, Huamin Li¹, Dongyin Li¹, Huaibin Li³ and Zhenhua Li^1,*

¹ School of Energy Science and Engineering, Henan Polytechnic University, Jiaozuo 454003, China

² Department of Civil Engineering, Monash University, Melbourne, VIC 3800, Australia

³ School of Resources and Civil Engineering, Northeastern University, Shenyang 110819, China

Energies 2018, 11(2), 428; https://doi.org/10.3390/en11020428 - 13 Feb 2018

Cited by 8 | Viewed by 3219

Abstract

The massive emission of low concentrations (≤0.5%) of methane (CH₄) from ventilation roadways results in resource waste and environmental pollution. To mitigate these emissions, an enrichment tower for low-concentration methane is designed, and segregation and non-segregation experiments are conducted. The results [...] Read more.

The massive emission of low concentrations (≤0.5%) of methane (CH₄) from ventilation roadways results in resource waste and environmental pollution. To mitigate these emissions, an enrichment tower for low-concentration methane is designed, and segregation and non-segregation experiments are conducted. The results reveal that stable concentrations of methane under segregation and non-segregation states in the enrichment tower gradually increase with height, with a maximum methane concentration of 0.64% and 0.54%, respectively. This shows that the methane enrichment effect in free diffusion conditions is more significant under the segregation state than under the non-segregation state. The stable concentration of methane in the middle and upper sections of the enrichment tower shows an increasing trend. However, the stable concentration of methane in the lower section of the enrichment tower has an increasing trend (less than 0.50%). According to the methane molecule Boltzmann distribution law, methane concentration enrichment decreases with height, and the conversion of the methane from the segregated to non-segregated is irreversible. Consequently, industrial applications of methane enrichment from buoyant forces are not feasible for low concentrations of methane. Full article

(This article belongs to the Section L: Energy Sources)

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25 pages, 11481 KiB

Open AccessArticle

Aircraft Noise Assessment—From Single Components to Large Scenarios

by Jan Delfs¹, Lothar Bertsch¹

, Christoph Zellmann²

, Lennart Rossian¹, Ehsan Kian Far³, Tobias Ring³

and Sabine C. Langer^3,*

¹ DLR, Institute of Aerodynamics and Flow Technology, 38108 Braunschweig, Germany

² Laboratory for Acoustics/Noise Control, Empa - Swiss Federal Laboratories for Material Science and Technology, 8600 Dübendorf, Switzerland

³ TU Braunschweig, Institute for Engineering Design, 38106 Braunschweig, Germany

Energies 2018, 11(2), 429; https://doi.org/10.3390/en11020429 - 13 Feb 2018

Cited by 16 | Viewed by 8187

Abstract

The strategic European paper “Flightpath 2050” claims dramatic reductions of noise for aviation transport scenarios in 2050: “...The perceived noise emission of flying aircraft is reduced by 65%. These are relative to the capabilities of typical new aircraft in 2000...”. There is a [...] Read more.

The strategic European paper “Flightpath 2050” claims dramatic reductions of noise for aviation transport scenarios in 2050: “...The perceived noise emission of flying aircraft is reduced by 65%. These are relative to the capabilities of typical new aircraft in 2000...”. There is a consensus among experts that these far reaching objectives cannot be accomplished by application of noise reduction technologies at the level of aircraft components only. Comparably drastic claims simultaneously expressed in Flightpath 2050 for carbon dioxide and NOX reduction underline the need for step changes in aircraft technologies and aircraft configurations. New aircraft concepts with entirely different propulsion concepts will emerge, including unconventional power supplies from renewable energy sources, ranging from electric over hybrid to synthetic fuels. Given this foreseen revolution in aircraft technology the question arises, how the noise impact of these new aircraft may be assessed. Within the present contribution, a multi-level, multi-fidelity approach is proposed which enables aircraft noise assessment. It is composed by coupling noise prediction methods at three different levels of detail. On the first level, high fidelity methods for predicting the aeroacoustic behavior of aircraft components (and installations) are required since in the early stages of the development of innovative noise reduction technology test data is not available. The results are transferred to the second level, where radiation patterns of entire conventional and future aircraft concepts are assembled and noise emissions for single aircraft are computed. In the third level, large scale scenarios with many aircraft are considered to accurately predict the noise exposure for receivers on the ground. It is shown that reasonable predictions of the ground noise exposure level may be obtained. Furthermore, even though simplifications and omissions are introduced, it is shown that the method is capable of transferring all relevant physical aspects through the levels. Full article

(This article belongs to the Special Issue Towards a Transformation to Sustainable Aviation Systems)

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19 pages, 3664 KiB

Open AccessArticle

Insulation Coordination of Arcing Horns on HVDC Electrode Lines: Protection Performance Evaluation, Influence Factors and Improvement Method

by Xiandong Li^1,2,3,*

, Hua Li^1,2,3,*, Yi Liu^1,2,3 and Fuchang Lin^1,2,3

¹ State Key Laboratory of Advanced Electromagnetic Engineering and Technology, Huazhong University of Science & Technology, Wuhan 430074, China

² School of Electrical and Electronic Engineering, Huazhong University of Science & Technology, Wuhan 430074, China

³ Key Laboratory of Pulsed Power Technology (Huazhong University of Science and Technology), Ministry of Education, Wuhan 430074, China

Energies 2018, 11(2), 430; https://doi.org/10.3390/en11020430 - 13 Feb 2018

Cited by 6 | Viewed by 4623

Abstract

Arcing horns are widely used in high voltage overhead lines to protect insulator strings from being destroyed by the free burning arcs caused by lightening faults. In this paper, we focus on the insulation coordination of arcing horns on the electrode lines of [...] Read more.

Arcing horns are widely used in high voltage overhead lines to protect insulator strings from being destroyed by the free burning arcs caused by lightening faults. In this paper, we focus on the insulation coordination of arcing horns on the electrode lines of a 5000 MW, ±800 kV high voltage direct current (HVDC) system. The protection performance of arcing horns are determined by the characteristics of not only the external system but also the fault arc. Therefore, the behaviors and characteristics of long free burning arcs are investigated by the experiments at first. In order to evaluate the protection performance of arcing horns, the static stability criterion U-I characteristic method is introduced. The influence factors on the protection performance of arcing horns are analyzed theoretically. Finally, the improvement methods for the protection performance of arcing horns are proposed, and the diversified configuration strategy of arcing horns is recommended for cost saving. Full article

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16 pages, 4760 KiB

Open AccessArticle

Harmonic Analysis of Single-Phase Neutral-Point-Clamped Cascaded Inverter in Advanced Traction Power Supply System Based on the Big Triangular Carrier Equivalence Method

by Pengcheng Han¹

, Xiaoqiong He^1,2,*, Yi Wang¹, Haijun Ren¹, Xu Peng¹ and Zeliang Shu¹

¹ School of Electrical Engineering, Southwest Jiaotong University, Chengdu 611756, China

² National Rail Transit Electrification and Automation Engineering Technique Research Center, Chengdu 611756, China

Energies 2018, 11(2), 431; https://doi.org/10.3390/en11020431 - 14 Feb 2018

Cited by 6 | Viewed by 3762

Abstract

An advanced traction power supply system based on a single phase neutral-point-clamped (NPC) cascaded inverter is studied. The big triangular carrier equivalence method in double coordinate system is proposed, which can reduce one coordinate system, thus simplifying the calculation. Based on the big [...] Read more.

An advanced traction power supply system based on a single phase neutral-point-clamped (NPC) cascaded inverter is studied. The big triangular carrier equivalence method in double coordinate system is proposed, which can reduce one coordinate system, thus simplifying the calculation. Based on the big triangular carrier equivalence method, the harmonic characteristics of a single phase NPC cascaded inverter are calculated by double Fourier transform and voltage harmonics expressions of 5-level, 9-level and 13-level output waveforms are derived. Finally, the performance and calculated results of the proposed method were verified by simulations and experiments. The result provides a theoretical basis for further studies on traction network resonance. Full article

(This article belongs to the Section D: Energy Storage and Application)

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35 pages, 2025 KiB

Open AccessFeature PaperArticle

Challenges of Microgrids in Remote Communities: A STEEP Model Application

by Daniel Akinyele^1,2,*

, Juri Belikov³

and Yoash Levron¹

¹ Andrew and Erna Viterbi Faculty of Electrical Engineering, Technion—Israel Institute of Technology, Haifa 3200003, Israel

² Department of Electrical and Computer Engineering, Elizade University, P. M. B 002 Ilara-Mokin, Ondo State, Nigeria

³ Department of Computer Systems, Tallinn University of Technology, Akadeemia tee 15a, 12618 Tallinn, Estonia

Energies 2018, 11(2), 432; https://doi.org/10.3390/en11020432 - 14 Feb 2018

Cited by 147 | Viewed by 13888

Abstract

There is a growing interest in the application of microgrids around the world because of their potential for achieving a flexible, reliable, efficient and smart electrical grid system and supplying energy to off-grid communities, including their economic benefits. Several research studies have examined [...] Read more.

There is a growing interest in the application of microgrids around the world because of their potential for achieving a flexible, reliable, efficient and smart electrical grid system and supplying energy to off-grid communities, including their economic benefits. Several research studies have examined the application issues of microgrids. However, a lack of in-depth considerations for the enabling planning conditions has been identified as a major reason why microgrids fail in several off-grid communities. This development requires research efforts that consider better strategies and framework for sustainable microgrids in remote communities. This paper first presents a comprehensive review of microgrid technologies and their applications. It then proposes the STEEP model to examine critically the failure factors based on the social, technical, economic, environmental and policy (STEEP) perspectives. The model details the key dimensions and actions necessary for addressing the challenge of microgrid failure in remote communities. The study uses remote communities within Nigeria, West Africa, as case studies and demonstrates the need for the STEEP approach for better understanding of microgrid planning and development. Better insights into microgrid systems are expected to address the drawbacks and improve the situation that can lead to widespread and sustainable applications in off-grid communities around the world in the future. The paper introduces the sustainable planning framework (SPF) based on the STEEP model, which can form a general basis for planning microgrids in any remote location. Full article

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14 pages, 6805 KiB

Open AccessArticle

Application of the X-in-the-Loop Testing Method in the FCV Hybrid Degree Test

by Haiyu Gao¹, Tong Zhang¹, Huicui Chen^1,*, Zhiguo Zhao² and Ke Song³

¹ School of Automotive Studies, Tongji University, Shanghai 201804, China

² Clean Energy Automotive Engineering Center, Tongji University, Shanghai 201804, China

³ National Fuel Cell Vehicle and Powertrain System Engineering Research Center, Tongji University, Shanghai 201804, China

Energies 2018, 11(2), 433; https://doi.org/10.3390/en11020433 - 14 Feb 2018

Cited by 13 | Viewed by 4993

Abstract

With the development of fuel cell vehicle technology, an effective testing method that can be applied to develop and verify the fuel cell vehicle powertrain system is urgently required. This paper presents the X-in-the-Loop (XiL) testing method in the fuel cell vehicle (FCV) [...] Read more.

With the development of fuel cell vehicle technology, an effective testing method that can be applied to develop and verify the fuel cell vehicle powertrain system is urgently required. This paper presents the X-in-the-Loop (XiL) testing method in the fuel cell vehicle (FCV) hybrid degree test to resolve the first and key issues for the powertrain system design, and the test process and scenarios were designed. The hybrid degree is redefined into the static hybrid degree for system architecture design and the dynamic hybrid degree for vehicle control strategy design, and an integrated testing platform was introduced and a testing application was implemented by following the designed testing flowchart with two loops. Experimental validations show that the sizing of the FCE (Fuel Cell Engine), battery pack, and traction motor with the powertrain architecture can be determined, the control strategy can be evaluated seamlessly, and a systematic powertrain testing solution can be achieved through the whole development process. This research has developed a new testing platform and proposed a novel testing method on the fuel cell vehicle powertrain system, which will be a contribution to fuel cell vehicle technology and its industrialization. Full article

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18 pages, 3822 KiB

Open AccessArticle

A Power System Network Splitting Strategy Based on Contingency Analysis

by Nur Zawani Saharuddin^1,2,*, Izham Zainal Abidin², Hazlie Mokhlis³

, Abdul Rahim Abdullah¹ and Kanendra Naidu⁴

¹ Faculty of Electrical Engineering, Universiti Teknikal Malaysia Melaka, 76100 Durian Tunggal, Melaka, Malaysia

² Institute of Power Engineering, Universiti Tenaga Nasional, Jalan Ikram- Uniten, 43000 Kajang, Selangor, Malaysia

³ Department of Electrical Engineering, Faculty of Engineering, University of Malaya, 50603 Kuala Lumpur, Malaysia

⁴ Electrical Technology Section, Universiti Kuala Lumpur, British Malaysian Institute, 53100 Gombak, Kuala Lumpur, Malaysia

Energies 2018, 11(2), 434; https://doi.org/10.3390/en11020434 - 14 Feb 2018

Cited by 8 | Viewed by 4965 | Correction

Abstract

This paper proposes a network splitting strategy following critical line outages based on N-1 contingency analysis. Network splitting is the best option for certain critical outages when the tendency of severe cascading failures is very high. Network splitting is executed by splitting the [...] Read more.

