Unified Digital Phase-Locked Loop With Multiple Complex Resonators for Both Single- and Three-Phase Grid Synchronization

Grid synchronization is one of the critical techniques used in grid-connected systems, such as distributed generation, energy storage, and harmonic compensation equipment. To acquire efficient grid-connection or harmonic compensation performance, the accurate and real-time information of phase, frequency and amplitude is required, especially when the grid voltage contains disturbed or other unexpected components. According to different application fields, two kinds of phase-locking structures exist-single- and three-phase phase-locked loop (PLL), which are not cross compatible. In this paper, a novel unified digital PLL with multiple complex resonators for both single- and three-phase systems is proposed. First, single-phase and three-phase voltage signal is transformed uniformly to a similar complex form that consists of positive and negative sequence components rotating in counterclockwise and clockwise directions, respectively. Then, synchronous rotating frame PLL with a generalized prefilter is introduced. The proposed filtering structure consists of multiple complex resonators that can filter out harmonic frequency components and maintain fundamental positive sequence components accurately. Furthermore, a simplified structure of the complex resonator for single-phase system and an operation method for resonant factor are introduced. Finally, the validity and effectiveness of the proposed method are proven by the simulated and experimental results of a three-phase four-leg shunt active power filter.