Low-speed high-precision tracking control method for unmanned surface vehicle

Abstract

This invention discloses a low-speed, high-precision tracking control method for unmanned surface vessels (USVs). The method includes: expressing the USV's mission planning path parametrically; selecting the USV's projection point on the path; calculating curvature and position deviation based on the selected projection point; selecting the USV's forward-looking distance on the path based on the curvature and position deviation; obtaining the guidance point coordinates based on the projection point and forward-looking distance; calculating the desired heading value; calculating the speed-heading control rate and heading control rate based on the desired heading value and desired speed; and achieving tracking control of the USV based on these control rates. This invention, through its designed tracking control method, calculates the speed-heading control rate and heading control rate, and achieves tracking control of the USV based on these rates. This enables high-precision tracking control of USVs at low speeds, fulfilling the mission requirements of unconventional control scenarios such as autonomous navigation in narrow and complex waters and autonomous berthing in dock areas.

Description

Technical Field

[0001] This invention relates to the field of autonomous navigation control technology for unmanned surface vessels, and in particular to a low-speed, high-precision tracking control method for unmanned surface vessels. Background Technology

[0002] In unmanned surface vessels (USVs) navigating narrow and complex waterways, trajectory tracking and control methods are crucial to ensuring the vessel can safely and efficiently follow a predetermined route and ultimately reach its target location. For example, in collision avoidance trajectory tracking after entering port, the USV needs to follow a specific route to avoid other vessels and obstacles, ensuring safe navigation in a complex marine environment. Similarly, when performing berthing tasks, trajectory tracking for entering a berth requires the USV to navigate accurately in narrow waterways, ensuring the vessel can accurately dock at the designated location. However, due to navigational safety requirements, these scenarios often only allow the USV to navigate at relatively low speeds. In such conditions, the motion control of small USVs is easily affected by environmental disturbances, leading to a decrease in trajectory tracking accuracy. Therefore, this situation places higher robustness requirements on the USV's navigation and tracking control algorithms. Summary of the Invention

[0003] To address the shortcomings of existing technologies, this invention provides a low-speed, high-precision tracking control method for unmanned surface vessels (USVs) to achieve high-precision tracking control for small USVs in low-speed navigation scenarios.

[0004] Therefore, the technical solution adopted by the present invention is as follows:

[0005] A method for low-speed, high-precision tracking control of an unmanned surface vessel (USV) is provided, the method comprising:

[0006] The unmanned surface vessel (USV) mission planning path is expressed using parametric equations, and the USV's projection points on the path are selected based on the parametric equation-expressed mission planning path.

[0007] The curvature and position deviation are calculated based on the selected projection points, and the forward sight distance of the unmanned surface vessel on the track path is selected based on the curvature and position deviation.

[0008] The coordinates of the guidance point are obtained based on the projection point and the forward sight distance, and the desired heading value is calculated based on the coordinates of the guidance point.

[0009] The speed and heading control rate and the heading control rate are calculated based on the desired heading value and the set desired speed. The tracking control of the unmanned surface vessel is realized based on the control rate. The tracking control of the unmanned surface vessel includes the control of the unmanned surface vessel's speed and heading.

[0010] According to the above scheme, the specific points for selecting the projection of the unmanned surface vessel on the path include:

[0011] The distance between the unmanned surface vessel's position and any point on the mission planning path is set as the cost function. The optimization accuracy and optimization starting point are set, and the points on the path are optimized using the bisection method. The point on the path corresponding to the optimal value is taken as the projection point of the unmanned surface vessel on the path.

[0012] According to the above scheme, the parametric equation expression of the unmanned surface vessel mission planning path is as follows:

[0013] Assuming the task planning path is in and The path segment equations between are ,make The original equation is transformed into:

[0014] ,

[0015] in, These are the parameter values ​​for the parametric equation. =0 indicates the starting point of the path. =1 indicates the end point of the path.

[0016] According to the above scheme, the specific method for calculating the forward sight distance of the flight path is as follows:

[0017] ,

[0018] in, Indicates the forward sight distance. This indicates the upper limit of the forward sight distance. This indicates the lower limit of the forward sight distance. This indicates the maximum curvature limit for tracking. Indicates positional deviation. This represents the parameter value of the projection point.

