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Energies, Volume 12, Issue 21 (November-1 2019)

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Cover Story (view full-size image) The evolution of the transportation sector is a critical factor to enable a sustainable, green, [...] Read more.
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Open AccessArticle
Modeling Latent Carbon Emission Prices for Japan: Theory and Practice
Energies 2019, 12(21), 4222; https://doi.org/10.3390/en12214222 - 05 Nov 2019
Abstract
Climate change and global warming are significantly affected by carbon emissions that arise from the burning of fossil fuels, specifically coal, oil, and gas. Accurate prices are essential for the purposes of measuring, capturing, storing, and trading in carbon emissions at regional, national, [...] Read more.
Climate change and global warming are significantly affected by carbon emissions that arise from the burning of fossil fuels, specifically coal, oil, and gas. Accurate prices are essential for the purposes of measuring, capturing, storing, and trading in carbon emissions at regional, national, and international levels, especially as carbon emissions can be taxed appropriately when the price is known and widely accepted. This paper uses a novel Capital (K), Labor (L), Energy (E) and Materials (M) (or KLEM) production function approach to calculate the latent carbon emission prices, where carbon emission is the output and capital (K), labor (L), energy (E) (or electricity), and materials (M) are the inputs for the production process. The variables K, L, and M are essentially fixed on a daily or monthly basis, whereas E can be changed more frequently, such as daily or monthly, so that changes in carbon emissions depend on changes in E. If prices are assumed to depend on the average cost pricing, the prices of carbon emissions and energy may be approximated by an energy production model with a constant factor of proportionality, so that carbon emission prices are a function of energy prices. Using this novel modeling approach, this paper estimates the carbon emission prices for Japan using seasonally adjusted and unadjusted monthly data on the volumes of carbon emissions and energy, as well as energy prices, from December 2008 to April 2018. The econometric models show that, as sources of electricity, the logarithms of coal and oil, though not Liquefied Natural Gas (LNG,) are statistically significant in explaining the logarithm of carbon emissions, with oil being more significant than coal. The models generally displayed a high power in predicting the latent prices of carbon emissions. The usefulness of the empirical findings suggest that the methodology can also be applied for other countries where carbon emission prices are latent. Full article
(This article belongs to the Special Issue Multivariate Modelling of Fossil Fuel and Carbon Emission Prices)
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Open AccessArticle
Investigation on an Injection Strategy Optimization for Diesel Engines Using a One-Dimensional Spray Model
Energies 2019, 12(21), 4221; https://doi.org/10.3390/en12214221 - 05 Nov 2019
Abstract
Common rail systems have been widely used in diesel engines due to the stricter emission regulations. The advances in injector technology and ultrahigh injection pressure greatly promote the development of multiple-injection strategy, leading to the shorter injection duration and more variable injection rate [...] Read more.
Common rail systems have been widely used in diesel engines due to the stricter emission regulations. The advances in injector technology and ultrahigh injection pressure greatly promote the development of multiple-injection strategy, leading to the shorter injection duration and more variable injection rate shape, which makes the mixing process more significant for the formation of pollutant emission. In order to study the mixing process of diesel sprays under variable injection rate shapes and find the optimized injection strategy, a one-dimensional spray model was modified in this paper. The model was validated by the measured spray penetrations based on shadowgraphy experiments with the varying injection rate. The simulations were performed with five injection rate shapes, triangle, ramping-up, ramping-down, rectangle and trapezoid. Their spray penetrations, entrainment rates and equivalence ratios along spray axial distance are compared. The potentials of multiple-injection and gas-jet after end-of-injection (EOI) to improve mixing process and emission reduction are discussed finally. The results indicated that ramping-up injection rate obtains the highest entrainment rate after EOI, and it needs 1.5 times of injection duration for the entrainment wave to arrive at the spray tip. For the other four injection rates, the sprays can be treated as a steady-like state, needing twice of injection duration from EOI to the time the entrainment wave reaches the spray tip. The multiple-injection with proper injection rate shape enhanced the entrainment rate, and the gas-jet after EOI affected the mixture distribution and entrainment rate in spray tail under ramping-down injection rate. Full article
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Open AccessArticle
Analysis on the Force and Life of Gearbox in Double-Rotor Wind Turbine
Energies 2019, 12(21), 4220; https://doi.org/10.3390/en12214220 - 05 Nov 2019
Abstract
In order to study the force and life of the key components in the gearbox of an existing double-rotor wind turbine, the design and structural parameters of the gearbox in the traditional National Renewable Energy Laboratory (NREL) 5 MW single-rotor wind turbine are [...] Read more.
In order to study the force and life of the key components in the gearbox of an existing double-rotor wind turbine, the design and structural parameters of the gearbox in the traditional National Renewable Energy Laboratory (NREL) 5 MW single-rotor wind turbine are adopted, and the fixed ring gear of the first planetary stage transmission is released to form a differential gearbox suitable for a double-rotor wind turbine with two inputs. The double input is used to connect the double rotor. Subsequently, the characteristics of the gearbox in a double-rotor wind turbine are discussed. On the basis of the constant rated power of the whole wind turbine, the total power is divided into two parts, which are allocated to the double rotors, then two rotational speeds of the two inputs are given according to different power ratios by complying with the matching principle of force and moment. Furthermore, the force acting on the pitch circle of the planet gear, as well as the force and life of the planet bearing of the two-stage planetary transmission are calculated and compared with a single-rotor wind turbine. The results show that the structural advantages of a double-rotor wind turbine can reduce the stress of key components of the gearbox and increase the life span of the planet bearing, thereby the life of the whole gearbox is improved and the downtime of the whole wind turbine is reduced. Full article
(This article belongs to the collection Wind Turbines) Printed Edition available
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Open AccessArticle
Comprehensive Second-Order Adjoint Sensitivity Analysis Methodology (2nd-ASAM) Applied to a Subcritical Experimental Reactor Physics Benchmark: I. Effects of Imprecisely Known Microscopic Total and Capture Cross Sections
Energies 2019, 12(21), 4219; https://doi.org/10.3390/en12214219 - 05 Nov 2019
Abstract
The subcritical polyethylene-reflected plutonium (PERP) metal fundamental physics benchmark, which is included in the Nuclear Energy Agency (NEA) International Criticality Safety Benchmark Evaluation Project (ICSBEP) Handbook, has been selected to serve as a paradigm illustrative reactor physics system for the application of the [...] Read more.
