Intelligent vehicle lane hold steering motor control method

Abstract

The application provides a kind of intelligent vehicle steer-by-wire motor control method, and the steer-by-wire motor adopts double closed-loop control of rotation angle ring and current loop;The rotation angle ring is controlled by an improved nonlinear active-disturbance rejection controller, and the current loop is controlled by a fractional order PID controller;The improved nonlinear active-disturbance rejection controller includes an improved third-order nonlinear extended state observer and a nonlinear state error feedback control law, wherein the nonlinear state error feedback control law adopts a super-spiral second-order sliding mode control.The method enhances the anti-interference and robustness of the steer-by-wire motor system, improves the estimation accuracy of the observer, and improves the tracking performance of the steer-by-wire motor.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of automobile auxiliary driving, and in particular to a tracking method of an intelligent steer-by-wire system. BACKGROUND

[0002] Steer-by-wire technology is based on the traditional steering mode, and uses electronic devices to replace the mechanical connection between the steering wheel and the wheels, so as to realize the decoupling of the force transmission characteristics and the angle 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 system, and 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, the control of the steer-by-wire motor mostly adopts control methods such as PID control, neural network control, sliding mode control and active disturbance rejection control, and there are problems such as low tracking accuracy, poor robustness and poor disturbance rejection. PID control has the attribute of no model, and does not have to rely on specific models in the design process, has the characteristics of simple principle and strong adaptability, but also leads to the difficulty of mechanism research, and in the face of complex working conditions, the calibration work of control parameters is complex and tedious. The neural network algorithm has both calculation accuracy and efficiency, but it is very complex, and there is a contradiction between the network size and the instance size in practical application. The traditional sliding mode control has many advantages such as the invariance of matching disturbance when the system is in the sliding mode, and the simple realization of the controller, but in actual application, the traditional sliding mode control has the following defects: (1) chattering problem; (2) control accuracy problem; (3) relative order limitation.

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

[0004] Active disturbance rejection control is a new type of control algorithm without the need to establish an accurate motor model, including three parts: tracking differentiator, extended state observer and nonlinear state error feedback law, and the extended state observer is the core of the active disturbance rejection control. The active disturbance rejection control inherits the advantages of the PID control and improves the defect of the rapid overshoot, has strong anti-disturbance and robustness. Compared with the traditional active disturbance rejection control, the observer of the 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 the number of controller parameter settings is significantly reduced. The nonlinear active disturbance rejection control considers the influence of internal disturbances, external disturbances, model uncertainties and other factors, and its tracking accuracy is higher than that of the linear active disturbance rejection control. SUMMARY

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

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

[0007] The improved nonlinear active disturbance rejection controller includes a nonlinear extended state observer and a nonlinear state error feedback control law. 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-spiral second-order sliding mode controller to enhance the tracking performance of the intelligent vehicle's steer-by-wire motor.

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

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

[0010]

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

[0012] S1.2, The electromagnetic torque equation of the steer-by-wire motor is established as follows:

[0013]

[0014] In the formula, p n T represents the number of pole pairs of the steer-by-wire motor. e Electromagnetic torque;

[0015] S1.3, The mechanical motion equations of the steer-by-wire motor are established as follows:

[0016]

[0017] In the formula, θ is the output angle of the steer-by-wire motor; J is the moment of inertia; B is the damping coefficient; T LThis is the load torque;

[0018] S1.4. Rewrite the mechanical motion equation of the steerable motor in formula (3) into the general form of the improved nonlinear active disturbance rejection control:

[0019]

[0020] In the formula, f1 is the total unknown disturbance of the system to be estimated; y is the output angle of the steer-by-wire motor; u is the current loop current of the steer-by-wire motor; b0 is the parameters of the steer-by-wire motor's moment of inertia, number of pole pairs, and flux linkage. The estimate is given by b, where b0 and b are not equal and contain errors; f2 represents the information of the steer-by-wire motor model, i.e., the known system dynamics; t represents time; f in is the unknown disturbance inside the system to be estimated; w is the disturbance caused by time-varying characteristics and other unknown external factors to be estimated.

[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 extended state variable;

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

[0025]

[0026] In the formula, e represents 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, and x3, respectively, and z3 is the estimated value of the total perturbation. Design an improved third-order nonlinear extended state observer that satisfies 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 As 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 superspiral second-order sliding mode controller includes the following steps:

[0030] S2.1 The mechanical motion equations of the steer-by-wire motor are rewritten as follows:

[0031]

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

[0033] S2.2, the deviation amount of the target angle and the actual angle of the steer-by-wire motor is taken as the control variable, and the control variable of the steer-by-wire motor angle tracking system is defined as:

[0034] e = θ d - z1 (9)

[0035] wherein e is the control variable; θ d is the target angle input by the steer-by-wire motor system;

[0036] S2.3, the control variable e is differentiated:

[0037]

[0038] S2.4, the sliding surface function s of the super-spiral second-order sliding mode control is defined as:

[0039]

[0040] wherein c is a parameter to be designed;

[0041] S2.5, the formula (11) is differentiated to obtain:

[0042]

[0043] S2.6, the formula (8) is brought into the formula (12) to obtain:

[0044]

[0045] S2.7, the global control output of the super-spiral second-order sliding mode controller is composed of an equivalent control term and a super-spiral control term; the global control output is defined as:

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

[0047] wherein u0 is the global control output of the super-spiral second-order sliding mode controller; u eq is the equivalent control term; u st is the super-spiral control term;

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

[0049]

[0050] S2.9, the super-spiral 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 in time, and the expression is:

[0051]

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

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

[0054]

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

[0056]

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

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

[0059] The improved nonlinear active disturbance rejection controller is used in the steer-by-wire motor angle loop, which takes into account the influence of internal disturbances, external disturbances, model uncertainties and other factors, and has higher tracking accuracy than linear active disturbance rejection control, inherits the advantages of PID control, improves the shortcomings of rapid overshoot, and has the characteristics of strong anti-disturbance and robustness; the improved nonlinear extended state observer of the improved nonlinear active disturbance rejection controller is constructed using known information of the system, and has higher estimation accuracy than the conventional extended state observer; the nonlinear state error feedback control law uses super-spiral second-order sliding mode control, which does not require derivative information of the sliding variable, overcomes the defects of traditional sliding mode, solves the problem of weak robustness of the steer-by-wire system to external disturbances, suppresses the chattering of the system, and effectively enhances the tracking performance of the steer-by-wire motor; therefore, it has wide market application prospect. BRIEF DESCRIPTION OF DRAWINGS

[0060] Figure 1 It is an improved nonlinear active disturbance rejection control method for the intelligent vehicle steer-by-wire motor angle loop. DETAILED DESCRIPTION

[0061] The technical solutions of the present application will be further described in detail below in combination with the drawings:

[0062] The application can be implemented in many different forms and should not be considered limited to the embodiments described herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the application to those skilled in the art. In the drawings, components are exaggerated for clarity.

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

[0064] The steering-by-wire motor adopts double-closed-loop control of an angle ring and a current ring, wherein the angle ring adopts an improved nonlinear active disturbance rejection controller for control, and the current ring adopts a fractional order PID controller for control.

[0065] The improved nonlinear active disturbance rejection controller comprises 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-spiral second-order sliding mode controller to enhance the tracking performance of the intelligent vehicle steering-by-wire motor.

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

[0067] S1.1, establish a steering-by-wire motor voltage equation:

[0068]

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

[0070] S1.2, the electromagnetic torque equation of the steering-by-wire motor is established as:

[0071]

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

[0073] S1.3, the mechanical motion equation of the steering-by-wire motor is established as:

[0074]

[0075] In the formula, θ is the output angle of the steer-by-wire motor; J is the moment of inertia; B is the damping coefficient; T L This is the load torque;

[0076] S1.4. Rewrite the mechanical motion equation of the steerable motor in formula (3) into the general form of the improved nonlinear active disturbance rejection control:

[0077]

[0078] In the formula, f1 represents the total unknown disturbance of the system to be estimated; y represents the output angle of the steer-by-wire motor; u represents the current loop current of the steer-by-wire motor; and b0 represents the parameters of the steer-by-wire motor, including its moment of inertia, number of pole pairs, and flux linkage. The estimate is given by b, where b0 and b are not equal and contain errors; f2 represents the information of the steer-by-wire motor model, i.e., the known system dynamics; t represents time; f in is the unknown disturbance inside the system to be estimated; w is the disturbance caused by time-varying characteristics and other unknown external factors to be estimated.

[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 extended state variable;

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

[0083]

[0084] In the formula, e represents 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, and x3, respectively, and z3 is the estimated value of the total perturbation. Design an improved third-order nonlinear extended state observer that satisfies z3→f1; nonlinear function g i (i = 1, 2, 3) can be represented as:

[0085]

[0086] In the formula, δ is a positive constant; α i As 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 ring super-hyperbolic second-order sliding mode controller includes the following steps:

[0088] S2.1, rewriting the mechanical motion equation of the steer-by-wire motor as:

[0089]

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

[0091] S2.2, taking the deviation amount of the target angle and the actual angle of the steer-by-wire motor as the control variable, and defining the control variable of the steer-by-wire motor angle tracking system as:

[0092] e = θ d -z1 (9)

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

[0094] S2.3, taking the derivative of the control variable e:

[0095]

[0096] S2.4, defining the sliding surface function s of the super-hyperbolic second-order sliding mode control as:

[0097]

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

[0099] S2.5, taking the derivative of formula (11) to obtain:

[0100]

[0101] S2.6, formula (8) is brought into formula (12) to obtain:

[0102]

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

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

[0105] In the formula, u0 is the global control output of the super-hyperbolic second-order sliding mode controller; u eq is the equivalent control term; u st is the super-hyperbolic control term;

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

[0107]

[0108] S2.9, the super-spiral 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 in time, and its expression is:

[0109]

[0110] In the formula, λ and γ are both 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-spiral second-order sliding mode controller of the steer-by-wire motor angle loop is:

[0112]

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

[0114]

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

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

[0117] The above specific embodiments further illustrate the purpose, technical solutions and beneficial effects of the present application. It should be understood that the above description is only a specific embodiment of the present application and is not intended to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application should be included in the protection scope of the present application.​

Claims

1. A method for controlling a drive-by-wire steering motor in an intelligent vehicle, characterized in that, The steer-by-wire motor adopts dual closed-loop control of angle loop and 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. The improved nonlinear active disturbance rejection controller includes a nonlinear extended state observer and a nonlinear state error feedback control law. 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-spiral second-order sliding mode controller to enhance the tracking performance of the intelligent vehicle's steer-by-wire motor. The establishment of the improved third-order nonlinear extended state observer includes the following steps: S1.1 Establish the voltage equation for the steer-by-wire motor: In the formula, u d u q These are the d-axis and q-axis components of the stator voltage, respectively; i d i q These are the d-axis and q-axis components of the stator current, respectively; R is the stator resistance; w e It is the electric angular velocity; L d L q These are the d-axis and q-axis inductance components, respectively; ψ f Represents permanent magnet flux linkage; S1.2, The electromagnetic torque equation of the steer-by-wire motor is established as follows: In the formula, p n T represents the number of pole pairs of the steer-by-wire motor. e Electromagnetic torque; S1.3, The mechanical motion equations of the steer-by-wire motor are established as follows: In the formula, θ is the output angle of the steer-by-wire motor; J is the moment of inertia; B is the damping coefficient; T L This is the load torque; S1.

4. Rewrite the mechanical motion equation of the steerable motor in formula (3) into the general form of the improved nonlinear active disturbance rejection control: In the formula, f1 represents the total unknown disturbance of the system to be estimated; y represents the output angle of the steer-by-wire motor; u represents the current loop current of the steer-by-wire motor; and b0 represents the parameters of the steer-by-wire motor, including its moment of inertia, number of pole pairs, and flux linkage. The estimate is given by b, where b0 and b are not equal and contain errors; f2 represents the information of the steer-by-wire motor model, i.e., the known system dynamics; t represents time; f in is the unknown disturbance inside the system to be estimated; w is the disturbance caused by time-varying characteristics and other unknown external factors to be estimated. S1.5 Define state variables: In the formula, x1 and x2 are the system's state variables; x3 is the new extended state variable; S1.6 Establish an improved third-order nonlinear extended state observer: In the formula, e represents 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, and x3, respectively, and z3 is the estimated value of the total perturbation. Design an improved third-order nonlinear extended state observer that satisfies z3→f1; nonlinear function g i (i = 1, 2, 3) is represented as: In the formula, δ is a positive constant; α i As 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.

2. The intelligent vehicle steer-by-wire motor control method according to claim 1, characterized in that, The establishment of the superspiral second-order sliding mode controller includes the following steps: S2.1 The mechanical motion equations of the steer-by-wire motor are rewritten as follows: In the formula, K t This refers to the torque coefficient of the steer-by-wire motor. S2.

2. The deviation between the target angle and the actual angle of the steer-by-wire motor is taken as the control variable, and the control variable of the steer-by-wire motor angle tracking system is defined as follows: e=θ d -z1 (9) In the formula, e is the control variable; θ d The target steering angle input to the steer-by-wire motor system; S2.3, Differentiate with respect to the control variable e: S2.

4. Define the sliding surface function s for the superspiral second-order sliding mode control as: In the formula, c is the parameter to be designed; S2.5, Differentiating equation (11) yields: S2.6 Substituting equation (8) into equation (12), we get: S2.7 The global control output of the superspiral second-order sliding mode controller consists of an equivalent control term and a superspiral control term. The global control output is defined as follows: u0=u eq +u st (14) In the formula, u0 is the global control output of the superspiral second-order sliding mode controller; u eq For equivalent control items; u st For superhelical control terms; S2.8, Equivalent control terms are obtained by solving the equation. get: S2.9 The superspiral 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 both constants greater than 0; v represents an intermediate variable; S2.10, combined with equations (15) and (16), yields the global control output of the second-order sliding mode controller for the steering motor's angle ring super-spiral:

3. The intelligent vehicle steer-by-wire motor control method according to any one of claims 1 and 2, characterized in that, The output of the improved nonlinear active disturbance rejection controller is: In the formula, i q * The output is for the improved nonlinear active disturbance rejection controller of the corner loop.

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