Showing papers in "IEEE Transactions on Energy Conversion in 2010"
TL;DR: In this paper, the authors proposed analytical expressions for finding optimal size and power factor of four types of distributed generation (DG) units, i.e., real power, reactive power, real power and absorbing reactive power.
Abstract: This paper proposes analytical expressions for finding optimal size and power factor of four types of distributed generation (DG) units. DG units are sized to achieve the highest loss reduction in distribution networks. The proposed analytical expressions are based on an improvement to the method that was limited to DG type, which is capable of delivering real power only. Three other types, e.g., DG capable of delivering both real and reactive power, DG capable of delivering real power and absorbing reactive power, and DG capable of delivering reactive power only, can also be identified with their optimal size and location using the proposed method. The method has been tested in three test distribution systems with varying size and complexity and validated using exhaustive method. Results show that the proposed method requires less computation, but can lead optimal solution as verified by the exhaustive load flow method.
599 citations
TL;DR: In this paper, the ground current in a 1.5kW PV installation is measured under different conditions and used to build a simulation model, which allows the study of the influence of the harmonics injected by the inverter on the ground currents.
Abstract: For low-power grid-connected applications, a single-phase converter can be used. In photovoltaic (PV) applications, it is possible to remove the transformer in the inverter to reduce losses, costs, and size. Galvanic connection of the grid and the dc sources in transformerless systems can introduce additional ground currents due to the ground parasitic capacitance. These currents increase conducted and radiated electromagnetic emissions, harmonics injected in the utility grid, and losses. Amplitude and spectrum of the ground current depend on the converter topology, the switching strategy, and the resonant circuit formed by the ground capacitance, the converter, the ac filter, and the grid. In this paper, the ground current in a 1.5-kW PV installation is measured under different conditions and used to build a simulation model. The installation includes a string of 16 PV panel, a full-bridge inverter, and an LCL filter. This model allows the study of the influence of the harmonics injected by the inverter on the ground current.
418 citations
TL;DR: In this article, a simple analytical method is developed to compare the combinations of stator and rotor pole numbers in flux-switching permanent magnet (PM) machines in terms of back electromotive force (EMF) and electromagnetic torque.
Abstract: A simple analytical method is developed to compare the combinations of stator and rotor pole numbers in flux-switching permanent magnet (PM) machines in terms of back electromotive force (EMF) and electromagnetic torque The winding connections and winding factors of machines having all poles and alternate poles wound, and different numbers of phases, from two to six, are determined by the coil-EMF vectors Their differences from analyzing the conventional fractional-slot PM machines with concentrated nonoverlapping windings are highlighted The general conditions are established for balanced symmetrical back-EMF waveform It shows that the optimized rotor pole number should be close to the number of stator poles, whereas larger torque can be obtained by the machine with relatively higher rotor pole number The analysis is validated by finite-element analyses and experiment
367 citations
TL;DR: In this paper, an open-loop optimal control scheme was proposed to incorporate the operating constraints of the battery energy storage system (BESS), such as state of charge limits, charge/discharge current limits, and lifetime.
Abstract: Integrating a battery energy storage system (BESS) with a large wind farm can make a wind farm more dispatchable. This paper focuses on development of a control strategy for optimal use of the BESS for this purpose. The paper considers an open-loop optimal control scheme to incorporate the operating constraints of the BESS, such as state of charge limits, charge/discharge current limits, and lifetime. The goal of the control is to have the BESS to provide as much smoothing as possible, so that the wind farm can be dispatched on an hourly basis based on the forecasted wind conditions. The effectiveness of this control strategy has been tested by using an actual wind farm data. Furthermore, a real-time implementation strategy using model predictive control is also proposed. Finally, it is shown that the control strategy is very important in improving the BESS performance for this application.
327 citations
TL;DR: In this article, a minimum threshold rotor-crowbar method is presented to improve fault response by reducing crowbar application periods to 11-16 ms, successfully diverting transient overcurrents, and restoring good power control within 45 ms of both fault initiation and clearance.
