Vehicle platoon adaptive control method based on prescribed performance and fixed-time sliding mode

Abstract

This invention discloses an adaptive control method for vehicle queuing based on specified performance and fixed-time sliding mode, relating to the field of distributed vehicle queuing control technology. The method includes: establishing a vehicle dynamics model; designing a piecewise continuous function based on a constant spacing strategy to constrain follower tracking errors; designing an error transformation function with specified time performance constraints to transform the constrained problem into an unconstrained problem and constructing a fixed-time sliding surface; constructing a controller by combining adaptive parameter estimation to compensate for unknown nonlinear terms and disturbances, estimating parameters, and achieving vehicle queuing stability within a fixed time; and integrating specified performance and fixed-time sliding mode control to achieve fixed-time convergence and transient and steady-state error performance, thereby improving the reliability of queuing control.

Description

Technical Field

[0001] This invention relates to the field of distributed vehicle queuing control technology, and more specifically, to an adaptive vehicle queuing control method based on specified performance and fixed-time sliding mode. Background Technology

[0002] Vehicle platooning control technology is one of the core derivative technologies of intelligent transportation systems and automated highway systems. Its initial research and technological iterations are deeply rooted in practical problems in the road traffic field, addressing a series of issues commonly found in current roads, such as traffic congestion, inefficient vehicle fuel consumption, environmental pollution caused by exhaust emissions, and road safety hazards caused by improper following distances and human error. Faced with these increasingly prominent challenges in urban traffic and highway transportation, traditional traffic management methods are no longer sufficient to meet the demands for efficient, green, and safe development, necessitating innovative technological solutions to optimize and upgrade traffic operation. The development of intelligent transportation system technology provides a scientifically feasible technical path and implementation framework for overcoming these traffic development bottlenecks. Vehicle platooning control technology, through the collaborative perception, decision-making, and control of the driving status of multiple vehicles, demonstrates significant application potential and broad development prospects in alleviating traffic congestion, improving fuel efficiency, and promoting the green and low-carbon development of road traffic. Therefore, the academic community has conducted extensive research on vehicle platooning control from multiple dimensions, including vehicle longitudinal dynamics, spacing strategies, platoon stability, and homogeneous and heterogeneous vehicles.

[0003] In practical engineering applications of vehicle platoon control, ensuring that the platoon tracking error strictly meets preset performance specifications in both the transient response and steady-state operation phases is a key research focus in the design and implementation of platoon tracking control systems. These performance specifications clearly define the core indicators of the system's dynamic response, mainly including the convergence rate of the platoon error, the maximum allowable overshoot, and the upper limit of the error under steady-state operation. Among these, specified performance control is widely used in the research of error constraint control for vehicle platoons. The core design idea of ​​this control method is to construct a performance constraint function with preset convergence characteristics and a nonlinear error transformation function to achieve a nonlinear transformation of the bounded tracking deviation, transforming the original constrained tracking problem into an equivalent unconstrained tracking problem. Through this transformation, it can be theoretically guaranteed that the tracking error of the closed-loop platoon control system monotonically converges along the preset performance function curve and eventually stabilizes in the neighborhood of the origin, thus accurately meeting the dual constraints of transient and steady-state performance. However, the constraint functions used in existing specified performance control strategies can only guarantee asymptotic convergence to zero, which is not advantageous for vehicle platoons with time requirements. Therefore, achieving preset steady-state performance within a specified time is also a problem worthy of attention.

