Fault-tolerant control method of steer-by-wire system

Abstract

The invention provides a fault-tolerant control method for a steer-by-wire system, which fully considers multiple uncertainties such as parameter perturbation, system disturbance and actuator fault of the steer-by-wire system and controller input limitation, and solves a guaranteed performance control law by defining a quadratic form performance index and constructing a linear matrix inequality. Therefore, more accurate and stable fault-tolerant tracking control of the steer-by-wire system is realized. Besides, in order to further improve the response speed of the system to a control instruction, a feed-forward control mechanism is combined, control output is adjusted through prejudgment of ideal input, and robust guaranteed performance-feed-forward cooperative fault-tolerant control is formed, so that the time required by the system to reach an expected state is effectively shortened on the basis of not sacrificing the steady-state performance, and the system performance is improved. And the steering tracking speed is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of autonomous driving, and particularly to a fault-tolerant control method for a steer-by-wire system. Background Art

[0002] In recent years, with the rapid development of electronic technology, the steer-by-wire system has shown great application potential in the fields of new energy vehicles and intelligent driving due to its advantages such as high flexibility, low energy consumption, and easy integration. The steer-by-wire system eliminates the traditional mechanical connection and controls the steering actuator in the form of electronic signals, realizing the decoupling of the driver's operation and the front-wheel steering movement. This design not only improves the response speed of the steering system but also provides the possibility to achieve higher-level intelligent driving functions. However, since the steer-by-wire system completely relies on electronic signals and electronic control units, higher requirements are imposed on its functional safety and reliability. In practical applications, due to the large number of electronic components in the steer-by-wire system, it may face various faults, such as sensor faults, actuator faults, electronic control unit faults, etc. These faults may not only lead to the failure of the steering system but also have a serious impact on driving safety.

[0003] To improve the functional safety and reliability of the steering system, it is crucial to introduce redundant design in the existing hardware architecture and incorporate fault-tolerant strategies into the steering function algorithm. However, the driving conditions of automobiles are highly complex and unpredictable, and noise interference and the uncertainty of the external environment often affect the accuracy of the fault-tolerant mechanism. Among many nonlinear robust control methods, performance-preserving control exhibits significant advantages in dealing with the fault-tolerant problems of the steer-by-wire system due to its excellent robustness. Although there are studies on performance-preserving control in the field of steer-by-wire technology, most of the existing studies do not fully consider the system uncertainty when designing the controller, which limits the wide applicability of the research results. More critically, the existing studies often tend to sacrifice the response speed of the steering system in exchange for ultra-high steady-state accuracy. Therefore, how to effectively improve the response speed of the steer-by-wire system on the premise of ensuring its high steady-state accuracy, fully consider the multiple uncertainties in actual operation, and achieve more accurate and stable fault-tolerant tracking control of the steer-by-wire system, thereby effectively reducing the probability of faults and their harmful effects, is a technical problem that needs to be solved urgently by those skilled in the art. Summary of the Invention

[0004] In view of this, the present invention provides a fault-tolerant control method for a steer-by-wire system to effectively improve its response speed on the premise of ensuring the high steady-state accuracy of the steer-by-wire system, fully consider the multiple uncertainties in actual operation, and achieve more accurate and stable fault-tolerant tracking control of the steer-by-wire system.

[0005] A fault-tolerant control method for a steer-by-wire system includes: Step S1, construct a dynamics model of the steer-by-wire system. The dynamics model of the steer-by-wire system includes an equivalent model of the steering execution assembly of the steer-by-wire system and a dynamics model of the road feel motor. Obtain the front wheel angle based on the equivalent model and obtain the reference front wheel angle based on the dynamics model of the road feel motor; Step S2, construct a system state vector based on the front wheel angle and the reference front wheel angle; Step S3, define multiple uncertainties, and establish a state equation of the steer-by-wire system based on the system state vector and the multiple uncertainties. The state equation of the steer-by-wire system contains a system uncertainty matrix and an input uncertainty matrix; Step S4, reconstruct the system uncertainty matrix and the input uncertainty matrix; Step S5, substitute the reconstructed system uncertainty matrix and input uncertainty matrix into the state equation of the steer-by-wire system, and derive a linear matrix inequality I in combination with the Lyapunov stability equation; Step S6, define a quadratic performance index, and obtain a linear matrix inequality II in combination with the linear matrix inequality I; Step S7, combine the linear matrix inequality I and the linear matrix inequality II, and derive a linear matrix inequality III according to the definition of the ellipsoid; Step S8, obtain a guaranteed cost control law based on the linear matrix inequality I, the linear matrix inequality II, and the linear matrix inequality III; Step S9, design a feedforward control law, and combine it with the guaranteed cost control law to obtain a guaranteed cost-feedforward cooperative control law, and perform fault-tolerant control on the steer-by-wire system through the guaranteed cost-feedforward cooperative control law.

