Multi-unmanned aerial vehicle flight collision avoidance method for improving hybrid reciprocal speed obstacle

Abstract

The invention provides a multi-unmanned aerial vehicle flight collision avoidance method for improving hybrid reciprocal speed obstacles, and relates to the technical field of unmanned aerial vehicle flight safety. The method comprises the following steps: the unmanned aerial vehicle continuously receives and processes ADS-B data to obtain the latest ground position of the unmanned aerial vehicle; establishing a flight protection area of the unmanned aerial vehicle, and establishing a collision cone model for flight conflict detection; determining an HRVO area and the flight speed of the unmanned aerial vehicle by adopting a hybrid reciprocal speed obstacle method, and realizing flight conflict collision avoidance of multiple unmanned aerial vehicles; collision cone areas are classified according to the relative speed of the two unmanned aerial vehicles; and finally, different HRVO regions are obtained according to different collision cone regions, an improved and optimized hybrid reciprocal speed obstacle region OHRVO is obtained, and the unmanned aerial vehicle A selects a speed vector closest to the optimal speed outside the OHRVO region as a new flight speed. According to the method, whether flight conflicts exist or not and whether emergency collision avoidance measures need to be taken or not are judged by considering the flight speed, direction and size of the unmanned aerial vehicle.

Description

Technical Field

[0001] The invention relates to the technical field of unmanned aerial vehicle flight safety, and in particular to a multi-unmanned aerial vehicle flight collision avoidance method with improved mixed reciprocal speed barriers. Background Art

[0002] As low-altitude urban airspace continues to open up, drones have been widely used. Drones are used in many applications such as the transportation industry and emergency rescue. It is predicted that this will lead to traffic densities that are several orders of magnitude higher than those currently observed in manned aviation. The more drones there are, the less airspace resources are available. The rapid growth in their number will also lead to a gradual increase in the incidence of collision accidents during drone flights in urban areas. If a drone crashes due to a collision or loss of stability, it will pose a serious threat to the lives and property of people on the ground. In order to ensure the smooth and safe flight of drones, it is very important to take necessary flight conflict detection and collision avoidance measures.

[0003] Recently, the applications of Unmanned Aircraft Systems (UAS) have been intensively explored, especially for the inspection and monitoring of several urban infrastructures. In these applications, autonomous and safe flight of UAS is crucial, as the UAS must be able to perform autonomous flight conflict detection and collision avoidance without human intervention. In order to achieve this autonomy, a strategy must be defined to prevent the UAS from colliding with various obstacles, including static obstacles (such as trees, buildings, etc.) and mobile obstacles (especially hot air balloons, birds, etc.). In a constantly changing environment, it is a challenging task to extend the collision avoidance method from static obstacles to mobile obstacles. Especially when there are a large number of UAS in the same limited urban airspace, avoiding mobile obstacles may lead to collision avoidance instability. This instability manifests itself as fluctuations or oscillations in the flight direction, which is called "jitter". This jitter greatly affects the flight stability of the UAS, so it is particularly important to optimize a smoother flight avoidance path.

[0004] Therefore, in response to these challenges, it is necessary to develop an efficient flight conflict avoidance method to ensure that drones can fly safely and stably in complex urban environments. This method needs to take into account the various obstacles that may exist in urban airspace, and be able to identify and avoid these obstacles in a timely and accurate manner, thereby ensuring the flight safety and efficiency of drones. At present, the conflict avoidance methods for drone flights include but are not limited to the A* method, artificial potential field method, speed obstacle method and geometric optimization method. These methods can all achieve flight conflict detection and collision avoidance, and have contributed to achieving airspace flight safety. However, due to the common problems of complex mathematical models, low collision avoidance efficiency, and easy generation of severe flight jitters in previous conflict detection and collision avoidance methods, more and more scientific researchers have optimized previous methods. Summary of the invention

[0005] The technical problem to be solved by the present invention is to provide a multi-UAV flight collision avoidance method with improved hybrid reciprocal speed barriers to achieve low-altitude UAV flight collision avoidance. The method is applied to two-dimensional vector space and can be further extended to three-dimensional vector space.