[0004] In practical applications, vehicle platooning faces complex driving environments, including external disturbances such as road slope, crosswinds, and traffic flow disturbances, as well as internal uncertainties such as vehicle dynamics heterogeneity and communication delays. Fixed-time sliding mode control (RTD) combines the strong robustness of sliding mode control with the convergence characteristics of fixed-time control, exhibiting unique advantages in adapting to the actual operating conditions of vehicle platoons and becoming one of the core technologies for vehicle platoon control in complex scenarios. RTD, through the variable structure characteristics of sliding mode control, effectively separates the system from system parameter perturbations and external disturbances after entering the sliding mode, thoroughly mitigating the adverse effects of these uncertainties on system control performance. Simultaneously, the fixed-time convergence design prevents the convergence process from being infinitely delayed due to disturbances, significantly improving the platoon's anti-interference capability under complex road conditions. However, research on vehicle platoon control with fixed-time sliding mode is limited. Summary of the Invention

[0005] To address the aforementioned problems, the present invention aims to provide an adaptive vehicle queuing control method based on specified performance and fixed-time sliding mode, which is intended to achieve fixed-time sliding mode vehicle queuing control and provide a new technical approach for vehicle queuing control technology.

[0006] To achieve the above technical objectives, this application provides a vehicle queuing adaptive control method based on specified performance and fixed-time sliding mode, comprising the following steps: Based on the constructed vehicle dynamics model, and according to the constant spacing strategy, the tracking error of the following vehicle is limited to the specified performance range; Construct an error transformation function that adapts to the specified performance constraints at a given time, and transform the original tracking error system, which is limited by time-varying performance boundaries, into an equivalent unconstrained error system to obtain a fixed-time sliding surface; Using the fixed-time sliding surface as the core and combining adaptive parameter estimation technology, an adaptive fixed-time sliding mode controller is built to perform adaptive control on the vehicle queue.

[0007] Preferably, when constructing the vehicle dynamics model, based on the state information and parameter information of each vehicle, and considering external disturbances and unknown nonlinear terms, a vehicle dynamics model referencing Newton's second law is established, wherein the state information includes the vehicle's position information, velocity information, and acceleration information.

[0008] Preferably, in the process of limiting the tracking error of the following vehicle within a specified performance range, a piecewise continuous performance function is designed based on a constant spacing strategy. The tracking error of the following vehicle is then limited within the specified performance range according to the piecewise continuous performance function, wherein the piecewise continuous performance function is expressed as: in, As the initial performance boundary, For steady-state performance boundary, This indicates the set time, i.e., the maximum permissible error stabilization time.

[0009] Preferably, when acquiring the tracking error, after converting the vehicle dynamics model into a state-space expression, the tracking error is designed using the state-space expression, wherein the state-space expression is expressed as: in, Indicates time, Represents the measurable system state, i.e., the first... The vehicle's position, speed, and acceleration They are The derivative of Indicates the first Time-varying input disturbance of the vehicle It is the first Vehicle control inputs, It is the first The quality of the vehicle ,in It is air density. It is the cross-sectional area of ​​the vehicle. It is the air drag coefficient. It is the first Road gradient function for vehicles , It is gravitational acceleration. It is the roadbed slope. It is the rolling resistance coefficient. Indicates the first The engine time constant of a vehicle.

[0010] Preferably, when acquiring the tracking error, the tracking error is expressed as: in, For vehicle spacing, , Indicates the first The length of the car For the desired safe distance, Indicates the first The vehicle's expected trajectory, , , and These are the weighting coefficients.

[0011] Preferably, when designing a fixed-time sliding surface, the constrained error is converted into an unconstrained variable through nonlinear mapping, and the first-order, second-order, and second-order time derivatives of the unconstrained variable are obtained to design the fixed-time sliding surface.

[0012] Preferably, when building an adaptive fixed-time sliding mode controller, a continuous hyperbolic tangent function is used to suppress chattering in sliding mode control.

[0013] Preferably, when performing adaptive control on the vehicle platoon, an adaptive fixed-time sliding mode controller is built to counteract unknown nonlinear factors and external disturbances in the vehicle model, and unknown parameters are estimated using an adaptive law to ensure that the vehicle platoon meets the specified performance and platoon stability requirements within a fixed time.

[0014] The present invention discloses the following technical effects: (1) The piecewise continuous performance constraint function proposed in this invention, compared with the traditional performance constraint function, can ensure an arbitrarily fast convergence time by setting different specified times, and is independent of the initial state of the system and the controller parameters.

