This paper reviews the relative merits of induction, switched reluctance, and permanent-magnet (PM) brushless machines and drives for application in electric, hybrid, and fuel cell vehicles, with particular emphasis on PM brushless machines. The basic operational characteristics and design requirements, viz. a high torque/power density, high efficiency over a wide operating range, and a high maximum speed capability, as well as the latest developments, are described. Permanent-magnet brushless dc and ac machines and drives are compared in terms of their constant torque and constant power capabilities, and various PM machine topologies and their performance are reviewed. Finally, methods for enhancing the PM excitation torque and reluctance torque components and, thereby, improving the torque and power capability, are described

Electrical Machines and Drives for Electric, Hybrid, and Fuel Cell Vehicles

This paper reviews the relative merits of induction, switched reluctance, and permanent-magnet (PM) brushless machines and drives for application in electric, hybrid, and fuel cellvehicles,withparticularemphasisonPMbrushlessmachines. The basic operational characteristics and design requirements, viz. a high torque/power density, high efficiency over a wide operatingrange,andahighmaximumspeedcapability,aswell as the latest developments, are described. Permanent-magnet brushless dc and ac machines and drives are compared in terms of their constant torque and constant power capabilities, and various PM machine topologies and their performance are reviewed. Finally, methods for enhancing the PM excitation torque and reluctance torque components and, thereby, improv- ing the torque and power capability, are described.

Electrical Machines and Drives for Electric, Hybrid, and Fuel Cell Vehicles Induction and switched-reluctance machines can provide the needed characteristics, but permanent magnet brushless machines offer a higher efficiency and torque density.

This paper reviews the current technologies used in high-speed electrical machines through an extensive survey of different topologies developed and built in the industry and academia for several applications. Developments in materials and components, including electrical steels and copper alloys, are discussed, and their impact on the machines' operating physical boundaries is investigated. The main application areas pulling the development of high-speed machines are also reviewed to better understand the typical performance requirements.

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High-Speed Electrical Machines: Technologies, Trends, and Developments

The cost reduction of power-electronic devices, the increase in their reliability, efficiency, and power capability, and lower development times, together with more demanding application requirements, has driven the development of several new inverter topologies recently introduced in the industry, particularly medium-voltage converters. New more complex inverter topologies and new application fields come along with additional control challenges, such as voltage imbalances, power-quality issues, higher efficiency needs, and fault-tolerant operation, which necessarily requires the parallel development of modulation schemes. Therefore, recently, there have been significant advances in the field of modulation of dc/ac converters, which conceptually has been dominated during the last several decades almost exclusively by classic pulse-width modulation (PWM) methods. This paper aims to concentrate and discuss the latest developments on this exciting technology, to provide insight on where the state-of-the-art stands today, and analyze the trends and challenges driving its future.

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The Essential Role and the Continuous Evolution of Modulation Techniques for Voltage-Source Inverters in the Past, Present, and Future Power Electronics

For vehicles using grid power to charge the battery, traction circuit components are not engaged during the charging time, so there is a possibility to use them in the charger circuit to have an onboard integrated charger. The battery charger can be galvanically isolated or nonisolated from the grid. Different examples of isolated or nonisolated integrated chargers are reviewed and explained. Moreover, a novel isolated-high-power three-phase battery charger based on a split-phase permanent-magnet motor and its winding configuration is presented in this paper. The proposed charger is a bidirectional high-power charger with a unity power factor operation capability that has high efficiency.

Grid-Connected Integrated Battery Chargers in Vehicle Applications: Review and New Solution

A novel and simple nonlinear logical torque-sharing function (TSF) for a switched reluctance motor (SRM) drive is proposed. This novel scheme using nonlinear TSF manipulates currents in two adjacent phases during commutation, so that efficiency and torque ripple in an SRM drive can be considerably improved. For constant torque generation, the switching of one-phase windings is regulated, and torque reference for the other phase stays at the previous state under the condition of a certain current limit given by the overall drive power rating. Every torque state monitored by the nonlinear logical condition determines a regulated or nonregulated torque control among two phases overlapped in commutation region, where one phase is incoming to produce the majority of torque and the outgoing current in the other phase is decreasingly controlled by the logical condition. Due to the same switching state in a nonregulated phase and the reduction of commutation period by the proposed control method, the switching number can be significantly reduced, and hence, the switching loss can be reduced. In case that one-phase regulation cannot satisfy a proper torque reference required for minimum torque ripple operation, a two-phase regulation mode is employed in the novel nonlinear TSF. In order to include magnetic nonlinearity in torque control and decrease a current tail at the end of commutation, the current of the incoming phase needs to be controlled in an increasing manner, and at the same time, the outgoing phase current tracks on an opposite direction so that torque sharing between two phases can be smoothly achieved with a minimum current crossover. The proposed control scheme is verified by some computer simulations and experimental results.

