Voltage Stability of Inverter-Based Systems: Impact of Parameters and Irrelevance of Line Dynamics

TL;DR

This paper analyzes voltage stability in inverter-based power systems, deriving sensitivity expressions for stability margins and identifying key control parameters, while showing line dynamics are irrelevant to bifurcations.

Contribution

It provides an analytical framework for stability margin sensitivity and highlights the dominant control parameters for different inverter types, simplifying stability analysis.

Findings

Reactive loading setpoint and current controller gain are crucial for GFL inverters.

Voltage controller's feedforward gain is key for GFM inverters.

Line dynamics do not affect bifurcations in inverter-based systems.

Abstract

This paper investigates voltage stability in inverter-based power systems concerning fold and saddle-node bifurcations. An analytical expression is derived for the sensitivity of the stability margin using the normal vector to the bifurcation hypersurface. Such information enables efficient identification of effective control parameters in mitigating voltage instability. Comprehensive analysis reveals that reactive loading setpoint and current controller's feedforward gain are the most influential parameters for enhancing voltage stability in a grid-following (GFL) inverter system, while the voltage controller's feedforward gain plays a dominant role in a grid-forming (GFM) inverter. Notably, both theoretical and numerical results demonstrate that transmission line dynamics have no impact on fold/saddle-node bifurcations in these systems. Results in this paper provide insights for efficient analysis and control in future inverter-dominated power systems through reductions in parameter space and model complexity.