Primary Frequency Regulation with Li-Ion Battery Based Energy Storage System - Evaluation and Comparison of Different Control Strategies

The increased grid penetration levels of renewable sources are at the expense of the conventional power plants. This means that the grid support functions, traditionally achieved by the conventional power plants, need to be provided by new technologies. Since grid support with energy storage devices is becoming more attractive, the aim of this paper is to analyse the viability of providing primary frequency regulation with Lithium-ion based energy storage systems. Three control strategies of the energy storage system are analysed and compared in terms of economic benefits on the Danish energy market. The revenues and degradation of the Lithium-ion batteries are obtained by simulations. Furthermore, an energy management strategy based on variable state-of-charge (SOC) set-point is evaluated. Preliminary, the influence of different state-of-charge levels on the cycle lifetime is estimated. Finally, the economic analysis is based on simulations performed with different bidding ratios, i.e. different SOC set-points, for primary upward and primary downward frequency regulation. The results showed that all three control strategies were associated with considerable economic benefits even though different degradation levels of the Lithium-ion batteries were observed. Furthermore, it was found that the economic benefits are declining by increasing the batteries' SOC set-point.