Research is under way for a possible hybrid battery/ultracapacitor system that would be used in small electric vehicles.
Representatives from Aalborg University in Denmark and the Illinois Institute of Technology presented a paper on the work at the SAE 2009 World Congress. The system allows the batteries to function as the main energy storage source of the vehicle supplying average power to the load. The ultracapacitors then are used to meet the power demands during transients.
During the course of the study, the researchers were able to connect the battery pack and ultracapacitor in parallel to the DC link using bi-directional two quadrant buck-boost converters. The system is then controlled using a power flow management methodology based on load demand.
The vehicle target is a small electric vehicle, similar to a neighbourhood electric vehicle, with a speed limit of 25-31mph and weight at around 800kg.
According to the initial results of the study, the power management based on hybrid system reduces the stress in the battery current without a drop in performance. This provides a reduced battery size with a longer lifetime.
