A Novel Control Strategy to Enhance the Transient Performance of Grid-Forming Converters

In response to the issues of transient power angle instability and fault current (FC) over-limit under severe grid three-phase symmetrical faults for grid-forming voltage source converters (GFM-VSCs), this article proposes a novel joint control method combining second-order sliding mode control (SOSMC) with voltage adaptive regulation. Initially, an improved integral sliding surface is introduced into the active power-frequency loop of the GFM-VSC, and a Lyapunov function is constructed, which pertains to a large-signal problem. Based on this stability criterion, an output power control law is designed to strictly limit the fluctuation of the power angle. Subsequently, a reactive power–voltage loop switching control is employed to provide stable reactive power and support grid voltage, while ensuring that the steady-state current (SSC) is maintained within a safe threshold. Additionally, during faults, a virtual impedance is engaged, and the transient current (TC) can be suppressed by adjusting the ratio of resistance-to-inductance (<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">R</i>/<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</i>) and recovery resistance. This method achieves power angle stability (PAS) and fault current suppression (FCS) simultaneously, even during grid voltage sags accompanied by phase changes. Finally, the correctness and effectiveness of the proposed method are validated on the real-time test platform.