Study On The Control Strategy Of Hybrid Electric Vehicle Based On Instantaneous Optimization

Facing the two serious problems of oil shortage and air pollution, which are against the sustainable development of the global automotive industry, hybrid electric vehicles (HEVs) have been accepted world wide as one of the most feasible solutions to the problems. Because of incorporating the advantages of both the battery electric vehicle and the conventional internal combustion engine (ICE) vehicle, it is of high fuel efficiency, low emissions, long driving range, and affordable price. In some west countries that have advanced automotive industry, governments and automobile manufacturers have invested a lot for the development of HEVs. The Ministry of Science and Technology of China has also set the development of HEVs and HEV components as one of the most important sub-projects in the 863 Program.The driving cycle, parameter design and control strategy are the key technologies of HEVs, they interact. Driving cycle is the base of parameter design, control strategy development and vehicle performance evaluation; parameter design determines the most energy-saving potential of design proposal in the target driving cycle; the characteristic of control strategy will determine degree that the control strategy brings into play the energy-saving potential of design proposal. How to evaluate the energy-saving potential of certain design proposal and development degree of certain control strategy is an important study aspect of HEVs. With the hybrid drive train parameter optimization design and control strategy study and application project of the national 863 Program as its background, the main topic of this study is the evaluation of parameter design energy-saving potential and the control impact of control strategy and the development of control strategy based on instantaneous optimization control strategy.First of all, hybrid electric vehicle instantaneous optimization control strategy was built based on the Instantaneous Equivalent Consumption Minimization Strategy (ECMS). Energy flow routes of basic operating mode and efficiency characteristics of hybrid electric vehicle drive train main components were analyzed. The use of electric energy of battery at the present time was divided into electric energy future compensation and future consumption mode, to represent complex operating modes of battery during the driving cycle of HEV. The equivalent fuel consumption of battery electric energy in the two modes is calculated based on Energy Saving Mechanism and the efficiency characteristic of HEV. After taking into account battery SOC sustaining and, the free energy receiving from regeneration brake, the expression of equivalent instantaneous fuel consumption was built.Based on ADVISOR and modeFRONTIER joint simulation and optimization platform, energy-saving potential of certain parameter design of HEV bus was study. Instantaneous optimization control strategy worked as evaluating control strategy, battery energy future compensation equivalent fuel consumption conversion factor f eq _dis and future consumption equivalent fuel consumption conversion factor f eq _chg worked as control optimizing parameters. The energy-saving potential of the parameter design in the Beijing city bus driving cycle was obtained, it was on the level of present HEV energy management control strategy.Based on the joint simulation and optimization platform, the control parameters of logic threshold control strategy were optimized, to obtain the best fuel economy of parameter design in the Beijing city bus driving cycle. This value was the real fuel economy of the energy-saving potential of the parameter design exerted by logic threshold control strategy. The ratio of this value and the energy-saving potential was regarded as benchmark an index to evaluate the control efficiency of HEV control strategy.Real time control strategy that could be used for real vehicle was developed based the control rules from instantaneous optimization control strategy. By assuming SOC was always target value and not taking into account free energy from regeneration braking, simplifying the instantaneous optimization control strategy, the engine driving torque was attained at each required driving speed and torque. The developed new HEV control strategy determined engine driving torque based on present required driving speed and torque by looking up table. Then, the control strategy adjusted engine output torque based on the difference of present battery SOC and target SOC, to sustain the balance of battery energy. At last, the performance of the developed new HEV control strategy were validated, it could improve the fuel economy of HEV.The thesis is about the key technologies of HEV from the 863-project, which provides the foundation for the parameters design and control of HEV. At the same time the research achievement is the basis for the acceleration and grasp of independent development, and is also the embodiment of the significance for this thesis.