Scheduling Power-Intensive Operations of Battery Energy Storage Systems and Application to Hybrid Hydropower Plants

TL;DR

The paper tackles inaccuracies in static BESS power constraints by introducing Dynamic Power Constraints (DPCs) that embed voltage and current limits as functions of the State of Charge (SOC). Under mild assumptions, these DPCs are linear in the BESS power, enabling seamless retrofitting into convex scheduling problems while preserving tractability. The approach is demonstrated on a hybrid hydropower plant with a 230 MW HPP and a 500 kWh BESS, where DPC-based scheduling reduces BESS current-constraint violations by up to 93% compared with traditional static constraints and DPCs lacking voltage constraints. This SOC-aware, voltage-inclusive framework improves scheduling reliability for power-intensive BESS applications and is adaptable to other storage technologies and market services.

Abstract

This paper proposes a novel set of power constraints for Battery Energy Storage Systems (BESSs), referred to as Dynamic Power Constraints (DPCs), that account for the voltage and current limits of the BESS as a function of its State of Charge (SOC). These constraints are formulated for integration into optimization-based BESS scheduling problems, providing a significant improvement over traditional static constraints. It is shown that, under mild assumptions typically verified during practical operations, DPCs can be expressed as a linear function of the BESS power, thus making it possible to retrofit existing scheduling problems without altering their tractability property (i.e., convexity). The DCPs unify voltage and current constraints into a single framework, filling a gap between simplified models used in BESS schedulers and more advanced models in real-time controllers and Battery Management Systems (BMSs). By improving the representation of the BESS's power capability, the proposed constraints enable schedulers to make more reliable and feasible decision, especially in power-intensive applications where the BESS operates near its rated power. To demonstrate the effectiveness of the DPCs, a simulation-based performance evaluation is conducted using a hybrid system comprising a 230 MW Hydropower Plant (HPP) and a 750 kVA/500 kWh BESS. Compared to state-of-the-art formulations such as static power constraints and DPC formulations without voltage constraints the proposed method reduces BESS constraint violations by 93% during real-time operations.

Figures (10)

• Figure 1: A diagram of a BESS connected to the grid showing the (steady-state) equivalent circuit of a BESS, the DC bus and the DC-to-AC power converter.
• Figure 2: BESS discharging power and power limits determined by the scheduler under different constraints with Static Power Constraints (SPCs) in (a), and with Dynamic Power Constraints (DPCs) in (b).
• Figure 3: Open-circuit voltage as a function of the battery state of charge for the lithium-ion BESS considered in this paper's case study.
• Figure 4: The feasible power area of the BESS as a function of the battery SOC considering both voltage and current constraints (blue lines) and without voltage constraints (dashed black lines)
• Figure 5: The control scheme of a hybrid hydropower plant.