A cross-entropy-based synergy method for capacity configuration and SOC management of flywheel energy storage in primary frequency regulation

Energy storage systems, coupled with power sources, are applied as an important means of frequency regulation support for large-scale grid connection of new energy. Flywheel energy storage systems (FESS) are considered short-term energy storage solutions due to their capacity for rapid and efficient energy storage and release. However, the power output characteristic of flywheels is potentially correlated to the state of charge (SOC) in the process of continuous operation while the SOC distribution would be attributed to the output power and duration of the flywheel. This study theoretically developed analytical correlations between SOC distribution and flywheel dynamic characteristics on statistical performance based on a cross-entropy method under wide range sampling scenarios of SOC. The results demonstrate that various operation states of FESS have a disparity effect on the statistical performance of modules. A SOC management and capacity configuration method considering continuous operation states is proposed, and the results illustrate that the capital expenditure of capacity configuration cuts approximately 8.2 % attaining the SOC stability under the homogenous frequency regulation scenario. Therefore, capacity configurations of FESS can effectively compensate for the capital loss caused by detrimental SOC so that the cross-entropy correlation method conducted in series has the capacity advantages.