中文摘要：

针对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。该策略让低压单元参与脉宽调制（PWM）,采用6个频率不同的层叠载波对正弦调制波进行混合调制,以得到各开关器件的触发脉冲。该策略能实现连续PWM,且在保障输出电压波形质量的同时,也彻底解决了电流倒灌问题。以II型混合级联型七电平逆变器为例,对所提出的控制策略进行了理论分析,以及仿真和实验验证,研究结果证明了改进的混合频率载波调制策略的正确性和可行性。

英文摘要：

An improved hybrid frequency carrier-based pluse width modulation （PWM） control strategy is presented based on the II-type hybrid cascaded multi-level inverter with the problem of the current flowing backwards of the low-voltage cell,when intput level.The low-voltage cell of the hybrid power converter can participate in PWM control by the proposed strategy, which six carriers with different frequencies and the sine wave is used to get the trigger pulses of the switch devices.Continuous PWM 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 hybrid cascaded multi-level inverter composed by two H-bridge cells is taken as the examples, and the new strategy is researched, simulated and the results verify the validity of the proposed strategy.