Trajectory tracking control method and system for automatic driving vehicle based on four-wheel distributed driving

Abstract

The invention discloses an automatic driving vehicle trajectory tracking control method and system based on four-wheel distributed driving. The method comprises the steps that the current speed of a four-wheel distributed driving vehicle and the expected speed of a user are obtained; a four-wheel distributed driving bicycle is simplified into an ideal two-degree-of-freedom bicycle model, wherein the model comprises an ideal rear wheel and an ideal front wheel; the absolute position of the ideal rear wheel of the four-wheel distributed driving vehicle at the current moment is determined, the steering radius of the ideal two-degree-of-freedom bicycle model and the steering angle of the ideal front wheel are calculated, and the expected track of the four-wheel distributed driving vehicle is obtained; calculating the basic rotating speed of each wheel of the four-wheel distributed driving vehicle; calculating the compensation speed of each wheel of the four-wheel distributed driving vehicle; and based on the basic speed of each wheel and the compensation speed of each wheel, obtaining the total expected rotating speed of each wheel. According to the invention, trajectory tracking control of the four-wheel distributed driving vehicle is realized with relatively high real-time performance.

Description

Technical Field

[0001] The present invention belongs to the technical field of autonomous driving, and in particular to a trajectory tracking control method and system for an autonomous driving vehicle based on four-wheel distributed drive. Background Art

[0002] Distributed drive vehicles developed in recent years generally work in a mode where several drive motors output independently controllable speed and torque to complete the steering and travel of the vehicle. Thanks to their strong reliability and high energy efficiency, distributed drive vehicles are widely used in many fields such as park distribution, urban connection, and scientific and educational research. However, distributed drive vehicles also have the disadvantages of poor control stability and insufficient control sensitivity, which in some aspects limits the possibility of large-scale promotion and industrial use. At present, only a few solution providers at home and abroad have developed control methods that can be deployed to various platforms and run well, and it is difficult for ordinary users to customize them for specific needs. The distributed drive solution involves the coordination of software and hardware between multiple groups of drive units, and the debugging steps are cumbersome, which greatly increases the threshold for the landing of vehicle autonomous driving in the above scenarios. There are many factors that affect the distributed drive vehicle to follow the expected trajectory. The error of the perception and positioning device will cause the monitoring of kinematic states such as posture and heading, which will indirectly interfere with the output of the execution unit; the expected trajectory of the pre-decision may have a dead zone that does not meet the vehicle dynamics constraints, resulting in the vehicle having an out-of-control condition such as excessive slip rate during trajectory tracking, which gradually expands the path error. These factors have a great negative impact on driving safety and limit the realization of autonomous driving functions. Therefore, designing a control method to correct the following error is a problem that the industry must face. For four-wheel distributed drive vehicles that cannot adjust the steering angle, the wheels will slip and wear significantly under all other conditions except straight-line driving. This will not only damage the mechanical structure of the vehicle and shorten its service life, but also affect the vehicle's trajectory tracking performance, and it will take a lot of time to converge the error when it deviates too much from the expected trajectory. Summary of the invention

[0003] In order to solve the above technical problems, the present invention proposes an autonomous driving vehicle trajectory tracking control method and system based on four-wheel distributed drive, which can significantly improve the accuracy and real-time performance of trajectory tracking while minimizing vehicle slippage, and realize multi-dimensional effective tracking of heading and speed.

[0004] On the one hand, to achieve the above-mentioned purpose, the present invention provides a trajectory tracking control method for an autonomous driving vehicle based on four-wheel distributed drive, comprising:

[0005] Obtaining the current speed of the four-wheel distributed drive vehicle and the user's expected speed;

[0006] The four-wheel distributed drive vehicle is simplified into an ideal two-degree-of-freedom bicycle model, where the model includes an ideal rear wheel and an ideal front wheel;

[0007] Determine the absolute position of the ideal rear wheel of the four-wheel distributed drive vehicle at the current moment, calculate the turning radius of the ideal two-degree-of-freedom bicycle model and the turning angle of the ideal front wheel, and obtain the expected trajectory of the four-wheel distributed drive vehicle;

[0008] Calculating the basic rotation speed of each wheel of the four-wheel distributed drive vehicle;

[0009] Calculating the compensation speed of each wheel of the four-wheel distributed drive vehicle;

[0010] Based on the basic speed of each wheel and the compensation speed of each wheel, a total expected rotation speed of each wheel is obtained.

