Showing papers in "IEEE Transactions on Industry Applications in 2012"

Power Electronics Converters for Wind Turbine Systems

Abstract: The steady growth of installed wind power together with the upscaling of the single wind turbine power capability has pushed the research and development of power converters toward full-scale power conversion, lowered cost pr kW, increased power density, and also the need for higher reliability. In this paper, power converter technologies are reviewed with focus on existing ones and on those that have potential for higher power but which have not been yet adopted due to the important risk associated with the high-power industry. The power converters are classified into single- and multicell topologies, in the latter case with attention to series connection and parallel connection either electrical or magnetic ones (multiphase/windings machines/transformers). It is concluded that as the power level increases in wind turbines, medium-voltage power converters will be a dominant power converter configuration, but continuously cost and reliability are important issues to be addressed.

Forecasting Power Output of Photovoltaic Systems Based on Weather Classification and Support Vector Machines

Abstract: Due to the growing demand on renewable energy, photovoltaic (PV) generation systems have increased considerably in recent years. However, the power output of PV systems is affected by different weather conditions. Accurate forecasting of PV power output is important for system reliability and promoting large-scale PV deployment. This paper proposes algorithms to forecast power output of PV systems based upon weather classification and support vector machines (SVM). In the process, the weather conditions are divided into four types which are clear sky, cloudy day, foggy day, and rainy day. In this paper, a one-day-ahead PV power output forecasting model for a single station is derived based on the weather forecasting data, actual historical power output data, and the principle of SVM. After applying it into a PV station in China (the capability is 20 kW), results show the proposed forecasting model for grid-connected PV systems is effective and promising.

Comparison of Induction and PM Synchronous Motor Drives for EV Application Including Design Examples

Abstract: Three different motor drives for electric traction are compared, in terms of output power and efficiency at the same stack dimensions and inverter size. Induction motor (IM), surface-mounted permanent-magnet (PM) (SPM), and interior PM (IPM) synchronous motor drives are investigated, with reference to a common vehicle specification. The IM is penalized by the cage loss, but it is less expensive and inherently safe in case of inverter unwilled turnoff due to natural de-excitation. The SPM motor has a simple construction and shorter end connections, but it is penalized by eddy-current loss at high speed, has a very limited transient overload power, and has a high uncontrolled generator voltage. The IPM motor shows the better performance compromise, but it might be more complicated to be manufactured. Analytical relationships are first introduced and then validated on three example designs and finite element calculated, accounting for core saturation, harmonic losses, the effects of skewing, and operating temperature. The merits and limitations of the three solutions are quantified comprehensively and summarized by the calculation of the energy consumption over the standard New European Driving Cycle.

Negative-Sequence Reactive-Power Control by a PWM STATCOM Based on a Modular Multilevel Cascade Converter (MMCC-SDBC)

Abstract: This paper presents the application of a modular multilevel cascade converter based on single-delta bridge cells (SDBCs) to a STATic synchronous COMpensator (STATCOM), particularly for negative-sequence reactive-power control. The SDBC is characterized by cascade connection of multiple single-phase H-bridge (or full bridge) converter cells per leg, thus facilitating flexible circuit design, low-voltage steps, and low-electromagnetic-interference emissions. This paper designs, constructs, and tests a 100-V 5-kVA pulsewidth-modulated STATCOM based on the SDBC, with focus on the operating principle and performance. Experimental results verify that it can control not only positive-sequence reactive power but also negative-sequence reactive power and low-frequency active power intended for flicker compensation of arc furnaces.

Recent Advances in Axial-Flux Permanent-Magnet Machine Technology

Abstract: This paper reviews the progress that has been made in the analysis and design of axial-flux permanent-magnet machines over the past decade, with particular attention to aspects such as electromagnetic and thermal modeling, materials, manufacturing, pulsating torque, and extended speed range. Comparisons with other machine types and applications are also reviewed.

