Research On Control Strategy Of Regenerative Braking Of Four In-wheel-motor Drive Electric Vehicle

Electric vehicles had become one of the effective solutions to solve the current energy shortage and alleviate the environmental crisis because they have the advantage of less pollution and do not require traditional petroleum energy as a power source.Among them,the distributed drive electric vehicle had become the research focus because of its advantages of good dynamic control performance,short transmission chain and high energy transmission efficiency.However,it has the disadvantage of low cruising range,so the use of braking energy recovery to increase cruising range has become an important research content of distributed driving electric vehicles.This paper mainly studies the reasonable distribution of braking torque and the control of motor torque in the bottom brake system.Firstly,the vehicle dynamics model is established and the parameters of the key components of the power system are matched according to the vehicle parameters and performance indicators.This determines the parameters and model of the drive motor and power battery that meet the power performance requirements.A preliminary simulation of the determined parameters is then performed to verify that it meets the dynamic requirements.Secondly,a hierarchical control strategy is proposed for regenerative braking control of electric vehicles driven by four-wheel hub motors.The upper control strategy determines the magnitude of the electro-hydraulic target braking torque on each wheel,and the underlying control strategy is responsible for quickly and accurately tracking the target torque.The upper control strategy firstly distributes the front and rear axle braking forces according to the requirements of the braking strength.Then,according to the slip ratio,the braking condition is divided into two conditions:normal braking and anti-lock braking.Conventional operating conditions aim at energy recovery,and electro-hydraulic torque distribution is performed taking into account the constraints of different constraints.The anti-locking condition is aimed at stability.The slip mode control method is used to control the slip ratio within the optimal range and recover the braking energy as much as possible while ensuring stability.The main research object of the underlying control strategy is the hub motor,which controls the motor and hydraulic system to quickly and accurately track the target torque based on the target torque obtained by the upper control strategy.It uses vector control method combined with torque outer loop and current inner loop control to control single motor torque,and uses the advantages of rapid motor response and accurate tracking to actively compensate the error caused by hydraulic system hysteresis.In the case of mode switching or a large change in torque,it reduces the fluctuation of the total torque of each wheel to make the braking smoother.Finally,in order to verify the effect of the control strategy,combined with the basic parameters of the vehicle and key components,MATLAB/Simulink and Carsim software were used to build the joint simulation model.The control strategy was simulated and analyzed under different braking strength conditions.The results show that the low-intensity braking time is relatively long under normal braking conditions,and the vehicle energy recovery rate is large.At the same time,the compensation effect of the motor makes the total braking force fluctuate little,and the braking smoothness can be ensured.Under emergency braking conditions,the wheel slip ratio can be maintained within the optimal range,and the vehicle stability is better on the basis of ensuring good braking performance.The rationality of the proposed control strategy is verified.