[0006] According to the fault-tolerant control method of the steer-by-wire system provided by the present invention, multiple uncertainties such as parameter perturbation, system disturbance, and actuator failure of the steer-by-wire system are fully considered. By defining a quadratic performance index and constructing a linear matrix inequality, a guaranteed cost control law is obtained, so as to realize more accurate and stable fault-tolerant tracking control of the steer-by-wire system. In addition, in order to further improve the response speed of the system to control commands, the present invention combines a feedforward control mechanism, adjusts the control output by predicting the ideal input, and forms a robust guaranteed cost-feedforward cooperative fault-tolerant control, so as to effectively reduce the time required for the system to reach the desired state without sacrificing the steady-state performance and improve the steering tracking speed. Description of the Drawings

[0007] Figure 1 is a flowchart of the fault-tolerant control method of the steer-by-wire system provided by the embodiment of the present invention; Figure 2 is a comparison diagram of the tracking error control effect; Figure 3It is a comparison chart of the input torque control effect. Detailed implementation manners

[0008] The embodiments of the present invention will be described in detail below. The examples of the embodiments are shown in the accompanying drawings, where the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below by referring to the accompanying drawings are exemplary and are intended to explain the embodiments of the present invention, and should not be construed as a limitation to the present invention.

[0009] Please refer to Figure 1 , the embodiments of the present invention provide a fault-tolerant control method for a steer-by-wire system, including steps S1 to S9: Step S1, construct a dynamic model of the steer-by-wire system. The dynamic model of the steer-by-wire system includes an equivalent model of the steering execution assembly of the steer-by-wire system and a dynamic model of the road feel motor. Based on the equivalent model, the front wheel angle is obtained, and based on the dynamic model of the road feel motor, the reference front wheel angle is obtained.

[0010] The steer-by-wire system includes a road feel feedback assembly and a steering execution assembly. In the process of constructing the dynamic model of the steer-by-wire system, the road feel feedback assembly part is represented by the dynamic model of the road feel motor, and the steering execution assembly part is represented by an equivalent model that combines the dynamic model of the steering motor and the dynamic model of the front steering wheel. That is, the equivalent model includes the dynamic model of the steering motor and the dynamic model of the front steering wheel.

[0011] Among them, step S1 specifically includes: According to the motor voltage balance equation and the electromagnetic torque equation, the motor torque ripple interference is obtained ; According to the two-degree-of-freedom driving motion equation and the mechanical equation of the vehicle, the friction resistance torque and the self-aligning torque are obtained; Substitute the motor torque ripple interference into the dynamic model of the steering motor, substitute the friction resistance torque and the self-aligning torque into the dynamic model of the front steering wheel, and combine the dynamic model of the steering motor and the dynamic model of the front steering wheel through the transmission ratio between the front wheel angle and the motor angle to obtain the equivalent model; Based on the equivalent model, the front wheel angle is obtained, and based on the dynamic model of the road feel motor, the reference front wheel angle is obtained.

[0012] Step S2, construct a system state vector based on the front wheel angle and the reference front wheel angle.

[0013] In step S2, the constructed system state vector is: ; where, is the system state vector, is the reference front wheel steering angle and the front wheel steering angle error, is the differential of time ; is integral; is the first-order differential of the front wheel steering angle ; represents transpose.

[0014] In step S3, multiple uncertainties are defined. The multiple uncertainties include the perturbation of the moment of inertia, the perturbation of the viscous damping, the torque fault factor of the steering motor, and the system disturbance. Based on the system state vector and the multiple uncertainties, a state equation of the steer-by-wire system is established. The state equation of the steer-by-wire system contains a system uncertainty matrix and an input uncertainty matrix.

[0015] In step S3, the multiple uncertainties include the perturbation of the moment of inertia , the perturbation of the viscous damping , the torque fault factor of the steering motor and the system disturbance ; The established state equation of the steer-by-wire system is: ; ; ; ; ; where, is first-order differential, is the guaranteed cost control law, and , is the control matrix, is the system matrix, is the system uncertainty matrix, is the input matrix, is the input uncertainty matrix; is the first intermediate moment of inertia, , is the ideal moment of inertia; is the second intermediate moment of inertia, , is the actual moment of inertia, ; is the ideal viscous damping.

[0016] Step S4, reconstruct the system uncertainty matrix and the input uncertainty matrix.

[0017] Among them, since 、 are norm-bounded, they can be written in the following form: ; ; ; ; ; Among them, 、 、 are known constant matrices, which reflect the structural information of the uncertainty; is a time-varying matrix, which can be time-varying; and satisfies , is the identity matrix.