Abstract: Doubly fed induction generator (DFIG) technology is the dominant technology in the growing global market for wind power generation, due to the combination of variable-speed operation and a cost-effective partially rated power converter. However, the DFIG is sensitive to dips in supply voltage and without specific protection to “ride-through” grid faults, a DFIG risks damage to its power converter due to overcurrent and/or overvoltage. Conventional converter protection via a sustained period of rotor-crowbar closed circuit leads to poor power output and sustained suppression of the stator voltages. A new minimum-threshold rotor-crowbar method is presented in this paper, improving fault response by reducing crowbar application periods to 11-16 ms, successfully diverting transient overcurrents, and restoring good power control within 45 ms of both fault initiation and clearance, thus enabling the DFIG to meet grid-code fault-ride-through requirements. The new method is experimentally verified and evaluated using a 7.5-kW test facility.
309 citations
TL;DR: In this article, the authors examine the system integration issues associated with distributed energy systems and show the benefits of using power electronic interfaces for such applications, and show that using PE interfaces for DE systems can increase functionality through improved power quality and voltage/volt-ampere reactive support.
Abstract: With the increasing use of distributed energy (DE) systems in industry and its technological advancement, it is becoming more important to understand the integration of these systems with the electric power systems. New markets and benefits for DE applications include the ability to provide ancillary services, improve energy efficiency, enhance power system reliability, and allow customer choice. Advanced power electronic (PE) interfaces will allow DE systems to provide increased functionality through improved power quality and voltage/volt-ampere reactive (VAR) support, increase electrical system compatibility by reducing the fault contributions, and flexibility in operations with various other DE sources, while reducing overall interconnection costs. This paper will examine the system integration issues associated with DE systems and show the benefits of using PE interfaces for such applications.
303 citations
TL;DR: In this paper, a direct active and reactive power control (DPC) for grid-connected doubly fed induction generator (DFIG)-based wind turbine systems is proposed, which employs a nonlinear sliding-mode control scheme to directly calculate the required rotor control voltage so as to eliminate the instantaneous errors of reactive powers without involving any synchronous coordinate transformations.
Abstract: This paper presents a new direct active and reactive power control (DPC) of grid-connected doubly fed induction generator (DFIG)-based wind turbine systems. The proposed DPC strategy employs a nonlinear sliding-mode control scheme to directly calculate the required rotor control voltage so as to eliminate the instantaneous errors of active and reactive powers without involving any synchronous coordinate transformations. Thus, no extra current control loops are required, thereby simplifying the system design and enhancing the transient performance. Constant converter switching frequency is achieved by using space vector modulation, which eases the designs of the power converter and the ac harmonic filter. Simulation results on a 2-MW grid-connected DFIG system are provided and compared with those of classic voltage-oriented vector control (VC) and conventional lookup table (LUT) DPC. The proposed DPC provides enhanced transient performance similar to the LUT DPC and keeps the steady-state harmonic spectra at the same level as the VC strategy.
281 citations
TL;DR: In this paper, a series dynamic resistor (SDR) was proposed to avoid the doubly-fed induction generator (DFIG) control being disabled by conventional crowbar protection during fault conditions.
Abstract: This paper proposes a new converter protection method, primarily based on a series dynamic resistor (SDR) that avoids the doubly-fed induction generator (DFIG) control being disabled by crowbar protection during fault conditions. A combined converter protection scheme based on the proposed SDR and conventional crowbar is analyzed and discussed. The main protection advantages are due to the series topology when compared with crowbar and dc-chopper protection. Various fault overcurrent conditions (both symmetrical and asymmetrical) are analyzed and used to design the protection in detail, including the switching strategy and coordination with crowbar, and resistance value calculations. PSCAD/EMTDC simulation results show that the proposed method is advantageous for fault overcurrent protection, especially for asymmetrical faults, in which the traditional crowbar protection may malfunction.
279 citations
TL;DR: In this paper, the authors proposed a coaxial magnetic gear that offers higher torque density, lower cogging torque, and lower iron losses than its counterparts, which employs a Halbach permanent magnet array to constitute the PM poles in the inner rotor and a partial Halbach array for the outer rotor.
Abstract: This paper proposes a coaxial magnetic gear that offers higher torque density, lower cogging torque, and lower iron losses than its counterparts. The key is to newly employ a Halbach permanent-magnet (PM) array to constitute the PM poles in the inner rotor and a partial Halbach array (two segments per pole) for the outer rotor. The corresponding magnetic field distributions, torque transmission, and torque ripples are analytically discussed. Then, the corresponding performances are quantitatively assessed by using the finite-element method.
