Optimal PWM for Minimization of Current Harmonic Distortion in Three-Level Inverter Fed Induction Motor Drives

Offline pulse width modulation (PWM) techniques are employed to reduce the line current distortion in induction motor (IM) drives where the switching frequency is highly constrained. An optimal PWM technique is proposed here for a neutral point clamped (NPC) inverter fed IM drive to minimize the motor current distortion, subject to constraints on number of switching instants per quarter cycle. Two types of pole voltage waveforms of the NPC inverter are considered, namely type-I and type-I I. This paper reports optimal switching angles for both type-I and type-I I waveforms to minimize the resulting total harmonic distortion (THD) in motor current. In general optimal type-I I is found to result in lower THD than optimal type-I PWM. The optimal type-I I PWM offers superior performance in terms of motor current distortion than synchronized sine-triangle PWM and selective harmonic elimination PWM, as shown by simulation and experimental results on an NPC inverter fed 3.7 kW induction motor drive