A virtual motor-based distributed steer-by-wire control method

Abstract

This invention discloses a distributed steer-by-wire control method based on virtual motors, comprising: obtaining the desired yaw rate and desired sideslip angle using a two-degree-of-freedom vehicle model; solving for the reference angles of the steering motors of the four wheels and the reference angle of the virtual motor; solving for the reference speeds of the steering motors of the four wheels and the virtual motor; outputting speed compensation based on the reference speeds of the steering motors of the four wheels and the virtual motor and the actual speed; subtracting the reference speed from both the speed compensation and the actual speed, and using the difference as the output current of the speed controller to control the steering motor deflection, thus completing the steering action. This invention effectively solves the problem of synchronous control of multiple motors at different speeds in a distributed steering system, enabling all wheel angles to quickly and accurately track the target angle, and achieving synchronous control of different speeds during the tracking process, thereby improving the handling performance and accuracy of vehicle trajectory tracking control in distributed steer-by-wire vehicles.

Description

Technical Field

[0001] This invention belongs to the field of automotive steering system technology, specifically relating to a distributed steer-by-wire control method based on a virtual motor. Background Technology

[0002] During vehicle cornering, all wheels must coordinate to complete the turning motion. Due to the Ackermann steering principle, each wheel's turning angle is different, necessitating synchronized control at varying speeds. Furthermore, because the system parameters and external resistance differ for each wheel in a distributed steering system, the tracking of each wheel's steering angle requires both speed-dependent control at different steering angular velocities and synchronized control to simultaneously reach unequal target steering angles. Therefore, speed-dependent synchronized control in distributed steering systems is a critical technology.

[0003] Currently, traditional research mainly focuses on the synchronous control between the various corner modules of a distributed steering system. However, synchronous control ignores the Ackermann steering principle, which inevitably leads to problems such as vehicle deviation from the reference trajectory, reduced vehicle handling stability, and uneven tire wear. Chinese invention patent application number CN201710347018.2, entitled "A Differential Power Steering Control System and Method for a Distributed Drive Electric Vehicle," discloses calculating the generalized yaw moment required by the entire vehicle based on its overall state and using a PI control algorithm to distribute torque to the left and right wheels to achieve differential power steering. However, this method does not consider the impact of tire adhesion differences on differential power steering when the four wheel angles are different. Chinese invention patent application number CN201710758764.0, entitled "A Centralized-Distributed Control System for a Four-Wheel Independent Drive Independent Steering Electric Vehicle," uses four independent single-wheel controllers to control wheel rotation, achieving optimal motion control of vehicle energy, but does not consider the impact of four-wheel angle synchronization on vehicle stability. Summary of the Invention

[0004] In view of the shortcomings of the prior art, the purpose of this invention is to provide a distributed steer-by-wire control method based on a virtual motor, so as to solve the problem of non-synchronization of different speeds in existing distributed steering systems.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] The present invention provides a distributed drive-by-wire steering control method based on a virtual motor, comprising the following steps:

[0007] 1) Based on the vehicle steering wheel angle and the vehicle's real-time speed, the desired yaw rate and desired centroid sideslip angle of the vehicle are obtained by using a two-degree-of-freedom reference model.

[0008] 2) Based on the desired yaw rate and desired centroid sideslip angle obtained in step 1), and the real-time motion state information of the vehicle, the reference steering angles of the steering motors and the reference steering angles of the virtual motors of the four wheels are obtained by using the four-wheel steering angle distributor.

[0009] 3) Based on the deviation between the reference rotation angle and the actual rotation angle of the steering motor and virtual motor of the four wheels, the reference rotation speed of the steering motor and virtual motor of the four wheels is obtained.

[0010] 4) Output speed compensation based on the reference speed and actual speed of the steering motors and virtual motors of the four wheels;

[0011] 5) The reference speed is subtracted from the speed compensation and the actual speed, and the difference is output to the speed controller. The speed controller controls the steering motor to deflect, thus completing the steering action.

