A Communication-Less Synchronous Frequency Restoration Strategy Based on Voltage Zero-Crossing Detection for Islanded Microgrid

To ensure good power quality, frequency secondary restoration is one of the most significant parts of a microgrid. Its key technology is to realize synchronous control among all the converters. Under the event-trigger-based method, the specific event serves as a uniform signal to activate secondary control, providing an effective solution for converter synchronization. However, the lack of a global synchronous clock and the event detection delay may still result in an out-of-sync state during the secondary restoration process. As a solution, this paper proposes a synchronization secondary control strategy based on voltage zero-crossing detection, which can effectively realize synchronous frequency restoration. Under the proposed strategy, the zerocrossing point of the voltage is used as the global synchronous clock, and the communication line is not required. Besides, an automatic adjustment algorithm is designed to eliminate the compensation error caused by the detection delay. Simulation and experimental results have verified the effectiveness of the proposed strategy.