An energy-based method for the assessment of battery and battery-ultracapacitor energy storage systems in pulse-load applications

A new energy-based method is described for studying the performance of battery or battery-ultracapacitor energy storage systems (ESS) in pulse load applications. The method estimates the total energy available in each ESS from a small number of discrete measurements at different states-of-charge. This considerably reduces experiment time, when compared to slowly depleting the ESS over the course of several hours. To illustrate the use of this method, experiments are performed for nickel-metal hydride (NiMH) batteries and lithium-iron phosphate (LiFePO4) batteries as well as their corresponding battery-ultracapacitor paralleled systems, under various pulse-load profiles and with different ratios of capacitor rating to battery energy. The results show accuracy of the method on the order of 0.5% and the improvements in total energy by incorporating ultracapacitors range from 3% to 47%, depending upon load profiles, experimental conditions and battery-ultracapacitor combinations.