Open AccessArticle
Control Strategy of Single-Phase Three Level Neutral Point Clamped Cascaded Rectifier
Energies 2017, 10(5), 592; doi:10.3390/en10050592 -
Abstract
Single-phase 3-level neutral point clamped cascaded rectifier (3LNPC-CR) has been successfully made its way into traction drive system as a high-voltage traction converter. In this passage, the control issue of the 3LNPC-CR is considered. A transient current control strategy, combined with proportional integral
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Single-phase 3-level neutral point clamped cascaded rectifier (3LNPC-CR) has been successfully made its way into traction drive system as a high-voltage traction converter. In this passage, the control issue of the 3LNPC-CR is considered. A transient current control strategy, combined with proportional integral (PI) controllers, is adopted to achieve unity power factor, satisfactory sinusoidal grid current, regulated overall dc voltage, and even efficient voltage balance between each module. Besides, with regard to the instinct voltage fluctuation problem among dc-link capacitors in one 3-level neutral point clamped (3LNPC) rectifier module, a phase shift carrier space vector pulse width modulation (PSC-SVPWM) worked along with a reasonable redundancy selection scheme is addressed. In addition, two auxiliary balancing circuits for a single-phase 3LNPC rectifier is proposed. The voltage balancing capacity of these internal-module balancing schemes are analyzed and compared. Finally, the control performance of these proposed strategies are verified by simulations and experiments. Full article
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Open AccessReview
In Situ Stress Measurement Techniques on Li-ion Battery Electrodes: A Review
Energies 2017, 10(5), 591; doi:10.3390/en10050591 -
Abstract
Li-ion batteries experience mechanical stress evolution due in part to Li intercalation into and de-intercalation out of the electrodes, ultimately resulting in performance degradation. In situ measurements of electrode stress can be used to analyze stress generation factors, verify mechanical deformation models, and
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Li-ion batteries experience mechanical stress evolution due in part to Li intercalation into and de-intercalation out of the electrodes, ultimately resulting in performance degradation. In situ measurements of electrode stress can be used to analyze stress generation factors, verify mechanical deformation models, and validate degradation mechanisms. They can also be embedded in Li-ion battery management systems when stress sensors are either implanted in electrodes or attached on battery surfaces. This paper reviews in situ measurement methods of electrode stress based on optical principles, including digital image correlation, curvature measurement, and fiber optical sensors. Their experimental setups, principles, and applications are described and contrasted. This literature review summarizes the current status of these stress measurement methods for battery electrodes and discusses recent developments and trends. Full article
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Open AccessArticle
Probabilistic Power Flow Method Considering Continuous and Discrete Variables
Energies 2017, 10(5), 590; doi:10.3390/en10050590 -
Abstract
This paper proposes a probabilistic power flow (PPF) method considering continuous and discrete variables (continuous and discrete power flow, CDPF) for power systems. The proposed method—based on the cumulant method (CM) and multiple deterministic power flow (MDPF) calculations—can deal with continuous variables such
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This paper proposes a probabilistic power flow (PPF) method considering continuous and discrete variables (continuous and discrete power flow, CDPF) for power systems. The proposed method—based on the cumulant method (CM) and multiple deterministic power flow (MDPF) calculations—can deal with continuous variables such as wind power generation (WPG) and loads, and discrete variables such as fuel cell generation (FCG). In this paper, continuous variables follow a normal distribution (loads) or a non-normal distribution (WPG), and discrete variables follow a binomial distribution (FCG). Through testing on IEEE 14-bus and IEEE 118-bus power systems, the proposed method (CDPF) has better accuracy compared with the CM, and higher efficiency compared with the Monte Carlo simulation method (MCSM). Full article
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Open AccessArticle
China Building Energy Consumption: Definitions and Measures from an Operational Perspective
Energies 2017, 10(5), 582; doi:10.3390/en10050582 -
Abstract
China building energy consumption (BEC) has been gradually derived and also sparked attention. However, something worth discussing is estimating the BEC based on the definition of life cycle or building operation. In addition, there exists discrepancy in the previous studies and the real