The subcritical polyethylene-reflected plutonium (PERP) metal fundamental physics benchmark, which is included in the Nuclear Energy Agency (NEA) International Criticality Safety Benchmark Evaluation Project (ICSBEP) Handbook, has been selected to serve as a paradigm illustrative reactor physics system for the application of the Second-Order Adjoint Sensitivity Analysis Methodology (2nd-ASAM) that was developed by Cacuci. The 2nd-ASAM enables the exhaustive deterministic computation of the exact values of the 1st-order and 2nd-order sensitivities of a system response to the parameters underlying the respective system. The PERP benchmark is numerically modeled in this work by using the deterministic multigroup neutron transport equation discretized in the spatial and angular independent variables. Thus, the numerical model of the PERP benchmark developed includes the following imprecisely known uncertain parameters: 180 group-averaged total microscopic cross sections, 21,600 group-averaged scattering microscopic cross sections, 120 fission process parameters, 60 fission spectrum parameters, 10 parameters describing the experiment’s nuclear sources, and six isotopic number densities. Thus, the numerical simulation model for the PERP benchmark comprises 21,976 uncertain parameters, which implies that, for any response of interest, there are a total of 21,976 first-order sensitivities and 482,944,576 second-order sensitivities with respect to the model parameters. Computing these sensitivities exactly represents the largest sensitivity analysis endeavor ever carried out in the field of reactor physics. Only 241,483,276 are distinct from each other, and some of these turned out to be zero due to the symmetry of the 2nd-order sensitivities. The numerical results for all of these sensitivities, together with discussions of their major impacts, will be presented in a sequence of publications in the Special Issue of Energies dedicated to “Sensitivity Analysis, Uncertainty Quantification and Predictive Modeling of Nuclear Energy Systems”. This work is the first in this sequence, presenting formulas of general use for neutron transport problems, along with the numerical results that were produced by these formulas for the 180 first-order and 32,400 second-order sensitivities of the PERP leakage response with respect to the neutron transport model’s group-averaged isotopic total cross sections. For comparison, this work also presents formulas of general use and numerical results for the 180 first-order and 32,400 second-order sensitivities of the PERP leakage response with respect to the neutron transport model’s group-averaged isotopic capture cross sections. It has been widely believed hitherto that, for reactor physics systems modeled by the neutron transport or diffusion equations, the second-order sensitivities are all much smaller than the first-order ones. However, contrary to this widely held belief, the numerical results that were obtained in this work prove, for the first time ever, that many of the 2nd-order sensitivities are much larger than the corresponding 1st-order ones, so their effects can become much larger than the corresponding effects stemming from the 1st-order sensitivities. For example, the 2nd-order sensitivities of the PERP leakage response cause the expected value of this response to be significantly larger than the corresponding computed value. The importance of the 2nd-order sensitivities increases as the relative standard deviations for the cross sections increase. For the extreme case of fully correlated cross sections, for example, neglecting the 2nd-order sensitivities would cause an error as large as 2000% in the expected value of the leakage response and up to 6000% in the variance of the leakage response. The significant effects of the mixed 2nd-order sensitivities underscore the need for reliable values for the correlations that might exist among the total cross sections, which are unavailable at this time. The 2nd-order sensitivities with respect to the total cross sections also cause the response distribution to be skewed towards positive values relative to the expected value. Hence, neglecting the 2nd-order sensitivities could potentially cause very large non-conservative errors by under-reporting of the response variance and expected value. Full article
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Open AccessArticle
Innovative Membrane Electrode Assembly (MEA) Fabrication for Proton Exchange Membrane Water Electrolysis
Energies 2019, 12(21), 4218; https://doi.org/10.3390/en12214218 - 05 Nov 2019
Abstract
In order to increase the hydrogen production rate as well as ozone production at the anode side, increased voltage application and more catalyst utilization are necessary. The membrane electrode assembly (MEA) produces hydrogen/ozone via proton exchange membrane water electrolysis (PEMWE)s which gives priority [...] Read more.
In order to increase the hydrogen production rate as well as ozone production at the anode side, increased voltage application and more catalyst utilization are necessary. The membrane electrode assembly (MEA) produces hydrogen/ozone via proton exchange membrane water electrolysis (PEMWE)s which gives priority to a coating method (abbreviation: ML). However, coating takes more effort and is labor-consuming. This study will present an innovative preparation method, known as flat layer (FL), and compare it with ML. FL can significantly reduce efforts and largely improve MEA production. Additionally, MEA with the FL method is potentially durable compared to ML. Full article
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Open AccessArticle
Assessment of Overvoltage and Insulation Coordination in Mixed HVDC Transmission Lines Exposed to Lightning Strikes
Energies 2019, 12(21), 4217; https://doi.org/10.3390/en12214217 - 05 Nov 2019
Abstract
Many geographical constraints and aesthetic concerns necessitate the partial use of cable sections in the High Voltage DC (HVDC) transmission line, resulting in a mixed transmission line. The overhead sections of mixed lines are exposed to lightning strikes. The lightning strikes can not [...] Read more.
Many geographical constraints and aesthetic concerns necessitate the partial use of cable sections in the High Voltage DC (HVDC) transmission line, resulting in a mixed transmission line. The overhead sections of mixed lines are exposed to lightning strikes. The lightning strikes can not only result in flashover of overhead line (OHL) insulators but can enter the cable and permanently damage its insulation if adequate insulation coordination measures are not taken. In this work, we have analyzed the factors that affect the level of overvoltage inside the cable by simulating a fast front model in PSCAD. It has been determined that surge arresters must be provided at cable terminals when the length of cable sections is less than 16 km to limit the core-ground overvoltage within the lightning impulse protective level (LIPL). The level of sheath-ground overvoltage is independent of the length of cable; however, it can be limited within LIPL by lowering the sheath grounding impedance to 1.2 Ω. Insulation coordination measures do not impact the likelihood of OHL insulators’ flashover. The flashover performance of OHL can be improved by lowering the footing impedance of the second tower closest to the cable terminals, which is otherwise most likely to flashover. Full article
(This article belongs to the Section Electrical Power and Energy System)
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Open AccessFeature PaperArticle
Towards Overcoming the Curse of Dimensionality: The Third-Order Adjoint Method for Sensitivity Analysis of Response-Coupled Linear Forward/Adjoint Systems, with Applications to Uncertainty Quantification and Predictive Modeling
Energies 2019, 12(21), 4216; https://doi.org/10.3390/en12214216 - 05 Nov 2019
Abstract
This work presents the Third-Order Adjoint Sensitivity Analysis Methodology (3rd-ASAM) for response-coupled forward and adjoint linear systems. The 3rd-ASAM enables the efficient computation of the exact expressions of the 3rd-order functional derivatives (“sensitivities”) of a general system response, which depends on both the [...] Read more.
