电网严重畸变情况下的锁相策略研究

针对传统三相软件锁相环PLL(phase-locked loop)在电网电压同时含有较低次谐波分量和负序分量等严重畸变情况下不能完成精准锁相的问题,提出基于滑动离散傅里叶变换DFT(discrete Fourier transform)滤波原理的新型三相软件PLL。滑动DFT算法可以准确地从含有各次谐波的电网电压中提取单位基波信息,再结合基于延时信号对消的基波正负序分量分离方法提取出基波中的正序分量,最后采用同步参考坐标系锁相环SRF-PLL(synchronous reference frame phase locked loop)得到基波正序相位信息。结果表明,新型锁相环在电网电压同时处于不平衡、含有高次谐波和低次谐波以及直流分量的情况下均能够完成精准的锁相。

Research on Phase-locked Strategy under Severe Distortions of Power Grid

Aimed at the problem that the traditional three-phase software phase-locked loop(PLL)cannot achieve accu?rate phase-locking under serious distortions such as lower-order harmonic components and negative-sequence compo?nents in grid voltage at the same time,a novel three-phase software PLL is proposed based on the filtering principle of sliding discrete Fourier transform(DFT).The sliding DFT algorithm can accurately extract the information about the unit fundamental wave from the grid voltage with various harmonics.Then,the positive-sequence components can be ex?tracted from the fundamental wave by combining the extraction method for positive-and negative-sequence components of fundamental wave based on delayed signal cancellation.Finally,the fundamental wave positive-sequence phase infor?mation is obtained by using the synchronous reference frame phase locked loop(SRF-PLL).Simulation results show that the novel PLL technology can achieve accurate phase-locking even when there exist unbalanced grid voltage,highand low-order harmonics,and DC components at the same time.