Switching frequency variation based on current ripple analysis of a 3‐L PMSM drive system considering neutral point balance

Abstract

The output current ripple of the three-level (3-L) inverter is important to the performance of the 3-L permanent magnetic synchronous motor (PMSM) drive system, but the neutral point (NP) balance for the 3-L T-type inverter is not considered in the analysis of current ripple up to this point. The NP balance algorithms change the current ripple distribution and it is necessary to develop novel methods for current ripple analysis. In this study, the sinusoidal pulse width modulation with zero-order voltage injection and virtual space vector PWM (VSV-PWM) are utilised to balance the NP potential of the 3-L inverter in the PMSM drive system. The analytical methods of current ripple under these two modulation methods are proposed and the effects of these two NP balance methods on the output current ripple are investigated, respectively. Based on the analysis of current ripple, two variable switching frequency PWM (VSF-PWM) methods considering the NP balance are proposed. The proposed VSF-PWM methods can not only reduce the switching loss but also suppress the electro-magnetic interference noise while keeping the NP potential balanced. Especially, the proposed variable switching frequency VSV-PWM (VSF-VSV-PWM) can effectively alleviate the intrinsic problem of high switching loss of VSV-PWM.