Fault Tolerant Control Method for Steer-By-Wire System

Abstract

The present invention provides a fault-tolerant control method for a steer-by-wire system. This method fully considers multiple uncertainties such as parameter perturbation of the steer-by-wire system, system disturbance, actuator failure, etc., and controller input limitations. By defining a quadratic performance index and constructing a linear matrix inequality, a guaranteed performance control law is obtained, thereby realizing more accurate and stable fault-tolerant tracking control for 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. By predicting the ideal input to adjust the control output, a robust guaranteed performance-feedforward collaborative fault-tolerant control is formed, 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.

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 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 makes it possible 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, and electronic control unit faults. These faults may not only cause 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 vehicles 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 non-linear 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 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 while 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 urgently solved 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 while 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:

[0006] 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;

[0007] Step S2, construct a system state vector based on the front wheel angle and the reference front wheel angle;

[0008] 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;

[0009] Step S4, reconstruct the system uncertainty matrix and the input uncertainty matrix;

[0010] 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;

[0011] Step S6, define a quadratic performance index, and obtain a linear matrix inequality II in combination with the linear matrix inequality I;

[0012] 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;

[0013] Step S8, obtain a performance-preserving control law based on the linear matrix inequality I, the linear matrix inequality II, and the linear matrix inequality III;

[0014] Step S9, design a feedforward control law, and combine it with the performance-preserving control law to obtain a performance-preserving - feedforward cooperative control law, and perform fault-tolerant control on the steer-by-wire system through the performance-preserving - feedforward cooperative control law.

[0015] 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 to obtain a performance-preserving control law, more accurate and stable fault-tolerant tracking control of the steer-by-wire system is realized. 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 performance-preserving - feedforward cooperative fault tolerance 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. Description of the Drawings

[0016] Figure 1 Flowchart of the fault-tolerant control method for a steer-by-wire system provided by an embodiment of the present invention;

[0017] Figure 2 Comparison chart of the tracking error control effect;

[0018] Figure 3 Comparison chart of the input torque control effect. Specific embodiments

[0019] The embodiments of the present invention will be described in detail below. The examples of the embodiments are shown in the 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 with reference to the drawings are exemplary and are intended to explain the embodiments of the present invention, but should not be construed as limiting the present invention.

[0020] Please refer to Figure 1 , an embodiment of the present invention provides a fault-tolerant control method for a steer-by-wire system, including steps S1 to S9:

[0021] 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.

[0022] 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 dynamic model of the road feel motor is used to represent the road feel feedback assembly part, and the equivalent model combining the dynamic model of the steering motor and the dynamic model of the front steering wheel is used to represent the steering execution assembly part. That is, the equivalent model includes the dynamic model of the steering motor and the dynamic model of the front steering wheel.

[0023] Among them, step S1 specifically includes:

[0024] According to the motor voltage balance equation and the electromagnetic torque equation, the motor torque ripple interference ;

[0025] According to the two-degree-of-freedom driving motion equation and the mechanical equation of the vehicle, the frictional torque and the self-aligning torque ;

[0026] Substitute the motor torque ripple interference into the dynamic model of the steering motor, substitute the frictional torque and the self-aligning torque into the dynamic model of the front steering wheel, and through the front wheel angle and the motor angle The transmission ratio between Merge the steering motor dynamics model and the front wheel dynamics model to obtain the equivalent model;

[0027] Obtain the front wheel steering angle based on the equivalent model , and obtain the reference front wheel steering angle based on the road feel motor dynamics model .

[0028] Step S2: Construct a system state vector based on the front wheel steering angle and the reference front wheel steering angle.

[0029] In step S2, the constructed system state vector is:

[0030] ;

[0031] where is the system state vector, is the reference front wheel steering angle and the front wheel steering angle error, is the time derivative, is integral, is the front wheel steering angle first derivative, represents the transpose.

[0032] Step S3: Define multiple uncertainties, which 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, establish a steer-by-wire system state equation, and the steer-by-wire system state equation contains a system uncertainty matrix and an input uncertainty matrix.

[0033] 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 ;

[0034] The established steer-by-wire system state equation is:

[0035] ;

[0036] ;

[0037] ;

[0038] ;

[0039] ;

[0040] wherein, is the first-order differential of is the performance-preserving 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.

[0041] Step S4, reconstruct the system uncertainty matrix and the input uncertainty matrix.

[0042] wherein, since , are norm-bounded, they can be written in the following form:

[0043] ;

[0044] ;

[0045] ;

[0046] ;

[0047] ;

[0048] wherein, , , 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.

[0049] 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.

[0050] wherein, select the Lyapunov function , is a symmetric positive definite weight matrix. Let , , be the first intermediate weight matrix, be 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 matrices, the first linear matrix inequality is obtained as follows:

[0051] ;

[0052] where , are the polynomial coefficients generated during the inequality transformation process, , are the given symmetric positive definite weighted matrices.

[0053] Step S6: Define the quadratic performance index and combine it with the first linear matrix inequality to obtain the second linear matrix inequality.

