CN115171414A - CACC following traffic flow control system based on Frenet coordinate system - Google Patents

Abstract

The invention provides a CACC following vehicle flow control system based on a Frenet coordinate system, which relates to the technical field of unmanned control and vehicle-road cooperation. The adjusted running state information is collected by the information collection module, so that the vehicle can always keep a safe and comfortable following state. The method can accurately and efficiently solve the problem of control decision of the following state of the CACC vehicle under various traffic scenes and conditions, and help the CACC vehicle to automatically and safely complete a driving task.

Description

A CACC Car-Following Traffic Flow Control System Based on Frenet Coordinate System

technical field

The invention relates to the technical field of unmanned control and vehicle-road coordination, in particular to a CACC following traffic flow control system based on the Frenet coordinate system.

Background technique

In the vehicle-road cooperative environment, cooperative adaptive cruise control (CACC) vehicles have the functions and characteristics of information exchange and sharing, accurate perception of surrounding traffic conditions, and stable and rapid decision-making control. Compared with ordinary vehicles, CACC vehicles can follow the vehicle with a smaller time-to-vehicle distance.

At present, most of the coordinate systems used in the control algorithm for CACC vehicle following state are Cartesian coordinate system, odometer coordinate system, polar coordinate system, etc. However, in the process of implementing these algorithms, these coordinate systems have certain drawbacks: (1) In the algorithm based on the global coordinate system, the trajectory information is limited by the local map, and the timeliness of sampling and the fitting of the model are affected by the length of the trajectory. (2) The algorithm based on the Cartesian coordinate system, the efficiency restricts the bottleneck of the optimization of the decision-making system. (3) The algorithm calculation based on the odometer coordinate system has a large cumulative error.

The Frenet coordinate system uses the variable s representing the distance along the road and the variable d representing the left and right positions on the road to describe the position of the vehicle on the road or reference path. Using the Frenet coordinate system to describe the motion trajectory of the vehicle has nothing to do with the absolute position of the vehicle, but only the selection of the road reference line. The computational cost of model fitting will be greatly reduced, and the efficiency and performance of the system will also be greatly improved.

SUMMARY OF THE INVENTION

The purpose of the present invention is to keep the CACC vehicle in a safe and comfortable following state continuously and efficiently, and provides a CACC following traffic flow control system based on the Frenet coordinate system.

The object of the present invention is achieved through the following technical solutions: a CACC-following traffic flow control system based on the Frenet coordinate system, comprising the following steps:

A CACC following traffic flow control system based on the Frenet coordinate system, the system includes:

an information collection module, the information collection module collects the trajectory information of the preceding vehicle and the own vehicle, and the information collection module transmits the collected information to the trajectory transformation module;

a trajectory transformation module, the trajectory transformation module converts the trajectory information to the Frenet coordinate system according to the Cartesian coordinate system, and obtains the trajectory information under the Frenet coordinate system;

The control module controls and adjusts the running state of the own vehicle according to the trajectory information obtained in the Frenet coordinate system, and the adjusted running state information is continuously collected by the information collection module, so that the own vehicle maintains a safe and comfortable car-following state.

Further, the control module includes a decision-making unit, an upper-level controller and a lower-level controller; the decision-making unit calculates and analyzes the current safe and comfortable car-following state to be maintained by the own vehicle and the required distance to be maintained by the preceding vehicle according to the safety distance model. Minimum safety distance, and input this information into the upper controller;

The upper layer controller calculates the current speed and acceleration trajectory information required to be maintained by the own vehicle, and at the same time sends the required speed and acceleration trajectory information to the lower layer controller, and the lower layer controller controls and adjusts the running state of the own vehicle.

Further, the trajectory transformation module converts the trajectory information to the Frenet coordinate system according to the Cartesian coordinate system as:

The relationship between the vehicle trajectory in the Frenet coordinate system and the Cartesian coordinate system is transformed. In the Cartesian coordinate system, let p(x _p , y _p ) be the closest point to the trajectory point x (x _x , y _y ); then in In the Frenet coordinate system, the ordinates of point p and point x are equal;

The position and speed trajectory information of the CACC vehicle is input into the trajectory conversion module, and the conversion from the Cartesian coordinate system to the Frenet coordinate system is expressed by the following formula:

s=s _p (1)

d'=(1-dk _p )tan(θ _x -θ _p ) (4)

