Research On Vehicle Stability Control And Optimization Of Torque Distribution Based On Phase Plane Domain

Because the car equipped with four-wheel hub motor has the advantages of independent control of each wheel,motor speed and torque can be measured,small pollution and saving resources,it has become the general trend of modern automobile development,so for its stability research has become the focus of the world automobile industry.According to literature review,in order to improve the stability performance of electric vehicles,domestic and foreign scholars have designed on-board stability control units based on different control theories.However,the Model Predictive Control(MPC)algorithm is a powerful rolling optimization control algorithm for multi-constraint optimization problems,it has advantages that other advanced control theories cannot surmount.However,the stability control strategy designed based on MPC can only solve the objective function according to the fixed constraints set in advance.It cannot measure and analyze the current driving state of the vehicle and set the time-varying constraint region for specific solution.Therefore,further research is needed to improve the constraint accuracy of the MPC vehicle stability controller.In order to solve the problem that the stability controller based on MPC design in electric vehicles with four-wheel hubs needs to be further improved due to the limited constraint accuracy,this paper designed to classify the linear stability domain of the phase plane of the vehicle’s center of mass yaw angle-yaw angle velocity(γ-β),and studied the advanced MPC stability control strategy by introducing the boundary function of the stability domain so that the MPC constraints are generated in real time with the current driving state of the vehicle.To sum up,this paper improves the accuracy of the output sequence of the controller and the stability performance of the vehicle by designing MPC state constraints that change with the vehicle state in real time.The specific work content of this paper mainly includes the following points:Firstly,this paper establishes the whole vehicle system model of the four-wheel hub electric vehicle.It includes a two-degree-of-freedom vehicle model that reflects the dynamic characteristics of the vehicle,a magic tire model that reflects the nonlinear characteristics of the tire,a wheel model that includes the motion parameters of the wheel and a motor torque tracking model,and calculates the state reference value of the running vehicle.For the following stability control unit and motor torque distribution optimization unit design made full preparation work.Secondly,the phase plane stability boundary is designed.Based on the established twodegree-of-freedom vehicle model and tire model,the phase plane of the vehicle under the current driving parameters is drawn,and the stability region boundary of the phase plane is reasonably simplified,so as to quantitatively calculate the boundary function of the stability region boundary,which lays a foundation for introducing MPC to improve the calculation accuracy of controllerThirdly,the control strategy of MPC stability element based on introduced phase plane and torque optimization distribution element is proposed.In order to solve the problem that the MPC stability controller cannot accurately identify the vehicle state,and thus the control accuracy is low,this paper introduces the phase plane stability domain boundary function into the MPC state variable constraint,so that the MPC control sequence can be calculated in real time along with the change of the vehicle state,and the stability controller can accurately control the vehicle instability trend.The torque optimization distribution unit is designed to distribute the calculated additional torque reasonably to the four wheels.Finally,a Matlab/Simulink and CarSim co-simulation platform is built to verify the effectiveness of the proposed control strategy.The results show that the MPC stability control strategy with the introduction of phase plane stability domain boundary function can make the vehicle state value follow the expected value with higher accuracy,and under the premise of small tire attachment rate,the torque can be reasonably distributed among four wheels,leaving a large ground stability margin,and the vehicle stability and safety are improved.