Research On Regenerative Braking Charging Safety And Braking Stability For Battery Electric Vehicle

Battery Electric Vehicle(BEV)holds a central position in the development of new energy vehicles due to its simple structure, zero emission and high energy utilization characteristics. Energy management is a key technology of the BEV development, and Regenerative Braking(RB) that improves vehicle economy and prolongs driving range plays an important role in energy management procedure. RB control is a multi-objective dynamic procedure which involves in battery charging safety, vehicle braking stability and energy recovery rate, etc. The RB control target is to recover maximum energy under the precondition of safety.Safety and Stability control of RB is the frontier technology in the field of BEV. This thesis is supported by Chongqing Natural Science Fund Project “electric vehicle powertrain matching optimization and integrated control”(2011BA3019) and conducted with the cooperation of Changan automobile company. It carried out a research on coordination control of regenerative braking charging safety, electric-hydraulic joint braking stability for BEV. The study involves in baking force distribution, battery charging safety as well as the coordination control of RB and ABS/ESP. The main works are as follows:① Based on the effect factors analysis on RB energy recovery, an ideal braking force distribution based braking force distribution method is raised. The effect factors include braking force distribution relationship, braking stability, braking strength as well as motor and battery. And energy recovery rate is determined to be the evaluation index of energy recovering ability.② The motor working efficiency is obtained by motor bench test, and the maximum motor output torque is constrained by motor generating efficiency and motor temperature. And from the analysis of battery charging-discharging characteristics, the motor braking torque is also limited by the battery charging current. The joint working curve of the motor and battery is optimized to get the optimum joint working efficiency with maximum braking energy recovery. On this basis, the optimum Pareto motor barking torque is derived using intelligent optimization algorithm.③ On the basis of battery charging-discharging characteristics as well as battery open-circuit-voltage(OCV) characteristics’ analysis, a battery real-time thermal model is established with integration of vehicle driving model. And a battery charging current active control method is proposed to manage battery temperature rise. Through the combined model, the battery real-time thermal response is achieved. Simulations under typical driving cycles are carried out and the results show that the effect of regenerative braking on battery thermal response lies in the charging current and charging time. The active control of battery charging current is realized by a fuzzy logic controller, which can adjust the ratio of motor braking force. The input of the fuzzy controller is battery SOC and temperature, and the output is motor braking force ratio. The simulation results indicate that by the active control method, the proportion of large charging current is decreased and small charging current is increased, the temperature rise is lowered effectively.④ Modeling work is carried out, including braking force model, slip rate model, magic formula tire model as well as hydraulic braking system model. A coordination control strategy of electric and hydraulic anti-block braking is proposed for the front tire, the electric and hydraulic braking force is coordinated through the model based self-adapting filter. In order to make fully utilization of road adhesion, the braking force distribution control is turned into slip ratio distribution control. The stability and ride comfort is improved due to the proposed control scheme.⑤ A 9-DOF corner braking force model and longitudinal-lateral joint tire model are built, and the relationship between the longitudinal and lateral as well as the slip ratio is achieved. A joint braking stability control strategy of ESP and motor is proposed, and a yaw moment fuzzy controller is designed to acquire revision yaw moment. The revision yaw moment is applied by adjusting the longitudinal force of the tire to keep vehicle stable.Finally, with the coordination controller centered, the motor and battery system as well as vehicle stability module are associated and constrained. The object of the proposed control algorithm is to achieve optimal individual function. Simulation results show that the battery temperature and vehicle stability are improved to some extent.