Research On Braking Energy Efficiency Receding Optimal Control Of Four In-wheel Motors Electric Vehicles

The new energy automobile,especially electric vehicles has become an important development industry of our country,the government has taken it as a comprehensive national strategy.However,in the process of practical promotion and application,the limited driving range,short battery life and low charging efficiency have severely limited the development of electric vehicles.Therefore,it is important to deeply study the energy management system of electric vehicles to reduce energy consumption and improve energy regenerative efficiency.Braking energy recovery technology can use electric motors for regenerative braking,converting part of the kinetic energy into electric energy during the braking process and storing it in batteries or other energy storage elements.However,the factors that affect energy loss and recovery during the braking process are very complex,such as the internal characteristics of the motor system,hydraulic system,and battery system and their mutually restrictive relationships,and how to design a multi-actuator coordinated control strategy to take into account the braking safety and energy efficiency,that have brought challenges to the research of electric vehicle energy optimal control.Four in-wheel motors electric vehicle have the advantages of direct and independent control of each in-wheel motor,the torque and speed of the wheel can be measured in real time,making the vehicle dynamics control more convenient and flexible,which can improve the maneuverability and stability of the vehicle.These advantages of four in-wheel motors electric vehicle provide a great optimization space for braking energy recovery technology.Therefore,the research on braking energy optimization of four in-wheel motors electric vehicle is necessary.This article takes four in-wheel motors electric vehicle as the controlled object,and focuses on two control goals of braking safety and energy efficiency.The research focuses on the coordinated optimization of regenerative braking and friction braking modes based on the model predictive control theory in the hybrid braking system.It aims to solve the mutual coupling and constraints between multiple actuators in the braking energy recovery system,and the multi-variable,multi-objective,and multi-constraint problems in the nonlinear optimization problem.Under the premise of ensuring the safety of the brake,the research fully improves the braking economy of the electric vehicle.Firstly,an integrated braking energy recovery maximization control strategy is proposed for the compound brake distribution control problem of a four in-wheel motors electric vehicle.Under the constraints of each actuator and the battery system,the motor and hydraulic braking torque of front and rear wheels are optimized simultaneously,taking into account the driver's braking requirement and energy regenerative efficiency.Model predictive control method is used to design the integrated controller to deal with the system constraints uniformly and explicitly,which helps to avoid the limitation of the energy optimization space by the hierarchical control strategy,and realize the receding optimmal control of the braking energy.Secondly,in order to fully exploit the potentiality of braking energy recovery,an energy optimization method for braking conditions with terminal velocity and distance constraints is proposed,and the braking energy optimization is realized by the velocity optimization.According to the braking energy loss model,an optimal control problem is constructed,and a decreasing distance domain model predictive controller is designed.By adding the objective function of terminal state penalty term,and the time domain to distance domain transformation of the optimization problem,the terminal constraints are processed.This strategy gets an optimized velocity trajectory through the coordinated allocation of front and rear motor and hydraulic braking torque,and finally futher improves the optimization space of the braking energy regenerative efficiency.Thirdly,the braking optimal control of electric vehicles is studied under the emergency braking condition.Combining the advantages and disadvantages of the motor and hydraulic braking modes,a hierarchical anti-lock control method of regenerative braking and friction braking coordination is proposed.This method reduces the complexity of multi-variable and multi-objectives in the optimization problem,fully takes advantage of the motor characteristic of fast response and high control accuracy.The proposed strategy improves the accuracy and stability of the tire slip ratio control,and ensures the safety and stability of the emergency braking process,it also improves the braking regenerative efficiency.Finally,according to the relationship between the battery energy recovery and the battery life loss during the braking process,a coordinated control strategy of motor and hydraulic braking torque is presented based on the model predictive control theory.The braking energy recovery and the battery life are optimized at the same time.Then from the economic point of view,a unified economic evaluation index of braking energy loss and battery life loss is proposed,and a braking economic model predictive controller is designed.The control target of optimal economy in the braking process is achieved under the premise of satisfying the braking requirements.Through the exploration and research of the above contents,the coordinated optimal control of the braking torque of a four in-wheel motors electric vehicle is completed,and the receding optimal control of the braking safety and energy efficiency is realized.The velocity optimized braking energy optimization is studied based on the research of the uniform deceleration braking energy optimization,which further extends the potential space of the energy recovery.Compared with the normal braking conditions,the emergency braking conditions have higher requirements for the braking safety.Therefore,a hierarchical decoupled braking anti-lock control strategy is proposed,which improves not only the braking safety and reliability,but the regenerative energy of the electric vehicle during an emergency braking situation.In addition,since the regenerative braking process of electric vehicles interact with the battery performance,taking the battery aging characteristics and the high cost into consideration,a braking economy optimal control strategy is finally proposed to improve the integral braking economy of an electric vehicle.