Optimal Charging and Discharging Strategies for Independent Energy Storage Systems in Ancillary Service Markets Considering Frequency Regulation Mileage

It is significantly important to introduce frequency support from independent energy storage systems (IESS) to strengthen the flexibility of low-inertia systems under complex stochastic scheduling processes and an external electricity market for frequency-related auxiliary services. To tackle this, a two-stage scheduling model considering frequency regulation characteristics from IESS, such as frequency regulation mileage (FRM), security state-of-charge (SOC) requirement, is extended in this work. Remarkably, a new set of reformulated constraints regarding maximizing social benefit considering FRM and SOC is constructed to describe actual arbitrage behaviors under the electrical auxiliary-service market for frequency regulation. These constructed constraints are then integrated into a unified scheduling framework where the arbitrage from conventional generators and renewable resources is also taken into account. Case studies on a modified IEEE 30 bus test system demonstrate the benefit of IESS through optimized FRM/SOC management.