This work presents the Third-Order Adjoint Sensitivity Analysis Methodology (3rd-ASAM) for response-coupled forward and adjoint linear systems. The 3rd-ASAM enables the efficient computation of the exact expressions of the 3rd-order functional derivatives (“sensitivities”) of a general system response, which depends on both the forward and adjoint state functions, with respect to all of the parameters underlying the respective forward and adjoint systems. Such responses are often encountered when representing mathematically detector responses and reaction rates in reactor physics problems. The 3rd-ASAM extends the 2nd-ASAM in the quest to overcome the “curse of dimensionality” in sensitivity analysis, uncertainty quantification and predictive modeling. This work also presents new formulas that incorporate the contributions of the 3rd-order sensitivities into the expressions of the first four cumulants of the response distribution in the phase-space of model parameters. Using these newly developed formulas, this work also presents a new mathematical formalism, called the 2nd/3rd-BERRU-PM “Second/Third-Order Best-Estimated Results with Reduced Uncertainties Predictive Modeling”) formalism, which combines experimental and computational information in the joint phase-space of responses and model parameters, including not only the 1st-order response sensitivities, but also the complete hessian matrix of 2nd-order second-sensitivities and also the 3rd-order sensitivities, all computed using the 3rd-ASAM. The 2nd/3rd-BERRU-PM uses the maximum entropy principle to eliminate the need for introducing and “minimizing” a user-chosen “cost functional quantifying the discrepancies between measurements and computations,” thus yielding results that are free of subjective user-interferences while generalizing and significantly extending the 4D-VAR data assimilation procedures. Incorporating correlations, including those between the imprecisely known model parameters and computed model responses, the 2nd/3rd-BERRU-PM also provides a quantitative metric, constructed from sensitivity and covariance matrices, for determining the degree of agreement among the various computational and experimental data while eliminating discrepant information. The mathematical framework of the 2nd/3rd-BERRU-PM formalism requires the inversion of a single matrix of size Nr Nr, where Nr denotes the number of considered responses. In the overwhelming majority of practical situations, the number of responses is much less than the number of model parameters. Thus, the 2nd-BERRU-PM methodology overcomes the curse of dimensionality which affects the inversion of hessian matrices in the parameter space. Full article
Open AccessArticle
Experimental Investigation of Displacer Seal Geometry Effects in Stirling Cycle Machines
Energies 2019, 12(21), 4215; https://doi.org/10.3390/en12214215 - 05 Nov 2019
Abstract
This contribution deals with an experimental investigation of the optimization potential of Stirling engines and similar regenerative machines by an enhanced design of the cylinder liner and the seal. The latter is mounted at the bottom end of the gap surrounding pistons and [...] Read more.
This contribution deals with an experimental investigation of the optimization potential of Stirling engines and similar regenerative machines by an enhanced design of the cylinder liner and the seal. The latter is mounted at the bottom end of the gap surrounding pistons and displacers that separate cylinder volumes at different temperature levels. The thermal loss associated with this gap may amount to more than 10% of the heat input into these machines. Mostly, its design is reduced to an estimation of the optimum width by analytical models, which usually do not account for further relevant optimization parameters, such as a step in the cylinder wall. However, a recently developed, enhanced analytical model predicts that this loss may be significantly reduced by such a step. In this work, this design was realized and investigated experimentally according to this prediction by modification of the cylinder liner and the seal of an extensively tested laboratory-scale machine. The results confirm that such a design actually reduces the thermal loss substantially, presumably by reducing the cyclic mass flows through the open end of the gap. Additionally, it even improves the net power output due to a reduced volumetric displacement by the piston or displacer, resulting in smaller flow losses and thermal regenerator losses, whereas the pressure amplitude remains virtually unchanged, contrary to initial expectations. This has led to the remarkable conclusion that the design of most Stirling engines is possibly suboptimal in this respect and may be improved a posteriori by a minor modification; i.e., a reduction of the effective displacer seal diameter. Full article
(This article belongs to the Section Energy Fundamentals and Conversion)
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Open AccessArticle
Environmental Impact Evaluation of Distributed Renewable Energy System Based on Life Cycle Assessment and Fuzzy Rough Sets
Energies 2019, 12(21), 4214; https://doi.org/10.3390/en12214214 - 05 Nov 2019
Abstract
The distributed renewable energy system, integrating various renewable energy resources, is a significant energy supply technology within energy internet. It is an effective way to meet increasingly growing demand for energy conservation and environmental damage reduction in energy generation and energy utilization. In [...] Read more.
The distributed renewable energy system, integrating various renewable energy resources, is a significant energy supply technology within energy internet. It is an effective way to meet increasingly growing demand for energy conservation and environmental damage reduction in energy generation and energy utilization. In this paper, the life cycle assessment (LCA) method and fuzzy rough sets (FRS) theory are combined to build an environmental evaluation model for a distributed renewable energy system. The ReCiPe2016 method is selected to calculate the environmental effect scores of the distributed energy system, and the FRS is utilized to identify the crucial activities and exchanges during its life cycle from cradle to grave. The generalized evaluation method is applied to a real-world case study, a typical distributed energy system located in Yanqing District, Beijing, China, which is composed of wind power, small-scale hydropower, photovoltaic, centralized solar thermal power plant and a biogas power plant. The results show that the environmental effect of per kWh power derived from the distributed renewable energy system is 2.06 × 10−3 species disappeared per year, 9.88 × 10−3 disability-adjusted life years, and 1.75 × 10−3 USD loss on fossil resources extraction, and further in the uncertainty analysis, it is found that the environmental load can be reduced effectively and efficiently by improving life span and annual utilization hour of power generation technologies and technology upgrade for wind turbine and photovoltaic plants. The results show that the proposed evaluation method could fast evaluate the environmental effects of a distributed energy system while the uncertainty analysis with FRS successfully and effectively identifies the key element and link among its life span. Full article
(This article belongs to the Special Issue Life Cycle Assessment of Renewable Energy Sources)
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Open AccessArticle
Techno-Economic Analysis of a Novel Two-Stage Flashing Process for Acid Gas Removal from Natural Gas
Energies 2019, 12(21), 4213; https://doi.org/10.3390/en12214213 - 05 Nov 2019
Abstract
Excessive CO2 content will reduce the natural gas calorific value and increase the energy consumption of the regenerator in natural gas desulfurization and decarbonization. This paper uses Aspen HYSYS to model a novel two-stage flash process of acid gas removal process from [...] Read more.
