抑制双馈风场MMC-HVDC系统次同步振荡子模块电容电压控制器仿真研究

Sub-module capacitor voltage controller simulation research of MMC-HVDC system in doubly fed wind farm

针对双馈风电场并入模块化多电平换流器的高压直流输电系统,为解决模块化多电平换流器内部子模块结构相互作用时产生次同步振荡,影响系统稳定运行的问题,提出一种考虑子模块电容电压与抑制循环电流结合的控制结构。通过建立一种更精确的模块化多电平换流器直流阻抗模型,减小子模块的二阶循环电流,并利用奈奎斯特判据分析了不同控制器调节下系统稳定性以及电压和电流的变化。结果表明,所建立的新模型与实际模块化多电平换流器内部结构的匹配性更好,能够正确地预测直流系统的稳定性,验证了环流抑制器结合子模块电容电压控制后的有效性。

To solve the problem of sub-synchronous oscillation caused by the interaction of sub-module structures in modular multilevel converters,which affects the stable operation of the system,a control structure is proposed,which considers the combination of the voltage of the sub module capacitor and the suppression of cyclic current.By establishing a more accurate DC impedance model of the modular multi-stage converter,the second-order cyclic current of the sub-module is reduced.And Nyquist criterion was used to analyze system stability and voltage and current changes under different controller adjustments.The results show that the new model has a better fit with the internal structure of the actual modular multi-stage converter,and can accurately predict the stability of the DC system.This verifies the effectiveness of the circulating current suppressor combined with the voltage control of the sub module capacitor.