Optimal Control Strategy for LVRT and Quasi-Synchronous Droop-Controlled Inverter Considering Voltage Drop on the Distribution

Transient issues arising from voltage drops in distribution networks with high penetration of renewable energy, as well as post-fault reclosing challenges, are often addressed separately through low-voltage ride-through (LVRT) and quasi-simultaneous control, without a comprehensive stability analysis covering the entire fault stage. This paper reveals the temporal correlation between LVRT control and quasi-simultaneous control and proposes an integrated optimal control strategy. The strategy enhances the transient stability of droop-controlled inverters following voltage drops, ensures reliable load supply during off-grid operation, and achieves seamless grid reconnection without current surges during reclosing. During the LVRT phase, the inverter power reference is dynamically adjusted based on power angle characteristics and reactive power-current relationships to stabilize the power angle and limit output current. In the reclosing transition phase, a combined frequency and phase angle regulation mechanism is employed to minimize discrepancies in voltage frequency and phase angle, accounting for transient operating condition changes. The effectiveness and practicality of the proposed strategy are validated through simulations and experimental results.