[0012] Furthermore, in step 1), the desired yaw rate γ of the vehicle is obtained by solving using a two-degree-of-freedom reference model of the vehicle. * And the expected centroid side slip angle β * The specific steps are as follows:

[0013] 11) Establish a two-degree-of-freedom reference model for the vehicle:

[0014]

[0015] 12) When the vehicle enters a steady state, We can obtain:

[0016]

[0017]

[0018] Where u is the vehicle speed and L is the wheelbase. For stability factors, m is the vehicle mass, and C is the weight of the vehicle. f and C r Let be the equivalent lateral stiffness of the front and rear wheels, respectively; 'a' be the distance from the front axle to the center of gravity; and 'b' be the distance from the rear axle to the center of gravity. z Let δ be the moment of inertia about the z-axis. f This refers to the steering angle of the front wheels.

[0019] Furthermore, the real-time motion status information of the vehicle in step 2) specifically includes: vehicle center of gravity sideslip angle, yaw rate, vehicle speed, lateral acceleration, roll angle, tire lateral force, and tire vertical load.

[0020] Furthermore, the specific steps for solving the reference steering angles of the steering motors and the virtual motors for the four wheels in step 2) are as follows:

[0021] 21) The desired yaw rate γ obtained in step 1) * Adding the yaw rate corrections in the left and right steering domains, the desired centroid sideslip angle β is obtained. * Adding the sideslip angle corrections for the left and right steering domains, the reference yaw rate and reference sideslip angle for the left and right steering domains are obtained as follows:

[0022]

[0023] In the formula, Δγ i,d Δβ is the correction factor for the yaw rate in the left and right turning domains. i,d γ is the correction amount for the centroid sideslip angle in the left and right steering domains. i,d β is the reference yaw rate for the left and right steering domains. i,d The reference centroid sideslip angle for the left and right steering domains;

[0024] 22) Let the state variable be X l =[β l γ l ] T The control variable is The left-turn domain model is established as follows:

[0025]

[0026] In the formula, A l and B l Let β be a constant real matrix. l γ is the actual centroid sideslip angle in the left-turning domain. l δ represents the actual yaw rate in the left-turning domain. fl， δ rl These are the steering angles of the left front wheel and the left rear wheel, respectively.

[0027] Let the state variable be X r =[β r γ r ] T The control variable is The right-turn domain model is established as follows:

[0028]

[0029] In the formula, A r and B r Let β be a constant real matrix. r γ is the actual centroid sideslip angle in the right-turn domain. r δ represents the actual yaw rate in the right-turn domain. fr δ rr These are the steering angles of the right front wheel and the right rear wheel, respectively.

[0030] 23) Based on the reference yaw rate and reference sideslip angle, design a controller to obtain the corresponding front and rear wheel steering angles; define the differences between the reference yaw rate and reference sideslip angle in the left and right steering domains and the actual yaw rate and actual sideslip angle as e, respectively. l,1 e r,1 and e l,2 e r,2 We can obtain:

[0031]

[0032]

[0033] In the formula, e i The difference matrix is ​​represented by i = l, r, which indicates the left and right turning domains; X i,d Indicates the reference state of the left and right turning domains;

[0034] Differentiating the above equation, we get:

[0035]

[0036] In the formula, A i and B i Let U be the coefficient matrix of the system, d(x,t) be the external disturbance, and U be the coefficient matrix of the system. i,d This serves as the system's reference input.

[0037] The sliding surface is constructed as follows:

[0038]

[0039] In the formula, c1 and c2 are controller parameters, and s i,1 and s i,2 These are sliding surfaces constructed based on yaw rate and sliding surfaces constructed based on centroid side slip angle, respectively.

[0040] Differentiating with respect to the sliding surface, we get:

[0041]

[0042] Choose the isokinetic approach law:

[0043] S i =diag(g i )·sgn(S i )

[0044] In the formula, g i For controller parameters;

[0045] but:

[0046]

[0047] In the formula, the controller parameter g i,1 g i,2 Greater than 0;

[0048] Setting the external disturbance d(x,t) = 0, we can obtain:

[0049]

[0050] Therefore, the reference steering angle for the front and rear wheel steering motors in the left steering domain can be obtained as U. l The reference steering angle for the front and rear wheel steering motors in the right steering domain is U. r ;

[0051]

[0052] In the formula, U lf U is the reference steering angle for the left front wheel steering motor. lr U is the reference steering angle for the left rear wheel steering motor. rf U is the reference steering angle for the right front wheel steering motor. rr This is the reference angle for the right rear wheel steering motor;

[0053] The reference rotation angles of the four steering motors are summed, and the average value is taken as the reference rotation angle θ of the virtual motor. x_ref :

[0054]

[0055] Furthermore, step 3) specifically includes:

[0056] The speed controllers of the four steering motors and the virtual motor receive the reference angle and the actual angle, calculate the difference between the reference angle and the actual angle, and input the difference value into the PI controller. The PI controller outputs the value u(t) as the reference speed.

