Adaptive Hybrid Synchronization-Based Transient Stability Enhancement Strategy for Grid-Forming Converters in Weak Grid Scenarios

Driven by the large-scale application of distributed power sources, power systems are facing escalating frequency stability challenges in terms of inertia reduction. In this weak grid scenario, grid-connected converters are increasingly required to operate as high-inertia grid-forming (GFM) units to participate in the regulation of grid frequency. However, this high inertia will seriously impair the transient stability of GFM converters. To resolve the conflict, an adaptive hybrid synchronization-based transient enhancement strategy is proposed. Through integrating the traditional droop phase angle with the phase-locked loop-locked grid phase angle, the proposed control can effectively enhance transient stability under the full fault range from mild to severe voltage sags (with a voltage sag depth of up to 90%) without sacrificing system inertia. Moreover, benefiting from this, the proposed hybrid synchronization scheme also avoids the secondary overcurrent issue that occurs after fault clearance in traditional GFM control. Finally, the simulation and experimental results under various voltage sags verify the effectiveness of the proposed control strategy.