A Topological Reconfiguration Method for a Control System Communication Network Based on Multiple USVs

Abstract

The present invention provides a topology reconstruction method for a multi-USV containment control system communication network, including: identifying the follower-follower network topology; adding or deleting follower-follower network communication links to obtain the reconstructed follower-follower network topology; obtaining the system topology; based on the obtained system topology, calculating the distance between USVs, if the distance between USVs is greater than or equal to the set collision avoidance safety distance, the system has good collision avoidance performance, and generating the final multi-USV containment control system topology; otherwise, re-add or delete follower-follower network communication links and start a new round of topology reconstruction. From the perspective of the system communication topology, with the convergence of the multi-USV containment control system as the control target, by reconstructing the follower network communication topology, the present invention obtains a topology structure that ensures the relatively dispersed convergence positions of followers, thereby improving the anti-disturbance collision avoidance performance of the system and enabling the system to cope with the impact of complex marine environments on performance.

Description

Technical Field

[0001] The present invention relates to the technical field of unmanned surface vehicle control, and in particular, to a topology reconstruction method for a communication network of a multi-USV-based control system. Background Art

[0002] Marine agents such as unmanned surface vehicles (USVs) are widely used in environments such as marine commissioning, marine environmental monitoring, marine joint search and rescue, military operations, and marine patrols due to their advantages of being autonomous and flexible. With the continuous improvement of the complexity of tasks and the requirements for operation accuracy, a single unmanned surface vehicle can no longer meet the requirements for current marine tasks, so the realization of multi-boat cooperation is urgently needed. Unmanned surface vehicle swarm coordination refers to combining multiple single unmanned surface vehicles into a system for overall control design to perform specific tasks. The unmanned surface vehicle swarm coordination system is based on multi-agent system (MAS) theory, control theory, and network communication technology. Each unmanned surface vehicle in the system has a distributed controller and can independently process information and make decisions while coordinating. Facing the complex marine environment, the requirements of high intelligence and task diversification pose challenges to marine unmanned systems, especially multi-USV systems. Collision and interference, as two major factors threatening the safe operation of multi-USV systems, are issues that must be considered in various control problems.

[0003] Under the requirements of multi-objective tasks, containment control methods have been widely applied in ensuring the safe operation of the system. Because of a special advantage, that is, the leader agent equipped with sensors can form a dynamic safety zone according to the obstacle information detected during the movement. Under the containment control protocol, all follower agents can converge to this safety zone and move together with the leader agent through information exchange, thus achieving coordination. When the existing containment control theory is applied to multi-USV systems, in order to cope with various practical problems, methods for designing control protocols based on sampling time, event-triggering, and adaptive algorithms have emerged. However, due to the influence of complex marine environmental factors such as wind, waves, and currents, the collision avoidance conditions will be triggered multiple times, wasting a large amount of resources. When the USVs in the system are densely distributed, it may even lead to local jamming, resulting in a high collision risk. Due to the existence of interference, the convergence position of the USV will also change within a certain range and cannot converge to a fixed position, which also increases the collision risk between USVs. Therefore, under the action of these control protocols, although the multi-USV system can achieve convergence, there are still great limitations in collision avoidance and anti-interference. Summary of the Invention

[0004] To solve the above problems, the convergence positions of the follower USVs in the system should be as scattered as possible. From the perspective of algebraic graph theory, a smaller algebraic connectivity should be selected to reconstruct the communication network topology of the followers in the multi-USV containment control system to make up for the limitations of existing control algorithms. Starting from the algebraic connectivity of the system topology, this invention studies the problem of communication topology reconstruction for multi-USV containment control systems based on multi-agent theory. By analyzing the relationship between the algebraic connectivity of the network topology composed of follower USVs and the convergence positions of the follower USVs, a topology reconstruction method for multi-USV containment control systems based on algebraic connectivity is proposed. The method of this invention takes the desired algebraic connectivity as the control objective. Each USV in the system can distributively identify the USVs participating in cooperation and the communication connection relationships between them, and independently add and delete communication links. Based on the reconstructed follower network topology, by selecting the follower USVs that directly communicate with the leader USV, a multi-USV containment control system topology matching the control objective can be obtained. Under the reconstructed system topology, the positions where the followers finally converge are as scattered as possible. The system with this characteristic has good collision avoidance and anti-interference performance, making up for the limitations of traditional related algorithms in the complex marine environment.

