交流系统故障时MMC-HVDC系统的控制策略

Control Method of MMC-HVDC Systems During AC System Faults

交流系统故障时,基于模块化多电平换流器(modular multilevel converter,MMC)的柔性直流输电(voltage sourced converter-high voltage direct current,VSC-HVDC)系统的控制策略研究具有很重要的工程意义。为了解决传统的串级PI控制策略存在的PI调节器数量多、控制参数调试困难、系统的稳定工作区域小等缺点,设计了新的控制策略。文章分析了交流系统故障时MMC的特性,设计了基于反馈线性化原理的正负序双电流控制策略,该控制策略在交流电网正常及故障状态下均具有良好的控制性能。进一步分析了在负序电流得到抑制的情况下,直流侧电压和电流产生二倍频波动的原因,并且设计了直流电压纹波抑制器(direct current voltage ripple suppressing controller,DCVRSC)。通过仿真软件PSCAD/EMTDC验证了文章设计的控制策略的正确性。结果显示,与传统的串级PI控制策略相比,本文设计的控制策略的参数调试简单,系统的稳定性高,直流电压的波动得到有效抑制。

With the framework of the modular multilevel converter(MMC),the research of control method for the voltage source converter-high voltage direct current(VSC-HVDC)systems plays an important role in the engineering application When AC system malfunctions.A new control method is designed to alleviate the challenging,i.e.,the large number of the PI regulator,the difficulty of the control parameter debugging,the narrow stable work area of the system.The character of MMC is analysized when AC system occurs faults,and with the assistance of the feedback linearization theory,a dual-current control method of positive-sequence and negative-sequence is introdued,which indicates that the proposed method has perfect control performance when AC system is normal and enconter a failure.The reasons that the DC voltage and current have second-order harmonics when negative-sequence current has been suppressed are further analysized,and a DC voltage ripple suppressing controller(DCVRSC)is designed.The accuracy of the proposed method is validated by the simulation software PSCAD/EMTDC.Compared with the common cascade PI control method,the proposed method has advantages such as the parameter debugging is simple,the stability of the system is high and the direct current voltage is suppressed.