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When the proton exchange membrane fuel cell is used as a power source device to operate in a low temperature environment, the cell will have a series of problems such as difficulty in starting due to the overall low temperature, reduced output performance, and reduced life. External heating agent heating is one of the important methods to solve the above problems. In this paper, based on the most commonly used rectangular DC channel fuel cell model, a numerical simulation method is used to analyze the effect of different temperature heating agents on the continuous output performance of the cell at an ambient temperature of 253.15 K. By analyzing the cell polarization curve, temperature, material distribution, and current density under four operating conditions, it was found that the addition of an external heating agent helps to improve the output performance of the cell in a low-temperature environment. Among them, the optimization effect is most obvious when the temperature of the heating agent is 313.15 K in the studied temperature range. [ABSTRACT FROM AUTHOR]

In this study, Solar Cell Capacitance Simulator (SCAPS-1D) is utilized to examine the properties of cadmium telluride (CdTe) based solar cell. The key aim of this study is to explore the prospects of enhancing the efficiency of CdTe solar cells by adding a high resistivity transparent (HRT) layer to the conventional cell structure. For that purpose, novel HRT layer structures are suggested in CdTe solar cells between a cadmium sulfide (CdS) window layer and transparent conductive oxide (TCO) layer. Simulation results presented in this paper are from four proposed structures with three different HRT materials compared to the conventional design. The optimal parameters that offer the optimum functionality of the conventional design (SnO2/CdS/CdTe/MoTe2), with and without the HRT layer, are determined. Obtained results validate an enhancement in efficiency of the solar cell with Zn2SO4 as the HRT layer due to lower recombination loss and barrier height at the back contact region. The suggested cell with Zn2SO4 demonstrates an efficiency of 17.61% (Voc = 0.92 V, Jsc = 25.41 mA/cm2, FF = 75.35), with only 20 nm HRT layer and 25 nm CdS as a window layer. In the meantime, the reference cell (no HRT layer) depicts an efficiency of 17.01% with 4000 nm thick CdTe as an absorber layer. However, the normalized efficiency of the suggested cells decreases linearly with increased temperature. [ABSTRACT FROM AUTHOR]

In this paper, a single-phase extended-boost quasi-Z source (EqZS) cascaded multilevel inverter (CMI) for photovoltaic power systems is proposed. A phase-shifted pulse width amplitude modulation strategy based on dual switching frequency modulation (DFM-PWAM) for the inverter is also presented. Compared to the traditional quasi-Z source inverter, the EqZS network can significantly increase the dc-link voltage and achieve a higher voltage gain. Due to the inherent double-line-frequency (2ω) voltage and current ripples in the single-phase EqZS inverter (EqZSI), an accurate equivalent model based on the EqZSI module is established to design rational parameters of the EqZS network, which can limit the 2ω ripples in the required range. However, large capacitance and inductance are needed to restrain 2ω ripples through this method, which results in a bulky impedance-source network. Higher switching frequency can reduce the size of the impedance-source network but will increase the switching losses due to hard-switching. The proposed DFM-PWAM technique can not only keep a compact impedance-source network but also mitigate the switching frequency effect on the switching losses. Finally, simulation and experimental results validate the feasibility of the proposed topology and modulation technique and the correctness of theory. [ABSTRACT FROM AUTHOR]

This paper presents a hybrid global maximum power point tracking (MPPT) algorithm under partial shading conditions, which consists of five methods, including the global scanning method, the filtering method, the binary searching method, the three-point method, and the anti-restarting method. By making full use of the advantages of these methods, the proposed algorithm is able to improve tracking speed and efficiency, decrease oscillation, and avoid restarting. Among which, the global scanning method is used to find all the local intervals, the filtering method is used to reduce the search area, the binary searching method is used to reduce the search time, the three-point method is used to track the global maximum power point dynamically, and the anti-restarting method is used to prevent restarting the algorithm. To verify the proposed algorithm, experiments have been carried out in a standard environment, dynamic solar irradiation, and dynamic temperature, respectively. The performance of the proposed algorithm is verified by comparing it with a perturb and observe (P&O) based global scanning MPPT method and a modified P&O with checking MPPT method using computer simulations. [ABSTRACT FROM AUTHOR]