This paper proposes a network splitting strategy following critical line outages based on N-1 contingency analysis. Network splitting is the best option for certain critical outages when the tendency of severe cascading failures is very high. Network splitting is executed by splitting the power system network into feasible set of islands. Thus, it is essential to identify the optimal splitting solution (in terms of minimal power flow disruption) that satisfies certain constraints. This paper determines the optimal splitting solution for each of the critical line outage using discrete evolutionary programming (DEP) optimization technique assisted by heuristic initialization approach. Heuristic initialization provides the best initial cutsets which will guide the optimization technique to find the optimal splitting solution. Generation–load balance and transmission line overloading analysis are carried out in each island to ensure the steady state stability is achieved. Load shedding scheme is initiated if the power balance criterion is violated in any island to sustain the generation–load balance. The proposed technique is validated on the IEEE 118 bus system. Results show that the proposed approach produces an optimal splitting solution with lower power flow disruption during network splitting execution. Full article

(This article belongs to the Section F: Electrical Engineering)

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20 pages, 1645 KiB

Open AccessArticle

Network-Constrained Unit Commitment Based on Reserve Models Fully Considering the Stochastic Characteristics of Wind Power

by Gang Wang^*, Dahai You, Zhe Zhang, Li Dai, Qi Zou and Hengwei Liu

State Key Laboratory of Advanced Electromagnetic Engineering and Technology, Huazhong University of Science and Technology, No. 1037, Luoyu Road, Wuhan 430074, China

Energies 2018, 11(2), 435; https://doi.org/10.3390/en11020435 - 15 Feb 2018

Cited by 2 | Viewed by 2945

Abstract

The existing optimization approaches regarding network-constrained unit commitment with large wind power integration face great difficulties in reconciling the two crucial but contradictory objectives: computational efficiency and the economy of the solutions. This paper proposes a new network-constrained unit commitment approach, which aims [...] Read more.

The existing optimization approaches regarding network-constrained unit commitment with large wind power integration face great difficulties in reconciling the two crucial but contradictory objectives: computational efficiency and the economy of the solutions. This paper proposes a new network-constrained unit commitment approach, which aims to better achieve these two objectives, by introducing newly proposed reserve models and simplified network constraints. This approach constructs the reserve models based on a sufficiently large number of stochastic wind power scenarios to fully and accurately capture the stochastic characteristics of wind power. These reserve models are directly incorporated into the traditional unit commitment formulation to simultaneously optimize the on/off decision variables and system reserve levels, therefore, this approach can comprehensively evaluate the costs and benefits of the scheduled reserves and thus produce very economical schedule. Meanwhile, these reserve models bring in very little computational burden because they simply consist of a small number of continuous variables and linear constraints. Besides, this approach can evaluate the impact of network congestion on the schedule by just introducing a small number of network constraints that are closely related to network congestion, i.e., the simplified network constraints, and thus concurrently ensures its high computational efficiency. Numerical results show that the proposed approach can produce more economical schedule than stochastic approach and deterministic approach but has similar computational efficiency as the deterministic approach. Full article

(This article belongs to the Section F: Electrical Engineering)

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19 pages, 2380 KiB

Open AccessEditor’s ChoiceArticle

A Fully Three Dimensional Semianalytical Model for Shale Gas Reservoirs with Hydraulic Fractures

by Yuwei Li^1,*,†, Lihua Zuo^2,*,†

, Wei Yu^2,* and Youguang Chen³

¹ Department of Petroleum Engineering, Northeast Petroleum University, Daqing 163318, China

² Harold Vance Department of Petroleum Engineering, Texas A&M University, 3116 TAMU, College Station, TX 77843, USA

³ Department of Petroleum and Geosystems Engineering, University of Texas at Austin, Austin, TX 78705, USA

^† These authors contribute equally to this manuscript.

Energies 2018, 11(2), 436; https://doi.org/10.3390/en11020436 - 15 Feb 2018

Cited by 25 | Viewed by 4402

Abstract

Two challenges exist for modeling gas transport in shale. One is the existence of complex gas transport mechanisms, and the other is the impact of hydraulic fracture networks. In this study, a truly three dimensional semianalytical model was developed for shale gas reservoirs [...] Read more.

Two challenges exist for modeling gas transport in shale. One is the existence of complex gas transport mechanisms, and the other is the impact of hydraulic fracture networks. In this study, a truly three dimensional semianalytical model was developed for shale gas reservoirs with hydraulic fractures of various shapes. Using the instantaneous point source solution, the pressure are solved for a bounded reservoir with fully 3D, partially penetrated hydraulic fractures of different strike angles and dip angles. The fractures could have various shapes such as rectangles, disks and ellipses. The shale gas diffusion equations considers complex transport mechanism such as gas slippage and gas diffusion. This semianalytical model is verified with a commercial software and an analytical method for single fully penetrated rectangle fracture, and the production results of shale gas are consistent. The impacts of fracture height and strike angles are investigated by five systematically constructed models. The comparison shows that the production increases proportionally with the fracture height, and decreases with the increase of strike angles. The method proposed in this study could also be applied in well testing to analyze the reservoir properties and used to forecast the production for tight oil and conventional resources. Full article

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20 pages, 9626 KiB

Open AccessArticle

A Systematic Controller Design for a Grid-Connected Inverter with LCL Filter Using a Discrete-Time Integral State Feedback Control and State Observer

by Seung-Jin Yoon, Ngoc Bao Lai

and Kyeong-Hwa Kim^*

Department of Electrical and Information Engineering, Seoul National University of Science and Technology, 232 Gongneung-ro, Nowon-gu, Seoul 01811, Korea

Energies 2018, 11(2), 437; https://doi.org/10.3390/en11020437 - 16 Feb 2018

Cited by 29 | Viewed by 6127

Abstract

Inductive-capacitive-inductive (LCL)-type filters are currently preferred as a replacement for L-type filters in distributed generation (DG) power systems, due to their superior harmonic attenuation capability. However, the third-order dynamics introduced by LCL filters pose a challenge to design a satisfactory controller for such [...] Read more.

Inductive-capacitive-inductive (LCL)-type filters are currently preferred as a replacement for L-type filters in distributed generation (DG) power systems, due to their superior harmonic attenuation capability. However, the third-order dynamics introduced by LCL filters pose a challenge to design a satisfactory controller for such a system. Conventionally, an LCL-filtered grid-connected inverter can be effectively controlled by using a full-state feedback control. However, this control approach requires the measurement of all system state variables, which brings about more complexity for the inverter system. To address this issue, this paper presents a systematic procedure to design an observer-based integral state feedback control for a LCL-filtered grid-connected inverter in the discrete-time domain. The proposed control scheme consists of an integral state feedback controller and a full-state observer which uses the control input, grid-side currents, and grid voltages to predict all the system state variables. Therefore, only the grid-side current sensors and grid voltage sensors are required to implement the proposed control scheme. Due to the discrete-time integrator incorporated in the state feedback controller, the proposed control scheme ensures both the reference tracking and disturbance rejection performance of the inverter system in a practical and simple way. As a result, superior control performance can be achieved by using the reduced number of sensors, which significantly reduces the cost and complexity of the LCL-filtered grid-connected inverter system in DG applications. To verify the practical usefulness of the proposed control scheme, a 2 kW three-phase prototype grid-connected inverter has been constructed, and the proposed control system has been implemented based on 32-bit floating-point digital signal processor (DSP) TMS320F28335. The effectiveness of the proposed scheme is demonstrated through the comprehensive simulation and experimental results. Full article

(This article belongs to the Special Issue Sustainable and Renewable Energy Systems)

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17 pages, 2827 KiB

Open AccessArticle

Power-Balancing Based Induction Machine Model for Power System Dynamic Analysis in Electromechanical Timescale

by Ding Wang, Xiaoming Yuan^* and Meiqing Zhang

State Key Laboratory of Advanced Electromagnetic Engineering Technology, Huazhong University of Science and Technology, Wuhan 430074, China

Energies 2018, 11(2), 438; https://doi.org/10.3390/en11020438 - 15 Feb 2018

Cited by 14 | Viewed by 4378

Abstract

Power balance, including active and reactive power, between the system supply and the demand from induction motor loads is a potentially necessary condition for system stable operation. Motion of system states depends on the balancing of active and reactive powers. Therefore, this paper [...] Read more.

Power balance, including active and reactive power, between the system supply and the demand from induction motor loads is a potentially necessary condition for system stable operation. Motion of system states depends on the balancing of active and reactive powers. Therefore, this paper proposes an induction machine model in electromechanical timescale from a power balancing viewpoint, in which the induction motor load is modeled as a voltage vector driven by power balancing between the system supply and the demand from induction motor load, so as to describe the dynamic characteristics of induction motor loads in a physical way for power system dynamic analysis. Then a voltage magnitude-phase dynamic analysis with the proposed induction machine model is constructed. Based on the voltage magnitude-phase dynamic analysis, the characteristics of grid-connected induction motor loads are explored, and the instability mechanisms of grid-connected induction motor loads induced by a large disturbance are discussed. It is shown that the dynamic behavior of grid-connected induction motor loads can be described as the dynamic process of the terminal voltage vector driven by coupled active and reactive power balancing in different timescales. In this way, the dynamic behavior of induction motor loads in terms of voltage magnitude-phase dynamics and its physical characteristics are clearly illustrated. Time-domain simulation results are presented to validate the above analyses. Full article

(This article belongs to the Section F: Electrical Engineering)

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12 pages, 1728 KiB

Open AccessArticle

Power Loss Minimization for Transformers Connected in Parallel with Taps Based on Power Chargeability Balance

by Álvaro Jaramillo-Duque^1,*

, Nicolás Muñoz-Galeano¹

, José R. Ortiz-Castrillón¹

, Jesús M. López-Lezama¹

and Ricardo Albarracín-Sánchez²

¹ Research Group in Efficient Energy Management (GIMEL), Universidad de Antioquia, Calle 67 No. 53-108, 050010 Medellín, Colombia

² Departamento de Ingeniería Eléctrica, Electrónica, Automática y Física Aplicada, Escuela Técnica Superior de Ingeniería y Diseño Industrial, Universidad Politécnica de Madrid, Ronda de Valencia 3, 28012 Madrid, Spain

Energies 2018, 11(2), 439; https://doi.org/10.3390/en11020439 - 15 Feb 2018

Cited by 6 | Viewed by 4176

Abstract

In this paper, a model and solution approach for minimizing internal power losses in Transformers Connected in Parallel (TCP) with tap-changers is proposed. The model is based on power chargeability balance and seeks to keep the load voltage within an admissible range. For [...] Read more.

In this paper, a model and solution approach for minimizing internal power losses in Transformers Connected in Parallel (TCP) with tap-changers is proposed. The model is based on power chargeability balance and seeks to keep the load voltage within an admissible range. For achieving this, tap positions are adjusted in such a way that all TCP are set in similar/same power chargeability. The main contribution of this paper is the inclusion of several construction features (rated voltage, rated power, voltage ratio, short-circuit impedance and tap steps) in the minimization of power losses in TCP that are not included in previous works. A Genetic Algorithm (GA) is used for solving the proposed model that is a system of nonlinear equations with discrete decision variables. The GA scans different sets for tap positions with the aim of balancing the power supplied by each transformer to the load. For this purpose, a fitness function is used for minimizing two conditions: The first condition consists on the mismatching between power chargeability for each transformer and a desired chargeability; and the second condition is the mismatching between the nominal load voltage and the load voltage obtained by changing the tap positions. The proposed method is generalized for any given number of TCP and was implemented for three TCP, demonstrating that the power losses are minimized and the load voltage remains within an admissible range. Full article

(This article belongs to the Section F: Electrical Engineering)

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19 pages, 1989 KiB

Open AccessArticle

Adaptive Stabilization and Dynamic Performance Preservation of Cascaded DC-DC Systems by Incorporating Low Pass Filters

by Ahmed Aldhaheri^*,†

and Amir Etemadi^†

¹ Department of Electrical and Computer Engineering, The George Washington University, Washington, DC 20052, USA

^† These authors contributed equally to this work.

Energies 2018, 11(2), 440; https://doi.org/10.3390/en11020440 - 15 Feb 2018

Cited by 3 | Viewed by 3214

Abstract

This paper proposes a method to stabilize and enhance the dynamic performance of a cascaded DC-DC system by adaptively reshaping the source output impedance. The method aims to reduce the ratio of the source output impedance to the load input impedance, referred to [...] Read more.

This paper proposes a method to stabilize and enhance the dynamic performance of a cascaded DC-DC system by adaptively reshaping the source output impedance. The method aims to reduce the ratio of the source output impedance to the load input impedance, referred to as the minor loop gain, to eliminate the interaction between the load and the source systems. This interaction can deteriorate the dynamic performance or might lead to instability. Thus, the bus current is used to improve the dynamic performance by reducing the magnitude of the source’s output impedance adaptively according to the loading condition such that the dynamic performance is consistently improved. Utilizing the bus current facilitates the compatibility between the proposed controller and most widely used DC-DC converters controlled in voltage mode, including non-minimum phase converters. In addition to the flexibility the bus current provides to embed the proposed solution with conventional control schemes. Experimental results have validated the effectiveness of the proposed controller along with time-based simulation and theoretical analysis, for minimum and non-minimum phase converters. Full article

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15 pages, 1222 KiB

Open AccessArticle

A Novel Stochastic-Programming-Based Energy Management System to Promote Self-Consumption in Industrial Processes

by Jorge Barrientos¹, José David López¹

and Felipe Valencia^2,*

¹ SISTEMIC, Engineering Faculty, Universidad de Antioquia UDEA, Calle 70 No 52-21, 1226 Medellín, Colombia

² Energy Center, Faculty of Mathematical and Physical Sciences, University of Chile, 8370451 Santiago, Chile

Energies 2018, 11(2), 441; https://doi.org/10.3390/en11020441 - 15 Feb 2018

Cited by 4 | Viewed by 3361

Abstract

The introduction of non-conventional energy sources (NCES) to industrial processes is a viable alternative to reducing the energy consumed from the grid. However, a robust coordination of the local energy resources with the power imported from the distribution grid is still an open [...] Read more.

