Intelligent vehicle steer-by-wire motor control method

Abstract

The invention provides an intelligent vehicle steer-by-wire motor control method. A steer-by-wire motor adopts double closed-loop control of a corner loop and a current loop; the corner loop is controlled by an improved nonlinear active-disturbance-rejection controller, and the current loop is controlled by a fractional order PID (Proportion Integration Differentiation) controller; the improved non-linear active disturbance rejection controller comprises an improved third-order non-linear extended state observer and a non-linear state error feedback control law, wherein the non-linear state error feedback control law adopts super-spiral second-order sliding mode control. According to the method, the disturbance resistance and robustness of the steer-by-wire motor system are enhanced, the estimation precision of the observer is improved, and the tracking performance of the steer-by-wire motor is improved.

Description

Technical Field

[0001] The present invention relates to the field of automobile assisted driving, and in particular to a tracking method for a smart vehicle steer-by-wire system. Background Art

[0002] Steer-by-wire technology is based on the traditional steering method. It uses electronic devices to replace the mechanical connection between the steering wheel and the wheel, and realizes the decoupling of the force transmission characteristics and angular transmission characteristics of the steering system. The control of the steer-by-wire motor is closely related to the tracking accuracy of the steer-by-wire. Improving the tracking accuracy of the steer-by-wire motor is conducive to improving the performance of the entire steer-by-wire system. At present, most steer-by-wire motor control methods use PID control, neural network control, sliding film control and anti-disturbance control. There are still problems such as low tracking accuracy, poor robustness and poor anti-disturbance. PID control has a model-free property. It does not need to rely on a specific model during the design process. It has the characteristics of simple principle and strong adaptability, but it also makes it difficult to study the mechanism. When facing complex working conditions, the calibration of control parameters will be complicated and cumbersome. Neural network algorithms have both calculation accuracy and efficiency, but they are very complex. In practical applications, there is a contradiction between network scale and instance scale. Traditional sliding mode control has many advantages, such as invariance to matching disturbances when the system is in sliding mode and simple controller implementation. However, in practical applications, traditional sliding mode control has the following defects: (1) chattering problem; (2) control accuracy problem; (3) relative order limitation.

[0003] However, the super-helical second-order sliding mode control algorithm overcomes the defects of traditional sliding mode and plays an important role in high-order sliding mode control: first, it does not require the derivative information of the sliding mode variable and is a widely used continuous second-order sliding mode control method when the system relative order is 1; second, it is the theoretical basis of arbitrary order precise robust differentiators.

[0004] Active disturbance rejection control is a new control algorithm that does not require the establishment of an accurate motor model. It includes three parts: tracking differentiator, extended state observer and nonlinear state error feedback law, among which the extended state observer is the core of active disturbance rejection control. Active disturbance rejection control inherits the advantages of PID control, improves its disadvantage of rapid overshoot, and has strong anti-disturbance and robustness. Compared with traditional active disturbance rejection control, the observer of linear active disturbance rejection control can also estimate and compensate the total disturbance composed of the unmodeled dynamics and external disturbances of the system in real time, but significantly reduces the number of controller parameter settings. Nonlinear active disturbance rejection control takes into account the influence of factors such as internal disturbances, external disturbances, and model uncertainty of the system, and its tracking accuracy is higher than that of linear active disturbance rejection control. Summary of the invention

[0005] The purpose of the present invention is to propose a tracking method for a steer-by-wire system of an intelligent vehicle, enhance the anti-interference and robustness of the steer-by-wire motor system, improve the estimation accuracy of the observer, and improve the tracking performance of the steer-by-wire motor.

[0006] To achieve the above object, the technical solution of the present invention is: a control method for a wire-controlled steering motor of an intelligent vehicle, wherein the wire-controlled steering motor adopts a double closed-loop control of an angle loop and a current loop, wherein the angle loop is controlled by an improved nonlinear active disturbance rejection controller, and the current loop is controlled by a fractional-order PID controller;

[0007] The improved nonlinear anti-disturbance controller includes a nonlinear extended state observer and a nonlinear state error feedback control law, wherein the nonlinear extended state observer adopts an improved third-order nonlinear extended state observer, and the nonlinear state error feedback control law adopts a super-helical second-order sliding mode controller to enhance the tracking performance of the smart car's wire-controlled steering motor.

