Fault Current Limiting Control Strategy for GFM Converters Based on Direct Internal Voltage Control with Improved Transient Stability

The grid-forming (GFM) converters has the ability to provide frequency and voltage support like synchronous generators, therefore have good impact on stability of the new power system. However, it is still an unresolved issue that ensuring the transient stability of GFM converters while maintaining their voltage support capability under current limiting constraints. To address this problem, a fault current limiting control strategy for GFM converters based on direct internal voltage control (DIVC) with improved transient stability is proposed in this paper. Firstly, the control frame of DIVC that without inner loop is presented, then the current limiting mechanism of directly changing internal voltage of GFM converter according to the voltage at point of common coupling (PCC), is described based on the virtual synchronous generator (VSG) control model of GFM converter and the analysis of transit fault process. After that, the tripping criteria, amplitude and phase compensation, as well power reference modification modules are presented to form the proposed fault current limiting control strategy. Finally, the simulation results on PLECS verify the effectiveness on fault current limiting and the improvement on transient stability of proposed control strategy.