[0011] According to the trajectory tracking control method of the autonomous driving vehicle based on four-wheel distributed drive provided by the present invention, simplifying the four-wheel distributed drive vehicle into an ideal two-degree-of-freedom bicycle model includes:

[0012] The left front wheel and the right front wheel of the four-wheel distributed drive vehicle are equivalently converted into ideal front wheels, and the left rear wheel and the right rear wheel are equivalently converted into ideal rear wheels, and the ideal front wheel and the ideal rear wheel are both on the longitudinal center axis of the whole vehicle.

[0013] According to the trajectory tracking control method for an autonomous driving vehicle based on four-wheel distributed drive provided by the present invention, the method for calculating the turning radius of the ideal two-degree-of-freedom bicycle model is:

[0014] Absolute position p t and the expected tracking point p tar The distance between them is l;

[0015] The rolling direction of the ideal rear wheel and the straight line p t p tar The angle between them is θ;

[0016] Absolute position p t To the desired tracking point p tar During the tracking process, the path traveled by the ideal rear wheel is an arc, and the turning radius R of the ideal two-degree-of-freedom bicycle model is calculated as:

[0017] OP t =Op tar ,

[0018] According to the trajectory tracking control method for an autonomous driving vehicle based on four-wheel distributed drive provided by the present invention, the method for calculating the turning angle of the ideal front wheel of the ideal two-degree-of-freedom bicycle model is as follows: the intersection of the straight line where the ideal front wheel is located and the straight line where the ideal rear wheel is located is the turning center, the angle between the two straight lines is equal to the turning angle δ of the front wheel, and the distance from the ideal front wheel to the ideal rear wheel is l d ;

[0019] The ideal front wheel turning angle of the ideal two-degree-of-freedom bicycle model is calculated as:

[0020] Substitution have to

[0021] According to the trajectory tracking control method of the autonomous driving vehicle based on four-wheel distributed drive provided by the present invention, the method for calculating the basic rotation speed of each wheel of the four-wheel distributed drive vehicle is:

[0022] Based on the ideal two-degree-of-freedom bicycle model, the yaw angular velocity ω is calculated as:

[0023]

[0024] The basic speed is calculated based on the yaw rate:

[0025]

[0026] Among them, n lf 、n lr 、n rf 、n rr are the speeds of the left front wheel, left rear wheel, right front wheel and right rear wheel respectively, R w is the wheel radius; v t is the current speed of the four-wheel distributed drive vehicle; l d is the distance from the ideal front wheel to the ideal rear wheel; b is the wheelbase.

[0027] According to the trajectory tracking control method of the autonomous driving vehicle based on four-wheel distributed drive provided by the present invention, the method for calculating the compensation speed of each wheel of the four-wheel distributed drive vehicle is:

[0028] Calculate the compensation speed Δn of each wheel based on the speed error v :

[0029]

[0030] Where e(j) represents the speed difference error at the jth sampling moment; k p is the speed error proportional coefficient; e(t) is the speed error; k i is the velocity error integral coefficient;

[0031] Calculate the compensation speed Δn of each wheel based on the heading error d :

[0032]

[0033] Among them, e d (t) is the heading error; k dd is the heading error differential coefficient; e d (j) is the heading error at the jth moment; T is the control period; ψ t is the angle between the current vehicle heading and the x-axis of the earth coordinate system, ψ tar Represents the angle between the tangent line of the desired trajectory at the desired tracking point and the x-axis of the geodetic coordinate system;

[0034] Calculate the compensation speed Δn of each wheel based on the lateral error l :

[0035]

[0036] Among them, e l (t) represents the distance from the current vehicle position to the projection point on the desired trajectory; k l and B l They are the proportional coefficient and base number that can be adjusted manually.

