Braking Energy Recovery For Electric Vehicle With In-Wheel Motor Based On Model Predictive Control

With the promotion of energy conservation and emission reduction policies,the green travel concept has taken deep roots into the human mind.The popularity of high efficient and zero-polluting electric vehicle(EV)is imperative.EV charging infrastructure is gradually improving,but its disadvantages of battery cost and driving range are still not resolved perfectly.Braking energy recovery technology is the key technology of EV.The technology can extend driving range,provide a certain amount of braking torque,reduce the wear and heat recession of traditional braking system and improve braking security.So the reasonable and perfect control technique is the guarantee for EV to achieve maximal energy recovery in safe braking conditions.The research of braking energy recovery control system has important theoretical significance and practical value of engineering application.Both automakers and related scientific institutions strengthening their research and development.However the control problem of braking energy recovery system is so complex that many control methods can hardly achieve the ideal effect in practical engineering,and belongs to a constrainted multi-objective optimization problem.In view of the complicated control problem such as improve energy recovery’s effect,reasonable distribute braking force and ensure braking safety and stability,a braking energy recovery control system is designed for EV with in-wheel motor based on model predictive control(MPC)in this paper.MPC can effectively solve multi-objective constrainted problems.The core control problem of energy recovery is how to distribute and coordinate braking force to get more regenerative energy under the precondition of safety and stability.In order to ensure brake efficiency and stability,this paper introduced the limits of ideal braking force distribution curve and ECE regulations;Due to the physical limits of brake actuators,the actual motor and hydraulic braking torque are limited within maximum output torque.When the speed is very low,generating capacity of motor is limited.So the limit of motor speed is considered.The limit of battery SOC as threshold constraint is achieved outside of MPC algorithm.Motor and hydraulic braking system can collaborative work under the action of objective function.The ability of energy recovery is improved under the condition of satisfied driving requirement and braking stability.A high precision EV with in-wheel motor model built in AMESim software is used to verify the effectiveness and superiority of the proposed control system.The main contents of this paper:1.The whole vehicle model is built in AMESim according to structure characteristics of EV.This section focuses on parameters matching and dynamic performance analysis of key components.The simulation calibration map of motor efficiency is used to realtime get motor current optimum efficiency and optimize motor braking torque in MPC.Charging and discharging characteristics of battery are verified by real experimental data.The dynamic response characteristics of hydraulic braking system are analyzed.Finally the functional verification of vehicle model shows that the model considered output time delay of braking torque can better simulate the actual engineering situation.2.Based on the particularity of braking energy recovery system,this paper designs a braking energy recovery control system by introducing the idea of MPC rolling optimization control.The established mathematical model of control system is used to integrated control braking torque.The selected objective function include tracking of required braking torque,energy recovery efficiency and braking torque ripple,respectively used to meet the demand of driver braking,maximize recycling energy and ensure braking comfort.The motor and hydraulic maximum output braking torque limitation are considered as timevarying constraints,and limits of ECE braking regulation and motor lower limit speed are introduced at the same time.In addition,the constraint of battery highest SOC is also added to ensure safety.3.The co-simulation solution of AMESim and Matlab/Simulink is adopted for control system requirements.Combined with their respective advantages to establish the simulation conditions in AMESim and design control system in Simulink.The validity of the MPC control system is verified by simulation test of braking safety,stability,comfort and energy recovery effect.Finally,the comparison simulation experiment with braking energy recovery fuzzy control system proves that the application of MPC can greatly enhance the braking energy recovery efficiency.