A Simple Nonlinear Logical Torque Sharing Function for Low-Torque Ripple SR Drive

This paper presents the design and operation of a two-phase four-two pole switched reluctance motor (SRM) for a high-speed air blower. The air blower has unidirectional rotation and requires a wide positive torque region without torque dead zone. In order to achieve the requirements, a nonuniform air gap with asymmetric inductance profile is considered. For a flattop torque with a low torque ripple, the nonuniform air gap is also effective. Based on the output torque analysis at the rotor position for the given air gap, the air gap is modified to reduce the torque ripple. The optimized air gap at a given position cannot feel the effect of the air gap at a previous rotor position. Therefore, the output torque cannot fully satisfy the target torque in one optimization process. In order to satisfy the target torque and reduce the torque ripple, the second optimization process is implemented considering the output torque of the initial optimization process. The second target torque is determined by the torque error of the initial output torque and target torque of the first process. From this optimization sequence, the final air gap, as a function of the rotor position, can be determined to satisfy the torque ripple requirement. The proposed high-speed four-two pole SRM is tested to verify the high-efficiency and low-acoustic-noise characteristics.

Design and Operation Characteristics of Four-Two Pole High-Speed SRM for Torque Ripple Reduction

The inherent simplicity, ruggedness, and low cost of a switched reluctance motor (SRM) makes it a viable candidate for various general-purpose adjustable-speed applications such as industrial and home appliances. The primary disadvantage of an SRM is the vibration and acoustic noise compared with that of conventional machines. The main source of vibration in the SR drive is generated by rapid change of radial magnetic force when phase current is extinguished during commutation action. In this paper, a hybrid excitation method with C-dump inverter is proposed to reduce vibration and acoustic noise in the SR drive. The hybrid excitation has two-phase excitation by long dwell angle as well as conventional one-phase excitation. The vibration and acoustic noise are reduced because the scheme reduces abrupt change of excitation level by distributed and balanced excitation.

Hybrid excitation of SRM for reduction of vibration and acoustic noise

A new excitation strategy for a switched reluctance motor (SRM) is described and tested. This scheme excites two phases of an SRM simultaneously, which is similar to the two-phase excitation method of a step motor. In this scheme, the torque is produced by mutual-inductance as well as by self-inductance. The abrupt change of a phase excitation produces mechanical stresses, resulting in torque ripple and noise. The acoustic noise is reduced through a sequential two-phase excitation. Noise reduction occurs because the scheme reduces abrupt changes in excitation levels by distributed, balanced excitation and freewheeling during commutation. The operational principle and a characteristic comparison to that of the conventional SRM show that this novel excitation scheme has some advantages, including torque ripple and noise reduction, as well as simple inverter topology.

A three-phase switched reluctance motor with two-phase excitation

This paper presents the direct compensation of the switching interval error of the effective voltage vectors by the dead time of a pulsewidth modulation voltage source inverter (PWM-VSI). The output voltages of a three-phase PWM-VSI are distorted and have voltage errors from the dead time to avoid the shoot-through of inverter arms and the time delay of the gate drive. Voltage distortion increases the harmonics of the output voltages and decreases control performance. This paper presents a simple and direct compensation technique to solve this problem in a three-phase VSI. The practical switching output voltages are determined by the dc-link voltage, the switching signals of each phase, the dead time, the time delay, and the current polarities of each phase. For these reasons, output voltage errors are not constant. In order to analyze the dead-time effect in the actual switching voltages of each phase, the practical switching voltages in a sampling period of a space vector PWM (SVPWM) method are calculated according to the current polarity. In the calculation, the dead time, the time delay of devices, and the voltage drops on power devices are included to consider nonlinear voltage distortion. From these practical switching voltages during the switching intervals in a sampling period, the average output voltages of each phase can be derived, and the output voltage errors between the voltage commands and the average output voltages of each phase are obtained. The SVPWM switching intervals of each phase can be derived by the average output voltages that are calculated according to the current polarity and nonlinear voltage distortion to compensate for the output voltage errors. With the simple detection of the current polarity, the practical errors of the switching intervals of each phase can be compensated by the addition of the compensated switching time. Simulation and experimental results validating the proposed compensation method are presented in this paper.

Jin-Woo Ahn

Papers

A Simple Nonlinear Logical Torque Sharing Function for Low-Torque Ripple SR Drive

Design and Operation Characteristics of Four-Two Pole High-Speed SRM for Torque Ripple Reduction

Hybrid excitation of SRM for reduction of vibration and acoustic noise

A three-phase switched reluctance motor with two-phase excitation

A Simple and Direct Dead-Time Effect Compensation Scheme in PWM-VSI