Hybrid Energy Storage System of an Electric Scooter Based on Wireless Power Transfer

The aim of this paper is to present the design and implementation of a hybrid energy storage system (HESS) with wireless power transfer (WPT). This study combines a battery bank and a supercapacitor bank to achieve high performance energy sources for electric scooters. The proposed system can be employed on commercial 48-V electric scooters for evaluation. The presented approach follows the WPT frequency standard of SAE J2954 to build the energy transmission. Based on the control of the state of charge on the battery bank, this paper proposes a three-mode strategy for hybrid energy management. The proposed HESS makes three compact and integrated contributions. First, it acts as the regulator to manage the input energy from WPT. Second, it manipulates the energy distributions to the battery and supercapacitor. Third, it provides a mechanism to initiate a short period of “negative current” to avoid excessive exploitation of the battery and facilitates palliation upon polarization. This function has the ability to extend battery life. The system performance of the electric scooter, as a result, can be improved. A double-sided LCC coil with a 15-cm air gap for wireless charging was built on a 0.8-kW electric scooter. In the wireless stage, the efficiency from the dc source to the dc output after the rectifier is 90.362%. The overall system efficiency from the dc source to the battery and supercapacitor is 86.4%.