Generalized DFT-Based Synchronous Reference Frame Phase-locked Loop Applicable to Distorted Grid Conditions

The conventional synchronous reference frame phase-locked loop (SRF-PLL) is popular among various synchronization techniques in grid-connected applications. However, it exhibits unacceptable frequency and phase errors when the grid is distorted. To overcome these problems, incorporation the generalized discrete Fourier transform (GDFT) into the SRF-PLL is proposed in this paper to precisely and fast estimate the frequency and phase under distorted grid. The proposed PLL offers better harmonic rejection ability compared with the traditional method. Besides, the frequency adaptability of GDFT is achieved by adaptively adjusting the sampling points number of DFT. Detailed method to design the control parameters is given. Experimental results are further provided to validate the effectiveness of the proposed PLL.