| Faced with the increasingly prominent contradictions between rapid development of China's automobile industry and environmental pollution issue, electric vehicle(EV), as it's zero-emission characteristic, is attracting more and more attention of Chinese government. The development of new energy vehicle such as EV has become an important direction of the automobile industry. In the research of new energy vehicle, regenerative braking technology is one of the key technologies. At the beginning of regenerative braking and driving of EV, the traction motor will generate high current which will greatly affected battery life. In order to solve the life problem of high power charging and discharging of battery, a hybrid energy storage system is usually adopted. The super capacitor has the advantages of high power density, short charge and discharge time, and so on. But the resistance is small and it is not easy to manage battery as well as parameters matching. There are also disadvantages such as poor safety, high cost and so on. By contrast, there is no electrical connection between the hydraulic system and the accumulator in the battery-hydraulic hybrid energy storage system which also has characteristic of high security as well as the advantages of super capacitor. Moreover, the cost of it is relatively low and technology is mature.A Changan's vehicle is selected to be application object, an electro-hydraulic hybrid powertrain system(EHHPS) of vehicle is designed based on the systematic study on braking process of the electric vehicle and the composite energy storage system. Parameters matching, regenerative braking control strategy formulation, system modeling comprehensively and co-simulation analysis for this system are carried on. The main research works of this paper are as follows:(1) The most suitable powertrain for this study is confirmed and the control circuit scheme of this system is designed after analyzes the characteristics of different EHHPS structure.Then the parameters matching design of the key components from this system is carried out by using the parameter matching method based on cyclic condition, include traction motor, battery, hydraulic pump/motor(secondary component), accumulator, transmission and so on.(2) In order to gain the maximum regenerate braking energy based on the condition of vehicle braking safety, the front and rear axle braking force distribution, the braking intensity threshold value and brake mode decision strategy are determined according to the braking regulation and dynamic conditions based on the analysis of vehicle braking process. Then high and low braking intensity control strategy and Fuzzy-PID ABS control strategy are formulated under these conditions.(3) Vehicle model, traction motor model, battery model, control system model, coupling mechanism model and tire road model are designed based on Matlab/simulink; Friction braking system model and hydraulic regenerative braking system model are designed based on AMEsim,the feasibility of this system is analyzed through the AMEsim-simulink co-simulation platform on this basis.(4) Firstly, the dynamic response and efficiency of hydraulic regenerative braking system under the condition of driving and braking are analyzed.Secondly, the dynamic response of the hydraulic control unit under the sine excitation is analyzed.Lastly, on the basis of different road adhesion coefficient and braking intensity, the proposed control strategy is simulated and analyzed based on the established co-simulation model.In this paper, an electro-hydraulic hybrid powertrain system is designed and parameters are matched, the regenerative braking control strategy for electro-hydraulic hybrid powertrain is proposed. The hydraulic system and the battery system are well coordinated, which can not only avoid the influence of large current charge and discharge on the life of power battery, but also increase the driving range of the electric vehicle.The whole work provides a new idea for the design of regenerative braking system of electric vehicle, and has a good application prospect. |
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