基于构网型MMC的环流抑制与调制策略研究

Research on circulating current suppression and modulation strategy based on networkconstructed MMC

针对虚拟同步发电机控制的模块化多电平换流器(MMC)参与一次调频时,传统环流抑制与调制策略无法有效抑制桥臂环流,导致输出电流总谐波畸变率(THD)高的问题,通过改进比例谐振控制器的控制方式以及引入桥臂环流修正的最近电平逼近调制(NLM)策略,提出一种联合环流抑制策略。在MATLAB/Simulink软件中进行仿真。结果表明:在电网频率未波动时,采用联合抑制策略的桥臂电流THD为2.79%,相比准比例谐振控制器(QPRC)的THD降低0.92%;在一次调频工况时,所提策略a相电流的THD为1.75%,比采用QPRC的THD降低1.03%。结果证明:构网型MMC在正常工况以及一次调频工况时,所提环流联合抑制策略能有效抑制桥臂环流,降低THD,提升电能质量。

Aiming at the problem that traditional circulating current suppression and modulation strategy cannot effectively suppress the arm circulating current while modular multilevel converter(MMC)controlled by virtual synchronous generator participating in primary frequency regulation,which results in high total harmonic distortion(THD)rate of output current,a combined circulating current suppression strategy is proposed by improving the control method of proportional resonant controller and introducing the nearest level approach modulation strategy corrected by arm circulating current.The simulation is carried out by MATLAB/Simulink software.The results show that when the grid frequency is not fluctuated,the THD of arm current by combined suppression strategy is 2.79%,which is reduced by 0.92%compared to that of quasiproportional resonant controller(QPRC);under working condition of primary frequency regulation,the THD of phase a current of the proposed strategy is 1.75%,which is 1.03%lower than that of QPRC.It is proved that the proposed circulating current suppression strategy can effectively suppress the arm circulating current,reduce THD and improve electric power quality under normal working conditions and primary frequency regulation conditions for gridforming MMC.