Large-Signal Stabilization of a DC-Link Supplying a Constant Power Load Using a Virtual Capacitor: Impact on the Domain of Attraction

Abstract: It is known that the interaction between poorly damped LC input filters and constant power loads (CPLs) leads to degradation of dynamic performance or system instability. This paper addresses a large-signal stability study and stabilization of an electrical system containing a dc power supply, an LC filter, and a CPL. This latter is realized here by a voltage source inverter supplying a motor drive. To stabilize the system, the control structure is slightly modified to implement a nonlinear stabilization block that virtually increases the dc-link capacitance and, hence, the damping of the system. The main idea consists in adding a capacitive power component to the CPL power reference. This allows reducing the real dc-link capacitance value and volume, which is, for weight and size reasons, an important issue in aerospace applications. The impact on the large-signal stability will be analyzed by estimating the domain of attraction of the operating point. An illustrative example consisted of an LC input filter connected to an inverter-permanent-magnet synchronous motor designed for aircraft applications treated by simulations and experimentation, which confirm the validity of the proposed approach.

PWM Switching Frequency Signal Injection Sensorless Method in IPMSM

Abstract: The rotor position of an interior permanent-magnet synchronous machine (IPMSM) can be estimated without a position sensor by signal injection sensorless control at standstill and/or in very low speed rotating condition. In the signal injection sensorless control, however, the fundamental control performance is limited by the frequency of the injected signal, and no negligible acoustic noise is generated. If the frequency of the injected voltage signal would increase to pulsewidth modulation (PWM) switching frequency and if the switching frequency is near or above audible range, the dynamics of the sensorless control can be improved, and the acoustic noise can be remarkably reduced or totally eliminated. This paper describes how to extract the rotor position information of IPMSM using the voltage signal injection whose frequency is the same as the PWM switching frequency. Compared to the conventional heterodyning process, the proposed method is simple to implement and appropriate for PWM switching frequency signal injection. The high-frequency voltage signal can be injected in the stationary reference frame or in the estimated rotor reference frame. In this paper, the 5- and 16-kHz signal injections are proposed, implemented, and compared. The experimental results confirm the effectiveness of the proposed method.

Test Results and Torque Improvement of the 50-kW Switched Reluctance Motor Designed for Hybrid Electric Vehicles

Abstract: A switched reluctance motor (SRM) has been developed as one of the possible candidates of rare-earth-free electric motors. A prototype machine has been built and tested. It has competitive dimensions, torque, power, and efficiency with respect to the 50-kW interior permanent magnet synchronous motor employed in the hybrid electric vehicles (Toyota Prius 2003). It is found that competitive power of 50-kW rating and efficiency of 95% are achieved. The prototype motor provided 85% of the target torque. Except the maximum torque, the most speed-torque region is found to be covered by the test SRM. The cause of discrepancy in the measured and calculated torque values is examined. An improved design is attempted, and a new experimental switched reluctance machine is designed and built for testing. The results are given in this paper.

A Switched-Capacitor DC–DC Converter With High Voltage Gain and Reduced Component Rating and Count

Abstract: This paper proposes a bidirectional switched-capacitor dc-dc converter for applications that require high voltage gain. Some of conventional switched-capacitor dc-dc converters have diverse voltage or current stresses for the switching devices in the circuit, not suitable for modular configuration or for high efficiency demand; some suffer from relatively high power loss or large device count for high voltage gain, even if the device voltage stress could be low. By contrast, the proposed dc-dc converter features low component (switching device and capacitor) power rating, small switching device count, and low output capacitance requirement. In addition to its low current stress, the combination of two short symmetric paths of charge pumps further lowers power loss. Therefore, a small and light converter with high voltage gain and high efficiency can be achieved. Simulation and experimental results of a 450-W prototype with a voltage conversion ratio of six validate the principle and features of this topology.

High-Efficiency Modular High Step-Up Interleaved Boost Converter for DC-Microgrid Applications

Abstract: In this paper, a modular interleaved boost converter is first proposed by integrating a forward energy-delivering circuit with a voltage-doubler to achieve high step-up ratio and high efficiency for dc-microgrid applications. Then, steady-state analyses are made to show the merits of the proposed converter module. For closed-loop control design, the corresponding small-signal model is also derived. It is seen that, for higher power applications, more modules can be paralleled to increase the power rating and the dynamic performance. As an illustration, closed-loop control of a 450-W rating converter consisting of two paralleled modules with 24-V input and 200-V output is implemented for demonstration. Experimental results show that the modular high step-up boost converter can achieve an efficiency of 95.8% approximately.

