Showing papers in "IEEE Transactions on Energy Conversion in 2015"

An Offline Torque Sharing Function for Torque Ripple Reduction in Switched Reluctance Motor Drives

Abstract: In this paper , an offline torque sharing function (TSF) for torque ripple reduction in switched reluctance motor (SRM) drives over a wide speed range is proposed. The objective function of an offline TSF is composed of two secondary objectives with a Tikhonov factor to minimize the square of the phase current (copper loss) and derivatives of current references (rate of change of flux linkage). The proposed TSFs with different Tikhonov factors are compared with the conventional TSFs including linear, cubic, and exponential TSFs in terms of efficiency and torque–speed performance while operating in both magnetic linear and saturation regions. Then, the Tikhonov factor is selected based on a tradeoff between the copper loss and torque–speed performance. The maximum torque-ripple-free speed of the selected offline TSF is validated to be seven times as high as the best case in these conventional TSFs. The performance of the offline TSF is verified by simulations and experiments with a 2.3-kW, three-phase 12/8 SRM. Results show that the proposed offline TSF can significantly reduce the torque ripple of SRM without increasing copper loss over a wide speed range.

Development of a Rare-Earth-Free SR Motor With High Torque Density for Hybrid Vehicles

Abstract: The increased price and the limited supply of rare-earth materials have been recognized as a problem by the international clean energy community. Rare-earth permanent magnets are widely used in electrical motors in hybrid and pure electrical vehicles, which are prized for improving fuel efficiency and reducing carbon dioxide (CO 2 ) emissions. Such motors must have characteristics of high efficiency, compactness, and high torque density, as well as a wide range of operating speeds. So far, these demands have not been achieved without the use of rare-earth permanent magnets. Here, we show that a switched reluctance motor that is competitive with rare-earth permanent-magnet motors can be designed. The developed motor contains no rare-earth permanent magnets, but rather, employs high-silicon steel with low iron loss to improve efficiency. Experiments showed that the developed motor has competitive or better efficiency, torque density, compactness, and range of operating speeds compared with a standard rare-earth permanent-magnet motor. Our results demonstrate how a rare-earth-free motor could be developed to be competitive with rare-earth permanent-magnet motors, for use as a more affordable and sustainable alternative, not only in electric and hybrid vehicles, but also in the wide variety of industrial applications.

Advanced Pitch Angle Control Based on Fuzzy Logic for Variable-Speed Wind Turbine Systems

Abstract: In this paper, an advanced pitch angle control strategy based on the fuzzy logic is proposed for the variable-speed wind turbine systems, in which the generator output power and speed are used as control input variables for the fuzzy logic controller (FLC). The pitch angle reference is produced by the FLC, which can compensate for the nonlinear characteristic of the pitch angle to the wind speed. With the control variables of the generator output power and speed, the wind turbine is smoothly controlled to maintain the aerodynamic power and its speed at the rated values without any fluctuation in the output power and speed in the high-wind-speed regions. The effectiveness of the proposed method is verified by simulation results for a 2-MW permanent-magnet synchronous generator (PMSG) wind turbine system, and experimental results for a reduced-scale PMSG wind turbine simulator.

Contribution of VSC-HVDC to Frequency Regulation of Power Systems With Offshore Wind Generation

Abstract: Modern large wind farms are required to provide frequency regulation service like conventional synchronous generation units. The frequency support capability of modern wind farms has been widely investigated and implemented. Remotely located large offshore wind farms are probably connected to the onshore system grid through voltage-source converter-based–high voltage direct current (VSC-HVdc) transmission systems. Due to the decoupling of VSC-HVdc and signal transmission delay, offshore wind farms may not be able to respond to the onshore grid frequency excursion in time and, consequently, the stability and security of the power system will be put at risk, especially for those with high wind penetration. This paper proposes a coordinated control scheme to allow VSC-HVdc link to contribute to the system frequency regulation by adjusting its dc-link voltage. By means of this approach, the dc capacitors of VSC-HVdc are controlled to absorb or release energy so as to provide frequency support. To further enhance the system frequency response, the frequency support from VSC-HVdc is also finely coordinated with that from offshore wind farm according to the latency of offshore wind farm responding to onshore grid frequency excursion. The control scheme is evaluated for both underfrequency and overfrequency events, and results are presented to demonstrate its effectiveness.