268 citations
TL;DR: In this article, a T-S fuzzy observer is developed to reduce the number of measured signals and a fuzzy direct MPPT controller is proposed to achieve asymptotic MPPT control in which the observer and controller gains are obtained by separately solving two sets of linear matrix inequalities.
Abstract: This paper presents maximum power point tracking (MPPT) control for stand-alone solar power generation systems via the Takagi-Sugeno (T-S) fuzzy-model-based approach. In detail, we consider a dc/dc buck converter to regulate the output power of the photovoltaic panel array. First, the system is represented by the T-S fuzzy model. Next, in order to reduce the number of measured signals, a T-S fuzzy observer is developed for state feedback. Then, a fuzzy direct MPPT controller is proposed to achieve asymptotic MPPT control, in which the observer and controller gains are obtained by separately solving two sets of linear matrix inequalities. Different from the traditional MPPT approaches, the proposed T-S fuzzy controller directly drives the system to the maximum power point without searching the maximum power point and measuring insolation. Furthermore, when considering disturbance and uncertainty, robust MPPT is guaranteed by advanced gain design. Therefore, the proposed method provides an easier implementation form under strict stability analysis. Finally, the control performance is shown from the numerical simulation and experimental results.
263 citations
TL;DR: In this article, the authors proposed a new dead time compensation method for a PWM inverter, which can be easily implemented by feedforwardly adding compensation voltages to the output reference voltage of the synchronous d-axis proportional-integral current regulator.
Abstract: A new dead time compensation method for a pulsewidth modulation (PWM) inverter is proposed. In the PWM inverter, voltage distortion due to the dead time effects produces fifth and seventh harmonics in the phase currents of the stationary reference frame, and a sixth harmonic in the d- and q-axis currents of the synchronous reference frame, respectively. In this paper, the sixth harmonic of the integrator output of the synchronous d-axis proportional-integral (PI) current regulator is used to compensate the output voltage distortion due to the dead time effects, since the integrator output has ripple corresponding to six times the stator fundamental frequency. The proposed method can be easily implemented by feedforwardly adding compensation voltages to the output reference voltage of the synchronous PI current regulator. The proposed method, therefore, has some significant advantages such as simple implementation without additional hardware, easy mathematical computation, no offline experimental measurements, and application in both the steady state and the transient state. The validity of the proposed compensation algorithm is shown through several experiments.
Abstract: This paper describes a position sensorless operation of permanent magnet brushless direct current (BLDC) motor. The position sensorless BLDC drive proposed, in this paper, is based on detection of back electromotive force (back EMF) zero crossing from the terminal voltages. The proposed method relies on a difference of line voltages measured at the terminals of the motor. It is shown, in the paper, that this difference of line voltages provides an amplified version of an appropriate back EMF at its zero crossings. The commutation signals are obtained without the motor neutral voltage. The effectiveness of the proposed method is demonstrated through simulation and experimental results.
TL;DR: In this article, a feed-forward transient current control (FFTCC) scheme was proposed for the rotor side converter (RSC) of a DIF to enhance its low-voltage ride-through capability.
Abstract: High penetration of wind power requires reliable wind energy generation. A successful low-voltage ride-through (LVRT) scheme is a key requirement to achieve reliable and uninterrupted electrical power generation for wind turbines equipped with doubly fed induction generators (DFIGs). This paper proposes a feed-forward transient current control (FFTCC) scheme for the rotor side converter (RSC) of a DFIG to enhance its LVRT capability. This new control scheme introduces additional feed-forward transient compensations to a conventional current regulator. When three phase faults occur, these compensation terms correctly align the RSC ac-side output voltage with the transient-induced voltage, resulting in minimum transient rotor current and minimum occurrence of crowbar interruptions. With little additional computational effort, the proposed control scheme helps relieve the transient current stress on the RSC and helps maintain an uninterrupted active and reactive power supply from the wind turbines to the power grid. Simulation results are shown to demonstrate the effectiveness of the proposed FFTCC scheme in suppressing transient rotor currents.
TL;DR: In this paper, a Hilbert-Huang transform was used to diagnose demagnetization in a permanent-magnet synchronous motor (PMSM) under nonstationary conditions of velocity.