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China building energy consumption (BEC) has been gradually derived and also sparked attention. However, something worth discussing is estimating the BEC based on the definition of life cycle or building operation. In addition, there exists discrepancy in the previous studies and the real status of BEC has not been known well. In order to settle the disputes over the calculation of BEC, this paper establishes an appropriate accounting method of building energy to present the BEC situation in China and lays the foundation for policymakers to develop appropriate energy saving policies. Meanwhile, this study attempts to clarify the BEC to help policymakers assess the effect of environmental policies. Using the method in this document, we find that the energy consumption of buildings just accounts for 15%–16% of the final total energy consumption in China; by contrast, the previous studies usually have double accounting through a top-down approach if central heat supply of buildings was taken into additional consideration. Full article
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Open AccessReview
Green and Sustainable Cellular Base Stations: An Overview and Future Research Directions
Energies 2017, 10(5), 587; doi:10.3390/en10050587 -
Abstract
Energy efficiency and renewable energy are the main pillars of sustainability and environmental compatibility. This study presents an overview of sustainable and green cellular base stations (BSs), which account for most of the energy consumed in cellular networks. We review the architecture of
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Energy efficiency and renewable energy are the main pillars of sustainability and environmental compatibility. This study presents an overview of sustainable and green cellular base stations (BSs), which account for most of the energy consumed in cellular networks. We review the architecture of the BS and the power consumption model, and then summarize the trends in green cellular network research over the past decade. As its major contribution, this study highlights the uses of renewable energy in cellular communication by: (i) investigating the system model and the potential of renewable energy solutions for cellular BSs; (ii) identifying the potential geographical locations for renewable-energy-powered BSs; (iii) performing case studies on renewable-energy-powered cellular BSs and suggesting future research directions based on our findings; (iv) examining the present deployment of sustainable and green BSs; and (v) studying the barriers that prevent the widespread use of renewable-energy-powered BSs and providing recommendations for future work. Full article
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Open AccessArticle
A Cost Optimized Fully Sustainable Power System for Southeast Asia and the Pacific Rim
Energies 2017, 10(5), 583; doi:10.3390/en10050583 -
Abstract
In this paper, a cost optimal 100% renewable energy based system is obtained for Southeast Asia and the Pacific Rim region for the year 2030 on an hourly resolution for the whole year. For the optimization, the region was divided into 15 sub-regions
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In this paper, a cost optimal 100% renewable energy based system is obtained for Southeast Asia and the Pacific Rim region for the year 2030 on an hourly resolution for the whole year. For the optimization, the region was divided into 15 sub-regions and three different scenarios were set up based on the level of high voltage direct current grid connections. The results obtained for a total system levelized cost of electricity showed a decrease from 66.7 €/MWh in a decentralized scenario to 63.5 €/MWh for a centralized grid connected scenario. An integrated scenario was simulated to show the benefit of integrating additional demand of industrial gas and desalinated water which provided the system the required flexibility and increased the efficiency of the usage of storage technologies. This was reflected in the decrease of system cost by 9.5% and the total electricity generation by 5.1%. According to the results, grid integration on a larger scale decreases the total system cost and levelized cost of electricity by reducing the need for storage technologies due to seasonal variations in weather and demand profiles. The intermittency of renewable technologies can be effectively stabilized to satisfy hourly demand at a low cost level. A 100% renewable energy based system could be a reality economically and technically in Southeast Asia and the Pacific Rim with the cost assumptions used in this research and it may be more cost competitive than the nuclear and fossil carbon capture and storage (CCS) alternatives. Full article
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Open AccessReview
Structured Literature Review of Electricity Consumption Classification Using Smart Meter Data