[0006] In order to solve the above technical problems, the technical solution adopted by the present invention is:

[0007] A multi-UAV flight collision avoidance method with improved hybrid reciprocal speed obstacles comprises the following steps:

[0008] Step 1: The drone continuously receives and processes ADS-B data and performs real-time coordinate conversion to obtain the latest ground position of the drone; decodes the ADS-B raw data received by each drone to obtain the real-time position information of the drone, and then obtains the flight information of the drone; and converts the decoded ADS-B data into ground coordinates to obtain the relative position of the drone to the ground;

[0009] Step 1.1: Obtain ADS-B data;

[0010] Get the drone position data broadcast by ADS-B;

[0011] Step 1.2: Decode ADS-B data;

[0012] The acquired binary ADS-B data needs to be decoded and converted into a readable text format. The decoded data contains the latitude, longitude, altitude and speed information of the drone.

[0013] Step 1.3: Convert the decoded ADS-B data to the WGS-84 ellipsoid coordinates of the ADS-B position of the drone and the reference position to the Earth-centered Earth-fixed coordinates (X, Y, Z), and then calculate the coordinates of the drone relative to the ground fixed reference point (x, y, z);

[0014] Step 2: Establish the flight protection zone of the drone according to the flight speed of the drone and the layout of the airspace buildings, and establish a collision cone model for flight conflict detection;

[0015] The two-dimensional coordinates of the drone relative to the ground fixed reference point are set to (x, y), and R is a two-dimensional real vector space, so as to determine the drone circular protection zone set V as shown in the following formula:

[0016]

[0017] Among them, d h Indicates the radius of the circular flight protection zone of the drone;

[0018] Assume that drones A and B are in the limited low-altitude airspace of the same city; define the flight speeds of drone A and drone B as u respectively. 1 and u 2 , take drone A as the origin, the line AB between drone A and drone B as the x-axis, draw a straight line perpendicular to AB as the y-axis, and establish a two-dimensional coordinate system. The flight speed v of the two drones 1 and v 2 As shown in the following formula:

[0019] v i =(u i cosε i ,u i sinε i ),i∈1,2 (2)

[0020] Among them, ε i represents the positive angle between the flight direction of the drone and the x-axis; and the corresponding protection zone radii of drone A and drone B are and

[0021] Assume that the displacement of UAV A or UAV B during the kth time period △t is Then the displacement of the UAV during the k+1th time period △t is as follows:

[0022]

[0023] A maximum velocity constraint v is defined max and the maximum acceleration constraint v max, which is used to limit the available speed and acceleration of the drone, as shown in the following formula:

[0024] ||v i ||≤v max ,i∈1,2 (4)

[0025] ||a i ||≤a max ,i∈1,2 (5)

[0026] Among them, ||·|| represents the modulus of the vector, a i is the acceleration of the drone, a max is the maximum acceleration of the drone;

[0027] In the two-dimensional plane, the flight speed of drone A is v 1 , the flight speed of drone B is v 2 , α is the angle between the line AB between the two UAVs and the boundary of the speed obstacle zone, that is, half of the collision cone vertex angle, γ is the angle between the line AB between the two UAVs and the relative speed v R The angle between them; define the relative collision cone RCC model, that is, the relative speed v at which the drone may collide R =v 1 -v 2 The speed set is shown in the following formula:

[0028]

[0029] in, is the relative speed v R The straight line where ⊙B is located; ⊙B is the flight safety protection zone of UAV B, and the collision cone boundary is tangent to ⊙B;

[0030] The collision cone model only considers the positional relationship and current state between drones. With drone B as the reference point, drone A moves relative to drone B. If the speed of drone A relative to drone B is within the collision cone, a flight conflict will occur between the two drones, otherwise there will be no flight conflict. Based on the collision cone model, the following geometric judgment method is used for the flight conflict detection between two drones: when α>γ, there is a flight conflict between the two drones, otherwise there is no flight conflict. The expressions of α and γ are given by the following formula:

[0031]

[0032] γ=∠(v R ,AB) (8)

[0033] Step 3: Use the hybrid reciprocal speed barrier method to determine the HRVO area and the flight speed of the UAV to achieve flight conflict avoidance of multiple UAVs;

[0034] The obstacle area is divided into a mixture of speed obstacle area and reciprocal speed obstacle area, which is called HRVO. The expression of the generated HRVO area is:

[0035]

[0036] Among them, v * represents the velocity vector from the RCC region vertex to the HRVO region vertex, Represents Minkowski and;

[0037] Set an optimal speed for drone A As shown in the following formula:

[0038]

[0039] in, Indicates the optimal flight speed of UAV A, P 1 Indicates the current position of drone A, represents the final position of UAV A, ||·|| 2 Represents the 2-norm of a vector;

[0040] Drone A selects a speed vector closest to the optimal speed outside the HRVO area as the new flight speed As shown in the following formula:

[0041]

[0042] Among them, v is the flight speed of UAV A at the next moment;

[0043] Step 4: Classify the collision cone area according to the relative speed of the two drones;

[0044] According to the relative speed of the two UAVs, the collision cone area is divided into three different areas and the boundary between every two areas, a total of five parts;

[0045] The relative velocities corresponding to the three regions and the two boundaries satisfy the following sets:

[0046]

[0047] Wherein, distance(P) is the distance function, which represents the distance from point P to the origin of the coordinate system in the two-dimensional Cartesian coordinate system. 1 and P 2 Indicates the current position of drone A and drone B, are the relative speeds corresponding to the three regions and two boundaries, and τ is the buffer time for UAV conflict avoidance;

[0048] When the relative speed v between drone A and drone B R When set (12) is satisfied, multiply the flight protection zone radius by the proportional coefficient. R When the set (13) is satisfied, the radius of the extended protection zone is smaller than d h Reduce a certain proportion; when v R When set (14) is satisfied, the radius of the extended protection zone is the same as the radius of the HRVO zone;

[0049] Step 5: Different HRVO areas are obtained according to different collision cone areas, and the HRVO area is optimized to obtain the improved and optimized hybrid reciprocal speed obstacle area OHRVO. UAV A selects a speed vector closest to the optimal speed outside the OHRVO area as the new flight speed, as shown in the following formula:

[0050]

[0051] In the simulation process, the most dangerous situation is given priority, that is, first determine whether the relative speed satisfies equation (14). If it satisfies equation (14), the corresponding OHRVO area is generated. Then consider whether it satisfies equation (16), and so on. Finally, consider whether it satisfies equation (12). The order of consideration is (14)-(16)-(13)-(15)-(12).

[0052] The beneficial effect of adopting the above technical solution is that: the present invention provides an improved hybrid reciprocal speed barrier multi-UAV flight collision avoidance method, which determines whether there is a flight conflict by considering the direction and size of the UAV flight speed, and whether emergency collision avoidance measures are needed if there is a flight conflict, thereby ensuring that the UAVs fly more safely and smoothly. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] Figure 1 A flowchart of realizing UAV collision avoidance using the optimized hybrid reciprocal speed obstacle method provided in an embodiment of the present invention;

[0054] Figure 2 A schematic diagram of an Earth-centered Earth-fixed coordinate system provided by an embodiment of the present invention;

[0055] Figure 3 A flight status diagram of two UAVs provided in an embodiment of the present invention;

[0056] Figure 4 A schematic diagram of a collision cone model provided by an embodiment of the present invention;

[0057] Figure 5 A schematic diagram of a hybrid reciprocal speed barrier area model provided in an embodiment of the present invention;

[0058] Figure 6A schematic diagram of RCC area division provided in an embodiment of the present invention;

[0059] Figure 7 Schematic diagram of the optimized hybrid reciprocal speed barrier area model provided in an embodiment of the present invention, wherein (a) is the OHRVO area corresponding to the proportional coefficient m, (b) is the OHRVO area corresponding to the proportional coefficient M, and (c) is the OHRVO area corresponding to the proportional coefficient k. DETAILED DESCRIPTION

[0060] The specific implementation of the present invention is further described in detail below in conjunction with the accompanying drawings and examples. The following examples are used to illustrate the present invention, but are not intended to limit the scope of the present invention.

