Analysis and Improvement of Transient Voltage Stability for Grid-Forming Converters

Grid-forming converters are gradually becoming the enablers of more-electronic power systems. However, the challenge of fault-ride through prevents the widespread adoption of grid-forming converters. Although the existing literature investigates active power-transfer limitations and transient stability problems of grid-forming converters during fault-ride through, few of them touch reactive power-transfer limitations. In this article, we reveal that grid-forming converters also face transient voltage stability problems, which are caused by the violation of reactive power absorption limitations between converters and grids. This is particularly of interest for grid-forming static compensators and different from conventional power system voltage stability problems. Moreover, this article derives the equilibrium points, reactive power absorption limitations, and stable regions of grid-forming converters with two typical reactive power controllers, namely, reactive power proportional–integral (PI) and voltage-droop control. To improve fault-ride through, this article further proposes and designs voltage inertia control, which smoothens the voltage amplitude change and extends the stable region. In addition, this article finds that the active power control deteriorates transient voltage stability. Finally, the experimental results verify the analysis and the impact of control on the transient voltage stability of grid-forming converters.