The introduction of non-conventional energy sources (NCES) to industrial processes is a viable alternative to reducing the energy consumed from the grid. However, a robust coordination of the local energy resources with the power imported from the distribution grid is still an open issue, especially in countries that do not allow selling energy surpluses to the main grid. In this paper, we propose a stochastic-programming-based energy management system (EMS) focused on self-consumption that provides robustness to both sudden NCES or load variations, while preventing power injection to the main grid. The approach is based on a finite number of scenarios that combines a deterministic structure based on spectral analysis and a stochastic model that represents variability. The parameters to generate these scenarios are updated when new information arrives. We tested the proposed approach with data from a copper extraction mining process. It was compared to a traditional EMS with perfect prediction, i.e., a best case scenario. Test results show that the proposed EMS is comparable to the EMS with perfect prediction in terms of energy imported from the grid (slightly higher), but with less power changes in the distribution side and enhanced dynamic response to transients of wind power and load. This improvement is achieved with a non-significant computational time overload. Full article

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15 pages, 2346 KiB

Open AccessArticle

Thermal Assessment of a Novel Combine Evaporative Cooling Wind Catcher

by Azam Noroozi^* and Yannis S. Veneris

School of Architecture, National Technical University of Athens, Section III, 42 Patission Av., 10682 Athens, Greece

Energies 2018, 11(2), 442; https://doi.org/10.3390/en11020442 - 15 Feb 2018

Cited by 16 | Viewed by 9788

Abstract

Wind catchers are one of the oldest cooling systems that are employed to provide sufficient natural ventilation in buildings. In this study, a laboratory scale wind catcher was equipped with a combined evaporative system. The designed assembly was comprised of a one-sided opening [...] Read more.

Wind catchers are one of the oldest cooling systems that are employed to provide sufficient natural ventilation in buildings. In this study, a laboratory scale wind catcher was equipped with a combined evaporative system. The designed assembly was comprised of a one-sided opening with an adjustable wetted pad unit and a wetted blades section. Theoretical analysis of the wind catcher was carried out and a set of experiments were organized to validate the results of the obtained models. The effect of wind speed, wind catcher height, and mode of the opening unit (open or closed) was investigated on temperature drop and velocity of the moving air through the wind catcher as well as provided sensible cooling load. The results showed that under windy conditions, inside air velocity was slightly higher when the pad was open. Vice versa, when the wind speed was zero, the closed pad resulted in an enhancement in air velocity inside the wind catcher. At wind catcher heights of 2.5 and 3.5 m and wind speeds of lower than 3 m/s, cooling loads have been approximately doubled by applying the closed-pad mode. Full article

(This article belongs to the Special Issue Building Energy Use: Modeling and Analysis)

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21 pages, 6503 KiB

Open AccessArticle

PWM Carrier Displacement in Multi-N-Phase Drives: An Additional Degree of Freedom to Reduce the DC-Link Stress

by Michela Diana^†, Riccardo Ruffo^† and Paolo Guglielmi^*,†

¹ Dipartimento Energia, Politecnico di Torino, 10129 Torino, Italy

^† These authors contributed equally to this work.

Energies 2018, 11(2), 443; https://doi.org/10.3390/en11020443 - 16 Feb 2018

Cited by 9 | Viewed by 5416

Abstract

The paper presents a particular Pulse Width Modulation (PWM) strategy to reduce the (Direct Current) DC-link capacitor stress for multi-n-phase drives. A multi-n-phase drive is composed of multiple independent systems of n inverter supplying a multi-n-phase electric machine. The paper focused on the [...] Read more.

The paper presents a particular Pulse Width Modulation (PWM) strategy to reduce the (Direct Current) DC-link capacitor stress for multi-n-phase drives. A multi-n-phase drive is composed of multiple independent systems of n inverter supplying a multi-n-phase electric machine. The paper focused on the investigation of the best phase shifting between carriers for a triple-3-phase drive compared to the 3-phase counterpart in order to reduce the capacitor bench design point. Simulation and experimental results show as the control technique proposed is able to reduce the value of the DC-link capacitor current in any operating condition including fault case. In this sense, the PWM carrier displacement appears like an additional degree of freedom that can be exploited in multi-n-phase drives but also in multi-motor application. Full article

(This article belongs to the Special Issue Emerging Power Electronics Technologies for Power Systems and Machine Drives)

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14 pages, 6392 KiB

Open AccessFeature PaperArticle

Analysis of Air-Side Economizers in Terms of Cooling-Energy Performance in a Data Center Considering Exhaust Air Recirculation

by Seonghyun Park¹

and Janghoo Seo^2,*

¹ Department of Architecture, Graduated School, Kookmin University, 77 Jeongneung-ro, Seongbuk-gu, Seoul 02707, Korea

² School of Architecture, Kookmin University, 77 Jeongneung-ro, Seongbuk-gu, Seoul 02707, Korea

Energies 2018, 11(2), 444; https://doi.org/10.3390/en11020444 - 17 Feb 2018

Cited by 13 | Viewed by 6333

Abstract

Demand is soaring for data centers with advanced data-processing capabilities. In data centers with high-temperature information technology (IT) equipment, enormous cooling systems are operated year-round. To date, studies have aimed to improve the cooling efficiency of server-room units, but cooling-energy-consumption analysis considering the [...] Read more.

Demand is soaring for data centers with advanced data-processing capabilities. In data centers with high-temperature information technology (IT) equipment, enormous cooling systems are operated year-round. To date, studies have aimed to improve the cooling efficiency of server-room units, but cooling-energy-consumption analysis considering the recirculation of exhaust air (EA) has not been researched to a sufficient degree. This study analyzed the cooling-energy saving effects considering the EA-recirculation and supply-air (SA)-temperature conditions when direct and indirect air-side economizers were applied to a data center in Korea. Thirteen case studies were conducted. The results showed that when the EA-recirculation ratio in the direct air-side economizer was 15%, its annual cooling-energy consumption increased by approximately 6.1% compared to the case with no recirculation. The indirect air-side economizer also exhibited an approximately 9% increase in cooling-energy consumption. On the other hand, when the SA temperature changed to 22 °C, the annual cooling-energy consumption of the direct and indirect air-side economizers decreased by approximately 67% and 55%, respectively, compared to a central chilled-water system. This indicates the importance of developing measures to prevent EA recirculation and of securing a wind path for the improvement of air-conditioning efficiency in data centers at the design stage. Full article

(This article belongs to the Section F: Electrical Engineering)

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24 pages, 789 KiB

Open AccessArticle

A General Mathematical Formulation for Winding Layout Arrangement of Electrical Machines

by Massimo Caruso¹

, Antonino Oscar Di Tommaso^1,*

, Fabrizio Marignetti²

, Rosario Miceli¹

and Giuseppe Ricco Galluzzo¹

¹ Department of Energy, Information Engineering and Mathematical Models (DEIM), University of Palermo, viale delle Scienze, Building nr. 9, 90128 Palermo, Italy

² Department of Electrical and Information Engineering (DIEI), University of Cassino and South Lazio, via G. Di Biasio, 43, 03043 Cassino, Italy

Energies 2018, 11(2), 446; https://doi.org/10.3390/en11020446 - 17 Feb 2018

Cited by 44 | Viewed by 13443

Abstract

Winding design methods have been a subject of research for many years of the past century. Many methods have been developed, each one characterized by some advantages and drawbacks. Nowadays, the star of slots is the most widespread design tool for electrical machine [...] Read more.

Winding design methods have been a subject of research for many years of the past century. Many methods have been developed, each one characterized by some advantages and drawbacks. Nowadays, the star of slots is the most widespread design tool for electrical machine windings. In this context, this paper presents a simple and effective procedure to determine the distribution of the slot EMFs over the phases and of the winding configuration in all possible typologies of electrical machines equipped with symmetrical windings. The result of this procedure gives a Winding Distribution Table (WDT), which can be used to define coils and coil groups connections and also to simply implement winding optimizations techniques, such as zone widening, imbrication, etc. Moreover, this procedure can be easily implemented on a computer in order to perform automated winding designs for rotating electrical machines. Several examples are provided in order to validate the proposed procedure. Full article

(This article belongs to the Section I: Energy Fundamentals and Conversion)

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13 pages, 3767 KiB

Open AccessArticle

Prediction Model of Photovoltaic Module Temperature for Power Performance of Floating PVs

by Waithiru Charles Lawrence Kamuyu¹

, Jong Rok Lim¹, Chang Sub Won² and Hyung Keun Ahn^1,*

¹ Konkuk University, 120 Neungdong-Ro, Gwanjin-Gu, Seoul 143-701, Korea

² LSIS R&D Campus 116 beongil 40 Anyang, Gyeonggi 431-831, Korea

Energies 2018, 11(2), 447; https://doi.org/10.3390/en11020447 - 18 Feb 2018

Cited by 168 | Viewed by 11448

Abstract

Rapid reduction in the price of photovoltaic (solar PV) cells and modules has resulted in a rapid increase in solar system deployments to an annual expected capacity of 200 GW by 2020. Achieving high PV cell and module efficiency is necessary for many [...] Read more.

Rapid reduction in the price of photovoltaic (solar PV) cells and modules has resulted in a rapid increase in solar system deployments to an annual expected capacity of 200 GW by 2020. Achieving high PV cell and module efficiency is necessary for many solar manufacturers to break even. In addition, new innovative installation methods are emerging to complement the drive to lower $/W PV system price. The floating PV (FPV) solar market space has emerged as a method for utilizing the cool ambient environment of the FPV system near the water surface based on successful FPV module (FPVM) reliability studies that showed degradation rates below 0.5% p.a. with new encapsulation material. PV module temperature analysis is another critical area, governing the efficiency performance of solar cells and module. In this paper, data collected over five-minute intervals from a PV system over a year is analyzed. We use MATLAB to derived equation coefficients of predictable environmental variables to derive FPVM’s first module temperature operation models. When comparing the theoretical prediction to real field PV module operation temperature, the corresponding model errors range between 2% and 4% depending on number of equation coefficients incorporated. This study is useful in validation results of other studies that show FPV systems producing 10% more energy than other land based systems. Full article

(This article belongs to the Special Issue PV System Design and Performance)

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15 pages, 245 KiB

Open AccessArticle

The Share Price and Investment: Current Footprints for Future Oil and Gas Industry Performance

by Ionel Jianu^*

and Iulia Jianu

Department of Accounting and Audit, The Bucharest University of Economic Studies, Romana Square, No. 6, 010374 Bucharest, Romania

Energies 2018, 11(2), 448; https://doi.org/10.3390/en11020448 - 19 Feb 2018

Cited by 16 | Viewed by 5910

Abstract

The share price has become a very important indicator for shareholders, banks, and financial institutions evaluating the performance of companies. The oil and gas industry seems to be in a difficult era of development, due to the market prices for its products. Moreover, [...] Read more.

The share price has become a very important indicator for shareholders, banks, and financial institutions evaluating the performance of companies. The oil and gas industry seems to be in a difficult era of development, due to the market prices for its products. Moreover, climate change and renewable energies are barriers for fossil energy. This state of affairs, and the fact that oil and gas shares are considered one of the most solid and reliable shares on the London Stock Exchange (LSE), have drawn our attention. International institutions encourage the investment in the oil and gas economic sector. This study investigates how investments of oil and gas companies in long-term assets influence the share price. Using the Ohlson share price model for a sample of 51 listed companies on the LSE proves that investments in long-term assets influence the share price in the case of companies which record losses. Investments in long-term assets are responsible for the attractiveness of the oil and gas company shares. Full article

14 pages, 3002 KiB

Open AccessArticle

Energy Analysis of a Rotary Drum Bioreactor for Composting Tomato Plant Residues

by Fahad N. Alkoaik^1,*, Ahmed M. Abdel-Ghany¹

, Mohamed A. Rashwan^1,2, Ronnel B. Fulleros¹

and Mansour N. Ibrahim¹

¹ Department of Agricultural Engineering, College of Food and Agriculture Sciences, King Saud University, Riyadh 11451, Saudi Arabia

² Department of Agriculture and Biosystems Engineering, Faculty of Agriculture, Alexandria University, Alexandria 21526, Egypt

Energies 2018, 11(2), 449; https://doi.org/10.3390/en11020449 - 19 Feb 2018

Cited by 28 | Viewed by 9202

Abstract

Energy produced from plant residue composting has stimulated great interest in heat recovery and utilization. Composting is an exothermic process often controlled through temperature measurements. However, energy analysis of the overall composting system, especially the rotary bioreactors, is generally not well known and [...] Read more.

