三电平直流变换器平衡中点电位的双移相PWM控制研究

摘要

在分析中频中压大容量三电平H桥直流变换器的电路拓扑和工作原理的基础上,针对中点电位波动问题,提出了一种双移相脉宽调制(PWM)复合控制策略.将原来只有单一移相角的移相PWM变为具有双移相角的移相PWM,从而造成调制不对称来对中点电位进行调节.分析了采用双移相PWM方法能够平衡中点电位能力的边界,设计了三电平H桥直流变换器的双移相PWM复合控制器,并结合传统单移相PWM控制器进行了对比实验研究.结果表明:负载电流流过中点是造成中点电位波动的原因；双移相PWM能够产生不对称PWM控制脉冲来实现中点电位的调节,且随着负载程度的增加调节能力逐渐增强；基于双移相PWM的复合控制策略能够较好地实现平衡中点电位控制,且具有较好的动态性能.%Circuit topology and working principle of high power middle voltage and frequency three-level H-bridge DC/DC converter are analyzed. Aiming at the neutral-point voltage unbalancing problem, a double phase-shift PWM control method is proposed, which transforms the conventional single angle phase-shift PWM to double angle phase-shift PWM, and the neutral-point voltage can be balanced due to the different phase-shift angle. The boundary of the neutral-point balancing ability is investigated, and a double phase-shift PWM complex controller is designed. Experiments are comparatively conducted between the new controller and conventional single phase-shift PWM controller. It is shown that the neutral-point current is the reason of unbalanced neutral-point; the double phase-shift PWM controller can generate the asymmetry pulses to balance neutral-point, and this ability gets more powerful with heavier loading with better dynamic property.