[0054] where the quadratic performance index has the following expression:

[0055] ;

[0056] According to the Schur property of matrices, the second linear matrix inequality is:

[0057] ;

[0058] where is the reciprocal of the upper bound of the quadratic performance index and is a positive number; is the initial system state vector.

[0059] 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.

[0060] 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:

[0061]

[0062] where is the torque upper limit.

[0063] 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.

[0064] Among them, step S8 specifically includes:

[0065] Solve the linear matrix inequality one, linear matrix inequality two, and linear matrix inequality three simultaneously to obtain the solution of the control matrix .

[0066] Substitute and the solution of the control matrix into the formula of the guaranteed cost control law to obtain the guaranteed cost control law .

[0067] 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.

[0068] Among them, the feedforward control law is:

[0069] ;

[0070] Among them, is the feedforward gain;

[0071] The guaranteed cost-feedforward cooperative control law is:

[0072] .

[0073] Use the above-mentioned guaranteed cost-feedforward cooperative control law to control the output torque of the steering motor, and complete the fault-tolerant control of the torque part failure fault of the steer-by-wire system.

[0074] Next, perform a simulation test on the method provided by the present invention.

[0075] 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 afterwards. 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 relatively small and more stable. 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 of fault occurrence 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.

[0076] In summary, the fault-tolerant control method of the steer-by-wire system according to the above embodiments fully considers multiple uncertainties such as parameter perturbation, system disturbance, and actuator failure of the steer-by-wire system, as well as controller input limitations. By defining a quadratic performance index and constructing a linear matrix inequality, a guaranteed performance control law is obtained, thereby realizing 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 performance-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.

[0077] The above-described embodiments merely represent several implementation manners of the present invention. The description thereof is relatively specific and detailed, but it should not be construed as a limitation on 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 modifications and improvements can still be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the present invention patent shall be subject to the appended claims.

Claims

1. A fault tolerance control method for a steer-by-wire system, characterized in that, Including: Step S1: Construct a dynamics model of a 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 a 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. The multiple uncertainties include perturbation of the moment of inertia, perturbation of the viscous damping, torque fault factor of the steering motor, and system disturbance. 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 one in combination with the Lyapunov stability equation; Step S6: Define a quadratic performance index, and obtain a linear matrix inequality two in combination with the linear matrix inequality one; Step S7: Combine the linear matrix inequality one and the linear matrix inequality two, and derive a linear matrix inequality three according to the definition of an ellipsoid; Step S8: Obtain a guaranteed cost control law based on the linear matrix inequality one, the linear matrix inequality two, and the linear matrix inequality three; Step S9: Design a feedforward control law, and obtain a guaranteed cost-feedforward cooperative control law in combination with the guaranteed cost control law. Perform fault-tolerant control on the steer-by-wire system through the guaranteed cost-feedforward cooperative control law; The equivalent model includes a dynamics model of a steering motor and a dynamics model of a steering front wheel; 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 mechanical equation of the vehicle, the frictional resistance moment and the aligning moment are obtained; Substitute the motor torque ripple interference into the steering motor dynamics model, and substitute the frictional torque and the self-aligning torque into the steering front wheel dynamics model. Then, through the transmission ratio between the front wheel angle and the motor angle merge the steering motor dynamics model and the steering front wheel dynamics model to obtain the equivalent model; Obtain the front wheel steering angle based on the equivalent model , obtain the reference front wheel steering angle based on the road feel motor dynamics model ; In Step S2, the constructed system state vector is: ； Among them, is the system state vector, is the reference front wheel steering angle and the front wheel steering angle error, is the time differential, is integral, is the front wheel steering angle first-order differential, denotes transpose; 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 perturbation ; The established state equation of the steer-by-wire system is: ； ； ； ； ； wherein, is the first-order differential of, is the performance-preserving 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; Step S4 satisfies the following formula: ； ； ； ； ； Among them, , , are known constant matrices, is a time-varying matrix and satisfies , is the identity matrix; In Step S5, the linear matrix inequality one is: ； Among them, is the first intermediate weight matrix, , is a symmetric positive definite weight matrix; is the second intermediate weight matrix, ; , are polynomial coefficients, , are given symmetric positive definite weighted matrices, is the upper limit of the perturbation; In step S6, the secondary performance index has the following expression: ； The linear matrix inequality two is: ； Among them, is the reciprocal of the upper bound of the quadratic performance index, is the initial system state vector; In Step S7, the linear matrix inequality three is: Among them, is the torque upper limit; Step S8 specifically includes: Solve the simultaneous linear matrix inequalities: Linear Matrix Inequality One, Linear Matrix Inequality Two, and Linear Matrix Inequality Three to obtain the solution of the control matrix ; Substitute and the control matrix into the formula of the guaranteed cost control law to obtain the guaranteed cost control law .

2. The fault-tolerant control method for a steer-by-wire system according to claim 1, characterized in that In step S9, the feedforward control law is as follows: ； Among them, is the feedforward gain; Guaranteed performance - feedforward cooperative control law is as follows: 。

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