Variable Switching Frequency DPWM for ZVS in AC Motor Drive Fed by Two Paralleled SiC Inverters With Coupled Inductors

For ac motor drive system with silicon carbide (SiC) based inverters, achieving the zero voltage switching (ZVS) performance is attractive but rather difficult. The difficulty is mainly due to the tight coupling of output current ripples and a wide range of operating conditions in ac motor drive system. This article solves above issues by a variable switching frequency discontinuous pulsewidth modulation (DPWM) strategy based on circulating current ripple prediction method, where the two paralleled SiC inverters are used with the coupled inductors. First, the PWM signals of paralleled phase-legs are interleaved by 180° to generate the circulating current ripple, and simultaneously provide a three-level voltage output for ac motors. Combining the sampled fundamental current and predicted high-frequency circulating current ripple, the turn-
on
current of all SiC devices can be easily calculated, where no additional auxiliary circuit is required. Second, a freedom of switching frequency can be utilized to control the turn-
on
current value or direction to achieve ZVS condition of all SiC switches. Third, to overcome the penalty of the semiconductors conduction loss and coupled inductor loss under ZVS condition, DPWM schemes are carefully investigated, which features lower RMS current and more uniform distribution of circulating current ripple, compared with the traditional space vector pulsewidth modulation. Finally, both theoretical analysis and experimental experiments are provided to verify the performance of proposed strategy.