Contents I. Introduction
Electric vehicles (EV) are gaining increasing attention for having unique features such as low emission, high efficiency, quiet operation, etc. [1]– [3]. Chemical batteries have long been used as the main energy storage system (ESS) in many industrial applications. They are currently the dominant technology in the electric car industry. However, the chemical batteries have many shortcomings, such as limited cycle-life, limited power density as well as high cost [1]–[4]. Electric double layer capacitors, known as supercapacitors, are high capacitance capacitors that offer many outstanding features such as high power density, long life-cycle, and wide operating temperature range. A qualitative comparison between the lead-acid batteries and supercapacitors is shown in Fig. 1 by the radar chart [4]. As shown, although the supercapacitor offers better performance in most of the terms, it cannot be used as the main ESS since its energy density is relatively low. Likewise, since the technology of the supercapacitors is recently developed, they are not as reliable as the conventional batteries. Complementary features of batteries and supercapacitors can be utilized in a hybrid energy storage system (HESS) [4]–[24]. The application of HESS has many advantages that are listed as follows.
High power density of the supercapacitor can be used to effectively harness the kinetic energy of the vehicle during braking.
Supercapacitor can assist the battery pack in peak power demands, which not only prolongs the battery life time but also improves the vehicle acceleration.
Since the braking energy could be effectively saved, the drive range of the vehicle can be considerably increased [25]– [31].
Qualitative comparison of the Lead–Acid battery and supercapacitor.
