High Performance Single-Phase PLL with Sliding Fourier Transform as a Phase Detector

A high performance single-phase phase-locked loop using sliding Fourier transform is proposed in this paper. The new PLL is using the sliding Fourier transform as a phase detector. The orthogonal signal is generated using a controlled transfer delay which is adjusted by the PLL estimated frequency. Feedback loops of the frequency and phase estimated by the PLL are used to drive the filters of the Fourier transform and to adjust the period of the transfer delay for implementing the sliding integrals. Unlike the synchronous reference frame PLL, the proposed SFT-based PLL (SFT-PLL) is adaptive to frequency changes and provides better harmonics and DC offset rejection while maintaining a constant sampling frequency. Therefore, the proposed method lends itself to digital implementation in a simple and straightforward manner. These distinguishing features allow the SFT-PLL to be especially appropriate for interfacing weak single phase micro-grids where high harmonic distortion and frequency variations are common characteristics. Experimental results and comparisons with the second order generalized integrator phase-locked loop (SOGI-PLL) are given to validate the effectiveness and advantages of the proposed method.