Research on Voltage Support of Grid-Forming SVG Based on VSG Control Under Weak Grid Conditions

Abstract

Long transmission lines in remote plateau regions exhibit high impedance, making the point-of-common-coupling (PCC) voltage vulnerable to load disturbances in weak grids. To address this problem, this paper develops a MATLAB/Simulink model comprising an upstream weak grid, line impedance, load, and a grid-forming static var generator (SVG). The SVG uses a three-phase voltage-source inverter and a virtual synchronous generator (VSG) control strategy, which integrates active power-frequency, reactive power-voltage, DC-side voltage, and cascaded voltage and current control loops. Under a short-circuit ratio of 2.76, the proposed strategy enables the SVG to inject approximately 86 kvar of reactive power, increasing the PCC rms line voltage from 314 V to 380 V. This corresponds to a recovery of approximately 100% of the voltage drop, while the grid-side power factor reaches 0.99. The results demonstrate that the VSG based grid-forming SVG can provide voltage support in weak grids and effective reactive power compensation.