为Frenet坐标系下轨迹点x纵向坐标对时间的导数，表示车辆沿参考线方向的速度，

为Frenet坐标系下轨迹点x纵向坐标对时间的二阶导数，表示车辆沿参考线方向的加速度，d为Frenet坐标系下轨迹点x的横向坐标，d′为Frenet坐标系下轨迹点x横向坐标对纵向坐标的一阶导数，d″为Frenet坐标系下轨迹点x横向坐标对纵向坐标的二阶导数，θ_x是笛卡尔坐标系下轨迹点x的方位角，θ_p是笛卡尔坐标系下点P的方位角，k_x是笛卡尔坐标系下轨迹点x的曲率，k_p是Frenet坐标系下点p的曲率，υ_x是笛卡尔坐标系下轨迹点x的速度，a_x是笛卡尔坐标系下点x的加速度,k_p′是笛卡尔坐标系下点p的曲率k_p的导数。Among them, S is the longitudinal coordinate of the trajectory point x in the Frenet coordinate system, sp is the longitudinal coordinate of a point _p closest to the trajectory point x in the Frenet coordinate system,

is the derivative of the longitudinal coordinate of the trajectory point x in the Frenet coordinate system to time, indicating the speed of the vehicle along the reference line,

is the second derivative of the longitudinal coordinate of the trajectory point x in the Frenet coordinate system to time, which represents the acceleration of the vehicle along the reference line, d is the lateral coordinate of the trajectory point x in the Frenet coordinate system, and d' is the trajectory point x in the Frenet coordinate system. The first derivative of the coordinate to the vertical coordinate, d″ is the second derivative of the horizontal coordinate of the trajectory point x to the vertical coordinate in the Frenet coordinate system, θ _x is the azimuth of the trajectory point x in the Cartesian coordinate system, θ _p is the Cartesian coordinate The azimuth of the point P under the system, k _x is the curvature of the trajectory point x in the Cartesian coordinate system, k _p is the curvature of the point p in the Frenet coordinate system, υ _x is the velocity of the trajectory point x in the Cartesian coordinate system, a _x is the acceleration of point x in the Cartesian coordinate system, and k _p ′ is the derivative of the curvature k _p of the point p in the Cartesian coordinate system.

Further, the safety distance model is specifically:

When the front vehicle is stationary, the minimum safe distance S _d is expressed as:

When the front vehicle is moving, the minimum safe distance S _d is expressed as:

分别表示Frenet坐标系下当前自身车辆和前车纵向的速度，d_自身、d_前车分别表示Frenet坐标系下当前自身车辆和前车的横向坐标，d′_自身表示Frenet坐标系下当前自身车辆的横向坐标对纵向坐标的一阶导数；s′_前车表示Frenet坐标系下当前前车的横向坐标对纵向坐标的一阶导数；

分别表示Frenet坐标系下当前自身车辆和前车的曲率。in,

Respectively represent the longitudinal speed of the current own vehicle and the preceding vehicle in the Frenet coordinate system, d _self and d _{preceding vehicle} respectively represent the lateral coordinates of the current own vehicle and the preceding vehicle in the Frenet coordinate system, and d' _itself represents the current own vehicle in the Frenet coordinate system. The first derivative of the transverse coordinate to the longitudinal coordinate; s' _{the preceding vehicle} represents the first derivative of the transverse coordinate of the current preceding vehicle in the Frenet coordinate system to the longitudinal coordinate;

respectively represent the curvature of the current ego vehicle and the preceding vehicle in the Frenet coordinate system.

Further, the upper-level controller uses the inputted vehicle position, distance, vehicle speed, and acceleration trajectory information to obtain the target speed and acceleration of the vehicle through a decision-making algorithm;

The lower-level controller controls the in-wheel motor torque and wheel speed according to the target speed and acceleration obtained by the upper-level controller to realize the driving and braking control of the own vehicle, so as to achieve the desired target control of the upper-level control.

Beneficial effects:

The invention proposes a CACC following traffic flow control system based on the Frenet coordinate system. The invention nests the Frenet coordinate system conversion module of the vehicle track into the CACC car following control system. The invention is suitable for the following state control scenarios of CACC vehicles under various traffic conditions such as human-machine mixed traffic flow and manual driving traffic flow, which can improve calculation efficiency and reduce the influence of road curvature, so that CACC vehicles can keep safe continuously and efficiently. Comfortable following.

Description of drawings

1 is a schematic diagram of the overall structure of the system of the present invention;

Fig. 2 is a schematic diagram of a system startup process;

Figure 3 is a schematic diagram of the relationship between the vehicle trajectory in the Frenet coordinate system and the Cartesian coordinate system;

FIG. 4 is a schematic diagram of the operation flow of the control module.