Excessive CO2 content will reduce the natural gas calorific value and increase the energy consumption of the regenerator in natural gas desulfurization and decarbonization. This paper uses Aspen HYSYS to model a novel two-stage flash process of acid gas removal process from natural gas. According to the results from the simulation, as well as running experiences in a natural gas processing plant in the middle east, it can be demonstrated that this new process, which has been used in the field of natural gas desulfurization and decarbonization, can meet the requirement of product specifications. Based on the steady state simulation, Aspen HYSYS sensitivity function is used to evaluate influence of key operating parameters, such as the second flash pressure and temperature, on the energy consumption. Compared to the traditional acid gas removal process and acid gas enrichment process, the new two-stage flash acid gas removal process has less energy consumption (2.2 × 109 kJ·h−1). In addition, two-stage flash acid gas removal process also improves the efficiency of acid gas enrichment, while the overall energy consumption is less than combination process of traditional process and acid gas enrichment process. Full article
(This article belongs to the Special Issue Modelling of Industrial Processes)
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Open AccessArticle
Selected Rolling Bearing Fault Diagnostic Methods in Wheel Embedded Permanent Magnet Brushless Direct Current Motors
Energies 2019, 12(21), 4212; https://doi.org/10.3390/en12214212 - 05 Nov 2019
Abstract
In recent years, the number of outer rotor permanent magnet brushless direct current (PM BLDC) motor drives has been intensively growing. Due to the specifics of drive operation, bearing faults are especially common, which results in motor stoppage. In a number of these [...] Read more.
In recent years, the number of outer rotor permanent magnet brushless direct current (PM BLDC) motor drives has been intensively growing. Due to the specifics of drive operation, bearing faults are especially common, which results in motor stoppage. In a number of these types of motor applications, the monitoring and diagnostics of bearing conditions is relatively rare. This article presents the results of research aimed at searching for simple and simultaneously effective methods for assessing the condition of bearings that can be built into the drive control system. In the experimental research, four vibration signal processing methods were analysed with regards to the identification accuracy of fault symptoms in the geometric elements of bearings (characteristic frequencies). The results are presented for three cases of bearing faults and compared with a new bearing, they were obtained based on a vibration signal analysis using the classical fast Fourier transform (FFT), Fourier transform of signal absolute values, Fourier transform of an envelope signal obtained using the Hilbert transform, and the Fourier transform of a signal filtered with the Teager–Kaiser energy operator (TKEO). Full article
(This article belongs to the Special Issue Condition Monitoring and Diagnosis of Electrical Machines)
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Open AccessArticle
Beyond Carbon Steel: Detecting Wellbore Shape and Cavities, and Cement Imperfections in Cased Wells
Energies 2019, 12(21), 4211; https://doi.org/10.3390/en12214211 - 05 Nov 2019
Abstract
The non-corrosive, electrically resistive fiberglass casing materials may improve the economics of oil and gas field projects. At moderate temperatures (<120 °C), fiberglass casing is superior to carbon steel casing in applications that involve wet CO2 injection and/or production, such as carbon [...] Read more.
The non-corrosive, electrically resistive fiberglass casing materials may improve the economics of oil and gas field projects. At moderate temperatures (<120 °C), fiberglass casing is superior to carbon steel casing in applications that involve wet CO2 injection and/or production, such as carbon capture and storage, and CO2-based enhanced oil recovery (EOR) methods. Without a perfect protective cement shell, carbon steel casing in contact with a concentrated formation brine corrodes and the fiberglass casing is superior again. Fiberglass casing enables electromagnetic logging for exploration and reservoir monitoring, but it requires the development of new logging methods. Here we present a technique for the detection of integrity of magnetic cement behind resistive fiberglass casing. We demonstrate that an optimized induction logging tool can detect small changes in the magnetic permeability of cement through a non-conductive casing in a vertical (or horizontal) well. We determine both the integrity and solidification state of the cement-filled annulus behind the casing. Changes in magnetic permeability influence mostly the real part of the vertical component of the magnetic field. The signal amplitude is more sensitive to a change in the magnetic properties of the cement, rather than the signal phase. Our simulations showed that optimum separation between the transmitter and receiver coils ranged from 0.25 to 0.6 m, and the most suitable magnetic field frequencies varied from 0.1 to 10 kHz. A high-frequency induction probe operating at 200 MHz can measure the degree of solidification of cement. The proposed method can detect borehole cracks filled with cement, incomplete lift of cement, casing eccentricity, and other borehole inhomogeneities. Full article
(This article belongs to the Special Issue Drilling Technologies for the Next Generations)
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Open AccessArticle
Mechanism Analysis of Sympathetic Inrush in Traction Network Cascaded Transformers Based on Flux-Current Circuit Model
Energies 2019, 12(21), 4210; https://doi.org/10.3390/en12214210 - 04 Nov 2019
Abstract
When electric multiple units (EMU) pass the neutral zone, the traction transformer may generate sympathetic inrush, which will cause a malfunction in the transformer differential protection. In order to study the mechanism of the sympathetic inrush of the cascaded traction transformer, the flux–current [...] Read more.
When electric multiple units (EMU) pass the neutral zone, the traction transformer may generate sympathetic inrush, which will cause a malfunction in the transformer differential protection. In order to study the mechanism of the sympathetic inrush of the cascaded traction transformer, the flux–current model of the transformer, line impedance, power system voltage source, and other loads was established. On the basis of the flux–current circuit model, the influence of different factors on the sympathetic inrush of the traction transformer was analyzed. The analysis results were verified by simulation. Research results show that the remanence, closing angle, line impedance, and load will affect the duration and amplitude of the sympathetic inrush. Full article
(This article belongs to the Section Electrical Power and Energy System)
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Open AccessArticle
Estimation of Single-Diode and Two-Diode Solar Cell Parameters by Using a Chaotic Optimization Approach
Energies 2019, 12(21), 4209; https://doi.org/10.3390/en12214209 - 04 Nov 2019
Abstract
Estimation of single-diode and two-diode solar cell parameters by using chaotic optimization approach (COA) is addressed. The proposed approach is based on the use of experimentally determined current-voltage (I-V) characteristics. It outperforms a large number of other techniques in terms of [...] Read more.
