Seok-Gyu Oh

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

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.

Design and Development of Low-Cost and High-Efficiency Variable-Speed Drive System With Switched Reluctance Motor

Low-cost switched-reluctance-motor (SRM) drive systems are actively sought for high-efficiency home appliances and power tools. Minimizing the number of switching devices has been in power converters that is the main method to reduce drive costs. Single-switch-per-phase converters have been cost effective due to the compactness of the converter package resulting in a possible reduction in their cost. However, some of the single-switch-per-phase converters have the drawbacks that include higher losses and low-system efficiency. In order to overcome these shortcomings, the choice narrows down to the split ac converter through the quantitative analysis in terms of device ratings, cost, switching losses, conduction losses, and converter efficiency. Simulations to verify the characteristics of the converter circuit and control feasibility are presented. The motor drive is realized with a novel two-phase flux-reversal-free-stator SRM and a split ac converter. The efficiency with various loads is numerically estimated and experimentally compared from the viewpoint of subsystem and system in details. The acoustic noise with no load and full load is also compared. The focus of this paper is to compare the considered split ac converter to the asymmetric converter through experiments and demonstrate that the split ac converter is the most advantageous with respect to cost, efficiency, and acoustic noise

Design and Development of Brushless Variable Speed Motor Drive for Low Cost and High Efficiency

Low cost brushless motor drive systems are actively sought for high efficiency home appliances and power tools. Minimizing the number of switching devices has been in power converters is the main method to reduce drive costs. Single-switch-per-phase converters have been cost-effective due to compactness of the converter package resulting in a possible reduction in their cost. However, some of single-switch-per-phase converters have the drawbacks that include higher losses and low system efficiency. In order to overcome these shortcomings, the choice narrows down to the split AC converter through the quantitative analysis in terms of device ratings, cost, switching losses, conduction losses, and converter efficiency. Simulations to verify the characteristics of the converter circuit and control feasibility are presented. The motor drive is realized with a novel two-phase flux-reversal-free-stator switched reluctance motor and a split AC converter. The efficiency with various loads is numerically estimated and experimentally compared in this paper. The acoustic noise with no load and full load is also compared. The focus of this paper is to compare the considered split AC converter to the asymmetric converter through experiments and demonstrate that the split AC converter is the most advantageous with respect to cost, efficiency, and acoustic noise

Digital PLL technique for precise speed control of SR drive

The switched reluctance drive is known to provide good adjustable speed characteristics. However, higher torque ripple and lack of the precise speed control are drawbacks. These problems lie in the fact that SR drive is not operated with an MMF current specified for dwell angle and input voltage. To reduce torque ripple and to have precise speed control, the SR drive has to control the dwell angle and input voltage instantaneously. In the paper, a PLL (phase locked loop) technique is adopted to regulate the dwell angle and input voltage. A PLL control technique in conjunction with a dynamic dwell angle control scheme has good speed regulation characteristics. The DSP based control system is used to realize this drive system. Test results show that the system has the ability to achieve good dynamic and precise speed control.

Switched reluctance motor with 2-phase excitation

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 inductances as well as by self inductances. The abrupt change of phase excitation produces mechanical stresses and results in torque ripple and noise. The acoustic noise is reduced remarkably through the sequential phase excitation in the two-phase excitation. This is because the scheme reduces abrupt changes in excitation levels by distributed, balanced excitation and free-wheeling 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.

Comparison of Two Switched Reluctance Motors with No Flux-Reversal in the Stator

A comparison of two configurations of a novel two-phase switched reluctance machine (SRM) with no flux reversal in the stator iron is presented in this paper. Conventional SRMs have flux reversals that occur in sections of the yoke during commutation. The two novel SRMs compared in this paper have six stator poles. Each phase comprises of three poles separated by 120deg. The two rotor configurations contain three poles and nine poles, respectively. The comparison includes inductance and torque profiles, self-starting capability and torque ripple, weight, radial forces, core losses and in addition the unique features of the flux-reversal-free-stator SRMs. The results provide an indication of which machine is best suited for a particular application. Data for the comparison is obtained from dynamic finite element simulations

DSP based high efficiency SR drive with precise speed control

The switched reluctance drive is known to provide good adjustable speed characteristics with high efficiency. However, higher torque ripple and lack of the precise speed control are drawbacks. These problems lie in the fact that SR drive is not operated with an mmf current specified for dwell angle and input voltage. To have precise speed control with a high efficiency drive, SIR drive has to control the dwell angle and input voltage instantaneously. In the paper, a PLL(Phase Locked Loop) technique is adopted to regulate the dwell angle instantaneously. A PLL control technique in conjunction with dynamic dwell angle control scheme has good speed regulation characteristics. The advance angle in the dwell angle control is adjusted to have high efficiency drive through efficiency testing. The F240 DSP based control system is used to realize this drive system. Test results show that the system has the ability to achieve good dynamic and precise speed control.

Reduction of vibration and acoustic noise of SRM with hybrid excitation method

Simple motor construction, low cost and fault tolerant power electronic drive have made the switched reluctance drive a strong contender for many applications. However, the switched reluctance drive does exhibit higher levels of vibration and acoustic noise than that of most competing drives. The main source of vibration in the switched reluctance drive is generated by rapid change of radial force when phase current is extinguished during commutation action. In this paper, a hybrid excitation method is proposed to reduce vibration and acoustic noise of the switched reluctance drive. The hybrid excitation has 2-phase excitation by long dwell angle as well as conventional 1-phase excitation. The vibration and acoustic noise are reduced because the scheme reduces abrupt change of excitation level by distributed and balanced excitation.

Study on optimal driving condition of SRM using GA-neural network

The torque of SRM depends on phase current and the derivative of inductance. But the inductance of SRM is nonlinearly changed according to rotor position angle and phase current because of saturation in magnetic circuit. Therefore this has a concern in torque ripple and speed variation, and it is difficult to control the desired torque. This paper proposes an optimization control scheme by adjusting both the turn-on and turn-off angle according to high efficiency points which are simulated by GA-neural network, which is used to simulate the reasonable switching angle which is nonlinearly varied with rotor speed and load.

Five-level inverter for optimal excitation of SRM drive

Energy recovery in the regenerative region is very important when SRM is used in a traction drive. This is to reduce energy loss during mechanical braking and/or to have a high efficiency drive during braking. To control excitation voltage in motor operation and regenerative voltage in the generator operation in the SRM, multi-level voltage control is effective. This paper suggests a multi-level inverter which is useful for motoring and regenerative operation in SRM.