Detailed ways

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, but not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

1 to 4, the present invention provides a CACC following traffic flow control system based on the Frenet coordinate system, the system includes:

an information collection module, the information collection module collects the trajectory information of the preceding vehicle and the own vehicle, and the information collection module transmits the collected information to the trajectory transformation module;

a trajectory transformation module, the trajectory transformation module converts the trajectory information to the Frenet coordinate system according to the Cartesian coordinate system, and obtains the trajectory information under the Frenet coordinate system;

The control module controls and adjusts the running state of the own vehicle according to the trajectory information obtained in the Frenet coordinate system, and the adjusted running state information is continuously collected by the information collection module, so that the own vehicle maintains a safe and comfortable car-following state.

The invention proposes a CACC following traffic flow control system based on the Frenet coordinate system, which can accurately and efficiently solve the control decision problem of the following state of CACC vehicles in various traffic scenarios and conditions, and help CACC vehicles to automatically and safely complete driving tasks;

The present invention adopts the Frenet coordinate system as the working coordinate system, which is significantly superior to other coordinate systems in the calculation of the driving behavior model. It reduces the influence of road curvature on trajectory calculation optimization, simplifies the calculation process of decision-making model, improves model efficiency, and finally obtains decision-making results that are safer, more comfortable and more efficient.

The car-following strategy of the present invention is based on the CACC control system, which can significantly improve the stability and safety of the human-machine mixed fleet, and reduce the risk of rear-end collision, vehicle fuel consumption and emission level.

The control module includes a decision-making unit, an upper-level controller and a lower-level controller; the decision-making unit calculates and analyzes the minimum safe distance that the vehicle in front needs to maintain a safe and comfortable car-following state according to the safety distance model. , and input this information into the upper controller;

The upper layer controller calculates the current speed and acceleration trajectory information required to be maintained by the own vehicle, and at the same time sends the required speed and acceleration trajectory information to the lower layer controller, and the lower layer controller controls and adjusts the running state of the own vehicle.

The trajectory transformation module converts the trajectory information to the Frenet coordinate system according to the Cartesian coordinate system as follows:

The relationship between the vehicle trajectory in the Frenet coordinate system and the Cartesian coordinate system is transformed. In the Cartesian coordinate system, let p(x _p , y _p ) be the closest point to the trajectory point x (x _x , x _y ); then in In the Frenet coordinate system, the ordinates of point p and point x are equal;

The position and speed trajectory information of the CACC vehicle is input into the trajectory conversion module, and the conversion from the Cartesian coordinate system to the Frenet coordinate system is expressed by the following formula:

s=s _p (1)

d'=(1-dk _p )tan(θ _x -θ _p ) (4)

为Frenet坐标系下轨迹点x纵向坐标对时间的导数，表示车辆沿参考线方向的速度，

为Frenet坐标系下轨迹点x纵向坐标对时间的二阶导数，表示车辆沿参考线方向的加速度，d为Frenet坐标系下轨迹点x的横向坐标，d′为Frenet坐标系下轨迹点x横向坐标对纵向坐标的一阶导数，d″为Frenet坐标系下轨迹点x横向坐标对纵向坐标的二阶导数，θ_x是笛卡尔坐标系下轨迹点x的方位角，θ_p是笛卡尔坐标系下点P的方位角，k_x是笛卡尔坐标系下轨迹点x的曲率，k_p是Frenet坐标系下点p的曲率，υ_x是笛卡尔坐标系下轨迹点x的速度，a_x是笛卡尔坐标系下点x的加速度,k_p是笛卡尔坐标系下点p的曲率k_p的导数。Among them, S is the longitudinal coordinate of the trajectory point x in the Frenet coordinate system, sp is the longitudinal coordinate of a point _p closest to the trajectory point x in the Frenet coordinate system,

is the derivative of the longitudinal coordinate of the trajectory point x in the Frenet coordinate system to time, indicating the speed of the vehicle along the reference line,

is the second derivative of the longitudinal coordinate of the trajectory point x in the Frenet coordinate system to time, which represents the acceleration of the vehicle along the reference line, d is the lateral coordinate of the trajectory point x in the Frenet coordinate system, and d' is the trajectory point x in the Frenet coordinate system. The first derivative of the coordinate to the vertical coordinate, d″ is the second derivative of the horizontal coordinate of the trajectory point x to the vertical coordinate in the Frenet coordinate system, θ _x is the azimuth of the trajectory point x in the Cartesian coordinate system, θ _p is the Cartesian coordinate The azimuth of the point P under the system, k _x is the curvature of the trajectory point x in the Cartesian coordinate system, k _p is the curvature of the point p in the Frenet coordinate system, υ _x is the velocity of the trajectory point x in the Cartesian coordinate system, a _x is the acceleration of point x in the Cartesian coordinate system, and k _p is the derivative of the curvature k _p of the point p in the Cartesian coordinate system.

