一种低共模电磁干扰SVPWM法的研究

为了消除传统的空间矢量脉宽调制(SVPWM)在变频器输出端产生较大的输出端共模电压突变,提出了新型SVPWM控制方式——三矢量合成SVPWM。在介绍了该控制方式的原理即:每个桥臂换流时,总有另一桥臂同时发生换流且换流方向与之相反,此时第三桥臂则不发生换流,总的共模电压不会发生跳变后,分析了由于死区时间及驱动信号传输延时不一致等非理想因素对该方法实际效果的影响。分析和实验表明,该SVPWM合成方式可有效抑制共模EMI,在实际应用中需采取死区补偿和驱动脉冲前沿的精细调整达到最佳效果。该方法的最大直流电压利用率仅0.67,对此可采用六矢量合成法进行改进。

New SVPWM Strategy with Low Common-mode EMI

Conventional space vector PWM(SVPWM) strategy causes sudden changes in common-mode voltage at the output of the inverters,which causes common-mode current to flow through the winding-to-ground parasitic capacitors of the electric machines,and therefore brings considerable common-mode electromagnetic interference(CM EMI).Thereby,a new SVPWM method,which employs only 3 of the total 6 effective voltage space vectors and produces no sudden changes of common-mode voltage,is investigated and evaluated.The essence of this method is: commutations always take place simultaneously at two of the three-phase legs,with the directions of the commutations always opposite to each other,and at the same time there is no commutation taking place at the third leg.This method causes no sudden changes in the output common-mode voltage theoretically.Therefore,the negative effects caused by dead time and uneven transmission delays of gating signals,which are inevitable in real products,are analyzed in details.These factors can severely reduce the effectiveness of the method.Analysis and experiments show that for best effect,the method should be used in combination with dead-time compensation and fine-tuning of the pulse edges of gating signals.A major drawback of this method is the low dc voltage utilization(0.67),which can be improved slightly with the 6-vector modification of the original method.