| Electric vehicle,as a new type of modern means of transport,it has environmental pollution free,energy diversification,and simple structure,so it has become the development trend of modern cars gradually.However,its driving range is not ideal,which affects the large-scale promotion of electric vehicles seriously.Increasing power and driving range is a key issue to be solved in the future development of electric vehicle.Regenerative braking technology is to maintain the electric vehicle under the premise of stable braking,and the vehicle's braking kinetic energy can be transformed into electrical energy stored in the energy source device by the regenerative braking system,which can extend the electric vehicle driving range.Therefore,the research of regenerative braking technology is great significant to the development of electric vehicles.The focus of this paper is on a precursor type electric vehicle.During the electric vehicle braking process,the dynamic optimization for braking force distribution and the braking control algorithm is designed in this paper,under the premise of ensuring the braking stability and safety.The proposed regenerative braking control strategy can recover more braking energy and it can be used to improve the vehicle regenerative braking process.The main research contents are as follows:(1)The optimization braking force distribution algorithm with variable ratio is designed during the electric vehicle braking process.In order to enhance the braking safety,the changes of brake strength are considered in this paper,and an optimization algorithm for braking force distribution is designed.The method is the variable ratio method,and it can change the braking force distribution rate of front and rear axles according to the brake strength variation,so its braking effect can be optimal.Through the theoretical calculation of electric vehicle braking performance,the stabilization and security of the optimization braking force distribution algorithm with variable ratio was verified.(2)Experimental study on the charging and discharging properties of Li Fe PO4 batteries for electric vehicles.In this paper,a series of charge and discharge experiments were done on 38.4V/40 Ah Li Fe PO4 batteries with ARBIN power battery test system.And the charge and discharge efficiency properties were analyzed with various current and SOC.The theoretic model and fitting model for battery efficiency are deduced based on the test results,and the fitting model formula is verified with new test data.(3)Test on driving and braking efficiency of motor system for electric vehicle.Experimental bench was set up based on two 6k W permanent magnet synchronous motor in this paper,the driving and braking characteristics of the motor system of the electric vehicle are tested under the condition of speed 500r/min-4000r/min and torque 5Nm-30 Nm.Solve motor driving and braking efficiency of motor system according to the test results,In addition,based on the Ordinary Least Squares,the relationship of motor drive system efficiency and brake system efficiency versus motor speed and torque was established by the method of fitting the experimental data curve.And the driving and braking efficiency model of the motor system are valid according to the experimental data fitting.(4)Formulate the control strategy of regenerative braking.In order to adapt to the effect of the changes of brake strength on the regenerative braking force distribution,a regenerative braking control strategy is proposed in this paper.For the regenerative braking strategy,the braking force distribution strategy of front and rear axles is optimized based on brake strength,and the restriction of ECE R13 braking regulations,the motor features and battery features on energy recovery are considered.(5)The modeling and simulation of Regenerative braking control strategy.The simulation model of the regenerative braking system was built in Matlab/Simulink by combining the test data with math models,and the simulation was done with international UDDS and NEDC drive cycles.The simulation results show that,under the premise of ensuring the braking stability and safety,the proposed regenerative braking control strategy can recover more braking energy and it can be used to improve the vehicle regenerative braking process.The features and innovation in this paper:(1)In order to further improve the vehicle braking stability and braking efficiency during the electric vehicle braking process,an optimization braking force distribution algorithm with variable ratio based on brake strength is designed in this paper,effectively improving the braking efficiency of the electric vehicle.(2)Through analyzing the influence factor of energy recovery,the characteristics of power battery and charging and discharging efficiency and motor driving condition and the efficiency of the braking condition were studied respectively.The built efficiency fitting model formulas can be used to optimize the electric vehicle performance on various driving conditions.(3)A regenerative braking control strategy is proposed in this paper.For the regenerative braking strategy,the braking force distribution strategy of front and rear axles is optimized based on brake strength,and the restriction of ECE R13 braking regulations,the motor features and battery features on energy recovery are considered,which can improve the braking energy recovery effectively. |
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