Path planning and control method for marine landing of unpowered composite wing unmanned aerial vehicle

Abstract

The embodiment of the invention provides an unpowered composite wing unmanned aerial vehicle maritime landing path planning and control method, which comprises the steps of calculating a theoretical maximum residual voyage based on a nonlinear dynamic model, establishing an energy change rule model, and performing unpowered landing simulation based on the nonlinear dynamic model. Carrying out average resistance equivalent calculation based on a flight resistance and time relationship, and judging whether unpowered landing can be carried out on the fixed offshore platform or not; the unpowered landing path planning based on the compensation function comprises the steps that according to the position and the speed direction of the composite wing unmanned aerial vehicle under the sudden unpowered condition, arc and straight line combined paths from all the composite wing unmanned aerial vehicles to a fixed offshore platform are calculated, and a path compensation function related to the flight attitude of the composite wing unmanned aerial vehicle is constructed; selecting a path enabling the compensation function to be the lowest as an unpowered landing path; and controlling the unmanned aerial vehicle to fly autonomously based on the unpowered landing control law. Therefore, the unmanned aerial vehicle can return and land without power.

Description

Technical Field

[0001] This invention relates to the field of path planning and control technology for maritime unmanned aerial vehicles (UAVs), and in particular to a path planning and control method for the landing of a powerless compound-wing UAV at sea. Background Technology

[0002] (1) Analysis of the use of marine composite-wing UAVs

[0003] Currently, the types of drones used at sea primarily focus on compound-wing drones, tethered drones (rotor-wing drones), and unmanned helicopters. Fixed-wing drones at sea are not widely used due to the immaturity of sea landing and recovery technology or the high cost of recovery. Compound-wing drones have wide applications in maritime reconnaissance and target tracking; tethered drones (rotor-wing drones), with their advantages of vertical takeoff and landing and ease of control, are widely used on land; unmanned helicopters, with their large payload, strong wind resistance, and long endurance, are more widely used in maritime rescue and marine monitoring, but their large size places high demands on landing platforms. Compound-wing drones, due to their vertical takeoff and landing capabilities, significantly reduce the requirements for landing platforms for fixed-platform drones at sea. Because the marine environment differs greatly from the land environment, compound-wing drones need to consider not only the impact of sea salt spray corrosion on drone components but also the high interference resistance requirements of sea wind conditions. Considering the usage context of compound-wing drones at sea, it is necessary to consider the movement under conditions of failure in some key systems, such as landing problems caused by engine or battery power system failures.

[0004] (2) Analysis of Maritime Unmanned Aerial Vehicle (UAV) Path Planning Technology

[0005] There is currently limited research on path planning for unmanned aerial vehicles (UAVs) at sea. This is partly due to the high-performance requirements of the marine environment, which prevents most UAVs from directly adapting to it, and partly due to the vastness of the sea area, where obstacle avoidance and other issues present in typical UAV local path planning problems are absent. Therefore, UAVs at sea do not require overly complex path planning. Current mainstream UAV path planning algorithms primarily employ methods such as A*, ant colony optimization, and artificial potential field methods to find the optimal path with the least computation time and shortest path. These algorithms focus more on solving the shortest path problem under obstacle avoidance. However, at sea, obstacle avoidance is not a primary concern; instead, path planning is used to better address issues such as takeoff and landing, and target search.

[0006] (3) Analysis of unpowered landing technology

[0007] Compound-wing UAVs can only perform flight missions when their power system is functioning normally. If the power system fails, and there is no corresponding emergency landing plan, they will be unable to complete their flight mission and may even crash. From an engineering perspective, landing a compound-wing UAV without power has three main characteristics: first, the UAV's total energy will only decrease, limiting its descent flight to a limited range; second, speed is difficult to control; and third, it is impossible to gain altitude for a go-around.

[0008] With the development of modern control theory, machine vision-based unpowered landing control strategies for UAVs have emerged. These strategies utilize the surrounding environment and parameters obtained from onboard electro-optical or radar platforms, applying neural network algorithms to calculate suitable landing points. However, this method only provides one landing point for unpowered UAV landings and cannot address the landing scenarios of fixed platforms at sea. Another approach is based on average drag calculation. This involves establishing a landing flight control law model through energy control strategies and estimating average drag based on dynamic model simulations. However, this method does not consider the control laws of the dynamic model during estimation, leading to errors in the estimated average drag. Yet another approach divides unpowered landing into three stages and designs the flight trajectory for each stage based on energy management strategies. This method only considers the energy-optimal flight trajectory design and does not take into account the UAV's flight state, particularly the impact of complex maritime environments on flight status.

[0009] It is clear that there is currently no better solution for unpowered landing technology of composite-wing UAVs at sea. Summary of the Invention

[0010] In view of the above-mentioned problems existing in the prior art, the present invention provides a path planning and control method for unpowered compound-wing UAV landing at sea, aiming to improve the probability of unpowered landing of compound-wing UAV on fixed platforms at sea in a large area. It can solve the problem that compound-wing UAV cannot land normally when it suddenly fails during return landing at sea (such as abnormal engine / battery damage) and loses power (i.e., no flight thrust). In order to improve the probability of successful return landing of compound-wing UAV on fixed platforms at sea in the case of unpowered conditions, it is necessary to maximize the range of compound-wing UAV in the case of unpowered conditions and ensure that compound-wing UAV can follow the trajectory through unpowered control law.

[0011] This invention provides a path planning and control method for the sea landing of a non-powered compound-wing unmanned aerial vehicle (UAV), comprising:

[0012] Step 1: Calculate the theoretical maximum remaining range based on the nonlinear dynamic model, including establishing an energy change law model, simulating unpowered descent based on the nonlinear dynamic model, and then performing an equivalent calculation of average resistance based on the relationship between flight resistance and time, and determining whether an unpowered landing to a fixed sea platform is possible.

[0013] Step 2: Unpowered landing path planning based on compensation function, including: calculating the combination of circular arcs and straight lines from all composite wing UAVs to the fixed sea platform according to the position and velocity direction of the composite wing UAV in the event of sudden unpowered landing; constructing the path compensation function related to the flight attitude of the composite wing UAV; and selecting the path that minimizes the compensation function as the unpowered landing path.