Estimation of single-diode and two-diode solar cell parameters by using chaotic optimization approach (COA) is addressed. The proposed approach is based on the use of experimentally determined current-voltage (I-V) characteristics. It outperforms a large number of other techniques in terms of average error between the measured and the estimated I-V values, as well as of time complexity. Implementation of the proposed approach on the I-V curves measured in laboratory environment for different values of solar irradiation and temperature prove its applicability in terms of accuracy, effectiveness and the ease of implementation for a wide range of practical environment conditions. The COA-based parameter estimation is, therefore, useful for PV power converter designers who require fast and accurate model for PV cell/module. Full article
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Open AccessArticle
Research on Overburden Movement Characteristics of Large Mining Height Working Face in Shallow Buried Thin Bedrock
Energies 2019, 12(21), 4208; https://doi.org/10.3390/en12214208 - 04 Nov 2019
Abstract
The overburden movement of the large mining height working face of shallow buried thin bedrock (SBTB) is a complex engineering problem with “time-space-intension”, which is of great significance to realize efficient and safe mining in the northern Shaanxi mining area. Based on the [...] Read more.
The overburden movement of the large mining height working face of shallow buried thin bedrock (SBTB) is a complex engineering problem with “time-space-intension”, which is of great significance to realize efficient and safe mining in the northern Shaanxi mining area. Based on the research object of No. 22201 working face in Zhangjiamao Coal Mine, the roof structure characteristics of large mining height working face in SBTB are researched by field drilling measurement, laboratory test, physical and numerical simulation. The results show that: (1) Based on the measured data of the drillholes, it is concluded that under the mining conditions of SBTB with large mining height, the roof movement is ahead of the weighting of the working face, and the working resistance has a significant time effect. The advanced movement distance is about 20 m, which can be used as an early warning index of the weighting. The lag movement distance in the roof with horizon of 30 m is two periodic weighting intervals, which are about 26 m. (2) The first weighting interval of the working face is 32 m. The roof first break has obvious step sinking phenomenon, and the measured surface appears at a position 45 m away from the transport slot. It is statistically concluded that the periodic weighting interval is 9.5~16.5 m, the average weighting interval is 13 m, which is equivalent to the periodic dynamic crack spacing of the surface. (3) The results of field measurement and physical simulation show that the breaking angle of the roof of the No. 22201 large mining height is about 66°, and the periodic stepping distance of the T-junction suspension area is 6~8m. Along the strike of the working face, the roof breaking is mainly arc arched. The research results ensure the safe and green mining of shallow coal seam. Full article
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Open AccessArticle
Evaluation Method for Penetration Limit of Renewable Energy Sources in Korean Power System
Energies 2019, 12(21), 4207; https://doi.org/10.3390/en12214207 - 04 Nov 2019
Abstract
As Korea aims to increase the extent to which renewable energy sources (RES) account for up to 20% of the total power generated in the country by 2030, the feasibility of this target is a major concern. This concern largely results from the [...] Read more.
As Korea aims to increase the extent to which renewable energy sources (RES) account for up to 20% of the total power generated in the country by 2030, the feasibility of this target is a major concern. This concern largely results from the Korean power system possessing unique characteristics, such as its electrical isolation and high density. To achieve the RES target, the reliable operation of the power system must coexist with an increased share of RES power generation. This study proposes a method to evaluate the penetration limit of RES in the Korean power system considering the existing plans for the long-term electricity supply and demand, as well as its operational requirements. The Korea electric power corporation (KEPCO) planning database of the Korean power system for the next 15 years was employed to determine the penetration limit of RES considering the reliability criteria, including the minimum power generation of conventional sources, primary frequency control requirement, 10-min reserve requirement, and frequency stability. Full article
(This article belongs to the Section Electrical Power and Energy System)
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Open AccessFeature PaperArticle
Technoeconomic Assessment of Hybrid Organosolv–Steam Explosion Pretreatment of Woody Biomass
Energies 2019, 12(21), 4206; https://doi.org/10.3390/en12214206 - 04 Nov 2019
Abstract
This study investigates technoeconomic performance of standalone biorefinery concepts that utilize hybrid organic solvent and steam explosion pretreatment technique. The assessments were made based on a mathematical process model developed in UniSim Design software using inhouse experimental data. The work was motivated by [...] Read more.
This study investigates technoeconomic performance of standalone biorefinery concepts that utilize hybrid organic solvent and steam explosion pretreatment technique. The assessments were made based on a mathematical process model developed in UniSim Design software using inhouse experimental data. The work was motivated by successful experimental applications of the hybrid pretreatment technique on lignocellulosic feedstocks that demonstrated high fractionation efficiency into a cellulose-rich, a hemicellulose-rich and lignin streams. For the biorefinery concepts studied here, the targeted final products were ethanol, organosolv lignin and hemicellulose syrup. Minimum ethanol selling price (MESP) and Internal rate of return (IRR) were evaluated as economic indicators of the investigated biorefinery concepts. Depending on the configuration, and allocating all costs to ethanol, MESP in the range 0.53–0.95 €/L were required for the biorefinery concepts to break even. Under the assumed ethanol reference price of 0.55 €/L, the corresponding IRR were found to be in the range −1.75–10.7%. Hemicellulose degradation and high steam demand identified as major sources of inefficiencies for the process and economic performance, respectively. Sensitivity of MESP and IRR towards the most influential technical, economic and market parameters performed. Full article
(This article belongs to the Special Issue Biorefineries for the Production of Fuel)
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Open AccessFeature PaperArticle
Optimization and Exergy Analysis of Nuclear Heat Storage and Recovery
Energies 2019, 12(21), 4205; https://doi.org/10.3390/en12214205 - 04 Nov 2019
Abstract
The APR1400 Nuclear Heat Storage and Recovery (NHS&R) System described here represents the conceptual design and interface of a tertiary cycle with the secondary system of the Korean nuclear reactor plant APR1400. The system is intended to reliably and efficiently store and recover [...] Read more.