[0037] According to the trajectory tracking control method of the autonomous driving vehicle based on four-wheel distributed drive provided by the present invention, the method for obtaining the total expected rotation speed of each wheel based on the basic speed of each wheel and the compensation speed of each wheel is:

[0038]

[0039] Among them, lf, rf, lr, rr are the subscripts of the physical quantities related to the left front wheel, right front wheel, left rear wheel and right rear wheel of the four-wheel distributed drive vehicle respectively; Δn lf , Δn rf , Δn lr , Δn rr is the total expected speed of the left front wheel, the right front wheel, the left rear wheel, and the right rear wheel of the four-wheel distributed drive vehicle; Δn v is the compensation speed of each wheel; Δn d is the compensation speed of each wheel; Δn l is the compensation speed of each wheel.

[0040] On the other hand, to achieve the above-mentioned purpose, the present invention also provides an autonomous driving vehicle trajectory tracking control system based on four-wheel distributed drive, including: a speed acquisition module, a model building module, a vehicle desired trajectory acquisition module, a vehicle basic speed calculation module, a vehicle compensation speed calculation module and a vehicle total desired speed calculation module;

[0041] The speed acquisition module is used to obtain the current speed of the four-wheel distributed drive vehicle and the user's expected speed;

[0042] The model building module is used to simplify the four-wheel distributed drive vehicle into an ideal two-degree-of-freedom bicycle model, wherein the model includes an ideal rear wheel and an ideal front wheel;

[0043] The vehicle expected trajectory acquisition module is used to determine the absolute position of the ideal rear wheel of the four-wheel distributed drive vehicle at the current moment, calculate the turning radius of the ideal two-degree-of-freedom bicycle model and the turning angle of the ideal front wheel, and obtain the expected trajectory of the four-wheel distributed drive vehicle;

[0044] The vehicle basic speed calculation module is used to calculate the basic speed of each wheel of the four-wheel distributed drive vehicle;

[0045] The vehicle compensation speed calculation module is used to calculate the compensation speed of each wheel of the four-wheel distributed drive vehicle;

[0046] The vehicle total expected speed calculation module is used to obtain the total expected speed of each wheel based on the basic speed of each wheel and the compensation speed of each wheel.

[0047] Technical effect of the invention: The present invention discloses a trajectory tracking control method and system for an autonomous driving vehicle based on four-wheel distributed drive, which solves the problem that the traditional control method for differential steering vehicles cannot meet the kinematic requirements. By introducing the expected tracking point and the ideal front and rear wheels, the difficult-to-analyze differential steering model is converted into an ideal two-degree-of-freedom model and the basic speed is calculated. Then, the trajectory is optimized from three aspects: lateral error, heading error and speed, and the compensation speed is solved. Based on multi-dimensional speed compensation, the trajectory tracking control of the four-wheel distributed drive vehicle is achieved with strong real-time performance while minimizing wheel slip and wear. The present invention has good effects in engineering applications and lowers the threshold for the implementation of unmanned driving of distributed drive vehicles. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] The drawings constituting a part of the present application are used to provide a further understanding of the present application. The illustrative embodiments and descriptions of the present application are used to explain the present application and do not constitute an improper limitation on the present application. In the drawings:

[0049] Figure 1It is a flow chart of a trajectory tracking control method of an autonomous driving vehicle based on four-wheel distributed drive according to an embodiment of the present invention;

[0050] Figure 2 This is a schematic diagram of the structure of a trajectory tracking control system for an autonomous driving vehicle based on four-wheel distributed drive according to an embodiment of the present invention;

[0051] Figure 3 A schematic diagram of solving a turning radius according to an embodiment of the present invention;

[0052] Figure 4 A schematic diagram of solving the ideal front wheel turning angle according to an embodiment of the present invention. DETAILED DESCRIPTION

[0053] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0054] It should be noted that the steps shown in the flowcharts of the accompanying drawings can be executed in a computer system such as a set of computer executable instructions, and that, although a logical order is shown in the flowcharts, in some cases, the steps shown or described can be executed in an order different from that shown here.