Energy produced from plant residue composting has stimulated great interest in heat recovery and utilization. Composting is an exothermic process often controlled through temperature measurements. However, energy analysis of the overall composting system, especially the rotary bioreactors, is generally not well known and very limited. This study presents detailed energy analysis in a laboratory-scale, batch-operated, rotary bioreactor used for composting tomato plant residues. The bioreactor was considered as a thermodynamic system operating under unsteady state conditions. The composting process was described, the input generated and lost energy terms as well as the relative importance of each term were quantitatively evaluated, and the composting phases were clearly identified. Results showed that the compost temperature peaked at 72 h of operation reaching 66.7 °C with a heat generation rate of 9.3 W·kg⁻¹ of organic matter. During the composting process, the accumulated heat generation was 1.9 MJ·kg⁻¹of organic matter; only 4% of this heat was gained by the composting material, and 96% was lost outside the bioreactor. Contributions of thermal radiation, aeration, cylindrical, and side-walls surfaces of the reactor on the total heat loss were 1%, 2%, 69%, and 28%, respectively. The information obtained is applicable in the design, management, and control of composting operations and in improvement of bioreactor effectiveness and productivity. Full article

(This article belongs to the Collection Bioenergy and Biofuel)

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13 pages, 1345 KiB

Open AccessArticle

Hydrothermal Disintegration and Extraction of Different Microalgae Species

by Michael Kröger^1,*, Marco Klemm¹ and Michael Nelles^1,2

¹ Deutsches Biomasseforschungszentrum gemeinnützige GmbH, Biorefineries Department, Torgauer Straße 116, 04347 Leipzig, Germany

² Faculty of Agricultural and Environmental Sciences, Chair ofWaste Management, University of Rostock, Justus-von-Liebig-Weg 6, 18059 Rostock, Germany

Energies 2018, 11(2), 450; https://doi.org/10.3390/en11020450 - 20 Feb 2018

Cited by 35 | Viewed by 6883

Abstract

For the disintegration and extraction of microalgae to produce lipids and biofuels, a novel processing technology was investigated. The utilization of a hydrothermal treatment was tested on four different microalgae species (Scenedesmus rubescens, Chlorella vulgaris, Nannochloropsis oculata and Arthorspira platensis (Spirulina)) [...] Read more.

For the disintegration and extraction of microalgae to produce lipids and biofuels, a novel processing technology was investigated. The utilization of a hydrothermal treatment was tested on four different microalgae species (Scenedesmus rubescens, Chlorella vulgaris, Nannochloropsis oculata and Arthorspira platensis (Spirulina)) to determine whether it has an advantage in comparison to other disintegration methods for lipid extraction. It was shown, that hydrothermal treatment is a reasonable opportunity to utilize microalgae without drying and increase the lipid yield of an algae extraction process. For three of the four microalgae species, the extraction yield with a prior hydrothermal treatment elevated the lipid yield up to six times in comparison to direct extraction. Only Scenedesmus rubescens showed a different behaviour. Reason can be found in the different cell wall of the species. The investigation of the differences in cell wall composition of the used species indicate that the existence of algaenan as a cell wall compound plays a major role in stability. Full article

(This article belongs to the Collection Bioenergy and Biofuel)

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14 pages, 1680 KiB

Open AccessArticle

A Comprehensive Energy Analysis and Related Carbon Footprint of Dairy Farms, Part 1: Direct Energy Requirements

by Giuseppe Todde^*

, Lelia Murgia, Maria Caria

and Antonio Pazzona

Department of Agricultural Science, University of Sassari, Viale Italia 39, 07100 Sassari, Italy

Energies 2018, 11(2), 451; https://doi.org/10.3390/en11020451 - 20 Feb 2018

Cited by 24 | Viewed by 5696

Abstract

Dairy cattle farms are continuously developing more intensive systems of management which require higher utilization of durable and not-durable inputs. These inputs are responsible of significant direct and indirect fossil energy requirements which are related to remarkable emissions of CO₂. This [...] Read more.

Dairy cattle farms are continuously developing more intensive systems of management which require higher utilization of durable and not-durable inputs. These inputs are responsible of significant direct and indirect fossil energy requirements which are related to remarkable emissions of CO₂. This study aims to analyze direct energy requirements and the related carbon footprint of a large population of conventional dairy farms located in the south of Italy. A detailed survey of electricity, diesel and Liquefied Petroleum Gas (LPG) consumptions has been carried out among on-farm activities. The results of the analyses showed an annual average fuel consumption of 40 kg per tonne of milk, while electricity accounted for 73 kWh per tonne of milk produced. Expressing the direct energy inputs as primary energy, diesel fuel results the main resource used in on-farm activities, accounting for 72% of the total fossil primary energy requirement, while electricity represents only 27%. Moreover, larger farms were able to use more efficiently the direct energy inputs and reduce the related emissions of carbon dioxide per unit of milk produced, since the milk yield increases with the herd size. The global average farm emissions of carbon dioxide equivalent, due to all direct energy usages, accounted for 156 kg CO₂-eq per tonne of Fat and Protein Corrected Milk (FPCM), while farms that raise more than 200 heads emitted 36% less than the average value. In this two-part series, the total energy demand (Part 1 + Part 2) per farm is mainly due to agricultural inputs and fuel consumption, which have the largest quota of the annual requirements for each milk yield class. These results also showed that large size farms held lower CO₂-eq emissions when referred to the mass of milk produced. Full article

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26 pages, 7908 KiB

Open AccessArticle

Big Data Mining of Energy Time Series for Behavioral Analytics and Energy Consumption Forecasting

by Shailendra Singh^*

and Abdulsalam Yassine

Department of Software Engineering at Lakehead Univerity, Thunder Bay, ON, P7B 5E1, Canada

Energies 2018, 11(2), 452; https://doi.org/10.3390/en11020452 - 20 Feb 2018

Cited by 197 | Viewed by 17959

Abstract

Responsible, efficient and environmentally aware energy consumption behavior is becoming a necessity for the reliable modern electricity grid. In this paper, we present an intelligent data mining model to analyze, forecast and visualize energy time series to uncover various temporal energy consumption patterns. [...] Read more.

Responsible, efficient and environmentally aware energy consumption behavior is becoming a necessity for the reliable modern electricity grid. In this paper, we present an intelligent data mining model to analyze, forecast and visualize energy time series to uncover various temporal energy consumption patterns. These patterns define the appliance usage in terms of association with time such as hour of the day, period of the day, weekday, week, month and season of the year as well as appliance-appliance associations in a household, which are key factors to infer and analyze the impact of consumers’ energy consumption behavior and energy forecasting trend. This is challenging since it is not trivial to determine the multiple relationships among different appliances usage from concurrent streams of data. Also, it is difficult to derive accurate relationships between interval-based events where multiple appliance usages persist for some duration. To overcome these challenges, we propose unsupervised data clustering and frequent pattern mining analysis on energy time series, and Bayesian network prediction for energy usage forecasting. We perform extensive experiments using real-world context-rich smart meter datasets. The accuracy results of identifying appliance usage patterns using the proposed model outperformed Support Vector Machine (SVM) and Multi-Layer Perceptron (MLP) at each stage while attaining a combined accuracy of 81.82%, 85.90%, 89.58% for 25%, 50% and 75% of the training data size respectively. Moreover, we achieved energy consumption forecast accuracies of 81.89% for short-term (hourly) and 75.88%, 79.23%, 74.74%, and 72.81% for the long-term; i.e., day, week, month, and season respectively. Full article

(This article belongs to the Special Issue Data Science and Big Data in Energy Forecasting)

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23 pages, 8154 KiB

Open AccessArticle

Insights into Dynamic Tuning of Magnetic-Resonant Wireless Power Transfer Receivers Based on Switch-Mode Gyrators

by Mohamed Saad^* and Eduard Alarcón

Department of Electronics Engineering, Technical University of Catalonia UPC, 08034 Barcelona, Spain

Energies 2018, 11(2), 453; https://doi.org/10.3390/en11020453 - 20 Feb 2018

Cited by 8 | Viewed by 5883

Abstract

Magnetic-resonant wireless power transfer (WPT) has become a reliable contactless source of power for a wide range of applications. WPT spans different power levels ranging from low-power implantable devices up to high-power electric vehicles (EV) battery charging. The transmission range and efficiency of [...] Read more.

Magnetic-resonant wireless power transfer (WPT) has become a reliable contactless source of power for a wide range of applications. WPT spans different power levels ranging from low-power implantable devices up to high-power electric vehicles (EV) battery charging. The transmission range and efficiency of WPT have been reasonably enhanced by resonating the transmitter and receiver coils at a common frequency. Nevertheless, matching between resonance in the transmitter and receiver is quite cumbersome, particularly in single-transmitter multi-receiver systems. The resonance frequency in transmitter and receiver tank circuits has to be perfectly matched, otherwise power transfer capability is greatly degraded. This paper discusses the mistuning effect of parallel-compensated receivers, and thereof a novel dynamic frequency tuning method and related circuit topology and control is proposed and characterized in the system application. The proposed method is based on the concept of switch-mode gyrator emulating variable lossless inductors oriented to enable self-tunability in WPT receivers. Full article

(This article belongs to the Special Issue Wireless Power Transfer and Energy Harvesting Technologies)

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14 pages, 3272 KiB

Open AccessArticle

Optimal Capacity Configuration of a Hybrid Energy Storage System for an Isolated Microgrid Using Quantum-Behaved Particle Swarm Optimization

by Hui Wang^1,*, Tengxin Wang¹

, Xiaohan Xie², Zhixiang Ling², Guoliang Gao² and Xu Dong²

¹ School of Electrical Engineering, Shandong University, 17923 Jingshi Road, Jinan, Shandong 250061, China

² State Grid Jinan Power Supply Company, 238 Luoyuan Street Road, Jinan, Shandong 250012, China

Energies 2018, 11(2), 454; https://doi.org/10.3390/en11020454 - 21 Feb 2018

Cited by 35 | Viewed by 4593

Abstract

The capacity of an energy storage device configuration not only affects the economic operation of a microgrid, but also affects the power supply’s reliability. An isolated microgrid is considered with typical loads, renewable energy resources, and a hybrid energy storage system (HESS) composed [...] Read more.

The capacity of an energy storage device configuration not only affects the economic operation of a microgrid, but also affects the power supply’s reliability. An isolated microgrid is considered with typical loads, renewable energy resources, and a hybrid energy storage system (HESS) composed of batteries and ultracapacitors in this paper. A quantum-behaved particle swarm optimization (QPSO) algorithm that optimizes the HESS capacity is used. Based on the respective power compensation capabilities of ultracapacitors and batteries, a rational energy scheduling strategy is proposed using the principle of a low-pass filter and can help to avoid frequent batteries charging and discharging. Considering the rated power of each energy storage type, the respective compensation power is corrected. By determining whether the charging state reaches the limit, the value is corrected again. Additionally, a mathematical model that minimizes the daily cost of the HESS is derived. This paper takes an isolated micrgrid in north China as an example to verify the effectiveness of this method. The comparison between QPSO and a traditional particle swarm algorithm shows that QPSO can find the optimal solution faster and the HESS has lower daily cost. Simulation results for an isolated microgrid verified the effectiveness of the HESS optimal capacity configuration method. Full article

(This article belongs to the Section D: Energy Storage and Application)

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26 pages, 9904 KiB

Open AccessArticle

Height Adjustment of Vehicles Based on a Static Equilibrium Position State Observation Algorithm

by Zepeng Gao¹, Sizhong Chen¹, Yuzhuang Zhao^1,* and Jinrui Nan²

¹ Automotive Research Institute, School of Mechanical Engineering, Institute of Technology (BIT), 5 South Zhongguancun Street, Haidian District, Beijing 100081, China

² National Engineering Laboratory for Electric Vehicles and Collaborative Innovation Center of Electric Vehicles in Beijing, Beijing Institute of Technology (BIT), 5 South Zhongguancun Street, Haidian District, Beijing 100081, China

Energies 2018, 11(2), 455; https://doi.org/10.3390/en11020455 - 21 Feb 2018

Cited by 14 | Viewed by 5694

Abstract

In this paper, a static state observer algorithm based on the static equilibrium position is proposed, which can realize accurate control of electric vehicle height adjustment with existing road excitation. The existence of road excitation can lead to deflection variation of the electronically [...] Read more.

In this paper, a static state observer algorithm based on the static equilibrium position is proposed, which can realize accurate control of electric vehicle height adjustment with existing road excitation. The existence of road excitation can lead to deflection variation of the electronically controlled air suspension (ECAS). The use of only dynamic deflection as the reference for the electric vehicle height adjustment will produce great errors. Therefore, this paper provides an observation algorithm, which can realize the accurate control of vehicle height. Firstly, the static equilibrium position equation of suspension is derived according to the theory of hydrodynamics and characteristics of pneumatic chamber. Secondly, a vehicle dynamics model with seven degrees of freedom (7-DOF) is established and the kinetic equations are discretized. Then, the unscented Kalman filter (UKF) algorithm is used to obtain the static equilibrium position of vehicle. According to the vehicle static equilibrium position obtained by UKF, the height of the vehicle is adjusted by using a fuzzy controller. The simulation and experimental results show that this proposed algorithm can realize the control of vehicle height with an accuracy of over 96%, which ensures the excellent driving performance of vehicles under different road conditions. Full article

(This article belongs to the Special Issue The International Symposium on Electric Vehicles (ISEV2017))

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16 pages, 5498 KiB

Open AccessArticle

Experimental and Numerical Vibrational Analysis of a Horizontal-Axis Micro-Wind Turbine

by Francesco Castellani^*, Davide Astolfi, Matteo Becchetti, Francesco Berno, Filippo Cianetti

and Alessandro Cetrini

Department of Engineering, University of Perugia, Via G. Duranti 93, 06125 Perugia, Italy

Energies 2018, 11(2), 456; https://doi.org/10.3390/en11020456 - 22 Feb 2018

Cited by 31 | Viewed by 6100

Abstract

Micro-wind turbines are energy conversion technologies strongly affected by fatigue, as a result of their size and the variability of loads, induced by the unsteady wind conditions, and modulated by a very high rotational speed. This work is devoted to the experimental and [...] Read more.

