Transient Stability Analysis and Control of Grid-Forming Converters Under Current Limiting Based on Relative Kinetic Energy

Under large disturbances, voltage-source inverters (VSIs) may experience transient power-angle instability similar to that of conventional synchronous machines; however, their limited overcurrent capability necessitates current-limiting mechanisms, under which the inverter may effectively behave as a current source, leading to more complex synchronization and stability challenges. To address transient instability induced by current saturation, this paper proposes an emergency control strategy based on the concept of relative kinetic energy, in which transient grid instability is identified in real time by analyzing the evolution of rotor speed deviation with respect to the virtual power angle. When impending angle instability is detected, the remaining acceleration area is calculated using relative kinetic energy theory, while the required active power adjustment is determined simultaneously, with the influence of control action delay explicitly incorporated to enhance reliability. Simulation results verify that the proposed strategy can effectively maintain system transient stability, and if the initial control action fails, a feedback-based closed-loop architecture can autonomously trigger secondary emergency control to ensure the system remains within a secure and stable operating region throughout the transient process. The proposed method eliminates the need for detailed modeling of power system components or explicit operating mode identification, relying only on measured generator power angles and rotor speeds to adapt to arbitrarily complex operating conditions and fault scenarios with low computational burden and high flexibility, thereby effectively preventing system deterioration and mitigating the risk of large-scale blackouts, which demonstrates strong practical engineering value for enhancing grid security and transient stability defense capabilities.