Intelligent controller for a hybrid energy storage system

Abstract

The performance and range of electric vehicles are largely determined by the characteristics of the energy storage system (EES) used. The EES should be sufficiently sized to be able to provide the necessary power and energy requirements of the vehicle. Batteries are typically energy dense, although batteries that are both energy and power dense exist, they are much more expensive. The life and usable capacity of batteries are negatively impacted by power impulses. Battery packs in electric vehicles (EV) are typically oversized to be able to provide enough power during these impulses experienced when the vehicle accelerates. An additional EES with a high power density, such as an ultracapacitor, can be used as a buffer to provide power during power surges to reduce the power impulses experienced by the battery. Isolating the battery from the power impulses would allow the EV to utilize more energy dense batteries, increasing the range of the EV as well as increasing the lifetime of the utilized batteries. A hybrid energy storage system (HESS) allows one to utilize the complimentary characteristics of both the battery and ultracapacitor in one system. The method proposed uses a fuzzy logic controller, multiple dc/dc converters, batteries and ultracapacitors in a HESS to minimize the power impulses experienced by the battery, thereby increasing the usable capacity of the battery, whilst being able to deliver high amounts of power for short durations