An anti-interference sliding mode control method for UAV formation

Abstract

The present invention discloses an anti-interference UAV formation sliding mode control method, including: considering external unknown interference, establishing the UAV state equation, giving the trajectory equation of the virtual leader, and giving the formation of the UAV; determining the formation function according to the formation, and determining the formation function of each UAV; giving the position error of each UAV according to the position information of the virtual leader and the formation function; designing a non-singular terminal sliding mode function according to the position error of the UAV, and establishing the anti-interference control law of the UAV; introducing an interference observer, observing the external unknown interference, and determining the interference compensation term in the control law according to the observation result. The present invention establishes a formation control law that can adapt to any formation requirements, and improves the control performance of the system in combination with the non-singular terminal sliding mode surface, and constructs an interference observer to enhance the anti-interference ability of the system.

Description

Technical Field

[0001] The invention relates to an anti-interference UAV formation sliding mode control method, belonging to the technical field of UAV control. Background Art

[0002] Drones have the advantages of zero casualties, long flight time, high maneuverability, and low production cost. However, a single drone has disadvantages such as insufficient load capacity and small working radius. Compared with a single drone, drone formations can improve redundancy and mission success rate to a certain extent. Therefore, drone formation technology is currently a research hotspot. In actual situations, drone formations will be affected by external interference, and external interference is usually difficult to accurately measure. In addition, facing different environments and different tasks, the formations of drones will also be different. The formation method for a specific formation is not enough to meet actual needs.

[0003] Finite-time stability has a greater advantage than asymptotic stability. It can ensure that the error of the system can converge to zero within a finite time. At present, many UAV formation controls use linear sliding surfaces. Compared with linear sliding surfaces, terminal sliding surfaces can achieve finite-time stability of the system, improve convergence speed, and enhance system robustness. The existing design of UAV formation control schemes using the leader-follower method, such as Chinese patent 202011045560.0, a UAV formation flight method and control system. In the UAV formation control scheme designed using this method, the follower UAV needs to obtain the real-time position information of the leader UAV. Once the follower UAV cannot receive the position information of the leader UAV due to some unexpected circumstances, it may lead to the failure of the formation flight mission. In addition, using the existing scheme, the formation of the UAV cannot change when flying in formation, and can only fly in a fixed formation, which cannot adapt to different environments and mission requirements. Therefore, in order to avoid the formation failure problem caused by the missing position information of a certain UAV, and to enable the UAVs to change formations during formation flying without being restricted to one formation, it is necessary to design a formation control method that can adapt to different formation requirements. Summary of the invention

[0004] The technical problem to be solved by the present invention is: to provide an interference-resistant UAV formation sliding mode control method, to establish a formation control law that can adapt to any formation requirements, to improve the control performance of the system by combining a non-singular terminal sliding mode surface, and to enhance the anti-interference ability of the system by constructing an interference observer.

[0005] The present invention adopts the following technical solutions to solve the above technical problems:

[0006] An anti-interference UAV formation sliding mode control method comprises the following steps:

[0007] Step 1, considering external unknown interference, establishing the drone state equation, presetting the virtual leader trajectory and establishing the virtual leader trajectory equation;

[0008] Step 2: preset the UAV formation, construct an inertial coordinate system with a pre-specified point on the ground as the origin, and determine the formation function of each UAV according to the inertial coordinate system;

[0009] Step 3, according to the formation function of each UAV and the trajectory equation of the virtual leader, the position error of each UAV is calculated;

[0010] Step 4: According to the position error of each UAV, a non-singular terminal sliding mode function is designed to further establish the anti-disturbance control law of each UAV;

[0011] Step 5: Design a disturbance observer to observe external unknown disturbances and determine the disturbance compensation term in the anti-disturbance control law.

[0012] Compared with the prior art, the present invention adopts the above technical solution and has the following technical effects:

[0013] 1. The present invention adopts a centralized control method to determine the formation function according to the formation requirements, and determines the UAV position error accordingly. The formation control law designed on this basis can make the UAV formation adapt to any formation, thereby improving the versatility of the control method.

[0014] 2. Aiming at the formation control problem of UAVs, the present invention adopts a non-singular terminal sliding surface instead of a traditional linear sliding surface, thereby reducing overshoot and improving the system control effect.