[0019] According to the above scheme, the guidance point coordinates are obtained by adding the forward-looking distance and the projection point parameter value, and then substituting the guidance point parameter value into the task planning path expressed by the parametric equation to obtain the guidance point coordinates; the guidance point parameter value is specifically the parameter value corresponding to the projection point on the task planning path expressed by the parametric equation.

[0020] According to the above scheme, the specific calculation method for the expected heading value is as follows:

[0021] ,

[0022] in, and This indicates the current coordinates of the unmanned surface vessel. and This represents the coordinates of the current position of the unmanned surface vessel within the coordinates of the mission planning path expressed in parametric equations.

[0023] According to the above scheme, the specific calculation method for the speed and heading control rate is as follows:

[0024] ,

[0025] in, , , Indicates the value of the control parameter. This indicates the speed error value. This represents the speed error value at the previous time step.

[0026] According to the above scheme, the selection of the unmanned surface vessel's projection point on the path is constrained by the following constraints:

[0027] The unmanned surface vessel initially uses the starting point of the mission-planned path as its projection point;

[0028] When the difference between the guidance point parameter value at a certain moment and the previous moment exceeds a certain threshold, the cost function value at that moment is recorded. Modify the starting point of the optimization and start the optimization process again to obtain the cost function value after the optimization. ,like and If the difference is less than a certain threshold, then the points of the re-optimized task planning path will be used as projection points.

[0029] According to the above scheme, the guidance point coordinate calculation can be optimized by the look-ahead distance (LOS) method. The LOS method specifically involves converting the portion of the look-ahead distance exceeding the threshold into the look-ahead distance calculation for the next task planning path when the calculated look-ahead distance is greater than a certain threshold.

[0030] A computer storage medium is provided, which stores a computer program that can be executed by a processor, the computer program performing the low-speed, high-precision tracking control method for unmanned surface vessels described above.

[0031] The beneficial effects of this invention are as follows: This invention calculates the speed and heading control rate and the heading control rate through the designed tracking control method, and realizes the tracking control of the unmanned surface vessel based on the heading control rate and the heading control rate. It can realize high-precision tracking control of the unmanned surface vessel at low speed, so as to meet the mission requirements of unconventional control scenarios such as autonomous navigation in narrow and complex waters and autonomous berthing in dock areas.

[0032] Furthermore, the present invention constrains the selection of the projection point of the unmanned surface vessel (USV) on the mission planning path through constraint conditions, which can ensure the continuity of the USV's guidance point and the integrity of the USV's tracking, and avoid guidance with incorrect projection points or the phenomenon of the projection point changing in a continuous time.

[0033] Furthermore, this invention uses the LOS method to optimize the calculation of guidance point coordinates, which can avoid sudden decreases in the expected heading value and guidance point blockage and jump phenomena, ensuring a smooth transition of speed and heading control rates and heading control rates in the tracking control of the unmanned surface vessel. Attached Figure Description

[0034] Figure 1 This is a schematic diagram of the LOS method logic according to an embodiment of the present invention;

[0035] Figure 2 This is a schematic flowchart of a low-speed, high-precision tracking control method for an unmanned surface vessel according to an embodiment of the present invention.

[0036] Figure 3 This is a schematic diagram of a multi-projection point scenario according to an embodiment of the present invention;

[0037] Figure 4(a) is a schematic diagram of an embodiment of the present invention where the forward sight distance value is too large;

[0038] Figure 4(b) is a schematic diagram of the forward sight distance being too small according to an embodiment of the present invention;

[0039] Figure 5 This is a schematic diagram illustrating the abrupt decrease in the expected heading value according to an embodiment of the present invention;

[0040] Figure 6 This is a schematic diagram of the pre-pass point LOS method according to an embodiment of the present invention;

[0041] Figure 7 This is a schematic diagram of the controller structure according to an embodiment of the present invention;

[0042] Figure 8 This is a diagram showing the experimental results of the unmanned surface vessel's straight-line tracking in an embodiment of the present invention; where (a) represents changes in heading; (b) represents changes in error; (c) represents changes in rudder angle; (d) represents changes in throttle; (e) represents changes in position; and (f) represents changes in speed.

