On the comparison of two hybrid energy storage systems: Parallel connection of battery-RC ultracapacitor/- multibranch ultracapacitor circuits

Double-layer capacitors, known as ultra-capacitors (UCaps), are energy storage devices that can be connected in parallel with batteries to create a hybrid energy storage system (HESS) for electric vehicles (EV). This HESS plays an important role in increasing the efficiency and the performance of EV due to the use of the advantages of each technology; the high density energy of the battery as well as the high power of the ultracapacitor. Moreover, batteries subjected to pulsed transient power generate dc voltages with dips that can exceed the voltage regulation band. So, it is revealed that this HESS can assist in maintaining the bus voltage within the regulatory limits, resulting in reduced system losses and prolonged power system life. The purpose of this paper is to investigate the performance of a HESS which consists of an ultracapacitor placed in parallel with a battery, following the injection of constant power pulses. A comparison study between two hybrid configurations is achieved: (i) a battery-RC ultracapacitor circuit and (ii) a battery-multibranch ultracapacitor circuit.