Cooperative Control Of Regenerative Braking And Electromechanical Coupling Systems Of Electric Vehicle

Regenerative braking is one of the key technologies of new-energy vehicles to improve the energy efficiency.In order to improve the efficiency of regenerative braking,the distribution of regenerative braking force and hydraulic braking force should be optimized to maximize the motor braking force.On the other hand,cooperative control of motor braking and transmission system is needed to expand motor's high efficiency area.In order to ensure braking safety,cooperative control between ABS and regenerative braking system is needed to make vehicles remain stable in emergency braking.A hardware-in-the-loop platform for regenerative braking tests is built based on Electronic Stability Control(ESC)hardware and Automated Mechanical Transmission(AMT).The regenerative braking strategies are implemented in ESC controller.The vehicle dynamics model is replaced by CarSim vehicle model,which runs on lower computer in real time.This HIL platform can provide a complete running environment for regenerative braking controller of real vehicles,which helps to realize high precision simulation tests.This paper studies the downshifting control of an electric vehicle with a two-speed AMT during regenerative braking process,and a hierarchical control strategy is brought forward to give a systemic solution to the cooperative control of motor,AMT and hydraulic braking system.In the upper controller,a series distribution strategy is proposed to distribute the braking force between motor and hydraulic braking system,and an off-line optimization and on-line look-up table method is proposed to obtain optimal downshift point in real-time.In the medium controller,a nonlinear sliding mode observer(SMO)is designed to estimate the hydraulic brake torques of front and rear wheels.In the lower controller,cooperative control of regenerative braking and hydraulic braking is given,and a resembling pulse width modulation method is proposed to regulated the hydraulic brake torque.The proposed algorithm helps to improve the efficiency of regenerative braking and expand the high efficiency area of the motor.A switching compensation control strategy is proposed to realize the cooperative control of regenerative braking and ABS.In normal braking condition,the hydraulic braking is used to compensate for the motor braking,which can maximize the recycled energy while meeting driver's braking demand.In emergency braking condition,the motor braking is used to compensate for the hydraulic braking,which helps to eliminate side effects caused by hysteresis characteristic of hydraulic braking system.The proposed algorithm helps to enhance the control effect of ABS while maintaining the regenerative braking efficiency.Performance of the proposed downshift strategy is verified through MATLAB/Simulink and HIL tests.The results show that the proposed strategy is effective in improving the regenerative braking efficiency under different conditions.Performance of the proposed cooperative control strategy of regenerative braking and ABS is validated through CarSim-MATLAB/Simulink.The simulation results show that the methods presented are effective in compensating the hysteresis characteristic of hydraulic braking system,thus enhancing the control effect of ABS in transient condition.