Vehicle queue cooperative adaptive cruise control method based on periodic event trigger transmission strategy

Abstract

The invention provides a vehicle queue cooperative adaptive cruise control method based on a periodic event trigger transmission strategy, and belongs to the field of vehicle control. According to the invention, a periodic event trigger control transmission strategy is adopted. For sampling values transmitted through wireless network communication, a zero-order holder is used for holding. Aiming at discreteness in vehicle queue cooperative adaptive cruise control based on a periodic event trigger transmission strategy, hybrid system modeling is adopted. According to the vehicle queue cooperative adaptive control based on the periodic event trigger transmission strategy, network communication resources can be greatly saved, and the utilization rate of the network communication resources is improved. And realizing cooperative adaptive cruise control of the vehicle queue according to the information of the vehicles in the vehicle queue.

Description

Technical Field

[0001] The present application relates to the technical field of vehicle control, and particularly to a vehicle platoon cooperative adaptive cruise control method based on a periodic event-triggered transmission strategy. Background Art

[0002] In recent years, the research on vehicle platoons has received extensive attention. According to whether a vehicle can obtain information of adjacent vehicles through sensors or on-vehicle radars, control methods can be divided into vehicle following control, bilateral control, and hybrid control. In the vehicle following control mode, adaptive cruise control and cooperative adaptive cruise control have been widely studied. Since cooperative adaptive cruise control can maintain the desired distance between vehicles and ensure that disturbances in the entire formation are attenuated, it plays an increasingly important role in autonomous driving. Compared with adaptive cruise control, a vehicle with cooperative adaptive cruise control obtains the acceleration control input of the preceding vehicle through wireless network communication. Therefore, a vehicle platoon system with cooperative adaptive cruise control can be regarded as a networked control system. A networked control system refers to a closed-loop system in which actuators, sensors, and controllers communicate through a network. Considering the inherent discrete characteristics of computer hardware platforms, controllers are usually discrete. A networked control system with a discrete controller is also called a sampled-data system. To ensure the normal operation of the data sampling system, a data transmission strategy must be applied in the networked control system. The most common data transmission strategies mainly include time-triggered control, event-triggered control, dynamic event-triggered control, and periodic event-triggered control. In recent years, event-triggered control has been widely applied in many fields, such as vehicles, robots, and cyber-physical systems. Combining event-triggered control and periodic time-triggered control, periodic event-triggered control has been proposed and applied. Compared with periodic time-triggered control, periodic event-triggered control can not only save network communication resources but also avoid continuous detection. Therefore, it is crucial to select an appropriate strategy to maintain the performance and stability of the sampled-data system. Summary of the Invention

[0003] The technical problem to be solved by the present invention is that in the existing vehicle platoon cooperative adaptive cruise control, network communication resources are wasted and the utilization rate of communication resources is low. To this end, the present invention provides a method for vehicle platoon cooperative adaptive cruise control based on a periodic event-triggered transmission strategy.

[0004] For the cooperative adaptive cruise control method with wireless network communication, the present invention adopts a periodic event-triggered control transmission strategy. For the sampled values transmitted through wireless network communication, the present invention uses a zero-order hold to hold them. For the discreteness existing in the vehicle platoon cooperative adaptive cruise control based on the periodic event-triggered transmission strategy, the present invention adopts a hybrid system modeling.

[0005] The technical solution adopted by the present invention to solve its technical problems is as follows:

[0006] A vehicle queue cooperative adaptive cruise control method based on a periodic event-triggered transmission strategy, comprising the following steps:

[0007] Step 1, according to the physical properties of the vehicle, establish an open-loop dynamic equation of the vehicle controlled by acceleration, where the displacement, speed, acceleration, and desired acceleration of the vehicle are defined, and at the same time, the vehicle driveline time constant and the vehicle reaction time are explained;

[0008] Step 2, use on-vehicle radar to measure the distance between vehicles, and obtain the speed error after derivation. Define the error induced by the desired distance and the actual distance between vehicles, which is called the distance-induced error. Define the static distance between vehicles and the vehicle length, and assume that the static distances, vehicle lengths, and vehicle reaction times between all vehicles in the vehicle queue are the same;

