准PR控制的三电平逆变器及中点平衡策略

Quasi-PR controlled three-level inverter and neutral-point balance strategy

针对二极管钳位式三电平逆变器(NPC)的中点电位不平衡问题,在空间矢量调制(SVPWM)下,提出一种混合式中点电位平衡策略。在低调制度下,采用十三矢量法调制,该调制只使用1个零矢量、6个中矢量和6个大矢量来合成参考矢量,可以取得更好的平衡效果;在高调制度下,对传统七段式调制加以改进,调节正负小矢量的作用,最大限度减小中点电位波动。并采用准PR控制跟踪指令电流,根据最优二阶系统理论整定了参数。最后,在MATLAB/Simulink中搭建了仿真模型,验证了的中点平衡策略和准PR控制的正确性。

Aimed at the neutral-point unbalance problem of neutral-point clamped（ NPC） three-level inverter,this paper proposed a hybrid neutral-point balance strategy under space vector pulse width modulation（ SVPWM）. Under low modulation index,thirteen-vector modulation was used to gain relatively batter neutral-point balance effect. This method employed 1 zero vector,6 medium vectors and 6 large vectors to synthesize the reference vector. Under high modulation index,a method which modified the traditional seven-stage centered modulation was adapted. It could minimize the fluctuation of neutral-point potential by adjusting the function time of positive or negative small vectors.Quasi-PR controller was adapted to track the command current. The parameters were chosen according to optimal theory of second-order system. At last,a simulation model was established in MATLAB / simulink to verify the correctness of middle point balancing strategy and quasi-PR control.