Design and control strategy for a new hybrid energy storage system

In this paper, a new hybrid energy storage system (HESS) with batteries and ultracapacitors (UCs) is proposed. The proposed topology adopts a smaller power capacity bi-directional dc-dc converter compared with the traditional HESS by adding two switches and diodes. The cost, volume and weight of the whole system can be reduced while the power demand of DC bus is satisfied. Three working modes of the proposed HESS are discussed in detail in this paper. In addition, new control strategy for the proposed HESS is presented based on the last step working conditions and the next step power demand of DC bus. The control strategy is to choose a right operation mode and distribute the power between the battery bank and the UC bank. The proposed control strategy insures no current shock happens during the process of mode switching while the battery bank and the bi-directional dc-dc converter work within the power limitation. Both of the structure and the control method are proved to be viable by the simulation and experimental results.