Regenerative Braking Control And Driving Efficiency Analysis Of Electric Vehicle With Series Composite Power Supply

The development of electric vehicle is restricted by problems such as short driving range and short battery life.Super capacitor has the characteristics of high power density and fast charge-discharge.Combining super capacitor with battery into a composite power supply as vehicle energy storage device.The battery working environment and energy utilization of electric vehicles can be improved.Aiming at the composite power supply composed of battery and super capacitor,a passive series topological structure is proposed.Based on the structure,the regenerative braking system of electric vehicle is designed,the current control in regenerative braking process is studied.The driving test of composite power is carried out in order to use the recovered energy for vehicle driving.The driving efficiency of the series type composite power supply is analyzed.The main work is as follows:The components of the composite power system of electric vehicle are described.The commonly used topology of composite power supply is compared,and a passive series structure is proposed.According to the current flow direction of the main circuit,4 working modes of the system are divided: No regenerative braking deceleration mode,normal regenerative braking mode,composite power driving mode and battery independent driving mode.On this basis,the control logic of series composite power system is proposed.The regenerative braking system model is established,and the current control strategy in regenerative braking process is proposed.The control method based on fixed duty ratio is simple which can roughly distinguish different electric braking intensity,but the braking current decreases with the vehicle speed.The constant current control based on super capacitor SOC can change duty cycle according to the change of vehicle speed and capacitor voltage,so as to maintain constant braking current.In the MATLAB/Simulink environment,the simulation of regenerative braking process is carried out,the feasibility of the two control strategies is verified.The function requirements of control system are analyzed.Based on Atmega16,the hardware system,software system and host computer program are designed,and the vehicle test is carried out.The regenerative braking effect is analyzed through 30%,60% and 100% fixed duty cycle tests.When the initial vehicle speed is 30km/h and the initial super capacitor voltage is 10 V,the recovery efficiency of the system is up to 51.2%.On this basis,the constant current control test of 50 A and 70 A is carried out.In the effective regenerative braking interval,the duty cycle continues to increase to keep the current constant.The test results conform to the simulation and the effectiveness of the constant current control strategy is verified.The driving test of series composite power supply is carried out on the bench.The accelerated test shows that the series composite power supply can effectively consume the capacitance energy for driving,reduce vehicle acceleration time and improve the maximum speed.ECE city test shows that the series composite power supply system can save energy 41.2kJ per kilometer,the contribution rate of driving mileage reached 13.7%.The research shows:the series composite power supply system has the advantages of simple structure,small volume and uncomplicated control strategy.In the regenerative braking process,all energy is recovered to super capacitor,the battery working condition is improved and the regenerative braking process is not restricted by battery SOC.In the driving process,the energy of super capacitor is consumed quickly,the efficiency of the battery is promoted.The application of series composite power system to electric vehicle can achieve ideal recovery efficiency and increase driving range.