Adaptive Model Preditive Control Research On Regenerative Braking For Electric Bus Cruising Downhill

When travelling in the mountain area,vehicles often need to travel downhill and turning driving.In order to ensure traffic safety,vehicles' speed should be controlled exactly.During this period,the brake systems are kept in the continuous braking condition for a long time.For the traditional internal combustion vehicles,the heat load of brakes is quite large which may lead to lose of braking ability.In this case,the auxiliary braking systems have been taken to relieve the load of brakes.Auxiliary braking systems cannot be installed in the electric vehicles(EV).But the electric vehicles have a function of regenerative braking,so the regenerative braking method can be used as the auxiliary braking system for EVs to relieve the load of the mechanical braking system,and then the braking safety can be improved.Furthermore,through the regenerative braking process,the kinetic energy of driving will be transformed into the electric energy to store in the energy storing devices,then the electric energy can be reuse and the endurance mileage of EVs will be increased.For the downhill braking condition of electric vehicles,the distribution of the regenerative braking force and the mechanical braking force is researched to obtain the constant speed when the road gradient is time varying.The principle and structure of EV's regenerative braking system are introduced briefly;the constraints of the regenerative braking system are provided according to the actual situation.And then the electric bus is taken as the example,the mathematical model of the braking system is established.Ranges of each variable of the mathematical model are given.The least square algorithm is used to identify the road gradient in the real time.This system is simulated by Matlab/Simulink and the simulation result shows that the least square algorithm can identify the change of the road gradient well.In order to ensure that the speed of the vehicle can hold constant when the road gradient change,the adaptive model predictive control method is adopted to design the controller according to the mathematical model of the braking system.This control system is mainly accomplishing few steps of the input of the predictive model,rolling optimization,on-line correction etc.The result of the identified road gradient is used as the measured disturbance signal to the control system.The vehicles' speed can be adjusted adaptively according to the change of the road gradient.Moreover,the PID control method without the adaptive mechanism is used to control the speed,and the result is compared with the control result of the adaptive model predictive control.These control process is simulated by Matlab/Simulink,the results show that the adaptive model predictive control method can track the ideal speed better;the change of the road gradient has a smaller influence on the control results.At last,models of the electric bus's various components are established by Matlab/Simulink,which includes the vehicle longitudinal dynamic model,motor model,battery model and brake mode switching model.Based on the characteristics of batteries,speed and other conditions,when the SOC of the battery is higher than a certain value,the brake mode switching model can change the braking mode to only mechanical brake mode and the regenerative braking system is closed at this period.The simulation results of the braking system with the control model shows that the vehicles speed can be controlled effectively to ensure the safety of downhill travel,and this system can regenerate energy well.