[0014] Step 3: Control the drone to fly autonomously based on the unpowered landing control law.

[0015] In some embodiments of the present invention, in step 1, the method includes:

[0016] Step 11: Establish a model of energy change patterns;

[0017] Establish an energy change planning model based on the initial and final states of the compound-wing UAV:

[0018]

[0019] In equation (1), m is the mass of the compound-wing UAV, and V s H is the flight speed without power. s This refers to the flight altitude without power.

[0020] The termination state can be divided into two cases. One is when the compound-wing UAV first reaches zero horizontal speed and its flight altitude is greater than the landing platform altitude on the fixed sea platform. In this case, V... e H represents the vertical velocity of the compound-wing UAV when it lands and its horizontal velocity reaches zero. e The first scenario is the altitude of the compound-wing UAV at this point; the second is the situation where the compound-wing UAV first reaches the landing platform height on a fixed offshore platform and its horizontal speed is not zero. e V represents the landing platform height on a fixed offshore platform. e This is the flight speed at this time;

[0021] D se For a compound-wing UAV to land at an initial speed of V without power, the initial state is as follows: e Height is H e The average resistance under the condition of time, S se The flight distance during the landing process of the compound-wing UAV;

[0022] The formula for calculating the flight speed of a compound-wing UAV when there is crosswind, tailwind, or headwind is as follows:

[0023]

[0024] In equation (2), Vg Ground speed, which is the velocity of the compound-wing UAV relative to the ground, V w For wind speed, θ gw It is the angle between the direction of ground speed and the wind direction, that is, V when there is crosswind, tailwind, or headwind. s and V e This is the result of the vector superposition of ground speed and wind speed.

[0025] In some embodiments of the present invention, step 1 further includes:

[0026] Step 12: Simulation of unpowered descent based on a nonlinear dynamic model;

[0027] In a maritime fixed platform simulation computer, the conditions for conducting unpowered landing simulation of a compound-wing UAV based on its nonlinear dynamic model are as follows:

[0028] Condition 1: The initial state is the state of the compound wing UAV when it is unpowered. The state of the compound wing UAV when it is unpowered includes its flight speed, flight altitude and flight attitude.

[0029] Condition 2 is terminated when the compound-wing UAV first reaches the altitude of the landing platform in the fixed sea platform and the horizontal speed is not zero.

[0030] Condition 3: The flight control law adopts a longitudinal control method for unpowered descent control.

[0031] Condition 4: Taking into account the influence of current sea wind speed, construct a path compensation function based on the relationship between the flight attitude and trajectory of the compound wing UAV, which is caused by the horizontal distance loss after the UAV turns due to the trajectory tilt angle. Then, based on the above-mentioned unpowered landing path as the flight trajectory, perform path tracking flight.

[0032] Based on all the above conditions, a simulation was conducted. Based on the nonlinear dynamic model of the compound wing UAV, the relationship between flight drag and time throughout the process was recorded using equation (3):

[0033]

[0034] In equation (3), D(t) is the flight drag, ρ is the air density at sea, and V r (t) represents the flight speed during the simulation of the compound-wing UAV, S f C is the reference area of ​​the wing of the compound-wing UAV. D (α(t)) is the flight drag coefficient, which is related to the real-time angle of attack α(t) of the UAV.

[0035] In some embodiments of the present invention, step 1 further includes:

[0036] Step 13: Equivalent calculation of average drag based on the relationship between flight drag and time;

[0037] Based on the relationship between D(t) and time t in step 12, the average resistance is calculated using equation (4):

[0038]

[0039] In equation (4), T is the simulation time from the start to the end of the simulation.

[0040] In some embodiments of the present invention, step 1 further includes:

[0041] Step 14: Determine whether a non-powered descent to a fixed offshore platform is feasible;

[0042] Substituting equation (4) into equation (1), we obtain the following formula for calculating the remaining range:

[0043]

[0044] According to equation (5), determine S se The distance S between the unpowered position of the compound-wing UAV and the landing platform position of the fixed sea platform r Size:

[0045]

[0046] Based on the fact that compound-wing UAVs are affected by various factors that cannot be simulated in other simulations during actual flight, the S calculated by simulation is... se With the actual S′ se There is an error ε se Error ε se The estimation was made by comparing the results of multiple simulations with those of real experiments, as follows:

[0047]

[0048] In equation (7), S se (i) represents the distance calculated in the i-th simulation, S′ se (i) represents the distance obtained from the actual experiment corresponding to the i-th simulation calculation, and n is the number of simulations;

[0049] Based on the mean error of equation (7), the criterion in equation (5) is replaced by the true value of the simulated distance estimate, that is:

[0050]

[0051] Depending on the actual situation, if it is determined that the composite wing UAV cannot be landed on the fixed offshore platform using the above methods, the fixed offshore platform needs to develop other emergency landing plans for emergency landing.

[0052] When it is determined that the compound-wing UAV can land on a fixed sea platform using the above method, the compound-wing UAV will perform a powerless landing according to the above method.

[0053] In some embodiments of the present invention, step 2 includes:

[0054] Step 21: Calculate the return route combination set;

[0055] From the position of the compound wing UAV when it is unpowered, plan an arc-shaped path to turn the flight direction of the compound wing UAV to the fixed sea platform, and then plan a straight path to the fixed sea platform.

[0056] Based on the latitude, longitude, and altitude P of the current compound-wing UAV when unpowered S Flight speed and direction (V) s ,θ s and turning radius r s and the latitude and longitude P above the landing platform of the fixed offshore platform M Speed ​​and direction of motion (V) M ,θ M According to equation (9), the composite wing UAV in P is calculated. S The left and right center positions are given by equation (9) as follows:

[0057]

[0058] In equation (9), P S For three-dimensional coordinates of longitude, latitude, and altitude, O rs O ls P respectively S The coordinates of the right center and the left center of the circle at the location;

[0059] Calculate P S The lengths of the trajectories of the left and right arc segments and the straight line segments:

[0060]

[0061]

[0062] In equations (10) and (11), S RC S LC These are the path lengths of the compound-wing UAV flying with a right-turning arc segment plus a straight segment and the path lengths of the UAV flying with a left-turning arc segment plus a straight segment, respectively.

