A novel phase-locked-loop and its application in STATCOM system

Phase-Locked-Loop (PLL) plays important role in grid connected power electronics system. A good PLL system can detect the grid phase angle and frequency fast and accurately, and additionally it can extract the positive sequence exactly. In real applications, source signal (voltage or current) usually includes harmonic distortion, unbalanced components. Conventional PLL strategy cannot solve the unbalanced and harmonic distortion problems. Different PLL solutions are proposed in literature in recent years. The general considerations for these different approaches are to design positive sequence estimator to eliminate the negative sequence components and use filters to filter out the higher order harmonic distortions. In this paper, a novel moving average filter based synchronous reference frame PLL with positive sequence estimation feature is presented. The proposed PLL has good performances in filtering harmonic, eliminating unbalanced components. To verify the proposed PLL, a STATCOM system is built in Matlab/Sim PowerSystems. Simulation results of different operation modes are shown in this paper.