Dynamic power sharing strategy for active hybrid energy storage systems

Batteries have been used as main energy storage devices in hybrid electric vehicles and portable electronics for many years and they are good in the medium-term low-power applications, but low dynamics and relatively shorter lifespan are their main week points. Due to their fast power response, high power density and high cycling capability, supercapacitors or double-layer capacitors are becoming a promising option for short-term high-power applications. Therefore, it is desirable to combine supercapacitors and batteries in a hybrid energy storage system. This paper presents a dynamic strategy for the active power sharing in hybrid battery/supercapacitor energy storage systems. The power sharing ratio can be dynamically changed during the runtime. The battery may be predominant in the charging or discharging mode when the load demand is relatively low. When the load is rising, the power sharing ratio of the battery is decreasing, while the power ratio of the supercapacitor is increasing simultaneously. This dynamic strategy enables power sharing to depend upon the load demand and makes full use of different capabilities of the battery and supercapacitor. Different dynamic power sharing strategies are tested under different repetitive pulsed load conditions. The effects of different power sharing ratios on the battery and supercapacitor state of charge are also investigated.