[0057] The expression for the PI controller is as follows:

[0058] u(t) = K p e(t)+K i ∫e(t)dt

[0059] In the formula, u(t) is the output value K of the PI controller. p K is the proportionality coefficient. i Here, is the integral coefficient, and e(t) is the input difference signal.

[0060] Furthermore, step 4) specifically includes:

[0061] 41) The speed compensation device receives the actual speeds of the steering motors of the four wheels and the actual speeds of the virtual motors. It calculates the difference between the actual speeds of the virtual motors and the actual speeds of the steering motors of the four wheels, and then sums these differences to obtain the speed compensation value ω of the virtual motors. x_comp :

[0062]

[0063] In the formula, λ x ω is the speed compensation coefficient for the virtual motor. x ω represents the actual rotational speed of the virtual motor. j The actual rotational speed of the steering motor of the wheel, j = 1, 2, 3, 4; This represents the number of steering motors, and its value is 4.

[0064] 42) Compare the reference speed of the virtual motor with the speed compensation value ω of the virtual motor. x_comp The difference between the actual speed and the speed is sent to the speed controller of the virtual motor. The speed controller of the virtual motor outputs control current to the virtual motor to control the virtual motor to rotate.

[0065] 43) The speed coordination compensator receives the actual speeds of the steering motors of the four wheels and the actual speeds of the virtual motors, calculates the difference between the two, and multiplies the difference by the speed compensation coefficient of each of the four wheels to obtain the speed compensation value ω for each of the four wheels. i_comp :

[0066] ω i_comp =λ i (ω i -ω x ), i = 1, 2, 3, 4 (2)

[0067] In the formula, λ i The speed compensation coefficient for the steering motors of the four wheels;

[0068] 44) Compare the reference speeds of the four wheels with their actual speeds, and the speed compensation values ​​ω for the four wheels. i_comp The difference is calculated and sent to the speed controller of each of the four wheels. The speed controller outputs control current to the steering motor and controls the steering motor to rotate to complete the wheel deflection.

[0069] The voltage equation for the virtual motor is as follows:

[0070]

[0071] In the formula, u d u q These represent the d-axis and q-axis components of the stator voltage of the virtual motor, respectively; R is the stator resistance of the virtual motor; i d iq These represent the d-axis and q-axis components of the stator current of the virtual motor, respectively; ω e L represents the rotor angular velocity of the virtual motor. d L q These are the d-axis and q-axis inductance components, respectively; ψ f For permanent magnet flux linkage;

[0072] electromagnetic torque T of the virtual motor e Represented as:

[0073]

[0074] In the formula, p is the number of pole pairs of the virtual motor;

[0075] The mechanical motion equation of the virtual motor is expressed as:

[0076]

[0077] In the formula, J is the moment of inertia of the virtual motor; B is the damping coefficient of the virtual motor; T L ω represents the load torque of the virtual motor. m This represents the mechanical angular velocity of the virtual motor.

[0078] The beneficial effects of this invention are:

[0079] This invention can effectively solve the problem of different speed synchronization of multiple motors in a distributed steering system, enabling all wheel angles to quickly and accurately track the target angle, and realizing different speed synchronization control during the tracking process, thereby improving the handling performance and accuracy of vehicle trajectory tracking control of distributed steer-by-wire vehicles.

[0080] In this invention, when the number of motors in the distributed steer-by-wire system increases, it is only necessary to add the speed difference between the new motor and the virtual motor to the speed coordination compensator, without changing the original system's coordination compensator.

[0081] This invention eliminates the need to switch control structures or control frameworks after a fault, maintaining consistency of the control framework before and after the fault, which helps reduce jitter during the switching moment before and after a fault. Attached Figure Description

[0082] Figure 1 This is a block diagram illustrating the principle of the control method of the present invention.