[0015] 3. The present invention takes the problem of unknown external interference into consideration, designs an interference observer, and determines the interference compensation term in the control law based on the observation results of the observer, which offsets the influence of the unknown interference to a certain extent, so that the system has a certain anti-interference ability. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a flow chart of an anti-interference UAV formation sliding mode control method of the present invention;

[0017] Figure 2 is a schematic diagram of the formation of a UAV fleet proposed in an embodiment of the present invention;

[0018] Figure 3 , Figure 4 and Figure 5 They are three drones according to the embodiment of the present invention. direction, direction, Schematic diagram of direction position error;

[0019] Figure 6 , Figure 7 and Figure 8 They are three drones according to the embodiment of the present invention. direction, direction, Schematic diagram comparing the control effects of the two methods in terms of direction;

[0020] Fig. 9 , Fig.10 and Fig.11 They are three drones according to the embodiment of the present invention. direction, direction, Schematic diagram of directional interference estimation error;

[0021] Fig.12 , Fig.13 and Fig.14 They are three drones according to the embodiment of the present invention. direction, direction, Schematic diagram of the directional interference observation effect;

[0022] Fig.15 Schematic diagram of actual flight trajectories of three UAVs according to an embodiment of the present invention. DETAILED DESCRIPTION

[0023] The embodiments of the present invention are described in detail below, and examples of the embodiments are shown in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and cannot be interpreted as limiting the present invention.

[0024] like Figure 1 As shown, the present invention proposes an anti-interference UAV formation sliding mode control method, the formation adopts a centralized control method, the motion trajectory of the virtual leader is determined in advance, the formation formation is determined by the formation function, and each UAV determines its own position based on the position information of the virtual leader and the formation function, thereby realizing the overall formation flight. The specific steps are as follows:

[0025] Step 1: Considering external unknown interference, establish the drone state equation and the virtual leader trajectory equation, and give the drone formation. The specific process is as follows:

[0026] S101. Establish the drone state equation:

[0027] ,

[0028] in, Indicates No. drone. Respectively represent Drone direction, direction, The position coordinates of the direction. Respectively represent Drone direction, direction, Direction speed. Respectively represent Drone direction, direction, Direction control input. Respectively represent Drone direction, direction, Unknown interference signal in the direction.

[0029] S102. The equation for the change of the virtual leader's position over time is:

[0030] ,

[0031] The drone formation control method provided by the present invention is applicable to any formation. This embodiment takes a triangle formation formed by three drones at the same height as an example. Figure 2 As shown, , Considering aesthetics, the triangle is set to an equilateral triangle with a side length of 2.

[0032] Step 2: Determine the formation function of each UAV based on the formation requirements.

[0033] The expected motion trajectory of UAV No. 1 is specified as the virtual leader trajectory. In order to form the expected formation, UAV No. 2, No. 3 and UAV No. 1 are specified to move in the same direction. The distance in the direction is 1, The distance in the direction is , The distance in the direction is 0. Looking from top to bottom, UAV No. 2 is behind UAV No. 1 to the left, UAV No. 3 is behind UAV No. 1 to the right, and UAV No. 1 coincides with the virtual leader. For the The formation function of the UAV is:

[0034] .

[0035] Step 3: According to the formation function of each UAV and the position information of the virtual leader, the position error of each UAV is given. The specific process is as follows:

[0036] The position error of UAV No. 1 is:

[0037] ,

[0038] in, UAV No. 1 direction, direction, Position error in direction.

[0039] The position error of UAV 2 is:

[0040] ,

[0041] The position error of UAV 3 is:

[0042] ,

[0043] When faced with formation requirements different from those of the present embodiment, it is only necessary to determine the formation function of each UAV and then determine the position error of each UAV, and then design a control strategy on the premise of meeting the formation requirements.

[0044] Step 4: Based on the position error of the UAV, a non-singular terminal sliding mode function is designed to establish the anti-disturbance control law of the UAV. The specific process is as follows:

[0045] S401. Design of non-singular terminal sliding mode function:

[0046] ,

[0047] in, Respectively represent Drone direction, direction, The non-singular terminal sliding mode function used in the direction is is a parameter greater than zero, Satisfaction relationship: and All are positive odd numbers.

[0048] S402. Establish the anti-disturbance control law of the UAV:

[0049] ,

[0050] in, are all parameters greater than zero. .

[0051] The Lyapunov method is used to prove that the designed control law meets the system stability requirements:

[0052] by Direction, for example, When we select Lyapunov function , and take its derivative:

[0053] ,

[0054] because are greater than zero, is a positive odd number and ,so , .

[0055] Lemma 1: Assume is an open interval containing the origin, The domain is is a smooth positive definite function of , and satisfies the following inequality:

[0056] ,

[0057] in, , are constants, is the initial time of the system. It can converge to zero in a finite time, and the finite convergence time satisfies the following relationship:

[0058] ,

[0059] According to Lemma 1, can converge to zero in a finite time, then It can also converge to zero in a finite time.