Multiobjective Optimization of Switched Reluctance Motors Based on Design of Experiments and Particle Swarm Optimization

Abstract: This paper proposes a comprehensive framework for multiobjective design optimization of switched reluctance motors (SRMs) based on a combination of the design of experiments and particle swarm optimization (PSO) approaches. First, the definitive screening design was employed to perform sensitivity analyses to identify significant design variables without bias of interaction effects between design variables. Next, optimal third-order response surface (RS) models were constructed based on the Audze–Eglais Latin hypercube design using the selected significant design variables. The constructed optimal RS models consist of only significant regression terms, which were selected by using PSO. Then, a PSO-based multiobjective optimization coupled with the constructed RS models, instead of the finite-element analysis, was performed to generate the Pareto front with a significantly reduced computational cost. A sample SRM design with multiple optimization objectives, i.e., maximizing torque per active mass, maximizing efficiency, and minimizing torque ripple, was conducted to verify the effectiveness of the proposed optimal design framework.

On Inertial Dynamics of Virtual-Synchronous-Controlled DFIG-Based Wind Turbines

Abstract: This paper is to investigate the inertial dynamics of virtual-synchronous-controlled (VSynC) doubly fed induction generator (DFIG)-based wind turbines (WTs). VSynC, different from the conventional synchronization method based on phase-locked-loop (PLL) synchronizing technique, makes DFIG-based WT synchronize with power grid via the active power control (APC), and thus provide the desired inertial support to power grid. Further, an effective approach for describing the inertial dynamics of DFIG-based WT with VSynC is proposed by establishing the WT's electromechanical motion equation. The approach synthetically considers the impacts of the WT's different controller parameters, operating points, and, in particular, the variations of mechanical power caused by the rotational speed or pitch angle changes during the inertial response period. It also makes the essential of DFIG-based WT's inertia clearer, which, as a matter of fact, is controllable and manifests frequency-dependent characteristics, and noticeably differs from the fixed inertia time constant featured in synchronous generator (SG). The impacts of different controller parameters and operating points on single WT's frequency response characteristics are studied. Simulated results also validate the superiority of VSynC on inertial support capability and operation stability to the typical PLL-based vector control (VC), especially for weak grid conditions. Finally, the frequency response on wind power plant (WPP) level is initially explored and further research to improve VSynC is discussed.

Operating Characteristics of the P&O Algorithm at High Perturbation Frequencies for Standalone PV Systems

Abstract: The perturb and observe (P&O) algorithm is one of the most commonly utilized maximum power point tracking (MPPT) control schemes for photovoltaic (PV) generators. However, the operation of this algorithm at high perturbation frequencies, when the system response to MPPT perturbations is never allowed to settle, has not been given adequate attention in the literature. This paper characterizes system behavior in this mode of operation for standalone PV systems feeding resistive loads and motor-pump loads. Simulation and experimental results show that the P&O algorithm operating at a high perturbation frequency may offer higher energy utilization efficiency and better system performance, despite the resulting nonperiodic waveforms of the system.

Reliability Comparison of Wind Turbines With DFIG and PMG Drive Trains

Abstract: Modern wind turbines vary greatly in their drive train configurations. With the variety of options available, it can be difficult to determine which type is most suitable for on and offshore applications. A large percentage of modern drive trains consist of either doubly fed induction generators with partially rated converters or permanent magnet generators with fully rated converters. These configurations are the focus of this empirical reliability comparison. The turbine population for this analysis contains over 1800 doubly fed induction generators, partially rated converter wind turbines, and 400 permanent magnet generator fully rated converter wind turbines. The turbines analyzed are identical except for their drive train configurations and are modern MW scale turbines making this population the largest and most modern encountered in the literature review. Results of the analysis include overall failure rates, failure rates per operational year, failure rates per failure mode, and failure rates per failure cost category for the two drive train configurations. These results contribute toward deciding on the most suitable turbine type for a particular site, as well as toward cost of energy comparisons for different drive train types. A comparison between failure rates from this analysis and failure rates from similar analyses is also shown in this paper.