[0083] Figure 2 This is a block diagram of the principle of a variable speed synchronizer.

[0084] Figure 3 This is a flowchart of the control method of the present invention. Detailed Implementation

[0085] To facilitate understanding by those skilled in the art, the present invention will be further described below with reference to embodiments and accompanying drawings. The content mentioned in the embodiments is not intended to limit the present invention.

[0086] Reference Figures 1-3 As shown, the distributed drive-by-wire steering control method based on a virtual motor according to the present invention comprises the following steps:

[0087] 1) Based on the vehicle steering wheel angle and the vehicle's real-time speed, the desired yaw rate and desired centroid sideslip angle of the vehicle are obtained by using a two-degree-of-freedom reference model.

[0088] The desired yaw rate r of the vehicle can be obtained by solving using a two-degree-of-freedom reference model. * And the expected centroid side slip angle β * The specific steps are as follows:

[0089] 11) Establish a two-degree-of-freedom reference model for the vehicle:

[0090]

[0091] 12) When the vehicle enters a steady state, We can obtain:

[0092]

[0093]

[0094] Where u is the vehicle speed and L is the wheelbase. For stability factors, m is the vehicle mass, and C is the weight of the vehicle. f and C r Let be the equivalent lateral stiffness of the front and rear wheels, respectively; 'a' be the distance from the front axle to the center of gravity; and 'b' be the distance from the rear axle to the center of gravity. z Let δ be the moment of inertia about the z-axis. f This refers to the steering angle of the front wheels.

[0095] 2) Based on the desired yaw rate and desired centroid sideslip angle obtained in step 1), and the real-time motion state information of the vehicle, the reference steering angles of the steering motors and the reference steering angles of the virtual motors of the four wheels are obtained by using the four-wheel steering angle distributor.

[0096] The vehicle's real-time motion status information specifically includes: vehicle center of gravity sideslip angle, yaw rate, vehicle speed, lateral acceleration, roll angle, tire lateral force, and tire vertical load.

[0097] The specific steps for determining the reference steering angles of the steering motors for the four wheels and the reference steering angle of the virtual motor are as follows:

[0098] 21) The desired yaw rate γ obtained in step 1) *Adding the yaw rate corrections in the left and right steering domains, the desired centroid sideslip angle β is obtained. * Adding the sideslip angle corrections for the left and right steering domains, the reference yaw rate and reference sideslip angle for the left and right steering domains are obtained as follows:

[0099]

[0100] In the formula, Δγ i,d Δβ is the correction factor for the yaw rate in the left and right turning domains. i,d γ is the correction amount for the centroid sideslip angle in the left and right steering domains. i,d β is the reference yaw rate for the left and right steering domains. i,d The reference centroid sideslip angle for the left and right steering domains;

[0101] 22) Let the state variable be X l =[β l γ l ] T The control variable is The left-turn domain model is established as follows:

[0102]

[0103] In the formula, A l and B l Let β be a constant real matrix. l γ is the actual centroid sideslip angle in the left-turning domain. l δ represents the actual yaw rate in the left-turning domain. fl δ rl These are the steering angles of the left front wheel and the left rear wheel, respectively.

[0104] Let the state variable be X r =[β r γ r ] T The control variable is The right-turn domain model is established as follows:

[0105]

[0106] In the formula, A r and B r Let β be a constant real matrix. r γ is the actual centroid sideslip angle in the right-turn domain. r δ represents the actual yaw rate in the right-turn domain. fr δ rr These are the steering angles of the right front wheel and the right rear wheel, respectively.

[0107] 23) Based on the reference yaw rate and reference sideslip angle, design a controller to obtain the corresponding front and rear wheel steering angles; define the differences between the reference yaw rate and reference sideslip angle in the left and right steering domains and the actual yaw rate and actual sideslip angle as e, respectively. l,1 e r,1 and e l,2 e r,2 We can obtain:

[0108]

[0109]

[0110] In the formula, e i The difference matrix is ​​represented by i = l, r, which indicates the left and right turning domains; X i,d Indicates the reference state of the left and right turning domains;

[0111] Differentiating the above equation, we get:

[0112]

[0113] In the formula, A i and B i Let U be the coefficient matrix of the system, d(x,t) be the external disturbance, and U be the coefficient matrix of the system. i,d This serves as the system's reference input.

