Grid Synchronization during Non-Ideal Grid Conditions Based on Double Integration Method

Modular multilevel converter (MMC) has numerous advantages already discussed in the literature. Grid voltage synchronization is a critical component of grid-connected power converters. Synchronous reference frame (SRF)-PLL traditionally synchronizes MMC voltage to the grid. However, non-ideal grid circumstances induce phase angle inaccuracies since phase angle is obtained by integrating grid frequency. The three-phase dual integration method (DIM) is used in the grid synchronization of a three-phase MMC inverter in this study. It integrates grid phase voltage twice to generate reference signals for the MMC grid side converter. Furthermore, it enables a smooth start during balanced and non-ideal grid conditions a) voltage unbalance; and b) frequency unbalance, as the generated signal remains in phase with the current. The proposed process reduces THD to almost less than (< 0.09%). The simulation results demonstrate the suggested method's efficacy in grid synchronization.