Analysis of the Power Output Capabilities of Grid-Forming Inverters Under Reactive Power Control Mode in Ultraweak Grid

GFM inverters have been widely recognized for their enhanced stability in weak grid conditions compared to GFL inverters. However, their power output capability (P–Q capability) may still be limited by both physical and stability-related constraints, particularly under low short-circuit ratio (SCR) conditions. While numerous studies have investigated P–Q capability in voltage control mode with constant voltage set points, a comprehensive characterization of P–Q capability in the widely adopted reactive power control mode, where significant voltage variations arise from elevated grid impedance, remains limited. This study provides a thorough evaluation of the P-Q capability in reactive power control mode, taking into account the combined constraints of inverter voltage limit, current limit, angle stability limit, and voltage stability limit. The explicit mathematical models of these capab…