无需锁相环的柔直变流器负序电流补偿方法

Negative-sequence Current Compensation Method for Flexible DC Converter without Phase-locked Loop

电网电压不平衡时,锁相环PLL(phase-locked loop)需对电网电压进行重新追踪,此时锁相不准或锁相时间过长均会造成后续柔性直流输电系统中控制性能降低。为了避免锁相环带来的不利影响,提出1种无锁相环的改进型变流器控制策略。首先对传统锁相方案与无锁相方案的本质区别进行分析,进一步在无锁相环环境下提出1种瞬时正、负序分量提取方案;其次对无锁相环的变流器控制系统进行设计,并以补偿负序电流为控制目标;最后在实验样机下验证所提策略的正确性与有效性。

When the grid voltage is unbalanced,the phase-locked loop(PLL)needs to retrack the grid voltage.At this moment,an inaccurate phase lock or an overlong phase lock time will cause the degradation of control performance for the subsequent flexible DC transmission system.Therefore,to avoid the adverse effects caused by PLL,an improved control strategy for converter without PLL is proposed.First,the difference between the traditional PLL scheme and the proposed scheme without PLL is analyzed,and an instantaneous positive-and negative-sequence component extraction scheme is put forward in an environment without PLL.Second,a converter control system without PLL is designed,and the compensation of negative-sequence current is taken as its control target.Finally,the validity and correctness of the proposed strategy was verified by the experimental results of a prototype.