Research On Active Fault Tolerant Control Strategy For Electric Drive System Of X-by-wire Electric Vehicle With Four Wheels Independent Control

Compared with the other chassis systems of X-by-wire electric vehicle with four wheels independent control,the drive-by-wire system has the following characteristics: Firstly,the number of actuators is large,and all kinds of controllable actuators are widely applied and distributed in space.The mechanical coupling between subsystems is relatively weakened so that electrification characteristics are more obvious.Thus,the faults are more concealed and abrupt.Secondly,the in-wheel motor needs to be started frequently to cope with the time-varying driving conditions so that the drive-by-wire systems are often in the unsteady state.Thirdly,multi-executor redundancy structure makes multiple control systems share the same sensors,actuators or control variables,which will cause interference or conflict between the execution systems.Considering the particularity of the drive-by-wire systems,it is necessary to establish a fault tolerant control mechanism for electric drive system of X-by-wire electric vehicle with four wheels independent control,which is of great significance for improving vehicle safety.At present,for the problem of electric drive system failure of X-by-wire electric vehicle with four wheels independent control,the rule-based passive fault tolerant control strategy is mostly applied,which is suitable for pre-set failure mode response and robust to a particular fault.Considering the unpredictability of drive-by-wire systems fault,it is obvious that the effect of active fault tolerance control strategy isbetter.However,the active fault tolerant control strategy for electric drive system of X-by-wire electric vehicle with four wheels independent control is still in the research stage,and many problems need to be solved.Generally,the following points are summarized: firstly,the active fault tolerant control strategy based on reconfigurable control allocation,which is transformed into the control allocation problem in the integrated control framework by decoupling electric vehicle dynamic control.There is only from the point of vehicle control and lack of comprehensive consideration of the characteristics of the underlying drive actuators.Secondly,the active fault tolerant control strategy based on reconfigurable control allocation,the single objective optimization based on constraint is adopted when reconfigurable control allocation cost function is designed.Considering that the failure of the drive-by wire systems will affect the dynamic characteristics of vehicle,it is impossible to guarantee the optimal and feasible solution in the reconfigurable control allocation.Thirdly,the functional units of the drive-by-wire systems are unified into a functional whole,and it is lack of qualitative analysis of the interrelation between the drive actuators.The disabled drive-by-wire systems are reated by direct zero input so that fault compensation capability of each drive-by-wire system is ignored,thus the efficiency of actuators are reduced.Funded by the National Natural Science Foundation Project “Research on Reconfigurable Integrated Control Strategy of a Full drive-by-wire Distributed Electric Vehicle”(No.51505178),“Research on Hierarchical Fault-tolerant Control Method for Multi-agent Steer-by-wire System”(No.51505179)and “Control Mechanism and Evaluation Method of New Type of Steering System Based on Driver Characteristics”(No.51575223),this dissertation is about key technology for intelligent electronic chassis,and starts from the fundamental principle of vehicle dynamics and automatic control theory,and studies the operating characteristics and failure mechanism of the electric drive system of X-by-Wire electric vehicle with four wheels independent control,so that vehicle can meet dynamic needs as much as possible under the premise of vehicle driving safety.The fault tolerant control strategyfor electric drive system of X-by-Wire electric vehicle with four wheel independent control based on double layer architecture is proposed.The upper is vehicle control-oriented layer,which considers failure factors and fault constraints of the actuators.The fault tolerant control strategy based on control reconfiguration is proposed to focus on the coordinated control between each drive-by-wire system.The lower is drive execution-oriented layer.The fault tolerant control strategy based on fault compensation is proposed to focus on the tolerant control in each drive-by-wire system.The functional requirements of each layer control algorithm are defined.Both the bench experiment and real vehicle experiment are conducted so as to verify proposed control strategy.The concrete content of this dissertation is as follows:(1)Fault diagnosis algorithm for drive-by-wire system based on residual theoryFor the in-wheel motor fault of drive-by-wire system,the fault diagnosis algorithm of in-wheel motor based on parameter estimation is proposed.Based on Unscented Kalman Filter algorithm and discrete model of in-wheel motor,a parameter estimator of in-wheel motor is established to identify in-wheel motor parameter.Combined with resistance residues,the fault diagnosis algorithm of in-wheel motor is achieved.For the power inverter open circuit fault of drive-by-wire system,the fault diagnosis algorithm of power inverter based on state estimation is proposed.On the basis of analyzing the working characteristics of power inverter,the logic model of vehicle power inverter is established.Considered the switching logic of the power tube and the continuous characteristics of the phase current and combined with discrete model of in-wheel motor,a state estimator of in-wheel motor is established to estimate phase current.Combined with current residues,the fault diagnosis algorithm of power inverter is achieved.For the hall sensor fault of drive-by-wire system,the fault diagnosis algorithm of power inverter based on signal analysis is proposed.Using the method fusion,the hall signal is used to estimate the transient change of wheel speed.Combined with wheel speed residues,the fault diagnosis algorithm of hall sensor is achieved.The simulation results show that the fault diagnosis algorithm for drive-by-wire system can effectively identify and locatethe fault.