[0114] The sliding surface is constructed as follows:

[0115]

[0116] In the formula, c1 and c2 are controller parameters, and s i,1 and s i,2 These are sliding surfaces constructed based on yaw rate and sliding surfaces constructed based on centroid side slip angle, respectively.

[0117] Differentiating with respect to the sliding surface, we get:

[0118]

[0119] Choose the isokinetic approach law:

[0120] S i =diag(g i )·sgn(S i )

[0121] In the formula, g i For controller parameters;

[0122] but:

[0123]

[0124] In the formula, the controller parameter g i,1 g i,2 Greater than 0;

[0125] Setting the external disturbance d(x,t) = 0, we can obtain:

[0126]

[0127] Therefore, the reference steering angle for the front and rear wheel steering motors in the left steering domain can be obtained as U. l The reference steering angle for the front and rear wheel steering motors in the right steering domain is U. r ;

[0128]

[0129] In the formula, U lf U is the reference steering angle for the left front wheel steering motor. lr U is the reference steering angle for the left rear wheel steering motor. rf U is the reference steering angle for the right front wheel steering motor. rr This is the reference angle for the right rear wheel steering motor;

[0130] The reference rotation angles of the four steering motors are summed, and the average value is taken as the reference rotation angle θ of the virtual motor. x_ref :

[0131]

[0132] 3) Based on the deviation between the reference and actual steering angles of the steering motors and virtual motors of the four wheels, the reference speeds of the steering motors and virtual motors of the four wheels are calculated; specifically including:

[0133] The speed controllers of the four steering motors and the virtual motor receive the reference angle and the actual angle, calculate the difference between the reference angle and the actual angle, and input the difference value into the PI controller. The PI controller outputs the value u(t) as the reference speed.

[0134] The expression for the PI controller is as follows:

[0135] u(t) = K p e(t)+K i ∫e(t)dt

[0136] In the formula, u(t) is the output value K of the PI controller. p K is the proportionality coefficient. i Here, is the integral coefficient, and e(t) is the input difference signal.

[0137] 4) Output speed compensation based on the reference speed and actual speed of the steering motors and virtual motors of the four wheels; specifically including:

[0138] 41) The speed compensation device receives the actual speeds of the steering motors of the four wheels and the actual speeds of the virtual motors. It calculates the difference between the actual speeds of the virtual motors and the actual speeds of the steering motors of the four wheels, and then sums these differences to obtain the speed compensation value ω of the virtual motors. x_comp :

[0139]

[0140] In the formula, λ x ω is the speed compensation coefficient for the virtual motor. x ω represents the actual rotational speed of the virtual motor. j The actual rotational speed of the steering motor of the wheel, j = 1, 2, 3, 4; The number of steering motors is set to 4.

[0141] 42) Compare the reference speed of the virtual motor with the speed compensation value ω of the virtual motor. x_comp The difference between the actual speed and the speed is sent to the speed controller of the virtual motor. The speed controller of the virtual motor outputs control current to the virtual motor to control the virtual motor to rotate.

[0142] 43) The speed coordination compensator receives the actual speeds of the steering motors of the four wheels and the actual speeds of the virtual motors, calculates the difference between the two, and multiplies the difference by the speed compensation coefficient of each of the four wheels to obtain the speed compensation value ω for each of the four wheels. i_comp :

[0143] ω i_comp =λ i (ω i -ω x ), i = 1, 2, 3, 4 (2)

[0144] In the formula, λ i The speed compensation coefficient for the steering motors of the four wheels;

[0145] 44) Compare the reference speeds of the four wheels with their actual speeds, and the speed compensation values ​​ω for the four wheels. i_comp The difference is calculated and sent to the speed controller of each of the four wheels. The speed controller outputs control current to the steering motor and controls the steering motor to rotate to complete the wheel deflection.

