Quantitative Efficiency and Temperature Analysis of Battery-Ultracapacitor Hybrid Energy Storage Systems

This paper provides quantitative analysis on system efficiency and battery temperature rise in battery-alone system, passive, battery semiactive, and capacitor semiactive hybrid energy storage systems (HESSs). First the system efficiencies and the temperature rises in battery are derived under a pulsed load profile and the four different topologies. Sensitivity analysis is then performed to investigate the influences of the factors (the characteristics of the load profile, the state of charge of battery, and the efficiency of the dc-dc converter) on the four energy storage systems. The proper usage of the HESSs is discussed later based on the results of the sensitivity analysis. It is found that in the most cases the capacitor semiactive HESS is superior in both system efficiency and the suppression of the battery temperature rise. Meanwhile, its behavior is more complicated than that of the battery semiactive HESS. The battery semiactive HESS is suitable for the highly dynamic loads, but its performance more depends on the efficiency of the dc-dc converter. Finally experiments are conducted that validate the previous theoretical discussions.