A Transient Current-Limiting Control for the Grid-Forming (GFM) Cascaded H-Bridge (CHB) Converter

The Cascaded H-Bridge (CHB) converter features modularity and high capacity, with its stepped voltage waveform and output reactance emulating the internal potential and output reactance of a generator, making it an ideal solution for inner-loop-free medium-voltage direct grid-forming (GFM) applications. To address the challenges of slow response at low switching frequency and overload ratio limitation, this paper proposes a transient current limiting approach that integrates a current-clamped negative feedback control strategy (CCNFC) with a hierarchical module-level fast current reaction control strategy (HMCC). This approach ensures stable GFM operation under normal conditions while enhancing grid-support performance through optimized parameters under fault conditions. The rapid reaction of bottom controllers suppresses transient overcurrent, ensuring the CHB converter’s safety and reliable grid support performance. Simulations and experiments validate the proposed approach.