三电平PWM整流器中点平衡控制技术的研究

研究了三电平PWM整流器优化设计问题，由于在流侧中点电压不平衡，引起输出波形质量不好，系统不稳定。为了解决中点平衡问题，分析了造成中点电压不平衡的原因以及小矢量对中点电压的影响。针对小矢量引起中点电压不平衡，提出了一种基于9段式与7段式混合调制的矢量调制方法。在该方法中，对小矢量未能成对参与调制的扇区，根据中点电压的大小选择采用9段式的矢量调制方法或7段式的矢量调制方法。在9段式矢量调制算法中，有两对小矢量参与调制，选择作用时间长的那对小矢量，结合时间分配因子，重新分配时间。最后采用Matlab软件搭建模型，对中点平衡算法进行仿真，实验结果验证了该算法对中点电压平衡控制的有效性。

Research on control technology of neutral-point balance for three-level PWM rectifier

The optimization design of the three-level PWM rectifier is researched. Due to the imbalance of neutral-yoint voltage of DC bus, the auality of outyut waveform is bad and the system is not stable. In order to solve the problems of neutral-Doint voltage balance, the causes which result in unbalanced neutral-Point voltage and the influence of the small vector on neutral-voint voltage are analyzed. In view of the neutral-point voltage imbalance caused bv small vectors, a method of vector modulation based on hvbrid modulation of nine-stage and seven-statue is vroDosed. In this method, in regard to the sectors in which small vectors could not be involved in vairs, a method of vector modulation of nine-stage or seven-stage is selected according to the magnitude of the neutral-point voltage. In the vector modulation algorithm of nine-stage, two Dairs of small sectors are involved. The pair which has longer action time is selected to redistribute time combining time distribution factors. Finallv, the neutral-point balancing algorithm is simulated by Matlab models, the exDerimental results verifv the effectiveness of the algorithm to the neutral-Doint voltage balance control.