A novel torque ripple minimization strategy for a 6/4 SRM drive with reduced switching frequency variation

Switched reluctance motors, due to their simple constructions, are drawing the attentions for industrial applications. It is superior to other electrical machines because of less manufacturing cost, reduced losses and greater reliability. But these machines have a severe drawback that they have large torque ripples which make the operation noisy and increase the wear and tear in the SRM drive. The objective of the paper is to reduce torque ripples and switching frequency variations. Generally the commutation signals for a SRM are square pulses but in this work the commutation signal wave shape are changed to be sinusoids which help in reduction of torque ripples. Again as hysteresis band controllers are used for the current control purpose, they result in variable switching frequency which causes very low switching frequencies generally at no load or light load conditions, which results in an increased filter cost and size. This work proposes a hysteresis band current controller whose band width is varied according to the load torque and commutation signals such that the variations in switching frequency are reduced. The decision is made from a fuzzy logic controller which decides the band width of the hysteresis band controllers. The stress has been given on the wave shape of the commutation signal and hysteresis band current controller to reduce the torque ripples and switching frequency variations. The SRM performances are studied for both the conventional and proposed systems and compared in this work.