[0009] Step 3, construct a controller for the cooperative adaptive cruise control vehicle, which includes a proportional derivative control module and a feedforward component module. The proportional derivative module calculates the distance-induced error and the derivative of the distance-induced error, and the feedforward module processes the sampled quantity held by the hold after being transmitted through wireless network communication;

[0010] Step 4, define the error induced by the network, equip a transmission strategy for wireless network communication, and select a periodic event-triggered transmission strategy. After the data is sampled and judged by the event trigger condition of the periodic time-triggered strategy, if the trigger condition is satisfied, the data is transmitted to the following vehicle through wireless network communication, and the transmitted data is held by a zero-order hold;

[0011] Step 5, based on Steps 1 to 4, construct a closed-loop system for vehicle queue cooperative adaptive cruise control based on the periodic event-triggered transmission strategy;

[0012] Step 6, based on the characteristics of periodic detection of the periodic event-triggered transmission strategy, define a timer variable to record the time from the start of the last transmission to the present moment. Combining the timer variable, further construct a hybrid system for vehicle queue cooperative adaptive cruise control based on the periodic event-triggered transmission strategy, including a flow set, a flow map, a jump set, and a jump map;

[0013] Step 7, construct a hybrid Lyapunov function, and study the change of the hybrid Lyapunov function in the flow set and the jump set respectively, to prove that the vehicle queue cooperative adaptive cruise control system based on the periodic event-triggered transmission strategy is string stable;

[0014] Step 8, use numerical simulation for verification.

[0015] Furthermore, in Step 1, define the vehicle Displacement q i , velocity v i , acceleration a i and desired acceleration u i , define based on the vehicle Driveline time constant τ d , τ d This represents the relationship between the given acceleration of the vehicle and the actual acceleration of the vehicle, define the vehicle Response time h i , the acceleration follows the desired acceleration through a first-order low-pass filter with τ d as the time constant, and the desired acceleration follows the output of the controller of the vehicle system through a first-order low-pass filter with h i as the time constant, thereby constructing an open-loop dynamic model of the vehicle.

[0016] Furthermore, in step two, define the actual distance d between the two vehicles i = q i-1 - q i - L i , desired distance where q i-1 and q i are the displacements of vehicle and vehicle respectively, r i is the distance at rest between vehicle and vehicle , L i is the length of vehicle . For the convenience of analysis, without affecting the results, let L0 = L1 = … = L N = L, r1 = r2 = … = r N = r, h1 = h2 = … = h N = h; define the error induced by the desired distance and the actual distance Differentiating the error e i gives

[0017] Furthermore, in step three, in the controller of the cooperative adaptive cruise control vehicle, the proportional derivative control module sums the proportional part k p e i of the distance-induced error and the differential part of the distance-induced error; the feedforward component module is where u i-1 is sampled by the sampling system and then transmitted to vehicle through wireless network communication and held by the hold. Thus, the controller of the cooperative adaptive cruise control vehicle is where χi is the output of the controller, k p is the proportional gain of the proportional-derivative controller, k d is the derivative gain of the proportional-derivative controller.

[0018] Furthermore, to smoothly implement wireless network communication and ensure that the wireless network communication can operate according to the given strategy, for this purpose, the periodic event-triggered transmission strategy is equipped to the wireless network communication. And the network-induced error is defined wherein, is held by the zero-order hold, and its dynamics is when data is not transmitted, when at the data transmission moment, Furthermore, the periodic event-triggered transmission strategy is to give a time sequence for event detection, and this event sequence is at equal time intervals, 0 = s0 < s1 < … < s k <… < ∞, s k -s k-1 = T, t k is defined as the trigger moment, and the trigger moment is where is the trigger condition.

[0019] Furthermore, based on the characteristic of periodically detecting the event trigger condition of the periodic event-triggered transmission strategy, to record the time elapsed since the last detection until this moment, in step six, the timer variable τ is defined i-1 , where the variable τ i-1 has the dynamic equation of τ i-1 ∈(s k , s k+1 ), Since the timer variable and the periodic event-triggered transmission strategy have both the characteristics of continuous-time dynamics and jump characteristics, a hybrid system of vehicle queue cooperative adaptive cruise control based on the periodic event-triggered transmission strategy is constructed, where the hybrid system includes a flow set, a flow map, a jump set, and a jump map.

