On Inertia Distribution, Inter-Area Oscillations and Location of Electronically-Interfaced Resources

This paper explores the relationships between inertia distribution, inter-area oscillations, and location of electronically-interfaced resources that are enabled with either damping or inertia emulation controllers (EIRs). A two-machine system with an EIR is used for analytical derivations. Explicit analytical expressions are found for: (a) the location of the center of inertia (COI), which depends on the H-inertia constant and voltage set-points of the machines, and (b) the residue of the system transfer function, which is convex in terms of the EIR location. These expressions are validated using full-order models for machines, exciters, and governors; the results support the idea of placing EIRs further away from the COI, or equivalently, in areas with low inertia to attain the highest possible oscillation damping. In the case of large-scale systems, an inertia distribution index is proposed which allows estimating the distance from any bus to the COI location. The efficacy of the proposed index is tested in a real system. The system areas with less inertia are proved to be the best places to deploy EIRs. The proposed index does not require computationally expensive calculations as those from modal analysis and it seems promising to better reinforce power system dynamics through EIRs.