Design of Switched Reluctance Motor Competitive to 60-kW IPMSM in Third-Generation Hybrid Electric Vehicle

Abstract: In this paper, the design of a switched reluctance motor (SRM) having torque, power, speed-range, and efficiency values competitive to those of the interior permanent-magnet synchronous motor (IPMSM) employed in the 2009 Toyota Prius has been investigated. The outer diameter and axial length are the same as those of the IPMSM. A maximum torque of 207 N·m is needed up to the knee speed of 2768 r/min. An output power of 60 kW is required in the speed range from 2768 to 13 900 r/min. It is shown that the aforementioned requirements can be satisfied by the designed SRM, although the current density and weight are slightly increased. At high speed, the simulation results show that the output of the designed SRM is greatly enhanced with respect to that of the IPMSM.

A Nine-Phase Permanent-Magnet Motor Drive System for an Ultrahigh-Speed Elevator

Abstract: This paper presents a nine-phase permanent-magnet synchronous motor (PMSM) drive system based on multiple three-phase voltage source inverters. The nine-phase PMSM was developed as a traction motor for an ultrahigh-speed elevator. The mathematical model of the motor was simplified through symmetry of the system. Using the simplified model, the drive system can be controlled by the well-known d-q control theory. The feasibility and validity of the drive system were experimentally demonstrated at the world's tallest elevator test tower. Moreover, an additional experiment was performed to ensure the fault-tolerance capability of the system.

Model Predictive Pulse Pattern Control

Abstract: Industrial applications of medium-voltage drives impose increasingly stringent performance requirements, particularly with regard to harmonic distortions of the phase currents of the controlled electrical machine. An established method to achieve very low current distortions during steady-state operation is to employ offline calculated optimized pulse patterns (OPP). Achieving high dynamic performance, however, proves to be very difficult in a system operated by OPPs. In this paper, we propose a method that combines the optimal steady-state performance of OPPs with the very fast dynamics of trajectory tracking control. A constrained optimal control problem with a receding horizon policy, i.e., model predictive control (MPC), is formulated and solved. Results show that the combination of MPC with OPPs satisfies both the strict steady-state as well as the dynamic performance requirements imposed by the most demanding industrial applications. The estimation of the fundamental components of the machine variables separately from their respective harmonic components is not required. As a result, complicated structures such as observers can be avoided, contrary to state-of-the-art methods. A further advantage of the MPC method is the use of a receding horizon policy, which provides feedback and a high degree of robustness.

A New Measurement Method for Power Signatures of Nonintrusive Demand Monitoring and Load Identification

Abstract: Based upon the analysis of load signatures, this paper presents a nonintrusive load monitoring (NILM) technique. With a characterizing response associated with a transient energy signature, a reliable and accurate recognition result can be obtained. In this paper, artificial neural networks, in combination with turn-on transient energy analysis, are used to improve recognition accuracy and computational speed of NILM results. To minimize the distortion phenomenon in current measurements from the hysteresis of traditional current transformer (CT) iron cores, a coreless Hall CT is adopted to accurately detect nonsinusoidal waves to improve NILM accuracy. The experimental results indicate that the incorporation of turn-on transient energy algorithm into NILM significantly improve the recognition accuracy and the computational speed.

Active Islanding Detection Using High-Frequency Signal Injection

Abstract: Islanding detection is of great importance for reliable operation of smart grids. Islanding-detection methods can be classified into three different groups, i.e., active, passive, and communication-based methods. Active methods inject a disturbing signal (typically a voltage) and analyze the system response (typically in the current). These techniques have a low nondetection zone (NDZ) but present the inconvenience inherent to injecting a disturbing signal. Passive methods monitor the grid condition from the grid variables. These techniques are easy to implement but present a large NDZ. Communication methods have the inconvenience of relying on communications, currently being of limited use. This paper proposes a new active islanding-detection method, based on the measurement of the grid high-frequency impedance by means of the injection of a high-frequency voltage. The advantages of the method are almost negligible adverse effects due to the injected high-frequency voltage and accurate and fast islanding detection, i.e., in the range of a few milliseconds. Furthermore, the estimated high-frequency impedance can be used for the adaptive control of the power converter.

