Four-wheel Drive Steering Fusion Control Strategy And Experimental Study For Electric Vehicles

As the degree of air pollution become more and more serious,energy saving and emission reduction to alleviate environmental pressure were the measures that must be taken at present.In order to reduce the pollution of automobile exhaust emissions to the air,the development of the new energy automobile industry had become the only way for the country.Among them,the electric motor driven by the wheel hub motor had received wide attention from all walks of life.As a new type of driving mode,the hub motor drives the electric vehicle,which improves the transmission efficiency of the vehicle power,optimizes the chassis structure of the whole vehicle and can realize complex driving forms,A large number of researches had been carried out in universities at home and abroad.In this paper,the four-wheel drive four-wheel steering electric vehicle driven by hub motor is taken as the research object,and the research is mainly carried out from the following aspects:(1)Design of the hub motor control system and the establishment of the simulation modelAiming at the drive control of brushless DC hub motor,the control system of single motor speed and current double closed loop is modeled and simulated based on Matlab/Simulink.Combining theory with simulation analysis,the relationship between the measurable physical variables such as motor phase current,speed and output torque in motor starting,steady state and speed regulation is discussed.(2)Research on the bench characteristics of single hub motorBased on the simulation of the hub motor,a bench test was carried out on the actual motor.Firstly,the pulse width modulation technology is used to adjust the speed regulation.The experimental results verify the conclusions obtained from the previous simulation model,and the experimental results show that the PWM voltage regulation and open-loop control mode is suitable for low speed and single road conditions.Secondly,the frequency control frequency modulation is used to verify that the actual motor can respond quickly and can suppress the speed fluctuations well.This control mode is suitable for different load conditions.(3)Development of Multi-motor Fusion Control System for Four-wheel Driven Four-wheel SteeringAiming at the coordinated control of steering motor and driving motor,this paper presents a hierarchical six-motor fusion control strategy.The upper layer performs the electronicdifferential algorithm,PID,acceleration and other parameters tuning.At the same time,the control instructions are issued step by step.The rotation angle and rotational speed of each wheel are synchronized once in each control cycle to monitor whether the wheel speed reaches the desired value.In the lower layer,the speed closed-loop of hub motor is processed by PID algorithm.Aiming at this architecture,the upper computer software of four-wheel drive four-wheel steering six-motor fusion control system is developed.(4)Development and experimental research of test sample vehicle platformOn the basis of the prototype car built by the research group,the four-wheel drive system and the front and rear axle steering system are developed,and the software and hardware of the vehicle platform are optimized at the same time.The dynamic model of four-wheel drive vehicle is established,and the theoretical analysis is carried out.Based on the optimized four-wheel drive test prototype platform,the test of the front-axle steering four-wheel drive and the steady-state rotation test of four-wheel steering with the same angle and different phase are carried out.The experimental results show that the four-wheel drive steering control strategy can achieve the electronic differential function well,and verify the rationality and effectiveness of the six-motor fusion control system based on the Labview software development of NI company.