[0008] Preferably, the establishment of the improved third-order nonlinear extended state observer comprises the following steps:

[0009] S1.1. Establish the voltage equation of the steer-by-wire motor:

[0010]

[0011] In the formula, u d 、u q are the d-axis and q-axis components of the stator voltage respectively; i d 、i q are the d-axis and q-axis components of the stator current respectively; R is the stator resistance; w e is the electrical angular velocity; L d , L q are the d-axis and q-axis inductance components respectively; ψ f represents the permanent magnet flux;

[0012] S1.2. Establish the electromagnetic torque equation of the wire-controlled steering motor:

[0013]

[0014] In the formula, p n is the pole pair number of the wire-controlled steering motor; T e is the electromagnetic torque;

[0015] S1.3. Establish the mechanical motion equation of the wire-controlled steering motor:

[0016]

[0017] Where θ is the output angle of the wire-controlled steering motor; J is the moment of inertia; B is the damping coefficient; T Lis the load torque;

[0018] S1.4. Rewrite the mechanical motion equation of the wire-controlled steering motor in formula (3) into the general expression of the improved nonlinear active disturbance rejection control:

[0019]

[0020] Where f1 is the unknown sum disturbance of the system to be estimated; y is the output angle of the wire steering motor; u is the current loop current of the wire steering motor; b0 is the moment of inertia, pole pair number and flux composition parameters of the wire steering motor is an estimate of the system dynamics. b is the ideal value. b0 and b are not equal and there is an error. f2 is the model information of the steer-by-wire motor, that is, the known system dynamics. t is the time. f in is the unknown disturbance to be estimated in the system; w is the disturbance to be estimated due to time-varying characteristics and other unknown external factors;

[0021] S1.5 Define state variables:

[0022]

[0023] In the formula, x1 and x2 are the state variables of the system, and x3 is the new expanded state variable;

[0024] S1.6 Establish an improved third-order nonlinear extended state observer:

[0025]

[0026] Where, e is the observation error; β i (i=1,2,3) are the parameters of the improved third-order nonlinear extended state observer; z1, z2, z3 are the estimated values ​​of x1, x2, x3 respectively, and z3 is the total disturbance estimate The improved third-order nonlinear extended state observer is designed to satisfy z3→f1; the nonlinear function gi (i=1,2,3) is expressed as:

[0027]

[0028] In the formula, δ is a positive constant; α i is a nonlinear function factor. When it is between 0 and 1, the fal function will have the characteristics of large error and small gain and small error and large gain.

[0029] Preferably, the establishment of the superhelical second-order sliding mode controller comprises the following steps:

[0030] S2.1. Rewrite the mechanical motion equation of the wire-controlled steering motor as:

[0031]

[0032] In the formula, K t is the torque coefficient of the steer-by-wire motor;

[0033] S2.2. Take the deviation between the target angle and the actual angle of the wire-controlled steering motor as the control variable, and define the control variable of the wire-controlled steering motor angle tracking system as:

[0034] e=θ d -z1 (9)

[0035] In the formula, e is the control variable; θ d A target turning angle input to the steer-by-wire motor system;

[0036] S2.3. Derivative the control variable e:

[0037]

[0038] S2.4. Define the sliding surface function s of the superhelical second-order sliding mode control as:

[0039]

[0040] In the formula, c is the parameter to be designed;

[0041] S2.5. Deriving equation (11) yields:

[0042]

[0043] S2.6, Substituting formula (8) into formula (12), we can obtain:

[0044]

[0045] S2.7. The global control output of the superhelical second-order sliding mode controller consists of an equivalent control term and a superhelical control term; the global control output is defined as:

[0046] u0=u eq +u st (14)

[0047] Where u0 is the global control output of the superhelical second-order sliding mode controller; u eq is an equivalent control item; u st is the supercoil control term;

[0048] S2.8, the equivalent control term is obtained by solving Eq. get:

[0049]

[0050] S2.9, the super-helix control algorithm consists of two parts. The first part is a continuous function of the sliding surface, and the second part is the integral of the sliding surface over time, expressed as:

[0051]

[0052] In the formula, λ and γ are constants greater than 0; v represents an intermediate variable;

[0053] S2.10, combined with equation (15) and equation (16), the global control output of the super-helical second-order sliding mode controller of the steer-by-wire motor angle loop is obtained as:

[0054]

[0055] Preferably, the output of the improved nonlinear active disturbance rejection controller is:

[0056]

[0057] In the formula, i q * It is the output of the improved nonlinear active disturbance rejection controller for the corner loop.

