三相四桥臂微网变流器在离网不平衡负载下的控制策略及其实现

因三相四桥臂变流器在不平衡系统应用中的优势，采用其作为微网变流器拓扑结构。为改善微网系统离网工况下带不平衡负载时的供电质量，提出了一种改进分序控制方法。采用基于广义二阶积分器的正负序分离方法提取负载电压的正负序分量，再将其变换至对应的旋转坐标系进行控制。在独立的零轴控制中，引入比例谐振调节器，增强零序电压的控制性能，简化控制算法。最后，对所提控制方法进行仿真与实验验证。结果表明，采用该控制方案的四桥臂变流器能够在负载不平衡的情况下维持输出电压的平衡，增强离网条件下的运行性能。

Islanded-mode control and implementation of a three-phase four-leg based microgrid converter under unbalanced load conditions

A three-phase four-leg topology is used in microgrid converter because of its advantages in unbalanced networks. To improve the islanded-mode power quality of microgrid system under unbalance load conditions, a modified control strategy using decomposed sequence components is presented. Positive and negative sequence components are extracted by a second order generalized integrator based detection method and controlled in positive and negative synchronous rotating reference frame respectively. A proportional resonant regulator is adopted in independent zero axis controller. It enhances the ability to suppress the zero sequence voltage and simplifies the control algorithm. Finally, the control strategy is verified by simulation and experiments. The results show that the proposed method is capable of maintaining the symmetrical output voltage under unbalanced load conditions and the performance of islanded-mode is enhanced.