[0055] like Figure 1 As shown, this embodiment provides a trajectory tracking control method for an autonomous driving vehicle based on four-wheel distributed drive, including:

[0056] Obtaining the current speed of the four-wheel distributed drive vehicle and the user's expected speed;

[0057] The four-wheel distributed drive vehicle is simplified into an ideal two-degree-of-freedom bicycle model, where the model includes an ideal rear wheel and an ideal front wheel;

[0058] Determine the absolute position of the ideal rear wheel of the four-wheel distributed drive vehicle at the current moment, calculate the turning radius and the ideal front wheel turning angle of the ideal two-degree-of-freedom bicycle model, and obtain the expected trajectory of the four-wheel distributed drive vehicle;

[0059] Calculate the basic rotation speed of each wheel of the four-wheel distributed drive vehicle;

[0060] Calculate the compensation speed of each wheel of the four-wheel distributed drive vehicle;

[0061] Based on the basic speed of each wheel and the compensation speed of each wheel, the total expected rotation speed of each wheel is obtained.

[0062] Specifically, the vehicle kinematic state is collected through wheel speed sensors and inertial measurement units to solve the vehicle speed, and is input into the vehicle controller together with the expected vehicle speed command from the user.

[0063] Furthermore, simplifying the four-wheel distributed drive vehicle to an ideal two-degree-of-freedom bicycle model includes:

[0064] The left front wheel and the right front wheel of the four-wheel distributed drive vehicle are equivalently converted into ideal front wheels, and the left rear wheel and the right rear wheel are equivalently converted into ideal rear wheels, and the ideal front wheel and the ideal rear wheel are both on the longitudinal center axis of the whole vehicle.

[0065] Specifically, the complex four-wheel differential model is converted into a simple two-degree-of-freedom single-track model; after solving the intermediate quantity of the front wheel turning angle required for the single-track model, the basic rotation speed required for each wheel is obtained by reverse solving, thus achieving the expected technical goal of four-wheel differential steering.

[0066] Further, such as Figure 3 As shown in Figure 2, the method for calculating the turning radius of an ideal two-degree-of-freedom bicycle model is:

[0067] Absolute position p t and the expected tracking point p tar The distance between them is l;

[0068] The rolling direction of the ideal rear wheel and the straight line p t p tar The angle between them is θ;

[0069] Absolute position p t To the desired tracking point p tar During the tracking process, the ideal rear wheel travels a circular arc. The turning radius R of the ideal two-degree-of-freedom bicycle model is calculated as:

[0070] Op t =Op tar ,

[0071] Further, such as Figure 4 As shown, the method for calculating the turning angle of the ideal front wheel of the ideal two-degree-of-freedom bicycle model is as follows: the intersection of the straight line where the ideal front wheel is located and the straight line where the ideal rear wheel is located is the turning center, the angle between the two straight lines is equal to the turning angle δ of the front wheel, and the distance from the ideal front wheel to the ideal rear wheel is l d ;

[0072] The ideal front wheel angle of the ideal two-degree-of-freedom bicycle model is calculated as:

[0073] Substitution have to

[0074] Furthermore, the method for calculating the basic rotation speed of each wheel of the four-wheel distributed drive vehicle is:

[0075] Based on the ideal two-degree-of-freedom bicycle model, the yaw angular velocity ω is calculated as:

[0076]

[0077] The basic speed is calculated based on the yaw rate:

[0078]

[0079] Among them, n lf 、n lr 、n rf 、n rr are the speeds of the left front wheel, left rear wheel, right front wheel and right rear wheel respectively, R w is the wheel radius; v t is the current speed of the four-wheel distributed drive vehicle; l d is the distance from the ideal front wheel to the ideal rear wheel; b is the wheelbase. When the vehicle deviates from the desired trajectory, the trajectory is optimized from three aspects: heading error, lateral error and speed until convergence, achieving high-precision tracking control.