[0061] In this embodiment, a multi-UAV flight collision avoidance method with improved hybrid reciprocal speed barriers is provided. Figure 1 As shown, the following steps are included:

[0062] Step 1: The drone continuously receives and processes ADS-B (Automatic Dependent Surveillance-Broadcast) data and performs real-time coordinate conversion to obtain the latest ground position of the drone; decodes the ADS-B raw data received by each drone to obtain the real-time position information of the drone, and then obtains the flight information of the drone; and converts the decoded ADS-B data into ground coordinates to obtain the relative position of the drone to the ground;

[0063] Step 1.1: Obtain ADS-B data;

[0064] Get the drone position data broadcast by ADS-B;

[0065] Step 1.2: Decode ADS-B data;

[0066] The acquired binary ADS-B data needs to be decoded and converted into a readable text format. The decoded data contains the latitude, longitude, altitude and speed information of the drone.

[0067] Step 1.3: Convert the decoded ADS-B data to the WGS-84 ellipsoid coordinates of the ADS-B position of the drone and the reference position into Earth-centered Earth-fixed coordinates (X, Y, Z), as follows: Figure 2 As shown, the coordinates (x, y, z) of the drone relative to the fixed reference point on the ground are calculated; in this embodiment, the application scope of the drone collision avoidance method is limited to a two-dimensional plane, so it is sufficient to obtain the two-dimensional coordinates (x, y);

[0068] Step 2: Establish the flight protection zone of the drone according to the flight speed of the drone and the layout of the airspace buildings, and establish a collision cone model for flight conflict detection;

[0069] The two-dimensional coordinates of the drone relative to the ground fixed reference point are set to (x, y), and R is a two-dimensional real vector space, so as to determine the drone circular protection zone set V as shown in the following formula:

[0070]

[0071] Among them, d h It indicates the radius of the circular flight protection zone of the drone. In actual flight, the distance between drones must not be less than the protection zone radius, otherwise a collision is likely to occur. That is, the protection zone radius is the minimum safe collision avoidance distance.

[0072] Because it is necessary to judge whether multiple drones have a flight conflict separately, it is sufficient to judge whether there is a flight conflict between any two drones. Assume that drones A and B are in the same city's limited low-altitude airspace; define the flight speeds of drone A and drone B as u respectively. 1 and u 2 , take drone A as the origin, the line AB between drone A and drone B as the x-axis, draw a straight line perpendicular to AB as the y-axis, and establish a two-dimensional coordinate system. The flight speed v of the two drones 1 and v 2 As shown in the following formula, the flight status is Figure 3 As shown:

[0073] v i =(u i cosε i ,u i sinε i ),i∈1,2 (2)

[0074] Among them, ε i represents the positive angle between the flight direction of the two drones and the x-axis; and the corresponding protection zone radii of drone A and drone B are and

[0075] Assume that the displacement generated by UAV A or UAV B during the kth time period △t is P ik , then the displacement of the UAV during the k+1th time period △t is as follows:

[0076]

[0077] A maximum velocity constraint v is defined max and the maximum acceleration constraint v max, which is used to limit the available speed and acceleration of the drone, as shown in the following formula:

[0078] ||v i ||≤v max ,i∈1,2 (4)

[0079] ||a i ||≤a max ,i∈1,2 (5) Among them, ||·|| represents the modulus of the vector, a i is the acceleration of the drone, a max is the maximum acceleration of the drone;

