中文摘要：

针对于II型混合级联型多电平逆变器混合调制中,输出电平切换时出现的低压单元直流侧电流倒灌问题,提出了一种改进的混合频率载波调制策略。该策略采用频率相差1倍,且幅值相同的6个层叠载波对正弦调制波进行混合调制,兼顾了低压单元和高压单元的性能,在保障输出电压波形质量的同时,完全解决了电流倒灌问题。以II型混合级联七电平逆变器为例,在给定相关参数下对该策略进行了仿真和实验验证,研究结果表明该策略下逆变器相电压和线电压总谐波畸变率分别为19.90%和17.34%,谐波主要分布在载波比两侧,直流侧电流倒灌问题被完全消除。

英文摘要：

An improved hybrid frequency carder-based PWM control strategy based on the II-type cascaded multilevel （ML） inverter is presented to solve the problem of the current flowing backwards of the low-voltage cell. The low-voltage cell of the hybrid power converter can participate in PWM control by the proposed strategy, in which six carders with different frequencies and the sine wave are used to get the trigger pulses of the switch devices. Continuous PWM modula- tion can be realized to solve the problem of the current flowing backwards without affecting the quality of the output voltage waveform. A seven-level II-type cascaded multilevel （ML） inverter composed of two H-bridge cells is taken as the examples, and the new strategy is researched with related parameters. The results show that the THD of inverter phase voltage and line voltage are 19.90% and 17.34%, respectively, the harmonic distributes on both sides with carder wave ratio. The TDC current intrusion problem is completely eliminated.