Transient Stability Impact of Reactive Power Control on Grid-Connected Converters

This paper presents a design-oriented transient stability analysis of a droop-controlled voltage-source converter (VSC), where the effect of reactive power control is in focus. By looking into the dynamic coupling between the active power loop and the reactive power loop, a large-signal model of the droop controller is built first. Based on this model, the transient responses of the droop-controlled VSC under grid faults are then evaluated using the phase portrait. It reveals that the reactive power control will generate a transient voltage drop to the VSC, which takes a positive feedback effect and deteriorates the transient stability. Fortunately, such a voltage drop can be offset by raising the reactive power reference. Finally, simulations and experiments are performed to verify the theoretical analysis.