Energies 2017, 10(5), 584; doi:10.3390/en10050584 -
Abstract
Smart meters for measuring electricity consumption are fast becoming prevalent in households. The meters measure consumption on a very fine scale, usually on a 15 min basis, and the data give unprecedented granularity of consumption patterns at household level. A multitude of papers
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Smart meters for measuring electricity consumption are fast becoming prevalent in households. The meters measure consumption on a very fine scale, usually on a 15 min basis, and the data give unprecedented granularity of consumption patterns at household level. A multitude of papers have emerged utilizing smart meter data for deepening our knowledge of consumption patterns. This paper applies a modification of Okoli’s method for conducting structured literature reviews to generate an overview of research in electricity customer classification using smart meter data. The process assessed 2099 papers before identifying 34 significant papers, and highlights three key points: prominent methods, datasets and application. Three important findings are outlined. First, only a few papers contemplate future applications of the classification, rendering papers relevant only in a classification setting. Second; the encountered classification methods do not consider correlation or time series analysis when classifying. The identified papers fail to thoroughly analyze the statistical properties of the data, investigations that could potentially improve classification performance. Third, the description of the data utilized is of varying quality, with only 50% acknowledging missing values impact on the final sample size. A data description score for assessing the quality in data description has been developed and applied to all papers reviewed. Full article
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Open AccessArticle
H∞ Repetitive Control Based on Active Damping with Reduced Computation Delay for LCL-Type Grid-Connected Inverters
Energies 2017, 10(5), 586; doi:10.3390/en10050586 -
Abstract
In the paper, the H∞ repetitive current control scheme based on active damping along with the design method is proposed for three-phase grid-connected inverters with inductor-capacitor-inductor (LCL) filters. The control scheme aims to reduce the harmonic distortion of the output currents and achieve
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In the paper, the H∞ repetitive current control scheme based on active damping along with the design method is proposed for three-phase grid-connected inverters with inductor-capacitor-inductor (LCL) filters. The control scheme aims to reduce the harmonic distortion of the output currents and achieve better efficiency. The design method introduces capacitor-current-feedback active damping into the H∞ controller design process by proposing an equivalent controlled plant. Additionally, based on the discrete model of the controlled plant with variable computation delay, the algebraic expression of the stable region for the feedback coefficient and the computation delay is obtained to avoid system instability caused by the digital control delay. Finally, the stability criterion is proposed to evaluate the stability of the discrete control system with the H∞ repetitive current control scheme. The theoretical analysis and experimental results prove that the control scheme presented in this paper not only can reject the harmonics of output currents, but is robust under the variation of the grid-impedance. Full article
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Open AccessArticle
Space Vector Modulation for an Indirect Matrix Converter with Improved Input Power Factor
Energies 2017, 10(5), 588; doi:10.3390/en10050588 -
Abstract
Pulse width modulation strategies have been developed for indirect matrix converters (IMCs) in order to improve their performance. In indirect matrix converters, the LC input filter is used to remove input current harmonics and electromagnetic interference problems. Unfortunately, due to the existence of
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Pulse width modulation strategies have been developed for indirect matrix converters (IMCs) in order to improve their performance. In indirect matrix converters, the LC input filter is used to remove input current harmonics and electromagnetic interference problems. Unfortunately, due to the existence of the input filter, the input power factor is diminished, especially during operation at low voltage outputs. In this paper, a new space vector modulation (SVM) is proposed to compensate for the input power factor of the indirect matrix converter. Both computer simulation and experimental studies through hardware implementation were performed to verify the effectiveness of the proposed modulation strategy. Full article
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Open AccessArticle
