Enhancing Low-Speed Torque Profile in a Self-Commutated 12-Pulse CSI Fed Multi-Phase Induction Machine Using a Novel PWM Scheme

Silicon Controlled Rectifier (SCR) based Current Source Inverter (CSI) topologies are recognized for their reliability, cost-effectiveness, and high-power handling, making them prevalent in high-power drive applications. Despite their strengths, they struggle with low-frequency harmonic torque oscillations caused by the quasi-square wave nature of the machine currents. During low-speed and startup operations, these oscillations have the potential to cause mechanical resonance and damage to the drive. This paper proposes a Selective Harmonic Minimization-based Pulse Width Modulation (SHM-PWM) method for a 12-pulse CSI multi-phase induction machine drive. The technique reduces the lower order torque harmonics and provides a smooth torque profile, significantly improving the drive’s performance during starting and low-speed operation. The methodology has been experimentally validated with a 75 kW multi-phase induction machine featuring two 1.6 kV MV windings and a 400 V LV winding.