The safety distance model is specifically:

When the front vehicle is stationary, the minimum safe distance S _d is expressed as:

When the front vehicle is moving, the minimum safe distance S _d is expressed as:

分别表示Frenet坐标系下当前自身车辆和前车纵向的速度，d_自身、d_前车分别表示Frenet坐标系下当前自身车辆和前车的横向坐标，d′_自身表示Frenet坐标系下当前自身车辆的横向坐标对纵向坐标的一阶导数；d′_前车表示Frenet坐标系下当前前车的横向坐标对纵向坐标的一阶导数；

分别表示Frenet坐标系下当前自身车辆和前车的曲率。in,

Respectively represent the longitudinal speed of the current own vehicle and the preceding vehicle in the Frenet coordinate system, d _self and d _{preceding vehicle} respectively represent the lateral coordinates of the current own vehicle and the preceding vehicle in the Frenet coordinate system, and d' _itself represents the current own vehicle in the Frenet coordinate system. The first derivative of the transverse coordinate to the longitudinal coordinate; d' _{the preceding vehicle} represents the first derivative of the transverse coordinate of the current preceding vehicle in the Frenet coordinate system to the longitudinal coordinate;

respectively represent the curvature of the current ego vehicle and the preceding vehicle in the Frenet coordinate system.

The upper-layer controller uses the inputted vehicle position, distance, vehicle speed, and acceleration trajectory information to obtain the target speed and acceleration of the vehicle through a decision-making algorithm;

The lower-level controller controls the in-wheel motor torque and wheel speed according to the target speed and acceleration obtained by the upper-level controller to realize the driving and braking control of the own vehicle, so as to achieve the desired target control of the upper-level control.

Specific embodiment two:

The overall structure of the system of the present invention is shown in FIG. 1 . First, the information collection module composed of various sensors continuously collects the trajectory information such as the position, distance, vehicle speed, and acceleration of the own vehicle and the preceding vehicle, and transmits this information to the trajectory transformation module. The trajectory transformation module converts the trajectory information in the Cartesian coordinate system into the trajectory information in the Frenet coordinate system according to the formula for converting the Cartesian coordinate system to the Frenet coordinate system. At the same time, the transformed trajectory information will be input into the decision-making unit of the control module. According to the safety distance model, the decision-making unit calculates and analyzes the minimum safety distance that the own vehicle needs to maintain in a safe and comfortable following state and the preceding vehicle, and inputs this information to the upper controller. Then, the upper-layer controller calculates the trajectory information such as the speed and acceleration that the own vehicle currently needs to maintain, and sends this trajectory information to the lower-layer controller at the same time. The lower-level controller controls and adjusts the running state of the own vehicle accordingly. The adjusted operating status information will be collected by the information collection module again, and this pattern will continue to circulate. In the end, the own vehicle has been kept in a safe and comfortable following state.

The system of the present invention is controlled and started by the CACC control system, and the start-up process is shown in FIG. 2 . First, the vehicle is started, the initial state information will be input into the system, and the system will check whether the vehicle's Adaptive Cruise Control (ACC) function is normal. If it is normal, continue to check the CACC system, otherwise it will enter the manual driving state. When the CACC system functions normally, the vehicle will enter the CACC control state. At this time, it means that the recognition function of the preceding vehicle is normal, and the modules of the CACC following traffic flow control system based on the Frenet coordinate system will be able to operate normally, so the system is activated. Otherwise, the vehicle enters the ACC control state, and the system is not activated.

The decision-making unit in the control module of the system of the present invention calculates the minimum safe distance that the current own vehicle wants to maintain a safe and comfortable car-following state with the preceding vehicle. Consideration factors include: when there is an emergency ahead, the distance between the own vehicle and the preceding vehicle should be sufficient for the driver to recognize and react; the distance between the own vehicle and the preceding vehicle should be sufficient for the driver to decelerate according to his own expectations to eliminate the distance between the vehicle and the vehicle ahead. The time for the relative speed of the front car; after the relative speed is eliminated, the own vehicle must still maintain a certain distance from the front car.

A CACC car-following traffic flow control system based on the Frenet coordinate system provided by the present invention has been described in detail above. In this paper, specific examples are used to illustrate the principles and implementations of the present invention. The descriptions of the above embodiments are only used for In order to help understand the method of the present invention and its core idea; at the same time, for those skilled in the art, according to the idea of the present invention, there will be changes in the specific implementation and application scope. In summary, this specification The contents should not be construed as limiting the present invention.