Evaluation of Interface Defects in Inaccessible Reactor Shrink Fit Nozzle Welds Using Ultrasonic Waves
Energies 2017, 10(5), 589; doi:10.3390/en10050589 -
Abstract
This study proposes an effective method to inspect inaccessible nuclear power reactor head nozzles using interface waves that propagate along the shrink fit boundary of a reactor head. The reactor head is relatively thick, which makes it difficult to inspect from the outside
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This study proposes an effective method to inspect inaccessible nuclear power reactor head nozzles using interface waves that propagate along the shrink fit boundary of a reactor head. The reactor head is relatively thick, which makes it difficult to inspect from the outside by conventional ultrasonic testing. However, interface waves can propagate a long distance from a fixed transducer position. The inside of the nuclear reactor has limited access due to the high radiation, so the transducers are located outside the nuclear reactor head, and interface waves propagate into the nuclear reactor to detect defects. A numerical simulation and experiments were carried out to validate the method. Various defect cases that simulate field failures are also presented, and the proposed technique shows satisfactory defect classification. Full article
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Open AccessArticle
A Short-Current Control Method for Constant Frequency Current-Fed Wireless Power Transfer Systems
Energies 2017, 10(5), 585; doi:10.3390/en10050585 -
Abstract
Frequency drift is a serious problem in Current-Fed Wireless Power Transfer (WPT) systems. When the operating frequency is drifting from the inherent Zero Voltage Switching (ZVS) frequency of resonant network, large short currents will appear and damage the switches. In this paper, an
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Frequency drift is a serious problem in Current-Fed Wireless Power Transfer (WPT) systems. When the operating frequency is drifting from the inherent Zero Voltage Switching (ZVS) frequency of resonant network, large short currents will appear and damage the switches. In this paper, an inductance-dampening method is proposed to inhibit short currents and achieve constant-frequency operation. By adding a small auxiliary series inductance in the primary resonant network, short currents are greatly attenuated to a safe level. The operation principle and steady-state analysis of the system are provided. An overlapping time self-regulating circuit is designed to guarantee ZVS running. The range of auxiliary inductances is discussed and its critical value is calculated exactly. The design methodology is described and a design example is presented. Finally, a prototype is built and the experimental results verify the proposed method. Full article
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Open AccessFeature PaperArticle
Double-Carrier Phase-Disposition Pulse Width Modulation Method for Modular Multilevel Converters
Energies 2017, 10(4), 581; doi:10.3390/en10040581 -
Abstract
Modular multilevel converters (MMCs) have become one of the most attractive topologies for high-voltage and high-power applications. A double-carrier phase disposition pulse width modulation (DCPDPWM) method for MMCs is proposed in this paper. Only double triangular carriers with displacement angle are needed for
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Modular multilevel converters (MMCs) have become one of the most attractive topologies for high-voltage and high-power applications. A double-carrier phase disposition pulse width modulation (DCPDPWM) method for MMCs is proposed in this paper. Only double triangular carriers with displacement angle are needed for DCPDPWM, one carrier for the upper arm and the other for the lower arm. Then, the theoretical analysis of DCPDPWM for MMCs is presented by using a double Fourier integral analysis method, and the Fourier series expression of phase voltage, line-to-line voltage and circulating current are deduced. Moreover, the impact of carrier displacement angle between the upper and lower arm on harmonic characteristics is revealed, and further the optimum displacement angles are specified for the circulating current harmonics cancellation scheme and output voltage harmonics minimization scheme. Finally, the proposed method and theoretical analysis are verified by simulation and experimental results. Full article
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Open AccessArticle
Influences of Winding MMF Harmonics on Torque Characteristics in Surface-Mounted Permanent Magnet Vernier Machines
Energies 2017, 10(4), 580; doi:10.3390/en10040580 -
Abstract
This paper presents the influences of winding magneto-motive force (MMF) harmonics on the torque characteristics in surface-mounted permanent magnet vernier (SPMV) machines. Based on the magnetic gearing effects, the armature magnetic field of the SPMV machines is modulated by flux modulation poles (FMPs).
