Improved Low Voltage Ride-Through Performance of Single-phase Power Converters using Hybrid Grid Synchronization

Loss of synchronization (LOS) in case of synchronous reference frame based phase-locked loop (SRFPLL) affects the low voltage ride-through performance of grid-connected power converters. To avoid this issue, this paper proposes a hybrid grid synchronization technique that includes two frequency and two phase-angle estimators. It uses the frequency and phase-angle estimation by the SRFPLL during normal grid operation and switches to the arctangent based phase-angle and corresponding frequency estimation in the αβ-frame during grid faults. To avoid sudden mode transfer between these estimators a common transition algorithm is proposed as well, which is controlled by the phase-angle difference between them. The proposed hybrid grid synchronization transition is implemented in the frequency dependent proportional and resonant current controller of the converter. The controller is run with the low voltage ride-through strategy during the faults. It is observed that the converter having the proposed grid synchronization technique provides robust current controller performance as the fast tracking of grid current on the fault inception and recovery.