A Novel Phase-Locked Loop under Grid Fault Condition

Tracking the frequency and phase information of the power grid quickly and accurately when the power grid has unbalanced, distorted grid voltage and fluctuant frequency is very important for power system control and protection and power electronics converter application. However, the traditional phase locked loop will lose its effect in this case. To solve this problem, a novel grid frequency detection method is proposed in this paper. Firstly, with the theory of fan-in vector transformation, the three-phase system is transferred to the single-phase system, which simplifies the detection method. Secondly, the cascaded delayed signal cancellation method is used to extract the fundamental positive sequence voltage from the harmonics. Then, the state observer with self-adaptive frequency is designed to get the frequency and phase information from the fundamental positive sequence voltage. In the end, the simulation results verify that the proposed novel method is able to track the frequency and phase information of the power grid quickly and accurately under the condition of unbalanced, distorted grid voltage and fluctuant frequency.