Research on Self-synchronization Strategy of Grid-connected Inverters in Weak Power Grid

Abstract

In order to ensure good power quality, the grid-connected inverter mostly uses phase-locked loop (PLL) to maintain synchronization with large power grid. But the PLL will cause a negative-impact on the stability of grid-connected inverter under weak grids. The paper analyzes the equivalent impedance of the PLL under the weak grid firstly. Then the paper proposed a self-synchronization strategy using DC bus voltage and reactive power control to synchronize the frequency and amplitude with the grid-connected inverter instead of the applying PLL. Applying the proposed method to the on/off grid switching condition, a pre-synchronization control strategy based on virtual power is proposed to achieve seamless switching of the grid-connected inverter. At last, the designed self-synchronization control strategy and pre-synchronization strategy are verified on the Plecs simulation platform.