Nine-phase variable speed drive system with reduced switching PWM

Multiphase variable speed drive systems have gained more and more interest recently because of their lower torque ripple as a result of the harmonic cancellation effects between phases. This paper presents a nine phase variable speed drive system with reduced frequency PWM control scheme. The proposed PWM scheme is tailored for multiphase winding to reduce torque ripple and associated rotor losses. Even though the line current has fairly high harmonic contents, there is no significant power losses increase in the motor. On the other hand, the power converter can benefit significantly from the reduced switching frequency and switching losses. Simulation results and experimental results on a 160 kW 9-phase motor have been shown to support the conclusion.