Contribution of Current Harmonics to Average Torque and Torque Ripple in Switched Reluctance Machines

Abstract

This paper investigates the contribution of current harmonics to average torque and torque ripple in switched reluctance machines. In order to account for the magnetic saturation under different current amplitudes and waveforms, the self-inductances are obtained by finite element calculation using frozen permeability method and subsequently used in the analytical derivation of an instantaneous torque equation based on the Fourier series analyses. Five different current waveforms are also considered in order to identify the contribution of current harmonics. It is found that the average torque is mainly contributed by the dc, first, and second current harmonics. Meanwhile, the fourth and fifth current harmonics have high influence on the torque ripple but much lower contribution to the average torque. In addition, the optimization of current waveforms in terms of the maximum average torque under a given RMS current is also discussed. All analytical analyses are validated by direct nonlinear finite element and experimental results.