[0043] Figure 9 This is a diagram showing the experimental results of unmanned surface vessel (USV) trajectory tracking in an embodiment of the present invention; where (a) represents changes in heading; (b) represents changes in error; (c) represents changes in tipping; (d) represents changes in throttle; (e) represents changes in position; and (f) represents changes in speed. Detailed Implementation

[0044] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0045] Line-of-sight (LOS) guidance is a classic guidance algorithm widely used in surface-to-air missile and autopilot research. It boasts advantages such as strong anti-jamming capabilities and independence from precise modeling of the controlled object. Furthermore, it is applicable not only to straight-line path guidance with zero curvature but also to complex curved path guidance. Benefiting from the advantages of LOS, its use in designing trajectory tracking algorithms for unmanned surface vessels (USVs) has also become widespread. The basic logic of the fundamental LOS method is to simplify the position deviation control of the tracking control into the control of the heading deviation. A schematic diagram of the LOS method is shown below. Figure 1 As shown. When using the LOS method, if the task path is a straight line, the coordinates of the unmanned surface vessel's (USV) projection points on the path can be obtained relatively easily. However, when the path is curved, the usual method is to discretize the curve into several concatenated curves and solve it using a straight-line approach. However, the number of discretizations in this approach is closely related to the curve length and curvature, and a large number of discretizations increases the computational load and affects the overall algorithm's solution speed. Since the USV's tracking path segment always has length boundaries or ranges, whether it's a straight or curved path, converting it into parametric equations allows for the mapping of points on the path to parameters. One-to-one correspondence, then by taking the pairs The method of value optimization is used to quickly find the projection point of any point on the curve. Therefore, to unify the way the LOS method finds the projection point of the unmanned surface vessel's position on the path, the path expression equation is unified into a parametric equation form. Based on this, the present invention provides a low-speed, high-precision tracking control method for unmanned surface vessels, such as... Figure 2 As shown, the method includes:

[0046] S1. Express the unmanned surface vessel (USV) mission planning path parametrically, and select the USV's projection point on the path based on the parametrically expressed mission planning path.

[0047] S2. Calculate the curvature and position deviation based on the selected projection points, and select the forward sight distance of the unmanned surface vessel on the track path based on the curvature and position deviation.

[0048] S3. Obtain the coordinates of the guidance point based on the projection point and the forward sight distance, and calculate the desired heading value.

[0049] S4. Calculate the speed and heading control rate and the heading control rate based on the desired heading value and desired speed. Control the unmanned surface vessel's (USV) tracking based on these control rates. The tracking control includes controlling the USV's speed and heading. The desired speed can be set.

[0050] Specifically, in this embodiment, the parametric equation of LOS is reduced to:

[0051] Assuming the task planning path is in and The path segment equations between are ,make The original equation is transformed into:

[0052] .

[0053] in, These are the parameter values ​​for the parametric equation. =0 indicates the starting point of the path. =1 indicates the end point of the path. The distance between the unmanned surface vessel's location and a point on the path is defined as the cost function. Set the optimization precision Starting point for finding the best And the parameters are obtained by bisection. The value is optimized to select the projection point of the unmanned surface vessel on the path. .

[0054] This includes situations where the curved path is complex and the unmanned surface vessel (USV) happens to be located near the curve, resulting in the USV having multiple closest points on the curve simultaneously, such as... Figure 3 Cost function shown When multiple extreme points exist, to avoid the unmanned surface vessel (USV) using incorrect projection points for guidance or causing the projection point to jump continuously within a time frame, and to ensure the continuity of the USV's guidance points and the integrity of its tracking, the following constraints are preferably imposed on the selection of the projection points:

[0055] When the unmanned surface vessel receives a mission and searches for the guidance point for the first time, it prioritizes the path start point as the projection point to ensure that the unmanned surface vessel reaches the start point first.

[0056] During the tracking process, when the guidance point parameter value at a certain moment... When the difference from the previous moment is large, take this value. Record the cost function value at this time. The starting point for optimization was then modified to... Then, the optimization is performed again to obtain the cost function value. If the difference between the two cost function values ​​is less than 1, then the second parameter value is taken as the result of this optimization to obtain the projection point.

