Research On Drive Mode Switching Control Of Electric Vehicle With Dual-rotor In-wheel Motor

Pure electric vehicles have the advantages of zero emissions and low noise,which make them as one of the key product types promoted by many governments and automobile companies around the world in the vigorous development of energy-saving and new energy vehicles.Among the driving motors for vehicles,in-wheel motor has the advantages of simple and compact structure,efficient transmission,independent control of driving and braking torques,and represents an important direction for the development of the next generation of electric vehicles.However,the existing two types of in-wheel motors of outer rotor direct drive and inner rotor deceleration drive have certain shortcomings in practical applications,and the applicable occasions are limited.The dual-rotor motor is an electric power-coupling device proposed ten years ago that could be applied to hybrid vehicles.The electromechanical energy can be freely converted between multiple electrical ports and mechanical ports to achieve power splitting,and it has a variety of operating modes to meet the multiple operating conditions of electric vehicles.Therefore,the research on dual-rotor in-wheel motor electric vehicle drive technology and its control strategy is developed to expand the adaptation occasions of traditional in-wheel motor electric vehicles,and make full use of the efficient operation area of the motors to reduce the energy consumption of the whole vehicle,which has important academic exploration significance and engineering practice value.Based on the proposed dual-rotor in-wheel motor scheme,this paper studies the multi-objective optimization method of its structural parameters,the energy management strategy of the vehicle in the driving mode and the mode switching coordinated control strategy.The main research work is as follows:First,an integrated structure of dual-rotor in-wheel motor suitable for electric vehicles is proposed,which can realize multiple working modes,such as single inner motor drive,single outer motor drive,and torque coupling drive.It can meet the needs of the vehicle's changing driving conditions.Also it has the advantages of both deceleration drive and direct drive type in-wheel motor,which solves the limited application of traditional in-wheel motor electric vehicles.Aiming at the structure of the dual-rotor in-wheel motor highly integrated by the inner and outer motors and its numerous dimensional parameters,a multi-objective optimization method based on comprehensive sensitivity to stratify design variables is proposed.Then the design variables with medium and high sensitivity were optimized by response surface method and multi-objective genetic algorithm,respectively.After comprehensively weighing the optimization goals of output torque,torque ripple,usage amount of permanent magnets and degree of magnetic coupling between inner and outer motors,three candidate design solutions with high satisfaction were screened out.Based on the comprehensive performance evaluation of the motors,the optimal design scheme and structural size value were finally determined.So the rapid and efficient optimization of the structural parameters of the dual-rotor in-wheel motor was realized.The distribution of magnetic field lines,no-load characteristics,torque performance and magnetic coupling characteristics of the dual-rotor in-wheel motor were analyzed by using the finite element method.The results show that the proposed motor structure is reasonable and the multi-objective parameters optimization method is effective.Besides,based on the losses analysis of the inner and outer motors,the drive efficiency MAP diagrams are obtained.They provide the basis for formulating control strategies that can keep the motor running at high efficiency when the dual-rotor in-wheel motor works in different driving modes.Secondly,the longitudinal dynamics model of dual-rotor in-wheel motor electric vehicle based on single wheel is constructed.Also the key subsystem models are established,which include dual-rotor in-wheel motor,power battery,driver and electromagnetic clutch.Based on in-depth analysis of the driving characteristics in the three driving modes of dual-rotor in-wheel motor electric vehicles,a drive mode switching rule based on the optimal system efficiency is proposed,and the working intervals of various drive modes are divided in detail.In the coupled drive mode,a torque distribution strategy based on the minimum energy consumption of the system is proposed to maximize the high-energy conversion efficiency of the inner and outer motors.The effectiveness of the proposed strategies are verified by simulation analysis.Furthermore,taking the mode switching from the inner motor alone to the coupling driving of the inner and outer motors as the research object,a coordinated control strategy for switching the driving mode of the dual-rotor in-wheel motor is designed.Aiming at the characteristics of the mode switching process,a dynamic modeling method for drive mode switching of dual-rotor in-wheel motor based on the switching system theory is proposed.According to the critical switching conditions of each state,a mode switching control process and a switching rule expressed by a piecewise constant function are designed.During the electromagnetic clutch II engagement phase,a mode switching torque coordinated control strategy based on the model prediction and control distribution is proposed,and the stability of mode switching is analyzed by the Lyapunov method.The results show that,the proposed strategy can effectively reduce the impact of the vehicle and the slip power of the clutch under the premise of ensuring a fast response to mode switching and a steady increase in vehicle speed,which improves the switching quality of the mode switching process and ensures the driving performance of the vehicle.Finally,based on the optimized structure parameters of the dual-rotor in-wheel motor,an experimental prototype was made,and the drive system control program of the dual-rotor in-wheel motor was designed.Using the motor performance test platform,the basic characteristics and the control of driving mode switching of the dual-rotor in-wheel motor are experimentally studied.The experimental results show that,the rationality and effectiveness of the proposed dual-rotor hub motor structure scheme and its drive mode switching control strategy are verified,and the motor's ability to operate in multiple drive modes is confirmed,which has laid a certain experimental foundation for its potential application in in-wheel motor driven electric vehicles.