不平衡负载下离网型NPC三电平变流器控制策略研究

Study on the Control Strategy of Isolated NPC Three-level Converter at Imbalanced Load Conditions

本文主要研究不平衡负载下NPC三电平变流器控制策略,首先建立离网数学模型,通过对正负序解耦控制实现变流器在不平衡负载下输出电压的三相平衡,之后完成基于中间相调制波分解的调制策略,在独立控制变流器输出零序电压的基础上实现了直流母线电压中点平衡控制,保证两种目标协调解耦控制。最后搭建NPC三电平变流器离网不平衡负载实验平台,验证了协调控制策略的有效性。

In this paper, the control strategy of NPC three-level converter at imbalance load is studied. The isolated landed-mode mathematic model is established firstly and the three-phase balance of output voltage of converter at imbalance load is achieved by way of positive and negative decoupling. Then, the modulation strategy based on decomposition of middle phase modulation is finished,the neutral point balance control of DC bus voltage is achieved on the basis of controlling independently output zero sequence voltage of converter so to assure the coordination and decoupling of the two goals. Finally, the experimental platform of NPC three-level converter at isolated imbalance load is built and the effectiveness of the coordination control strategy is verified.