Energy management of electric vehicle supplied from battery /ultracapacitor hybrid energy storage system

Researches about alternative energy resources have been increased due to declining patrol reserves, increasing emission of exhaust gases as global warming alerting. For this aim, studies on electric vehicles are strongly motivated in recent years. The main energy source of the electric vehicles are batteries but they don't have high specific power so they cannot give high currents that often needed. Batteries can be damaged and their life are shortened in case of deep discharge and excessive charge. Ultracapacitors are attracts interest of researchers to improve drawbacks of the batteries as an energy storage device. It is proved that hybrid energy storage systems consist of battery and ultracapacitor can improve these drawbacks. When speed of a vehicle is decreased, for instance braking or driving at declining road, there is important kinetic energy which can be regenerated. In this study, regeneration of this energy and storing it in the battery and/or ultracapacitor via bidirectional converters are investigated. Firstly, electric vehicles are examined. Mechanic constructions of them, their power transmission devices and mathematical model of them are studied. Cell technologies of batteries and ultracapacitors are investigated. Protection and management systems for hybrid energy storage systems consist of battery and ultracapacitor are studied. Power converters are investigated to manage energy flow between storage devices and to control vehicle via electric motor. Forces acting on a vehicle dynamics are mathematically examined and simulated in 'MATLAB/Simulink' package program. Studies in literature about bidirectional power converters are investigated for energy management of hybrid energy storage systems. Ultracapacitor is used as secondary energy storage device supporting main energy source. By controlling cascade converter coupling ultracapacitor with battery, the current of the motor is participated by ultracapacitor and voltage of battery is not allowed to excessive fluctuations. Peak battery currents are reduced for efficient use of battery. It can be said that, battery is saved from deep discharge and excessive charge and its life is prolonged. Keywords: Electric vehicle, hybrid energy storage systems, battery, ultracapacitor, cascade DA/DA converter