Research On Control Strategy Of Braking Energy Recovery For Hybrid Commercial Vehicles

Vigorously developing new-energy and energy-saving vehicles are the responses to energy and environmental protection which are two major issues faced by the countries all over the world.Energy recovery technology during the braking process is effective to achieve energy conservation and emission reduction for new energy commercial vehicles.It is significant for braking safety,vehicle economy and ride comfort.This paper has taken the composite braking system of hybrid electric commercial vehicles as the research object and studied on the control strategy of braking energy recovery.The estimation models for vehicle load and centroid position were established,so that the formulated control strategy could adapt to the changes of vehicle load.A multi-objective optimal braking force distribution strategy was developed based on comprehensive consideration of braking safety and energy recovery.It used the feedforward-feedback controller based on PID and slip rate controller to coordinate the braking force of the composite braking system dynamically,and improved the braking ride comfort.Finally,effectiveness of the control strategy was verified by Simulink software.Specific research contents were as follows:(1)The longitudinal dynamics of the vehicle was analyzed.The vehicle dynamics model was established,and adopted the modular modeling method to model the vehicle power and transmission components.A rule-based vehicle torque management strategy was established.Combined with the working characteristics of engine and motor,the working mode division and torque distribution rules of hybrid commercial vehicles were designed.(2)The influence of braking regulations,vehicle loads,motor’s and battery’s characteristics,braking strength,vehicle speeds and other factors on energy recovery system were studied.The estimation methods of vehicle mass and centroid position to meet the simulation requirements were designed.The access conditions for vehicles to enter the energy recovery mode were formed,as well as the constraint space of braking force distribution coefficient and motor’s braking torque were achieved.The general law of energy recovery varying with braking intensity,vehicle speed and battery charge was established.(3)Braking force distribution strategy was researched.A multi-objective optimization model with braking force distribution coefficient and motor braking torque ratio as control variables was established to comprehensively consider braking safety and energy recovery.Genetic multi-objective optimization algorithm was used to obtain a set of optimal solutions that meeting the conditions.The ideal solution method based on fuzzy controller was to make decision meeting the braking demand.Simulink software was used for modeling and simulation,and common driving cycles were used as the inputs,to verify the superiority of the control strategy.(4)Dynamic coordination strategy of braking force was studied.According to the different response characteristics of the two different braking systems,a feedforwardfeedback based on PID controller was established.The motor’s force was regarded as a disturbance signal which was suppressed and eliminated by feed-forward braking.It has improved the response speed of the system;And the closed-loop control of total braking force on the driving wheels was achieved by using PID feedback control.Pneumatic braking torque was used to compensate motor braking torque.Combined with the slip rate controller,through monitoring the slip rate of front and rear wheels in real time,the braking forces of each wheels are dynamically adjusted to improve the braking stability of the system.