Inertia-Inhomogeneity-Aware Frequency-Security-Constrained Unit Commitment in High-Renewable-Penetration Power Systems

Power systems with rising renewable penetration face declining and geographically uneven inertia, making frequency security a regional rather than merely systemwide challenge. Conventional frequency-security-constrained unit commitment (FCUC) models generally approximate the whole-system frequency response (FR) with an average-system-frequency (ASF) metric, yielding UC schedules that underprotect weak regions. This paper proposes an inertia-inhomogeneity-aware FCUC (IIA-FCUC) method that explicitly safeguards regional frequency security while retaining operational tractability.

First, a nodal FR model that incorporates inhomogeneous inertia by modal diagonalization is established. Then, the inertia-weighted Gaussian elimination is introduced to partition the power network into reduced equivalent regions with similar FR propagation. Finally, an IIA-FCUC method is proposed, which embeds regional FRs by casting the rate of change of frequency (RoCoF) limits as piecewise-linear constraints.

Case studies on a modified IEEE 39-bus system demonstrate that IIA-FCUC avoids regional inertia depletion and achieves robust regional RoCoF compliance across all disturbance cases, whereas SCUC exhibits regional RoCoF violations and ASF-FCUC can trigger inter-generator rotor-angle instability. The results indicate that accounting for inertia inhomogeneity is essential to obtain frequency-secure and feasible schedules in high-renewable-penetration power systems.