五电平电压型逆变器的变频SHE-PWM控制策略

SHE-PWM control strategy with variable frequency for series-connected five-level inverters

采用两重H桥串联电压型逆变器输出五电平相电压,使用IGCT器件时可输出6kV线电压,适用于6kV电机变频调速装置。为改善逆变器输出电压的谐波特性,解决串桥之间功率的均分问题,提出了两种五电平SHE-PWM控制策略,给出了其实现原理,计算了3～50Hz内的变频变调制比的SHE-PWM开关角度,并在此基础上用数字仿真计算了各频率段下输出电压谐波含量。结果表明在不增加开关频率的前提下,比三电平逆变器消除的输出电压谐波次数更多,使逆变器输出LC滤波器的设计更加容易,同时可有效地均分两重串桥的有功功率输出。

A cascaded H-Bridge inverter utilizing two three-level cells has a five-level output phase voltage with the output line-line voltage reaching 6 kV when IGCTs are employed, which makes it suitable for 6 kV motor drives. The output voltage quality was improved and real power between cells was equalized with a 5-level selective harmonic elimination pulsewidth modulation (SHE-PWM) control strategy. The SHE-PWM switching angles for frequencies from 3 Hz to 50 Hz were calculated and the harmonics of the output voltage at various frequencies were calculated by digital simulation. The simulation results show that the output voltage quality without increasing the switching frequency is much better than that of an NPC 3-level inverter. In addition, the LC filter design is easier, and the real power output between cells is equalized with the control strategy.