[0063] S L S C Path lengths for straight line segments and circular arc segments respectively;

[0064] The center O of the right-turn arc rs With P M The length of the line connecting the positions and the center O of the left-turn arc ls With P M The horizontal length component of the line connecting the positions;

[0065] The center O of the right-turn arc rs With P M The azimuth angle of the line connecting the positions and the center O of the left-turn arc ls With P M The azimuth of the line connecting the locations;

[0066] γ s The tilt angle of the trajectory for the compound-wing UAV;

[0067] Based on equations (10) and (11), different turning radii r are obtained. s The set of left and right turn paths below;

[0068]

[0069] Equation (12) represents the maximum set of paths S under different turning radii. max (r s ), φ max To limit the maximum roll angle of the compound-wing UAV, V s_z V is the vertical component of the flight velocity when unpowered. s_x The horizontal component of the flight velocity when unpowered. The horizontal distance between the position of the compound-wing UAV when it is unpowered and the position of the landing platform of the fixed sea platform.

[0070] In some embodiments of the present invention, step 2 of the method further includes:

[0071] Step 22: Construct attitude-related path compensation functions;

[0072] Combining equation (12), a path compensation function is constructed for the horizontal distance loss caused by the turning of a compound-wing UAV based on the track tilt angle:

[0073]

[0074] At this time, H in equation (12) e The height of the landing platform for a fixed offshore platform;

[0075] Combining equations (10) to (12), the path compensation function in equation (13) is only related to the turning radius r. s and track inclination angle γ s Related;

[0076] In equation (13), the turning radius r s and track inclination angle γ s The value range is obtained by combining the flight attitude calculation of the compound wing UAV.

[0077] In some embodiments of the present invention, step 2 of the method further includes:

[0078] Step 23: Select the path that minimizes the path compensation function;

[0079] Based on the path compensation function of the two-objective optimization shown in Equation (13), in order to minimize the path compensation function, a genetic algorithm is selected to optimize Equation (13).

[0080] Based on the path compensation function, a genetic algorithm is used to obtain multiple sets of turning radii r that minimize the relative path compensation function. g and track angle γ g Each solution meets the flight requirements;

[0081] Select the track angle γ from multiple solutions. g The smallest group, track angle γ g The lift-to-drag ratio of the compound wing UAV is minimized, and the altitude loss is minimized. The optimal flight path can then be obtained according to equation (12).

[0082] In some embodiments of the present invention, step 3 includes:

[0083] Based on the fact that turning maneuvers without power will reduce flight altitude, roll angle is introduced into the longitudinal control for altitude control compensation, and the deflection of the elevator of the compound wing UAV is controlled to reduce altitude loss during turning.

[0084] In lateral control, vertical speed control compensation is added to longitudinal control;

[0085] The calculation process of the boot instruction is shown in formula (14):

[0086]

[0087] In equation (14), H g This is the altitude guidance command, where H0 is the altitude without power, and K... v D is the high-intensity guiding factor. c φ represents the actual flight distance of the compound-wing UAV, calculated from the point of no power. g For roll angle command, V cFor the real-time flight speed of the compound-wing UAV, r g γ g The turning radius and the desired track inclination angle;

[0088] The control law is shown in formula (15):

[0089]

[0090] In equation (15), δ e δ r δ d These are the elevator deflection angle command, rudder deflection angle command, and aileron deflection angle command for the compound wing UAV, respectively, δ e0 δ r0 δ d0 These are the elevator deflection angle, rudder deflection angle, and aileron deflection angle of the compound-wing UAV when it is unpowered; K eHP , K eHI K eq K eθ K eφ K rφ K rp K rr K dφ K dp The guidance command coefficient for the corresponding control surface is ΔH = HH. g H represents the real-time flight altitude of the compound-wing UAV. g For flight altitude instructions;

[0091] V z The vertical component of the real-time flight speed (airspeed) is the vertical velocity. p, q, r, θ, and φ represent the real-time flight states of the compound wing UAV, such as roll rate, pitch rate, yaw rate, pitch angle, and roll angle.

[0092] Compared with the prior art, the beneficial effects of the path planning and control method for unpowered compound-wing UAV landing at sea provided by the embodiments of the present invention are as follows: in the path planning stage of the unpowered compound-wing UAV in the marine environment, the influence of the flight attitude of the compound-wing UAV on the flight path is comprehensively considered, so as to better plan the path and design the control law of the compound-wing UAV in the unpowered state, so as to maximize the range of the compound-wing UAV and thus increase the probability of the compound-wing UAV reaching the fixed platform at sea. Attached Figure Description

[0093] Figure 1 A flowchart of the unpowered simulation process in the path planning and control method for unpowered compound wing UAV landing at sea provided in an embodiment of the present invention.

[0094] Figure 2 This is a flowchart illustrating the implementation of the path planning and control method for the sea landing of a non-powered compound-wing UAV provided in an embodiment of the present invention. Detailed Implementation

[0095] To enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0096] Various embodiments and features of this application are described herein with reference to the accompanying drawings.

[0097] These and other features of this application will become apparent from the following description of preferred forms of embodiments given as non-limiting examples, with reference to the accompanying drawings.

[0098] It should also be understood that although this application has been described with reference to some specific examples, those skilled in the art can certainly implement many other equivalent forms of this application, which have the features described in the claims and are therefore all within the scope of protection defined herein.

[0099] The above and other aspects, features and advantages of this application will become more apparent when taken in conjunction with the accompanying drawings and in view of the following detailed description.

[0100] Specific embodiments of this application are described below with reference to the accompanying drawings; however, it should be understood that the claimed embodiments are merely examples of this application, which can be implemented in various ways. Well-known and / or repeated functions and structures are not described in detail to ascertain the true intent based on the user's historical operations, and to avoid unnecessary or redundant details that would obscure this application. Therefore, the specific structural and functional details claimed herein are not intended to be limiting, but merely serve as the basis and representative basis for the claims to teach those skilled in the art to use this application in various ways with substantially any suitable detailed structure.

[0101] This specification may use the phrases “in one embodiment,” “in another embodiment,” “in yet another embodiment,” or “in other embodiments,” all of which may refer to one or more of the same or different embodiments according to this application.

