Enhancing Transient Stability of PLL-Synchronized Converters by Introducing Voltage Normalization Control

This paper presents a novel phase-locked loop (PLL) structure for improving the transient stability of grid-connected converters by introducing voltage normalization control (VNC) in conventional PLL. First, underlying mechanism losing synchronization during grid fault is analyzed, and it revealed that key factor significant decrease magnitude at point common coupling (PCC). In order to avoid damping ratio due dips, method introduced controlling d-axis rated value even faults. To this end, can be improved Phase portraits when using PLL PLL+VNC are both visualized validating effectiveness proposed structure. The performance adding additional analyzed through small-signal large-signal models. Finally, experimental results presented verify enhancing stability.