[0020] Furthermore, in step seven, to prove the string stability of the hybrid system of vehicle queue cooperative adaptive cruise control based on the periodic event-triggered transmission strategy, the hybrid Lyapunov function is defined where P = P T ≥0, γ > 0, φ(τ i-1 ) represents an auxiliary function that is always positive definite and monotonically decreasing, W i represents the error function regarding the network-induced error Ωi represents a function of the desired acceleration with respect to the vehicle , V i (x i ) represents a Lyapunov function of the closed-loop system with respect to the vehicle , x i represents the state of the vehicle closed-loop system. And the dynamics of the hybrid Lyapunov function are analyzed in the flow set and the jump set respectively.

[0021] The beneficial effects of the present invention are that the vehicle queue cooperative adaptive control based on the periodic event-triggered transmission strategy of the present invention can greatly save network communication resources and improve the utilization rate of network communication resources. According to the information of the vehicles in the vehicle queue, the cooperative adaptive cruise control of the vehicle queue is realized. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The present invention will be further described below with reference to the drawings and embodiments.

[0023] Figure 1 is a schematic diagram of the positions of the vehicle queue of the present invention.

[0024] Figure 2 is a schematic diagram of the vehicle queue cooperative adaptive cruise control algorithm based on the periodic event-triggered transmission strategy of the vehicle queue of the present invention.

[0025] Figure 3 is a schematic diagram of interference.

[0026] Figure 4 is a schematic diagram of the vehicle speed change when using the traditional event-triggered control.

[0027] Figure 5 is a schematic diagram of the vehicle speed change when using the periodic time-triggered control.

[0028] Figure 6 is a schematic diagram of the vehicle speed change when using the periodic event-triggered control. DETAILED DESCRIPTION OF THE INVENTION

[0029] The present invention will now be described in further detail with reference to the drawings. These drawings are all simplified schematic diagrams, only illustrating the basic structure of the present invention in a schematic manner, so they only show the components related to the present invention.

[0030] A vehicle queue cooperative adaptive cruise control method based on a periodic event-triggered transmission strategy includes the following steps,

[0031] S1 Model the vehicle queue

[0032] S1.1 Establish an open-loop dynamics model of the vehicle queue

[0033]

[0034] In the formula, v i , a i , u i , χ i respectively represent the speed, acceleration, target acceleration of the i-th vehicle in the vehicle platoon, and the output of the controller of the i-th vehicle in the vehicle platoon . τ represents the time constant of the vehicle driveline, h d is the vehicle response time. The low-pass filter in the third equation of Equation (1) serves as a pre-compensator for the response time h i . In the vehicle platoon, q i , L i represent the position and vehicle length of the i-th vehicle in the vehicle platoon i . r represents the standstill distance between vehicle i and and . In the present invention, it is assumed that L0 = L1 = … = L N = L, r1 = r2 = … = r N = r, h1 = h2 = … = h N = h.

[0035] Furthermore, define d i and as the actual distance and the desired distance between vehicle and respectively, where d i = q i-1 - q i - L i , define the distance-induced error

[0036] S1.2 The vehicles in the vehicle platoon should maintain a safe distance and reach the desired distance. At the same time, the transmission of interference in the vehicle platoon should satisfy the characteristic of attenuation. The controller model of the i-th vehicle v i in the vehicle platoon is

[0037]

[0038] This controller includes a proportional-derivative control module determined by e i and and a feedforward component module. The feedforward component module is that u i-1 is sampled and transmitted from vehicle to vehicle Information maintained by a retainer. In this invention, it is stipulated that information can only be transmitted from the leading vehicle to the trailing vehicle via a wireless network.

