在不平衡负载下三相四桥臂逆变器的控制策略

Control Strategy of Three-phase Four-Leg Inverter under Unbalanced Load

为了简化三相四桥臂逆变器在不平衡负载下的空间矢量脉宽调制(SVPWM),文章设计了一种基于SVPWM的单载波调制方法:将前三桥臂与第N桥臂分开调制。若前三桥臂采用SVPWM则需要进行三角函数计算和扇区判断,调制难度较大;而单载波调制策略是利用开关管的作用规律推导出对应的调制波,再将调制波与载波进行比较,得到对应的开关信号,此过程避免了大量的三角函数计算,大大降低调制难度。同时,文章分析和推导不平衡负载下的中性点电压,并将中性点电压控制为相应的零序电压,从而可以对第N桥臂进行独立控制,最终实现在平衡负载和不平衡负载下都输出三相对称正弦电压。最后通过仿真验证了该调制技术是可行的。

In order to simplify the space vector pulse width modulation(SVPWM)of three-phase four-leg inverters under unbalanced loads,this paper presents a single carrier modulation method based on SVPWM,which can modulate the first three legs and the N-th leg separately.If SVPWM is used for the front three axle arms,trigonometric function calculation and sector determination are required.This means that the modulation become very difficult.The single carrier modulation strategy uses the action law of the switch to derive the corresponding modulation wave,and then compares the modulation wave with the carrier wave to obtain the corresponding switching signal.This process avoids a large number of trigonometric function calculations,greatly reduces the modulation difficulty.At the same time,the neutral voltage under unbalanced load is analyzed and derived,and the neutral voltage is controlled to the corresponding zero sequence voltage,so that the N-th bridge arm can be independently controlled.The final realization is to output three-phase symmetrical sinusoidal voltage under both balanced and unbalanced loads.Finally,the feasibility of the modulation technology is verified by simulation.