Techniques for Multilevel Design Optimization of Permanent Magnet Motors

Abstract: The multilevel method has been presented for design optimization of electrical machines and drive systems for optimal system performances and efficiency in our previous work. For framework design of the multilevel optimization method, four techniques are presented in this paper, including the sizing equation, local sensitivity analysis, global sensitivity analysis, and design of experiments techniques. For each technique, a general and theoretical analysis procedure is presented before the application study. To demonstrate the effectiveness, a permanent magnet claw-pole motor with soft magnetic composite core and 3-D finite-element analysis model is investigated to minimize the material cost and maximize the output power while keeping the volume constant. The calculated motor performance based on this 3-D finite-element model has been verified by the experimental results. As shown, these techniques are simple to implement, and the resultant multilevel optimization framework can significantly improve the motor performance and reduce the required sample number of finite-element analysis.

Acoustic Noise and Vibration Reduction of SRM by Elimination of Third Harmonic Component in Sum of Radial Forces

Abstract: A novel method to reduce an acoustic noise and the vibration of a switched reluctance motor has been proposed. In this method, driving current is a sum of dc, fundamental, the second- and the third-harmonic components. This driving current is determined to eliminate the third harmonic component in the sum of radial forces of the stator teeth. Consequently, an acoustic noise and a vibration are reduced. The effectiveness of the proposed method is confirmed by means of finite-element method and test machine experiments.

Implementation of a New MRAS Speed Sensorless Vector Control of Induction Machine

Abstract: In this paper, a novel rotor speed estimation method using model reference adaptive system (MRAS) is proposed to improve the performance of a sensorless vector control in the very low and zero speed regions. In the classical MRAS method, the rotor flux of the adaptive model is compared with that of the reference model. The rotor speed is estimated from the fluxes difference of the two models using adequate adaptive mechanism. However, the performance of this technique at low speed remains uncertain and the MRAS loses its efficiency, but in the new MRAS method, two differences are used at the same time. The first is between rotor fluxes and the second between electromagnetic torques. The adaptive mechanism used in this new structure contains two parallel loops having Proportional-integral controller and low-pass filter. The first and the second loops are used to adjust the rotor flux and electromagnetic torque. To ensure good performance, a robust vector control using sliding mode control is proposed. The controllers are designed using the Lyapunov approach. Simulation and experimental results show the effectiveness of the proposed speed estimation method at low and zero speed regions, and good robustness with respect to parameter variations, measurement errors, and noise is obtained.

Hybrid Microgrid Model Based on Solar Photovoltaic Battery Fuel Cell System for Intermittent Load Applications

Abstract: Microgrids are a subset of the modern power structure using distributed generation to supply power to communities rather than vast regions. The relatively smaller scale mitigates transmission loss with better control, greater security, increased reliability, and design flexibility. This study explores the modeled performance and cost viability of a hybrid grid-tied microgrid that utilizes the combination of solar photovoltaic (PV), batteries, and fuel cell (FC) systems. The proposed concept highlights that each community home is equipped with more solar PV than is required for normal operation. As the homes are part of a microgrid, excess or unused energy from one home is collected for use elsewhere within the microgrid footprint. The surplus power that would have been discarded becomes a community asset and is used to run intermittent services. The modeled community does not have parking adjacent to each home allowing for the installment of a privately owned slower Level 2 charger. This makes electric vehicle (EV) ownership untenable. Based on this study, an optimum configuration is recommended to provide a Level 3 dc quick charger for an intermittent service. The addition of batteries and FCs is meant to increase load leveling, improved reliability, and instill limited island capability.

Model-Predictive Flux Control of Induction Motor Drives With Switching Instant Optimization

Abstract: Conventional model-predictive torque control (MPTC) requires tedious and time-consuming tuning work for stator flux weighting factor, and presents relatively high torque ripples. To solve these problems, this paper proposes a model-predictive flux control (MPFC) for two-level inverter-fed induction motor (IM) drives. The references of stator flux magnitude and torque in conventional MPTC are converted into an equivalent reference of stator flux vector in the proposed MPFC. As only the tracking error of stator flux vector is required in the cost function, the use of weighting factor is eliminated. The optimal voltage vector is selected based on the principle of stator flux error minimization and its switching instant is optimized rather than being in the beginning of each control period. The proposed MPFC with and without switching instant optimization are both implemented in a 32-bit floating digital signal processor, and they are compared in detail in terms of torque ripple, current harmonics, and average switching frequency. Both digital simulations and experimental tests were carried out on a two-level inverter-fed IM drive, and the obtained results validate the effectiveness of the proposed method.