[0039] S2 Network transmission strategy based on periodic event triggering

[0040] S2.1 To maintain the desired distance between vehicles in the vehicle queue and to achieve attenuation of interference in the vehicle queue, cooperative adaptive cruise control is applied to this vehicle queue. Different from adaptive cruise control, the vehicle Obtains the position q of the leading vehicle through on-vehicle radar i-1 , speed v i-1 and acceleration a i-1 , based on obtaining q i-1 , v i-1 , a i-1 through on-vehicle radar, the desired acceleration u of the vehicle is obtained through wireless network communication . i-1

[0041] S2.2 Corresponding to wireless network communication, design a suitable network transmission strategy to match wireless network communication, and adopt a periodic event-triggered transmission strategy. Define the error induced by the network The periodic event-triggered transmission strategy is as follows:

[0042] Given a time series for event detection, this event series is at equal time intervals, 0 = s0 < s1 < … < s k <… < ∞, s k -s k-1 = T, t k is defined as the triggering moment, and the triggering moment is

[0043]

[0044] where is the triggering condition. This triggering mechanism is described as follows. If the information will not be transmitted; if and then the information will be transmitted. Wireless network communication includes two stages. First, the data is sampled, and then the data is transmitted. In this invention, it is assumed that wireless network communication is completed immediately, that is, the communication time delay is 0.

[0045] S2.3 Considering the discrete characteristics of network communication, it is necessary to set a retainer. Therefore, in this invention, it is maintained through a zero-order hold, and its dynamic change is

[0046]

[0047] Hybrid System Modeling of S3 Vehicle Platoon

[0048] S3.1 Further, define x i =[v i-1 a i-1 u i-1 e i v i a i u i T , χ i-1 As the output of the vehicle controller, it can also be regarded as the external disturbance of the vehicle . Based on (1), (2), (3), (4), the dynamic equation of the closed-loop cooperative adaptive cruise control vehicle platoon is

[0049]

[0050] where

[0051]

[0052] S3.2 Define the timer variable τ i , and the timer variable is used to record how much time has elapsed since the last trigger moment. The dynamic equation of the timer variable τ i-1 is

[0053]

[0054] Lemma 1, define the differential equation

[0055]

[0056] where denotes the square of φ i (s), φ i (s) represents a function that is always positive definite and monotonically decreasing, λ ∈ (0, 1), and define the initial value where the design parameter γ > 0. It can be found that for any s ∈ [0, T], φ(s, γ) is monotonically decreasing, and when s ≥ T, φ(s, ·) = λ. By choosing an appropriate λ, the upper limit T max can be determined. Select a T ≤ T max , and the trigger condition of the periodic event-triggered transmission strategy is

[0057]

[0058] where

[0059] ​S3.3 Based on the periodic event-triggered transmission strategy, when the closed-loop cooperative adaptive cruise control vehicle platoon system is at a jump occurs. Define ξ i =(x i , e ui-1 , τ i-1 ). The closed-loop cooperative adaptive cruise control vehicle platoon system is modeled as a hybrid system, and the hybrid system is

[0060]

[0061] In the hybrid system, the flow map is defined on the flow set where represents the dimension of the variable ξ i , Δ represents the upper bound of the timer variable, that is, the time length of the detection period of the periodic event-triggered transmission strategy, and A 11 =A + EC, A 12 =E, A 13 =B, C = [0 0 1 0 0 0], u i-1 =Cx i .

[0062] The jump map

[0063]

[0064] where and the jump set

[0065] S4 Stability analysis of the hybrid system

[0066] S4.1 Definition (string stability) A hybrid system is string stable if for any external input the output satisfies for any state x i such that

[0067] Then it can be shown that this hybrid system is string stable, where β represents the K ∞ class function, and the K ∞ class function is a class of strictly monotonically increasing functions with the domain [0, +∞). When the independent variable is 0, the function value is 0, and when the independent variable approaches positive infinity, the function value approaches positive infinity.

[0068] Lemma 2, for all matrices P = P T ≥0, constants μ > 0, γ > 0, such that the matrix ​

[0069]

[0070] Among them, C z = [k d 0 1k p -k d -k d h0], D z = 1, and ∈ represents a sufficiently small positive constant.

[0071] S4.2 String stability proof. For the hybrid system, the present invention considers the following candidate hybrid Lyapunov function

[0072]

[0073] Among them, P = P T ≥ 0, γ > 0, λ ∈ (0, 1).

[0074] Obviously, there exist two functions such that

[0075] Among them λ max (P) represents the largest eigenvalue of matrix P, and λ min (P) represents the smallest eigenvalue of matrix P.

