An Improved Energy Management Strategy for a Battery/Ultracapacitor Hybrid Energy Storage System in Electric Vehicles

Battery/Ultracapacitor (UC) Hybrid Energy Storage Systems for Electric Vehicles have been proposed to increase battery cycle life and driving range. Existing works focus on power management strategies of the battery and UC, while energy management strategies are still relatively empirical. We propose a more rigorous method of setting the target UC energy level using a speed-dependent band. This allows the UC to contain sufficient energy for future accelerations, and have sufficient capacity to store energy from future regenerative braking. Furthermore, by adjusting the band height, the UC size in terms of energy stored can be reduced significantly. We show other works cannot achieve both goals simultaneously unless their UCs are sized larger (up to three times).