A novel method for synchronization stability enhancement of grid connected converters based on equal area criterion

Penetration of inverter-based distributed energy (DG) resources into power grid has notably risen in recent years. Hence, new grid code standards require DGs to remain connected to the main grid even during faults and inject a certain amount of reactive power. However, in weak grids and during severe voltage faults, converters may fail to maintain their synchronization with the main grid. A main cause for this synchronization instability is the improper operation of synchronization unit which is phase locked loop (PLL). In literature, imitating the tran-sient stability analysis of synchronous generators, swing equation and Equal Area Criterion (EAC) are applied to study the synchronization of grid-connected converters. In this paper, a new method based on EAC and swing equation is proposed to keep the damping coefficient in the swing equation positive, and consequently increase the maximum buffer area in EAC. Hence, the synchronization stability of voltage source converters (VSCs) connected to weak grids is enhanced. When the fault is detected, the proposed technique simply adds a certain gain of frequency deviation to the PLL and does not need any additional information of grid changes. The simulation results in MATLAB verify the viability of the proposed controller.