Optimal Design and Management of a Hybrid Energy Storage System

Electric Vehicles (EVs) are powered by a large number of battery cells, which must be managed effectively/efficiently to deliver the required power/energy during their warranty period. An EV's operation requires large and fluctuating power from its battery pack, but its battery cells have only limited tolerance to (dis)charge stress, accelerating their degradation. Moreover, battery cells have different (dis)charge stresses depending on their physical positions in the battery pack, causing different degradation rates and thus the unbalanced State-of-Health (SoH) or State-of-Charge (SoC). To address this problem, we design, implement and evaluate a novel energy storage system with energy buffers and an SoC-balancing circuit, to extend both the battery life and EV's operation-time. We first design a hybrid energy storage system that efficiently meets the EV's representative power requirement. We then develop an optimal power distribution to minimize the EV's energy consumption and its battery cells' stress. We prototyped and evaluated this solution, demonstrating a reduction of discharge/charge stress by about 21.8%, and thus extending battery lifetime while balancing cells' SoC.