Towards Optimal Primary- and Secondary-control Design for Networks with Generators and Inverters

TL;DR

This paper develops a framework for designing optimal primary and secondary control strategies in power grids with mixed synchronous generators and inverter-based resources, ensuring economic efficiency and proper power sharing.

Contribution

It extends existing control design methods to accommodate diverse grid resources, providing conditions for optimal power sharing and economic operation in mixed-generation systems.

Findings

Derived conditions for active-power droop slopes.

Established criteria for AGC participation factors.

Validated control strategies for diverse grid configurations.

Abstract

For power grids predominantly featuring large synchronous generators (SGs), there exists a significant body of work bridging optimization and control tasks. A generic workflow in such efforts entails: characterizing the steady state of control algorithms and SG dynamics; assessing the optimality of the resulting operating point with respect to an optimal dispatch task; and prescribing control parameters to ensure that (under reasonable ambient perturbations) the considered control nudges the system steady state to optimality. Well studied instances of the aforementioned approach include designing: i) automatic generation control (AGC) participation factors to ensure economic optimality, and ii) governor frequency-droop slopes to ensure power sharing. Recognizing that future power grids will feature a diverse mix of SGs and inverter-based resources (IBRs) with varying control structures, this work examines the different steps of the optimization-control workflow for this context. Considering a representative model of active power-frequency dynamics of IBRs and SGs, a characterization of steady state is put forth (with and without secondary frequency control). Conditions on active-power droop slopes and AGC participation factors are then derived to ascertain desired power sharing and ensure economically optimal operation under varying power demands.