Detection and Classification of Rotor Demagnetization and Eccentricity Faults for PM Synchronous Motors

Abstract: Condition monitoring of rotor problems such as demagnetization and eccentricity in permanent-magnet synchronous motors (PMSMs) is essential for guaranteeing high motor performance, efficiency, and reliability. However, there are many limitations to the offline and online methods currently used for PMSM rotor quality assessment. In this paper, an inverter-embedded technique for automated detection and classification of PMSM rotor faults is proposed as an alternative. The main concept is to use the inverter to perform a test whenever the motor is stopped and to detect rotor faults independent of operating conditions or load torque oscillations, which is not possible with motor current signature analysis (MCSA). The d -axis is excited with a direct-current+alternating-current signal, and the variation in the inductance pattern due to the change in the degree of magnetic saturation caused by demagnetization or eccentricity is observed for fault detection. An experimental study on a 7.5-kW PMSM verifies that demagnetization and eccentricity can be detected and classified independent of the load with high sensitivity.

A Thermal Improvement Technique for the Phase Windings of Electrical Machines

Abstract: In electrical machines, a higher torque/force density can usually be achieved by increasing the current density in the windings. However, the resulting increase in copper losses leads to higher temperatures in the coils, particularly in the center of the slots where the thermal resistance to the ambient/cooling surfaces is highest. In this paper, a novel, simple technique is presented in which a higher thermal conductivity path between the center of the slot and the cooling arrangement is created, thus increasing the heat flow away from the slot center. A lumped-parameter thermal model is presented and used along with finite-element analysis to investigate the effectiveness of the proposed technique. The lumped-parameter model is also used for optimizing the high conductivity path for maximum air-gap shear stress and to obtain a compromise between the reduced slot area and the improved temperature distribution. Experimental validation is then presented to compare the predicted results with the measured results on a purposely built instrumented setup.

A Novel Permanent-Magnet Flux Switching Machine With an Outer-Rotor Configuration for In-Wheel Light Traction Applications

Abstract: This paper proposes a novel permanent-magnet (PM) flux switching (PMFS) machine with an outer-rotor configuration for in-wheel light traction applications. The geometric topology of the outer-rotor PMFS machine is introduced, and the analytical sizing equations are derived to determine the main design parameters of the machine. Two-dimensional finite-element analysis (FEA) models are developed to investigate and optimize the machine performance. Furthermore, the flux-weakening capability of the machine is analyzed and further improved by segmental PMs with iron bridges. The machine performance predictions by 2-D FEA models are validated by experimental tests on the prototype machine. The suitability of the proposed outer-rotor PMFS machine for in-wheel light traction application is demonstrated.

Performance Enhancement of Stand-Alone DFIG Systems With Control of Rotor and Load Side Converters Using Resonant Controllers

Abstract: In this paper, the control of a stand-alone doubly fed induction generator (DFIG)-based wind power conversion system with unbalanced and nonlinear loads is investigated. Under these load conditions, the quality of stator voltage and current waveforms of the DFIG is strongly affected due to the negative and distorted components, reducing the performance of other normal loads connected to the DFIG. To tackle this problem, the control strategy is comprehensively developed in both rotor-side converter (RSC) and load-side converter (LSC) of the DFIG. The LSC is used as an active power filter to compensate for unbalanced and distorted stator currents whereas the RSC is developed to fully eliminate unbalanced and harmonic voltages at the point of common coupling. The proposed compensation method is based on current controllers in either the RSC or the LSC, which employ a proportional integral plus a resonant controller. These current controllers are controlled in the positive synchronous reference frame so that the rotor current and stator current are directly regulated without decomposing sequential components. Analytical issues on how to eliminate unbalanced and distorted components in the stator voltage and current are also described in this paper. To verify the effectiveness of the proposed control strategy, experimental results with 2.2-kW DFIG topology are presented and discussed in the paper.

FLC-Based DTC Scheme to Improve the Dynamic Performance of an IM Drive

Abstract: This paper presents a fuzzy logic hysteresis comparator-based direct torque control (DTC) scheme of an induction motor (IM) under varying dynamic conditions. The fuzzy logic controller (FLC) is used to adjust the bandwidth of the torque hysteresis controller in order to reduce the torque and flux ripples and, hence, to improve motor dynamic response. The effects of torque hysteresis bandwidth on the amplitude of torque ripples of an IM are also discussed in this paper. Based on the slopes of motor-estimated torque and stator current, an FLC is designed to select the optimum bandwidth of the torque hysteresis controller. This paper also proposes a simpler algorithm than the conventional trigonometric function-based algorithm to evaluate the sector number (required for DTC scheme) of the stator flux-linkage space vector. The proposed algorithm reduces the computational burden on the microprocessor. In order to test the performance of the proposed FLC-based DTC scheme for IM drive, a complete simulation model is developed using MATLAB/Simulink. The proposed FLC-based DTC scheme is also implemented in real time using DSP board DS1104 for a prototype 1/3 hp motor. The performance of the proposed drive is tested in both simulation and experiment.