[0080] In the two-dimensional plane, the flight speed of drone A is v 1 , the flight speed of drone B is v 2 , α is the angle between the line AB between the two UAVs and the boundary of the speed obstacle zone, that is, half of the collision cone vertex angle, γ is the angle between the line AB between the two UAVs and the relative speed v R The angle between them; define the relative collision cone (RCC) model, that is, the relative speed v at which drones may collide R =v 1 -v 2 The speed set is shown in the following formula:

[0081]

[0082] in, is the relative speed v R The straight line where the drone B is located; ⊙B is the flight safety protection zone of drone B (the radius of the protection zone is d h ), and the collision cone boundary is tangent to ⊙B;

[0083] The collision cone model only considers the position relationship and current status between drones, such as Figure 4 As shown in the figure, with drone B as the reference point, drone A moves relative to drone B. If the speed of drone A relative to drone B is within the collision cone, a flight conflict will occur between the two drones, otherwise there will be no flight conflict. Based on the collision cone model, the following geometric judgment method is used to detect the flight conflict between the two drones: when α>γ, there is a flight conflict between the two drones, otherwise there is no flight conflict. The expressions of α and γ are given by the following formula:

[0084]

[0085] γ=∠(v R ,AB) (8)

[0086] Step 3: Use the hybrid reciprocal speed barrier method to determine the HRVO area and the flight speed of the UAV to achieve flight conflict avoidance of multiple UAVs;

[0087] In order to solve the reciprocal oscillation problem caused by multiple UAV flight conflicts in the Reciprocal Velocity Obstacle (RVO) method, the Hybrid Reciprocal Velocity Obstacle (HRVO) method is introduced. The HRVO method further changes the vertex position of the RVO area so as to select a new collision avoidance speed for the UAVs according to the flight status of UAVs A and B.

[0088] For drone A and drone B, if the flight speed of drone A is v 1 In RVO A|B The area is above the axis AXIS in the RVO area of ​​drone A relative to drone B. Then, by symmetry, the flight speed of drone B is v 2 In RVO A|B Below the central axis of the area, I hope that drone A will continue to choose RVO A|B The speed above the axis of the area is used to reduce the change of flight state. The same is true in reverse.

[0089] To achieve this goal, RVO A|B The area below the central axis is replaced by the velocity obstacle (Velocity Obstacle, VO) of UAV A relative to UAV B. A|B ) area to expand the reciprocity of the speed barrier. The resulting obstacle area vertices correspond to RVO A|B The intersection of the upper edge of the region and the lower edge of . If v 1 Below the center line, mirror this process and swap the upper and lower areas, that is, the obstacle area vertex corresponds to RVO A|B The lower edge of the region is VO A|B The obstacle area is divided into a mixture of speed obstacle area and reciprocal speed obstacle area, which is called HRVO. The expression of the generated HRVO area is as follows: Figure 5 The filled area is shown below:

[0090]

[0091] Among them, v * represents the velocity vector from the RCC region vertex to the HRVO region vertex, Represents Minkowski and;

[0092] Set an optimal speed for drone A As shown in the following formula:

[0093]

[0094] in, Indicates the optimal flight speed of UAV A, P 1 Indicates the current position of drone A, represents the final position of UAV A, ||·|| 2 Represents the 2-norm of a vector;

[0095] Drone A selects a speed vector closest to the optimal speed outside the HRVO area as the new flight speed As shown in the following formula:

[0096]

[0097] Among them, v is the flight speed of UAV A at the next moment;

[0098] The hybrid reciprocal speed barrier method is mainly based on v 1 The HRVO area is determined by which side of the axis in the RVO area it is located on. This method will select the VO or RVO method at different flight speeds, which solves the possibility of reciprocal jitter generated by the RVO method. At the same time, it will not overly restrict the movement of each UAV, and is effective in achieving conflict avoidance in multi-UAV airspace.

