Profit-Maximizing Planning and Control of Battery Energy Storage Systems for Primary Frequency Control

TL;DR

This paper develops a theoretical framework for profit-maximizing planning and control of battery energy storage systems in primary frequency control markets, emphasizing a low-complexity, state-invariant control strategy and optimal sizing.

Contribution

It introduces a novel, low-complexity control strategy that remains invariant to system state and provides a convex optimization approach for optimal BESS sizing.

Findings

Optimal control is state-invariant and can be computed offline.

Minimum operating cost decreases convexly with BESS capacity.

Optimal BESS sizing balances investment and operational costs.

Abstract

We consider a two-level profit-maximizing strategy, including planning and control, for battery energy storage system (BESS) owners that participate in the primary frequency control (PFC) market. Specifically, the optimal BESS control minimizes the operating cost by keeping the state of charge (SoC) in an optimal range. Through rigorous analysis, we prove that the optimal BESS control is a "state-invariant" strategy in the sense that the optimal SoC range does not vary with the state of the system. As such, the optimal control strategy can be computed offline once and for all with very low complexity. Regarding the BESS planning, we prove that the the minimum operating cost is a decreasing convex function of the BESS energy capacity. This leads to the optimal BESS sizing that strikes a balance between the capital investment and operating cost. Our work here provides a useful theoretical framework for understanding the planning and control strategies that maximize the economic benefits of BESSs in ancillary service markets.