A New Single-Phase PLL Based On Discrete Fourier Transform

A new single-phase synchronous reference frame phase-locked loop (SRF-PLL) is proposed in this paper. The key point to implement single-phase SRF-PLL is how to generate the orthogonal signal accurately, even under polluted grids with harmonics and DC components. In this paper, the generation of the orthogonal signal is achieved by the discrete Fourier transform (DFT) filter. Compared with conventional SRF-PLLs, the DFT-based PLL (DFT-PLL) proposed offers better harmonics immunity and DC component rejection capacity. Besides, the proposed method incorporates grid frequency variations by adjusting the sampling period of DFT according to the estimated frequency. Also, digital implementation of DFT-PLL is simple and straightforward with low computational burden. These advantages make the proposed DFT-PLL especially suitable for harmonically distorted and frequency-varying applications. Experimental results and comparisons with two another widely used SRF-PLLs are given to validate the effectiveness and advantages of the proposed method.