The APR1400 Nuclear Heat Storage and Recovery (NHS&R) System described here represents the conceptual design and interface of a tertiary cycle with the secondary system of the Korean nuclear reactor plant APR1400. The system is intended to reliably and efficiently store and recover thermal energy from a Nuclear Power Plant (NPP) steam system in order to allow flexible power generation using an economical and scalable design. The research incorporates a comprehensive performance analysis of three interface configurations with comparisons based on the 1st and 2nd Laws of Thermodynamics. The investigated configurations are also ranked based on impact analysis of the NHS&R System on the plant configuration and operation. Input data used in the analysis is based on calibrated thermodynamic models of the system arrangements. Results were used to select the preferred APR1400 NHS&R System design configuration as characterized by: (i) maximum system efficiency, (ii) minimized energy losses, (iii) limited impact on existing plant Systems, Structures, and Components (SSC), and (iv) limited impact on plant operations. Case 3 offers several comparative advantages including: (i) high round trip efficiency, (ii) minimal impact on existing plant and equipment, (iii) high utilization of the heat transport and storage media, and (iv) good system control options. Full article
(This article belongs to the Section Energy Storage and Application)
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Open AccessArticle
Study on Multi-DOF Actuator for Improving Power Density
Energies 2019, 12(21), 4204; https://doi.org/10.3390/en12214204 - 04 Nov 2019
Abstract
This study focuses on improving the power density of a spherical multi-degree-of-freedom (multi-DOF) actuator. A spherical multi-DOF actuator that can operate in three DOFs is designed. The actuator features a double air gap to reduce eddy current loss. However, a multi-DOF actuator driven [...] Read more.
This study focuses on improving the power density of a spherical multi-degree-of-freedom (multi-DOF) actuator. A spherical multi-DOF actuator that can operate in three DOFs is designed. The actuator features a double air gap to reduce eddy current loss. However, a multi-DOF actuator driven by a single actuator exhibits low power density. Therefore, a Halbach magnet array is applied to improve the power density of a spherical multi-DOF actuator, and its output characteristics are compared with those of an existing spherical multi-DOF actuator via finite element analysis. Additionally, the output characteristics are analyzed based on changes in the coil pitch angle and magneto-motive force of the rotating winding. Furthermore, it is necessary for a spherical multi-DOF actuator to move to the command position. Hence, a stability analysis is performed to ensure that the spherical multi-DOF actuator is stably driven based on the command position. Full article
(This article belongs to the Special Issue Permanent Magnet Electrical Machines)
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Open AccessArticle
Circuit Topology Analysis for LED Lighting and its Formulation Development
Energies 2019, 12(21), 4203; https://doi.org/10.3390/en12214203 - 04 Nov 2019
Abstract
Light emitted diode (LED) is becoming more popular in the illumination field, and the design of LED lighting is generally made to provide illumination at lower power usage, helping save energy. A power electronic converter is needed to provide the power conversion for [...] Read more.
Light emitted diode (LED) is becoming more popular in the illumination field, and the design of LED lighting is generally made to provide illumination at lower power usage, helping save energy. A power electronic converter is needed to provide the power conversion for these LEDs to meet high efficiency, reduce components, and have low voltage ripple magnitude. The power supply for LED is revisited in this paper. The LEDs connected in series with diode, transistor, or inductor paths are examined. The formulation for each of the cases is described, including the classical converters of buck, boost, buck–boost, and Ćuk. The circuit reductions of the classic circuit, circuit without the capacitor, and without a freewheeling diode are studied. Using LED to replace freewheeling diodes is proposed for circuit component reduction. General equations for different connection paths have been developed. The efficiency and output ripple amplitude of the proposed power converters are investigated. Analytical study shows that the efficiency of proposed circuits can be high and voltage ripple magnitude of proposed circuits can be low. The results show that the proposed circuit topologies can be easily adapted to design LED lighting, which can meet the criteria of high efficiency, minimum components, and low-voltage ripple magnitude at the same time. Full article
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Open AccessArticle
Development of a Control Platform for a Building-Scale Hybrid Solar PV-Natural Gas Microgrid
Energies 2019, 12(21), 4202; https://doi.org/10.3390/en12214202 - 04 Nov 2019
Abstract
Building-scale microgrids are a type of behind-the-meter microgrids where the building operator has control of the distributed energy resources, including, in this case, a natural gas-fired microturbine in addition to solar PV and battery energy storage systems. There is a growing trend in [...] Read more.
Building-scale microgrids are a type of behind-the-meter microgrids where the building operator has control of the distributed energy resources, including, in this case, a natural gas-fired microturbine in addition to solar PV and battery energy storage systems. There is a growing trend in deploying behind-the-meter microgrids due to their benefits including the resiliency of serving critical loads, especially in regions with abundant natural gas. In order to ensure distributed energy resources are dispatched optimally for the desired mode of operation, a hierarchical control platform including a centralized controller was developed and installed. The platform includes communication and control infrastructure that interface with controllers for distributed energy resources and the building automation system of a recently built energy efficient commercial building. Based on desirable outcomes under different grid and building conditions, operational modes were defined for the microgrid controller. The controller is programmed to map each mode to respective operational modes for distributed energy resources controllers. Experimental data for test runs corresponding to two operational modes confirm the communication and control infrastructure can execute hierarchical control commands. Finally, dispatch optimization for a year-long simulation of system operation is presented and the benefits of the hybrid solar PV-natural gas setup are evaluated. Full article
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Open AccessReview
System Planning of Grid-Connected Electric Vehicle Charging Stations and Key Technologies: A Review
Energies 2019, 12(21), 4201; https://doi.org/10.3390/en12214201 - 04 Nov 2019
Abstract
The optimal planning of electric vehicle (EV) charging stations (ECSs) with advanced control algorithms is very important to accelerate the development of EVs, which is a promising solution to reduce carbon emissions of conventional internal combustion engine vehicles (ICEVs). The large and fluctuant [...] Read more.