[0102] To facilitate understanding of the path planning and control method for sea landing of a non-powered compound-wing UAV provided in the embodiments of this application, further supplementary explanations of the prior art are provided below:

[0103] Under normal circumstances, after the UAV path planning is completed, automatic flight control is used to achieve path tracking. However, in the absence of power, the compound-wing UAV may not be able to complete the planned path based on the shortest flight path. The reasons are as follows:

[0104] In the vertical direction: On the one hand, compound-wing UAVs lose some lift during mid-air turns, leading to increased acceleration and speed during descent, thus reducing loiter time. If the planned path involves excessively long turns or too many turns, the range will be shortened, making it impossible to complete the planned path tracking flight and ultimately preventing landing on a fixed sea platform. On the other hand, there is a strong correlation between the angle of attack and lift coefficient of compound-wing UAVs. When the angle of attack increases to the critical angle of attack (also known as the "stall angle of attack"), the lift coefficient increases (almost linearly) with the angle of attack. Beyond the critical angle of attack, the lift coefficient drops sharply, and the UAV enters a stall state. Based on this characteristic, if only increasing the UAV's loiter time and reducing descent acceleration and speed is considered, the lift needs to be increased, thus increasing the angle of attack. However, increasing the angle of attack also increases horizontal aerodynamic drag, resulting in a shorter horizontal flight range.

[0105] In the horizontal direction: there is a significant correlation between the angle of attack and the aerodynamic drag coefficient of a compound-wing UAV. When the angle of attack is small, the drag coefficient mainly consists of frictional drag and pressure drag, both of which gradually increase with increasing angle of attack, but at a relatively slow rate. As the angle of attack approaches the critical angle of attack, the drag coefficient begins to increase sharply. Once the UAV enters stall, the drag coefficient reaches a peak, and even further increases in the angle of attack will not significantly change the drag coefficient. At this point, the airfoil can no longer effectively generate lift, and aerodynamic performance is greatly reduced. Based on this characteristic, to ensure the UAV's loiter time, the angle of attack should be increased to increase lift. However, a certain degree of increase in the angle of attack will increase drag, resulting in a shorter flight range in the underwater direction.

[0106] Based on the above analysis, maximizing loiter time and range cannot be considered solely from the vertical and horizontal directions, nor can path planning be performed without considering flight attitude. In other words, while maximizing range is the objective, the attitude control of the compound-wing UAV should be considered simultaneously during path planning.

[0107] This invention provides a path planning and control method for the sea landing of a non-powered compound-wing unmanned aerial vehicle (UAV), such as... Figure 1 and Figure 2 As shown, the method includes:

[0108] Step 1: Calculate the theoretical maximum remaining range based on the nonlinear dynamic model, including establishing an energy change law model, simulating unpowered descent based on the nonlinear dynamic model, and then performing an equivalent calculation of average resistance based on the relationship between flight resistance and time, and determining whether an unpowered landing to a fixed sea platform is possible.

[0109] Step 2: Unpowered landing path planning based on compensation function, including: calculating the combination of circular arcs and straight lines from all composite wing UAVs to the fixed sea platform according to the position and velocity direction of the composite wing UAV in the event of sudden unpowered landing; constructing the path compensation function related to the flight attitude of the composite wing UAV; and selecting the path that minimizes the compensation function as the unpowered landing path.

[0110] Step 3: Control the drone to fly autonomously based on the unpowered landing control law.

[0111] To facilitate understanding of the above technical solutions, a detailed explanation is provided below with reference to the accompanying drawings and specific examples:

[0112] exist Figure 1 In this study, unpowered simulation is performed on a simulation computer on a fixed offshore platform. Simulation is used because the computational power of the compound-wing UAV itself is limited, while the fixed offshore platform has strong computational capabilities. Therefore, the optimal path and guidance commands are obtained through simulation on the fixed offshore platform, and then the compound-wing UAV performs path tracking and control. The key lies in the pre-stored nonlinear dynamic model of the compound-wing UAV in the simulation computer. Combined with the actual wind speed and direction environment at sea, an accurate unpowered nonlinear dynamic model of the compound-wing UAV is constructed. This nonlinear dynamic model utilizes the unpowered control law from technical point three of this patent, as well as the optimized path and flight attitude planned from technical point two of this patent. This allows for the simulation of unpowered landing of the compound-wing UAV in the simulation computer. This method effectively utilizes simulation technology in practical applications and solves the problem of the limited computational power of the compound-wing UAV itself.

[0113] exist Figure 2 First, after determining that a powerless landing is feasible according to the method described in Technical Point 1 of this patent, the fixed maritime platform transmits the powerless descent path and desired flight attitude, as described in Technical Point 2 of this patent, to the compound-wing UAV via the communication link between the fixed maritime platform and the UAV. The compound-wing UAV then performs attitude control and path tracking flight according to the descent control law, as described in Technical Point 3 of this patent, which is pre-set in its flight control computer, until it reaches the airspace above the fixed maritime platform. Finally, it lands using either a circling descent or manual control. Finally, by comparing the simulation results from the fixed maritime platform's simulation computer with the actual flight results of the compound-wing UAV, the methods described in the three technical points of this patent are continuously optimized and improved, iteratively updating the guidance command coefficients in the optimal path planning and control method suitable for the corresponding compound-wing UAV.

[0114] The path planning and control method for landing a powerless compound-wing UAV on a fixed sea platform provided in the above embodiments of the present invention requires that the compound-wing UAV meet the following conditions:

[0115] 1) The compound-wing UAV only lost power, while the airframe structure, controller, and communication link between the offshore fixed platform and the UAV remained undamaged;

[0116] 2) The non-powered control law described in the third technical point of this patent should be pre-installed in the flight control computer of the compound wing UAV.

[0117] Offshore fixed platforms should meet the following conditions:

[0118] 1) Fixed offshore platforms should be equipped with simulation computers and corresponding nonlinear dynamic models of compound-wing UAVs, and be able to construct nonlinear dynamic models of real compound-wing UAVs under unpowered conditions based on actual offshore wind direction, wind speed and other environmental factors.