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This paper presents the influences of winding magneto-motive force (MMF) harmonics on the torque characteristics in surface-mounted permanent magnet vernier (SPMV) machines. Based on the magnetic gearing effects, the armature magnetic field of the SPMV machines is modulated by flux modulation poles (FMPs). In the modulated magnetic field, a working harmonic which corresponds to the number of the rotor pole pairs generates torque. Unlike regular PM machines, the winding MMF harmonics in the SPMV machines can produce the working harmonic by adjusting the FMP shapes. In order to investigate the effects of the winding MMF harmonics, the operating principle of the SPMV machines is elaborated by an analytical method using the winding MMF distribution and air-gap permeance function. After that, the design method of the FMP shapes that can improve the output torque by using the winding MMF harmonics is proposed. For the SPMV machine having 6 slots and 24 FMPs, the effects of the winding MMF harmonics and the validity of the proposed design method are confirmed by the finite element analysis method. It is shown that the proposed design method can improve the performances of the SPMV machine in terms of the torque density, induced electromagnetic force, and efficiency. Full article
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Open AccessArticle
Multi-Objective History Matching with a Proxy Model for the Characterization of Production Performances at the Shale Gas Reservoir
Energies 2017, 10(4), 579; doi:10.3390/en10040579 -
Abstract
This paper presents a fast, reliable multi-objective history-matching method based on proxy modeling to forecast the production performances of shale gas reservoirs for which all available post-hydraulic-fracturing production data, i.e., the daily gas rate and cumulative-production volume until the given date, are honored.
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This paper presents a fast, reliable multi-objective history-matching method based on proxy modeling to forecast the production performances of shale gas reservoirs for which all available post-hydraulic-fracturing production data, i.e., the daily gas rate and cumulative-production volume until the given date, are honored. The developed workflow consists of distance-based generalized sensitivity analysis (DGSA) to determine the spatiotemporal-parameter significance, fast marching method (FMM) as a proxy model, and a multi-objective evolutionary algorithm to integrate the dynamic data. The model validation confirms that the FMM is a sound surrogate model working within an error of approximately 2% for the estimated ultimate recovery (EUR), and it is 11 times faster than a full-reservoir simulation. The predictive accuracy on future production after matching 1.5-year production histories is assessed to examine the applicability of the proposed method. The DGSA determines the effective parameters with respect to the gas rate and the cumulative volume, including fracture permeability, fracture half-length, enhanced permeability in the stimulated reservoir volume, and average post-fracturing porosity. A comparison of the prediction accuracy for single-objective optimization shows that the proposed method accurately estimates the recoverable volume as well as the production profiles to within an error of 0.5%, while the single-objective consideration reveals the scale-dependency problem with lesser accuracy. The results of this study are useful to overcome the time-consuming effort of using a multi-objective evolutionary algorithm and full-scale reservoir simulation as well as to conduct a more-realistic prediction of the shale gas reserves and the corresponding production performances. Full article
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Open AccessArticle
Aerodynamic Analysis of a Helical Vertical Axis Wind Turbine
Energies 2017, 10(4), 575; doi:10.3390/en10040575 -
Abstract
Vertical axis wind turbines (VAWTs) are gradually receiving more and more interest due to their lower sensitivity to the yawed wind direction. Compared with straight blades VAWT, blades with a certain helicity show a better aerodynamic performance and less noise emission. Nowadays computational
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Vertical axis wind turbines (VAWTs) are gradually receiving more and more interest due to their lower sensitivity to the yawed wind direction. Compared with straight blades VAWT, blades with a certain helicity show a better aerodynamic performance and less noise emission. Nowadays computational fluid dynamics technology is frequently applied to VAWTs and gives results that can reflect real flow phenomena. In this paper, a 2D flow field simulation of a helical vertical axis wind turbine (HVAWT) with four blades has been carried out by means of a large eddy simulation (LES). The power output and fluctuation at each azimuthal position are studied with different tip speed ratio (TSR). The result shows that the variation of angle of attack (AOA) and blade-wake interaction under different TSR conditions are the two main reasons for the effects of TSR on power output. Furthermore, in order to understand the characteristics of the HVAWT along the spanwise direction, the 3D full size flow field has also been studied by the means of unsteady Reynold Averaged Navier-Stokes (U-RANS) and 3D effects on the turbine performance can be observed by the spanwise pressure distribution. It shows that tip vortex near blade tips and second flow in the spanwise direction also play a major role on the performance of VAWTs. Full article