[0058] Compared with the prior art, the present invention has the following beneficial effects:

[0059] The angle loop of the steer-by-wire motor adopts an improved nonlinear active disturbance rejection controller, which takes into account the influence of factors such as internal disturbances, external disturbances, and model uncertainty of the system. Its tracking accuracy is higher than that of linear active disturbance rejection control, inherits the advantages of PID control, improves its disadvantages of rapid overshoot, and has the characteristics of strong disturbance rejection and robustness; the improved nonlinear extended state observer of the improved nonlinear active disturbance rejection controller is constructed using the known information of the system, and its estimation accuracy is higher than that of the conventional extended state observer; the nonlinear state error feedback control law adopts super-helical second-order sliding mode control, which does not require the derivative information of the sliding mode variable, overcomes the defects of the traditional sliding mode, solves the problem of weak robustness of the steer-by-wire system to external disturbances, and suppresses the system's jitter, effectively enhancing the tracking performance of the steer-by-wire motor; therefore, it has broad market application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0060] Figure 1 It is a schematic diagram of the improved nonlinear anti-disturbance control method for the steering angle loop of the smart car steer-by-wire motor of the present invention. DETAILED DESCRIPTION

[0061] The technical solution of the present invention is further described in detail below in conjunction with the accompanying drawings:

[0062] The present invention can be implemented in many different forms and should not be considered to be limited to the embodiments described herein. On the contrary, these embodiments are provided to make this disclosure thorough and complete, and will fully express the scope of the present invention to those skilled in the art. In the accompanying drawings, components are enlarged for clarity.

[0063] like Figure 1 As shown, the parameters in the figure will be defined below, where i q ' is the feedback current of the wire-controlled steering motor; the intelligent vehicle wire-controlled steering motor control method comprises the following steps:

[0064] The wire-controlled steering motor adopts dual closed-loop control of an angle loop and a current loop, wherein the angle loop is controlled by an improved nonlinear anti-disturbance controller and the current loop is controlled by a fractional-order PID controller;

[0065] The improved nonlinear anti-disturbance controller includes a nonlinear extended state observer and a nonlinear state error feedback control law, wherein the nonlinear extended state observer adopts an improved third-order nonlinear extended state observer, and the nonlinear state error feedback control law adopts a super-helical second-order sliding mode controller to enhance the tracking performance of the smart car's wire-controlled steering motor.

[0066] The establishment of the improved third-order nonlinear extended state observer comprises the following steps:

[0067] S1.1. Establish the voltage equation of the steer-by-wire motor:

[0068]

[0069] In the formula, u d 、u q are the d-axis and q-axis components of the stator voltage respectively; i d 、i q are the d-axis and q-axis components of the stator current respectively; R is the stator resistance; w e is the electrical angular velocity; L d , L q are the d-axis and q-axis inductance components respectively; ψ f represents the permanent magnet flux;

[0070] S1.2. Establish the electromagnetic torque equation of the wire-controlled steering motor:

[0071]

[0072] In the formula, p n is the pole pair number of the wire-controlled steering motor; T e is the electromagnetic torque;

[0073] S1.3. Establish the mechanical motion equation of the wire-controlled steering motor:

[0074]

[0075] Where θ is the output angle of the wire-controlled steering motor; J is the moment of inertia; B is the damping coefficient; T L is the load torque;

[0076] S1.4. Rewrite the mechanical motion equation of the wire-controlled steering motor in formula (3) into the general expression of the improved nonlinear active disturbance rejection control:

[0077]