[0119] 2) Based on the nonlinear dynamic model of the compound wing UAV, it has the ability to simulate the technical points one, two, and three described in this patent;

[0120] 3) The communication link between the fixed offshore platform and the compound-wing UAV is normal.

[0121] In this embodiment, the path planning and control method for the unpowered compound-wing UAV to land on a fixed maritime platform includes:

[0122] (1) Based on the calculation theory of maximum remaining range using a nonlinear dynamic model, taking the unpowered state of the compound-wing UAV as the starting state, a simulation of unpowered landing using a nonlinear dynamic model is conducted through a simulation computer on a fixed maritime platform. Considering the current maritime environment, the unpowered descent control law described in point three of this patent and the unpowered landing path described in point two of this patent are adopted. The simulation method can determine whether the compound-wing UAV can perform an unpowered landing. This method effectively utilizes simulation technology and applies it to actual UAV landing; specifically including:

[0123] 1) Establish a model of energy change patterns

[0124] Establish an energy change planning model based on the initial and final states of the compound-wing UAV:

[0125]

[0126] In equation (1), m is the mass of the compound-wing UAV, and V s H represents the airspeed (speed of flight without power). s This refers to the flight altitude without power. The termination state has two scenarios: one is when the compound-wing UAV first reaches zero horizontal speed and its flight altitude is greater than the landing platform altitude on a fixed sea platform; in this case, V... eH represents the flight speed of the compound-wing UAV when it lands and its horizontal velocity is zero (this flight speed is the same as its vertical velocity). e The first scenario is the altitude of the compound-wing UAV at this point; the second is the situation where the compound-wing UAV first reaches the landing platform height on a fixed offshore platform and its horizontal speed is not zero. e V represents the landing platform height on a fixed offshore platform. e This is the flight speed at that moment. (D) se For a compound-wing UAV to land at an initial speed of V without power, the initial state is as follows: e Height is H e The average resistance under the condition of time, S se This refers to the flight distance during the landing process of the compound-wing UAV.

[0127] Considering the high variability of sea winds, this patent only considers the impact of conventional sea winds such as crosswinds, tailwinds, or headwinds on the compound-wing UAV. The formula for calculating the flight speed (airspeed) of the compound-wing UAV when crosswinds, tailwinds, or headwinds are present is as follows:

[0128]

[0129] In equation (2), V g Ground speed (the speed of the compound-wing UAV relative to the ground), V w For wind speed, θ gw It is the angle between the direction of ground speed and the wind direction. That is, V when there is crosswind, tailwind, or headwind. s and V e This is the result of the vector superposition of ground speed and wind speed.

[0130] 2) Simulation of unpowered descent based on nonlinear dynamic model

[0131] In a simulation computer for a fixed offshore platform, a simulation of unpowered landing of a compound-wing UAV is conducted based on a nonlinear dynamic model of the compound-wing UAV, with the following four conditions:

[0132] ①The initial state is the state of the compound wing UAV when it is unpowered (mainly including flight speed, flight altitude and flight attitude);

[0133] ②The termination condition is the case where the compound-wing UAV first reaches the horizontal speed of zero and the flight altitude is greater than the landing platform height in the fixed sea platform, or the compound-wing UAV first reaches the landing platform height in the fixed sea platform and the horizontal speed is not zero.

[0134] ③ The flight control law adopts the unpowered descent control law described in point three of this patent's technical specifications;

[0135] ④ Taking into account the current wind speed at sea, the path tracking flight is carried out using the unpowered landing path described in the second technical point of this patent as the flight trajectory.

[0136] Based on all the above conditions, a simulation is performed. The simulation process is as follows: Figure 1 As shown. Based on the nonlinear dynamic model of the compound-wing UAV, the relationship between flight drag and time throughout the process is recorded by equation (3):

[0137]

[0138] In equation (3), D(t) is the flight drag, ρ is the air density at sea, and V r (t) represents the flight speed (airspeed) during the simulation of the compound-wing UAV, which is calculated as a vector speed based on actual wind speed. f C is the reference area of ​​the wing of the compound-wing UAV. D (α(t)) is the flight drag coefficient, which is related to the real-time angle of attack α(t) of the UAV.

[0139] 3) Equivalent calculation of average drag based on the relationship between flight drag and time

[0140] Based on the relationship between D(t) and time t in step 2), the average resistance is calculated using equation (4):

[0141]

[0142] In equation (4), T is the simulation time from the start to the end of the simulation.

[0143] 4) Determine whether a non-powered descent to a fixed offshore platform is feasible.

[0144] Substituting equation (4) into equation (1), we obtain the following formula for calculating the remaining range:

[0145]

[0146] The meanings of the parameters in equation (5) are consistent with those in equations (1) to (4).

[0147] According to equation (5), determine S se The distance S between the unpowered position (latitude, longitude, and altitude) of the compound-wing UAV and the landing platform position (latitude, longitude, and altitude) of the fixed marine platform. r Size:

[0148]

[0149] Considering that the actual flight of the compound-wing UAV is affected by various factors that cannot be simulated in other simulations, the S calculated by simulation is... se With the actual S′ seThere is a certain error ε between them se Error ε se Estimation can be made by comparing the results of multiple simulations with those of real experiments:

[0150]

[0151] In equation (7), S se (i) represents the distance calculated in the i-th simulation, S′ se (i) represents the distance obtained from the actual experiment corresponding to the i-th simulation calculation, and n represents the number of simulations.

[0152] Based on the mean error of equation (7), the criterion in equation (5) is replaced by the true value of the simulated distance estimate, that is:

[0153]

[0154] Depending on the actual situation, when the compound-wing UAV cannot perform a powerless landing, i.e., when the method described in this patent determines that it cannot land on a fixed maritime platform, the fixed maritime platform needs to develop other emergency landing plans for an emergency landing, which will not be described in detail in this patent. When the method described in this patent determines that a powerless landing is possible, the compound-wing UAV performs a powerless landing according to technical points two and three of this patent.

