交流系统不平衡对MMC-HVDC运行影响分析及其保护控制

交流系统不平衡会引起模块化多电平变流器(modular multilevel converter,MMC)输出功率的波动与输出电流的不平衡,同时也会导致基于模块化多电平换流器的高压直流输电(modular multilevel converter-high voltage direct current transmission,M M C-HVDC)系统内部桥臂电流与子模块电压出现更大的波动,危及变流器的安全运行。文章分析了交流系统不平衡度以及控制参数对MMC桥臂电流与子模块电压的影响,构建了不平衡分量、控制参数与桥臂电流、子模块电压的三维函数。进而通过一次拟合的方式,得到了不同跌落程度下使桥臂电流峰值最小的控制参数值,最大程度地保证了MMC运行的安全稳定。最后搭建了静止坐标系下MMC控制系统,仿真验证了理论分析的正确性。

MMC-HVDC Operation Under Unbalanced Grid Conditions and Its Protection Control

AC system imbalance will cause the fluctuation on output power and the imbalance of output current in modular multilevel converter (MMC),and also lead the bridge arm current and sub module voltage to be greater volatility in modular multilevel converter-high voltage direct current transmission (MMC-HVDC),which may endanger the security operation of the converter.This paper analyzes the influence of AC system unbalance and control parameters on the bridge arm current of MMC and sub module voltage,and constructs a 3-D function among unbalance component,control parameters,bridge arm current and sub module voltage.Then,through the first fitting method,we obtain the control parameter that makes the bridge arm current minimum in different situation and ensures the safety and stability of MMC at utmost.Finally,we establish the control system of MMC on stationary coordinate and verify the correctness of the theoretical analysis through simulation.