Alternative Energy Storage System for Hybrid Electric Vehicles

In this thesis an alternative energy storage system in the drive train of a hybrid electric vehicle is investigated. In particular, it concentrates on the potential reduction of the stresses of the battery when electrochemical capacitors, a.k.a supercapacitors, are added as a high power energy storage. The energy storage system is described and a simplified drive train is simulated in the simulation software MATLAB®/SIMULINK®. Different control strategies are tested and an estimation of the performance is given. With the simulation results at hand, a downscaled HEV drive train consisting of NiMH batteries, electrochemical capacitors, a DC/DC converter and an external load, is built and tested. A comparison between simulated and experimental results is made, in terms of estimated battery stresses and efficiency. The results show a significantly reduction in battery stresses and a good agreement between the models used in simulations and the laboratory system. To further investigate the potential of a battery-electrochemical capacitor system, a full-scale system for a city bus is dimensioned and simulated. This simulation shows that the total weight of the energy storage system could be reduced significantly when batteries are combined with a bank of electrochemical capacitors. Moreover, an increased durability of the battery would be expected by this alternative energy storage system