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.
关键词
高压直流输电/无锁相环/电压不平衡/负序电流
Key words
HVDC transmission/without phase-locked loop(PLL)/unbalanced voltage/negative-sequence current
维普
万方数据