Self-Synchronization Grid Forming Inverters Connected to a Microgrid System Consisting of a Diesel Synchronous Generator

Synchronization must be implemented before and after connecting an inverter to a power grid. Virtual synchronous generator-controlled grid-forming (VSG-GFM) inverters have been reported that can emulate synchronous generators to achieve synchronization in general systems. However, when VSG-GFM inverters operate in microgrids with large frequency fluctuations, inrush current, and frequency oscillation can occur when an inverter is connected to the grid, causing a protective shutdown of the inverters. This paper proposes an improved self-synchronization method for VSG-GFM inverters, which can operate even when the frequency fluctuation of the microgrid is large. The effectiveness of the proposed synchronizing method was verified in a microgrid consisting of a VSG-GFM inverter and a diesel synchronous generator, using extreme grid frequencies of 48.0 and 52.0 Hz, respectively.