直流电容电压自平衡的新型五电平NPC变流器空间矢量调制策略

DC Capacitor Voltage Self-Balancing Space Vector Modulation Strategy of Five-Level NPC Converter

针对五电平中点钳位(Neutral Point Clamped,NPC)变流器直流电容电压平衡问题,分析了五电平NPC变流器空间矢量调制中各开关矢量对直流电容电压平衡的影响,阐述了分调制比区域实现五电平NPC变流器空间矢量调制的控制思想,提出了一种新型直流电容电压自平衡的五电平NPC变流器空间矢量调制策略。该策略将空间矢量图按调制比分区,在低调制比区域(mSV≤0.5),采用目标函数与参考电压分解相结合的方法,在高调制比区域(mSV>0.5),采用平衡矢量优化选择法(Optimized Balancing Vectors Selection,OBVS),分别实现了直流电容电压自平衡的五电平空间矢量调制。仿真和实验表明本文提出的新型调制策略兼具直流电容电压平衡控制功能,计算量小,实现简单,控制效果好。

DC capacitor voltage balance is one of the key issues in the control of five-level NPC(neutral point clamped) converter. In this paper, it analyses the influence of space vectors to the DC voltage balance in five-level NPC converter SVM(space vector modulation) strategy and explains the control thought of using different scheme to realize five-level SVM strategy in different modulation ratio region. Furthermore, it presents a novel DC capacitor voltage self-balancing SVM strategy of five-level NPC converter. The novel strategy divides the whole five-level space vector diagram into low modulation ratio region(mSV≤0.5) and high modulation ratio region(mSV>0.5). In low modulation region, it presents a DC capacitor voltage self-balancing SVM strategy which combines objective function scheme with reference voltage decomposition scheme. In high modulation area, it achieves DC capacitor voltage self-balancing SVM strategy by applying an optimal balancing vector selection(OBVS) scheme. Simulation and experimental results verify the DC voltage balancing characteristics of the proposed five-level NPC SVM strategy. The novel SVM strategy also has the characteristics of smaller amount of calculation, much simpler realization and better control effect.