Micro-wind turbines are energy conversion technologies strongly affected by fatigue, as a result of their size and the variability of loads, induced by the unsteady wind conditions, and modulated by a very high rotational speed. This work is devoted to the experimental and numerical characterization of the aeroelastic behavior of a test-case horizontal-axis wind turbine (HAWT) with a 2 m rotor diameter and a maximum power production of 3 kW. The experimental studies have been conducted at the wind tunnel of the University of Perugia and consisted of accelerometer measurements at the tower and the tail fin. The numerical setup was the Fatigue, Aerodynamics, Structures, and Turbulence (FAST) code for aeroelastic simulations, which was fed as input with the same wind conditions employed in the wind tunnel tests. The experimental and numerical analyses were coupled with the perspective of establishing a reciprocal feedback, and this has been accomplished. On one hand, the numerical model is important for interpreting the measured spectrum of tower oscillations and, for example, inspires the detection of a mass unbalance at the blades. On the other hand, the measurements inspire the question of how to interpret the interaction between the blades and the tower. The experimental spectrum of tail fin vibrations indicates that secondary elements, in terms of weight, can also transmit to the tower, giving meaningful contributions to the vibration spectra. Therefore, an integrated numerical and experimental approach is not only valuable but is also unavoidable, to fully characterize the dynamics of small wind-energy conversion systems. Full article

(This article belongs to the Special Issue Wind Turbine Loads and Wind Plant Performance)

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21 pages, 22211 KiB

Open AccessArticle

Suitability Evaluation of Specific Shallow Geothermal Technologies Using a GIS-Based Multi Criteria Decision Analysis Implementing the Analytic Hierarchic Process

by Francesco Tinti^*

, Sara Kasmaee, Mohamed Elkarmoty

, Stefano Bonduà

and Villiam Bortolotti

Department of Civil, Chemical, Environmental and Materials Engineering, University of Bologna, via Terracini 28, 40131 Bologna, Italy

Energies 2018, 11(2), 457; https://doi.org/10.3390/en11020457 - 22 Feb 2018

Cited by 38 | Viewed by 7493

Abstract

The exploitation potential of shallow geothermal energy is usually defined in terms of site-specific ground thermal characteristics. While true, this assumption limits the complexity of the analysis, since feasibility studies involve many other components that must be taken into account when calculating the [...] Read more.

The exploitation potential of shallow geothermal energy is usually defined in terms of site-specific ground thermal characteristics. While true, this assumption limits the complexity of the analysis, since feasibility studies involve many other components that must be taken into account when calculating the effective market viability of a geothermal technology or the economic value of a shallow geothermal project. In addition, the results of a feasibility study are not simply the sum of the various factors since some components may be conflicting while others will be of a qualitative nature only. Different approaches are therefore needed to evaluate the suitability of an area for shallow geothermal installation. This paper introduces a new GIS platform-based multicriteria decision analysis method aimed at comparing as many different shallow geothermal relevant factors as possible. Using the Analytic Hierarchic Process Tool, a geolocalized Suitability Index was obtained for a specific technological case: the integrated technologies developed within the GEOTeCH Project. A suitability map for the technologies in question was drawn up for Europe. Full article

(This article belongs to the Special Issue Geothermal Heating and Cooling)

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16 pages, 6681 KiB

Open AccessArticle

Selective Harmonic Elimination in a Wide Modulation Range Using Modified Newton–Raphson and Pattern Generation Methods for a Multilevel Inverter

by Mohammed Al-Hitmi¹, Salman Ahmad², Atif Iqbal^1,*

, Sanjeevikumar Padmanaban³

and Imtiaz Ashraf²

¹ Department of Electrical Engineering, Qatar University, Doha Post Box No. 2713, Qatar

² Department of Electrical Engineering, Aligarh Muslim University, Aligarh 202002, India

³ Department of Energy Technology, Aalborg University, 6700 Esbjerg, Denmark

Energies 2018, 11(2), 458; https://doi.org/10.3390/en11020458 - 22 Feb 2018

Cited by 47 | Viewed by 6135

Abstract

Considering the aim of having low switching losses, especially in medium-voltage and high-power converters, the pre-programmed pulse width modulation technique is very useful because the generated harmonic content can be known in advance and optimized. Among the different low switching frequency techniques, the [...] Read more.

Considering the aim of having low switching losses, especially in medium-voltage and high-power converters, the pre-programmed pulse width modulation technique is very useful because the generated harmonic content can be known in advance and optimized. Among the different low switching frequency techniques, the Selective Harmonics Elimination (SHE) modulation method is most suitable because of its direct control over the harmonic spectrum. This paper proposes a method for obtaining multiple solutions for selectively eliminating specific harmonics in a wide range of modulation indices by using modified Newton–Raphson (NR) and pattern generation techniques. The different pattern generation and synthesis approach provide more degrees of freedom and a way to operate the converter in a wide range of modulation. The modified Newton–Raphson technique is not complex and ensures fast convergence on a solution. Moreover, multiple solutions are obtained by keeping a very small increase in the modulation index. In the previous methods, solutions were not obtainable at all modulation indices. In this paper, only exact solutions to the low-order harmonics elimination for Cascaded H-bridge inverter are reported for all modulation indices. Analytical and simulation results prove the robustness and correctness of the technique proposed in this paper. Full article

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17 pages, 16671 KiB

Open AccessArticle

Real-Time Genetic Algorithms-Based MPPT: Study and Comparison (Theoretical an Experimental) with Conventional Methods

by Slimane Hadji^1,*

, Jean-Paul Gaubert²

and Fateh Krim³

¹ Electronic Department, University of Setif, Setif 19000, Algeria

² LIAS Laboratory ENSIP, University of Poitiers, 86000 Poitiers, France

³ LEPCI Laboratory, University of Setif, Setif 19000, Algeria

Energies 2018, 11(2), 459; https://doi.org/10.3390/en11020459 - 22 Feb 2018

Cited by 106 | Viewed by 7695

Abstract

Maximum Power Point Tracking (MPPT) methods are used in photovoltaic (PV) systems to continually maximize the PV array output power, which strongly depends on both solar radiation and cell temperature. The PV power oscillations around the maximum power point (MPP) resulting from the [...] Read more.

Maximum Power Point Tracking (MPPT) methods are used in photovoltaic (PV) systems to continually maximize the PV array output power, which strongly depends on both solar radiation and cell temperature. The PV power oscillations around the maximum power point (MPP) resulting from the conventional methods and complexity of the non-conventional ones are convincing reasons to look for novel MPPT methods. This paper deals with simple Genetic Algorithms (GAs) based MPPT method in order to improve the convergence, rapidity, and accuracy of the PV system. The proposed method can also efficiently track the global MPP, which is very useful for partial shading. At first, a review of the algorithm is given, followed with many test examples; then, a comparison by means Matlab/Simulink© (R2009b) is conducted between the proposed MPPT and, the popular Perturb and Observe (PO) and Incremental Conductance (IC) techniques. The results show clearly the superiority of the proposed controller. Indeed, with the proposed algorithm, oscillations around the MPP are dramatically minimized, a better stability is observed and increase in the output power efficiency is obtained. All these results are experimentally validated by a test bench developed at LIAS laboratory (Poitiers University, Poitiers, France) using real PV panels and a PV emulator which allows one to define a profile insolation model. In addition, the proposed method permits one to perform the test of linearity between the optimal current

I_{mp}

(current at maximum power) and the short-circuit current

I_{sc}

, and between the optimal voltage

V_{mp}

and open-circuit voltage

V_{oc}

, so the current and voltage factors can be easily obtained with our algorithm. Full article

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14 pages, 5051 KiB

Open AccessFeature PaperArticle

Estimation of Effective Diffusion Coefficient of O₂ in Ash Layer in Underground Coal Gasification by Thermogravimetric Apparatus

by Xi Lin, Qingya Liu and Zhenyu Liu^*

Beijing Advanced Innovation Center for Soft Matter Science and Engineering, and State Key Laboratory of Chemical Resource Engineering, Beijing University of Chemical Technology, Beijing 100029, China

Energies 2018, 11(2), 460; https://doi.org/10.3390/en11020460 - 22 Feb 2018

Cited by 4 | Viewed by 4567

Abstract

Underground coal gasification (UCG) proceeds generally in the presence of an ash layer on coal (or char) surface. The ash layer increases the mass transfer resistance of O₂ to the gasification surface, which may become the limiting step of whole process. This [...] Read more.

Underground coal gasification (UCG) proceeds generally in the presence of an ash layer on coal (or char) surface. The ash layer increases the mass transfer resistance of O₂ to the gasification surface, which may become the limiting step of whole process. This paper studies O₂ diffusion in ash layer formed on cylindrical char samples using a specially designed one-dimension setup in a thermogravimetric apparatus (TGA). The effective internal diffusion coefficient (D_e) is found to increase with an increase in ash layer thickness, due to an increase in median pore diameter. Methods are established to correlate D_e with operating conditions and to estimate the role of internal diffusion resistance in overall mass transfer resistance. Full article

(This article belongs to the Special Issue Biomass Chars: Elaboration, Characterization and Applications Ⅱ)

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31 pages, 13279 KiB

Open AccessArticle

A Steady-State Analysis Method for Modular Multilevel Converters Connected to Permanent Magnet Synchronous Generator-Based Wind Energy Conversion Systems

by Zhijie Liu¹, Kejun Li^1,*, Yuanyuan Sun¹, Jinyu Wang², Zhuodi Wang¹, Kaiqi Sun¹ and Meiyan Wang¹

¹ School of Electrical Engineering, Shandong University, Shandong 250061, China

² School of Electrical and Electronics Engineering, Nanyang Technological University, Singapore 639798, Singapore

Energies 2018, 11(2), 461; https://doi.org/10.3390/en11020461 - 22 Feb 2018

Cited by 24 | Viewed by 4936

Abstract

Modular multilevel converters (MMCs) have shown great potential in the area of multi-megawatt wind energy conversion system (WECS) based on permanent magnet synchronous generators (PMSGs). However, the studies in this area are few, and most of them refer to the MMC used in [...] Read more.

Modular multilevel converters (MMCs) have shown great potential in the area of multi-megawatt wind energy conversion system (WECS) based on permanent magnet synchronous generators (PMSGs). However, the studies in this area are few, and most of them refer to the MMC used in high-voltage direct current (HVDC) systems, and hence the characteristics of the PMSG are not considered. This paper proposes a steady-state analysis method for MMCs connected to a PMSG-based WECS. In the proposed method, only the wind speed (operating condition) is required as input, and all the electrical quantities in the MMC, including the amplitudes, phase angles and their harmonics, can be calculated step by step. The analysis method is built on the proposed d-q frame mathematical model. Interactions of electrical quantities between the MMC and PMSG are comprehensively considered. Moreover, a new way to calculate the average switching functions are adopted in order to improve the accuracy of the analysis method. Applications of the proposed method are also presented, which includes the characteristic analysis of capacitor voltage ripples and the capacitor sizing. Finally, the accuracy of the method and the correctness of the analysis are verified by simulations and experiments. Full article

(This article belongs to the Section F: Electrical Engineering)

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15 pages, 2462 KiB

Open AccessArticle

Fuzzy Logic-Based Perturb and Observe Algorithm with Variable Step of a Reference Voltage for Solar Permanent Magnet Synchronous Motor Drive System Fed by Direct-Connected Photovoltaic Array

by Mohamed Redha Rezoug^1,*, Rachid Chenni²

and Djamel Taibi¹

¹ Departement of Electrical Engineering, Kasdi Merbah University Ouargla, Ouargla 30000, Algeria

² MoDERNa Laboratory Mentouri, University of Constantine1, Constantine 25000, Algeria

Energies 2018, 11(2), 462; https://doi.org/10.3390/en11020462 - 22 Feb 2018

Cited by 19 | Viewed by 7923

Abstract

Photovoltaic pumping is considered to be the most used application amongst other photovoltaic energy applications in isolated sites. This technology is developing with a slow progression to allow the photovoltaic system to operate at its maximum power. This work introduces the modified algorithm [...] Read more.

Photovoltaic pumping is considered to be the most used application amongst other photovoltaic energy applications in isolated sites. This technology is developing with a slow progression to allow the photovoltaic system to operate at its maximum power. This work introduces the modified algorithm which is a perturb and observe (P&O) type to overcome the limitations of the conventional P&O algorithm and increase its global performance in abrupt weather condition changes. The most significant conventional P&O algorithm restriction is the difficulty faced when choosing the variable step of the reference voltage value, a good compromise between the swift dynamic response and the stability in the steady state. To adjust the step reference voltage according to the location of the operating point of the maximum power point (MPP), a fuzzy logic controller (FLC) block adapted to the P&O algorithm is used. This allows the improvement of the tracking pace and the steady state oscillation elimination. The suggested method was evaluated by simulation using MATLAB/SimPowerSystems blocks and compared to the classical P&O under different irradiation levels. The results obtained show the effectiveness of the technique proposed and its capacity for the practical and efficient tracking of maximum power. Full article

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13 pages, 1508 KiB

Open AccessArticle

A Comprehensive Energy Analysis and Related Carbon Footprint of Dairy Farms, Part 2: Investigation and Modeling of Indirect Energy Requirements

by Giuseppe Todde^*

, Lelia Murgia, Maria Caria

and Antonio Pazzona

Department of Agricultural Science, University of Sassari, Viale Italia 39, 07100 Sassari, Italy

Energies 2018, 11(2), 463; https://doi.org/10.3390/en11020463 - 22 Feb 2018

Cited by 36 | Viewed by 5289

Abstract

Dairy cattle farms are continuously developing more intensive systems of management, which require higher utilization of durable and non-durable inputs. These inputs are responsible for significant direct and indirect fossil energy requirements, which are related to remarkable emissions of CO₂. This [...] Read more.

