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.

中文翻译：

---

基于中性点平衡的3-L PMSM驱动系统基于电流纹波分析的开关频率变化

三级（3-L）逆变器的输出电流纹波对于3-L永磁同步电动机（PMSM）驱动系统的性能很重要，但是对于3-L T-型逆变器，中性点（NP）平衡到目前为止，在分析电流纹波时并未考虑使用这种类型的逆变器。NP平衡算法会改变电流纹波分布，因此有必要开发新颖的方法进行电流纹波分析。在这项研究中，利用零阶电压注入和虚拟空间矢量PWM（VSV-PWM）的正弦脉冲宽度调制来平衡PMSM驱动系统中3-L逆变器的NP电位。提出了两种调制方式下电流纹波的解析方法，分别研究了这两种NP平衡方式对输出电流纹波的影响。在分析电流纹波的基础上，提出了两种考虑NP平衡的可变开关频率PWM（VSF-PWM）方法。提出的VSF-PWM方法不仅可以降低开关损耗，而且可以在保持NP电位平衡的同时抑制电磁干扰噪声。特别地，所提出的可变开关频率VSV-PWM（VSF-VSV-PWM）可以有效地缓解VSV-PWM的高开关损耗的固有问题。