A Method for Online Capacity Estimation of Lithium Ion Battery Cells Using the State of Charge and the Transferred Charge

Abstract: In this paper, a method to estimate the capacity of individual lithium ion battery cells during operation is presented. When having two different states of charge of a battery cell as well as the transferred charge between these two states, the capacity of the battery cell can be estimated. The method is described in detail and validated on a battery cell with a current pulse test cycle. It is then applied to a real-life cycle; the accuracy is analyzed and discussed.

A Voltage-Controlled PFC Cuk Converter-Based PMBLDCM Drive for Air-Conditioners

Abstract: This paper deals with a Cuk dc-dc converter as a single-stage power-factor-correction converter for a permanent-magnet (PM) brushless dc motor (PMBLDCM) fed through a diode bridge rectifier from a single-phase ac mains. A three-phase voltage-source inverter is used as an electronic commutator to operate the PMBLDCM driving an air-conditioner compressor. The speed of the compressor is controlled to achieve optimum air-conditioning using a concept of the voltage control at dc link proportional to the desired speed of the PMBLDCM. The stator currents of the PMBLDCM during step change in the reference speed are controlled within the specified limits by an addition of a rate limiter in the reference dc link voltage. The proposed PMBLDCM drive (PMBLDCMD) is designed and modeled, and its performance is evaluated in Matlab-Simulink environment. Simulated results are presented to demonstrate an improved power quality at ac mains of the PMBLDCMD system in a wide range of speed and input ac voltage. Test results of a developed controller are also presented to validate the design and model of the drive.

High-Bandwidth Explicit Model Predictive Control of Electrical Drives

Abstract: Field-oriented control (FOC) has proven effective for controlling ac drives with good dynamic performance. However, operation at low-switching frequencies and the sensitivity of traditional feedforward loops to system parameters pose severe limitations on the achievable performance and require a tedious tuning procedure. In this paper, we present a systematic cascade explicit model predictive control framework for the FOC of electrical drives, resolving the aforementioned issues while being sufficiently simple to be widely implemented on various ac drive systems. The resulting closed-loop system exhibits high dynamic performance for all operating points, even at low-switching frequencies. We present experiments with a permanent-magnet machine and an induction motor, demonstrating the practical feasibility and the merits of the proposed framework over traditional controller designs for electrical drives.

A Comparison of Smart Grid Technologies and Progresses in Europe and the U.S.

Abstract: This paper discusses historical and technical events in the U.S. and Europe over the last few years that are aimed at modernizing the electric power grid. The U.S. federal government has ratified the “smart grid initiative” as the official policy for modernizing the electricity grid including unprecedented provisions for timely information and control options to consumers and deployment of “smart” technologies. European countries are unified in researching and developing related technologies through various structures supported by the European Union. This paper presents the development of smart grids and an analysis of the methodologies, milestones, and expected evolutions of grid technologies that will transform society in the near future.

Comparative Study of PMSM Drive Systems Based on Current Control and Direct Torque Control in Flux-Weakening Control Region

Abstract: This paper examines the control performance of permanent-magnet synchronous motor drive systems based on current control and direct torque control (DTC) when flux-weakening control is applied. The control law in the M-T frame, which is used in the DTC, requires only armature resistance, whereas the control law in the d-q frame, which is used in current control, requires many motor parameters for flux-weakening control. The experimental results clarify the influence of parameter variation on the control characteristics of flux weakening and torque limiting. The DTC-based motor drive system combined with the control laws in the M-T frame has several advantages, including insensitivity to parameter variation, simplicity of calculation, and stable control.