[0060] make ,

[0061] ,

[0062] Select the Lyapunov function , and take its derivative:

[0063]

[0064] because , , so we can derive from Lemma 1 that It can converge to zero in a finite time, so can converge to zero. Proof of direction and The same applies to the direction.

[0065] when When , the control law can be simplified as:

[0066] ,

[0067] by Direction as an example, it is known ,Will Substituting in:

[0068] ,

[0069] because There is always ,so Will not affect the sliding surface The finite time convergence property of . Proof of direction and In summary, the control law established in S402 can stabilize the system.

[0070] Step 5: Design a disturbance observer to observe external unknown disturbances and determine the disturbance compensation term in the control law.

[0071] Design a disturbance observer:

[0072] ,

[0073] in, Respectively Drone direction, direction, The interference estimate of the direction, is the auxiliary state variable, is a parameter greater than zero. Based on the disturbance estimate observed by the disturbance observer, the disturbance compensation term in the control law can be determined , thereby offsetting the actual interference to a certain extent The impact brought about.

[0074] Use Lyapunov's method to test the observation performance of the observer:

[0075] When considering external unknown interference, direction as an example, define the interference estimation error :

[0076] ,

[0077] Define the Lyapunov function , and take its derivative:

[0078] ,

[0079] when When: , assuming , For some constant greater than zero, solve this differential equation and process it to obtain:

[0080] ,

[0081] Exist at a certain moment ,when hour .

[0082] In summary:

[0083] ,

[0084] Design parameters , so that , so that .at this time Direction disturbance error converges asymptotically to zero. Proof of direction and The same applies to the direction.

[0085] In order to evaluate the effectiveness and innovation of the designed control strategy, a simulation verification was carried out based on the embodiment. The parameters are: the initial positions of UAVs 1, 2, and 3 in the ground system are (3, 2, 0), (5, 1, 0), and (6, 2, 0), and the initial velocities are (0.03, 0.04, 0), (0.1, 0.1, 0.1), and (0.1, 0.1, 0.1).

[0086] , each drone in the simulation The interference directions are .

[0087] Figures 3 to 15 It is the simulation result of the system under the control law established by S402. Figure 3 , Figure 4 , Figure 5 It shows that the position errors of the three UAVs in three directions converge to zero. Figure 6 , Figure 7 , Figure 8 The results show that the control strategy designed by the present invention reduces overshoot and improves system performance compared with the control strategy using a linear sliding surface. Fig. 9 , Fig.10 , Fig.11 It shows that the interference estimation errors of the three UAVs in three directions converge to zero. Fig.12 , Fig.13 , Fig.14 It shows that the adopted disturbance observer is capable of observing unknown disturbances. Fig.15 The drone formation flight trajectory shows that the three drones are able to form a formation and fly according to the predetermined trajectory.

[0088] Based on the same inventive concept, an embodiment of the present application provides a computer device, including a memory, a processor, and a computer program stored in the memory and executable on the processor. When the processor executes the computer program, the steps of the aforementioned anti-interference UAV formation sliding mode control method are implemented.

[0089] Based on the same inventive concept, an embodiment of the present application provides a computer-readable storage medium, which stores a computer program. When the computer program is executed by a processor, the steps of the aforementioned anti-interference UAV formation sliding mode control method are implemented.

[0090] It will be appreciated by those skilled in the art that embodiments of the present invention may be provided as methods, systems, or computer program products. Therefore, the present invention may take the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware. Furthermore, the present invention may take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0091] The present invention is described with reference to flowcharts and / or block diagrams of methods, devices (systems), and computer program products according to embodiments of the present invention. It should be understood that each process and / or block in the flowchart and / or block diagram, as well as the combination of processes and / or blocks in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0092] These computer program instructions may also be stored in a computer-readable memory capable of directing a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer-readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 A process or multiple processes and / or boxes Figure 1 A function specified in one or more boxes.

[0093] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process in the computer or other programmable device. Figure 1 A process or multiple processes and / or boxes Figure 1 The steps for the functions specified in one or more boxes.

[0094] The above embodiments are only for illustrating the technical idea of ​​the present invention, and cannot be used to limit the protection scope of the present invention. Any changes made on the basis of the technical solution in accordance with the technical idea proposed by the present invention shall fall within the protection scope of the present invention.

