Equivalent Series Resistance-based Real-time Control of Battery-Ultracapacitor Hybrid Energy Storage Systems

This paper proposes an equivalent series resistance (ESR)-based control, namely a circuit-level approach, to efficiently distribute load in battery-ultracapacitors (UC) hybrid energy storage systems (HESSs). The ESR circuit model of an example capacitor semiactive HESS is first built representing the energy losses at both circuit and system levels. The analytical derivations show that the overall energy loss of the HESS solely depends on the ratio of the dynamic load provided by the battery pack to the entire dynamic load. This energy loss is minimized following the load distribution determined by the ratio of the ESR of the battery pack to those of the UC pack and dcdc converter. An ESR-based real-time control strategy is then developed to minimize the energy loss and regulate UC state-of-charge (SOC) to avoid overcharge/overdischarge. Both the simulation and experimental results verify the effectiveness of the proposed ESR-based control in terms of improvements in energy efficiency, usage of UC pack, and temperature rise reduction in batteries. The ESR-based control achieves a performance close to that using the ideal dynamic programming method. Compared with the battery-alone system, the total energy loss and battery temperature rise in the example HESS are averagely reduced by 44.9 and 51.9, respectively, under the proposed ESR-based control.