说明：  针对三电平PWM整流器所固有的直流侧电容中点电压平衡问题,提出根据每相输入电流方向和中点电压波动方向来优化选取冗余的正小矢量和负小矢量,实现中点电压平衡控制的方法。
(Aiming at the inherent problem of neutral point voltage balance of DC side capacitor in three-level PWM rectifier, a method is proposed to realize neutral point voltage balance control by selecting redundant positive and negative small vectors according to input current direction and neutral point voltage fluctuation direction of each phase.)