[0155] (2) Unpowered landing path planning based on compensation function

[0156] Based on the position and velocity direction of the compound-wing UAV in the event of sudden powerlessness, the combined circular and straight-line paths from all compound-wing UAVs to the fixed offshore platform are calculated. A path compensation function related to the flight attitude of the compound-wing UAV is constructed, and the path that minimizes the compensation function is selected as the powerless landing path. Specifically, by exploring the relationship between the flight attitude (track tilt angle) and the track of the compound-wing UAV, a path compensation function is constructed based on the track tilt angle to account for the horizontal distance loss caused by the UAV turning. The correlation between the path compensation function and the turning radius and track tilt angle can be obtained. This method introduces the track tilt angle into the planning stage of the powerless landing path of the compound-wing UAV, considering the influence of the UAV attitude on the path planning, resulting in a better path for the powerless landing of the compound-wing UAV. The significance of this path is that it takes into account the maximum path under the constraints of the flight attitude of the compound-wing UAV and the minimum altitude loss caused by turning.

[0157] The detailed steps are as follows:

[0158] 1) Calculate the return route combination set

[0159] From the position of the compound-wing UAV when it is unpowered, plan an arc-shaped path to turn the UAV's flight direction to the fixed offshore platform, and then plan a straight path to the fixed offshore platform.

[0160] First, based on the latitude, longitude, and altitude P of the current compound-wing UAV when it is unpowered... S Flight speed and direction (V) s ,θ s and turning radius r s and the latitude and longitude P above the landing platform of the fixed offshore platform M Speed ​​and direction of motion (V) M ,θ M According to equation (9), the composite wing UAV in P is calculated. S The left and right center positions:

[0161]

[0162] In equation (9), P S For three-dimensional coordinates (longitude, latitude, altitude), O rs O ls P respectively S The coordinates of the right center and the left center of the circle at the location.

[0163] Calculate P S The lengths of the trajectories of the left and right arc segments and the straight line segments:

[0164]

[0165]

[0166] In equations (10) and (11), S RC S LC These represent the path lengths of the compound-wing UAV flying with a right-turn circular arc segment plus a straight line segment, and the path lengths of the UAV flying with a left-turn circular arc segment plus a straight line segment, respectively. L S C Calculate the path lengths of the straight line segment and the circular arc segment, respectively. The center O of the right-turn arc rs With P M The length of the line connecting the positions and the center O of the left-turn arc ls With P M The horizontal length component of the line connecting the positions. The center O of the right-turn arc rs With P M The azimuth angle of the line connecting the positions and the center O of the left-turn arc ls With P M The azimuth angle of the line connecting the positions. γ s The tilt angle of the trajectory of the compound-wing UAV.

[0167] Based on equations (10) and (11), different turning radii r can be obtained. s The set of left and right turn paths below.

[0168]

[0169] Equation (12) represents the maximum set of paths S under different turning radii. max (r s ), φ max The maximum roll angle limit for compound-wing UAVs (determined by the performance of each UAV), V s_z V is the vertical component of the unpowered flight speed (airspeed). s_x This represents the horizontal component of the unpowered flight speed (airspeed). The horizontal distance between the position of the unpowered compound-wing UAV and the landing platform of the fixed sea platform is given. All other parameters are consistent with those in equations (1) to (11).

[0170] 2) Construct attitude-related path compensation functions

[0171] Combining equation (12), a path compensation function is constructed for the horizontal distance loss caused by the turning of a compound-wing UAV based on the track tilt angle:

[0172]

[0173] The parameters in equation (13) are the same as those in equations (1) to (12) (Note: H in equation (12) is the same in this case). e (Height of the landing platform of the fixed offshore platform). Combining equations (10) to (12), the path compensation function in equation (13) is only related to the turning radius r. s and track inclination angle γ s Related. In equation (13), the turning radius r s and track inclination angle γ s The range of values ​​is obtained by combining the flight attitude calculation of the compound wing UAV.

[0174] 3) Select the path that minimizes the path compensation function.

[0175] Based on the path compensation function of the two objectives shown in Equation (13), in order to minimize the path compensation function, a genetic algorithm (other multi-objective optimization algorithm) is selected to solve the optimization problem shown in Equation (13). Since this patent does not improve the genetic algorithm (other multi-objective optimization algorithm), this patent will not repeat the principle of the genetic algorithm (other multi-objective optimization algorithm). It is sufficient to solve the multi-objective problem of Equation (13).

[0176] Based on the path compensation function, multiple sets of turning radii r that minimize the relative path compensation function can be obtained through genetic algorithms (or other multi-objective optimization algorithms). g and track angle γ g (In multi-objective optimization problems, it is generally impossible to obtain an optimal solution), and each set of solutions meets the flight requirements. This patent suggests selecting the track angle γ from multiple sets of solutions. g The smallest group is due to the track angle γ. g The lift-to-drag ratio of the compound wing UAV is minimized, and the altitude loss is minimized. The optimal flight path can then be obtained according to equation (12).

[0177] (3) Autonomous flight control of UAV based on unpowered landing control law. Since there is no thrust, only one of the longitudinal control and flight speed control of compound wing UAV can be selected. This patent adopts the longitudinal control method and provides an unpowered altitude control law for control. Combined with the trajectory tilt angle control of compound wing UAV, the maximum range of compound wing UAV is better guaranteed.

[0178] Since thrust is zero in the absence of power, the control law for a compound-wing UAV in normal flight cannot meet the requirements for its return-to-home maneuver in this condition. Considering the reduction in altitude during turns in the absence of power, roll angle is introduced into the longitudinal control for altitude compensation, i.e., controlling the deflection of the UAV's elevator to reduce altitude loss during turns. In lateral control, roll angle commands are the primary focus. Since there is no thrust, speed control cannot be achieved through thrust alone. To minimize horizontal speed loss, vertical speed compensation is added to the longitudinal control.

[0179] The calculation process of the boot instruction is shown in formula (14):

[0180]

[0181] In equation (14), H g This is the altitude guidance command, where H0 is the altitude without power, and K... v D is the high-intensity guiding factor. c φ represents the actual flight distance of the compound-wing UAV, calculated from the point of no power. g For roll angle command, V c For the real-time flight speed (airspeed) of the compound-wing UAV, r g γ g The turning radius and the desired trajectory inclination angle are as required in the second technical point of this patent.