[0057] After determining the projection point of the unmanned surface vessel (USV) on the path, the guidance point needs to be calculated based on the forward-looking distance. As shown in Figure 4(a), if the forward-looking distance is too large, the USV's tracking accuracy may decrease significantly where the curvature of the tracking curve is too large. As shown in Figure 4(b), if the forward-looking distance is too small, the USV's expected heading may still have a large difference from the actual heading even when the deviation is small, leading to overshoot and overexcitation of the USV's response. Therefore, in this embodiment, the specific calculation method for the forward-looking distance of the trajectory path is as follows:

[0058] ,

[0059] in, This indicates the forward sight distance; to prevent the forward sight distance from being too large or too small, upper and lower limits are set on it. This indicates the upper limit of the forward sight distance. This represents the lower limit of the forward-looking distance. Due to the limitations of actual unmanned surface vessel (USV) maneuverability, USVs have a minimum turning radius, which is the minimum radius of curvature of the navigation path. Therefore, there is a corresponding maximum curvature limit for tracking. Indicates the maximum curvature limit for tracking; Indicates positional deviation. This represents the parameter values ​​of the projection point. When the position deviation... When it increases, or the curvature Increase forward sight distance Decrease, and when , When the forward sight distance reaches its maximum .

[0060] Specifically, the guidance point coordinates are obtained by adding the forward-looking distance and the projection point parameter value to obtain the guidance point parameter value, and then substituting the guidance point parameter value into the parametric LOS equation to obtain the desired guidance point coordinates; specifically expressed as:

[0061] ,in Indicates the guidance point parameter value, Substituting back into the parametrically simplified LOS equations, the desired guidance point coordinates can be obtained. .

[0062] Preferably, the guidance point coordinate calculation can be optimized by the look-ahead distance (LOS) method. The LOS method specifically involves: when the calculated look-ahead distance is greater than a certain threshold, the portion of the look-ahead distance exceeding the threshold is converted into the look-ahead distance calculation for the next task planning path.

[0063] In the common LOS method, due to the difference between the accuracy range of passing the point and the forward shift range of the LOS guidance point selection, when the unmanned surface vessel (USV) approaches the end of the path, the LOS guidance point may be fixed at the end of the path. Therefore, as the USV approaches the end of the current tracking path but has not yet passed the point, the LOS method will experience guidance point blocking, causing the desired heading to continuously increase as the USV approaches the end of the path. Once the point is passed, a guidance point jump phenomenon will occur, causing the guidance point to jump from the end of the previous path to the nearest guidance point on the next path, resulting in a sudden decrease in the desired heading. Figure 5As shown. Therefore, at the junction of the two paths, the guidance heading will experience a significant fluctuation, causing oscillations that deviate from the path when the unmanned surface vessel (USV) performs smooth path following. Therefore, the following is proposed... Figure 6 The pre-pass point LOS method shown is used for multi-path stitching guidance of unmanned surface vessels, and the original guidance point selection is deselected. Value constraint, when If the distance exceeds one, the excess portion is converted into the forward look-ahead distance calculation for the next path, thereby adjusting the calculated guidance point coordinates and selecting guidance points from the next path. This avoids guidance point blocking and jump phenomena, ensuring a smooth transition of the algorithm's guidance.

[0064] In this embodiment, after calculating the speed and heading control rates and the heading control rate, the following method is used: Figure 7 The controller shown performs tracking control on the unmanned surface vessel. This controller is designed using a superspiral sliding mode algorithm, and the control law typically consists of two parts.

[0065] (3)

[0066] Where s is the state-space hyperplane, i.e., the sliding surface, sgn(s) is the sign function, k1 and k2 are the sliding mode adjustment parameters, and v is an auxiliary variable used to compensate for system uncertainties, external disturbances, or certain complex dynamics of the system itself. As can be seen from the above equation, in the design process of the super-spiral sliding mode controller, only the sliding surface needs to be established, and the controller design can be carried out based on the sliding surface. Using the second-order nonlinear response model of the unmanned surface vessel and the design method based on the super-spiral sliding mode algorithm, the heading controller is designed, and the control law and desired heading of the heading controller are obtained. The control function relationship between the error value e and the error value e is as follows: .

