Transient Stability Improvement of Grid-Forming Inverters During Grid Fault Considering Voltage Dynamic Characteristics

The grid-forming converter is extensively utilized in grid interfaces which has the ability to flexibly adjust voltage and frequency. However, the interactions among control loops during grid disturbances complicate the analysis of transient synchronous stability in current-limited conditions. In this paper, the transient stability of the grid-forming converter is studied, which not only completes the comprehensive and accurate characterization of the dynamic characteristics of the virtual synchronous machine under the virtual impedance control, but also illustrates the mechanism of the transient switching operation mode under the current limited state, which has the phenomenon of ineffective controller integration. Considering the influence of VSG main control parameters on the transient stability of the system, an improved fault crossing control strategy is proposed, which can effectively improve the transient stability and smooth switching degree. Finally, the correctness of the above theoretical analysis is verified by simulation