[0005] The technical means adopted in this invention are as follows:

[0006] A topology reconstruction method for a communication network of a multi-USV containment control system, including:

[0007] Identify the follower-follower network topology;

[0008] Add or delete communication links of the follower-follower network;

[0009] Reconstruct the follower-follower network topology with added or deleted communication links of the follower-follower network to obtain the reconstructed follower-follower network topology;

[0010] Based on the reconstructed follower-follower network topology, obtain the system topology;

[0011] Based on the obtained system topology, calculate the distances between USVs. If the distances between USVs are greater than or equal to the set collision avoidance safety distance, the system has good collision avoidance performance, and generate the final multi-USV containment control system topology; otherwise, re-add or delete communication links of the follower-follower network and start a new round of topology reconstruction.

[0012] Furthermore, the identification of the follower-follower network topology includes:

[0013] Input each follower USV into the initial local adjacency matrix And interact with adjacent follower USVs;

[0014] Each USV synchronously updates its local adjacency matrix until the local adjacency matrices of all follower USVs are the same and remain unchanged. At this time, it indicates that the follower-follower topology identification of the system is completed, and each follower USV has obtained the accurate underlying follower-follower communication topology.

[0015] Furthermore, the adding or deleting of follower-follower network communication links includes:

[0016] Given a relatively small and appropriate algebraic connectivity λ 2d as the performance objective for the reconstruction of the follower-follower network topology, use the algorithm to add or delete communication links in the network.

[0017] Furthermore, the reconstruction of the follower-follower network topology for the adding or deleting of follower-follower network communication links to obtain the reconstructed follower-follower network topology includes:

[0018] Calculate the error between the expected algebraic connectivity and the algebraic connectivity of the current communication network

[0019] Determine whether the reconstruction is completed: Judge whether each USV evaluation meets the requirements of the error range. If not, re-add or delete the follower-follower network communication links and recalculate the error between the expected algebraic connectivity and the algebraic connectivity of the current communication network If so, determine that the reconstruction is completed and obtain the follower-follower communication network topology.

[0020] Furthermore, obtaining the system topology based on the reconstructed follower-follower network topology includes:

[0021] Based on the reconstructed follower-follower network topology, calculate the degrees of each USV node and the sum of the degrees of the USV nodes in its neighbor set, and select m nodes as the followers that communicate directly with the leader to obtain the multi-USV control system topology.

[0022] Furthermore, the algorithm for the follower nodes that communicate directly with the leader specifically includes:

[0023] Calculate the degree of each follower USV node Determine m nodes with the smallest degrees as the set of candidate nodes If the number of elements in the set is m, the set of follower nodes that communicate directly with the leader

[0024] If the number of elements in the set is greater than m, calculate the sum of the degrees of the USV nodes corresponding to the elements in each USV neighbor set, and determine m nodes with the largest sum of degrees as the set of candidate nodes

[0025] Determine the set of follower nodes that directly communicate with the leader

[0026] Furthermore, if there are multiple nodes with the same degree, the number of elements in the set of candidate nodes is greater than m.

[0027] Compared with the prior art, the present invention has the following advantages:

[0028] 1. The topology reconstruction method of the multi-USV containment control system communication network provided by the present invention takes the desired algebraic connectivity as the control target. It distributes the identification of the USVs participating in the cooperative task and the communication links between them. Each USV in the system can independently add and delete communication links, so as to obtain a system topology that matches the control target. Under the reconstructed system topology, the final convergence positions of the followers are relatively dispersed. The containment control system with such characteristics has good collision avoidance and anti-interference performance. Under the action of the consensus control protocol, it is realized that all followers can converge into the convex hull formed by the leaders and keep the same speed as the leaders.

