Fault Observer Based Fault-tolerant Control Of A Distributed Vehicle

Compared with traditional vehicles,modern four-wheel-independent-drive(4WID)vehicles have got more and more focus from researchers around the world,due to its system characteristic,fast output responses and its independent controllable in-wheel motors.However,due to the structural of the 4WID vehicle itself,the number of sensors and actuators has increased,which will lead to reliability problems.If one of the in-wheel motor is malfunction,the motor would not provide expected torque.Under such circumstances traditional control methods are hard to meet the longitudinal and lateral force requirements of the vehicle,and its control performance drops.In order to improve the stability of a malfunction 4WID vehicle,a fault observer is established to obtain the fault information at real-time,an active or a passive fault tolerant upper level controller is established,and the optimal allocation of motor torque is also studied.In this master thesis,a seven-degree of freedom(7-DOF)non-linear vehicle dynamic model including longitudinal,lateral,yaw and wheel rotations is established.Its validity and accuracy are tested.Then,using the 7-DOF vehicle model as reference and the wheel speed signal as input,a model reference adaptive theory base fault observer is established to observer the current failure factors in real-time.In the form of hierarchical control structure,the active/passive fault tolerant control systems are studied.The yaw angular velocity and the slip angle are selected as input variables in upper controller,and a two-degree of freedom linear bicycle vehicle is selected as a reference model.An active fault tolerant controller based on model predictive control(MPC)and a passive fault controller based on slide mode control theory are designed,they are used to calculate the additional front wheel steering angle and the external yaw moment that helps a fault vehicle to track the reference state.On this basis,the vehicle states should be evaluated,and the better upper control method should be determined by some kind of rules,so as to give full play to the advantages of active/passive fault-tolerant control.Then a lower torque distribution controller considering actuator constraints and ground attachment conditions is designed,it could get the optimal output of each wheel under multiple constraints.In order to test the performance of the fault tolerant control system designed in this master thesis,a hardware-in-loop simulation test system was built.After some typical tests,the results show that the fault tolerant control proposed in this master thesis has ability to observe the current fault information,and it is effectively to improve the stability of a malfunction vehicle.