模块化多电平换流器的主动谐波谐振抑制策略

联接云南电网与南方电网主网的鲁西背靠背直流异步联网工程异步联网工程投产初期,广西侧送出交流线路受故障影响仅剩一回,随后广西侧母线电压和输出电流中出现了频率为1 270 Hz的谐波分量,引起柔性直流单元换流变压器分接开关频繁动作,最终导致柔性直流单元跳闸。首先,从鲁西背靠背直流异步联网工程高频谐振事件入手,分析大容量模块化多电平换流器(modular multilevel converter,MMC)与交流系统的谐振机理;接着,给出了MMC谐波阻抗的计算方法,利用阻抗分析法分析了高频谐振的条件,并提出MMC的控制结构改进方法,有效抑制了其输出电流的高频谐波分量;最后,通过PSCAD/EMTDC仿真对谐振事故现象进行了复现,证明了所提抑制策略可以实现对高频谐波谐振的有效抑制。

Active Harmonic Oscillation Suppression Strategy for Modular Multilevel Converter

In the initial operation stage of Luxi back-to-back asynchronous interconnection HVDC project between Yunnan Power Grid and the main grid of China Southern Power Grid, only one circuit of outgoing AC transmission line at Guangxi side was affected by the fault. Afterwards, harmonic components with a frequency of 1 270 Hz appeared in the bus voltage and the output current, which caused frequent action of the VSC-HVDC converter transformer tap changer and finally led to tripping. This paper firstly introduces the high-frequency resonance event of Luxi back-to-back asynchronous interconnection HVDC project and explains the resonance mechanism between the modular multilevel converter(MMC) based VSC-HVDC and the AC system. Secondly, it deduces the calculation method for MMC harmonic impedance, and uses the impedance analysis method to analyze conditions of high-frequency resonance. Meanwhile, it proposes an improved method for the control structure for MMC which can effectively suppress high-frequency harmonic components of the output current. Finally, it reproduces the phenomenon of resonance event by means of PSCAD/EMTDC simulation and proves validity of the proposed method in suppressing high-frequency harmonic resonance.