Study On Vertical Dynamics Simulation And Predictive Control Of Electric Vehicle Driven By In-wheel Motor

With the development and promotion of new energy vehicles,electric vehicles have derived two main driving modes: centralized drive mode and distributed drive mode.Distributed drive mode can be subdivided into dual motor drive mode,by-wheel motor drive mode and in-wheel motor drive mode.Electric vehicles driven by in-wheel motors have advantages of flexible control and high transmission efficiency.However,the special layout of in-wheel motor increases the unsprung mass of the suspension system,aggravates the vibration of the unsprung components,and reduces the suspension performance of electric vehicle driven by in-wheel motors.In addition,the stator and rotor of in-wheel motor will produce relative displacement under the joint effects of road excitation and suspension force,which leads to the distortion of air gap magnetic field.The distorted magnetic field causes unbalanced electromagnetic force,which aggravates the vibration of motor and worsens suspension performance of electric vehicle.In order to improve the performance of suspension and suppress the negative vibration of in-wheel motor,the existing researches usually use the active suspension which has high energy consumption and cost.Besides,few researches consider both the suspension performance and vibration suppression of in-wheel motor.Air suspension with auxiliary chamber is a kind of derivative structure of air suspension.Its stiffness coefficient and damping coefficient are adjustable,which makes great potential in improving vehicle ride comfort and driving safety.Therefore,this paper carries out simulation and control research on the electric vehicles driven by in-wheel motors with air suspension.Firstly,according to the working principle of the brushless direct current motor,the model of brushless direct current in-wheel motor is established.Then the unbalanced electromagnetic force model is built according to the generation theory of air gap magnetic field.The working principle of air suspension with auxiliary chamber is introduced.Considering the pipe throttling and hysteresis effects,the model of air suspension with auxiliary chamber is established based on the theories of hydrodynamics and engineering thermodynamics.The coupling mechanism between in-wheel motor and air suspension with auxiliary chamber is discussed,then the model of hub direct drive air suspension system is established.Bump excitation model and random road excitation model are established.The in-wheel motor system model and unbalanced electromagnetic force model are verified by test bench.Secondly,in order to analyze the two-way effects of in-wheel motor system and air suspension system,the relationships between motor eccentricity,unbalanced electromagnetic force,sprung mass acceleration,suspension dynamic travel,tire dynamic load,unsprung mass acceleration RMS values and auxiliary chamber volume,damping coefficient are simulated and analyzed in MATLAB/Simulink.The motor eccentricity,sprung mass acceleration,suspension dynamic travel and tire dynamic load transfer characteristics to road roughness are discussed.Finally,considering the semi-active suspension limits and suspension dynamic travel constraints,nonlinear model predictive control algorithm is applied to hub direct drive air suspension system,and the nonlinear model predictive controller is established to reduce the sprung mass acceleration,in-wheel motor eccentricity and tire dynamic load.Genetic algorithm is used to optimize the specifications of the controller.According to the measurable state variables of hub direct drive air suspension system and considering the nonlinear characteristics,the extended kalman observer is built to meet the requirements of the nonlinear model predictive controller.The simulation results show that nonlinear model predictive controller can effectively reduce the sprung mass acceleration,tire dynamic load and in-wheel motor eccentricity.The air suspension performance is improved and the negative vibration of in-wheel motor is suppressed.