[0078] Where f1 is the unknown sum disturbance of the system to be estimated; y is the output angle of the wire steering motor; u is the current loop current of the wire steering motor; b0 is the moment of inertia, pole pair number and flux composition parameters of the wire steering motor is an estimate of the system dynamics. b is the ideal value. b0 and b are not equal and there is an error. f2 is the model information of the steer-by-wire motor, that is, the known system dynamics. t is the time. f in is the unknown disturbance to be estimated in the system; w is the disturbance to be estimated due to time-varying characteristics and other unknown external factors;

[0079] S1.5 Define state variables:

[0080]

[0081] In the formula, x1 and x2 are the state variables of the system, and x3 is the new expanded state variable;

[0082] S1.6 Establish an improved third-order nonlinear extended state observer:

[0083]

[0084] Where, e is the observation error; β i (i=1,2,3) are the parameters of the improved third-order nonlinear extended state observer; z1, z2, z3 are the estimated values ​​of x1, x2, x3 respectively, and z3 is the total disturbance estimate Design an improved third-order nonlinear extended state observer to satisfy z3→f1; the nonlinear function g i (i=1,2,3) can be expressed as:

[0085]

[0086] In the formula, δ is a positive constant; α i is a nonlinear function factor. When it is between 0 and 1, the fal function will have the characteristics of large error and small gain and small error and large gain.

[0087] The establishment of the corner loop superhelical second-order sliding mode controller comprises the following steps:

[0088] S2.1. Rewrite the mechanical motion equation of the wire-controlled steering motor as follows:

[0089]

[0090] In the formula, K t is the torque coefficient of the steer-by-wire motor;

[0091] S2.2. Take the deviation between the target angle and the actual angle of the wire-controlled steering motor as the control variable, and define the control variable of the wire-controlled steering motor angle tracking system as:

[0092] e=θ d -z1 (9)

[0093] In the formula, e is the control variable; θ d A target turning angle input to the steer-by-wire motor system;

[0094] S2.3. Derivative the control variable e:

[0095]

[0096] S2.4. Define the sliding surface function s of the superhelical second-order sliding mode control as:

[0097]

[0098] In the formula, c is the parameter to be designed;

[0099] S2.5. Deriving equation (11) yields:

[0100]

[0101] S2.6, Substituting formula (8) into formula (12), we can obtain:

[0102]

[0103] S2.7. The global control output of the superhelical second-order sliding mode controller consists of an equivalent control term and a superhelical control term; therefore, the global control output is defined as:

[0104] u0=u eq +u st (14)

[0105] Where u0 is the global control output of the superhelical second-order sliding mode controller; u eq is an equivalent control item; u st is the supercoil control term;

[0106] S2.8, the equivalent control term can be obtained by solving Eq. get:

[0107]

[0108] S2.9, the super-helix control algorithm consists of two parts. The first part is a continuous function of the sliding surface, and the second part is the integral of the sliding surface over time, which is expressed as:

[0109]

[0110] In the formula, λ and γ are constants greater than 0; v represents an intermediate variable;

[0111] S2.10, combined with equation (15) and equation (16), the global control output of the super-helical second-order sliding mode controller of the steer-by-wire motor angle loop is obtained as:

[0112]

[0113] The output of the improved nonlinear active disturbance rejection controller is:

[0114]

[0115] In the formula, i q * It is the output of the improved nonlinear active disturbance rejection controller for the corner loop.

[0116] It will be understood by those skilled in the art that, unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as those generally understood by those skilled in the art in the art to which the present invention belongs. It should also be understood that terms such as those defined in common dictionaries should be understood to have meanings consistent with the meanings in the context of the prior art, and will not be interpreted with idealized or overly formal meanings unless defined as herein.

[0117] The specific implementation methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation method of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for controlling a steer-by-wire motor of an intelligent vehicle, characterized in that: The wire-controlled steering motor adopts dual closed-loop control of an angle loop and a current loop, wherein the angle loop is controlled by an improved nonlinear anti-disturbance controller and the current loop is controlled by a fractional-order PID controller; The improved nonlinear anti-disturbance controller includes a nonlinear extended state observer and a nonlinear state error feedback control law, wherein the nonlinear extended state observer adopts an improved third-order nonlinear extended state observer, and the nonlinear state error feedback control law adopts a super-helical second-order sliding mode controller to enhance the tracking performance of the smart car's wire-controlled steering motor.