[0015] (2) This invention innovatively combines specified performance at a specified time with fixed-time sliding mode control to design a novel adaptive fixed-time sliding mode controller. While ensuring convergence at a fixed time, it strictly constrains the transient and steady-state performance indicators of the tracking error, and can achieve convergence within a specified time. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 This is a structural framework diagram of the vehicle queuing system of the present invention; Figure 2 This is a schematic diagram of the method flow of the present invention; Figure 3 This is a schematic diagram of an actual vehicle queue provided in Embodiment 1 of the present invention; Figure 4 This is a simulation diagram in Prescan of a vehicle queue comprising one leader and three followers according to the present invention. Figure 5 This is a comparison chart of the convergence characteristics of the piecewise continuous performance constraint function designed in this invention and the traditional performance constraint function; Figure 6This invention includes a position tracking trajectory diagram of a vehicle convoy comprising one leader and three followers; Figure 7 This invention comprises a speed trajectory diagram of a vehicle convoy consisting of one leader and three followers; Figure 8 This invention relates to an acceleration trajectory diagram of a vehicle convoy comprising one leader and three followers; Figure 9 This invention relates to a trajectory diagram showing the spacing error of a vehicle convoy comprising one leader and three followers. Figure 10 This invention comprises a speed error trajectory diagram of a vehicle convoy consisting of one leader and three followers; Figure 11 This is a sliding surface trajectory diagram of the three followers of this invention; Figure 12 This is the adaptive parameter trajectory diagram of the three followers of this invention; Figure 13 This is the control input trajectory diagram of the three followers of this invention. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. The components of the embodiments of this application described and shown in the accompanying drawings can generally be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of this application provided in the accompanying drawings is not intended to limit the scope of the claimed application, but merely represents selected embodiments of this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.

[0019] like Figures 1-13 As shown, this invention discloses an adaptive fixed-time sliding mode control method for vehicle queuing with specified performance over a given time, comprising the following steps: S10. Establish a vehicle dynamics model.

[0020] S20. Design a piecewise continuous performance function based on a constant spacing strategy, and limit the tracking error of the following vehicle to a specified performance range according to the piecewise continuous performance function; S30. Construct an error transformation function that adapts to the specified performance constraints at a given time, transforming the original tracking error system, which is limited by time-varying performance boundaries, into an equivalent unconstrained error system; and complete the design of a fixed-time sliding surface based on the transformed system state.

[0021] S40. Using the established fixed-time sliding surface as the core, and combining it with adaptive parameter estimation technology, an adaptive fixed-time sliding mode controller is built. This controller can counteract unknown nonlinear factors and external disturbances in the vehicle model, and use adaptive laws to estimate unknown parameters to ensure that the vehicle platoon meets the specified performance and platoon stability requirements within a fixed time.

[0022] As a further implementation, before establishing the vehicle dynamics model, it is necessary to acquire the state and parameter information of each vehicle. This is achieved through information transmission between the leader vehicle and multiple follower vehicles, allowing each follower vehicle to obtain the state and parameter information of the other vehicles. The state information includes the vehicle's position, velocity, and acceleration. Based on the acquired state and parameter information of each vehicle, and considering external disturbances and unknown nonlinear terms, a vehicle dynamics model referencing Newton's second law is established.

[0023] As a further implementation method, the composition of the vehicle queuing system is as follows: Figure 1 As shown, the first The dynamic model of the vehicle is transformed into a state-space expression as follows: in, Indicates time, Represents the measurable system state, i.e., the first... The vehicle's position, speed, and acceleration They are The derivative of Indicates the first Time-varying input disturbance of the vehicle It is the first Vehicle control inputs, It is the first The quality of the vehicle ,in It is air density. It is the cross-sectional area of ​​the vehicle. It is the air drag coefficient. It is the first Road gradient function for vehicles , It is gravitational acceleration. It is the roadbed slope. It is the rolling resistance coefficient. Indicates the first The engine time constant of a vehicle.

