Smooth Switching Strategy of DC Side of Flexible Interconnect Device Based on Virtual Synchronous Control

The key to the stable operation of the FID (flexible interconnection device) is the voltage stability of the DC (direct current) bus. However, when transient events occur on the DC side of the flexible interconnection device and the operation mode needs to be switched, the traditional master-slave control strategy can not be switched in time due to a certain delay of the communication system, resulting in the damage of the device. To solve this problem, this paper proposes a smooth switching strategy based on virtual synchronous control for flexible interconnection devices, which can stabilize the DC bus voltage within the range of power grid operation when transient events occur in the system. When the operation mode of the flexible interconnection device is switched, the voltage and current on the DC side can be smoothly transitioned, and the inertia and damping support can be provided for the power grid during steady operation. The proposed strategy is verified by the simulation of flexible interconnection device under three conditions: switching from two-terminal power supply to two-terminal isolated power supply, active command step in single-terminal power supply, and frequency reduction in double-terminal power supply.