Structural Decoupling and Current-Angle Steering for Post-Fault Recovery of Current-Limited Grid-Forming Inverters
For grid-forming inverter control, this work addresses a critical post-fault recovery failure mode, but the solution is incremental (combining known techniques).
The paper identifies that interaction between PI-based voltage control and current limiters creates a moving recovery boundary causing post-fault trapping or oscillations in grid-forming inverters. It proposes a decoupled virtual admittance control with current-angle steering, experimentally validated on a 3-kVA prototype, eliminating these failures under symmetrical and unsymmetrical sags.
Reliable fault recovery of grid-forming (GFM) converters under current-limited conditions is increasingly important as inverter-based resources replace synchronous generation. Existing current-limiting strategies primarily focus on current-angle regulation and synchronization trajectory shaping, while the interaction between the current limiter and the voltage control structure remains insufficiently understood. Consequently, post-fault recovery may exhibit converter trapping in current-limited control (CLC) or oscillatory transitions between CLC and constant voltage control (CVC). This paper shows that, under conventional PI-based voltage control, the interaction between the voltage controller and the current limiter creates a moving recovery boundary that contributes to these recovery failures. To address this issue, a post-fault recovery framework is proposed that combines structurally decoupled virtual admittance voltage control with current-angle steering. The proposed framework simultaneously improves synchronization trajectory evolution and stabilizes the recovery boundary during fault recovery. Experimental validation on a 3-kVA GFM inverter prototype confirms reliable post-fault synchronization recovery under both symmetrical and unsymmetrical voltage sag conditions, with trapping and oscillatory CLC-CVC transitions eliminated.