An improved decoupled double synchronous reference frame phase locked loop and its application in grid connection system of permanent-magnet synchronous motor

Phase locked loop(PLL) is one of the key techniques in the grid connection system of permanent-magnet synchronous motor(PMSM). Different types of the PLL are analyzed and compared. In order to overcome the traditional PLL shortcomings, an improved decoupled double synchronous reference frame software phase locked loop(DDSRF_SPLL) is proposed. This PLL is based on least error square filter(LES) and decoupled algorithm. And it is able to follow the grid frequency and phase angle more quickly and accurately. Besides, its anti-interference ability is strong, especially for low harmonics. The correctness and effectiveness of the improved DDSRF_SPLL is proved by the simulation on various conditions and experiment. The experiment platform consists of three level back-to-back converter and PMSM. This improved DDSRF_SPLL performs well in the grid connection system of PMSM.