Abstract: This paper presents a novel method to diagnose demagnetization in permanent-magnet synchronous motor (PMSM). Simulations have been performed by 2-D finite-element analysis in order to determine the current spectrum and the magnetic flux distribution due to this failure. The diagnostic just based on motor current signature analysis can be confused by eccentricity failure because the harmonic content is the same. Moreover, it can only be applied under stationary conditions. In order to overcome these drawbacks, a novel method is used based upon the Hilbert-Huang transform. It represents time-dependent series in a 2-D time-frequency domain by extracting instantaneous frequency components through an empirical-mode decomposition process. This tool is applied by running the motor under nonstationary conditions of velocity. The experimental results show the reliability and feasibility of the methodology in order to diagnose the demagnetization of a PMSM.
TL;DR: A new speed-estimation adaptation law is derived using Lyapunov theory to ensure estimation stability, as well as fast error dynamics in both modes of operations.
Abstract: In this paper, two novel adaptation schemes are proposed to replace the classical PI controller used in model reference adaptive speed-estimation schemes that are based on rotor flux. The first proposed adaptation scheme is based on sliding-mode theory. A new speed-estimation adaptation law is derived using Lyapunov theory to ensure estimation stability, as well as fast error dynamics. The other adaptation mechanism is based on fuzzy-logic strategy. A detailed experimental comparison between the new and conventional schemes is carried out in both open- and closed-loop sensorless modes of operation when a vector control drive is working at very low speed. Superior performance has been obtained using the new sliding-mode and fuzzy-logic adaptation mechanisms in both modes of operations.
TL;DR: In this paper, the power output of a variable-speed wind turbine generator is monitored using a wavelet in order to extract the strength of particular frequency components, characteristic of faults.
Abstract: With an increasing number of wind turbines being erected offshore, there is a need for cost-effective, predictive, and proactive maintenance. A large fraction of wind turbine downtime is due to bearing failures, particularly in the generator and gearbox. One way of assessing impending problems is to install vibration sensors in key positions on these subassemblies. Such equipment can be costly and requires sophisticated software for analysis of the data. An alternative approach, which does not require extra sensors, is investigated in this paper. This involves monitoring the power output of a variable-speed wind turbine generator and processing the data using a wavelet in order to extract the strength of particular frequency components, characteristic of faults. This has been done for doubly fed induction generators (DFIGs), commonly used in modern variable-speed wind turbines. The technique is first validated on a test rig under controlled fault conditions and then is applied to two operational wind turbine DFIGs where generator shaft misalignment was detected. For one of these turbines, the technique detected a problem 3 months before a bearing failure was recorded.
TL;DR: In this article, a novel maximum power point (MPP) tracking (MPPT) algorithm for grid-connected wind energy generation systems (WEGS) is presented, which is a rapid tracking algorithm that uses the fact that the value of?s,? an intermediate variable, especially defined for the purpose, remains constant ( =sMPP ) for a given WEGS at the MPP irrespective of the wind velocity.
Abstract: This paper presents a novel maximum power point (MPP) tracking (MPPT) algorithm for grid-connected wind energy generation systems (WEGS). This is a rapid tracking algorithm that uses the fact that the value of ?s,? an intermediate variable, especially defined for the purpose, remains constant ( =sMPP ) for a given WEGS at the MPP irrespective of the wind velocity. The value of sMPP is known in advance. The algorithm works in two stages. In the first stage, it uses large steps to quickly drive the operating point to lie within a narrow band with limits smax and smin. In the second stage, exact MPP is tracked using the ?perturb and observe? method. No extra hardware or measurements (sensors) are required compared to the existing algorithms. Hence, the cost is not increased. Application of the proposed algorithm to an example WEGS shows that the time taken by the system to reach MPP is much smaller compared to most of the existing algorithms. A prototype matrix converter has been developed for grid interfacing and the proposed MPPT scheme has been implemented in conjunction with Venturini and space-vector-modulation-based switching schemes. All the results of this study are presented.
TL;DR: In this article, the authors presented an optimum design of a PM-type transverse flux linear motors (TFLM) to reduce the weight of motor with constraints of thrust and detent force using response surface methodology (RSM) and genetic algorithms (GAs).