[0029] 2. The topology reconstruction method of the multi-USV containment control system communication network provided by the present invention is different from the existing method of using a designed local control algorithm for collision avoidance. From the perspective of the system communication topology, taking the convergence of the multi-USV containment control system as the control target, by reconstructing the communication topology of the follower network, a topology structure that ensures the relatively dispersed convergence positions of the followers is obtained, thereby improving the anti-interference and collision avoidance performance of the system and enabling the system to cope with the influence of complex marine environments on performance.

[0030] 3. From the perspective of the system topology, based on the analysis of the relationship between the algebraic connectivity and the degree of dispersion of the follower convergence positions, a topology reconstruction method for the multi-USV containment control system is proposed, that is, by selecting a smaller and appropriate algebraic connectivity to reconstruct the topology of the underlying follower-follower communication network to make it reach the expected performance level. Description of the Drawings

[0031] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the accompanying drawings required for the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other accompanying drawings can be obtained based on these drawings.

[0032] Figure 1 The flow chart of the control system topology reconstruction algorithm for the multi-USV system based on algebraic connectivity of the present invention.

[0033] Figure 2 The initial communication topology of the multi-USV system at the start of networking provided by the embodiment of the present invention.

[0034] Figure 3 The follower-follower network communication topology obtained by reconstruction provided by the embodiment of the present invention.

[0035] Figure 4 The communication topology of the multi-USV including the control system obtained by reconstruction provided by the embodiment of the present invention.

[0036] Figure 5 The parametric paths of the leader USV and the follower USV on the x-axis and y-axis during the convergence process provided by the embodiment of the present invention.

[0037] Figure 6 The state trajectories of the leader USV and the follower USV provided by the embodiment of the present invention.

[0038] Figure 7 The comparison chart of the convergence of the follower USV before and after topology reconstruction provided by the embodiment of the present invention. Detailed implementation manners

[0039] It should be noted that, without conflict, the embodiments in the present invention and the features in the embodiments can be combined with each other. The following will describe the present invention in detail with reference to the accompanying drawings and in combination with the embodiments.

[0040] To make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with 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, rather than all of the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and in no way restrictive of the present invention and its application or use. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts fall within the scope of protection of the present invention.

[0041] It should be noted that the terms used herein are for the purpose of describing specific embodiments only and are not intended to limit the exemplary embodiments of the present invention. As used herein, unless the context clearly indicates otherwise, the singular forms are also intended to include the plural forms. In addition, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they specify the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0042] Unless otherwise specifically stated, the relative arrangements of components and steps, numerical expressions, and numerical values set forth in these embodiments do not limit the scope of the present invention. At the same time, it should be clear that, for the sake of convenience of description, the dimensions of the various parts shown in the drawings are not drawn in actual proportional relationships. Technologies, methods, and devices known to those of ordinary skill in the relevant art may not be discussed in detail, but where appropriate, such technologies, methods, and devices should be regarded as part of the authorized specification. In all the examples shown and discussed herein, any specific values should be construed as merely exemplary and not as a limitation. Therefore, other examples of the exemplary embodiments may have different values. It should be noted that like reference numerals and letters denote like items in the following drawings, and thus, once an item is defined in one drawing, it does not require further discussion in subsequent drawings.

[0043] In the description of the present invention, it should be understood that the orientation or positional relationships indicated by orientation words such as "front, rear, upper, lower, left, right", "lateral, vertical, perpendicular, horizontal", and "top, bottom" are generally based on the orientation or positional relationships shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description. Without contrary description, these orientation words do not indicate and imply that the devices or elements referred to must have a specific orientation or be constructed and operated in a specific orientation, and thus should not be construed as limiting the protection scope of the present invention. The orientation words "inside, outside" refer to the inside and outside relative to the contours of the respective components.

