应用于STATCOM的级联U-Cell拓扑直流电压控制策略

Voltage control strategy of cascaded U-Cell topology STATCOM

采用级联U-Cell拓扑相比传统级联H桥拓扑,静止同步补偿器(staticsynchronouscompensator,STATCOM)使用的开关器件更少,损耗更小,设备经济性更高。但级联U-Cell同样存在直流侧电容电压不平衡的问题,严重时可使系统无法运行。针对该问题,首先搭建级联U-Cell拓扑数学模型,详细分析了电容充放电以及实现相内电容电压平衡的工作原理。基于此,提出了一种冗余开关状态轮换与基于开关状态叠加有功电压矢量相结合的控制策略,并将该策略应用推广到任意奇数电平。该策略能够使器件损耗更加均匀,实现了级联U-Cell相内电容电压平衡控制,提高了系统的可靠性。最后分别搭建了基于五电平级联U-Cell拓扑的STATCOM仿真和实验平台,验证了所述理论及控制策略的正确性。

Compared with traditional cascade H bridge topology, cascaded U-Cell topology of static synchronous compensator (STATCOM) has few switch devices, low loss and good economic value. However, cascaded U-Cell also exists the problem of unbalanced capacitor voltage, which affects the system reliable operation in severe cases. A mathematical model of cascaded U-Cell is built for this problem, and the principle of capacitor charging and phase-capacitor voltage balance are analyzed in detail. Based on this, a control strategy combining redundant switching states rotation and active voltage vector superimposed by switching state is put forward in the paper, of which is extended to arbitrary odd number level. This strategy can make the device loss more uniform, achieved the balance of the capacitor voltage in the cascade U-Cell, and improve the reliability of the system. Finally, the simulation and experiment platforms of STATCOM based on five-level cascaded U-Cell topology are built to verify the correctness of the theory and control strategy.