Abstract: Permanent magnet (PM) type transverse flux linear motors (TFLMs) are electromagnetic devices, which can develop directly powerful linear motion. These motors have been developed to apply to high power system, such as railway traction, electrodynamics vibrator, free-piston generator, etc. This paper presents an optimum design of a PM-type TFLM to reduce the weight of motor with constraints of thrust and detent force using response surface methodology (RSM) and genetic algorithms (GAs). RSM is well adapted to make analytical model of motor weight with constraints of thrust and detent forces, and enable objective function to be easily created and a great computational time to be saved. Finite element computations have been used for numerical experiments on geometrical design variables in order to determine the coefficients of a second-order analytical model for the RSM. GAs are used as a searching tool for design optimization of TFLM to reduce the weight of motor and improve the motor performance.
TL;DR: In this article, equivalent electric circuit models of a commercial 1.2-kW proton exchange membrane (PEM) fuel cell stack are proposed based on AC impedance studies, and the circuit parameters are obtained by fitting a curve to the experimental impedance data.
Abstract: In this paper, equivalent electric circuit models of a commercial 1.2-kW proton exchange membrane (PEM) fuel cell stack are proposed based on AC impedance studies. The PEM fuel cell stack was operated using room air and pure hydrogen (99.995%). Using electrochemical impedance spectroscopy (EIS) technique, impedance data were collected in the laboratory under various loading conditions. Impedance data were analyzed and circuit models developed using basic circuit elements like resistors and inductors, and distributed elements such as Warburg and constant-phase elements. A nonlinear least-square fitting technique is employed to obtain the circuit parameters by fitting a curve to the experimental impedance data. Two circuit models of the fuel cell, one for low and one for high currents are proposed. The average ohmic resistance for the whole stack is estimated to be 41 mΩ. Double-layer capacitances are determined at anode and cathode at various current densities. As expected, cathode charge transfer resistance turns out to be much higher than the anode charge transfer resistance because of slower kinetics of the oxygen reduction reaction. At higher load currents, a significant increase in mass transfer resistance as well as low-frequency inductive effects is observed. These low-frequency inductive effects are recognized and modeled in the fuel cell models of this work. Finally, a semiquantitative analysis was used to determine the contribution of individual performance factors to the overall fuel cell voltage drop. The transient response of the fuel cell circuit models is simulated using MATLAB/Simulink and their performance is validated by comparison with experimental data.
TL;DR: In this article, a new switched reluctance machine with a double-stator configuration (DSSRM) is introduced, which is based on optimization of the motional forces, which leads to a high-grade electromechanical energy conversion process.
Abstract: In this paper, a new switched reluctance machine with a double-stator configuration (DSSRM) is introduced. The proposed design is based on optimization of the motional forces, which leads to a high-grade electromechanical energy conversion process. A local examination of the force densities within and throughout a conventional switched reluctance machine (SRM) shows that the majority of the force produced is in the radial direction and does not contribute to motion. If the normal forces happen to be in the direction of motion, a larger motional force profile for SRM is yield. Based on these guidelines, a new SRM (DSSRM) is proposed. To compare energy conversion efficiency of DSSRM with that of the conventional SRM, a finite element model is constructed. An experimental prototype of the proposed machine is developed, and the phase inductance is measured. The results of our investigations indicate that the proposed geometry offers superior performance in terms of higher power density and higher percentage of the motional forces.
TL;DR: In this paper, a novel maximum power point tracking (MPPT) controller with an adaptive compensation control is first proposed for a microscale wind power generation system (WPGS) based on the adaptive control, the dynamic response is improved and more wind energy can be captured during wind velocity variations.
Abstract: In this paper, a novel maximum power point tracking (MPPT) controller with an adaptive compensation control is first proposed for a microscale wind power generation system (WPGS) Based on the adaptive control, the dynamic response is improved and more wind energy can be captured during wind velocity variations For cost and reliability consideration, no mechanical sensors are used in this proposed WPGS A single-stage ac-to-dc converter is then proposed to replace the traditional two-stage converter and incorporate the MPPT control for achieving higher efficiency and lower total harmonic distortion (THD) To further improve the efficiency of the converter, a quasi-synchronous rectification (QSR) algorithm is proposed to control the active switches for reducing the conduction loss of the body diodes The analytic closed form duty ratios of the corresponding active switches are also derived for easy implementation Furthermore, a prototype system is constructed and the proposed MPPT controller and QSR algorithm are both implemented using a DSP, namely, TMS320F2812 Some experimental results are given to verify the validity of the proposed microscale WPGS It is found that the total output energy can be increased by 13% for the microscale WPGS
TL;DR: In this article, the authors presented a systematic analytical approach for the well-being assessment of small autonomous power systems (SAPSs) with wind and solar energy sources, which accounts for the uncertainties associated with solar irradiance, wind speed, demand, and outages of various generating units.
