低开关频率下混合脉宽调制方法研究

Study on a hybrid PWM method under low switching frequency

大功率轨道牵引传动系统的开关频率较低,而调速范围较宽,导致了载波比变化范围大,需要设计混合脉宽调制策略以满足要求.本文分析了一种低开关频率下SVPWM和特定谐波消除PWM(Selective Harmonic Eliminate PWM,SHEPWM)混合脉宽调制方法,即在低频阶段采用异步调制的SVPWM,在高频阶段采用不同载波比的SHEPWM,最后转入方波工况.研究了它们之间的切换条件,实现了异步调制的SVPWM、不同载波比的SHEPWM和方波之间的平滑切换.仿真和实验结果证实了本文的混合调制方法具有较好的谐波特性和SVPWM,以及不同载波比SHEPWM间切换方法的正确性,减小了电流冲击.

The maximum switching frequency of railway high power traction converter is generally a few hundred Hertz, and the range of operating frequency is large, which leads to the carrier ratio vary very large. So a hybrid PWM modulation strategy is required to meet the low frequency control re- quirements. This paper presents SVPWM and SHEPWM hybrid PWM method under a low switching frequency, which uses asynchronous carrier modulation SVPWM at low frequency, and SHEPWM at high frequency, a square wave after rated conditions. The transitive strategy is proposed to realize smooth transition of individual modes including SVPWM, SHE PWM and square wave. Simulation and experimental results confirm this hybrid modulation method and their transition is reasonable and corrected.