Improved Phase-Locked Loop Algorithm for Synchronization Under Grid Faults

This paper presents an improved phase-locked loop (PLL) algorithm for synchronization of a grid-connected converter (GCC) under grid faults. The proposed algorithm takes into consideration the asymmetry in the grid voltages that generally appears during the grid faults by employing asymmetrical transformations in its structure. Comparing it with the existing solutions, this feature provides benefit of compensation of any transfer function inserted in the grid voltage characteristics estimation scheme, such as compensation of the phase shift of a low-pass filter (LPF). Proposed control algorithm was tested on the hardware-in-the-loop (HIL) setup and the results that verify the proposed control strategy are presented.