An Improved Reactance Control for Stability Enhancement of Grid-Forming Converter Based on Series-Regulated Branch

Virtual admittance control can enhance the stability of grid-forming converters in stiff grid. However, admittance control may induce a negative damping effect during reverse power operation, leading to system instability. Furthermore, under low dc-link voltage conditions, grid-forming converters implementing virtual admittance control are prone to over-modulation, resulting in control failure. To address these issues, this article proposes an improved reactance control that adjusts the set reactance to compensate for the deviation in equivalent reactance based on the frequency difference. Additionally, this article introduces a scheme that adopts a series of Boost circuits as a series-regulated branch to achieve the proposed reactance control. Theoretical analysis shows that the proposed method can achieve effective output of high damping voltage and positive damping enhancement of power across the entire range compared with the conventional virtual admittance and other voltage-based damping methods. Quantitative analysis and comparison are conducted using the Lyapunov direct method and the attraction region. The efficacy of the proposed method and the theoretical analysis are substantiated through prototype experiments.