Optimization Of Regenerative Braking Strategy For A Medium HEV At Cruising Downhill

Hybrid electric vehicles (HEVs) is a type of vehicles combining the traditional internal-combustion vehicles and pure electric vehicles, which inherits the advantages of low missions and high efficiency of electric vehicles, and keeps the excellent performance and long driving distance of traditional internal-combustion vehicles . It is an effective tool to solve the energy shortage and improve the environment. HEVs is presently a new generation of clear vehicles that is most feasible and capable of mass production.Regenerative braking is one of key technology for HEVs, which has a direct impact on fuel economy, emission and driving security. When HEVs is braking, the kinetic energy or potential energy of vehicles is converted to electrical energy to store in battery packs by generator, which realizes the energy recover and produces the required whole braking forces or partial braking forces at the same time. The braking and deceleration are not only realized, the fuel consumption and emission are also decreased effectively.Optimization of regenerative braking strategy for a medium HEV at cruising downhill was studied. The dynamics of hybrid electric vehicles for regenerative braking process at cruising downhill was analyzed. Based on the charging efficiency, temperature model of battery and efficiency model of generator, instantaneous and global optimal control strategy were proposed, with the target of maximum of instantaneous regenerative braking energy and total regenerative braking energy of HEVs respectively. The efficiency of regenerative braking energy at roads with different slope and slope length was calculated. The results show the global optimal control strategy is better than the instantaneous optimal control strategy, as the temperature augment of battery is effectively controlled by global optimal control strategy, and the efficiency of regenerative braking energy is enhanced. The results also show the larger of slope or the longer of slope length, the more distinct of increase of efficiency of regenerative braking energy for global optimal control strategy is. The influence of battery temperature on efficiency of regenerative braking energy of HEVs was also discussed according to the results. The influence of vehicle speed on efficiency of regenerative braking energy of HEVs was analyzed. The research show that when the slope and slope length is constant with vehicles speed at a certain speed range, the efficiency of regenerative braking energy of both global and instantaneous optimal control strategy reduces with the rising of HEVs speed, and the optimal control effects of former is better than the latter one.