[0018] Step S5, substitute the reconstructed system uncertainty matrix and the input uncertainty matrix into the state equation of the steer-by-wire system, and derive the linear matrix inequality one in combination with the Lyapunov stability equation.

[0019] Among them, select the Lyapunov function , is a symmetric positive definite weight matrix, let , , is the first intermediate weight matrix, is the second intermediate weight matrix. Assume that the system disturbance satisfies , is a positive number, representing the upper limit of the disturbance. According to the Lyapunov stability equation and the Schur property of the matrix, the linear matrix inequality one is obtained as follows: ; Among them, 、 are the polynomial coefficients generated in the process of inequality transformation, 、 are the given symmetric positive definite weighted matrices.

[0020] Step S6, define the quadratic performance index, and combine it with the linear matrix inequality one to obtain the linear matrix inequality two.

[0021] Among them, the quadratic performance index has the following expression: ; According to the Schur property of the matrix, the second linear matrix inequality is: ; Among them, is the reciprocal of the upper bound of the quadratic performance index and is a positive number; is the initial system state vector.

[0022] Step S7: Combine the first linear matrix inequality and the second linear matrix inequality, and derive the third linear matrix inequality according to the definition of the ellipsoid.

[0023] Considering that the output torque of the steering actuator motor is limited, and taking the control input constraint as one of the conditions of the solver, the third linear matrix inequality is:

[0024] Among them, is the torque upper limit.

[0025] Step S8: Based on the first linear matrix inequality, the second linear matrix inequality, and the third linear matrix inequality, obtain the guaranteed cost control law.

[0026] Among them, Step S8 specifically includes: Simultaneously solve the first linear matrix inequality, the second linear matrix inequality, and the third linear matrix inequality to obtain the solution of the control matrix ; Substitute and the solution of the control matrix into the formula of the guaranteed cost control law to obtain the guaranteed cost control law .

[0027] Step S9: Design the feedforward control law, and combine it with the guaranteed cost control law to obtain the guaranteed cost - feedforward cooperative control law, and perform fault - tolerant control on the steer - by - wire system through the guaranteed cost - feedforward cooperative control law.

[0028] Among them, the feedforward control law is: ; Among them, is the feedforward gain; The guaranteed cost - feedforward cooperative control law is: .

[0029] The output torque of the steering motor is controlled by using the above performance-preserving - feedforward cooperative control law to complete the fault-tolerant control of the torque part failure fault of the steer-by-wire system.

[0030] The method provided by the present invention is simulated and tested below.

[0031] Please refer to Figure 2 and Figure 3 , which describes a scenario of a step steering fault-tolerant control test. Among them, the torque fault of the steering motor occurs at the 7th second, the torque fault factor is 0.3, and it remains 0.3 thereafter. The perturbation of the moment of inertia and the perturbation of the viscous damping are both 5%. It can be seen from Figure 2 that the tracking error of the traditional PID method is relatively large, and the tracking error of the method of the present invention is smaller and smoother. It can be seen from Figure 3 that compared with the traditional PID method, the method of the present invention has significantly smaller fluctuations in the control torque at the moment when the fault occurs, and can recover to stability in a shorter time. In summary, the performance of the method of the present invention is superior to that of the traditional PID method.

[0032] In summary, for the fault-tolerant control method of the steer-by-wire system according to the above embodiments, multiple uncertainties such as parameter perturbation, system disturbance, and actuator failure of the steer-by-wire system and controller input limitations are fully considered. By defining a quadratic performance index and constructing a linear matrix inequality, a performance-preserving control law is obtained, so as to realize more accurate and stable fault-tolerant tracking control of the steer-by-wire system. In addition, in order to further improve the response speed of the system to control commands, the present invention combines a feedforward control mechanism to adjust the control output by predicting the ideal input, forming a robust performance-preserving - feedforward cooperative fault-tolerant control, thereby effectively reducing the time required for the system to reach the desired state without sacrificing the steady-state performance and improving the steering tracking speed.

[0033] The above-described embodiments only represent several implementation manners of the present invention, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several deformations and improvements can still be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the invention patent should be subject to the appended claims.

