Coordinated Control Research On The Regenerative And Frictional Composite Braking System For An In-wheel Motors Driven Electric Vehicle

The electric vehicles(EVs)have an outstanding advantage of zero emission when driving,so they have been favored by automobile science and technology workers all over the world.However,on the basis of the current technological bottlenecks of the power battery,the EVs still have two major shortcomings,namely,the high initial manufacturing cost and short driving mileage.Compared with the centralized driven EVs,the distributed in-wheel motors(IWMs)driven EVs have an higher driving efficiency and the superior braking energy recovery effect.Therefore,considered with the present difficulty of achieving substantive breakthroughs on the increase in battery power,the IWMs driven EV has a better potential to improve the driving mileage.Due to various constraints,regenerative braking system is not always sufficiently large to satisfy the vehicles’ braking demands.Hence,it needs to cooperate with the traditional friction braking system for fulfilling the necessary braking control effect.In order to further extend the driving mileage of IWMs driven EV on the premise of maintaining an outstanding braking performance,it has great theoretical values and engineering significances to research the coordinated control strategy for the regenerative and frictional composite braking system.On the basis of the proposed voltage variable charging control strategy(VVCCS),the modified optimal sliding mode control algorithm,and double-loop predictive control algorithm,this paper studies the coordinated control strategy for the regenerative and frictional composite braking system under the emergency and non-emergency braking conditions,respectively.The main research works are described as follows:First,the longitudinal dynamic model of IWMs driven EV is established.The vehicle longitudinal-single wheel rotation dynamics model and vehicle longitudinal-two wheel rotation dynamics model are constructed,respectively.The former is mainly composed of the longitudinal dynamics model and the single wheel rotation model,which is used to study the ideal slip tracking control mechanism of the IWMs driven EV under the emergency braking condition.The latter takes into account the influences of the load transfer including air,tire roll,and hill climbing resistances detailly,which is used to explore the coordinated distribution strategy of regenerative braking force with a optimal braking energy recovery and friction braking force under the non-emergency braking condition.Furthermore,the tire model,IWM model,hydraulic braking model and the brake actuator model are established,respectively.Second,a novel voltage variable charging control(VVCC)strategy is researched.By the supervision function of battery management system(BMS),the proposed scheme can achieve the function of selecting the number of the charged cell,and single battery cells with low actual voltage are prioritized for charging simultaneously.Furthermore,it can realize the regenerative braking torque control and braking energy recovery without the energy loss of power control circuit.Then,the least square fitting method is used to fit the key parameters of VVCC equivalent model.The control algorithms of charging voltage acquisition based on both the ideal regenerative braking torque and the maximum energy recovery power demands are proposed based on the above-mentioned equivalent model,respectively.The simulation results are presented to validate the effectiveness of the two control algorithms on the aspects of regenerative braking torque and braking energy recovery efficiency,respectively.Third,the anti-lock braking control strategy is proposed for the composite braking system under the emergency braking conditions.A single-wheel anti-lock braking control state equation considering the maximum energy recovery efficiency and an evaluation index for tracking the ideal slip rate are established.The road adhesion coefficient is estimated by the longitudinal dynamic equations and a real-time vehicle velocity predictor is designed by using Kalman observation control method.The reason for the failure of the common optimal sliding mode control algorithm used to design anti-lock controller is examined by theoretical derivation.A modified optimal sliding mode control algorithm is proposed to design the anti-lock controller through adding some virtual damping and infinitely small terms in the design process of Riccati function.Under the three different road conditions of high,low,and varying adhesive coefficients,the simulation results verify that the effectiveness of the proposed modified optimal sliding mode control algorithm.Then,the braking forces/torques distribution control strategy is designed for the composite braking system under the non-emergency braking conditions.On the one hand,a double-loop predictive control scheme is developed.The control system consists of the ground braking force predictive loop,the front/rear axle braking force distribution unit,and wheel braking torque predictive loop.By transforming several state variables into differential equations in accordance with the minimum phase system and adding some infinitely small-sized items in the cost function to meet the working conditions of the optimal control strategy,the ground braking force predictive loop is applied to evaluate the ideal total braking force in accordance with the driver’s braking command.The wheel braking torque predictive loop is presented to track the ideal slip ratio of wheel by using the full information optimal sliding mode control method,which can be used to predict the braking torque accurately.On the other hand,a coordinated control strategy based on the VVCCS is proposed for the composite braking system,and the ideal wheel total braking torque calculated by double-loop predictive control system can be redistributed by the proposed coordinated control strategy.The effectiveness of the proposed control strategy is verified for various braking conditions.Finally,the experimental study of the braking control strategies is investigated.An experimental test bench is set up and the variable voltage charging characteristics of the IWM and the fitting accuracy of the charging voltage acquisition equation are verified by the bench experiment.Then the anti-lock controller including the hardware circuit and control strategy is designed and the effectiveness of the controller is verified under the emergency braking condition.