Abstract: This paper presents a systematic analytical approach for the well-being assessment of small autonomous power systems (SAPSs) with wind and solar energy sources. The proposed technique accounts for the uncertainties associated with solar irradiance, wind speed, demand, and outages of various generating units. The impact of wind power fluctuation on the system stability is also assessed by limiting the wind power dispatch to a certain percentage of system load. Well-being assessment and production costing simulation for SAPS are performed using proposed analytical approach and Monte Carlo simulation (MCS) method, and then, obtained results are compared in terms of accuracy and computational time. The comparison shows that the developed technique requires less computational time than MCS method, with reasonable accuracy, and thus, validates the usefulness of proposed analytical method. The impact of renewable energy penetration on a SAPS is also analyzed using the proposed method.
TL;DR: In this article, a coordination control strategy for wind farms with line commutated converter-based HVDC delivery for participating in inertial response and primary frequency control is presented.
Abstract: This paper develops a coordination control strategy for wind farms with line commutated converter-based HVdc delivery for participating in inertial response and primary frequency control. The coordination philosophy is to feedback the grid frequency and its derivative and adjust the delivery power of the HVdc link according to the feedback signals. The feedback loop employing the derivative of the grid frequency aims to improve the inertial response while the feedback loop employing the grid frequency deviation introduces a droop at the rectifier control loop. When the grid frequency is too high or too low, active power flow through the HVdc link will be ramped down or up. In turn, the wind generation will increase or decrease the blade angles to reduce or increase the captured wind power through pitch control. A case study demonstrates the effectiveness of the inertial enhancement and frequency droop in HVdc control. Simulation results in transient security assessment tool are given.
TL;DR: In this paper, the authors proposed coordination of the selection of stators with odd number of slots per pole pair and IPM rotors with multiple layers of flux barriers in order to reduce torque ripple.
Abstract: This paper develops analytical principles for torque ripple reduction in interior permanent magnet (IPM) synchronous machines. The significance of slot harmonics and the benefits of stators with odd number of slots per pole pair are highlighted. Based on these valuable analytical insights, this paper proposes coordination of the selection of stators with odd number of slots per pole pair and IPM rotors with multiple layers of flux barriers in order to reduce torque ripple. The effectiveness of using stators with odd number of slots per pole pair in reducing torque ripple is validated by applying a finite-element-based Monte Carlo optimization method to four IPM machine topologies, which are combinations of two stator topologies (even or odd number of slots per pole pair) and two IPM rotor topologies (one- or two-layer). It is demonstrated that the torque ripple can be reduced to less than 5% by selecting a stator with an odd number of slots per pole pair and the IPM rotor with optimized barrier configurations, without using stator/rotor skewing or rotor pole shaping.
TL;DR: In this paper, the effect of both circumferential and axial segmentations on losses' reduction in various conditions, concerning the skin effect, was evaluated. And the authors proposed a criterion to determine range of parameters leading to this unexpected situation.
Abstract: Rare earth permanent magnet synchronous machines with the pulsewidth modulated supply are exposed to magnets' heating due to harmonic fields, which rotate in relation to rotor. In cases when skin effect is negligible, the corresponding eddy-current losses in magnets can be reduced by segmentation of magnets. In this paper, we propose an analytical method to evaluate the effect of both circumferential and axial segmentations on losses' reduction in various conditions, concerning the skin effect. With the skin effect operating, the magnets' division may lead to increase rather than decrease of the eddy-current losses. A criterion to determine range of parameters leading to this unexpected situation is presented. Finite-element calculation confirms the results of the analysis.
TL;DR: In this paper, a partially linearized (in battery power) input-output battery model was developed for lead-acid batteries in a hybrid electric vehicle, which can be extended to different battery types, such as lithium-ion, nickel-metal hydride, and alkaline.
