Operational Validation of a Power Distribution Algorithm for a Modular Megawatt Battery Storage System

Large-scale battery storage systems have become popular for various grid services in recent years. A worldwide market growth for battery storage has led to increased competition in several grid service markets. Modular large-scale battery storage systems require a safe, highly available, and intelligent energy management system (EMS) in order to be economically competitive. One component of this EMS is the control for distributing the power requests between individual battery units of the large-scale battery storage system. As the EMS is usually undisclosed intellectual property of the system manufacturers, there is only little information on real-world operation available. To contribute, we present a rule-based power distribution algorithm (SPDA) in this paper and validate it through field tests on a 6 MW/7.5 MWh system that is providing frequency containment reserve to the German power grid. The results show that especially when combining different battery technologies, the SPDA can exploit individual technological strengths. In this way, the state of charge of the batteries, energy throughput and power load of the batteries can be controlled to extend the lifetime. Moreover, the SPDA managed to shift nearly 80 % of the energy throughput to one battery unit to protect less cyclic stable batteries and make use of the advantage of cyclic stable battery technologies, while fulfilling all grid service requirements. By shifting those large quantities of the energy throughput to more cyclic stable battery units, the large-scale battery storage system experienced in sum up to 45 % less cyclic aging with the SPDA than with a symmetrical power distribution algorithm. Furthermore, the operational efficiency of a large-scale battery storage system can be significantly improved via additional software adaptations of the power distribution, depending on the system layout.

Automated summary

Large-scale battery storage systems have become popular for grid services, leading to increased competition in the market. An intelligent energy management system (EMS) is necessary for these systems, including a power distribution algorithm (SPDA) to control battery units. Field tests on a 6 MW/7.5 MWh system validated the SPDA's ability to exploit individual technological strengths and reduce cyclic aging by shifting energy throughput.