[0024] As a further implementation, this invention designs a simplified linearized leader system model: in, This represents the measurable system state, namely the leader's position, velocity, and acceleration. They are The derivative of .

[0025] As a further implementation, this invention establishes a piecewise continuous performance constraint function as follows: in, As the initial performance boundary, For steady-state performance boundary, This indicates the set time, i.e., the maximum permissible error stabilization time.

[0026] The tracking error is defined as: in, For vehicle spacing, , Indicates the first The length of the car For the desired safe distance, Indicates the first The vehicle's expected trajectory, , , and These are the weighting coefficients.

[0027] As a further implementation, this invention transforms constrained errors into unconstrained variables through nonlinear mapping. : in, Indicates an upper bound constraint. This indicates a lower bound constraint.

[0028] Unconstrained variables The first and second time derivatives are calculated as follows: in, Design a fixed-time sliding surface: in, It is a nonlinear function. , , These are the parameters used in the design.

[0029] in, Select the following coupling sliding surfaces: in, For positive parametric coupling, the following relationship can then be obtained: Subsequently, the controller was designed as follows: in, and It is a positive number. It is an unknown constant. It is a continuous hyperbolic tangent function, which can effectively suppress chattering in sliding mode control. It is a relatively small positive scalar. and It is a positive parameter, and .

[0030] in addition, in, , yes The derivative of .

[0031] In fact, the parameters in the vehicle Since it is unknown and cannot be directly used in the controller, we can use its estimated value. To design the controller: The following adaptive law is adopted: in, It is a positive parameter. It is a small constant.

[0032] As a further implementation, in order to analyze whether the actual controller design can enable the entire vehicle queue to achieve internal stability and string stability, we select the following Lyapunov candidate function. : For the selected Lyapunov function By taking the derivative, we can calculate: Here, by scaling the inequalities, we obtain: in addition, Substituting into the formula, we get: Further calculations yielded: in, but The derivative can be further written as: To analyze whether the designed actual controller can achieve internal stability and chain stability for the entire vehicle queue, we select the following global Lyapunov candidate function. : For the selected Lyapunov function Taking the derivative, we get: in, .

[0033] also, It can converge to the following region within a fixed time: in, It is a constant and And the convergence time satisfies the following condition: .

[0034] Therefore, it can be concluded that all state signals of the vehicle queuing closed-loop system are stable over a fixed time, and the tracking error converges to a small neighborhood near the origin within a preset fixed time, independent of the initial conditions. Furthermore, theoretical analysis rigorously proves that the system simultaneously satisfies both individual vehicle stability and queuing cascade stability. Thus, the stability of the system is proven.

[0035] To demonstrate the feasibility, effectiveness, and correctness of this example, the present invention provides the following simulation examples: In this simulation experiment, an adaptive fixed-time sliding mode controller was designed and constructed for a vehicle platoon system with external disturbances. This controller effectively overcomes the influence of external disturbances and unknown nonlinear terms, achieving precise synchronous tracking control of the lead vehicle's time-varying position by following vehicles in the platoon. Furthermore, based on achieving synchronization, the system's tracking accuracy and transient performance were improved. The time-varying reference speed of the leader is used for driving under approximate road conditions.