2. The intelligent vehicle steer-by-wire motor control method according to claim 1, characterized in that: The establishment of the improved third-order nonlinear extended state observer comprises the following steps: S1.

1. Establish the voltage equation of the steer-by-wire motor: In the formula, u d 、u q are the d-axis and q-axis components of the stator voltage respectively; i d 、i q are the d-axis and q-axis components of the stator current respectively; R is the stator resistance; w e is the electrical angular velocity; L d , L q are the d-axis and q-axis inductance components respectively; ψ f represents the permanent magnet flux; S1.

2. Establish the electromagnetic torque equation of the wire-controlled steering motor: In the formula, p n is the pole pair number of the wire-controlled steering motor; T e is the electromagnetic torque; S1.

3. Establish the mechanical motion equation of the wire-controlled steering motor: Where θ is the output angle of the wire-controlled steering motor; J is the moment of inertia; B is the damping coefficient; T L is the load torque; S1.

4. Rewrite the mechanical motion equation of the wire-controlled steering motor in formula (3) into the general expression of the improved nonlinear active disturbance rejection control: Where f1 is the unknown sum disturbance of the system to be estimated; y is the output angle of the wire steering motor; u is the current loop current of the wire steering motor; b0 is the moment of inertia, pole pair number and flux composition parameters of the wire steering motor is an estimate of the system dynamics. b is the ideal value. b0 and b are not equal and there is an error. f2 is the model information of the steer-by-wire motor, that is, the known system dynamics. t is the time. f in is the unknown disturbance to be estimated in the system; w is the disturbance to be estimated due to time-varying characteristics and other unknown external factors; S1.5 Define state variables: In the formula, x1 and x2 are the state variables of the system; x3 is the new expanded state variable; S1.6 Establish an improved third-order nonlinear extended state observer: Where, e is the observation error; β i (i=1,2,3) are the parameters of the improved third-order nonlinear extended state observer; z1, z2, z3 are the estimated values ​​of x1, x2, x3 respectively, and z3 is the total disturbance estimate The improved third-order nonlinear extended state observer is designed to satisfy z3→f1; the nonlinear function gi (i=1,2,3) is expressed as: In the formula, δ is a positive constant; α i is a nonlinear function factor. When it is between 0 and 1, the fal function will have the characteristics of large error and small gain and small error and large gain.

3. The intelligent vehicle steer-by-wire motor control method according to claim 1, characterized in that: The establishment of the super-helical second-order sliding mode controller comprises the following steps: S2.

1. Rewrite the mechanical motion equation of the wire-controlled steering motor as: In the formula, K t is the torque coefficient of the steer-by-wire motor; S2.

2. Take the deviation between the target angle and the actual angle of the wire-controlled steering motor as the control variable, and define the control variable of the wire-controlled steering motor angle tracking system as: e=θ d -z1 (9) In the formula, e is the control variable; θ d A target turning angle input to the steer-by-wire motor system; S2.

3. Derivative the control variable e: S2.

4. Define the sliding surface function s of the superhelical second-order sliding mode control as: In the formula, c is the parameter to be designed; S2.

5. Deriving equation (11) yields: S2.6, Substituting formula (8) into formula (12), we can obtain: S2.

7. The global control output of the superhelical second-order sliding mode controller consists of an equivalent control term and a superhelical control term. The global control output is defined as: Where u0 is the global control output of the superhelical second-order sliding mode controller; u eq is an equivalent control item; u st is the supercoil control term; S2.8, the equivalent control term is obtained by solving Eq. get: S2.9, the super-helix control algorithm consists of two parts. The first part is a continuous function of the sliding surface, and the second part is the integral of the sliding surface over time, expressed as: In the formula, λ and γ are constants greater than 0; v represents an intermediate variable; S2.10, combined with equation (15) and equation (16), the global control output of the super-helical second-order sliding mode controller of the steer-by-wire motor angle loop is obtained as:

4. The control method of the smart vehicle steer-by-wire motor according to any one of claims 2 and 3, characterized in that: The output of the improved nonlinear active disturbance rejection controller is: In the formula, i q * It is the output of the improved nonlinear active disturbance rejection controller for the corner loop.

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