The optimal planning of electric vehicle (EV) charging stations (ECSs) with advanced control algorithms is very important to accelerate the development of EVs, which is a promising solution to reduce carbon emissions of conventional internal combustion engine vehicles (ICEVs). The large and fluctuant load currents of ECSs can bring negative impacts to both EV-related power converters and power distribution systems if the energy flow is not regulated properly. Recent review papers related to EVs found in open literature have mainly focused on the design of power converter-based chargers and power interfaces, analyses of power quality (PQ) issues, the development of wireless charging techniques, etc. There is currently no review paper that focuses on key technologies in various system configurations, optimal energy management and advanced control issues in practical applications. To compensate for this insufficiency and provide timely research directions, this paper reviews 143 previously published papers related to the aforementioned topics in recent literature including 17 EV-related review papers found in Institute of Electrical and Electronics Engineers (IEEE)/Institution of Engineering and Technology (IET) (IEEE/IET) Electronic Library (IEL) and ScienceDirect OnSite (SDOS) databases. In this paper, existing system configurations, related design methods, algorithms and key technologies for ECSs are systematically reviewed. Based on discussions given in the reviewed papers, the most popular ECS configuration is a hybrid system design that integrates renewable energy (RE)-based power generation (REBPG), various energy storage systems (ESSs), and utility grids. It is noteworthy that the addition of an ESS with properly designed control algorithms can simultaneously buffer the fast, fluctuant power demand during charging, smooth the intermittent power generation of REBPG, and increase the overall efficiency and operating flexibility of ECSs. In addition, verifying the significance of the flexibility and possible profits that portable ESSs provide in ECS networks is a potential research theme in ECS fields, in which the potential applications of portable ESSs in the grid-tied ECSs are numerous and could cover a full technical spectrum. Full article
(This article belongs to the Special Issue Impact of Electric Vehicles on the Power System)
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Open AccessArticle
Thermodynamic Performance of a Double-Effect Absorption Refrigeration Cycle Based on a Ternary Working Pair: Lithium Bromide + Ionic Liquids + Water
Energies 2019, 12(21), 4200; https://doi.org/10.3390/en12214200 - 04 Nov 2019
Abstract
For an absorption cycle, a ternary working pair LiBr–[BMIM]Cl(2.5:1)/H2O was proposed as a new working pair to replace LiBr/H2O. The thermodynamic properties including specific heat capacity, specific enthalpy, density, and viscosity were systematically measured and fitted by the least-squares [...] Read more.
For an absorption cycle, a ternary working pair LiBr–[BMIM]Cl(2.5:1)/H2O was proposed as a new working pair to replace LiBr/H2O. The thermodynamic properties including specific heat capacity, specific enthalpy, density, and viscosity were systematically measured and fitted by the least-squares method. The thermodynamic performance of a double-effect absorption refrigeration cycle based on LiBr–[BMIM]Cl(2.5:1)/H2O was investigated under different refrigeration temperatures from 5 °C to 12 °C. Results showed that the ternary working pair LiBr–[BMIM]Cl(2.5:1)/H2O had advantages in the operating temperature range and corrosivity. Compared with LiBr/H2O, the operating temperature range was 20 °C larger, and the corrosion rates of carbon steel and copper were reduced by more than 50% at 453.15 K. However, the double-effect absorption refrigeration cycle with LiBr–[BMIM]Cl(2.5:1)/H2O achieved a coefficient of performance (COPc) from 1.09 to 1.46 and an exergetic coefficient of performance (ECOPc) from 0.244 to 0.238, which were smaller than those based on LiBr/H2O due to the higher generation temperature and larger flow ratio. Full article
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Open AccessArticle
The Characteristics of Oil Migration due to Water Imbibition in Tight Oil Reservoirs
Energies 2019, 12(21), 4199; https://doi.org/10.3390/en12214199 - 04 Nov 2019
Abstract
In tight oil reservoirs, water imbibition is the key mechanism to improve oil production during shut-in operations. However, the complex microstructure and composition of minerals complicate the interpretation of oil migration during water imbibition. In this study, nuclear magnetic resonance (NMR) T2 [...] Read more.
In tight oil reservoirs, water imbibition is the key mechanism to improve oil production during shut-in operations. However, the complex microstructure and composition of minerals complicate the interpretation of oil migration during water imbibition. In this study, nuclear magnetic resonance (NMR) T2 spectra was used to monitor the oil migration dynamics in tight oil reservoirs. The factors influencing pore size distribution, micro-fractures, and clay minerals were systematically investigated. The results show that the small pores corresponded to a larger capillary pressure and a stronger imbibition capacity, expelling the oil into the large pores. The small pores had a more effective oil recovery than the large pores. As the soaking time increases, the water preferentially entered the natural micro-fractures, expelling the oil in the micro-fractures. Subsequently, the oil in the small pores was slowly expelled. Compared with the matrix pores, natural micro-fractures had a smaller flow resistance and were more conducive to water and oil flow. Clay minerals may have induced micro-fracture propagation, which can act as the oil migration channels during water imbibition. In contrary to the inhibitory effect of natural micro-fractures, the new micro-fractures could contribute to the oil migration from small pores into large pores. This study characterized the oil migration characteristics and provides new insight into tight oil production. Full article
(This article belongs to the Special Issue Development of Unconventional Reservoirs)
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Open AccessArticle
The Role of Support in Formic Acid Decomposition on Gold Catalysts
Energies 2019, 12(21), 4198; https://doi.org/10.3390/en12214198 - 04 Nov 2019
Abstract
Formic acid (FA) can easily be decomposed, affording molecular hydrogen through a controllable catalytic process, thus attaining great importance as a convenient hydrogen carrier for hydrogen energetics. Supported gold nanoparticles are considered to be among the most promising catalysts for such applications. However, [...] Read more.
Formic acid (FA) can easily be decomposed, affording molecular hydrogen through a controllable catalytic process, thus attaining great importance as a convenient hydrogen carrier for hydrogen energetics. Supported gold nanoparticles are considered to be among the most promising catalysts for such applications. However, questions remain regarding the influence of the catalyst support on the reaction selectivity. In this study, we have examined the catalytic activity of typical gold catalysts, such as Au/TiO2, Au/SiO2, and Au/Al2O3 in decomposition of FA, and then compared it with the catalytic activity of corresponding supports. The performance of each catalyst and support was evaluated using a gas-flow packed-bed reactor. It is shown that the target reaction, FA → H2 + CO2, is provided by the presence of gold nanoparticles, whereas the concurrent, undesirable pathway, such as FA → H2O + CO, results exclusively from the acid-base behavior of supports. Full article
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Open AccessArticle
Mathematical Modeling of the Mojave Solar Plants
Energies 2019, 12(21), 4197; https://doi.org/10.3390/en12214197 - 03 Nov 2019
Abstract
Competitiveness of solar energy is one of current main research topics. Overall efficiency of solar plants can be improved by using advanced control strategies. To design and tuning properly advanced control strategies, a mathematical model of the plant is needed. The model has [...] Read more.