[0182] The control law is shown in formula (15):

[0183]

[0184] In equation (15), δ e δ r δ d These are the elevator deflection angle command, rudder deflection angle command, and aileron deflection angle command for the compound wing UAV, respectively, δ e0 δ r0 δ d0 These represent the elevator deflection angle, rudder deflection angle, and aileron deflection angle of the compound-wing UAV when it is unpowered. K eHP , K eHI K eq K eθ K eφ K rφ K rp K rr K dφ K dp The guidance command coefficient for the corresponding control surface is ΔH = HH. g H represents the real-time flight altitude of the compound-wing UAV. g This refers to the flight altitude command in the second key technical point of this patent. V z The vertical component of the real-time flight speed (airspeed) is the vertical velocity. p, q, r, θ, and φ represent the real-time flight states of the compound wing UAV, such as roll rate, pitch rate, yaw rate, pitch angle, and roll angle.

[0185] As can be seen from the above technical solutions, the path planning and control method for unpowered compound-wing UAV landing at sea provided by the above embodiments of the present invention comprehensively considers the influence of the flight attitude of the compound-wing UAV on the flight path in the path planning stage of the unpowered compound-wing UAV in the marine environment, so as to better plan the path and design the control law of the compound-wing UAV in the unpowered state, so as to maximize the range of the compound-wing UAV and thus increase the probability of the compound-wing UAV reaching the fixed platform at sea.

[0186] The above embodiments are merely exemplary embodiments of the present invention and are not intended to limit the present invention. The scope of protection of the present invention is defined by the claims. Those skilled in the art can make various modifications or equivalent substitutions to the present invention within its spirit and scope of protection, and such modifications or equivalent substitutions should also be considered to fall within the scope of protection of the present invention.

Claims

1. A path planning and control method for the sea landing of a non-powered compound-wing unmanned aerial vehicle (UAV), characterized in that, include: Step 1: Calculate the theoretical maximum remaining range based on the nonlinear dynamic model, including establishing an energy change law model, simulating unpowered descent based on the nonlinear dynamic model, and then performing an equivalent calculation of average resistance based on the relationship between flight resistance and time, and determining whether an unpowered landing to a fixed sea platform is possible. Step 2: Unpowered landing path planning based on compensation function, including: calculating the combination of circular arcs and straight lines from all composite wing UAVs to the fixed sea platform according to the position and velocity direction of the composite wing UAV in the event of sudden unpowered landing; constructing the path compensation function related to the flight attitude of the composite wing UAV; and selecting the path that minimizes the compensation function as the unpowered landing path. Step 3: Control the drone to fly autonomously based on the unpowered landing control law.

2. The path planning and control method for sea landing of a non-powered compound-wing UAV according to claim 1, characterized in that, In step 1, the method includes: Step 11: Establish a model of energy change patterns; Establish an energy change planning model based on the initial and final states of the compound-wing UAV: In equation (1), m is the mass of the compound-wing UAV, and V s H is the flight speed without power. s This refers to the flight altitude without power. The termination state can be divided into two cases. One is when the compound-wing UAV first reaches zero horizontal speed and its flight altitude is greater than the landing platform altitude on the fixed sea platform. In this case, V... e H represents the vertical velocity of the compound-wing UAV when it lands and its horizontal velocity reaches zero. e The first scenario is the altitude of the compound-wing UAV at this point; the second is the situation where the compound-wing UAV first reaches the landing platform height on a fixed offshore platform and its horizontal speed is not zero. e V represents the landing platform height on a fixed offshore platform. e This is the flight speed at this time; D se For a compound-wing UAV to land at an initial speed of V without power, the initial state is as follows: e Height is H e The average resistance under the condition of time, S se The flight distance during the landing process of the compound-wing UAV; The formula for calculating the flight speed of a compound-wing UAV when there is crosswind, tailwind, or headwind is as follows: In equation (2), V g Ground speed, which is the velocity of the compound-wing UAV relative to the ground, V w For wind speed, θ gw It is the angle between the direction of ground speed and the wind direction, that is, V when there is crosswind, tailwind, or headwind. s and V e This is the result of the vector superposition of ground speed and wind speed.

3. The path planning and control method for sea landing of a non-powered compound-wing UAV according to claim 2, characterized in that, In step 1, the method further includes: Step 12: Simulation of unpowered descent based on a nonlinear dynamic model; In a maritime fixed platform simulation computer, the conditions for conducting unpowered landing simulation of a compound-wing UAV based on its nonlinear dynamic model are as follows: Condition 1: The initial state is the state of the compound wing UAV when it is unpowered. The state of the compound wing UAV when it is unpowered includes its flight speed, flight altitude and flight attitude. Condition 2 is terminated when the compound-wing UAV first reaches the altitude of the landing platform in the fixed sea platform and the horizontal speed is not zero. Condition 3: The flight control law adopts a longitudinal control method for unpowered descent control. Condition 4: Taking into account the influence of current sea wind speed, construct a path compensation function based on the relationship between the flight attitude and trajectory of the compound wing UAV, which is caused by the horizontal distance loss after the UAV turns due to the trajectory tilt angle. Then, based on the above-mentioned unpowered landing path as the flight trajectory, perform path tracking flight. Based on all the above conditions, a simulation was conducted. Based on the nonlinear dynamic model of the compound wing UAV, the relationship between flight drag and time throughout the process was recorded using equation (3): In equation (3), D(t) is the flight drag, ρ is the air density at sea, and V r (t) represents the flight speed during the simulation of the compound-wing UAV, S f C is the reference area of ​​the wing of the compound-wing UAV. D (α(t)) is the flight drag coefficient, which is related to the real-time angle of attack α(t) of the UAV.

4. The path planning and control method for sea landing of a non-powered compound-wing UAV according to claim 3, characterized in that, In step 1, the method further includes: Step 13: Equivalent calculation of average drag based on the relationship between flight drag and time; Based on the relationship between D(t) and time t in step 12, the average resistance is calculated using equation (4): In equation (4), T is the simulation time from the start to the end of the simulation.