[0044] For the sake of convenience in description, spatial relative terms such as "above", "over", "on the upper surface", "upper" etc. can be used here to describe the spatial positional relationship between a device or feature shown in the figure and other devices or features. It should be understood that spatial relative terms are intended to include different orientations in use or operation other than the orientation described in the figure for the device. For example, if the device in the attached drawing is inverted, the device described as "above other devices or structures" or "over other devices or structures" will then be positioned as "below other devices or structures" or "under other devices or structures". Thus, the exemplary term "above" can include both the orientations of "above" and "below". The device can also be positioned in other different ways (rotated 90 degrees or in other orientations), and corresponding interpretations are made for the spatial relative descriptions used here.

[0045] In addition, it should be noted that using words such as "first", "second" etc. to limit components is only for the convenience of differentiating the corresponding components. Without further statement, the above words have no special meaning, and thus cannot be understood as a limitation to the protection scope of the present invention.

[0046] In this embodiment, the multi-USV includes a control system with the following characteristics:

[0047] The communication graph topology of the system has a directed spanning tree, whose root node is the leader in the system and other nodes are the followers in the system;

[0048] All the eigenvalues of the follower-follower network topology in the system have positive real parts;

[0049] The probability that every two USVs in the system communication topology are connected is the same;

[0050] The USVs in the system can all perform omni-directional information reception and transmission, and the measurement of the quality of a certain communication link by a USV conforms to the assumption of the Gaussian law.

[0051] On the basis of having the above characteristics, in the context of a temporarily networked task, in a distributed multi-USV system, since each USV can only know the information of itself and its neighboring USVs and cannot directly determine the complete system topology structure, in practical problems, topology reconstruction also involves the process of each USV identifying the system topology, that is, the total number of USVs in the system and their communication connection relationships. In the present invention, based on the reconstructed follower-follower network topology structure, the communication connection between the leader and the followers is determined through an algorithm. Therefore, the object of system topology identification is only the follower-follower network.

[0052] The present invention realizes the technical goal of improving the collision avoidance and anti-interference performance of the system by reconstructing the system topology, and the designed object does not contain the local control rate information of the system. Under this background, the kinematic model of the multi-USV system can be simplified into a second-order multi-agent system model containing position and velocity information. The multi-USV system designed by the present invention based on algebraic connectivity includes a control system topology reconstruction method, mainly including topology reconstruction based on the follower-follower network and the design of a follower selection algorithm for communicating with the leader. The multi-USV system involved in the present invention has a distributed network communication structure. Therefore, relevant concepts in graph theory are first introduced to represent the communication connection relationship between USVs. The topology structure of the follower-follower network is represented by an undirected graph G=(V,E), where V={v1,v2,...,v n} represents the node set of the follower-follower network, and E={(v i ,v j )|v i ,v j ∈V} represents the edge set. The connection relationship between the nodes in the graph is defined by the adjacency matrix A∈R n ×n , that is, if there is an edge pointing from node v j to node v i , then a ij = 1, otherwise a ij = 0. For an undirected graph, its adjacency matrix A∈R n×n is symmetric. The degree matrix D={d1,d2,...,d n} is a diagonal matrix, where represents the degree of the i-th node. The Laplacian matrix is defined as L = D - A. For an undirected graph, the eigenvalues of its Laplacian matrix are arranged in ascending order as λ1≤λ2≤...≤λ n . The second smallest eigenvalue λ2 of the Laplacian matrix is called algebraic connectivity, which is an important indicator to measure the system performance.