[0067] An incremental PID control algorithm is used to design the speed and heading control rate algorithm for the unmanned surface vessel (USV) speed controller. Incremental PID refers to using the difference between the current control quantity and the previous control quantity for control, and the output of the digital controller is only the increment of the control quantity. Its discrete expression is

[0068]

[0069] in, , , These represent control parameter values, which are adjusted according to the characteristics of different vessels in actual use. Furthermore, due to the operating characteristics of the waterjet propulsion system, after the main engine is fully engaged, there is a fixed idle speed at the lowest main engine speed, and the speed control has a lower limit. Within this speed limit, when the waterjet propulsion bucket is fully raised, the unmanned surface vessel (USV) will have a certain idle speed, which is a crucial control element in low-speed navigation control. Therefore, the speed control of the waterjet propulsion system needs to be divided into two stages: above the desired speed (keeping the bucket fully raised) and controlling only the main engine speed; below the desired speed (keeping the bucket at its minimum) and controlling only the bucket angle. When the bucket is fully lowered, the thrust generated by the waterjet propulsion system will be entirely directed towards the bow, achieving reverse control where the USV's longitudinal speed is less than 0. Furthermore, based on the properties of waterjet propulsion, when the tipping angle is at a certain value, the longitudinal thrust generated by the water jet from the waterjet nozzle and the longitudinal thrust generated by the water jet ejected from the tipping bucket will cancel each other out. At this point, if the nozzle angle is controlled, the unmanned surface vessel (USV) can perform a stationary bow turn while maintaining a longitudinal speed of 0. Since the output of speed control differs in the two different phases, and the USV's response characteristics also differ, the control algorithms for the two phases need to be divided. Under forward speed control above idle, the controller uses one set of control parameters, and the controller's control quantity is the propeller speed. Under speed control below idle and in reverse, the controller uses another set of control parameters, and the controller's control quantity is the tipping angle of the propeller.

[0070] Specifically, the expected heading value can be expressed as: , Indicates the expected heading value. and This indicates the current coordinates of the unmanned surface vessel. and This represents the coordinates of the current position of the unmanned surface vessel within the coordinates of the mission planning path expressed in parametric equations.

[0071] Specifically, the calculation method for the speed and heading control rate is as follows:

[0072]

[0073] in, , , Indicates the value of the control parameter. This indicates the speed error value. This represents the speed error value at the previous time step.

[0074] Based on the method proposed in this embodiment, a real-vessel track tracking test was conducted to verify the actual control capability of the method. The real-vessel track tracking test was divided into a straight-line track tracking test and a curved track tracking test, and the test was carried out in a reservoir area.

[0075] In the straight-line trajectory tracking test, at the set desired speed The following are the results of the live-ship straight-line trajectory tracking test. Figure 8 As shown in the figure, the experimental results demonstrate that under the control of the controller designed in this paper, the unmanned surface vessel (USV) can effectively track a straight trajectory. Specifically, the USV's bow reaches the desired heading for LOS guidance in approximately 8 seconds and maintains stable tracking. Since the desired speed is greater than the USV's idle speed, the engine speed is used for control. In this experiment, the upper and lower limits of the engine speed correspond to throttle values ​​ranging from 0% to 100%. Control is directly applied to the throttle value. Due to limitations imposed by the actual propeller throttle increase effect, the speed reaches the desired speed in approximately 25 seconds, but once reached, it can stably track the desired speed. Therefore, the experiment proves that the algorithm has the ability to stably track a straight trajectory.