Wind Speed and Rotor Position Sensorless Control for Direct-Drive PMG Wind Turbines

Abstract: This paper proposes a wind speed and rotor position sensorless control for wind turbines directly driving permanent magnetic generators (PMGs). A sliding-mode observer is designed to estimate the rotor position of the PMG by using the measured stator currents and the commanded stator voltages obtained from the control scheme of the machine-side converter of the PMG wind turbine. The rotor speed of the PMG (i.e., the turbine shaft speed) is estimated from its back electromotive force using a model adaptive reference system observer. Based on the measured output electrical power and estimated rotor speed of the PMG, the mechanical power of the turbine is estimated by taking into account the power losses of the wind turbine generator system. A back-propagation artificial neural network is then designed to estimate the wind speed in real time by using the estimated turbine shaft speed and mechanical power. The estimated wind speed is used to determine the optimal shaft speed reference for the PMG control system. Finally, a sensorless control is developed for the PMG wind turbines to continuously generate the maximum electrical power without using any wind speed or rotor position sensors. The validity of the proposed estimation and control algorithms are shown by simulation studies on a 3-kW PMG wind turbine and are further demonstrated by experimental results on a 300-W practical PMG wind turbine.

Loss-Minimizing Flux Level Control of Induction Motor Drives

Abstract: This paper applies a dynamic space-vector model to loss-minimizing control in induction motor drives. The induction motor model, which takes hysteresis losses and eddy-current losses as well as the magnetic saturation into account, improves the flux estimation and rotor-flux-oriented control. Based on the corresponding steady-state loss function, a method is proposed for solving the loss-minimizing flux reference at each sampling period. A flux controller augmented with a voltage feedback algorithm is applied for improving the dynamic operation and field weakening. Both the steady-state and dynamic performance of the proposed method is investigated using laboratory experiments with a 2.2-kW induction motor drive. The method improves the accuracy of the loss minimization and torque production, it does not require excessive computational resources, and it shows fast convergence to the optimum flux level.

High-Frequency-Injection-Assisted “Active-Flux”-Based Sensorless Vector Control of Reluctance Synchronous Motors, With Experiments From Zero Speed

Abstract: This paper presents a hybrid motion sensorless control of an axially laminated anisotropic reluctance synchronous machine (RSM). The zero- and low-speed sensorless method is a saliency-based high-frequency signal injection technique that uses the motor itself as a resolver. The second method is based on a state observer incorporating the “active-flux” concept used to deliver RSM rotor position and speed information for medium- and high-speed range. Even if both methods perform successfully in separate speed regions, estimation of the two algorithms is combined as a sensor fusion to improve the performance at zero and very low speeds. Experimental results validate the proposed control strategies.

Reduction of Common-Mode Voltage in Five-Phase Induction Motor Drives Using Predictive Control Techniques

Abstract: The common-mode voltage (CMV) is known to be a source of electromagnetic interference, and it is potentially dangerous for the machine windings' insulation and bearings. CMV has been analyzed for three-phase machines supplied by voltage-source inverters, showing that modified pulsewidth modulation and model predictive control (MPC) techniques can significantly reduce the CMV at the expense of increased current distortion. This paper analyzes the CMV for five-phase drives and proposes a modified MPC strategy that accounts for the CMV reduction. The MPC can adjust the weights of the cost function to find a good balance between CMV reduction and low current distortion. The MPC strategy is experimentally tested showing how the CMV can be effectively reduced, thus improving the multiphase drive performance.

A High-Torque-Density Permanent-Magnet Free Motor for in-Wheel Electric Vehicle Application

Abstract: A motor for in-wheel electric vehicle (EV) requires high efficiency and specific torque. In view of this, permanent-magnet brushless dc (PM BLDC) motor is most commonly employed for this application. However, due to the increasing cost of PMs, machines that do not use PMs are attracting interest. Switched reluctance motor (SRM), with its simple and robust construction, along with fault tolerant operation, is a viable option for in-wheel EV application. However, the SRM has low specific torque as compared with BLDC. Therefore, design improvements are required to make SRM a viable alternative to BLDC motor. In this paper, a new 12/26 pole SRM with high specific torque is proposed for in-wheel EV application. This machine has segmented-rotor-type construction. Also, concentrated-winding arrangement is used, ensuring low end-winding volume and copper loss. The developed machine also has high efficiency. In order to verify the design, the prototype of the machine is fabricated, and experimental results are presented.