[0080] Furthermore, the method for calculating the compensation speed of each wheel of the four-wheel distributed drive vehicle is:

[0081] Calculate the compensation speed Δn of each wheel based on the speed error v :

[0082]

[0083] Where e(j) represents the speed difference error at the jth sampling moment; k p is the speed error proportional coefficient; e(t) is the speed error; k i is the speed error integral coefficient; specifically, a PI controller is used so that the actual speed of the vehicle gradually converges to the desired speed when it approaches the tracking point until the error is 0. Since the platform used in this patent is a differential steering vehicle, the compensation speed Δn v Acts on each wheel without affecting the steering angle and yaw rate;

[0084] Calculate the compensation speed Δn of each wheel based on the heading error d :

[0085]

[0086] Among them, e d (t) is the heading error; k dd is the heading error differential coefficient; e d (j) is the heading error at the jth moment; T is the control period; ψ t is the angle between the current vehicle heading and the x-axis of the earth coordinate system, ψ tarIndicates the angle between the tangent of the desired trajectory at the desired tracking point and the x-axis of the earth coordinate system; specifically, a PD controller is used so that when the vehicle approaches the tracking point, its actual heading gradually converges smoothly to the desired heading to avoid high-frequency jitter. Since the platform used in this patent is a differential steering vehicle, the compensation speed Δn d Acting on the two front wheels, the speed changes of the inner and outer wheels are and

[0087] Calculate the compensation speed Δn of each wheel based on the lateral error l :

[0088]

[0089] Among them, e l (t) represents the distance from the current vehicle position to the projection point on the desired trajectory; k l and B l are the proportional coefficient and base number that can be adjusted manually; specifically, an exponential function relationship is used so that the lateral error of the vehicle approaches the tracking point, and gradually approaches 0. d It has acted on the two front wheels. Considering the constraints of hardware execution capability, the speed Δn will be compensated l For the two rear wheels, the speed changes of the inner and outer wheels are and

[0090] Furthermore, based on the basic speed of each wheel and the compensation speed of each wheel, the method for obtaining the total expected rotation speed of each wheel is:

[0091]

[0092]

[0093] Among them, lf, rf, lr, rr are the subscripts of the physical quantities related to the left front wheel, right front wheel, left rear wheel and right rear wheel of the four-wheel distributed drive vehicle respectively; Δn lf , Δn rf , Δn lr , Δn rr is the total expected speed of the left front wheel, the right front wheel, the left rear wheel, and the right rear wheel of the four-wheel distributed drive vehicle; Δn v is the compensation speed of each wheel; Δn d is the compensation speed of each wheel; Δn l is the compensation speed of each wheel.

[0094] Specifically, a PD controller is used to make the actual heading of the vehicle converge smoothly to the desired heading to avoid high-frequency oscillation. The required compensation speed Δn d Acting on the two front wheels to ensure the vehicle's responsiveness to this quantity; using a PI controller to make the vehicle's real-time speed converge quickly to the desired speed until the error is eliminated. The required compensation speed Δn l Acting on each wheel, it will not affect the yaw rate of the differential steering. An exponential function controller is used to make the lateral error of the vehicle converge quickly to 0. The required compensation speed Δn d Acts on the two rear wheels to protect each wheel so that its rotation speed does not exceed the constraints of the hardware execution capability.

[0095] like Figure 2 As shown, this embodiment also provides an autonomous driving vehicle trajectory tracking control system based on four-wheel distributed drive, including: a speed acquisition module, a model building module, a vehicle desired trajectory acquisition module, a vehicle basic speed calculation module, a vehicle compensation speed calculation module and a vehicle total desired speed calculation module;

[0096] The speed acquisition module is used to obtain the current speed of the four-wheel distributed drive vehicle and the user's expected speed;

[0097] Building a model module for simplifying the four-wheel distributed drive vehicle into an ideal two-degree-of-freedom bicycle model, wherein the model includes an ideal rear wheel and an ideal front wheel;

[0098] The vehicle expected trajectory acquisition module is used to determine the absolute position of the ideal rear wheel of the four-wheel distributed drive vehicle at the current moment, calculate the turning radius and the ideal front wheel turning angle of the ideal two-degree-of-freedom bicycle model, and obtain the expected trajectory of the four-wheel distributed drive vehicle;

[0099] The vehicle basic speed calculation module is used to calculate the basic speed of each wheel of the four-wheel distributed drive vehicle;

[0100] A vehicle compensation speed calculation module is used to calculate the compensation speed of each wheel of the four-wheel distributed drive vehicle;

[0101] The vehicle total expected speed calculation module is used to obtain the total expected speed of each wheel based on the basic speed of each wheel and the compensation speed of each wheel.

