Voltage stability improvement of weak grids using a new cascade droop control of grid-connected converter

The voltage control loop of a virtual synchronous generator (VSG) is typically governed by a conventional reactive power-voltage droop control, which may exhibit instability when encountering disturbances or operating under weak grid conditions. This paper proposes a new control approach to reduce voltage fluctuations and improve voltage stability in converter-dominated weak grids. The proposed controller extends the conventional droop control by introducing layered control loops named cascade droop control (CDC), enabling enhanced voltage support and grid stability even in weak grid case studies. The proposed methodology aims to enhance the grid-connected converter stability while maintaining simplicity in implementation. The proposed approach is assessed through analyses conducted in both the time and frequency domains. The stability analyses and simulation outcomes confirm the effectiveness of the new CDC technique in addressing weak grid conditions.