[0099] However, the HRVO method will exclude speeds within the mixed reciprocal speed obstacle area even if it takes a long time before the collision occurs, which will result in a narrow range of optional collision avoidance speed vectors for the UAV each time, a relatively long collision avoidance time, and low efficiency. This shortcoming also exists in the VO method and the RVO method. If the optimal speed near the target point exists in the excluded speed set for a long time before the collision occurs, the optimal flight speed will be lost.

[0100] Step 4: Classify the collision cone area according to the relative speed of the two drones;

[0101] The flight speed v of drone A relative to drone B R If it falls within the collision cone, a flight conflict will occur and a collision will occur at some point in the future. Otherwise, no collision will occur. At this time, the relative speed v of the drones needs to be changed by changing the speed of the two drones. R Move out the collision cone to avoid collision;

[0102] If v RIf the speed falls within the collision cone RCC but is too low, it will take a long time for the collision to occur. In the next flight, the radius of the collision cone, i.e. the radius of the flight protection zone of UAV B, is reduced, and the collision cone RCC area is reduced, temporarily increasing the speed area available to the UAV. Similarly, if v R The speed is high and a collision will occur soon, so the radius of the collision cone will be expanded by d at the next flight moment. h , thereby expanding the RCC and temporarily narrowing the speed range available for the UAV, that is, the size of the RCC is related to v R Different RCCs generate different HRVO areas.

[0103] Based on the above ideas, according to the relative speed of the two drones, the collision cone area is divided from left to right into three different areas and the boundary between each two areas, a total of five parts, such as Figure 6 As shown in the figure; in order to provide a certain buffer time τ for high-speed UAV to avoid collision, that is, to determine the end point of buffer displacement τv at the next moment R The position where the aircraft falls in the RCC area; the selection of τ is crucial. According to the regulations of the air traffic management system, when the collision avoidance buffer time is 20s to 30s, there is a potential collision risk and a collision avoidance decision must be made. In this embodiment, τ∈[20,30] is required. And τ is a constant.

[0104] is the protection zone radius of drone A. The relative speed in the left area is low, so it is difficult for a collision to occur in a short time. The relative speed in the middle area is second, and the relative speed in the right area is high, so it is easy for a collision to occur. The relative speeds corresponding to the three areas and the two boundaries satisfy the following set:

[0105]

[0106]

[0107] Wherein, distance(P) is the distance function, which represents the distance from point P to the origin of the coordinate system in the two-dimensional Cartesian coordinate system. 1 and P 2 Indicates the current position of drone A and drone B, are the relative speeds corresponding to the three regions and two boundaries, and τ is the buffer time for UAV conflict avoidance;

[0108] When the relative speed v between drone A and drone B R When the set (12) is satisfied, the radius of the flight protection zone is multiplied by the proportional coefficient (a number close to 0 is selected for the proportional coefficient). R When the set (13) is satisfied, the radius of the extended protection zone is smaller than d hReduce by a certain proportion (select a number close to 1 as the proportional coefficient); when v R When set (14) is satisfied, the radius of the extended protection zone is the same as the radius of the HRVO zone (the proportionality coefficient is 1);

[0109] Step 5: Obtain different HRVO areas according to different collision cone areas to optimize the HRVO area;

[0110] By modifying the collision cone area, different HRVO areas are obtained through the generation process of HRVO area. Figure 7 As shown in (a), (b), and (c), m, M, and k are specific numbers within the range of the proportional coefficient of the radius change of the extended protection area and satisfy 0<m≤M≤k=1. When the end point of the buffer displacement falls on two boundaries, the corresponding proportional coefficients w and W satisfy m≤w≤M, M≤W≤k=1 respectively; this method is the improved and optimized hybrid reciprocal velocity obstacle method (Optimal Hybrid Reciprocal Velocity Obstacle, OHRVO).