[0102] The present invention discloses a trajectory tracking control method and system for an autonomous driving vehicle based on four-wheel distributed drive, which solves the problem that the traditional control method for differential steering vehicles cannot meet the kinematic requirements. By introducing the expected tracking point and the ideal front and rear wheels, the difficult-to-analyze differential steering model is converted into an ideal two-degree-of-freedom model and the basic speed is calculated. Then, the trajectory is optimized from three aspects: lateral error, heading error and speed, and the compensation speed is calculated. Based on multi-dimensional speed compensation, the trajectory tracking control of the four-wheel distributed drive vehicle is achieved with strong real-time performance while minimizing wheel slip and wear. The present invention has good effects in engineering applications and lowers the threshold for the implementation of unmanned driving of distributed drive vehicles.

[0103] The above are only preferred specific implementations of the present application, but the protection scope of the present application is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed in the present application should be included in the protection scope of the present application. Therefore, the protection scope of the present application should be based on the protection scope of the claims.

Claims

1. A trajectory tracking control method for an autonomous driving vehicle based on four-wheel distributed drive, characterized in that: include: Obtaining the current speed of the four-wheel distributed drive vehicle and the user's expected speed; The four-wheel distributed drive vehicle is simplified into an ideal two-degree-of-freedom bicycle model, where the model includes an ideal rear wheel and an ideal front wheel; Determine the absolute position of the ideal rear wheel of the four-wheel distributed drive vehicle at the current moment, calculate the turning radius of the ideal two-degree-of-freedom bicycle model and the turning angle of the ideal front wheel, and obtain the expected trajectory of the four-wheel distributed drive vehicle; Calculating the basic rotation speed of each wheel of the four-wheel distributed drive vehicle; Calculating the compensation speed of each wheel of the four-wheel distributed drive vehicle; Based on the basic speed of each wheel and the compensation speed of each wheel, a total expected rotation speed of each wheel is obtained.

2. The trajectory tracking control method for an autonomous driving vehicle based on four-wheel distributed drive according to claim 1, characterized in that: Simplifying the four-wheel distributed drive vehicle into an ideal two-degree-of-freedom bicycle model includes: The left front wheel and the right front wheel of the four-wheel distributed drive vehicle are equivalently converted into ideal front wheels, and the left rear wheel and the right rear wheel are equivalently converted into ideal rear wheels, and the ideal front wheel and the ideal rear wheel are both on the longitudinal center axis of the whole vehicle.

3. The trajectory tracking control method for an autonomous driving vehicle based on four-wheel distributed drive according to claim 1, characterized in that: The method for calculating the turning radius of the ideal two-degree-of-freedom bicycle model is: Absolute position p t and the expected tracking point p tar The distance between them is l; The rolling direction of the ideal rear wheel and the straight line p t p tar The angle between them is θ; Absolute position p t To the desired tracking point p tar During the tracking process, the path traveled by the ideal rear wheel is an arc, and the turning radius R of the ideal two-degree-of-freedom bicycle model is calculated as: ON t =On tar , 4. The trajectory tracking control method for an autonomous driving vehicle based on four-wheel distributed drive according to claim 1, characterized in that: The method for calculating the turning angle of the ideal front wheel of the ideal two-degree-of-freedom bicycle model is as follows: the intersection of the straight line where the ideal front wheel is located and the straight line where the ideal rear wheel is located is the turning center, the angle between the two straight lines is equal to the turning angle δ of the front wheel, and the distance from the ideal front wheel to the ideal rear wheel is l d ; The ideal front wheel turning angle of the ideal two-degree-of-freedom bicycle model is calculated as: Substitution have to 5. The trajectory tracking control method for an autonomous driving vehicle based on four-wheel distributed drive according to claim 1, characterized in that: The method for calculating the basic rotation speed of each wheel of the four-wheel distributed drive vehicle is: Based on the ideal two-degree-of-freedom bicycle model, the yaw angular velocity ω is calculated as: The basic speed is calculated based on the yaw rate: Among them, n lf 、n lr 、n rf 、n rr are the speeds of the left front wheel, left rear wheel, right front wheel and right rear wheel respectively, R w is the wheel radius; v t is the current speed of the four-wheel distributed drive vehicle; l d is the distance from the ideal front wheel to the ideal rear wheel; b is the wheelbase.

