Design And Research Of Multi-stage Energy Recovery Strategy For Pure Electric Vehicle

At present,in the research on the control strategy of braking energy recovery for front-drive pure electric vehicles,researchers have paid more attention to the energy recovery by stepping on the brake pedal,but relatively little research on energy recovery in other stages.In addition,in the stage of stepping on the brake pedal,the front wheel braking force is mainly distributed by the motor’s regenerative braking force and the mechanical braking force in different proportions.Such a distribution method is not conducive to maximizing the motor’s regenerative braking torque.In view of the above problems,this subject is improved from two points.The first point is to add the accelerator pedal energy recovery phase,and the second point is to add the coasting phase to give full play to the motor’s regenerative braking torque.This subject simply starts from the design of the control strategy structure,so that the energy recovery starts from the accelerator pedal stage,and then goes through the coasting stage and the brake pedal stage to perform multi-stage energy recovery to improve the economy of the vehicle.The work done in this subject As follows.(1)Retract the accelerator pedal stage.When the accelerator pedal is retracted,it is easy to produce a speed difference.The wheels will drive the motor to simulate the reverse drag characteristics of the engine.At this time,fuzzy control is adopted,and the accelerator pedal displacement and pedal change rate are used as fuzzy inputs,and the motor’s regenerative braking torque changes As a fuzzy output,combined with the calculation formula of the electric machinery load signal(EM＿Load＿Signal)to obtain the EM＿Load＿Signal used to control the backward drag of the motor,so as to recover the energy.In addition,the problem of battery overcharging is considered,and then EM＿Load＿Signal is corrected to achieve a stable and safe control of the motor to enter the state of inverted power generation.(2)The taxiing stage.The main consideration is that when the vehicle is coasting without action and when the vehicle is going down a long slope,light braking is allowed for long-distance coasting braking.At this time,if the motor braking is used first,the advantages of motor regenerative braking can be fully utilized.When driving demand,the remaining braking force will be equally divided by the wheel mechanical brakes,which not only prolongs the braking time of the motor,but also facilitates braking stability and prevents overheating of the front wheel single brake brake pads on long slopes.This topic first intercepts the entry conditions of a short period of stepping on the brake pedal as the entry conditions of the coasting stage.According to the driving torque of the car wheels,it should show the same magnitude and opposite relationship as the wheel braking torque required by the whole car.The motor braking torque acting on the motor rotor port is then calculated according to the calculation formula of EM＿Load＿Signal to calculate the size of the motor load signal.The reverse derivation method can accurately calculate the stable EM＿Load＿Signal,and then use the overcharge protection of the accelerator pedal phase to correct the motor load signal.(3)Step on the energy recovery stage of the brake pedal.Since this stage mainly deals with the braking force distribution problem in the latter part of the coasting stage,this subject still uses the ECE braking code line control strategy.Finally,according to the entry conditions of the three different stages,the C language is used to selectively output the entry conditions of the three different stages of control strategies and the corresponding modes under different conditions.Finally,in the operating conditions of Chinese light-duty passenger vehicles,the simulation and comparative analysis of the control strategy of simply stepping on the brake pedal,the fuzzy control distribution strategy and the multi-stage control strategy designed in this topic are carried out.It can be seen from the final results that the control strategy designed in this topic has improved battery SOC(State of Charge,SOC),braking energy recovery efficiency and driving range contribution,thus verifying the rationality and rationality of this strategy.feasibility.