[0076] According to Lemma 2, the following conclusion can be drawn

[0077]

[0078] Among them, C z = [k d 0 1k p -k d -k d h0], D z = 1.

[0079] Furthermore, it can be obtained that

[0080]

[0081] Through Therefore

[0082]

[0083] First, analyze the jump dynamics of the hybrid system. For any Let Then it can be obtained that

[0084]

[0085] Furthermore, obtain For any It can be obtained that

[0086]

[0087] Since when

[0088]

[0089] Therefore So, for any It can be obtained that

[0090]

[0091] Furthermore, analyze the continuous dynamics of the hybrid system. For any

[0092]

[0093] By Young's inequality It can be obtained that Therefore, further

[0094]

[0095] Because Then

[0096]

[0097] Through It can be obtained that

[0098]

[0099] Furthermore, define the hybrid norm Furthermore,

[0100]

[0101] Because So

[0102]

[0103] Through It can be obtained that Furthermore, there must exist a function β ∈ K ∞ , such that

[0104]

[0105] Thus, the hybrid system is proven to be string stable.

[0106] Example: Select a vehicle platoon consisting of two vehicles, set the simulation step size to 0.05 s, τ d = 0.1, h = 0.4, k p = 0.2, k d = 0.7. Given an interference χ1, such as Figure 3 . Using traditional event-triggered control, the vehicle speed changes as Figure 4 , and the number of trigger times within 70 s is 555 times. Using periodic time-triggered control, set the period to 0.1 s, the vehicle speed changes as Figure 5 , and the number of trigger times within 70 s is 669 times. Using periodic event-triggered control, set the period to 0.1 s, the vehicle speed changes as Figure 6 , and the number of trigger times is 111 times. According to Figure 4 , Figure 5 and Figure 6 , we verified that the vehicle formation based on cooperative adaptive cruise control can still closely follow the leading vehicle and ensure the stability of the vehicle platoon when facing significant interference from the leading vehicle. Compared with traditional event-triggered control, although the response of vehicle v2 using periodic event-triggered control is relatively slow, it greatly saves network communication resources. Compared with traditional periodic time control that can ensure the stability of the vehicle platoon, periodic event-triggered control can significantly reduce the number of trigger times and greatly save the utilization of network communication resources.

Claims

1. A vehicle platoon cooperative adaptive cruise control method based on a periodic event triggered transmission strategy, characterized in that: The following steps are included: Step 1: Based on the physical properties of the vehicle, an open-loop dynamic equation of the vehicle controlled by acceleration is established, in which the displacement, velocity, acceleration and expected acceleration of the vehicle are defined, and the vehicle transmission line time constant and vehicle reaction time are explained; Step 2: Use the vehicle-mounted radar to measure the distance between vehicles and obtain the speed error after differentiation; define the error induced by the expected distance and the actual distance between vehicles, called the distance induced error, define the static distance between vehicles and the vehicle length, and assume that all vehicles in the vehicle queue have the same static distance, the same vehicle length, and the same vehicle reaction time; Step 3, constructing a controller of a cooperative adaptive cruise control vehicle, which includes a proportional differential control module and a feedforward component module; the proportional differential module calculates the distance induced error and the derivative of the distance induced error, and the feedforward module processes the sampled amount held by the holder after being transmitted by the wireless network communication; Step 4: define the error induced by the network, configure the transmission strategy for the wireless network communication, and select the periodic event trigger transmission strategy; after the data is sampled, it is judged by the event trigger condition of the periodic time trigger strategy. If the trigger condition is met, the data is transmitted to the following vehicle through the wireless network communication, and the transmitted data is held by the zero-order holder; Step 5: Based on steps 1 to 4, a closed-loop system of vehicle platoon cooperative adaptive cruise control based on a periodic event-triggered transmission strategy is constructed; Step 6: Based on the characteristics of periodic event-triggered transmission strategy periodic detection, define a timer variable to record the time from the last transmission to this moment; Combined with timer variables, a hybrid system of vehicle platoon cooperative adaptive cruise control based on periodic event-triggered transmission strategy is constructed, including flow sets, flow mapping, jump sets and jump mapping; Step 7: Construct a hybrid Lyapunov function, and study the changes of the hybrid Lyapunov function on the flow set and the jump set, respectively, to prove that the vehicle platoon cooperative adaptive cruise control system based on the periodic event triggered transmission strategy is serially stable. Step 8: Verify using numerical simulation.

