Definition and Formulation of Inertia Service Incorporating Inverter-Based Resources

TL;DR

This paper introduces a power-oriented definition of inertia service that unifies synchronous and virtual inertia, enabling effective market integration and economic dispatch of inertia resources.

Contribution

It proposes a new inertia definition based on inertial response, aligning SI and VI, and formulates a security-constrained dispatch framework demonstrating practical benefits.

Findings

The new definition ensures price signals reflect inertia's economic value.

Simulation results validate the effectiveness of the proposed framework.

The approach facilitates market integration of inverter-based inertia resources.

Abstract

Increasing concerns over the scarcity of inertia have motivated the procurement of inertia as an ancillary service (AS). Despite numerous academic and practical efforts, there remains a lack of consensus regarding the definition and treatment of inertia service in market operations, particularly the specification of inertia variables and the separation between synchronous inertia (SI) from synchronous generators and virtual inertia (VI) from inverter-based resources. To address these issues, this paper proposes a power-oriented (P-oriented) definition based on inertial response, which establishes conceptual consistency between SI and VI and makes the inertia service commensurable with other ASs. This definition explicitly incorporates both positive and negative inertial responses during frequency drop events. We then formulate a security-constrained economic dispatch framework based on this P-oriented definition and demonstrate its practical effectiveness through simulations. Case studies on a modified IEEE 30-bus system show that the proposed bidirectional service definition ensures price signals that reflect the economic value of inertial provision.