Fuzzy Control Based Regenerative Braking System Research For Electric Vehicles At Downhill

In order to ensure the driving safety,the travel speed needs necessary control when the car traveling in the mountain area is in downhill condition.In this period,the vehicle brake system is under continuous braking condition.In case of large heat load of brakes,the load in the brake of the conventional vehicle can be released with the auxiliary braking.Electric vehicle can reduce the mechanical braking load by using the regenerative braking as the auxiliary braking.Consequently,the brake generate less heat and the braking safety can be improved.In the meantime,inertia energy is transformed to electric energy storing to the energy accumulator through the regenerative braking,thus the driving range of electric vehicle can be prolonged.Firstly,this paper gives a brief introduction to the principle and influencing factors for the regenerative braking of cars.On this basis,this paper emphatically analyzes the influence of the charging capacity of lead-acid battery on the regenerative braking system.Taking the medium electric cars from ADVISOR for example,the constant charging capacity of batteries could only ensure that the cars go down in uniform velocity a slope with a slope gradient less than 4.5%.Therefore,this paper proposes a method combining regenerative braking system and the mechanic braking system to realize uniform-velocity of electric cars when going down slopes.Afterwards,on the basis of analyzing the ideal braking force distribution curve of two-axle cars and the restriction on the braking force distribution to the front and rear axles by the ECE braking regulation,aiming at the braking stability and increasing the braking energy recycling efficiency,this paper studies the coordinated distribution of regenerative braking force and mechanic braking force while going down a long slope and proposes the braking force distribution control strategy that meets the ECE braking regulation's requirement while ensuring uniform velocity of electric cars going down slopes.According to different braking strength,this strategy determines the percentage of the braking force on the front axle and rear axle and the percentage of the mechanic braking force and regenerative braking force.Then,through dynamic analysis on the braking process of electric cars in uniform velocity,this paper establishes the fuzzy control-based braking force control strategy for electric cars in uniform velocity.This strategy could adjust the braking force on a real-time basis according to the changes of slope gradient of roads and the difference between the target speed and actual speed of the car to realize and maintain the cars going down slopes in uniform velocity.Finally,this paper uses Matlab/Simulink to establish a simulating model of critical components of electric cars,including the longitudinal dynamic model for a car going down slopes,the motor model,the storage battery model,the braking force distribution model and the braking mode transformation model,etc.Through simulating analysis,following conclusions are drawn out:using the fuzzy control-based braking force control strategy proposed in this paper could realize reliable control on cars going down slopes in uniform velocity;meanwhile,t also shows that using regenerative braking could only control the stable speed of cars on small slopes(such as i 4.5%)with poor dynamic characteristics;on a large slope(such as i>4.5%),to realize retarding brake and maintain stable speed,the complex mechanic and electric braking is also needed.