电压不平衡时单同步坐标系锁相环的改进算法

Improved algorithm for phase-locked loop of single synchronous coordinate system under unbalanced three-phase voltage

为了在电网电压不平衡时能跟踪电网电压基波相位和频率,分析了单同步坐标系的三相软件锁相环(SSRF-SPLL)在电网电压不平衡时不能准确快速锁定基波电压相位的原因,即电网电压不平衡时,dq变换得到的eq中含有二次谐波分量,在使用PI控制时,此二次谐波分量将导致PI难以实现无误差跟踪,影响锁相输出角度。在提高稳态性能并考虑动态性能的基础上,提出了在PI调节器之前增加2次陷波器和特定截止频率的低通滤波器的改善方案。最后通过搭建仿真和实验平台验证了方案的可行性和有效性。

In order to track the phase and frequency of grid fundamental voltage under unbalanced voltage condition,the reason for the single synchronous coordinate phase-locked loop cannot target on the grid fundamental voltage is analyzed in this paper. Namely,when the grid voltage is unbalanced,eqtransformed from dq contains the second harmonic,which causes PI difficult to achieve error-free tracking and the output angle of PLL is imprecise.On the basis of improving the steady-state performance and considering the dynamic-state performance,an improved algorithm increasing a 2nd notch filter and a specific cut-off frequency low-pass filter before the PI regulator is proposed. At last,the simulation and experimental results are presented to verify the improved algorithm.