一种基于载波层叠脉宽调制的倍频调制方法

A Double Frequency Modulation Method Based on the Level-Shifted Pulse Width Modulation

对于直流侧电压比为1∶2的混合级联H桥七电平逆变器而言,需要对传统的调制方法进行改进,以提高该拓扑的实用性。常规的混合调制方法在一定的调制比区间内存在功率倒灌问题,单极性调制方法虽然有效地解决了这个问题,但是高压单元在部分区间内参与高频工作,限制了整个系统开关频率的提高,混合频率调制方法在一定程度上可以降低高压单元的开关频率,但输出电压谐波特性又会受到影响。针对以上问题,提出一种基于载波层叠脉宽调制(LS-PWM)的倍频调制方法,一方面解决传统混合调制方法固有的功率倒灌问题,另一方面在高压单元开关频率较低的情况下保证逆变器输出电压具有良好的谐波特性。仿真和实验结果证明了理论分析的正确性。

For the hybrid cascaded seven-level inverter with a DC-side voltage ratio of 1∶2, it is necessary to ameliorate the conventional modulation method to improve the practicality of the topology. The general hybrid modulation method has a power reverse problem in some modulation ratio interval. Although the unipolar pulse width modulation（PWM） method solves this problem, the high voltage cell working at high frequency in some interval limits the switching frequency of the whole system. The hybrid frequency method reduces the switching frequency of the high voltage cell to a certain extent, but the harmonic characteristics of output voltage will be affected. In view of this, a double frequency modulation method based on the level-shifted PWM（LS-PWM） is proposed in this paper, which not only avoids the power reverse problem but also has a good harmonic characteristic with low switching frequency in high voltage cell. Computer simulations and experiments have verified the proposed method.