| Summary: | In microgrid, virtual synchronous generators can enhance the system stability by simulating the operation mechanism of synchronous generators. However, a large impact current could be triggered during the grid-access of VSG inverters, resulting in switching failure. Aiming at this problem, based on real-time digital simulator (RTDS), this paper proposes a complete and simple pre-synchronization control strategy based on secondary frequency modulation and voltage regulation. Firstly, the grid-access structure of VSG was defined, and a mathematical model of VSG was constructed, followed by the design of power-frequency and excitation regulators. Next, secondary frequency and voltage regulation was performed on the microgrid in islanded mode to eliminate the frequency and voltage bias induced by load changes. On this basis, the grid phase was collected by phase-locked loop, the phases were synchronized through phase difference detection, and the grid-access synchronization was completed, realizing the seamless switching between islanded and grid-connected modes. Compared with the universality of applying matlab simulation software, real-time digital simulator (RTDS) has great advantages compared with physical simulation and general simulation software. Finally, the proposed strategy was proved effective with a self-designed RTDS simulation model. © 2022 Faculty of Engineering, Alexandria University
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