Research on fast phase synchronization scheme for three-phase unbalanced power system

Prompt and accurate phase detection is an essential qualification for the control of grid-connected inverters. However, the commonly used phase-locked loop methods consume too much time, longer than one grid period, to lock the new phase under severe grid unbalance condition, resulting in failing to satisfy the need for high speed and accuracy of phase synchronization. In order to solve this problem, an open-loop phase locking scheme was proposed in this paper. By constructing virtual orthogonal signals and adopting the method of symmetrical components, this scheme first realizes the fast fundamental-frequency positive sequence (FFPS) components extracting from the unsymmetrical grid voltages within 3 ms, and these FFPS components are further employed to perform open-loop phase calculation that is free from self-tuning closed-loop control and thus improves the dynamic performance remarkably. Finally, an improved orthogonal signal generation algorithm was presented, remarkably improving the immediacy and precision of signal configuration. The proposed method is characterized by easy implementation, strong robustness and remarkable rapidness, which are verified by experimental results.