Research On Coordinated Control Of Electro-hydraulic Composite Brake Based On Distributed Electric Drive Vehicle

The integration of the electric motor of the distributed electric drive vehicle in the wheel improves the transmission efficiency.The advantages of regenerative braking with all four wheels can greatly improve energy efficiency and improve vehicle economy.Friction braking is the main braking method of the vehicle,and its reliability is also a guarantee for the safety performance of the vehicle brake.Therefore,the electric vehicle brake system has to select the composite brake system composed of feedback brake and friction brake.The existing composite brake study considers the motor and hydraulic brake as a static model,focusing only on the braking torque distribution strategy.However,the mechanism of motor regenerative braking and hydraulic friction braking is different,and the dynamic characteristics of the two are quite different.The dynamic response process of regenerative braking and friction braking has a great influence on the braking performance of the vehicle.Therefore,it is very necessary to study the dynamic coordinated control method between regenerative braking and friction braking.(1)Research on pressure control of electronic hydraulic brake system.For the electro-hydraulic brake control process,the simulation model of the electronic hydraulic brake system is established based on Simulink\Simscape,including the fast switch valve,accumulator,and brake wheel cylinder model.The research on the pressure-reducing characteristics of the wheel cylinder under the PWM control of the fast switching valve was carried out.Based on the characteristics of the wheel cylinder,the bang-bang controller and PID controller are designed for fast and precise control of wheel cylinder pressure.The advantages and disadvantages of logic threshold control and PID control for realizing the ABS function of the car are analyzed.The research results show that the rate of change of the wheel cylinder pressure can be effectively controlled by adjusting the duty ratio of the fast switching valve;PID control can meet the requirements of electro-hydraulic composite brake for precise control of wheel cylinder pressure;Both the logic threshold control and the PID control can realize ABS function;The logic threshold parameter depends on the test,and the brake distance controlled by the PID is less than the logic threshold control.(2)Research on vector control and characteristics of PMSM.For the regenerative braking process of PMSM,the simulation model of PMSM vector control is established based on Simulink\Simscape.The effects of IGBT voltage drop and power supply harmonics on the control characteristics of the motor braking torque are analyzed.The research results show that the PMSM has 6 times and 12 times of torque ripple,which is mainly related to the IGBT voltage drop and modulation algorithm.The motor torque ripple frequency is low at low speeds and the pulsation amplitude assembly causes large longitudinal force fluctuations of the tire;Braking power consumption at low speeds of the motor is not conducive to improving the cruising range,so the motor should not be used for braking at low speeds.(3)Research on Electro-hydraulic Compound Braking Coordination Control Algorithm.For the electro-hydraulic compound braking process,the dynamic characteristics of braking torque of the regenerative braking of PMSM and the friction braking of the electro-hydraulic braking system are studied.Three composite braking torque distribution algorithms are summarized.Based on the model predictive control,a dynamic braking torque dynamic allocation algorithm is designed to realize the coordinated distribution control of composite braking torque.The research results show that the dynamic torque distribution algorithm has higher energy recovery efficiency and better dynamic performance.(4)Research on hierarchical control structure of distributed drive vehicle brake system.Taking the distributed electric drive vehicle as the research object,the hierarchical control structure of the whole vehicle brake system is designed.The brake system is divided into a four-wheel torque distribution module(upper-level controller),a slip ratio monitoring module and a dynamic torque distribution algorithm(middle-level controller),and a motor controller and an electro-hydraulic controller(underlayer actuator).Based on the ideal braking force distribution,a four-wheel torque distribution module is designed for the calculation and distribution of the four-wheel desired braking torque.Based on the pole placement method,the slip ratio monitoring module is designed to implement the ABS function.The research results show that the brake system layered control structure can achieve the braking function well;The vehicle brake layering control system has better torque tracking accuracy and higher energy recovery efficiency in conventional braking;Better dynamic response in emergency braking can effectively shorten the emergency braking distance and improve braking safety.