Magnitude detection and phase synchronization of unbalanced and distorted grid voltage with novel extended PLL loop filter

In gird-connected power electronic systems, a fast and accurate tracking method of fundamental grid voltage is required to synchronize the converters with the mains. The Synchronous Reference Frame (SRF) based voltage magnitude and phase detection method is able to track three phase balanced grid voltage. But its performance is very poor when the gird-voltage is unbalanced and/or distorted. Improved SRF based detection methods can partially achieve either fast postfault resynchronization or steady-state unbalanced and distorted voltage rejection. However, its overall performance is not satisfying. This paper proposes a novel detection method based on SRF Phase-Locked Loop (PLL), in which a Low Pass Filter (LPF) and a Phase Sequence Separator (PSS) are combined to reach a tradeoff between fast detection speed and steady-state detection accuracy. Simulation including comparison of traditional methods and the proposed one under different grid fault conditions has been performed. The results validate the correctness and effectiveness of the proposed strategy.