This paper addresses an intelligent control scheme using the artificial neural network (ANN) technique for modeling and simulating a central tower receiver (CTR) plant with thermal energy storage (TES). The multilayer perceptron neural network (MLPNN) was implemented with two input parameters, one output parameter, and one hidden layer. The inputs comprise the receiver inlet temperature and the receiver thermal power. The output includes the mass flow rate of heat transfer fluid. A total of 888 datasets and three types of training algorithms, Levenberg-Marquardt (LM), Quasi-Newton, and Scaled Conjugate Gradient, are applied for training the proposed MLPNN model. Among all the investigated learning algorithms, the adopted LM with 40 neurons in the first hidden layer displayed superior ability to efficiently estimate the required performance compared to other learning algorithms. Based on the statistical evaluations, the optimized LM delivered preferred values for the root mean square error (0.0037), the coefficient of variance (0.0011), and the coefficient of determination (0.9999) during the training process. Hence, the MLPNN with LM-40 is an effective technique to precisely control the mass flow rate and subsequently the receiver outlet temperature regardless of the variations in the direct solar radiation and receiver inlet temperature. Furthermore, the generation strategy was modified to regulate CTR/TES output through electricity generation according to the hot storage system conditions. The performance of the adopted CTR-ANN model is presented and compared with the System Advisor Model (SAM) results. The results demonstrate better compatibility between the adopted CTR-ANN model and SAM outputs. The simplicity and minimum required input data of our proposed model make it appropriate for evaluating the power system reliability by using the Monte Carlo method. [ABSTRACT FROM AUTHOR]

DC microgrids are desired to provide the electricity for the remote areas which are far from the main grid. The microgrid gets popularity because DC power sources such as photovoltaics (PVs), battery banks, and fuel cells can be interconnected without AC/DC converters. The stochastic nature of PV power and variation in the demand are responsible for voltage fluctuations in the DC microgrids. The voltage stability is a most important issue in the case of DC microgrids. The challenging thing is to maintain the microgrid voltage up to a reference value for the variable load. This paper focuses on designing a controller to obtain the voltage stability of the microgrid. Two controllers [PI and fuzzy logic PI (FL-PI)] are designed for the voltage stability analysis of the DC microgrid. Real-time simulation results show that upon appropriate choice of controller parameters, the DC microgrid voltage can be kept constant regardless of the wide range of voltage variations of the source and the load. The simulation results show the comparison of two controllers. The FL-PI controller shows much better performance than the conventional PI controller for the DC grid voltage control. With the inclusion of the proposed controllers, controlled voltage will be obtained, whatever may be the load and its variation. [ABSTRACT FROM AUTHOR]

As the power demand for electric vehicles, the estimations of state of charge (SOC) and state of health (SOH) for the lithium-ion battery are important in a battery management system. In this paper, a method for SOC and SOH joint estimation based on a dual sliding mode observer (DSMO) has been presented considering the capacity fading factor. An equivalent circuit model with one resistor and capacitor network is built to represent the dynamic behaviors of lithium-ion batteries. Moreover, the uncertainties of model are considered to improve the accuracy of the battery model. One observer of DSMO is used to estimate the terminal voltage and SOC. The other observer is used to estimate the battery capacity and then to calculate SOH. The convergence of DSMO for SOC and SOH estimation is proved by the Lyapunov stability theory. Based on the proposed battery model with uncertainties, DSMO can avoid the chattering effects and improve the estimation accuracy. AMESim and Simulink co-simulation is adopted to evaluate the performance of DSMO. The results show that the proposed DSMO has good performance and robustness. [ABSTRACT FROM AUTHOR]

The present paper focuses on the numerical investigation and the assessment of finite water depth effects on the performance (hydrodynamic behavior and energy absorption) of a wave farm. The farm consists of nine, free floating, mutually interacting, heaving Wave Energy Converters (WECs), arranged in a 3 × 3 rectilinear grid. The WECs' Power Taking Off (PTO) mechanism, actuated from their heave motion, is modelled as a linear damping system. Linear frequency domain analysis is implemented under the action of head regular and irregular waves, while three different installation depths are examined. For defining the PTO's damping coefficient, the water depth effect on the heave radiation damping coefficient is considered. Moreover, in the case of irregular waves, an incident wave spectrum with finite depth spectral formulation (TMA spectrum) is deployed for taking into account limited water depth conditions. Constructive and destructive interactions among the WECs in terms of power absorption are appropriately quantified, and the water depth effects on the existence and the extent of these interactions are assessed. The results of the present study illustrate that water depth effects are pronounced in the case of irregular waves, where the water depth's decrease leads to a significant decrease in the WECs' response and the farm's absorbed power, especially for the smallest examined installation depth. However, the comparison of absorbed power losses with power resource losses demonstrates that although the farm's installation at smaller water depth results in significant power resource losses, the farm's capture efficiency is not so intensively reduced. [ABSTRACT FROM AUTHOR]

