Abstract：To address issues like overcurrent，power oscillations，and insufficient dynamic response in

traditional virtual synchronous generator（VSG）control during grid voltage sags，an improved VSG- low voltage

ride through（LVRT）mode-switching control strategy for grid-forming inverters was proposed. The strategy

dynamically switched between two modes depending on the real-time detected voltage sag depth：under normal

operation and mild sags，it employed impedance-reshaping-based VSG control to enhance current loop dynamics

and stability by reconstructing virtual impedance；during deep sags，it switched to a power-fast-response LVRT

mode，optimizing active/reactive power distribution，adjusting the inertia coefficient，and compensating dynamic

reactive power to provide fault-period reactive support and rapid power regulation. A state follower was also

designed to coordinate voltage magnitude/phase synchronization during fault recovery，suppressing inrush currents during mode transitions. PSCAD/EMTDC simulations validate the strategy's correctness and effectiveness.

      Key words：grid-forming inverter；low voltage ride through（LVRT）；virtual synchronous generator（VSG）；

state following