Fractional Slot Concentrated Winding PMSM With Consequent Pole Rotor for a Low-Speed Direct Drive: Reduction of Rare Earth Permanent Magnet

Abstract: This paper deals with a 44pole-48slot fractional slot concentrated winding permanent magnet synchronous machine (FSCW PMSM) for a low-speed direct drive. Two different rotor topologies, a surface permanent magnet (SPM) rotor and a consequent pole (CP) rotor, are optimized and compared both analytically and experimentally. The experimental results confirmed that an FSCW PMSM with a CP rotor can achieve almost equivalent performance at the rated state when compared to an FSCW PMSM with an SPM rotor with 33% less permanent magnet material.

Dynamic Energy Management of Hybrid Energy Storage System With High-Gain PV Converter

Abstract: In this paper, fast acting dc-link voltage-based energy management schemes are proposed for a hybrid energy storage system fed by solar photovoltaic (PV) energy. Using the proposed control schemes, quick fluctuations of load are supplied by the supercapacitors and the average load demand is controlled by the batteries. Fast dc-link voltage, effective energy management, and reduced current stress on battery are the main features achieved from the proposed control schemes. The effectiveness of the proposed control schemes are compared with the unified cascaded control. Small-signal control gains are formulated to design the voltage and current loops of the proposed energy management schemes. Detailed stability analysis is also presented to find the boundary values of compensator gains. In addition, a high-gain PV converter is proposed for extraction of maximum power from the solar panels. High voltage gain, reduced reverse recovery of diodes, and less duty cycle operation are the key features obtained from the proposed high-gain converter. The validity of the proposed energy management schemes with high-gain converter is verified by the detailed simulation and experimental studies.

A Fuzzy Clustering Algorithm-Based Dynamic Equivalent Modeling Method for Wind Farm With DFIG

Abstract: With the increasing capacity of grid connected wind farms, the influence of wind power to stable operation of an electric power system is becoming more and more important. In order to analyze the active power output characteristics of wind farm, a multimachine representation dynamic equivalent method based on the fuzzy clustering algorithm is proposed. First, indicators which can characterize the active power output performance of a doubly fed induction wind generator (DFIG) are researched. Second, a fuzzy C-means (FCM) clustering algorithm is first applied to the modeling of wind farm. DFIGs are divided into groups by analyzing the indicator data with FCM. Finally, DFIGs of the same group are equivalent as one DFIG to realize the dynamic equivalent modeling of wind farm with DFIG. Simulation results demonstrated that the established dynamic equivalent model can reflect the active power dynamic response characteristics of wind farm with DFIG effectively; meanwhile, the model of wind farm is simplified and computation complexity is reduced.

Improved Fault Diagnosis of Ball Bearings Based on the Global Spectrum of Vibration Signals

Abstract: This research deals with the discrimination between conditions of faults in rolling element bearings based on a global spectral analysis This global spectral analysis allows to obtain spectral features with significant discriminatory power These features are extracted from the envelope spectra of vibration signals without prior knowledge of the bearings specific parameters and the characteristic frequencies These extracted spectral features will then be the global spectral signature produced by the bearing faults Since the signature produced by the faults in bearing balls is very weak, and hard to be detected and identified, this paper proposes the linear discriminant analysis as part of the global spectral analysis method in order to improve the diagnosis of ball faults The application on experimental vibration data acquired from bearings containing different types of faults with different small sizes shows the proficiency of the overall method The Bhattacharyya distance is used to confirm the efficiency of the obtained results

Flexible System Architecture of Stand-Alone PV Power Generation With Energy Storage Device