C u 2 ZnSn S 4 ( CZTS ) is a non-toxic earth abundant material and a promising quaternary semiconductor compound of groups I − I I − I V − V I having a kesterite symmetrical structure. Due to its optimum direct bandgap, it has been considered as a suitable material for absorber layers for photovoltaic cell applications. This paper presents the numerical simulation and modeling of CZTS based thin film kesterite photovoltaic cells using SCAP-1D software. The influence of device parameters such as the carrier concentration, thickness, densities of absorber, buffer and window layers, defect densities and the temperature effect on the performance of the Z n O / C d S / CZTS / M o photovoltaic cell structure are analyzed. Defect densities are added to the absorber layer and the interface between the buffer layer and the absorber layer. This type of solar cell does not comprise any toxic material and can lead to non-toxic thin film photovoltaic cells with outstanding optical properties. In this work, promising optimized results had been achieved with a conversion efficiency of 23.72%, a fill factor of 82.54%, a short-circuit current ( J s c ) of 44.87 mA / cm 2 , and an open circuit voltage ( V o c ) of 0.64V. [ABSTRACT FROM AUTHOR]

This paper proposes a novel control strategy of a star-connected cascaded static synchronous compensator with a battery energy storage system (STATCOM/ BESS) under unbalanced and distorted grid voltage conditions. Cascaded secondorder generalized integrators are utilized to effectively extract the fundamental positive- and negative-sequence components from the adverse grid voltage. Moreover, proportional multi-complex integral current controllers are adopted to improve the harmonic characteristic of the grid-connected current with zero steady-state error and rapid dynamic response in the stationary αβ reference frame. However, unbalanced grid voltage along with the control target of obtaining the fundamental positive-sequence grid-connected current leads to unbalanced active powers among the three phase clusters. This issue will result in an unbalanced clustered state of charge of battery units and seriously affect the battery life and system performance. Accordingly, clustered active-power-balancing control is presented to solve this issue by injecting an appropriate zero-sequence voltage. Simulation results show the good operational performance of the cascaded STATCOM/BESS and verify the validity and effectiveness of the proposed control strategy. [ABSTRACT FROM AUTHOR]

Increasing environmental concerns have led to a push for renewable energy sources to be extensively used to reduce emissions. In this paper, we investigate a hybrid dynamic economic emission dispatch (HDEED) problem involving thermal, wind, and photovoltaic (PV) generation systems. Our formulation considers the stochastic nature of both wind and PV generated power, and differences because of mismatches between the actual and allocated wind and PV power. A hybrid backtracking search algorithm with sequential quadratic programming was used to minimize the total operational costs and emissions, while dispatching power to the committed generation units subject to all operational constraints. To verify the efficacy, we applied the proposed technique to solve the dynamic economic emission dispatch problem on five and ten unit test systems. The proposed technique was also used to solve the HDEED problem on IEEE 30 bus, 6-unit and IEEE 57 bus, 7-unit test systems, with and without renewable generation. The results of our numerical simulations show the efficiency of the proposed technique with respect to reducing operational costs and emissions. Moreover, our results show that by incorporating renewable energy into existing power systems, we can reduce operational costs and emissions. [ABSTRACT FROM AUTHOR]

Nine-switch converter has been recently known for its higher compactness with reduced switch count as compared to the back-to-back converter. The readily available dc-link capacitor made it an appropriate alternative for ac/dc/ac conversion in microgrids. Regardless of the complicated Pulse Width Modulation control scheme, this paper proposes a novel predictive power control for the nine-switch converter which is simple and allows concurrent control of real and reactive power flow between two islanded microgrids. The proposed control scheme adopts the virtual flux vectors and a newly defined reactive power to improve the power quality under the existence of grid voltage disturbances, i.e., voltage unbalance and voltage distortion. Simulation results of the proposed predictive power control guarantee decoupled active and reactive power controls, fast response, accurate power and dc-link voltage tracking, and sinusoidal current waveforms with low harmonic distortions under the various grid conditions. [ABSTRACT FROM AUTHOR]

