This work presents a multi-objective optimization based design method for battery/ultracapacitor hybrid energy storage systems used in electric vehicles. Long life mileage and low normalized cost are our optimization objectives. Firstly, the degradation model of lithium-ion battery and a rule based power splitting strategy are introduced. Then the multi-objective optimization is formulated to solve the optimal size and control parameters simultaneously. Finally, the solutions from the Pareto front are compared with the battery only system. The results show that the proposed design method can significantly reduce the battery’s degradation, with a whole life mileage increased by over 26%. Meanwhile, the recommended size of the hybrid energy storage system brings a normalized cost increase by 29.1%.
Keywords lithium-ion battery, hybrid energy storage system, energy management strategy, multi-objective optimization