Dairy cattle farms are continuously developing more intensive systems of management, which require higher utilization of durable and non-durable inputs. These inputs are responsible for significant direct and indirect fossil energy requirements, which are related to remarkable emissions of CO₂. This study focused on investigating the indirect energy requirements of 285 conventional dairy farms and the related carbon footprint. A detailed analysis of the indirect energy inputs related to farm buildings, machinery and agricultural inputs was carried out. A partial life cycle assessment approach was carried out to evaluate indirect energy inputs and the carbon footprint of farms over a period of one harvest year. The investigation highlights the importance and the weight related to the use of agricultural inputs, which represent more than 80% of the total indirect energy requirements. Moreover, the analyses carried out underline that the assumption of similarity in terms of requirements of indirect energy and related carbon emissions among dairy farms is incorrect especially when observing different farm sizes and milk production levels. Moreover, a mathematical model to estimate the indirect energy requirements of dairy farms has been developed in order to provide an instrument allowing researchers to assess the energy incorporated into farm machinery, agricultural inputs and buildings. Combining the results of this two-part series, the total energy demand (expressed in GJ per farm) results in being mostly due to agricultural inputs and fuel consumption, which have the largest share of the annual requirements for each milk yield class. Direct and indirect energy requirements increased, going from small sized farms to larger ones, from 1302–5109 GJ·y⁻¹, respectively. However, the related carbon dioxide emissions expressed per 100 kg of milk showed a negative trend going from class <5000 to >9000 kg of milk yield, where larger farms were able to emit 48% less carbon dioxide than small herd size farm (43 vs. 82 kg CO₂-eq per 100 kg Fat- and Protein-Corrected Milk (FPCM)). Decreasing direct and indirect energy requirements allowed reducing the anthropogenic gas emissions to the environment, reducing the energy costs for dairy farms and improving the efficient utilization of natural resources. Full article

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12 pages, 6957 KiB

Open AccessArticle

Modulation Strategy of a 3 × 5 Modular Multilevel Matrix Converter

by Rutian Wang^*

, Dapeng Lei, Yanfeng Zhao, Chuang Liu and Yue Hu

School of Electrical Engineering, Northeast Electric Power University, Jilin 132012, China

Energies 2018, 11(2), 464; https://doi.org/10.3390/en11020464 - 23 Feb 2018

Cited by 5 | Viewed by 4232

Abstract

In this paper, a modulation strategy of a 3 × 5 modular multilevel matrix converter (M3C) is proposed. The circuit of 3 × 5 M3C is firstly introduced. Then, operation rules of 3 × 5 M3C are illustrated, and a connection pattern of [...] Read more.

In this paper, a modulation strategy of a 3 × 5 modular multilevel matrix converter (M3C) is proposed. The circuit of 3 × 5 M3C is firstly introduced. Then, operation rules of 3 × 5 M3C are illustrated, and a connection pattern of branches is determined based on these rules. Different voltage states in the input and output side can be achieved by different connection patterns. These voltage states are represented in the form of vector. It is hard to synthesize five-phase output with the three-level synthesis method. Therefore, the five-level synthesis method is adopted in this paper; i.e., is the branch states have been increased. Ten effective vectors and a zero vector are selected based on the five-level synthesis method. With this modulation strategy, we achieve output line-to-line voltages that are in line with the trend of a sine wave. The segment division and duty cycle calculation are very simple, and the modulation strategy can be implemented easily. The simulation model of 3 × 5 M3C is constructed based on Matlab/Simulink, and the corresponding experimental platform is set up. The results of simulation and experiment show that the proposed method is reasonable and correct. Full article

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13 pages, 2409 KiB

Open AccessEditor’s ChoiceArticle

PV Hosting Capacity Dependence on Harmonic Voltage Distortion in Low-Voltage Grids: Model Validation with Experimental Data

by Tiago E. C. de Oliveira^1,2,*, Pedro M. S. Carvalho^1,*, Paulo F. Ribeiro^2,* and Benedito D. Bonatto^2,*

¹ Instituto Superior Técnico and INESC-ID, University of Lisbon, Av. Rovisco Pais, 1049-001 Lisbon, Portugal

² Advanced Power Technologies and Innovations in Systems and Smart Grids Group, Federal University of Itajubá; Av. BPS, 1303, 37500-903 Itajubá, Brazil

Energies 2018, 11(2), 465; https://doi.org/10.3390/en11020465 - 23 Feb 2018

Cited by 46 | Viewed by 6151

Abstract

This paper introduces a brief analysis on hosting capacity and related concepts as applied to distribution network systems. Furthermore, it addresses the applicability of hosting capacity study methodologies to harmonic voltage distortion caused by photovoltaic panels (PV) connected at a low-voltage (LV) side [...] Read more.

This paper introduces a brief analysis on hosting capacity and related concepts as applied to distribution network systems. Furthermore, it addresses the applicability of hosting capacity study methodologies to harmonic voltage distortion caused by photovoltaic panels (PV) connected at a low-voltage (LV) side of a university campus grid. The analysis of the penetration of new distributed generation technologies, such as PV panels, in the distribution grid of the campus was carried out via measurement processes, and later by computer simulations analyzing a new concept of the hosting capacity approach in relation to voltage harmonics distortion. The voltage rise due to harmonic injection is analyzed and discussed with the aim of validating the discussed model and also putting forward recommendations for connecting PV generation across other network systems. Full article

(This article belongs to the Special Issue Distributed and Renewable Power Generation)

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15 pages, 3149 KiB

Open AccessArticle

Composite Reliability Evaluation of Load Demand Side Management and Dynamic Thermal Rating Systems

by Jiashen Teh¹

, Chia Ai Ooi¹, Yu-Huei Cheng²

, Muhammad Ammirrul Atiqi Mohd Zainuri¹

and Ching-Ming Lai^3,*

¹ School of Electrical and Electronic Engineering, Universiti Sains Malaysia (USM), Nibong Tebal 14300, Penang, Malaysia

² Department of Information and Communication Engineering, Chaoyang University of Technology, Taichung 41349, Taiwan

³ Department of Vehicle Engineering, National Taipei University of Technology, 1, Sec. 3, Chung-Hsiao E. Road, Taipei 10608, Taiwan

Energies 2018, 11(2), 466; https://doi.org/10.3390/en11020466 - 23 Feb 2018

Cited by 40 | Viewed by 5184

Abstract

Electric power utilities across the globe are facing higher demand for electricity than ever before, while juggling to balance environmental conservation with transmission corridor expansions. Demand side management (DSM) and dynamic thermal rating systems (DTR) play an important role in alleviating some of [...] Read more.

Electric power utilities across the globe are facing higher demand for electricity than ever before, while juggling to balance environmental conservation with transmission corridor expansions. Demand side management (DSM) and dynamic thermal rating systems (DTR) play an important role in alleviating some of the challenges faced by electric power utilities. In this paper, various DSM measures are explored and their interactions with the application of the DTR system in the transmission network are examined. The proposed modelling of DSM in this paper implements load shifting on load demand curves from the system, bus and load sector levels. The correlation effects of line ratings are considered in the DTR system modelling as the weather that influences line ratings is also correlated. The modelling of the line ratings was performed using the time series method, the auto regressive moving average (ARMA) model. Both the DSM and the DTR systems were implemented on the modified IEEE reliability test network. The modification was achieved by developing a load model starting from the perspective of the load sectors at each bus and a new collective hourly load curve for the system was obtained by combining the loads at all buses. Finally, the results in this paper elucidate the interaction of DSM and DTR systems. Full article

(This article belongs to the Section F: Electrical Engineering)

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14 pages, 8295 KiB

Open AccessArticle

Experimental Determination of Gas Relative Permeability Considering Slippage Effect in a Tight Formation

by Guangfeng Liu^1,*

, Zhaoqi Fan², Yang Lu³, Siying Li¹, Bo Feng¹, Yu Xia¹ and Qimeng Zhao¹

¹ CMOE Key Laboratory of Petroleum Engineering, China University of Petroleum-Beijing, Beijing 102249, China

² Chemical & Petroleum Engineering, University of Kansas, Lawrence, KS 66045, USA

³ School of Information Engineering, China University of Geosciences-Beijing, Beijing 100083, China

Energies 2018, 11(2), 467; https://doi.org/10.3390/en11020467 - 23 Feb 2018

Cited by 17 | Viewed by 4977

Abstract

In this paper, the gas relative permeability considering slippage effect has been experimentally examined under various experimental conditions (i.e., ambient, high confining pressure, and high temperature). Experimentally, Klinkenberg permeabilities of 12 core samples have been measured by using steady-state flow experiment. It has [...] Read more.

In this paper, the gas relative permeability considering slippage effect has been experimentally examined under various experimental conditions (i.e., ambient, high confining pressure, and high temperature). Experimentally, Klinkenberg permeabilities of 12 core samples have been measured by using steady-state flow experiment. It has been found that the Klinkenberg permeability is independent of the experimental temperature and dramatically decreases as confining pressure is increasing. Furthermore, linear correlations have been newly developed between the Klinkenberg permeability and the gas-measured permeability under various conditions. Subsequently, the developed correlations are correspondingly applied to calibrate the gas relative permeability. It has been found that the gas relative permeability can be overestimated without consideration of the slippage effect, i.e., Klinkenberg effect. In addition, the newly developed correlations have been applied to analyze the sensitivity of gas–water relative permeability to gas-measured permeability, confining pressure, and temperature. It is demonstrated that mobile water greatly alleviates the gas relative permeability in comparison to irreducible water. Although an increased confining pressure simultaneously reduces the effective water phase and gas phase permeability, the gas relative permeability increases and the water relative permeability decreases as the confining pressure increases. It is attributed to the fact that the effective water phase permeability is more sensitive to the confining pressure. Given an elevated experimental temperature, the gas relative permeability is reduced while the water relative permeability is enhanced, implying the significance of temperature effect on gas–water relative permeability measurements. Full article

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15 pages, 3074 KiB

Open AccessArticle

Multi-Rate and Parallel Electromagnetic Transient Simulation Considering Nonlinear Characteristics of a Power System

by Ji Han¹, Shihong Miao^1,*, Jing Yu², Yifeng Dong³, Junxian Hou³, Simo Duan¹ and Lixing Li¹

¹ State Key Laboratory of Advanced Electromagnetic Engineering and Technology, Hubei Electric Power Security and High Efficiency Key Laboratory, School of Electrical and Electronic Engineering, Huazhong University of Science and Technology, Wuhan 430074, China

² State Grid Jiangsu Electric Power Co., LTD, Nanjing 210000, China

³ State Key Laboratory of Power Grid Security and Energy Conservation, China Electric Power Research Institute, Haidian District, Beijing 100192, China

Energies 2018, 11(2), 468; https://doi.org/10.3390/en11020468 - 23 Feb 2018

Cited by 4 | Viewed by 3680

Abstract

The electromagnetic transient simulation of a power system with nonlinear characteristics is very time-consuming due to numerous inversion calculations of the admittance matrix. To speed up the simulation of the power system with nonlinear characteristics, a multi-rate and parallel electromagnetic transient simulation method [...] Read more.

The electromagnetic transient simulation of a power system with nonlinear characteristics is very time-consuming due to numerous inversion calculations of the admittance matrix. To speed up the simulation of the power system with nonlinear characteristics, a multi-rate and parallel electromagnetic transient simulation method is proposed. Firstly, a Multi-Area Thevenin Equivalents (MATE)-based parallel algorithm considering nonlinear characteristics of the power system is proposed. This method guarantees the admittance matrix is constant by considering changing branches as link current without dividing the subnet again. Secondly, considering the differences of the time constant of the AC/DC subnet, different simulation steps are used for these subnets. The Lagrange interpolation method is used for calculating the Thevenin voltage of the AC subnet in non-synchronous time. Calculation methods of the DC subnet Thevenin voltage is proposed by considering the simulation results during the entire large simulation step. Finally, the simulation process is optimized for improving the simulation efficiency further. The simulation results show that the proposed method could greatly improve the simulation efficiency without losing simulation accuracy too much compared with the traditional method. Full article

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18 pages, 7150 KiB

Open AccessArticle

A PSO-Optimized Fuzzy Logic Control-Based Charging Method for Individual Household Battery Storage Systems within a Community

by Yu-Shan Cheng¹, Yi-Hua Liu^2,*

, Holger C. Hesse³

, Maik Naumann³

, Cong Nam Truong³

and Andreas Jossen³

¹ Power Electronics Research Center, National Taiwan University of Science and Technology (NTUST), No.43, Sec. 4, Keelung Road, Taipei 106, Taiwan

² Department of Electrical Engineering, National Taiwan University of Science and Technology (NTUST), No.43, Sec. 4, Keelung Road, Taipei 106, Taiwan

³ Institute for Electrical Energy Storage Technology, Technical University of Munich (TUM), Arcisstr. 21, 80333 Munich, Germany

Energies 2018, 11(2), 469; https://doi.org/10.3390/en11020469 - 23 Feb 2018

Cited by 30 | Viewed by 5848

Abstract

Self-consumption of household photovoltaic (PV) storage systems has become profitable for residential owners under the trends of limited feed-in power and decreasing PV feed-in tariffs. For individual PV-storage systems, the challenge mainly lies in managing surplus generation of battery and grid power flow, [...] Read more.

