On the stability properties of power networks with time-varying inertia

TL;DR

This paper analyzes how time-varying inertia, due to virtual inertia control, impacts power system stability, providing conditions to ensure stability and highlighting potential instability risks through analytical and simulation results.

Contribution

It offers a scalable stability analysis framework for power networks with dynamic inertia variations, including conditions to prevent instability caused by inertia fluctuations.

Findings

Inertia variations can induce large frequency oscillations.

Proposed conditions can guarantee stability under inertia fluctuations.

Simulations validate the analytical stability criteria.

Abstract

A major transition in modern power systems is the replacement of conventional generation units with renewable sources of energy. The latter results in lower rotational inertia which compromises the stability of the power system, as testified by the growing number of frequency incidents. To resolve this problem, numerous studies have proposed the use of virtual inertia to improve the stability properties of the power grid. In this study, we consider how inertia variations, resulting from the application of control action associated with virtual inertia, may affect the stability properties of the power network within the primary frequency control timeframe. We consider the interaction between the frequency dynamics and a broad class of power supply dynamics in the presence of time-varying inertia and provide locally verifiable conditions, that enable scalable designs, such that stability is guaranteed. To complement the presented stability analysis and highlight the dangers arising from varying inertia, we provide analytic conditions that enable to deduce instability from single-bus inertia fluctuations. Our analytical results are validated with simulations on the Northeast Power Coordinating Council (NPCC) 140-bus and the IEEE New York/New England 68-bus systems, where we demonstrate how inertia variations may induce large frequency oscillations and show that the application of the proposed conditions yields a stable response.