The phase-locked loop(PLL)is a key aspect of grid-tied converters. A new PLL technique based on discrete Fourier transform(DFT)is proposed to improve the performances of conventional synchronous reference frame PLLs under distorted power grid conditions. The major challenge of the category of DFT based synchronization methods is how to accurately obtain the grid frequency. For this problem

this paper combines the DFT with the single-phase synchronous reference frame PLL. It utilizes the selective filtering and phase shifting properties of DFT to accurately extract the fundamental and generate its virtual orthogonal signals from the distorted grid. Then by transforming to the synchronous reference frame and properly control the q-component

accurate synchronization with zero steady state errors is achieved. Besides

grid frequency variations are incorporated by adjusting the sampling period of DFT according to the estimated frequency. Simulation and experimental results show that the proposed DFT-based PLL offers high harmonics immunity and DC component rejection capacity

while accurate phase locking is achieved under various power grid conditions

thus validating the effectiveness and advantages of the proposed method. This work is supported by Jiangsu Provincial Innovation Fund for Industry-university-research Cooperation of China(No. BY2014003-12).