Self-consumption of household photovoltaic (PV) storage systems has become profitable for residential owners under the trends of limited feed-in power and decreasing PV feed-in tariffs. For individual PV-storage systems, the challenge mainly lies in managing surplus generation of battery and grid power flow, ideally without relying on error-prone forecasts for both generation and consumption. Considering the large variation in power profiles of different houses in a neighborhood, the strategy is also supposed to be beneficial and applicable for the entire community. In this study, an adaptable battery charging control strategy is designed in order to obtain minimum costs for houses without any meteorological or load forecasts. Based on fuzzy logic control (FLC), battery state-of-charge (SOC) and the variation of SOC (∆SOC) are taken as input variables to dynamically determine output charging power with minimum costs. The proposed FLC-based algorithm benefits from the charging battery as much as possible during the daytime, and meanwhile properly preserves the capacity at midday when there is high possibility of curtailment loss. In addition, due to distinct power profiles in each individual house, input membership functions of FLC are improved by particle swarm optimization (PSO) to achieve better overall performance. A neighborhood with 74 houses in Germany is set up as a scenario for comparison to prior studies. Without forecasts of generation and consumption power, the proposed method leads to minimum costs in 98.6% of houses in the community, and attains the lowest average expenses for a single house each year. Full article

(This article belongs to the Section F: Electrical Engineering)

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13 pages, 4323 KiB

Open AccessArticle

Analysis of Switching Transients during Energization in Large Offshore Wind Farms

by Gang Liu¹

, Yaxun Guo^1,*, Yanli Xin¹, Lei You¹, Xiaofeng Jiang¹, Ming Zheng² and Wenhu Tang¹

¹ School of Electric Power Engineering, South China University of Technology, Guangzhou 510640, China

² Guangdong Electric Power Design Institute Co. Ltd. of China Energy Engineering Group, Guangzhou 510663, China

Energies 2018, 11(2), 470; https://doi.org/10.3390/en11020470 - 23 Feb 2018

Cited by 14 | Viewed by 6300

Abstract

In order to study switching transients in an offshore wind farm (OWF) collector system, we employ modeling methods of the main components in OWFs, including vacuum circuit breakers (VCBs), submarine cables, and wind turbine transformers (WTTs). In particular, a high frequency (HF) VCB [...] Read more.

In order to study switching transients in an offshore wind farm (OWF) collector system, we employ modeling methods of the main components in OWFs, including vacuum circuit breakers (VCBs), submarine cables, and wind turbine transformers (WTTs). In particular, a high frequency (HF) VCB model that reflects the prestrike characteristics of VCBs was developed. Moreover, a simplified experimental system of an OWF electric collection system was set up to verify the developed models, and a typical OWF medium voltage (MV) cable collection system was built in PSCAD/EMTDC based on the developed models. Finally, we investigated the influences of both the initial closing phase angle of VCBs and typical system operation scenarios on the amplitude and steepness of transient overvoltages (TOVs) at the high-voltage side of WTTs. Full article

(This article belongs to the Special Issue Emerging Power Electronics Technologies for Power Systems and Machine Drives)

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14 pages, 6132 KiB

Open AccessArticle

Analysis of dc-Link Voltage Switching Ripple in Three-Phase PWM Inverters

by Marija Vujacic

, Manel Hammami

, Milan Srndovic

and Gabriele Grandi^*

Department of Electrical, Electronic, and Information Engineering, University of Bologna, 40136 Bologna, Italy

Energies 2018, 11(2), 471; https://doi.org/10.3390/en11020471 - 23 Feb 2018

Cited by 63 | Viewed by 15519

Abstract

The three-phase voltage source inverter (VSI) is de facto standard in power conversion systems. To realize high power density systems, one of the items to be correctly addressed is the design and selection of the dc-link capacitor in relation to the voltage switching [...] Read more.

The three-phase voltage source inverter (VSI) is de facto standard in power conversion systems. To realize high power density systems, one of the items to be correctly addressed is the design and selection of the dc-link capacitor in relation to the voltage switching ripple. In this paper, effective formulas for designing the dc-link capacitor as a function of the switching voltage ripple amplitude are obtained, considering the operating conditions such as the modulation index and the output current amplitude. The calculations are obtained considering the requirements and restrictions referring to the high (switching)-frequency dc-link voltage ripple component. Analyses have been performed considering the dc source impedance (non-ideal dc voltage source at the switching frequency) and a balanced load. Analytical expressions are derived for the dc-link voltage switching ripple amplitude and its maximum value over the fundamental period. Different values of modulation index and output phase angle have been considered and different diagrams are presented. Analytical results were validated both by simulations and comprehensive experimental tests. Full article

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13 pages, 1967 KiB

Open AccessArticle

Estimation of the Diesel Particulate Filter Soot Load Based on an Equivalent Circuit Model

by Yanting Du, Guangdi Hu^*, Shun Xiang

, Ke Zhang, Hongxing Liu and Feng Guo

School of Mechanical Engineering, Southwest Jiaotong University, Chengdu 610031, China

Energies 2018, 11(2), 472; https://doi.org/10.3390/en11020472 - 23 Feb 2018

Cited by 16 | Viewed by 7331

Abstract

In order to estimate the diesel particulate filter (DPF) soot load and improve the accuracy of regeneration timing, a novel method based on an equivalent circuit model is proposed based on the electric-fluid analogy. This proposed method can reduce the impact of the [...] Read more.

In order to estimate the diesel particulate filter (DPF) soot load and improve the accuracy of regeneration timing, a novel method based on an equivalent circuit model is proposed based on the electric-fluid analogy. This proposed method can reduce the impact of the engine transient operation on the soot load, accurately calculate the flow resistance, and improve the estimation accuracy of the soot load. Firstly, the least square method is used to identify the flow resistance based on the World Harmonized Transient Cycle (WHTC) test data, and the relationship between flow resistance, exhaust temperature and soot load is established. Secondly, the online estimation of the soot load is achieved by using the dual extended Kalman filter (DEKF). The results show that this method has good convergence and robustness with the maximal absolute error of 0.2 g/L at regeneration timing, which can meet engineering requirements. Additionally, this method can estimate the soot load under engine transient operating conditions and avoids a large number of experimental tests, extensive calibration and the analysis of complex chemical reactions required in traditional methods. Full article

(This article belongs to the Special Issue Recent Advances in Internal Combustion Engines Operation and Emissions)

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Review

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36 pages, 644 KiB

Open AccessReview

Environmental Sustainability and Energy-Efficient Supply Chain Management: A Review of Research Trends and Proposed Guidelines

by Piera Centobelli¹, Roberto Cerchione^2,* and Emilio Esposito¹

¹ Department of Industrial Engineering, University of Naples Federico II, P.le Tecchio 80, 80125 Naples, Italy

² Department of Engineering, University of Naples Parthenope, Centro Direzionale di Napoli Isola C4, 80143 Naples, Italy

Energies 2018, 11(2), 275; https://doi.org/10.3390/en11020275 - 24 Jan 2018

Cited by 124 | Viewed by 14156

Abstract

This paper conducts a structured review on the topic of energy efficiency and environmental sustainability in the supply chain management context to define research trends on the topic and identify research gaps. The review is carried out using the largest databases of peer-reviewed [...] Read more.

This paper conducts a structured review on the topic of energy efficiency and environmental sustainability in the supply chain management context to define research trends on the topic and identify research gaps. The review is carried out using the largest databases of peer-reviewed literature (Scopus and Web of Science). A sample of 122 papers focusing on the topic of energy-efficient and sustainable supply chain management was selected and analyzed through descriptive and content analysis. The review highlights that despite there is a growing research trend on the topic, different research gaps remain to be covered. These gaps concern the factors influencing energy efficiency and environmental sustainability initiatives, the classification of energy efficiency and environmental sustainability initiatives, the impact of energy efficiency and environmental sustainability on supply chain performance, the customer perspective in sustainable and energy-efficient supply chain, and the different technologies supporting the energy efficiency and environmental sustainability initiatives. The research gaps and the research questions identified offer the opportunity to identify areas of investigation to design future research directions and propose guidelines in the field of supply chain management. Full article

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17 pages, 1032 KiB

Open AccessFeature PaperReview

Assessment and Public Reporting of Geothermal Resources in Germany: Review and Outlook

by Thorsten Agemar^*

, Josef Weber and Inga S. Moeck

Leibniz Institute for Applied Geophysics, Stilleweg 2, D-30655 Hannover, Germany

Energies 2018, 11(2), 332; https://doi.org/10.3390/en11020332 - 2 Feb 2018

Cited by 26 | Viewed by 6631

Abstract

Any geothermal resource assessment requires consistent and widely accepted terminology, methods, and reporting schemes that facilitate the comparison of geothermal resource estimates. This paper reviews common resource assessment methods, as well as reporting codes and terminology. Based on a rigorous analysis of the [...] Read more.

Any geothermal resource assessment requires consistent and widely accepted terminology, methods, and reporting schemes that facilitate the comparison of geothermal resource estimates. This paper reviews common resource assessment methods, as well as reporting codes and terminology. Based on a rigorous analysis of the portrayed concepts and methods, it discusses the appropriateness of the existing reporting codes for sustainable utilization of geothermal resources in Germany. Since the last quantitative geothermal resource assessment in Germany was done 15 years ago, a revised report is overdue. Unlike fossil energy commodities, geothermal energy replenishes naturally and heat recuperation increases in created heat sinks. This replenishment process offers the opportunity for sustainable reservoir management in the case of moderate production rates or cyclic operation. Existing reporting codes, however, regard geothermal resources in a similar way to fossil resources or focus too much on field development rather than on the whole assessment process. In order to emphasize the renewability of geothermal energy, we propose the reporting of geothermal capacities (per doublet or per km²) instead of recoverable heat energy which depends very much on project lifetime and other factors. As a first step, a new classification scheme for geothermal resources and reserves is outlined. Full article

(This article belongs to the Special Issue Geothermal Heating and Cooling)

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18 pages, 2220 KiB

Open AccessReview

A Review of Green Building Development in China from the Perspective of Energy Saving

by Ying Zhang^1,3

, Jian Kang^1,2,*

and Hong Jin¹

¹ School of Architecture, Harbin Institute of Technology, Harbin 150001, China

² Institute for Environmental Design and Engineering, The Bartlett, University College London, London WC1H 0NN, UK

³ Urban Construction Research Institute of Heilongjiang Province, Harbin 150001, China

Energies 2018, 11(2), 334; https://doi.org/10.3390/en11020334 - 2 Feb 2018

Cited by 92 | Viewed by 13963

Abstract

This paper reviews the history of green building development and assessment standards in China, particularly from the perspective of energy saving. It is divided into four parts: (1) the development of policies of green building in China that have been proposed for meeting [...] Read more.

This paper reviews the history of green building development and assessment standards in China, particularly from the perspective of energy saving. It is divided into four parts: (1) the development of policies of green building in China that have been proposed for meeting energy-conservation and emission-reduction targets; (2) the scientific research on green building by the Chinese government, including the promotion of maximum resource sustainability, environmental protection, and the reduction of pollution; (3) the development of assessment standards for green building in China; and (4) the development of green building technologies in China. Full article

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20 pages, 1209 KiB

Open AccessReview

Electro-Fermentation in Aid of Bioenergy and Biopolymers

by Prasun Kumar¹, Kuppam Chandrasekhar², Archana Kumari³, Ezhaveni Sathiyamoorthi¹ and Beom Soo Kim^1,*

¹ Department of Chemical Engineering, Chungbuk National University, Cheongju, Chungbuk 28644, Korea

² Department of Civil Engineering, Yeungnam University, Gyeongsan, Gyeongbuk 38451, Korea

³ Department of Biotechnology, Bodoland University, Kokrajhar, Assam 783370, India

Energies 2018, 11(2), 343; https://doi.org/10.3390/en11020343 - 2 Feb 2018

Cited by 86 | Viewed by 9150

Abstract

The soaring levels of industrialization and rapid progress towards urbanization across the world have elevated the demand for energy besides generating a massive amount of waste. The latter is responsible for poisoning the ecosystem in an exponential manner, owing to the hazardous and [...] Read more.

The soaring levels of industrialization and rapid progress towards urbanization across the world have elevated the demand for energy besides generating a massive amount of waste. The latter is responsible for poisoning the ecosystem in an exponential manner, owing to the hazardous and toxic chemicals released by them. In the past few decades, there has been a paradigm shift from “waste to wealth”, keeping the value of high organic content available in the wastes of biological origin. The most practiced processes are that of anaerobic digestion, leading to the production of methane. However; such bioconversion has limited net energy yields. Industrial fermentation targeting value-added bioproducts such as—H₂, butanediols; polyhydroxyalkanoates, citric acid, vitamins, enzymes, etc. from biowastes/lignocellulosic substrates have been planned to flourish in a multi-step process or as a “Biorefinery”. Electro-fermentation (EF) is one such technology that has attracted much interest due to its ability to boost the microbial metabolism through extracellular electron transfer during fermentation. It has been studied on various acetogens and methanogens, where the enhancement in the biogas yield reached up to 2-fold. EF holds the potential to be used with complex organic materials, leading to the biosynthesis of value-added products at an industrial scale. Full article

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24 pages, 3837 KiB

Open AccessReview

Performance Evaluation of Maximum Power Point Tracking Approaches and Photovoltaic Systems

by Haidar Islam^1,*

, Saad Mekhilef^1,*

, Noraisyah Binti Mohamed Shah², Tey Kok Soon³, Mehdi Seyedmahmousian⁴, Ben Horan⁴

and Alex Stojcevski⁴

¹ Power Electronics and Renewable Energy Research Laboratory (PEARL), Department of Electrical Engineering, University of Malaya, Kuala Lumpur 50603, Malaysia

² Department of Electrical, Engineering, University of Malaya, Kuala Lumpur 50603, Malaysia

³ Department of Computer System & Technology, Faculty of Computer Science & Information Technology, University of Malaya, Kuala Lumpur 50603, Malaysia

⁴ School of Engineering, Deakin University, Waurn Ponds, Victoria 3216, Australia

Energies 2018, 11(2), 365; https://doi.org/10.3390/en11020365 - 4 Feb 2018

Cited by 136 | Viewed by 8800

Abstract

This paper elaborates a comprehensive overview of a photovoltaic (PV) system model, and compares the attributes of various conventional and improved incremental conductance algorithms, perturbation and observation techniques, and other maximum power point tracking (MPPT) algorithms in normal and partial shading conditions. Performance [...] Read more.

