A New Method of Double Fundamental Frequency Phase-Locked Loop Based on Two Integrators

摘要

In order to realize the grid connected converter to connect to the grid in unbalanced and distorted grid conditions, in this paper, based on the Sinusoidal Amplitude Integrators (Sinusoidal Amplitude Integrator, SAI), and combined with the cascaded integrators (Second Order Generalized Integrator, SOGI), a new type of double fundamental frequency PLL method is proposed. The method uses the excellent filter performance of cascaded SOGI and frequency characteristics of SAI, and under the negative rotation coordinate system, the 2 times harmonic components generated by the unbalanced grid are separated, extracted and successfully locked in. Solving the problem of the double fundamental frequency fluctuation, when the PLL method of synchronous rotating coordinate system(synchronous rotating fram-PLL, SRF-PLL) is applied on the dq axis under the unbalanced power grid. This paper introduces the basic principle of the cascaded SOGI and SAI, and the mathematical deduction is carried out. Under unbalanced and distorted conditions of the power system, the simulation results are compared with the SRF-PLL method. The results show that the proposed method is feasible, and compared with the traditional PLL method, and the method can detect and extract the synchronization signals more quickly and accurately.