5. The path planning and control method for sea landing of a non-powered compound-wing UAV according to claim 4, characterized in that, In step 1, the method further includes: Step 14: Determine whether a non-powered descent to a fixed offshore platform is feasible; Substituting equation (4) into equation (1), we obtain the following formula for calculating the remaining range: According to equation (5), determine S se The distance S between the unpowered position of the compound-wing UAV and the landing platform position of the fixed sea platform r Size: Based on the fact that compound-wing UAVs are affected by various factors that cannot be simulated in other simulations during actual flight, the S calculated by simulation is... se With the actual S′ se There is an error ε se Error ε se The estimation was made by comparing the results of multiple simulations with those of real experiments, as follows: In equation (7), S se (i) represents the distance calculated in the i-th simulation, S s ' e (i) represents the distance obtained from the actual experiment corresponding to the i-th simulation calculation, and n is the number of simulations; Based on the mean error of equation (7), the criterion in equation (5) is replaced by the true value of the simulated distance estimate, that is: Depending on the actual situation, if it is determined that the composite wing UAV cannot be landed on the fixed offshore platform using the above methods, the fixed offshore platform needs to develop other emergency landing plans for emergency landing. When it is determined that the compound-wing UAV can land on a fixed sea platform using the above method, the compound-wing UAV will perform a powerless landing according to the above method.

6. The path planning and control method for sea landing of a non-powered compound-wing UAV according to claim 5, characterized in that, In step 2, the method includes: Step 21: Calculate the return route combination set; From the position of the compound wing UAV when it is unpowered, plan an arc-shaped path to turn the flight direction of the compound wing UAV to the fixed sea platform, and then plan a straight path to the fixed sea platform. Based on the latitude, longitude, and altitude P of the current compound-wing UAV when unpowered S Flight speed and direction (V) s ,θ s and turning radius r s and the latitude and longitude P above the landing platform of the fixed offshore platform M Speed ​​and direction of motion (V) M ,θ M According to equation (9), the composite wing UAV in P is calculated. S The left and right center positions of the circle are given by equation (9) as follows: In equation (9), P S For three-dimensional coordinates of longitude, latitude, and altitude, O rs O ls P respectively S The coordinates of the right center and the left center of the circle at the location; Calculate P S The lengths of the trajectories of the left and right arc segments and the straight line segments: In equations (10) and (11), S RC S LC These are the path lengths of the compound-wing UAV flying with a right-turning arc segment plus a straight segment and the path lengths of the UAV flying with a left-turning arc segment plus a straight segment, respectively. S L S C Path lengths for straight line segments and circular arc segments respectively; The center O of the right-turn arc rs With P M The length of the line connecting the positions and the center O of the left-turn arc ls With P M The horizontal length component of the line connecting the positions; The center O of the right-turn arc rs With P M The azimuth angle of the line connecting the positions and the center O of the left-turn arc ls With P M The azimuth of the line connecting the locations; γ s The tilt angle of the trajectory for the compound-wing UAV; Based on equations (10) and (11), different turning radii r are obtained. s The set of left and right turn paths below; Equation (12) represents the maximum path set S under different turning radii. max (r s ), φ max To limit the maximum roll angle of the compound-wing UAV, V s_z V is the vertical component of the flight velocity when unpowered. s_x The horizontal component of the flight velocity when unpowered. The horizontal distance between the position of the compound-wing UAV when it is unpowered and the position of the landing platform of the fixed sea platform.

7. The path planning and control method for sea landing of a non-powered compound-wing UAV according to claim 6, characterized in that, In step 2, the method further includes: Step 22: Construct attitude-related path compensation functions; Combining equation (12), a path compensation function is constructed for the horizontal distance loss caused by the turning of a compound-wing UAV based on the track tilt angle: At this time, H in equation (12) e The height of the landing platform for a fixed offshore platform; Combining equations (10) to (12), the path compensation function in equation (13) is only related to the turning radius r. s and track inclination angle γ s Related; In equation (13), the turning radius r s and track inclination angle γ s The value range is obtained by combining the flight attitude calculation of the compound wing UAV.

8. The path planning and control method for sea landing of a non-powered compound-wing UAV according to claim 7, characterized in that, In step 2, the method further includes: Step 23: Select the path that minimizes the path compensation function; Based on the path compensation function of the two-objective optimization shown in Equation (13), in order to minimize the path compensation function, a genetic algorithm is selected to optimize Equation (13). Based on the path compensation function, a genetic algorithm is used to obtain multiple sets of turning radii r that minimize the relative path compensation function. g and track angle γ g Each solution meets the flight requirements; Select the track angle γ from multiple solutions. g The smallest group, track angle γ g The lift-to-drag ratio of the compound wing UAV is minimized, and the altitude loss is minimized. The optimal flight path can then be obtained according to equation (12).

9. The path planning and control method for sea landing of a non-powered compound-wing UAV according to claim 8, characterized in that, In step 3, the method includes: Based on the fact that turning maneuvers without power will reduce flight altitude, roll angle is introduced into the longitudinal control for altitude control compensation, and the deflection of the elevator of the compound wing UAV is controlled to reduce altitude loss during turning. In lateral control, vertical speed control compensation is added to longitudinal control; The calculation process of the boot instruction is shown in formula (14): In equation (14), H g This is the altitude guidance command, where H0 is the altitude without power, and K... v D is the high-intensity guiding factor. c φ represents the actual flight distance of the compound-wing UAV, calculated from the point of no power. g For roll angle command, V c For the real-time flight speed of the compound-wing UAV, r g γ g The turning radius and the desired track inclination angle; The control law is shown in formula (15): In equation (15), δ e δ r δ d These are the elevator deflection angle command, rudder deflection angle command, and aileron deflection angle command for the compound wing UAV, respectively, δ e0 δ r0 δ d0 These are the elevator deflection angle, rudder deflection angle, and aileron deflection angle of the compound-wing UAV when it is unpowered; K eHP , K eHI K eq K eθ K eφ K rφ K rp K rr K dφ K dp The guidance command coefficient for the corresponding control surface is ΔH = HH. g H represents the real-time flight altitude of the compound-wing UAV. g For flight altitude instructions; V z The vertical component of the real-time flight speed (airspeed) is the vertical velocity. p, q, r, θ, and φ represent the real-time flight states of the compound wing UAV, such as roll rate, pitch rate, yaw rate, pitch angle, and roll angle.

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