Enhanced Transient Stability Strategy for Grid-Forming Converter Based on Current Limiting

Abstract

With the sustained increase in the penetration rate of grid-forming (GFM) converters in power systems, problems such as overcurrent and transient instability during system faults have drawn significant attention. This paper proposes an enhanced dynamic dq-axis current-limiting strategy (ED-CLiS) for GFM converters, which improves transient stability across all stages before and after current limiting. First, a dynamic dq-axis current-limiting strategy (D-CLiS) is proposed. This strategy regulates the power angle to prevent it from going out of control during current limiting, which is achieved by controlling the $d$- and $q$-axis current reference values to reshape the ${P}-\delta^{\prime}$ curve. Additionally, a large reverse acceleration area can induce excessive angle $\delta^{\prime}$ swings, causing the D-CLiS to be triggered repeatedly and resulting in converter instability after the control exit, even without faults. A reference power control structure (RPCS) is proposed, which suppresses the phenomenon by adjusting the power reference value to control the converter's reverse acceleration area. Finally, the control strategy is verified through simulations.