Claims

1. A fault-tolerant control method for a steer-by-wire system, characterized in that: include: Step S1, constructing a steer-by-wire system dynamics model, wherein the steer-by-wire system dynamics model includes an equivalent model of a steering actuator assembly of the steer-by-wire system and a road-sensing motor dynamics model, obtaining a front wheel steering angle based on the equivalent model, and obtaining a reference front wheel steering angle based on the road-sensing motor dynamics model; Step S2, constructing a system state vector based on the front wheel steering angle and the reference front wheel steering angle; Step S3, defining multiple uncertainties, the multiple uncertainties including the perturbation of the moment of inertia, the perturbation of the viscous damping, the torque fault factor of the steering motor and the system disturbance, and establishing a state equation of the wire steering system based on the system state vector and the multiple uncertainties, wherein the state equation of the wire steering system contains a system uncertainty matrix and an input uncertainty matrix; Step S4, reconstructing the system uncertainty matrix and the input uncertainty matrix; Step S5, substituting the reconstructed system uncertainty matrix and the input uncertainty matrix into the state equation of the steer-by-wire system, and combining with the Lyapunov stability equation to derive a linear matrix inequality 1; Step S6, defining a quadratic performance index, combining the linear matrix inequality 1, and obtaining the linear matrix inequality 2; Step S7, combining the linear matrix inequality 1 and the linear matrix inequality 2, and deriving the linear matrix inequality 3 according to the definition of the ellipsoid; Step S8, obtaining a guaranteed cost control law based on linear matrix inequality 1, linear matrix inequality 2 and linear matrix inequality 3; Step S9, designing a feedforward control law, and combining it with the guaranteed performance control law to obtain a guaranteed performance-feedforward cooperative control law, and performing fault-tolerant control on the steer-by-wire system through the guaranteed performance-feedforward cooperative control law.

2. The fault-tolerant control method of a steer-by-wire system according to claim 1, characterized in that: The equivalent model includes a steering motor dynamics model and a steering front wheel dynamics model; Step S1 specifically includes: According to the motor voltage balance equation and electromagnetic torque equation, the motor torque pulsation interference is obtained. ; According to the two-degree-of-freedom motion equation and mechanical equation of the car, the friction resistance torque is obtained and return torque ; The motor torque pulsation interference Substitute it into the steering motor dynamics model and convert the friction resistance torque and return torque Substitute into the steering front wheel dynamics model and use the front wheel angle With motor angle The transmission ratio between The steering motor dynamics model and the steering front wheel dynamics model are combined to obtain the equivalent model; Obtaining the front wheel turning angle based on the equivalent model , obtain the reference front wheel angle based on the road-sensing motor dynamics model .

3. The fault-tolerant control method of a steer-by-wire system according to claim 2, characterized in that: In step S2, the constructed system state vector is: ； in, is the system state vector, The reference front wheel angle Front wheel angle The error, For time The differential of for The integral of Front wheel angle The first-order differential of Indicates transpose.

4. The fault-tolerant control method of a steer-by-wire system according to claim 3, characterized in that: In step S3, the multiple uncertainties include the perturbation of the moment of inertia , the perturbation of viscous damping , Torque failure factor of steering motor and system disturbances ; The state equation of the wire control steering system is established as: ； ； ； ； ； in, for The first-order differential of To guarantee the performance control law, , is the control matrix, is the system matrix, is the system uncertainty matrix, is the input matrix, is the input uncertainty matrix; is the first intermediate moment of inertia, , is the ideal moment of inertia; is the second intermediate moment of inertia, , is the actual moment of inertia, ; is the ideal viscous damping.

5. The fault-tolerant control method of a steer-by-wire system according to claim 4, characterized in that: Step S4 satisfies the following formula: ； ； ； ； ； in, , , is a known constant matrix, is a time-varying matrix that satisfies , is the identity matrix.

6. The fault-tolerant control method of a steer-by-wire system according to claim 5, characterized in that: In step S5, the linear matrix inequality 1 is: ； in, is the first intermediate weight matrix, , is a symmetric positive definite weight matrix; is the second intermediate weight matrix, ; , are the polynomial coefficients, , is a given symmetric positive definite weighting matrix, is the upper limit of disturbance.

7. The fault-tolerant control method of a steer-by-wire system according to claim 6, characterized in that: In step S6, the secondary performance index The expression is: ； The second linear matrix inequality is: ； in, is the reciprocal of the upper bound of the quadratic performance index, is the initial system state vector.

8. The fault-tolerant control method of a steer-by-wire system according to claim 7, characterized in that: In step S7, the linear matrix inequality three is: in, The upper limit of torque.

9. The fault-tolerant control method of a steer-by-wire system according to claim 8, characterized in that: Step S8 specifically includes: Solve the linear matrix inequality 1, linear matrix inequality 2, and linear matrix inequality 3 simultaneously to obtain the control matrix The solution; Will and control matrix Substitute the solution into the formula of the guaranteed cost control law The guaranteed cost control law is obtained .

10. The fault-tolerant control method of a steer-by-wire system according to claim 9, characterized in that: In step S9, the feedforward control law for: ； in, is the feedforward gain; Guaranteed Cost-Feedforward Cooperative Control Law for: 。

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