Claims (5)

1. A CACC follow-up flow control system based on Frenet coordinate system, the system comprising:

the information acquisition module acquires track information of a front vehicle and a self vehicle and transmits the acquired information to the track transformation module;

the track conversion module converts the track information into a Frenet coordinate system according to a Cartesian coordinate system to obtain track information under the Frenet coordinate system;

and the control module controls and adjusts the running state of the vehicle according to the track information obtained under the Frenet coordinate system, and the adjusted running state information is continuously and circularly acquired by the information acquisition module, so that the vehicle keeps a safe and comfortable following state.

2. The CACC follow-up traffic flow control system based on Frenet coordinate system as claimed in claim 1, wherein the control module comprises a decision unit, an upper controller and a lower controller; the decision unit calculates and analyzes a current safe and comfortable following state of the vehicle and a minimum safe distance required to be maintained by the front vehicle according to the safe distance model, and inputs the information into the upper controller;

the upper layer controller calculates the speed and acceleration track information required to be kept by the vehicle at present, and simultaneously sends the speed and acceleration track information required to be kept to the lower layer controller, and the lower layer controller controls and adjusts the running state of the vehicle.

3. The CACC car flow control system based on Frenet coordinate system of claim 2, wherein the trajectory transformation module transforms the trajectory information into the Frenet coordinate system according to Cartesian coordinate system, and specifically comprises:

the relation of vehicle track in Frenet coordinate system and Cartesian coordinate system is transformed, and in Cartesian coordinate system, p (x) is set _p ，y _p ) Is a point x (x) of off-track _x ，y _y ) The closest point; then the ordinate of point p is equal to the ordinate of point x in the Frenet coordinate system;

the CACC vehicle position and speed track information input track conversion module converts a Cartesian coordinate system into a Frenet coordinate system and is represented by the following formula:

s＝s _p (1)

d′＝(1-dk _p )tan(θ _x -θ _p ) (4)

wherein S is the longitudinal coordinate of the track point x under the Frenet coordinate system, S _p Is the longitudinal coordinate of a point p closest to the tracing point x in the Frenet coordinate system,

the derivative of the longitudinal coordinate of the track point x under the Frenet coordinate system to the time represents the speed of the vehicle along the direction of the reference line,

the second derivative of the longitudinal coordinate of the track point x under the Frenet coordinate system to the time represents the acceleration of the vehicle along the direction of the reference line, d is the transverse coordinate of the track point x under the Frenet coordinate system, d 'is the first derivative of the transverse coordinate of the track point x under the Frenet coordinate system to the longitudinal coordinate, d' is the second derivative of the transverse coordinate of the track point x under the Frenet coordinate system to the longitudinal coordinate, theta _x Is the azimuth angle, theta, of the locus point x under the Cartesian coordinate system _p Is the azimuth, k, of a point P in a Cartesian coordinate system _x Is the curvature, k, of the locus point x in a Cartesian coordinate system _p Is the curvature, upsilon, of the point p in the Frenet coordinate system _x Is the velocity, a, of the locus point x in the Cartesian coordinate system _x Is the acceleration, k, of a point x in a Cartesian coordinate system _p Is the curvature k of a point p in a Cartesian coordinate system _p The derivative of (c).

4. The CACC following traffic flow control system based on Frenet coordinate system as claimed in claim 2 or 3, wherein the safe distance model is specifically:

when the front vehicle is stationary, the minimum safe distance S _d Expressed as:

when the front vehicle is moving, the minimum safe distance S _d Expressed as:

wherein,

respectively representing the longitudinal speeds of the current own vehicle and the preceding vehicle in the Frenet coordinate system, d _{Itself is provided with} 、d _{Front vehicle} Respectively representing FrenetTransverse coordinates, d ', of the current own vehicle and the preceding vehicle in a coordinate system' _{Itself is provided with} Representing the first derivative of the transverse coordinate of the current self vehicle to the longitudinal coordinate under the Frenet coordinate system; d' _{Front vehicle} Representing the first derivative of the transverse coordinate of the current front vehicle to the longitudinal coordinate under the Frenet coordinate system;

respectively representing the curvatures of the current own vehicle and the preceding vehicle in the Frenet coordinate system.

5. The CACC follow-up traffic flow control system based on the Frenet coordinate system is characterized in that the upper-layer controller obtains the target speed and acceleration of the vehicle through a decision algorithm by utilizing the input information of the position, distance, speed and acceleration track of the front vehicle;

the lower layer controller controls the torque and the wheel speed of the hub motor according to the target speed and the acceleration obtained by the upper layer controller so as to realize the driving and braking control of the vehicle, thereby achieving the target control expected by the upper layer controller.

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