非对称桥臂阻抗条件下MMC的控制策略

Control Strategy of MMC Under Asymmetric Bridge Arm Impedance

对模块化多电平变换器(MMC)在非对称桥臂阻抗条件下的运行进行了分析,并设计了对应控制策略。不同于MMC的对称运行,在非对称条件下,基频交流电流将在上、下桥臂分配不均,同时共模电流中的直流和倍频分量也将流入交流侧。为此,引入了不同频率的等效电路进行了分析,提出3个控制目标后设计了控制器以控制差模电流、共模电流和功率平衡。最后,通过仿真和试验对控制方案进行了试验验证。

The operation of modular multilevel converter(MMC)under the condition of asymmetric bridge arm impedance was analyzed and the corresponding control strategy was designed. Unlike the symmetrical operation of the MMC,under asymmetric conditions,the fundamental AC current is not split equally between the upper and lower arms,and the DC and double-frequency components in the common mode current will also flow into the AC side. To this end,the equivalent circuit of different frequencies was introduced for analysis,and three control targets were proposed. The controller was designed to control the differential mode current,common mode current and power balance. Finally,the control scheme was tested and verified by simulation and experiment.