Abstract: According to the hybrid energy storage system （HESS） in which supercapacitor and Li-ion battery were in parallel after boosted respectively by Buck-Boost bidirectional DC/DC converter, this paper analyzed the influencing factors of the current response characteristics of the HESS in detail. Based on the characteristics that supercapacitor had good power characteristics and Li-ion battery had large capacity, the roles of two energy storage mediums in HESS were analyzed. On this basis, this paper proposed a power allocation method in which the charging and discharging of battery did not respond directly to power instruction, but in accordance with the state of the state of supercapacitor. Finally, this paper introduced the capacity design basis of supercapacitor with this power allocation method, and presented examples combined with the fluctuation characteristics of output power in direct-drive wave power generation system.

Key words: hybrid energy storage system （HESS）, supercapacitor, current response, power allocation, capacity design