[0053] Embodiment

[0054] Based on the above description, taking a multi-USV control system with 3 leaders and 9 followers as an example, the technical solution of the present invention will be described in detail with reference to the accompanying drawings. Given an initial system communication topology as Figure 2 shown, as Figure 1 shown, the specific steps of its topology reconstruction method are as follows:

[0055] S1. Identify the topology of the follower-follower network;

[0056] S2. Add or delete communication links of the follower-follower network;

[0057] S3. Reconstruct the follower-follower network topology with added or deleted follower-follower network communication links to obtain the reconstructed follower-follower network topology;

[0058] S4. Based on the reconstructed follower-follower network topology, obtain the system topology;

[0059] S5. Based on the obtained system topology, calculate the distance between USVs. If the distance between USVs is greater than or equal to the set collision avoidance safety distance, the system has good collision avoidance performance, and generate the final multi-USV containment control system topology; otherwise, re-add or delete follower-follower network communication links and start a new round of topology reconstruction.

[0060] Specifically in implementation, as a preferred implementation manner of the present invention, in the step S1, identifying the follower-follower network topology includes:

[0061] When each USV forms a temporary network after receiving an instruction, a single USV cannot directly obtain the complete system topology, and the information it can obtain is limited to the USVs within its neighbor set. Input each follower USV into the initial local adjacency matrix Expressed as: a total of 9, and so on for the matrix form)

[0062]

[0063] And interact with adjacent follower USVs; perform distributed identification on the communication topology structure of the system, including the number of USVs in the system and their communication connection relationships.

[0064] Each USV synchronously updates its local adjacency matrix until the local adjacency matrices of all follower USVs Are the same and remain unchanged. At this time, it indicates that the identification of the system follower-follower topology is completed, and each follower USV has obtained the accurate underlying follower-follower communication topology.

[0065] Specifically in implementation, as a preferred implementation manner of the present invention, in the step S2, adding or deleting follower-follower network communication links includes:

[0066] Given a relatively small and appropriate algebraic connectivity λ 2d = 0.4 as the performance target for the reconstruction of the follower-follower network topology, and set the allowable error range to 0.1. Use the algorithm to add or delete communication links in the network.

[0067] In specific implementation, as a preferred implementation manner of the present invention, in the step S3, the follower-follower network topology with added or deleted follower-follower network communication links is reconstructed to obtain the reconstructed follower-follower network topology. Since the processing actions on the links are independently completed by each USV, at the end of each round of topology reconstruction, the algebraic connectivity of the entire follower-follower network is analyzed to determine whether it meets the requirements of the control objective. Specifically, it includes:

[0068] Calculate the error between the expected algebraic connectivity and the algebraic connectivity of the current communication network

[0069] Determine whether the reconstruction is completed: Judge whether each USV evaluation meets the requirements of the error range. If not, return to execute step S2, re-add or delete the follower-follower network communication links, and recalculate the error between the expected algebraic connectivity and the algebraic connectivity of the current communication network If so, determine that the reconstruction is completed, and obtain the follower-follower communication network topology as Figure 3 shown, corresponding to λ2 = 0.4131.

[0070] In specific implementation, as a preferred implementation manner of the present invention, in the step S4, based on the reconstructed follower-follower network topology, the system topology is obtained, including:

[0071] Based on the reconstructed follower-follower network topology, calculate the degrees of each USV node and the sum of the degrees of the USV nodes in its neighbor set, and select the 3 nodes with the smallest degrees as the followers directly communicating with the leader to obtain the multi-USV control system topology. Specifically, it includes:

[0072] Calculate the degree of each follower USV node Determine m nodes with the smallest degrees as the set of alternative nodes Among them, node 1 has the smallest degree, so it is directly determined to be one of the 3 followers communicating with the leader. The number of elements in the set is greater than 3, and further selection is still required for the remaining nodes in the set of alternative nodes.

[0073] Calculate the sum of the degrees of the USV nodes corresponding to the elements in

[0074]

[0075]

[0076]

[0077] Therefore, the set of alternative follower USV nodes is obtained. The three follower nodes that the leader communicates with directly are The multi-USV containment control system topology is obtained as Figure 4 As shown, the solid line with an arrow indicates that the communication between two USVs is one-way, and the solid line without an arrow indicates that the communication between two USVs is two-way.