(2)Fault tolerant control algorithm for drive-by-wire system based on control reconfigurationFor the vehicle control-oriented layer,a vehicle reference model based on 2-DOF linear model is constructed,which is used for calculating vehicle desired state.Combined with Model Prediction Control theory,the prediction model is structured.The cost function is designed aiming at improving the motion tracking performance of the vehicle.Considering the actuator constraints and rolling time domain optimization by quadratic programming method.The vehicle body control total forces are obtained when the vehicle reaches the desired state,and vehicle motion tracking is realized.The reconfiguration control allocation algorithm based on multi-objective optimization is designed.In the normal driving condition,the optimal allocation is achieved so that total workload of four wheels is minimized.In the drive failure condition,the reconfigurable allocation,considered failure factor,is achieved to meet the vehicle longitudinal force and yaw moment needs.Simplified tire friction circle constraint is taken into account in failure constraints,which considers vehicle stability,so that nonlinear constraints are translated into linear constraints.Making sure that optimal feasible solution is obtained in the control distribution of X-by-Wire Electric Vehicle with Four Wheels Independent Control.The simulation results show that fault tolerant control algorithm based on control reconfiguration,which makes the longitudinal and lateral force distribution of the drive failure vehicle can be adjusted actively to meet the needs of the whole vehicle dynamics with vehicle safety.(3)Fault tolerant control algorithm for drive-by-wire system based on fault compensationFor the drive execution-oriented layer,considering the drive controller fault,the function redundancy controller is designed.In the premise of satisfying the basic requirement of drive-by-wire system,the function redundancy is realized by hardware backup.According to the transmission direction of the control signal,the fault-tolerant control logic is divided,which make sure that function switch of the redundant controller is realized.For the power inverter open circuit fault of drive-by-wire system,the topological reconstruction of power inverter is proposed.By means of power switch redundancy,the conventional vehicle inverter six-switch topology is reconstructed into a four-switch topology.The hysteresis control strategy is adopted to realize the phase current compensation and solve the problem of phase current distortion caused by the back electromotive force effect in the four-switch topological applications.For the hall sensor fault of drive-by-wire system,the hall signal reconstruction based on phase compensation is proposed.The hall signal characteristics of fixed phase delay during adjacent commutation period are utilized and extracted from hall signal levels,the time benchmark,phase delay and phase compensation is determined to realize the hall sensor signal reconstruction.Through the fault compensation algorithm above,the fault tolerance of drive-by-wire system is realized to further improve the efficiency of drive-by-wire system.(4)Experimental research on active fault tolerant control algorithm for drive-by-wire systemIn order to verify the feasibility of the proposed active fault tolerant control algorithm,both the bench experiment and real vehicle experiment are conducted.Using a loading experiment platform,fault diagnosis algorithm and fault compensation algorithm for drive-by-wire system are verified.The primary experiment includes: the fault diagnosis algorithm of in-wheel motor,the fault diagnosis and topological reconstruction of power inverter,the fault diagnosis and signal reconstruction of hall sensor.An experiment platform of X-by-Wire electric vehicle with four wheels independent control is utilized to verify control reconfiguration algorithm,experiment condition includes: single wheel failure in straight line,double wheel failure in sinusoidal turn,double wheel failure in step turn.The results show that the proposed fault diagnosis algorithm based on residual theory,fault tolerant control algorithm based on control reconfiguration and based on fault compensation have a good control effect.The main innovations of this dissertation are as follows:(1)Proposing the active fault tolerant control strategy for electric drive system of X-by-Wire electric vehicle with four wheels independent control,which has the characteristics of "redundancy compensation" and the function of "online diagnosis" and "online fault tolerant",as well as,double layer architecture of “control reconfiguration” and “redundancy compensation”.The normal and limped driving of X-by-Wire electric vehicle with four wheels independent control is guaranteed.(2)Putting forward reconfiguration control allocation algorithm based on multi-objective optimization,which achieved optimal allocation during normal driving and reconfigurable allocation based on failure factor and fault constraints during drive system failure.The optimal feasible solution is obtained in the control distribution.(3)Focusing on the problem of ignoring actuators fault compensation in fault tolerant control strategy for electric drive system of X-by-Wire electric vehicle with four wheels independent control,“controller redundancy”,“vehicle power inverter current compensation” and “hall sensor phase compensation” are designed to realize “function reconstruction of controller”,“topology reconstruction of power inverter” and “signal reconstruction of hall sensor”,and improve the efficiency of drive-by-wire system.