Frequency Sharing Based Control of Battery/Ultracapacitor Hybrid Energy System in the Presence of Delay

Hybrid energy storage systems (HESS) involves two or more energy sources with complementary electrical charge/discharge characteristics to provide both energy and power requirements of the load. This paper presents an improved frequency sharing control algorithm used along with average current mode control for battery/ultracapacitor (UC) hybrid system in the presence of delay. The control algorithms implemented in different digital platforms have a delay due to computation and sampling time. The presence of delay limits the bandwidth (BW) of inner current loops. At such reduced BW, the improved algorithm proposes to compensate the battery current loop error during transients by UC current loop since the latter is faster. This leads to faster settling of the output. The control algorithm has been implemented in a microcontroller, and the effect of delay time has been considered for controller design to ensure system stability. For efficient HESS operation for load demand at all times, an EMA has also been proposed to charge/discharge the UC for ensuring its nominal voltage. An experimental prototype of the overall system is designed, and the effectiveness of the proposed control algorithm over conventional algorithm has been demonstrated.