Extension to Symmetrical and Asymmetrical n-Phase AC Drives of Simple Carrier-Based PWM for Prolonged High DC-Link Utilization

Recently, it was proposed to combine circulating-current (x-y) filters with a carrier-based pulsewidth-modulation (PWM) method, which injects harmonics in no-torque x-y subspaces (attenuated by the filter) of five-phase motors to achieve high dc-link utilization (DLU). The filter allows prolonged high DLU without overheating. Unlike square-wave switching, no torque ripple is introduced by the PWM. Compared with other PWM techniques capable of high-DLU operation (often called overmodulation), the one proposed for said filters is especially convenient because of its simplicity. However, it is unclear if this PWM method can be extended to machines of any phase number n and winding arrangement (symmetrical or asymmetrical). This paper extends this simple carrier-based PWM strategy to n-phase (symmetrical or asymmetrical) drives, and evaluates its behavior in terms of DLU. The improvement in DLU, compared with conventional PWM with zero-sequence injection, is considerable in most cases. Current distortion is negligible with suitable filter, and no torque ripple (unlike square-wave switching) is generated.