改善共模电压和中点电位的虚拟SVPWM策略

中性点箝位式(NPC)三电平逆变器的拓扑结构以及空间矢量脉宽调制的技术特点决定了逆变器存在中点电位波动和共模电压问题.为此,提出一种改进的虚拟空间矢量脉宽调制策略,可以兼顾中点电位波动抑制和降低共模电压.在分析传统虚拟空间矢量脉宽调制策略原理基础上通过优化基本电压矢量构成和基本矢量的作用顺序达到降低共模电压的目标;同时采用闭环控制策略,监测中点电位和中点电流流向,动态调整中矢量形式,将中点电位波动控制在目标范围内.为验证改进调制策略的实用性和有效性,搭建了仿真和实验平台,仿真和实验结果均表明该策略相较于传统虚拟空间矢量脉宽调制技术,共模电压可降低50％,且稳定状态下中点电位波动范围可控制在5V内.

A virtual SVPWM strategy to improve common-mode voltage and neutral-point potential

A neutral-point-clamped(NPC) three-level inverter normally faces the problems of neutral-point fluctuation and common-mode voltage due to its topological structure and technical characteristics of space vector pulse width modulation. In order to solve these problems, an improved virtual-space-vector pulse-with-modulation(PWM) strategy is proposed, which can balance the suppression of neutral-point potential fluctuation and the reduction of the common-mode voltage. On the basis of traditional virtual-space-vector PWM principle, this strategy achieves the goal of reducing the common-mode voltage by optimizing the basic voltage-vector composition and action order. Meanwhile, closed-loop control strategy is adopted to monitor the neutral-point potential and neutral-point current flow, and dynamically adjust the form of mid-vector to control the neutral-point potential fluctuation within the target range. To verify the practicability and effectiveness of the improved virtual-space-vector PWM strategy, the simulation and experiments were carried out. The results indicate that compared with the traditional virtual space vector PWM, the common-mode voltage can be reduced by 50%, and under the steady state, the neutral-point potential fluctuation can be controlled below 5 V.