Abstract: A standalone photovoltaic (PV) system with energy storage requires a complex control architecture to take into account the various operating modes. In many cases, a supervisory controller is necessary to manage the change of the control architecture according to the applied mode. This paper presents a flexible architecture of a PV power conditioning system with energy storage. The proposed conditioning unit contains a boost converter (BC), a single-phase inverter, and a bidirectional dc/dc converter connected to the PV side of the BC. The BC regulates the dc-link bus-voltage. The bidirectional dc/dc converter endures battery bank charge/discharge control and PV maximum power point tracking (MPPT). Such architecture guarantees nonchange in controller configuration when the storage disconnects. Therefore, the previously needed supervisory controller is eliminated. A system control strategy based on sliding-mode control (SMC) ensures a reliable output voltage regulation such as fast dynamic response, small steady-state error, and low total harmonic distortion (THD) under step changes and nonlinear loads. The controller structure, the dynamic behavior, and the design procedures are introduced. Finally, the validity of the proposed module with control strategy is verified through hardware experiments on a 500-W prototype test bed with a single TMS320F28335 DSP module.

Virtual Damping Flux-Based LVRT Control for DFIG-Based Wind Turbine

Abstract: This paper proposes a virtual damping flux-based low-voltage ride through (LVRT) control strategy for a doubly fed induction generator (DFIG)-based wind turbine. During the transient states of grid voltage drop and recovery, the proposed virtual damping flux-based strategy can suppress rotor current with a smooth electromagnetic torque. During steady-state faults, a negative sequence current compensation strategy is adopted to smooth the electromagnetic torque and reactive power for asymmetrical grid faults, while the conventional vector control is used to inject reactive power into the grid to support grid voltage for symmetrical grid faults. The effectiveness of the proposed strategies is examined by the simulation with a 2-MW DFIG in MATLAB/Simulink and verified by the experimental results from a scaled-down 7.5-kW DFIG controlled by a DSPACE1006. In addition, the impacts of the magnetic nonlinearity characteristics of a practical DFIG are investigated under asymmetrical grid faults. Although the magnetic nonlinearity characteristics degrade the control effects, the proposed strategies can still improve the DFIG performances during asymmetrical grid faults. The results clearly demonstrate that the proposed strategies can effectively improve the DFIG transient behavior and achieve LVRT performances.

Control of Brushless Doubly-Fed Reluctance Generators for Wind Energy Conversion Systems

Abstract: This paper presents the conceptual analysis, comparative simulation, and experimental evaluation of voltage and flux vector-oriented control of a promising low-cost brushless doubly-fed reluctance generator (BDFRG) technology for variable-speed wind turbines with maximum power point tracking. The BDFRG has been receiving increasing attention because of the use of partially rated power electronics and the high reliability of brushless design, while offering performance competitive to its popular slip-ring counterpart, the doubly-fed induction generator. The development and viability of the two parameter-independent controllers have been validated on a custom-made BDFRG prototype using the maximum torque per inverter ampere strategy for the speed and loading conditions commonly encountered in wind power applications.

Direct MPP Calculation in Terms of the Single-Diode PV Model Parameters

Abstract: In this paper, new expressions are introduced for the determination of the maximum power point (MPP) of photovoltaic (PV) systems as explicit functions of the five parameters of the single-diode model employing the Lambert W function. These equations provide the voltage and current at MPP in a direct and straightforward manner, thus dispensing with any need for iterative solution. They are initially derived for a PV system operating under uniform conditions, and subsequently extended for mismatched conditions at the PV string level. The novelty of these formulae lies in their solid theoretical foundation, which supports their validity in the general case and offers a well-founded symbolic formulation for the MPP evaluation problem. Extended simulations and experimental validation are performed to verify the accuracy and computational efficiency of the proposed equations compared with other methods available in the literature.

Transient Stability Enhancement of Doubly Fed Induction Machine-Based Wind Generator by Bridge-Type Fault Current Limiter

Abstract: Transient stability is a major concern for doubly fed induction machine (DFIM). A DFIM-based wind generator is readily affected by faults at the grid side as its stator windings are interfaced to grid. However, the wind generators need to remain connected and continue operation during faults at the grid side according to the grid code requirements. Therefore, it is important to enhance the transient stability of the DFIM-based wind generators. To achieve enhanced transient stability of the DFIM, a bridge-type fault current limiter (BFCL) is proposed in this study. Symmetrical as well as unsymmetrical faults were applied to the test system to check the efficacy of the BFCL in transient stability enhancement. Simulations were carried out in Matlab/Simulink environment. To demonstrate the effectiveness of the proposed BFCL, its performance is compared with that of the series dynamic braking resistor (SDBR). Simulation results show that the BFCL is a very effective device to attain better stabilization of the DFIM and outperforms the SDBR in all aspects.

