Effects of Injected Harmonics on Torque Pulsations of a Three Phase Induction Motor: Study on SPWM

This paper presents an analytical study of the effect of injected current harmonics on induction motor torque ripples. A three-phase induction motor (IM) when fed by an ideal three-phase sinusoidal voltage source produces a ripple-free torque output at the shaft. For better speed and torque control of induction motor, several methods have been proposed; such as V/F control, direct torque control, Field oriented control. All such control schemes involve pulse width modulation schemes with high frequency switching such as SPWM and SVPWM. These techniques provide excellent power optimization and control but induce harmonic currents at the stator winding, which in turn gives rise to torque ripples. In the present work, an analysis of the effects of injected harmonic currents on torque ripple is reported. Case study on SPWM by varying switching frequency and optimal switching frequency for least torque ripple are presented. It is reported that only higher frequency switching does not guarantee lower torque ripple. MATLAB Simulink Simscape toolbox is used for verifying the case study. Torque ripple corresponding to injected stator current ripple is presented for validation of the proposed analysis.