Design and Realization of Improved Phase Locked Loop Under Unbalanced Grid Voltage in Wind Power Systems

In order to ensure the grid side converter and static reactive compensator in wind power systems run safely and reliably under unbalanced grid voltage, it is the basic requirement that the phase and frequency of the positive sequence fundamental component of grid voltage are obtained quickly and accurately. Because the dynamic behavior of the phase locked loop (PLL) based on the synchronous reference frame is dissatisfactory under unbalanced and distorted grid voltage, the improved PLL based on the synchronous reference frame is put forward to not only extract the phase of positive sequence component of unbalance voltage and eliminate the effect of unbalance voltages on phase detection, but also suppress the influence of harmonics on phase detection. The results of simulation in PSCAD/EMTDC and experiment in C8051F410 based set-up verify the feasibility and correctness of the improved PLL proposed in the paper.