Sensorless Synchronization Method For a Grid-Side Converter With an LCL Filter Based On a Sliding Mode Observer and Discontinuous Operating Mode

When the grid-side converter (GSC) is switched on, a large inrush current may occur if the synchronization between the grid and the GSC is not performed well. Hence, a grid voltage and GSC output voltage vectors must be synchronized before the GSC is switched on. This study proposes a novel sensorless synchronization method based on discontinuous currents induced by the grid voltage after applying a series of controlled short circuits to the GSC terminals. Grid voltage angle is estimated using sampled current, a discrete sliding mode observer, and a double generalized second-order integrator with frequency locked loop in both discontinuous and continuous mode. The proposed method ensures the proper synchronization and GSC operation in the continuous operating mode under load conditions. The effectiveness of the proposed method is verified by simulations in Plexim PLECS.