Backstepping Control of Smart Grid-Connected Distributed Photovoltaic Power Supplies for Telecom Equipment

Abstract: Backstepping controllers are obtained for distributed hybrid photovoltaic (PV) power supplies of telecommunication equipment. Grid-connected PV-based power supply units may contain dc–dc buck–boost converters linked to single-phase inverters. This distributed energy resource operated within the self-consumption concept can aid in the peak-shaving strategy of ac smart grids. New backstepping control laws are obtained for the single-phase inverter and for the buck–boost converter feeding a telecom equipment/battery while sourcing the PV excess power to the smart grid or to grid supply the telecom system. The backstepping approach is robust and able to cope with the grid nonlinearity and uncertainties providing dc input current and voltage controllers for the buck–boost converter to track the PV panel maximum power point, regulating the PV output dc voltage to extract maximum power; unity power factor sinusoidal ac smart grid inverter currents and constant dc-link voltages suited for telecom equipment; and inverter bidirectional power transfer. Experimental results are obtained from a lab setup controlled by one inexpensive dsPIC running the sampling, the backstepping and modulator algorithms. Results show the controllers guarantee maximum power transfer to the telecom equipment/ac grid, ensuring steady dc-link voltage while absorbing/injecting low harmonic distortion current into the smart grid.

Partitioned Stator Flux Reversal Machine With Consequent-Pole PM Stator

Abstract: In this paper, partitioned stator flux reversal permanent magnet (PS-FRPM) machines having different stator/rotor pole combinations with consequent-pole PM (CPM) stator are proposed and analyzed. Compared with the conventional 12-stator-pole PS-FRPM machines having 10-, 11-, 13-, and 14-rotor-pole rotors and surface-mounted PM (SPM) stator, the PM volume in the proposed PS-FRPM machines with CPM stator can be saved by 28.33%, 30%, 30%, and 33.33%, respectively, while the torque density are similar, i.e., 98.59%, 96.69%, 95.50%, and 97.15%, respectively. Besides, the proposed PS-FRPM machines with CPM stator can exhibit only <1% smaller efficiency compared with the existing PS-FRPM machines with SPM inner stator.

PMSM Drive Position Estimation: Contribution to the High-Frequency Injection Voltage Selection Issue

Abstract: High-frequency injection (HFI) is an alternative method to estimate permanent magnet synchronous motor (PMSM) rotor position using magnetic saliency. Once the maximum fundamental electrical frequency and the power converter switching frequency are set, the HFI voltage amplitude tuning is generally based on trial and error. This paper proposes a methodology to select the appropriate high-frequency signal injection voltage amplitude for rotor position estimation. The technique is based on an analytical model taking into account the noise in the voltage supply to derive the resulting currents containing the information on the rotor position. This model allows setting the injection voltage amplitude that leads to the maximum acceptable position error for a given signal-to-noise ratio and a speed range. The approach is validated with the analytical and the global drive models through extensive simulations. Experimental results on a 1-kW PMSM drive confirm the interest of the proposed solution.

Analysis and Mitigation of Resonance Propagation in Grid-Connected and Islanding Microgrids

Abstract: The application of underground cables and shunt capacitor banks may introduce power distribution system resonances. In this paper, the impacts of voltage-controlled and current-controlled distributed generation (DG) units to microgrid resonance propagation are compared. It can be seen that a conventional voltage-controlled DG unit with an LC filter has a short-circuit feature at the selected harmonic frequencies, while a current-controlled DG unit presents an open-circuit characteristic. Due to different behaviors at harmonic frequencies, specific harmonic mitigation methods shall be developed for current-controlled and voltage-controlled DG units, respectively. This paper also focuses on developing a voltage-controlled DG unit-based active harmonic damping method for grid-connected and islanding microgrid systems. An improved virtual impedance control method with a virtual damping resistor and a nonlinear virtual capacitor is proposed. The nonlinear virtual capacitor is used to compensate the harmonic voltage drop on the grid-side inductor of a DG unit LCL filter. The virtual resistor is mainly responsible for microgrid resonance damping. The effectiveness of the proposed damping method is examined using both a single DG unit and multiple parallel DG units.

