A solid-state transformer (SST) can realize the voltage transformation and isolation of a traditional power transformer and flexible power regulation, but it does not have the mechanical characteristics and synchronous operation mechanism of a traditional synchronous generator. When distributed power generation is connected to the power grid through the SST, because of the randomness and power fluctuation of distributed power generation, it will impact the superior power grid and lead to grid voltage or frequency fluctuation. A control strategy for the SST AC port based on a virtual synchronous generator is proposed. First, the equivalent model of the modular multilevel input stage and synchronous generator is established, and the principle of the virtual synchronous generator is integrated into the input stage control strategy to improve the power quality, inertia, and damping characteristics of the SST grid connection port. It also gives it the ability to participate in power grid frequency regulation and voltage regulation. Second, auxiliary frequency modulation control of the energy storage device is proposed to ensure the balance of load power consumption of the low-voltage system when the SST participates in primary frequency modulation. Finally, the control strategy of output stage of the virtual synchronous generator is established to improve the load power response characteristics of the low-voltage AC port and realize the ‘friendliness’ of the SST to the superior power grid. The simulation model is established on the Matlab/Simulink platform to verify the correctness and effectiveness of the proposed SST topology and its control strategy.

This work is supported by Major Science and Technology Project of the Xinjiang Uygur Autonomous Region (No. 2022A01001-4).