Grid synchronization of three-phase converters using cascaded complex vector filter PLL

Synchronization is a key issue in distributed power generation and storage (DPGS), fast and accurate estimation of the grid voltage phase angle being requested. Synchronization methods can be roughly divided among a) zero-crossing-methods, b) Phase-Locked-Loop (PLL) and c) Frequency-Locked-Loop (FLL) methods, with PLL implemented in a synchronous reference frame (SRF-PLL) likely being the most popular choice. A drawback of these methods is that, in general, they do not implement harmonic rejection strategies, their performance in polluted networks being therefore compromised; also their implementation and tuning is not straight forward, often being made by trial and error. This paper proposes a pre-filtering based synchronization method using cascaded complex-coefficient-filters (CCCF) and a complex PLL. The CCCF allows selection of the harmonic isolated/rejected, while the CPLL obtains the phase of the positive sequence component of the fundamental voltage needed for synchronization. The proposed method provides high rejection/adaptation capabilities against unbalances, frequency drift and harmonic distortion of the line voltages.