A control strategy for hybrid energy storage system based on state of charge and variable filter coefficient

A hybrid energy storage system (HESS), which combines the advantages of different energy storage systems, can reduce the fluctuations of renewable energy output power effectively. In this study, we adopt the low-pass filtering algorithm, whose filter coefficient is mixed with the state of charge (SOC) of the HESS in order to dynamically adjust the goal output, and make the power fluctuations stable within the prescribed range. According to the SOCs of two energy storage mediums, the fuzzy control theory is adopted to distribute the power deviation reasonably. When the supercapacitors´ energy is adequate, supercapacitors compensate the power deviation independently to reduce the number of times of battery charging and discharging. Numerical results show that this control strategy can effectively level the fluctuations of renewable energy power, avoid the out-of-limit phenomenon of energy storage mediums, and extend the service life of the battery.