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Open AccessArticle
Primary and Albedo Solar Energy Sources for High Altitude Persistent Air Vehicle Operation
Energies 2017, 10(4), 573; doi:10.3390/en10040573 -
Abstract
A new class of the all electric airship to globally transport both passengers and freight using a ‘feeder-cruiser’ concept, and powered by renewable electric energy, is considered. Specific focus is given to photo-electric harvesting as the primary energy source and the associated hydrogen-based
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A new class of the all electric airship to globally transport both passengers and freight using a ‘feeder-cruiser’ concept, and powered by renewable electric energy, is considered. Specific focus is given to photo-electric harvesting as the primary energy source and the associated hydrogen-based energy storage systems. Furthermore, it is shown that the total PV output may be significantly increased by utilising cloud albedo effects. Appropriate power architectures and energy audits required for life support, and the propulsion and ancillary loads to support the continuous daily operation of the primary airship (cruiser) at stratospheric altitudes (circa 18 km), are also considered. The presented solution is substantially different from those of conventional aircraft due to the airship size and the inherent requirement to harvest and store sufficient energy during “daylight” operation, when subject to varying seasonal conditions and latitudes, to ensure its safe and continued operation during the corresponding varying “dark hours”. This is particularly apparent when the sizing of the proposed electrolyser is considered, as its size and mass increase nonlinearly with decreasing day-night duty. As such, a Unitized Regenerative Fuel Cell is proposed. For the first time the study also discusses the potential benefits of integrating the photo-voltaic cells into airship canopy structures utilising TENSAIRITY®-based elements in order to eliminate the requirements for separate inter-PV array wiring and the transport of low pressure hydrogen between fuel cells. Full article
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Open AccessArticle
Enhancing Oil Recovery from Chalk Reservoirs by a Low-Salinity Water Flooding Mechanism and Fluid/Rock Interactions
Energies 2017, 10(4), 576; doi:10.3390/en10040576 -
Abstract
Different Low Salinity Waters (LSWs) are investigated in this work to understand the role of some ions, which were recognized from our previous work and the literature for their effect on wettability alteration. Different flooding stages were followed. The primary stage was by
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Different Low Salinity Waters (LSWs) are investigated in this work to understand the role of some ions, which were recognized from our previous work and the literature for their effect on wettability alteration. Different flooding stages were followed. The primary stage was by injecting synthetic seawater (SSW) and the secondary stage was with SSW diluted by 10 (LSW 1:10) and 50 (LSW 1:50) times, single and two salt brines, such as Na2SO4, MgCl2, and NaCl+MgCl2 at 70 °C. The flooding sequence was due to that most of the fields in the North Sea were flooded with seawater. Two flooding rates were followed, 4 PV/day (PV = Pore Volume) and 16 PV/day in all the experiments. One of the observations was the increase of the pH during the flooding with LSW and single salt brines. The increase of the pH was attributed to mineral precipitation/dissolution as the results of ionic interactions. The effluent ion concentrations measured to understand the most likely oil recovery mechanisms. The results showed that the higher the SSW dilution the slower the oil recovery response. In presence of SO42−, Ca/Mg, higher oil recovery. The exchange between Ca/Mg, was in line with field observations. A geochemical simulation was done for a comparison with the experimental data. Full article
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Open AccessArticle
Automatic Tracking of the Modal Parameters of an Offshore Wind Turbine Drivetrain System
Energies 2017, 10(4), 574; doi:10.3390/en10040574 -
Abstract
An offshore wind turbine (OWT) is a complex structure that consists of different parts (e.g., foundation, tower, drivetrain, blades, et al.). The last decade, there has been continuous trend towards larger machines with the goal of cost reduction. Modal behavior is an important
