Simulation Study of Improved DDSRF-PLL under Distorted Grid Voltage

When the grid voltage is distorted and harmonic and DC components are mixed, the phase locking accuracy of decoupled double synchronous reference frame for phase-locked loop (DDSRF-PLL) will be greatly reduced. This paper proposes an improved DDSRF-PLL(IDDSRF-PLL) structure based on Frequency Adaptive Sliding Discrete Fourier Transform (FASDFT) filtering. A cascade SDFT structure is adopted for FASDFT filtering. The SDFT with fixed sliding window width at the front stage extracts the fundamental wave signal of power grid voltage to eliminate the influence of harmonics and DC components. The latter SDFT detects the sliding window width of power grid frequency update in real time through a nonlinear tracking differentiator (TD) to suppress spectrum leakage. Then DDSRFT-PLL is used to separate the positive and negative sequence of the fundamental signal and lock the phase. Finally, the simulation results in Matlab/Simulink verify the correctness and effectiveness of the proposed method.