HESS and Its Application in Series Hybrid Electric Vehicles

The combination of batteries and ultracapacitors has become an effective solution to satisfy the requirements of high power density and energy density for the energy storage system of electric vehicles. Three aspects of such combination are introduced. First, an integrated optimization framework is proposed and implemented to optimize the battery’s and ultracapacitor’s voltage level for the four typical hybrid energy-storage systems (HESSs). The optimized voltage levels of the batteries and ultracapacitors in each topology indicates that a higher voltage level usually results in better system performance. The advantages and disadvantages of the four topologies are summarized through evaluation of the efficiency and operating currents of the batteries and the ultracapacitors. Second, one of the HESS topologies is selected as the target system and its control strategy is optimized with the consideration of different battery states of health and temperature. Third, a case study of the application of HESS in hybrid electric vehicle is introduced and its control strategy is optimized. In the optimized control strategy, the output power between the battery packs and ultracapacitor packs is regulated by the model predictive control strategy, while the output power between the APU and HESS is allocated by a rule-based strategy.