[0036] First, the system model parameters are given: vehicle mass is Engine time constant Vehicle length Expected safe distance between vehicles Secondly, the leader's time-varying reference speed: The external disturbance term is: ; The initial system state is: , ; The relevant parameters for sliding surface control are: The relevant parameters of the piecewise continuous performance constraint function are: ; The relevant parameters for the controller are: The effectiveness of this simulation is further illustrated by referring to the accompanying diagram: Simulation results are as follows Figures 5-13 The simulation results are shown in the figure. Figure 5 A comparison chart of the convergence characteristics of the piecewise continuous performance constraint function of this disclosure and the traditional performance constraint function is presented. It can be seen that the traditional performance constraint function requires infinite time to approach the final value, while the piecewise continuous performance constraint function of this disclosure can reach the final value within a specified time. Figure 6 It depicts the positional changes of the vehicle platoon, regardless of whether the leader is accelerating, decelerating, or being disturbed, with no overlapping or collisions between vehicle positions, and the vehicles remain stable in the desired positions. Figure 7 The speed tracking effect of following vehicles 1-3 on the leader vehicle is depicted. Under acceleration and deceleration, the speed of the following vehicles shows a small instantaneous tracking deviation, and can quickly converge to the speed of the leader in a very short time, indicating that the following vehicles 1-3 have a good tracking effect on the leader vehicle. Figure 8 shows the acceleration change of the vehicle platoon. The acceleration of each vehicle changes smoothly without drastic fluctuations, avoiding the impact of sudden acceleration and deceleration on the driving stability of the vehicles, which meets the requirements of practical application. Figure 9It demonstrates that the spacing error of the vehicle platoon converges rapidly to a small neighborhood near zero and is constrained within the preset performance boundary throughout the process, thus meeting the string stability requirements in vehicle platoon tracking control. Figure 10 The display shows that the relative speed is actually stable over a fixed period of time, and a speed of 1-3 can track the speed of the leading vehicle. Figure 11 The sliding surface state curves of the followers in the vehicle platoon all converge quickly to near zero without continuous oscillation or divergence, proving the robustness of sliding mode control. Figure 12 The adaptive parameter curves are displayed, which effectively compensate for system uncertainties and further verify the effectiveness of the adaptive mechanism. Figure 13 The control input curve of the follower is shown, and the control input amplitude is within the physically realizable range. Thus, the simulation demonstrates the effectiveness of the proposed control scheme.

[0037] This example proposes an adaptive fixed-time sliding mode control method for a distributed vehicle queuing system, exhibiting performance characteristics within a specified time interval. First, a vehicle dynamics model is established. Second, a piecewise continuous performance constraint function is constructed, allowing the error to converge effectively within a specified time interval. By adjusting the specified time parameter, any desired convergence rate can be achieved. Based on this, an adaptive fixed-time sliding mode controller is constructed, balancing fixed-time convergence with transient and steady-state error performance, while simultaneously ensuring the internal and chain stability of the vehicle queuing. Finally, simulation examples verify the feasibility of the proposed vehicle queuing control method.

[0038] Example 2 Embodiment 2 of this disclosure provides a vehicle queuing adaptive fixed-time sliding mode control system with specified time performance, including: The model building module is configured to: build a vehicle dynamics model; The error limiting module is configured to: design a piecewise continuous function based on a constant spacing strategy, and limit the tracking error of the following vehicle within a specified performance range according to the piecewise continuous function; The signal compensation module is configured to: design an error transformation function based on specified time-defined performance constraints, transforming the original tracking error problem constrained by time-varying performance boundaries into an equivalent unconstrained error problem; and design a fixed-time sliding surface based on the transformed system state. The control module is configured to: construct an adaptive fixed-time sliding mode controller based on the designed fixed-time sliding mode surface and combined with an adaptive parameter estimation method; the controller is used to compensate for unknown nonlinear terms and external disturbances in the vehicle model, and to estimate unknown parameters through an adaptive law to achieve queue stability of the vehicle queue within a fixed time.

[0039] The more detailed steps are the same as in Example 1, and will not be repeated here.

[0040] Example 3 This disclosure provides a medium on which a program is stored, which, when executed by a processor, implements the steps of the vehicle queue adaptive fixed-time sliding mode control method with specified time performance as described in this disclosure, as in embodiment one.

[0041] The more detailed steps are the same as in Example 1, and will not be repeated here.