[0111] Three different constants are selected as the proportional coefficients of the radius change of the protection zone of different collision cone areas, one of which is fixed at 1. At this time, the relative speed of the two UAVs is large, the risk of collision is high, and emergency collision avoidance measures are needed; the other two constants are both between (0,1), and the larger constant corresponds to the second largest relative speed of the two UAVs and the second largest collision risk; the smaller constant corresponds to the second smallest relative speed of the two UAVs and the very low risk of collision. Certain collision avoidance measures need to be taken, but it is not necessary to avoid collision too early.

[0112] Drone A selects a speed vector closest to the optimal speed outside the OHRVO area as the new flight speed, as shown in the following formula:

[0113]

[0114] In the simulation process, the most dangerous situation is given priority, that is, first determine whether the relative speed satisfies equation (14). If it satisfies equation (14), the corresponding OHRVO area is generated. Then consider whether it satisfies equation (16), and so on. Finally, consider whether it satisfies equation (12). The order of consideration is (14)-(16)-(13)-(15)-(12).

[0115] Finally, it should be noted 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 aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some or all of the technical features therein. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope defined by the claims of the present invention.

Claims

1. A multi-UAV flight collision avoidance method with improved hybrid reciprocal speed barriers, characterized by: The following steps are involved: Step 1: The drone continuously receives and processes ADS-B data and performs real-time coordinate conversion to obtain the latest ground position of the drone; Step 2: Establish the flight protection zone of the drone according to the flight speed of the drone and the layout of the airspace buildings, and establish a collision cone model for flight conflict detection; Step 3: Use the hybrid reciprocal speed barrier method to determine the HRVO area and the flight speed of the UAV to achieve flight conflict avoidance of multiple UAVs; Step 4: Classify the collision cone area according to the relative speed of the two drones; Step 5: Different HRVO areas are obtained according to different collision cone areas, and the HRVO area is optimized to obtain the improved and optimized hybrid reciprocal speed obstacle area OHRVO. UAV A selects a speed vector closest to the optimal speed outside the OHRVO area as the new flight speed.

2. The multi-UAV flight collision avoidance method with improved hybrid reciprocal speed barrier according to claim 1 is characterized by: The step 1 decodes the ADS-B raw data received by each drone to obtain the real-time location information of the drone, and then obtains the flight information of the drone; The decoded ADS-B data is converted into ground coordinates to obtain the position of the drone relative to the ground, including: Step 1.1: Obtain ADS-B data; Get the drone position data broadcast by ADS-B; Step 1.2: Decode ADS-B data; The acquired binary ADS-B data needs to be decoded and converted into a readable text format. The decoded data contains the latitude, longitude, altitude and speed information of the drone. Step 1.3: Convert the decoded ADS-B data to the WGS-84 ellipsoid coordinates of the drone’s ADS-B position and the reference position into Earth-centered Earth-fixed coordinates (X, Y, Z), and then calculate the coordinates of the drone relative to the ground fixed reference point (x, y, z).

