A Carrier-Based Overmodulation Strategy With Minimum Voltage Distortion for Symmetrical Nine-Phase Induction Motor Drives

Multiphase machines have significant benefits over three-phase machines. One of them is the possibility of further exploiting the dc-link voltage by injecting non-torque-related voltage harmonics in the x–y planes. This allows reaching higher modulation indices in the overmodulation region of pulse width modulation (PWM) without causing torque ripple in motors with negligible space-harmonic effects. In this regard, this paper proposes an overmodulation strategy for symmetrical nine-phase induction motor drives with minimum voltage harmonic distortion. This is accomplished by injecting at each instant the minimum x–y voltage to the reference. As a consequence of achieving the minimum voltage distortion, the proposal attains the lowest current distortion compared with existing techniques. It relies on carrier-based PWM, and hence it is simpler than previous methods. Experimental results are provided.