[0078] Based on the reconstructed multi-USV containment control system topology, the consensus controller is designed as follows:

[0079]

[0080] where represents the position information of each USV, represents the speed information, and α, β are the controller parameters to be designed. In this example, α = 1, β = 1.

[0081] As Figure 5 shown, it is the parametric paths of the leader USV and the follower USVs on the x-axis and y-axis during the convergence process, where the dashed line represents the leader USV and the solid line represents the follower USVs. Figure 6 are the state trajectories of the leader USV and the follower USVs. In Figure 7 , Figure (a) shows the convergence of the follower USVs in the convex hull before the system topology reconstruction, and Figure (b) shows the convergence after the system topology reconstruction. It can be seen that in Figure (a), the USVs converge densely within the convex hull, making the risk of collision during the operation of the system relatively high. While in Figure (b), the convergence positions of the follower USVs are more dispersed, and there is a sufficient safety distance between each USV to avoid collision. When performing tasks at sea, a system equipped with this type of topology can ensure better safety performance for the follower USVs.

[0082] It should be noted later that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements for some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A topology reconstruction method for a control system communication network based on multiple USVs, characterized in that Including: Identifying the follower-follower network topology; Adding or deleting follower-follower network communication links; Reconstructing the follower-follower network topology with added or deleted follower-follower network communication links to obtain the reconstructed follower-follower network topology; Based on the reconstructed follower-follower network topology, obtaining the system topology, including: Based on the reconstructed follower-follower network topology, calculating the degrees of each USV node and the sum of the degrees of USV nodes in its neighbor set, and selecting m nodes as the followers for direct communication with the leader to obtain the multi-USV containment control system topology; The algorithm for the follower nodes for direct communication with the leader specifically includes: Calculate the degree of each follower USV node Determine the m nodes with the smallest degrees as the set of candidate nodes If the number of elements in the set is m, the set of follower nodes for direct communication by the leader If the number of elements in the set is greater than m, calculate the sum of the degrees of the USV nodes corresponding to the elements in each USV neighbor set, and determine m nodes with the largest sum of degrees as the candidate node set Determine the set of follower nodes that communicate directly with the leader Based on the obtained system topology, calculating the distances between USVs. If the distance between USVs is greater than or equal to the set collision avoidance safety distance, the system has good collision avoidance performance, and the final multi-USV containment control system topology is generated; Otherwise, re-add or delete the follower-follower network communication links and start a new round of topology reconstruction.

2. The topology reconstruction method based on the control system communication network of multiple USVs according to claim 1, wherein The identifying the follower-follower network topology includes: Input each follower USV into the initial local adjacency matrix And interact with adjacent follower USVs; Each USV synchronously updates its local adjacency matrix until the local adjacency matrices of all follower USVs are the same and remain unchanged. At this time, it indicates that the follower-follower topology identification of the system is completed, and each follower USV has obtained the accurate underlying follower-follower communication topology.

3. The topology reconstruction method based on a communication network of a control system for a multi-USV according to claim 1, wherein The adding or deleting the follower-follower network communication links includes: Given an algebraic connectivity λ 2d As the performance objective of the follower-follower network topology reconstruction, use the algorithm to add or delete communication links in the network.

4. The topology reconstruction method based on the communication network of the control system for multi-USV according to claim 1, characterized in that, The reconstructing the follower-follower network topology with added or deleted follower-follower network communication links to obtain the reconstructed follower-follower network topology includes: Calculate the error between the expected algebraic connectivity and the algebraic connectivity of the current communication network Determine whether the reconstruction is complete: Judge each USV evaluation to see if it meets the requirements of the error range. If not, re-add or delete follower-follower network communication links and recalculate the error between the expected algebraic connectivity and the algebraic connectivity of the current communication network If so, determine that the reconstruction is complete and obtain the follower-follower communication network topology.

5. The topology reconstruction method based on a communication network of a control system for a multi-USV according to claim 1, wherein If there are multiple nodes with the same degree, the number of elements in the alternative node set is greater than m.

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