This paper elaborates a comprehensive overview of a photovoltaic (PV) system model, and compares the attributes of various conventional and improved incremental conductance algorithms, perturbation and observation techniques, and other maximum power point tracking (MPPT) algorithms in normal and partial shading conditions. Performance evaluation techniques are discussed on the basis of the dynamic parameters of the PV system. Following a discussion of the MPPT algorithms in each category, a table is drawn to summarize their key specifications. In the performance evaluation section, the appropriate PV module technologies, atmospheric effects on PV panels, design complexity, and number of sensors and internal parameters of the PV system are outlined. In the last phase, a comparative table presents performance-evaluating parameters of MPPT design criterion. This paper is organized in such a way that future researchers and engineers can select an appropriate MPPT scheme without complication. Full article

(This article belongs to the Section A: Sustainable Energy)

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20 pages, 5018 KiB

Open AccessReview

Solar Energy Potentials and Benefits in the Gulf Cooperation Council Countries: A Review of Substantial Issues

by Abdullahi Abubakar Mas’ud^1,*

, Asan Vernyuy Wirba², Saud J. Alshammari³, Firdaus Muhammad-Sukki⁴

, Mu’azu Mohammed Abdullahi⁵

, Ricardo Albarracín⁶

and Mohammed Ziaul Hoq²

¹ Department of Electrical and Electronics Engineering, Jubail Industrial College, P.O. Box 10099, Jubail Industrial City 31261, Saudi Arabia

² Department of Management and Information Technology, Jubail Industrial College, P.O. Box 10099, Jubail Industrial City 31261, Saudi Arabia

³ Department of Electrical and Electronic Engineering, University of Sheffield, Western Bank, Sheffield S10 2TN, UK

⁴ School of Engineering, Robert Gordon University, Garthdee Road, Aberdeen AB10 7GJ, Scotland, UK

⁵ Department of Civil Engineering, Jubail University College, P.O. Box 10074, Jubail Industrial City 31261, Saudi Arabia

⁶ Departamento de Ingeniería Eléctrica, Electrónica, Automática y Física Aplicada, Escuela Técnica Superior de Ingeniería y Diseño Industrial, Universidad Politécnica de Madrid, Ronda de Valencia 3, 28012 Madrid, Spain

Energies 2018, 11(2), 372; https://doi.org/10.3390/en11020372 - 5 Feb 2018

Cited by 46 | Viewed by 11852

Abstract

It is a well-known fact that the fossil fuel industry has dominated the economy of the Gulf Cooperation Council (GCC) countries during the last few decades. However, recent developments show that most of the GCC countries plan to increase the share of renewable [...] Read more.

It is a well-known fact that the fossil fuel industry has dominated the economy of the Gulf Cooperation Council (GCC) countries during the last few decades. However, recent developments show that most of the GCC countries plan to increase the share of renewable energy (RE) in their future electrical power production. To ensure realistic increase in the share of RE in the production of electricity in the future, firm policies must be laid down with the objective to promote and market the benefit of RE to their citizens. Due to the high-solar radiation in the GCC region, the focus is now on solar energy development. This paper presents an up-to-date review of the progress made on solar energy in the GCC together with the challenges and the way forward. Some of the challenges and barriers hindering the development of RE in the GCC are in the area of technological know-how, policy development, and insufficient application of RE technology integrated in the buildings among others. Areas of improvement include promoting research and development, public/private initiatives, legislation and regulatory framework, solutions to technical issues and exchange of knowledge, scientific advice, and last but not the least is the issue of building integration with RE. Full article

(This article belongs to the Special Issue Sustainable and Renewable Energy Systems)

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34 pages, 7709 KiB

Open AccessReview

A Key Review of Non-Industrial Greywater Heat Harnessing

by Abdur Rehman Mazhar¹, Shuli Liu^1,2,* and Ashish Shukla¹

¹ School of Energy, Construction and Environment, Coventry University, Coventry CV1 2HF, UK

² School of Mechanical Engineering, Beijing Institute of Technology, Beijing 100081, China

Energies 2018, 11(2), 386; https://doi.org/10.3390/en11020386 - 7 Feb 2018

Cited by 38 | Viewed by 6865

Abstract

The ever-growing concerns about making buildings more energy efficient and increasing the share of renewable energy used in them, has led to the development of ultra-low carbon buildings or passive houses. However, a huge potential still exists to lower the hot water energy [...] Read more.

The ever-growing concerns about making buildings more energy efficient and increasing the share of renewable energy used in them, has led to the development of ultra-low carbon buildings or passive houses. However, a huge potential still exists to lower the hot water energy demand, especially by harnessing heat from waste water exiting these buildings. Reusing this heat makes buildings more energy-efficient and this source is considered as a third-generation renewable energy technology, both factors conforming to energy policies throughout the world. Based on several theoretical and experimental studies, the potential to harness non-industrial waste water is quite high. As an estimate about 3.5 kWh of energy, per person per day could be harnessed and used directly, in many applications. A promising example of such an application, are low temperature fourth generation District Heating grids, with decentralized sources of heat. At the moment, heat exchangers and heat pumps are the only viable options to harness non-industrial waste heat. Both are used at different scales and levels of the waste-water treatment hierarchical pyramid. Apart from several unfavourable characteristics of these technologies, the associated exergetic efficiencies are low, in the range of 20–50%, even when cascaded combinations of both are used. To tackle these shortcomings, several promising trends and technologies are in the pipeline, to scavenge this small-scale source of heat to a large-scale benefit. Full article

(This article belongs to the Section D: Energy Storage and Application)

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16 pages, 5997 KiB

Open AccessReview

A Unified Control Strategy for Inductor-Based Active Battery Equalisation Schemes

by Xintian Liu¹, Zhihao Wan¹, Yao He¹, Xinxin Zheng^1,*, Guojian Zeng¹ and Jiangfeng Zhang²

¹ Clean Energy Automotive Research Institute, Hefei University of Technology, Hefei 230009, China

² School of Electrical and Data Engineering, University of Technology Sydney, Ultimo, NSW 2007, Australia

Energies 2018, 11(2), 405; https://doi.org/10.3390/en11020405 - 9 Feb 2018

Cited by 22 | Viewed by 3422

Abstract

Series battery equalisation can improve battery charge and discharge reliability and extend battery life. Inductor-based battery equalisation schemes have the advantages of simple topologies and control strategies. According to the energy transfer pathway, inductor-based battery equalisation schemes can be divided into cell-to-cell and [...] Read more.

Series battery equalisation can improve battery charge and discharge reliability and extend battery life. Inductor-based battery equalisation schemes have the advantages of simple topologies and control strategies. According to the energy transfer pathway, inductor-based battery equalisation schemes can be divided into cell-to-cell and cell-to-pack equalisation schemes. The control strategies of the cell-to-cell schemes are simple; the inductor can only transfer energy between the neighbouring cells, so the equalisation speed is low. The cell-to-pack schemes are able to accomplish energy transfer between the cells and pack by charging and discharging the inductors. The equalisation speed is high, but the control strategies may be complex. In this paper, different equalisation topologies are reviewed, then a unified control strategy which is applicable to all of the inductor-based equalisation topologies is proposed. The equalisation speeds and efficiencies of these different schemes, including the newly-proposed unified control strategy, are analysed and compared. Based on the theoretical analysis, simulations, and experimental verifications, it is concluded that this unified control strategy can perform the battery equalisation process quickly and efficiently. Full article

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23 pages, 4123 KiB

Open AccessReview

Ensemble-Based Data Assimilation in Reservoir Characterization: A Review

by Seungpil Jung¹

, Kyungbook Lee²

, Changhyup Park^3,*

and Jonggeun Choe⁴

¹ E&P Business Division, SK Innovation, Seoul 03188, Korea

² Petroleum and Marine Research Division, Korea Institute of Geoscience and Mineral Resources, Daejeon 34132, Korea

³ Department of Energy and Resources Engineering, Kangwon National University, Chuncheon 24341, Kangwon, Korea

⁴ Department of Energy Systems Engineering, Seoul National University, Seoul 03080, Korea

Energies 2018, 11(2), 445; https://doi.org/10.3390/en11020445 - 17 Feb 2018

Cited by 28 | Viewed by 7110

Abstract

This paper presents a review of ensemble-based data assimilation for strongly nonlinear problems on the characterization of heterogeneous reservoirs with different production histories. It concentrates on ensemble Kalman filter (EnKF) and ensemble smoother (ES) as representative frameworks, discusses their pros and cons, and [...] Read more.

This paper presents a review of ensemble-based data assimilation for strongly nonlinear problems on the characterization of heterogeneous reservoirs with different production histories. It concentrates on ensemble Kalman filter (EnKF) and ensemble smoother (ES) as representative frameworks, discusses their pros and cons, and investigates recent progress to overcome their drawbacks. The typical weaknesses of ensemble-based methods are non-Gaussian parameters, improper prior ensembles and finite population size. Three categorized approaches, to mitigate these limitations, are reviewed with recent accomplishments; improvement of Kalman gains, add-on of transformation functions, and independent evaluation of observed data. The data assimilation in heterogeneous reservoirs, applying the improved ensemble methods, is discussed on predicting unknown dynamic data in reservoir characterization. Full article

(This article belongs to the Section L: Energy Sources)

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Other

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1 pages, 137 KiB

Open AccessAddendum

Addendum: Patiño-Cambeiro, F. et al. Multidisciplinary Energy Assessment of Tertiary Buildings: Automated Geomatic Inspection, Building Information Modeling Reconstruction and Building Performance Simulation. Energies 2017, 10, 1032

by Faustino Patiño-Cambeiro^1,*, Guillermo Bastos², Julia Armesto³ and Faustino Patiño-Barbeito²

¹ Industrial Engineering School, University of Vigo, Rúa Maxwell, 36310 Vigo, Spain

² Industrial Engineering School, University of Vigo, Rúa Conde de Torrecedeira 86, 36208 Vigo, Spain

³ Mining Engineering School, University of Vigo, Campus as Lagoas Marcosende, 36310 Vigo, Spain

Energies 2018, 11(2), 289; https://doi.org/10.3390/en11020289 - 25 Jan 2018

Cited by 1 | Viewed by 2276

Abstract

The authors would like to add the student Luis Gandarela Campos, from the University of Vigo, that contributed in some technical computations, in the Acknowledgement Section of their paper published in Energies [1].[...] Full article

(This article belongs to the Section A: Sustainable Energy)

16 pages, 2395 KiB

Open AccessCase Report

Low-Cost Syngas Shifting for Remote Gasifiers: Combination of CO₂ Adsorption and Catalyst Addition in a Novel and Simplified Packed Structure

by Ricardo A. Narváez C.^1,2,3,*

, Richard Blanchard³, Roger Dixon⁴, Valeria Ramírez¹

and Diego Chulde¹

¹ Instituto Nacional de Eficiencia Energética y Energías Renovables (INER), Quito EC170507, Ecuador

² Facultad de Ingeniería Química, Universidad Central del Ecuador, Quito EC170521, Ecuador

³ Centre for Renewable Energy Systems Technology (CREST), Wolfson School Mechanical, Manufacturing and Electrical Engineering, Loughborough University, Loughborough LE11 3GR, UK

⁴ Wolfson School Mechanical, Manufacturing and Electrical Engineering, Loughborough University, Loughborough LE11 3TU, UK

Energies 2018, 11(2), 311; https://doi.org/10.3390/en11020311 - 1 Feb 2018

Cited by 2 | Viewed by 3962

Abstract

This paper presents the technical validation of a novel, low-complexity alternative based on the inclusion of a patented (IEPI-MU-2016-185) packed bed for improving the performance of remote, small-scale gasification facilities. This study was carried out in an updraft, atmospheric-pressure gasifier, outfitted with a [...] Read more.

This paper presents the technical validation of a novel, low-complexity alternative based on the inclusion of a patented (IEPI-MU-2016-185) packed bed for improving the performance of remote, small-scale gasification facilities. This study was carried out in an updraft, atmospheric-pressure gasifier, outfitted with a syngas reflux line, air and oxygen feed, and an upper packed-bed coupled to the gasification unit to improve the syngas quality by catalytic treatment and CO₂ adsorption. The experimental facility is located in the rural community San Pedro del Laurel, Ecuador. Gasification experiments, with and without packed material in the upper chamber, were performed to assess its effect on the syngas quality. The assessment revealed that the packed material increases the carbon monoxide (CO) content in the syngas outlet stream while carbon dioxide (CO₂) was reduced. This option appears to be a suitable and low-complexity alternative for enhancing the content of energy vectors of syngas in gasification at atmospheric pressure since CO/CO₂ ratios of 5.18 and 3.27 were achieved against reported values of 2.46 and 0.94 for operations which did not include the addition of packed material. It is concluded that the upper packed-bed is an active element able to modify syngas characteristics since CO₂ content was reduced. Full article

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