3. The multi-UAV flight collision avoidance method with improved hybrid reciprocal speed barrier according to claim 2 is characterized by: The specific method of step 2 is: The two-dimensional coordinates of the drone relative to the ground fixed reference point are set to (x, y), and R is a two-dimensional real vector space, so as to determine the drone circular protection zone set V as shown in the following formula: Among them, d h Indicates the radius of the circular flight protection zone of the drone; Assume that drones A and B are in the limited low-altitude airspace of the same city; define the flight speeds of drone A and drone B as u1 and u2 respectively, take drone A as the origin, the line AB between drone A and drone B as the x-axis, and draw a straight line perpendicular to AB as the y-axis to establish a two-dimensional coordinate system. The flight speeds v1 and v2 of the two drones are shown in the following formula: v i =(u i cosε i ,u i sinε i ),i∈1,2 (2) Among them, ε i represents the positive angle between the flight direction of the drone and the x-axis; and the corresponding protection zone radii of drone A and drone B are and Assume that the displacement of UAV A or UAV B during the kth time period △t is Then the displacement of the UAV during the k+1th time period △t is as follows: (3) A maximum velocity constraint v is defined max and the maximum acceleration constraint v max , which is used to limit the available speed and acceleration of the drone, as shown in the following formula: ||in i ||≤v max ,i∈1,2 (4) ||a i ||≤a max ,i∈1,2 (5) Among them, ||·|| represents the modulus of the vector, a i is the acceleration of the drone, a max is the maximum acceleration of the drone; In the two-dimensional plane, the flight speed of UAV A is v1, the flight speed of UAV B is v2, α is the angle between the line AB between the two UAVs and the boundary of the speed obstacle zone, that is, half of the vertex angle of the collision cone, and γ is the angle between the line AB between the two UAVs and the relative speed v R The angle between them; define the relative collision cone RCC model, that is, the relative speed v at which the drone may collide R = the velocity set of v1-v2, as shown in the following formula: in, is the relative speed v R The straight line where ⊙B is located; ⊙B is the flight safety protection zone of UAV B, and the collision cone boundary is tangent to ⊙B; The collision cone model only considers the positional relationship and current state between drones. With drone B as the reference point, drone A moves relative to drone B. If the speed of drone A relative to drone B is within the collision cone, a flight conflict will occur between the two drones, otherwise there will be no flight conflict. Based on the collision cone model, the following geometric judgment method is used for the flight conflict detection between two drones: when α>γ, there is a flight conflict between the two drones, otherwise there is no flight conflict. The expressions of α and γ are given by the following formula: γ=∠(v R ,AB) (8)。 4. The multi-UAV flight collision avoidance method with improved hybrid reciprocal speed barrier according to claim 3 is characterized by: The specific method of step 3 is: The obstacle area is divided into a mixture of speed obstacle area and reciprocal speed obstacle area, which is called HRVO. The expression of the generated HRVO area is: Among them, v * represents the velocity vector from the RCC region vertex to the HRVO region vertex, Represents Minkowski and; Set an optimal speed for drone A As shown in the following formula: in, represents the optimal speed of drone A, P1 represents the current position of drone A, and P1 goal represents the final position of UAV A, ||·||2 represents the 2-norm of the vector; Drone A selects a speed vector closest to the optimal speed outside the HRVO area as the new flight speed As shown in the following formula: Among them, v is the flight speed of UAV A at the next moment.

5. The multi-UAV flight collision avoidance method with improved hybrid reciprocal speed barrier according to claim 4 is characterized by: The specific method of step 4 is: According to the relative speed of the two UAVs, the collision cone area is divided into three different areas and the boundary between every two areas, a total of five parts; The relative velocities corresponding to the three regions and the two boundaries satisfy the following sets: Wherein, distance(P) is a distance function, which represents the distance from point P to the origin of the coordinate system in a two-dimensional Cartesian coordinate system. P1 and P2 represent the current positions of drone A and drone B. are the relative speeds corresponding to the three regions and two boundaries, and τ is the buffer time for UAV conflict avoidance; When the relative speed v between drone A and drone B R When set (12) is satisfied, multiply the flight protection zone radius by the proportional coefficient. R When the set (13) is satisfied, the radius of the extended protection zone is smaller than d h Reduce a certain proportion; when v R When set (14) is satisfied, the radius of the extended protection zone is the same as the radius of the HRVO zone.

6. The multi-UAV flight collision avoidance method with improved hybrid reciprocal speed barrier according to claim 5, characterized in that: In step 5, UAV A selects a speed vector closest to the optimal speed outside the OHRVO area as the new flight speed, as shown in the following formula: In the simulation process, the most dangerous situation is given priority, that is, first determine whether the relative speed satisfies equation (14). If it satisfies equation (14), the corresponding OHRVO area is generated. Then consider whether it satisfies equation (16), and so on. Finally, consider whether it satisfies equation (12). The order of consideration is (14)-(16)-(13)-(15)-(12).

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