Parabolic solar troughs are amongst the most widely studied solar thermal technologies available today. Methods for improving efficiency include the use of selective coatings on the absorber which reduces dominant thermal radiation losses. In this paper, we model a different approach of reducing radiation losses: the glass cover around the absorber can be coated with a hot mirror film, which reflects infrared radiation back onto the absorber. In order to describe such a mechanism, it becomes necessary to model theoretically the long range thermal radiation interactions inside the receiver unit. Our model uses discretization of the active surfaces to account for all the dominant radiation interactions, and can be used in a simulation to establish a temperature profile for the receiver unit, from which thermal properties can be inferred. The results of the simulation are compared to existing simulations and experimental data, wherever possible. [ABSTRACT FROM AUTHOR]

This paper reviews the widely used weather file formats, namely, typical meteorological year (TMY) of evolved versions, test reference year (TRY), weather year for energy calculation (WYEC), design reference year (DRY) as well as synthetically generated meteorological year (SMY) used in energy simulation and renewable-energy studies. This paper examines the fundamentals underlying their structure as to how they support and interface with the available energy simulation and modeling software as well as computer systems on which they operate. The differences in TMY, TRY, WYEC, DRY, and SMY in the selection and weighting of weather parameters are discussed, outlining the pros and cons of each type. Finally, sample dry bulb temperature regimes from SMY and TMY weather files are presented to show the differences in average monthly maximum, minimum, and mean temperatures. [ABSTRACT FROM AUTHOR]

A numerical simulation for the wake deviation effect in a wind farm is carried out using the full rotor model of the National Renewable Energy Laboratory 5MW wind turbine. The downstream wind turbine decreases its performance significantly due to the upstream wake interference. To reduce this effect, a control strategy based on the yaw angle is adopted to skew the trajectory of an upstream wake, thereby avoiding the downstream wind turbine and improving the efficiency of whole wind farm power generation. In this paper, the commercial CFD software STAR-CCM+ was used to simulate the wind farm which contains two tandem wind turbines operating in the atmospheric boundary layer condition. The results show that the wind farm's total power increases when the upstream wind turbine applies a yaw angle intentionally. According to the analysis of velocity contours, wake centerlines, and vortex structures, a counter-rotating blade tip vortex pair is observed to be responsible for the wake deviation effects concentrated on the hub height, which reveals that the influence of a yawed wake on the downstream wind turbine may be slightly underestimated. [ABSTRACT FROM AUTHOR]

Making good use of vertical axis wind turbines (VAWTs) is an attractive and potential way to deal with the energy and environmental issues due to the unique superiorities of it. Computational Fluid Dynamics (CFD) technology is a useful tool for the design process of VAWTs. Various turbulence models have been developed and available for turbulent flow simulations. Currently, there have been few researchers studying on meshing strategies and turbulence model selections of VAWT simulations. In this paper, 2D unsteady models under 4 meshing strategies and 6 turbulence models were established and simulated to investigate the effect of the above two aspects on numerical simulations of VAWTs. The numerical results were compared with the experimental data of Oler et al. ("Dynamic stall regulation of the Darrieus Turbine," SAND Report No. 83-7029, Sandia National Laboratories, Albuquerque, 1983, pp. 67-96) and the analytical solution of Deglaire et al. (Eur. J. Mech., B: Fluids 28(4), 506-520 (2009)). The results reveal that a mesh of 213 656 grids is sufficient to meet the requirements of grid independence with the help of boundary layer and size function techniques. Besides, the realizable k-εmodel enables the closest CFD simulation of the experimental data and shows better prediction performance than the analytical model of Deglaire et al. and other turbulence models. [ABSTRACT FROM AUTHOR]

This paper presents an improved Fractional Short Circuit Current (FSCC) Maximum Power Point Tracking (MPPT) technique in which an additional control loop is used to find the proper moment to measure the SCC. The target is to reduce the power losses in MPPT process that occur as a result of intermittent time based short circuit current measurements. The proposed modification enables the conventional FSCC MPPT to decide intelligently about the measurement of SCC thus reduces the number of times the photovoltaic (PV) module is isolated from the load. Although number of algorithms for tracking MPPT has been reported, the proposed method suits well for low cost PV applications. A Matlab/Simulink based model is employed to test the functional abilities of the proposed method. The comparison of the proposed method and conventional time based FSCC method is also presented in the simulation analysis. Finally, a 130W prototype based on the dSPACE DS1104 controller and experimental results are presented to verify the effectiveness of the proposed method. The technique is verified under uniform shading conditions. The results show satisfactory performance against test conditions. [ABSTRACT FROM AUTHOR]

