Optimal provision of primary frequency control with battery systems by exploiting all degrees of freedom within regulation

Battery energy storage systems have a large potential for provision of grid ancilliary services. Specifically, large battery systems have been used for the provision of primary control reserve. Batteries providing this grid service must, using corrective energy measures and control algorithms, continuously keep their state of charge within limits in order to comply with European regulations. Operational degrees of freedom exist in the regulation which can be used by batteries to facilitate keeping the state of charge within desired levels. In this paper, such degrees of freedom are described, and the effect of their utilization on battery system operation analyzed.