Research On Dual-motor Autonomous Steering System Of Unmanned Vehicle And Its Fault Tolerant Control

Unmanned vehicle is an important part of future intelligent transportation system,and autonomous steering system is an important executive system for unmanned vehicle.In order to improve the reliability of autonomous steering,the dual-motor autonomous steering system with redundant backup and fault-tolerant control(FTC)have been widely investigated by scholars.Aiming at the problems in angle following the dual-motor autonomous steering system of unmanned vehicle,the research on coordinated control of dual-motor steering is carried out in this paper to ensure the accuracy of the angle following and improve the stability of steering motors.The methodologies of fault detection(FD)scheme and fault-tolerant control of steering motors are also built to improve the reliability of autonomous steering system and the safety of the unmanned vehicle.Firstly,the joint modeling and simulation of dual motor autonomous steering system of the unmanned vehicle are carried out.The steering motor model and the steering gear model are analyzed and built.Based on this,a dual-motor autonomous steering system is established,which is composed of angle motor controlled by three loops and torque motor controlled by current loop.Based on the vehicle dynamics model and kinematics model,the upper model predictive controller for trajectory tracking is built.In order to verify the model accuracy,the co-simulation platform based on CarSim and Simulink is built.The simulation results show that the dual-motor autonomous steering system has good angle following ability,and the unmanned vehicle based on the autonomous steering system has good trajectory tracking effect.Secondly,based on the architecture of dual motor autonomous steering system,the coordinated steering control method is studied.The causes of instability of steering motors during the load variation of trajectory tracking are analyzed.Therefore,the model of steering resistance moment is established.The change trend of the steering resistance moment under different speed and different front wheel angle is analyzed.Based on the change trend of steering resistance moment,combined with type-2 fuzzy algorithm,49 fuzzy rules are established,the vehicle speed and the angle are used as the inputs of the controller,and the coordination coefficient of the dual-motor is taken as the output of the controller,the coordinated steering controller for the angle motor and the torque motor is designed.The results show that the current and speed of the angle motor are more stable in the course of in-situ steering and double lane change under the coordinated steering controller,which demonstrates that the accuracy of the angle follow and the stability of the steering motor are ensured.Thirdly,the fault detection scheme of dual steering motor and the fault-tolerant control strategy for autonomous steering system are proposed.In order to improve the reliability of the autonomous steering system,the fault types of the steering motor are analyzed,and the fault detection schemes for the angle motor and the torque motor are proposed respectively,so as to locate the fault of the motor in time.Then,a passive FTC strategy for dual-motor coordinated steering is proposed,in which the insufficient torque caused by motor fault are compensated and angle following is ensured.For those serious motor fault,in order to reduce the uncertain influence of the fault motor on the whole autonomous steering system,an active FTC composed of backstepping control and global sliding mode control is proposed to control the non-fault motor to turn separately,consequently,the accuracy and robustness of the steering system in the angle following are increased.Finally,the hardware in the loop(HiL)semi-physical test of the autonomous steering system is carried out,and the feasibility of the proposed control strategy is verified in the actual controller.The dual-motor autonomous bogie and vehicle model,trajectory tracking algorithm,dual-motor coordinated steering algorithm,fault detection and fault-tolerant control algorithm are built,and the system communication configuration is carried out through the experimental software,so as to complete the dual-motor autonomous steering test platform of bogie-vehicle model-ECU.The results of HiL test show that the real time optimization of the target angle can be realized by the upper MPC trajectory tracking controller,and the angle is well followed by the built dual motor autonomous bogie.Under the action of the coordinated steering controller,the stability of the current and speed of the angle motor in the process of trajectory tracking is ensured;the proposed FD and FTC strategy can be implemented in time,at the same time,the accurate angle with different degrees of motor fault can be achieved in steering system,therefore,the safety of the unmanned vehicle is improved.