Transfer Control Method Between Grid-Connected and Off-grid Modes Based on Kalman Filter for Grid-Forming Inverter

Conventional seamless switching techniques require pre-synchronization control using a phase-locked loop (PLL) to achieve smooth switching control modes, which involves the design of three sets of PI parameters and a complex design process. In this paper, a new smooth transfer control method between two control modes is designed for grid-forming inverter. The proposed method uses the Kalman filter to achieve phase synchronization before and after switching modes was proposed. Compared with the traditional method of using PLL to achieve pre-synchronization, the proposed method reduces the parameter design process and avoids the influence of the PLL module on the system control. The switching method has been validated by a series of simulations and experiments (based on Simulink and Dspace platforms).