Thermal Modeling and Analysis of a Double-Stator Switched Reluctance Motor

Abstract: In this paper, thermal modeling and analysis of a 10 kW double-stator switched reluctance machine (DSSRM) is presented. Thermal management is an essential step of the machine design, since overheated windings and cores might destroy the insulation and lead to failure of the machine. A three-dimensional (3-D) finite-element method (FEM) has been used to numerically calculate the temperature distribution in different parts of the machine. Furthermore, to include the use of water as coolant, computational fluid dynamics (CFD) has been utilized. Thermal performance of the prototype is then analyzed at various load conditions. A 10 kW prototype of the DSSRM has been built and the results have been experimentally verified.

Mitigation of Turn-to-Turn Faults in Fault Tolerant Permanent Magnet Synchronous Motors

Abstract: This study presents a method to mitigate and alleviate the effects produced by a turn-to-turn short in a fault tolerant permanent magnet synchronous motor with single-layer concentrated windings. The rotor magnets are capable of inducing a high voltage across the fault contact point; this voltage has the potential to generate a high circulating current that promotes the rapid propagation of the fault due to the thermal stress created by the increased localized fault power losses. The scope of this study is for applications where postfault operation is desired, even if it means operating at reduced power capacity and lower speeds. Upon quick detection of a fault, the proposed technique can be used to decelerate the propagation of the fault and extend the machine's postfault life span. The technique consists of a magnetic field-weakening strategy at speeds below nominal, to reduce the voltage induced in the faulted portion. The concept is validated through finite element analysis, modeling, and experimental data. It is demonstrated that the proposed technique reduces the fault current magnitude and winding temperature.

Transient Reconfiguration and Coordinated Control for Power Converters to Enhance the LVRT of a DFIG Wind Turbine With an Energy Storage Device

Abstract: This paper proposes a novel transient reconfiguration solution and coordinating control strategy for power converters to enhance the fault ride through and transient voltage support capabilities of a doubly-fed induction generator with an energy storage device (DFIG-ESD). During a grid fault, the connection of the grid-side converter is reconfigured such that it is connected to the rotor circuit in parallel with the rotor-side converter to provide an additional route for the rotor current, while the ESD is responsible for dc-link voltage regulation. A coordinated demagnetizing and reactive current control strategy is designed for the reconfigured DFIG during transient conditions. Specifically, the demagnetizing current is used to counteract the dc and negative-sequence stator flux components so that the transient electromotive force will be reduced. Simultaneously, the reactive current is added to meet the reactive power support requirement. The enhanced low-voltage ride through (LVRT) and transient voltage support capabilities obtained from the proposed design are demonstrated on the DFIG-ESD wind conversion system under different severe fault scenarios (asymmetrical and symmetrical fault). Additionally, The enhanced transient voltage support capability of the proposed design is further demonstrated by comparing with different control strategies.

Quantitative Comparison of Integral and Fractional Slot Permanent Magnet Vernier Motors

Abstract: This paper presents and compares two permanent magnet vernier (PMV) motors with fractional slot concentrated windings (FSCWs) and integral slot distributed windings (ISDWs). The ISDW PMV motor is newly proposed and optimized for a fair comparison with the existing FSCW one. The equations of back electromotive force of both motors are investigated and derived showing that the ISDW PMV motor has the potential to obtain higher torque capability. Also, their electromagnetic performances, such as torque capability, fault tolerance, loss, and efficiency, are calculated and compared by using the finite-element analysis. Then, the maximum power strategy for PMV motors operating at high speed is presented. The simulated results show that both motors possess excellent flux weakening capability. Finally, the effectiveness of the theoretical analysis is verified by the finite-element analysis results and experiments on a prototype FSCW PMV motor.