Transient Stability of Low-Inertia Power Systems with Inverter-Based Generation

TL;DR

This paper investigates the transient stability of low-inertia power systems with inverter-based generation, introducing a new stability criterion and uncovering mechanisms of transient instability unique to such systems.

Contribution

It develops a hybrid IBG-SG model, identifies new loss-of-synchronization mechanisms, and proposes a sufficient energy-based stability criterion for low-inertia power systems.

Findings

Two types of loss-of-synchronization identified

Energy jumps at fault onset affect stability

Cosine damping contributes to system stability

Abstract

This study examines the transient stability of low-inertia power systems with inverter-based generation (IBG) and proposes a sufficient stability criterion. In low-inertia grids, transient interactions are induced between the electromagnetic dynamics of the IBG and the electromechanical dynamics of the synchronous generator (SG) under a fault. For this, a hybrid IBG-SG system is established and a delta-power-frequency model is developed. Based on this model, new mechanisms of transient instability different from those of conventional power systems from the energy perspective are discovered. First, two loss-of-synchronization (LOS) types are identified based on the relative power imbalance owing to the mismatch between the inertia of the IBG and SG under a fault. Second, the relative angle and frequency will jump at the moment of a fault, thus affecting the system energy. Third, the cosine damping coefficient induces a positive energy dissipation, thereby contributing to the system stability. A unified criterion for identifying the two LOS types is proposed using the energy function method. This criterion is proved to be a sufficient stability condition for addressing the effects of the jumps and cosine damping coefficient on the system stability. The new mechanisms and effectiveness of the criterion are verified based on simulation results.