DC offset elimination method of Phase-locked loop based on novel generalized integrator

Abstract

When the renewable energy power is connected to the grid, distortion voltage interference and grid voltage frequency fluctuation will occur, which will cause the inverter output current to be abnormal. So the grid-connected environment of weak grid puts forward higher requirements on the performance of phase-locked loop (PLL). The synchronous reference frame PLL(SRF-PLL) has become a usually adopted method in grid synchronization technique for its simple structure and strong stability. However, the conventional SRF-PLL has insufficient capability to suppress DC offset, which easily causes fundamental frequency and phase oscillations. Therefore, this paper presents a novel generalized integrator(NGI), and according to the presented NGI structure, a modified novel generalized integrator (MNGI) that can eliminate DC offset voltage is proposed. Then a novel PLL based on dual MNGI(DMNGI) is proposed. This method improves the capability of the phase-locked loop to suppress DC offset. At the same time, this paper designs the parameters of the PLL, and the rationality of the novel PLL is tested effectively through the experimental comparison with the other two methods.