Current-Synchronization Control of Grid-Forming Converters for Fault Current Limiting and Enhanced Synchronization Stability

Grid-forming (GFM) converters with the widely adopted power-synchronization controller (PSC) are exposed to the risk of losing synchronization, due to their limited power transfer capability under severe symmetrical faults. The output of the PSC, i.e., internal angular frequency, is forced to deviate from its reference, leading to an uncontrollable power angle during the fault. Hence, GFM converters become sensitive to fault depth and duration, suffering from long recovery time. This article proposes a current-limiting GFM control that is capable of limiting fault current and maintaining grid synchronization during severe faults. A current-synchronization controller (CSC) is developed to replace the PSC. The proposed CSC works compatibly with a current limiter and behaves as a PSC during normal conditions to provide synthetic inertia and a phase-locked loop during severe faults with enhanced synchronization stability. Based on the developed steady-state model, it shows that GFM converters under the proposed control directly transition to a faulted steady state when a fault occurs and maintain a constant power angle until the fault is cleared. This helps converters to regain the prefault steady state within a shorter recovery period. The proposed method is validated by a comprehensive comparison with existing current-limiting methods, as well as experimental results under different control parameters, power settings, and system strength.