Optimal PWM in Three Level Inverter FED Induction Motor Drives with Quarter Wave Symmetry Relaxed

PWM waveforms are employed generally with Half Wave Symmetry (HWS) and Quarter Wave Symmetry (QWS) being preserved to minimize the harmonic distortion in the line current (ITHD) of the ac motor drives. This paper investigates ideal switching angles for a three-phase, three level inverter with HWS but without QWS for switching angles N=2 and N=3 per quarter of a cycle. With the suppression of the low order voltage harmonics, the performance of the proposed method is superior than the existing PWM technique with QWS in terms of total harmonic distortion (THD%) of line-line voltage for the complete range of modulation index (M). A complete Simulink model is developed to validate and confirm the theoretical outcomes for a three level inverter driving a 2.2kW squirrel cage induction motor.