Claims

1. An anti-interference UAV formation sliding mode control method, characterized in that: The steps include: Step 1, considering external unknown interference, establish the drone state equation, preset the virtual leader trajectory and establish the equation of the virtual leader position changing with time; Step 2: preset the UAV formation, construct an inertial coordinate system with a pre-specified point on the ground as the origin, and determine the formation function of each UAV according to the inertial coordinate system; Step 3, according to the formation function of each UAV and the equation of the virtual leader's position changing over time, the position error of each UAV is calculated; Step 4: According to the position error of each UAV, a non-singular terminal sliding mode function is designed to further establish the anti-disturbance control law of each UAV; The non-singular terminal sliding mode function is as follows: Among them, s ix ,s iy ,s iz denote the non-singular terminal sliding mode functions used in the x-direction, y-direction, and z-direction of the i-th UAV, respectively, and e ix , e iy , e iz They represent the position errors of the i-th UAV in the x-, y-, and z-directions, respectively, and β i For parameters greater than zero, p and q satisfy the relationship: And p and q are both positive odd numbers; The specific anti-disturbance control law of the UAV is as follows: Among them, u ix ,u iy ,u iz denote the anti-disturbance control law of the i-th UAV in the x-direction, y-direction, and z-direction, respectively. ε and k are parameters greater than zero. sgn(·) denotes the sign function. c ,y c , z c Respectively represent the position information of the virtual leader in the x, y, and z directions, are the interference estimation values ​​of the i-th UAV in the x-, y-, and z-directions respectively; Step 5: Design a disturbance observer to observe external unknown disturbances and determine the disturbance compensation term in the anti-disturbance control law.

2. The anti-interference UAV formation sliding mode control method according to claim 1 is characterized in that: The drone state equation described in step 1 is as follows: Among them, i represents the i-th drone in the drone formation, x i ,y i , z i They represent the position coordinates of the i-th UAV in the x, y, and z directions, respectively, and v ix , v iy , v iz They represent the speed of the i-th UAV in the x-, y-, and z-directions, respectively, and u ix ,u iy ,u iz represents the control input of the i-th UAV in the x-, y-, and z-directions, respectively, and f ix (t), f iy (t), f iz (t) represents the unknown interference signals received by the i-th UAV in the x-direction, y-direction, and z-direction at time t.

3. The anti-interference UAV formation sliding mode control method according to claim 1 is characterized in that: In step 2, an inertial coordinate system is constructed with a pre-specified point on the ground as the origin, and the axes of the inertial coordinate system are parallel to the axes of the world coordinate system. The position coordinates of each UAV in the formation in the inertial coordinate system are determined, and the expected motion trajectory of any UAV in the UAV formation is used as the virtual leader trajectory, that is, the position of the UAV coincides with that of the virtual leader. The x-axis coordinate of each UAV is subtracted from the x-axis coordinate of the virtual leader to obtain the x-axis formation function of each UAV. Similarly, the y-axis and z-axis formation functions of each UAV are obtained.

4. The anti-interference UAV formation sliding mode control method according to claim 1 is characterized in that: In step 3, the position error of the drone is: Among them, e ix , e iy , e iz They represent the position errors of the i-th UAV in the x-, y-, and z-directions, respectively. c ,y c , z c They represent the position information of the virtual leader in the x, y, and z directions respectively. i ,y i , z i They represent the position coordinates of the i-th UAV in the x-, y-, and z-directions, respectively, and h ix ,h iy ,h iz They represent the formation functions of the i-th UAV in the x-, y-, and z-directions respectively.

5. The anti-interference UAV formation sliding mode control method according to claim 1 is characterized in that: In step 5, the interference observer is specifically as follows: in, are the interference estimates of the i-th UAV in the x-, y-, and z-directions, respectively. ix ,Z iy ,Z iz is an auxiliary state variable, L is a parameter greater than zero, x i ,y i ,z i They represent the position coordinates of the i-th UAV in the x-, y-, and z-directions, respectively, and u ix ,u iy ,u iz They represent the anti-disturbance control law of the i-th UAV in the x-direction, y-direction, and z-direction respectively.

6. A computer device comprising a memory, a processor, and a computer program stored in the memory and capable of running on the processor, characterized in that: When the processor executes the computer program, the steps of the anti-interference UAV formation sliding mode control method as described in any one of claims 1 to 5 are implemented.

7. A computer-readable storage medium storing a computer program, characterized in that: When the computer program is executed by a processor, the steps of the anti-interference UAV formation sliding mode control method as described in any one of claims 1 to 5 are implemented.

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