6. The trajectory tracking control method for an autonomous driving vehicle based on four-wheel distributed drive according to claim 1, characterized in that: The method for calculating the compensation speed of each wheel of the four-wheel distributed drive vehicle is: Calculate the compensation speed Δn of each wheel based on the speed error v : Where e(j) represents the speed difference error at the jth sampling moment; k p is the speed error proportional coefficient; e(t) is the speed error; k i is the velocity error integral coefficient; Calculate the compensation speed Δn of each wheel based on the heading error d : Among them, e d (t) is the heading error; k dd is the heading error differential coefficient; e d (j) is the heading error at the jth moment; T is the control period; ψ t is the angle between the current vehicle heading and the x-axis of the earth coordinate system, ψ tar Represents the angle between the tangent line of the desired trajectory at the desired tracking point and the x-axis of the geodetic coordinate system; Calculate the compensation speed Δn of each wheel based on the lateral error l : Among them, e l (t) represents the distance from the current vehicle position to the projection point on the desired trajectory; k l and B l They are the proportional coefficient and base number that can be adjusted manually.

7. The trajectory tracking control method for an autonomous driving vehicle based on four-wheel distributed drive according to claim 1, characterized in that: Based on the basic speed of each wheel and the compensation speed of each wheel, the method for obtaining the total expected rotation speed of each wheel is: Among them, lf, rf, lr, rr are the subscripts of the physical quantities related to the left front wheel, right front wheel, left rear wheel and right rear wheel of the four-wheel distributed drive vehicle respectively; Δn lf , Δn rf , Δn lr , Δn rr is the total expected speed of the left front wheel, the right front wheel, the left rear wheel, and the right rear wheel of the four-wheel distributed drive vehicle; Δn v is the compensation speed of each wheel; Δn d is the compensation speed of each wheel; Δn l is the compensation speed of each wheel.

8. A system for trajectory tracking control of an autonomous driving vehicle based on four-wheel distributed drive according to any one of claims 1 to 7, characterized in that: include: Speed ​​acquisition module, model building module, vehicle expected trajectory acquisition module, vehicle basic speed calculation module, vehicle compensation speed calculation module and vehicle total expected speed calculation module; The speed acquisition module is used to obtain the current speed of the four-wheel distributed drive vehicle and the user's expected speed; The model building module is used to simplify the four-wheel distributed drive vehicle into an ideal two-degree-of-freedom bicycle model, wherein the model includes an ideal rear wheel and an ideal front wheel; The vehicle expected trajectory acquisition module is used to determine the absolute position of the ideal rear wheel of the four-wheel distributed drive vehicle at the current moment, calculate the turning radius of the ideal two-degree-of-freedom bicycle model and the turning angle of the ideal front wheel, and obtain the expected trajectory of the four-wheel distributed drive vehicle; The vehicle basic speed calculation module is used to calculate the basic speed of each wheel of the four-wheel distributed drive vehicle; The vehicle compensation speed calculation module is used to calculate the compensation speed of each wheel of the four-wheel distributed drive vehicle; The vehicle total expected speed calculation module is used to obtain the total expected speed of each wheel based on the basic speed of each wheel and the compensation speed of each wheel.

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