[0146] The voltage equation for the virtual motor is as follows:

[0147]

[0148] In the formula, u d u q These represent the d-axis and q-axis components of the stator voltage of the virtual motor, respectively; R is the stator resistance of the virtual motor; i d iq These represent the d-axis and q-axis components of the stator current of the virtual motor, respectively; ω e L represents the rotor angular velocity of the virtual motor. d L q These are the d-axis and q-axis inductance components, respectively; ψ f For permanent magnet flux linkage;

[0149] electromagnetic torque T of the virtual motor e Represented as:

[0150]

[0151] In the formula, p is the number of pole pairs of the virtual motor;

[0152] The mechanical motion equation of the virtual motor is expressed as:

[0153]

[0154] In the formula, J is the moment of inertia of the virtual motor; B is the damping coefficient of the virtual motor; T L ω represents the load torque of the virtual motor. m This represents the mechanical angular velocity of the virtual motor.

[0155] 5) Subtract the reference speed and speed compensation from the actual speed, and output the difference to the speed controller. The speed controller outputs the corresponding current to the steering motor according to the difference, controls the steering motor to deflect, and completes the steering action.

[0156] This invention has many specific applications. The above description is only a preferred embodiment of this invention. It should be noted that for those skilled in the art, several improvements can be made without departing from the principle of this invention, and these improvements should also be considered within the scope of protection of this invention.

Claims

1. A distributed steer-by-wire control method based on a virtual motor, characterized in that, The steps are as follows: 1) Based on the vehicle's steering wheel angle and real-time speed, the desired yaw rate and desired centroid sideslip angle of the vehicle are obtained by using a two-degree-of-freedom reference model. 2) Based on the desired yaw rate and desired centroid sideslip angle obtained in step 1), and the real-time motion state information of the vehicle, the reference steering angles of the steering motors and the reference steering angles of the virtual motors of the four wheels are obtained by using the four-wheel steering angle distributor. 3) Based on the deviation between the reference rotation angle and the actual rotation angle of the steering motor and virtual motor of the four wheels, the reference rotation speed of the steering motor and virtual motor of the four wheels is obtained. 4) Output speed compensation based on the reference speed and actual speed of the steering motors and virtual motors of the four wheels; 5) Subtract the reference speed and speed compensation from the actual speed, and output the difference to the speed controller. The speed controller controls the steering motor to deflect, thus completing the steering action. In step 1), the desired yaw rate of the vehicle is obtained by using a two-degree-of-freedom reference model. And the expected centroid side slip angle The specific steps are as follows: 11) Establish a two-degree-of-freedom reference model for the vehicle: ； 12) When the vehicle enters a steady state, We can obtain: ； Where u is the vehicle speed and L is the wheelbase. For stability factors, m is the total vehicle mass. and denoted as the equivalent lateral stiffness of the front and rear wheels, respectively; 'a' is the distance from the front axle to the center of gravity, and 'b' is the distance from the rear axle to the center of gravity. Let z be the moment of inertia about the z-axis. The steering angle of the front wheels; The specific steps for solving the reference steering angles of the steering motors and the virtual motors for the four wheels in step 2) are as follows: 21) The desired yaw rate obtained in step 1) Adding the yaw rate corrections in the left and right steering domains, the desired centroid sideslip angle is... Adding the sideslip angle corrections for the left and right steering domains, the reference yaw rate and reference sideslip angle for the left and right steering domains are obtained as follows: ； In the formula, This is the correction amount for the yaw rate in the left and right turning domains. This is the correction amount for the centroid sideslip angle in the left and right steering domains. For the left and right steering domain reference yaw rate, The reference centroid sideslip angle for the left and right steering domains; 22) Take the state variable as The control variable is The left-turn domain model is established as follows: ； In the formula, and It is a constant real matrix. This represents the actual sideslip angle of the center of gravity in the left-turning domain. This represents the actual yaw rate in the left-turn domain. , These are the steering angles of the left front wheel and the left rear wheel, respectively. Take the state variable as The control variable is The right-turn domain model is established as follows: ； In the formula, and It is a constant real matrix. This is the actual sideslip angle of the centroid in the right-turn domain. This represents the actual yaw rate in the right-turn domain. , These are the steering angles of the right front wheel and the right rear wheel, respectively. 23) Based on the reference yaw rate and reference sideslip angle, design a controller to obtain the corresponding front and rear wheel steering angles; define the differences between the reference yaw rate and reference sideslip angle in the left and right steering domains and the actual yaw rate and actual sideslip angle, respectively. , and , We can obtain: ； ； In the formula, It is a difference matrix. Indicates the left and right turn fields; Indicates the reference state of the left and right turning domains; Differentiating the above equation, we get: ； In the formula, and Here is the coefficient matrix of the system. External disturbances This serves as the system's reference input. The sliding surface is constructed as follows: ； In the formula, and For controller parameters, and These are sliding surfaces constructed based on yaw rate and sliding surfaces constructed based on centroid side slip angle, respectively. Differentiating with respect to the sliding surface, we get: ； Choose the isokinetic approach law: ； In the formula, For controller parameters; but: ； In the formula, the controller parameters , Greater than 0; External disturbances = 0, therefore: ； Therefore, the reference steering angles for the front and rear wheel steering motors in the left steering domain can be obtained as follows: The reference steering angle for the front and rear wheel steering motors in the right steering domain is ; ； In the formula, This is the reference angle for the left front wheel steering motor; This is the reference angle for the left rear wheel steering motor; This is the reference steering angle for the right front wheel steering motor; This is the reference angle for the right rear wheel steering motor; The reference angles of the four steering motors are summed, and the average value is taken as the reference angle of the virtual motor. : 。 2. The distributed drive-by-wire steering control method based on a virtual motor according to claim 1, characterized in that, The real-time motion status information of the vehicle in step 2) specifically includes: vehicle center of gravity sideslip angle, yaw rate, vehicle speed, lateral acceleration, roll angle, tire lateral force, and tire vertical load.