Competitiveness of solar energy is one of current main research topics. Overall efficiency of solar plants can be improved by using advanced control strategies. To design and tuning properly advanced control strategies, a mathematical model of the plant is needed. The model has to fulfill two important points: (1) It has to reproduce accurately the dynamics of the real system; and (2) since the model is used to test advanced control strategies, its computational burden has to be as low as possible. This trade-off is essential to optimize the tuning process of the controller and minimize the commissioning time. In this paper, the modeling of the large-scale commercial solar trough plants Mojave Beta and Mojave Alpha is presented. These two models were used to test advanced control strategies to operate the plants. Full article
(This article belongs to the Section Solar Energy and Photovoltaic Systems)
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Open AccessArticle
Research on Micro-Grid Group Intelligent Decision Mechanism under the Mode of Block-Chain and Multi-Agent Fusion
Energies 2019, 12(21), 4196; https://doi.org/10.3390/en12214196 - 03 Nov 2019
Abstract
This paper aims to study the problems of surplus interaction, poor real-time performance, and excessive processing of information in the micro-grid scheduling and decision-making process. Firstly, the micro-grid dual-loop mobile topology structure is designed by using the method of block-chain and multi-agent fusion, [...] Read more.
This paper aims to study the problems of surplus interaction, poor real-time performance, and excessive processing of information in the micro-grid scheduling and decision-making process. Firstly, the micro-grid dual-loop mobile topology structure is designed by using the method of block-chain and multi-agent fusion, realizing the real-time update of the decision-making body. Secondly, on the basis of optimizing the decision-making body, a two-layer model of intelligent decision-making under the decentralized mechanism is established. Aiming at the upper model, based on the theory of block-chain consensus mechanism, this paper proposes an improved evolutionary game algorithm. The maximum risk-benefit in the decision-making process is the objective function, which realizes the evaluation and optimization of decision tasks. For the lower layer model, based on the block-chain distributed ledger theory, this paper proposes an improved hybrid game reinforcement learning algorithm, with the maximum controllable load participation as the objective function, and realizes the optimal configuration of distributed energy in the micro-grid. This paper reveals the rules of group intelligent decision making in micro-grid under multi-task. Finally, the effectiveness of the proposed algorithm is verified by using Beijing Jin-feng Energy Internet Park data. Full article
(This article belongs to the Section Smart Grids and Microgrids)
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Open AccessArticle
Brazil Offshore Wind Resources and Atmospheric Surface Layer Stability
Energies 2019, 12(21), 4195; https://doi.org/10.3390/en12214195 - 03 Nov 2019
Abstract
Brazil’s offshore wind resources are evaluated from satellite winds and ocean heat flux datasets. Winds are extrapolated to the height of modern turbines accounting for atmospheric stability. Turbine technical data are combined with wind and bathymetric information for description of the seasonal and [...] Read more.
Brazil’s offshore wind resources are evaluated from satellite winds and ocean heat flux datasets. Winds are extrapolated to the height of modern turbines accounting for atmospheric stability. Turbine technical data are combined with wind and bathymetric information for description of the seasonal and latitudinal variability of wind power. Atmospheric conditions vary from unstable situations in the tropics, to neutral and slightly stable conditions in the subtropics. Cabo Frio upwelling in the southeast tends to promote slightly stable conditions during the spring and summer. Likewise, Plata plume cold-water intrusions in southern shelf tends to create neutral to slightly stable situations during the fall and winter. Unstable (stable) conditions are associated with weaker (stronger) vertical wind shear. Wind technical resource, accounting for atmospheric stability and air density distribution, is 725 GW between 0–35 m, 980 GW for 0–50 m, 1.3 TW for 0–100 m and 7.2 TW for the Brazilian Exclusive Economic Zone (EEZ). Resources might vary from 2 to 23% according to the chosen turbine. Magnitudes are 20% lower than previous estimates that considered neutral atmosphere conditions. Strong winds are observed on the north (AP, PA), northeast (MA, PI, CE, RN), southeast (ES, RJ) and southern states (SC, RS). There is significant seasonal complementarity between the north and northeast shelves. When accounting for shelf area, the largest integrated resource is located on the north shelf between 0–20 m. Significant resources are also found in the south for deeper waters. Full article
(This article belongs to the Section Wind, Wave and Tidal Energy)
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Open AccessArticle
An Adiabatic Coaxial Line for Microcalorimeter Power Measurements in Wireless Communication for Smart Grid
Energies 2019, 12(21), 4194; https://doi.org/10.3390/en12214194 - 03 Nov 2019
Abstract
This paper presents the extended results and prototype of the adiabatic copper conductor constructed with two interruption points in the external conductor layer, for use as a microcalorimeter power standard in wireless communication for a smart grid frequency range. Gaps are intended to [...] Read more.
This paper presents the extended results and prototype of the adiabatic copper conductor constructed with two interruption points in the external conductor layer, for use as a microcalorimeter power standard in wireless communication for a smart grid frequency range. Gaps are intended to drive down the thermal transfer from the outer environment into microcalorimeter and to reduce measurement inaccuracies in the microcalorimeter. The proposed design method is based on the combination of thermal and electromagnetic finite-element method simulations by which the desired line performance has been tailored. A prototype of the proposed adiabatic line has been manufactured and measurements on the prototype are presented along with the design procedure. Measured results are in line with the ones predicted by numerical calculations. Full article
(This article belongs to the Special Issue 2nd International Colloquium on Smart Grid Metrology (SmaGriMet 2019))
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Open AccessArticle
Impact of Flexible AC Transmission System Devices on Automatic Generation Control with a Metaheuristic Based Fuzzy PID Controller
Energies 2019, 12(21), 4193; https://doi.org/10.3390/en12214193 - 02 Nov 2019
Abstract
The present work proposes a teaching–learning-based optimization (TLBO)-tuned fuzzy proportional-integral-derivative (PID) controller of two-area hydro-thermal generating units for automatic generation control (AGC). The proposed system takes into account the physical constraints such as transport delay (TD), generation rate constraint (GRC), and governor dead [...] Read more.
The present work proposes a teaching–learning-based optimization (TLBO)-tuned fuzzy proportional-integral-derivative (PID) controller of two-area hydro-thermal generating units for automatic generation control (AGC). The proposed system takes into account the physical constraints such as transport delay (TD), generation rate constraint (GRC), and governor dead band (GDB) nonlinearities. Firstly, fuzzy PID controllers were designed for both the areas and their gains were optimized using various minimization objective function criteria. Furthermore, applications of flexible alternating current transmission system (FACTS) devices such as static synchronous series compensator (SSSC), thyristor-controlled series capacitor (TCSC), thyristor-controlled phase shifter (TCPS), and unified power flow controller (UPFC) were investigated by integrating FACTS devices in appropriate locations of the system. The simulation results revealed that the minimum objective values were attained when the UPFC was placed in the system. Lastly, robustness analysis was done to observe the capability of the proposed controller with UPFC by changing system parameters and considering random load disturbances. Full article
(This article belongs to the Section Electrical Power and Energy System)
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