Abstract: Accurate information on battery state-of-charge, expected battery lifetime, and expected battery cycle life is essential for many practical applications. In this paper, we develop a nonchemically based partially linearized (in battery power) input-output battery model, initially developed for lead-acid batteries in a hybrid electric vehicle. We show that with properly tuned parameter values, the model can be extended to different battery types, such as lithium-ion, nickel-metal hydride, and alkaline. The validation results of the model against measured data in terms of power and efficiency at different temperatures are then presented. The model is incorporated with the recovery effect for accurate lifetime estimation. The obtained lifetime estimation results using the proposed model are similar to the ones predicted by the Rakhmatov and Virudhula battery model on a given set of typical loads at room temperature. A possible incorporation of the cycling effect, which determines the battery cycle life, in terms of the maximum available energy approximated at charge/discharge nominal power level is also suggested. The usage of the proposed model is computationally inexpensive, hence implementable in many applications, such as low-power system design, real-time energy management in distributed sensor network, etc.
TL;DR: In this article, a novel photovoltaic (PV) maximum power point tracking (MPPT) based on biological swarm chasing behavior is proposed to increase the MPPT performance for a module-integrated PV power system.
Abstract: In this paper, a novel photovoltaic (PV) maximum power point tracking (MPPT) based on biological swarm chasing behavior is proposed to increase the MPPT performance for a module-integrated PV power system. Each PV module is viewed as a particle, and as a result, the maximum power point is viewed as the moving target. Thus, every PV module can chase the maximum power point (MPP) automatically. A 525 W prototype constructed by three parallel-connected 175 W PV modules is implemented to assess the MPPT performance. Comparing with a typical perturb and observe (P & O) MPPT method, the MPPT efficiency ?MPPT is improved about 12.19% in transient state by the proposed MPPT as theoretical prediction.
TL;DR: In this paper, the direct torque control (DTC) for an IM-based FESS associated to a variable-speed wind generator was proposed, and proved through simulation and experimental results that it could be a better alternative.
Abstract: Flywheel energy storage systems (FESSs) improve the quality of the electric power delivered by wind generators, and help these generators contributing to the ancillary services. Presently, FESSs containing a flux-oriented controlled induction machine (IM) are mainly considered for this kind of application. The paper proposes the direct torque control (DTC) for an IM-based FESS associated to a variable-speed wind generator, and proves through simulation and experimental results that it could be a better alternative. This DTC application entails two specific aspects: 1) the IM must operate in the flux-weakening region, and 2) it must shift quickly and repeatedly between motoring and generating operation modes. DTC improvement for increasing the FESS efficiency, when it operates at small power values, is discussed. Some aspects concerning the flywheel design and the choice of the filter used in the FESS supervisor are also addressed.
TL;DR: This paper discusses short-horizon prediction of wind speed and power using wind turbine data collected at 10 s intervals, which demonstrates performance advantages provided by the data-driven approach.
Abstract: This paper discusses short-horizon prediction of wind speed and power using wind turbine data collected at 10 s intervals. A time-series model approach to examine wind behavior is studied. Both exponential smoothing and data-driven models are developed for wind prediction. Power prediction models are established, which are based on the most effective wind prediction model. Comparative analysis of the power predicting models is discussed. Computational results demonstrate performance advantages provided by the data-driven approach. All computations reported in the paper are based on the data collected at a large wind farm.
TL;DR: In this paper, a framework for analysis of harmonics in a doubly fed induction generator (DFIG) caused by nonsinusoidal conditions in rotor and unbalance in stator was developed.
Abstract: This paper develops a framework for analysis of harmonics in a doubly fed induction generator (DFIG) caused by nonsinusoidal conditions in rotor and unbalance in stator. Nonsinusoidal rotor voltages are decomposed into harmonic components and their corresponding sequences are identified. Induced harmonics in stator are analyzed and computed, from which the torques produced by these interactions between stator and rotor harmonic components can be found. During unbalanced stator conditions, symmetric component theory is applied to the stator voltage to get positive-, negative-, and zero-sequence components of stator and rotor currents. The steady-state negative-sequence equivalent circuit for a DFIG is derived based on the reference frame theory. Harmonic currents in the rotor are computed based on the sequence circuits. In both scenarios, the harmonic components of the electromagnetic torque are calculated from the interactions of the harmonic components of the stator and rotor currents. Three case studies are considered, namely: 1) nonsinusoidal rotor injection; 2) an isolated unbalanced stator load scenario; and 3) unbalanced grid-connected operation. The analysis is verified with results from numerical simulations in Matlab/Simulink. For illustration, the second case is verified using experiments. The simulation results and experimental results agree well with the results from analysis.