3. The distributed drive-by-wire steering control method based on a virtual motor according to claim 1, characterized in that, Step 3) specifically includes: The speed controllers for the four steering motors and the virtual motor receive reference and actual steering angles, calculate the difference between them, and input the difference into the PI controller. The PI controller then outputs a value. As a reference speed; The expression for the PI controller is as follows: ； In the formula, For the output value of the PI controller This is the proportionality coefficient. The integral coefficient is... This is the input difference signal.

4. The distributed drive-by-wire steering control method based on a virtual motor according to claim 1, characterized in that, Step 4) specifically includes: 41) The speed coordination compensator receives the actual speeds of the steering motors of the four wheels and the actual speeds of the virtual motors. It calculates the difference between the actual speeds of the virtual motors and the actual speeds of the steering motors of the four wheels, and then sums these differences to obtain the speed compensation value for the virtual motors. : ； In the formula, This is the speed compensation coefficient for the virtual motor; This represents the actual speed of the virtual motor. The actual speed of the steering motor of the wheel ; This represents the number of steering motors, and its value is 4. 42) Compare the reference speed of the virtual motor with the speed compensation value of the virtual motor. The difference between the actual speed and the speed is sent to the speed controller of the virtual motor. The speed controller of the virtual motor outputs control current to the virtual motor to control the virtual motor to rotate. 43) The speed coordination compensator receives the actual speed of the steering motors of the four wheels and the actual speed of the virtual motor, and calculates the difference between the two. The difference is then multiplied by the speed compensation coefficient of each of the four wheels to obtain the speed compensation value for each of the four wheels. : ； In the formula, The speed compensation coefficient for the steering motors of the four wheels; 44) Compare the reference speeds of the four wheels with the actual speeds and the speed compensation values ​​for the four wheels. The difference is calculated and sent to the speed controller of each of the four wheels. The speed controller outputs control current to the steering motor and controls the steering motor to rotate to complete the wheel deflection. The voltage equation for the virtual motor is as follows: ； In the formula, , These are the d-axis and q-axis components of the stator voltage of the virtual motor, respectively; R is the stator resistance of the virtual motor. , These are the d-axis and q-axis components of the stator current of the virtual motor, respectively. This represents the rotor angular velocity of the virtual motor. , These are the d-axis and q-axis inductance components, respectively. For permanent magnet magnetic flux; electromagnetic torque T of the virtual motor e Represented as: ； In the formula, p is the number of pole pairs of the virtual motor; The mechanical motion equation of the virtual motor is expressed as: ； In the formula, J is the moment of inertia of the virtual motor; B is the damping coefficient of the virtual motor. This represents the load torque of the virtual motor. This represents the mechanical angular velocity of the virtual motor.

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