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An offshore wind turbine (OWT) is a complex structure that consists of different parts (e.g., foundation, tower, drivetrain, blades, et al.). The last decade, there has been continuous trend towards larger machines with the goal of cost reduction. Modal behavior is an important design aspect. For tackling noise, vibration, and harshness (NVH) issues and validating complex simulation models, it is of high interest to continuously track the vibration levels and the evolution of the modal parameters (resonance frequencies, damping ratios, mode shapes) of the fundamental modes of the turbine. Wind turbines are multi-physical machines with significant interaction between their subcomponents. This paper will present the possibility of identifying and automatically tracking the structural vibration modes of the drivetrain system of an instrumented OWT by using signals (e.g., acceleration responses) measured on the drivetrain system. The experimental data has been obtained during a measurement campaign on an OWT in the Belgian North Sea where the OWT was in standstill condition. The drivetrain, more specifically the gearbox and generator, is instrumented with a dedicated measurement set-up consisting of 17 sensor channels with the aim to continuously track the vibration modes. The consistency of modal parameter estimates made at consequent 10-min intervals is validated, and the dominant drivetrain modal behavior is identified and automatically tracked. Full article
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Open AccessArticle
PTC Self-Heating Experiments and Thermal Modeling of Lithium-Ion Battery Pack in Electric Vehicles
Energies 2017, 10(4), 572; doi:10.3390/en10040572 -
Abstract
This paper proposes a positive temperature coefficient (PTC) self-heating method, in which EVs can be operated independently of external power source at low temperature, with a lithium-ion battery (LIB) pack discharging electricity to provide PTC material with power. Three comparative heating experiments have
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This paper proposes a positive temperature coefficient (PTC) self-heating method, in which EVs can be operated independently of external power source at low temperature, with a lithium-ion battery (LIB) pack discharging electricity to provide PTC material with power. Three comparative heating experiments have been carried out respectively. With charge/discharge tests implemented, results demonstrate the superiority of the self-heating method, proving that the discharge capability, especially the discharge capacity of the self-heated pack is better than that of the external power heated pack. In order to evaluate the heating effect of this method, further studies are conducted on temperature distribution uniformity in the heated pack. Firstly, a geometric model is established, and heat-generation rate of PTC materials and LIB are calculated. Then, thermal characteristics of the self-heating experiment processes are numerically simulated, validating the accuracy of our modeling and confirming that temperature distributions inside the pack after heating are kept in good uniformity. Therefore, the PTC self-heating method is verified to have a significant effect on the improvement of performance of LIB at low temperature. Full article
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Open AccessArticle
Performance Comparison between Selected Evaporative Air Coolers
Energies 2017, 10(4), 577; doi:10.3390/en10040577 -
Abstract
The aim of this study is to determine which of the heat exchangers is characterized by the highest efficiency in different applications. Various types of evaporative air coolers were compared: a typical counter-flow unit, the same unit operating as a heat recovery exchanger,
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The aim of this study is to determine which of the heat exchangers is characterized by the highest efficiency in different applications. Various types of evaporative air coolers were compared: a typical counter-flow unit, the same unit operating as a heat recovery exchanger, a regenerative unit and a novel, modified regenerative exchanger. The analysis includes comparing the work of evaporative heat exchangers during summer and winter season. The analysis is based on the original mathematical models. The numerical models are based on the modified ε-NTU (number of heat transfer units) method. It was established that selected arrangements of the presented exchangers are characterized by the different efficiency in different air-conditioning applications. The analysis faces the main construction aspects of those evaporative coolers and also compares two above-mentioned devices with modified regenerative air cooler, which can partly operate on cooled outdoor airflow and on the exhaust air from conditioned spaces. This solution can be applied in any climate and it is less dependent on the outdoor conditions. The second part of the study focuses on winter season and the potential of recovering heat with the same exchangers, but with dry working air channels. This allows establishing their total potential of generating energy savings during the annual operation. Full article
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