LVRT Grid Code Compliance in Individual Phases of VSG-Based Grid-Forming Inverters With Enhanced Post-Fault Dynamics

Abstract

Grid-forming inverters integrating renewable energy sources (RESs) into the power distribution grid are susceptible to damage under grid voltage sag conditions. Improving the low-voltage ride-through (LVRT) of both three-phase and single-phase grid-forming inverters in grid-connected mode has not been simultaneously addressed under both symmetrical and asymmetrical voltage sags. This paper proposes an LVRT grid code-based current limiting function (CLF) by utilizing the single-phase synchronous reference frame for the control system executed in natural reference frame and four-wire system to bridge this research gap. Moreover, an adaptive damping coefficient scheme for the virtual synchronous generator (VSG)-based grid-forming inverter is proposed to increase the damping property during the voltage sag condition based on the amount of voltage drop. The proposed damping scheme and freezing the integrator of the proportional-integral (PI) controller in the reactive power-voltage amplitude control loop improve the post-fault dynamics of the VSG-based grid-forming inverters. Simulation studies conducted in the MATLAB/SIMULINK environment illustrate the effect of each proposed scheme individually to justify their significance under voltage sag conditions. Lastly, a comparison is presented between q-prioritized current limiting method and the proposed LVRT method to demonstrate the proposed method’s advantages of reactive power injection during grid faults and post-fault dynamics.