[0042] Example 4 This disclosure provides an electronic device, including a memory, a processor, and a program stored in the memory and executable on the processor. When the processor executes the program, it implements the steps in the vehicle queue adaptive fixed-time sliding mode control method with specified time performance as described in this disclosure, as in embodiment one.

[0043] This invention is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart illustrations and / or block diagrams. Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0044] In the description of this invention, it should be understood that the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0045] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A vehicle queuing adaptive control method based on specified performance and fixed-time sliding mode, characterized in that, Includes the following steps: Based on the constructed vehicle dynamics model, and according to the constant spacing strategy, the tracking error of the following vehicle is limited to the specified performance range; Construct an error transformation function that adapts to the specified performance constraints at a given time, and transform the original tracking error system, which is limited by time-varying performance boundaries, into an equivalent unconstrained error system to obtain a fixed-time sliding surface; Using the fixed-time sliding surface as the core and combining adaptive parameter estimation technology, an adaptive fixed-time sliding mode controller is built to perform adaptive control on the vehicle queue.

2. The vehicle queuing adaptive control method based on specified performance and fixed-time sliding mode according to claim 1, characterized in that: When constructing a vehicle dynamics model, based on the state information and parameter information of each vehicle, and considering external disturbances and unknown nonlinear terms, a vehicle dynamics model referencing Newton's second law is established. The state information includes the vehicle's position information, velocity information, and acceleration information.

3. The vehicle queuing adaptive control method based on specified performance and fixed-time sliding mode according to claim 2, characterized in that: In the process of limiting the tracking error of the following vehicle within a specified performance range, a piecewise continuous performance function is designed based on a constant spacing strategy. The piecewise continuous performance function is used to limit the tracking error of the following vehicle within the specified performance range. The piecewise continuous performance function is expressed as follows: in, As the initial performance boundary, For steady-state performance boundary, This indicates the set time, i.e., the maximum permissible error stabilization time.

4. The vehicle queuing adaptive control method based on specified performance and fixed-time sliding mode according to claim 3, characterized in that: When acquiring the tracking error, the vehicle dynamics model is transformed into a state-space expression, and then the tracking error is designed using the state-space expression, wherein the state-space expression is expressed as: in, Indicates time, Represents the measurable system state, i.e., the first... The vehicle's position, speed, and acceleration They are The derivative of Indicates the first Time-varying input disturbance of the vehicle It is the first Vehicle control inputs, It is the first The quality of the vehicle ,in It is air density. It is the cross-sectional area of ​​the vehicle. It is the air drag coefficient. It is the first Road gradient function for vehicles , It is gravitational acceleration. It is the roadbed slope. It is the rolling resistance coefficient. Indicates the first The engine time constant of a vehicle.

5. The vehicle queuing adaptive control method based on specified performance and fixed-time sliding mode according to claim 4, characterized in that: When acquiring the tracking error, the tracking error is represented as: in, For vehicle spacing, , Indicates the first The length of the car For the desired safe distance, Indicates the first The vehicle's expected trajectory, , , and These are the weighting coefficients.

6. The vehicle queuing adaptive control method based on specified performance and fixed-time sliding mode according to claim 5, characterized in that: When designing a fixed-time sliding surface, the constrained error is converted into an unconstrained variable through nonlinear mapping, and the first-order, second-order, and second-order time derivatives of the unconstrained variable are obtained to design the fixed-time sliding surface.

7. The vehicle queuing adaptive control method based on specified performance and fixed-time sliding mode according to claim 6, characterized in that: When building an adaptive fixed-time sliding mode controller, a continuous hyperbolic tangent function is used to suppress chattering in sliding mode control.

8. The vehicle queuing adaptive control method based on specified performance and fixed-time sliding mode according to claim 7, characterized in that: When performing adaptive control on a vehicle platoon, an adaptive fixed-time sliding mode controller is built to counteract unknown nonlinear factors and external disturbances in the vehicle model. The unknown parameters are estimated using an adaptive law to ensure that the vehicle platoon meets the specified performance and platoon stability requirements within a fixed time.

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