Korea is a peninsula which is surrounded by the Yellow Sea (shallow sea), the southern sea and the East Sea (deep sea). These circumstances always make us consider that a platform could have good motion performances in both shallow and deep seas. In this paper, the typical spar type platform of the Offshore Code Comparison Collaboration Hywind Floating Offshore Wind Turbine (FOWT) has been modified and a new concept FOWT platform is suggested for both seas. Its motion performances are evaluated by both 1:80 scale model tests and full scale numerical simulations. [ABSTRACT FROM AUTHOR]

In this paper, a computational model for the prediction of direct solar radiation based on neural network analysis of atmospheric clearness is developed. It considers that the major portion of direct solar radiation reaching the earth's surface is governed by Sun-Earth geometry and atmospheric transmittance factors which are exactly calculable by clear day model. Additional variations are due to climate and weather phenomena characterized by relative humidity, mean duration of sunshine per hour, and rainfall, etc., in the atmosphere. These variations are taken into account with the help of a composite parameter referred to as atmospheric clearness index (CI) which is determined using artificial neural network analysis. The contour maps of CI as a function of latitude, time of the day, and month of the year are then prepared using the meteorological data of eleven stations. Model simulation and test results of the trained network for two typical locations (not used in training the network) are presented and compared with measured values. The deviations are well within acceptable error limits [percentage root mean square error values for Ahmedabad and Nagpur are 3.34 and 2.06, respectively]. The methodology, for predicting the direct solar radiation at an arbitrary location using the well known parameters such as altitude, latitude, time of the day, day of the year, and CI values derived from the contour maps, is discussed. The outcome of the present ANN model for four arbitrary locations is compared with NASA SSE data sets. [ABSTRACT FROM AUTHOR]

This paper investigates numerically a two-dimensional turbulent flow in a solar chimney due to free convection heat transfer. For evaluation of the fluid flow and heat transfer in the system, the basic equations including conservation of mass and momentum in the x, y directions and energy in the Cartesian coordinate are converted to the algebraic form using the finite volume method. This simulation (use the commercial CFD code) provides the profile of temperature, velocity, and mass flow rate variations in the solar chimney in different conditions. These results can be used to evaluate the effective parameters and optimize the performance of the system for natural evaporative cooling and ventilating the buildings. Based on climate conditions in Yazd, the optimum dimension of the width of the chimney is 0.3-0.4 m, inlet height is 0.3 m, and the flow rate created in the system and at the outlet is at 0.18 m3/s. The mean cooling rate resulted from the solar chimney is about 800 W/m2. Considering the long hot and sunny days of summer (about 12 h in Yazd), the use of this system in warm and dry region is recommended. We can save a considerable amount of energy sources such as natural gas or oil and lower CO2 emissions. [ABSTRACT FROM AUTHOR]

Cost of the photovoltaic (PV) systems and their peripherals has been always an issue when considering them for various applications. Using an inexpensive maximum power point tracking (MPPT) system is a simple but efficient solution to reduce the cost of the PV systems and increase the public acceptance. This paper presents the simulation and hardware implementation of incremental conductance algorithm using buck-boost converter and PIC18F4520 controller. Design and simulation of the proposed system are presented using matlab and simulink tools. The proposed system is also tested on KC85T PV module for constant and changing weather conditions. Experimental results indicated the capability and functionality of the proposed system on tracking maximum power point with the voltage ripple ratio = 0.006, which is near to the ideal mathematically calculated assessment. The proposed MPPT system helps to reduce the complexity and cost of the PV systems and also ensures the largest operating region of the PV module. [ABSTRACT FROM AUTHOR]

The efficiency of the fuel cell system nonlinearly depends on operating conditions and the air flow supplied to the fuel cell system is one of the most significant factors in determining the efficiency. The conventional method of controlling the air flow is to stabilize the oxygen supply at a predetermined constant rate for the optimal efficiency. However, in practice, the optimal point can deviate from the pre-set value due to the varying operating conditions, such as the uncontrollable load. Therefore, the maximum efficiency point tracking (MEPT) controller is necessary to maintain the optimal efficiency over a broad range of operating conditions. In this paper, the MEPT controller is designed based on the extremum seeking control algorithm for searching the optimal oxygen excess ratio in real time to maximize the efficiency of the fuel cell system. Simulation was conducted in the matlab/simulink environment and the results demonstrate that the proposed control method is able to track the maximum efficiency point when variations in operating conditions occur. [ABSTRACT FROM AUTHOR]