Control of Inertia-synchronization Controlled Wind Turbine Generators Under Symmetrical Grid Faults

Grid-forming wind turbine generators (WTGs) can provide independent and rapid support for grid frequency and voltage, which are the key equipment to construct the new power system. Based on the principle of autonomous sensing of DC-link voltage to grid frequency, the inertial-synchronization control (ISynC) makes the WTGs synchronize with the grid and perform frequency response, which is an effective way to implement grid-forming WTGs. However, when grid faults occur, the stable control of the DC-link voltage cannot be realized due to the limited output power of the grid-side converter (GSC), resulting in the GSC losing the synchronization function. In addition, the transient overcurrent problem of the ISynC under fault conditions is prone to take place, leading to the WTGs out of operation. To solve the above problems, this paper analyzes the impact of grid faults on the ISynC, including the damaged synchronization mechanism of the DC-link voltage and the cause of the transient overcurrent problem. Then, a transient control strategy that comprehensively coordinates grid synchronization, transient overcurrent limitation, and unloading circuit operation is proposed. Finally, the effectiveness of the proposed control strategy is verified using the Bladed+RTDS hardware-in-loop experimental platform.