2. The method for vehicle platoon cooperative adaptive cruise control based on periodic event triggered transmission strategy according to claim 1, characterized in that: In step 1, define the vehicle The displacement q i , speed v i , acceleration a i and the expected acceleration u i , defined based on vehicle The transmission line time constant τ d , τ d This represents the relationship between the given acceleration of the vehicle and the actual acceleration of the vehicle, defining the vehicle Reaction time h i , the acceleration is given by τ d A first-order low-pass filter with a time constant of follows the desired acceleration, which is expressed in h i A first-order low-pass filter with a time constant follows the controller output of the vehicle system, thereby constructing an open-loop dynamic model of the vehicle.

3. The method for vehicle platoon cooperative adaptive cruise control based on periodic event triggered transmission strategy according to claim 1, characterized in that: In step 2, define the actual distance d between the two vehicles i =q i-1 -q i -L i , expected distance where q i-1 and q i For vehicles and vehicles The displacement, r i For vehicles and vehicles The distance between them when they are stationary, L i For vehicles Length; For the convenience of analysis, without affecting the results, let L0 = L1 = ... = L N =L, r1=r2=…=r N =r,h1=h2=…=h N = h; defines the error induced by the expected distance and the actual distance Error e i The derivative is 4. The method for vehicle platoon cooperative adaptive cruise control based on periodic event triggered transmission strategy according to claim 1, characterized in that: In step 3, in the controller of the cooperative adaptive cruise control vehicle, the proportional derivative control module is composed of the proportional part k of the distance induced error p e i The differential part of the distance induced error The feedforward component module is is the sampling system u i-1 The sampling is then transmitted to the vehicle through wireless network communication. i and is maintained by the retainer; thus, the controller of the cooperative adaptive cruise control vehicle is where χ i is the output of the controller, k p is the proportional gain of the proportional-derivative controller, k d is the differential gain of the proportional-derivative controller.

5. The method for vehicle platoon cooperative adaptive cruise control based on periodic event triggered transmission strategy according to claim 1, characterized in that: In order to smoothly implement wireless network communication and ensure that wireless network communication can operate according to a given strategy, a periodic event-triggered transmission strategy is configured to wireless network communication; and the error induced by the network is defined. in, It is held by the zero-order holder, and its dynamics are that when data is not transmitted, When data transmission is in progress, Furthermore, the periodic event-triggered transmission strategy is to give a time sequence of event detection, where the event sequence is of equal time intervals, 0 = s0 <s1<…<s k <…<∞, s k -s k-1 =T,t k is defined as the trigger moment, the trigger moment is in is the trigger condition.

6. The method for vehicle platoon cooperative adaptive cruise control based on periodic event triggered transmission strategy according to claim 1, characterized in that: Based on the characteristics of the periodic event triggering transmission strategy, in order to record the time lost since the last detection, in step 6, the timer variable τ is defined i-1 , where the variable τ i-1 The kinetic equation is τ i-1 ∈(s k ,s k+1 ), Since timer variables and periodic event-triggered transmission strategies have both continuous-time dynamic characteristics and jump characteristics, a vehicle platoon cooperative adaptive cruise control hybrid system based on periodic event-triggered transmission strategy is constructed, in which the hybrid system includes flow sets, flow mappings, jump sets and jump mappings.

7. The method for vehicle platoon cooperative adaptive cruise control based on periodic event triggered transmission strategy according to claim 1, characterized in that: In step 7, in order to prove the string stability of the hybrid system of vehicle platoon cooperative adaptive cruise control based on periodic event-triggered transmission strategy, the hybrid Lyapunov function is defined in P=P T ≥0,γ>0,φ(τ i-1 ) represents an auxiliary function that is always positive and monotonically decreasing, W i Represents the network induced error The error function, Ω i About the vehicle The function of the expected acceleration, V i (x i ) indicates vehicle The Lyapunov function of the closed-loop system, x i Indicates vehicle The state of the closed-loop system; The dynamics of the hybrid Lyapunov function are analyzed in the flow set and jump set respectively.

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