[0076] In the curve trajectory tracking experiment, a third-order Bezier curve was used as the target path. The third-order Bezier curve can be uniquely determined by four control points, and its parametric equation is as follows:

[0077]

[0078] in, These are the coordinates of the four control points. In the curve trajectory tracking experiment conducted in this paper, the coordinates of the four control points obtained after coordinate transformation using the Bezier curve and the reference coordinates are: , , , Desired speed The results of the actual boat curve trajectory tracking test are as follows: Figure 9 As shown in the figure. The experimental results demonstrate that, under the control of the controller designed in this paper, the unmanned surface vessel (USV) can effectively track the curved trajectory of the actual vessel. Initially, since the desired heading is the same as the USV's heading, the USV maintains stable tracking of the desired heading from the start of the experiment. However, due to environmental interference and significant changes in fluid resistance during the actual trimaran's turning, the USV's heading fluctuates to some extent. However, as shown in the error variation curve, the heading remains stable within 2°, and the average heading error is less than 1°, which is within an acceptable range. Because the USV's speed is controlled by the tipping bucket at low speeds, and given the USV's large mass, the speed response is slow, reaching the desired speed in approximately 60 seconds. However, once reached, it can stably track the desired speed. Therefore, the experiment proves that this method has the ability to stably track curved trajectories.

[0079] In addition, this embodiment of the invention also provides a computer storage medium storing a computer program that can be executed by a processor. The computer program executes the low-speed, high-precision tracking control method for unmanned surface vessels described above in this embodiment.

[0080] This invention provides a low-speed, high-precision tracking control method for unmanned surface vessels (USVs). By designing the tracking control method, the speed and heading control rates are calculated, and the tracking control of the USV is achieved based on the heading and heading control rates. This enables high-precision tracking control of USVs at low speeds, thus meeting the mission requirements of unconventional control scenarios such as autonomous navigation in narrow and complex waters and autonomous berthing in dock areas.

[0081] Furthermore, the present invention constrains the selection of the projection point of the unmanned surface vessel (USV) on the mission planning path through constraint conditions, which can ensure the continuity of the USV's guidance point and the integrity of the USV's tracking, and avoid guidance with incorrect projection points or the phenomenon of the projection point changing in a continuous time.

[0082] Furthermore, this invention uses the LOS method to optimize the calculation of guidance point coordinates, which can avoid sudden decreases in the expected heading value and guidance point blockage and jump phenomena, ensuring a smooth transition of speed and heading control rates and heading control rates in the tracking control of the unmanned surface vessel.

[0083] It should be noted that, depending on the implementation needs, the various steps / components described in this application can be broken down into more steps / components, or two or more steps / components or parts of the operation of steps / components can be combined into new steps / components to achieve the purpose of this invention.

[0084] The order of the steps in the above embodiments does not imply the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this application.

[0085] It should be understood that those skilled in the art can make improvements or modifications based on the above description, and all such improvements and modifications should fall within the protection scope of the appended claims.

Claims

1. A low-speed, high-precision tracking control method for unmanned surface vessels, characterized in that, The method includes: The unmanned surface vessel (USV) mission planning path is expressed using parametric equations, and the USV's projection points on the path are selected based on the parametric equation-expressed mission planning path. The curvature and position deviation are calculated based on the selected projection points, and the forward sight distance of the unmanned surface vessel on the track path is selected based on the curvature and position deviation. The coordinates of the guidance point are obtained based on the projection point and the forward sight distance, and the desired heading value is calculated based on the coordinates of the guidance point. The speed and heading control rate and the heading control rate are calculated based on the desired heading value and the set desired speed. The tracking control of the unmanned surface vessel is realized based on the control rate. The tracking control of the unmanned surface vessel includes the control of the unmanned surface vessel's speed and heading. The specific calculation method for the forward sight distance of the flight path is as follows: ， in, Indicates the forward sight distance. This indicates the upper limit of the forward sight distance. This indicates the lower limit of the forward sight distance. This indicates the maximum curvature limit for tracking. Indicates positional deviation. Indicates the projection point parameter value. This represents the curvature of the projection point.

2. The low-speed, high-precision tracking control method for an unmanned surface vessel according to claim 1, characterized in that, The selection of the unmanned surface vessel's projection point on the path specifically includes: The distance between the unmanned surface vessel's position and any point on the mission planning path is set as the cost function. The optimization accuracy and optimization starting point are set, and the points on the path are optimized using the bisection method. The point on the path corresponding to the optimal value is taken as the projection point of the unmanned surface vessel on the path.

3. The low-speed, high-precision tracking control method for an unmanned surface vessel according to claim 1, characterized in that, The parametric equation expression of unmanned surface vessel (USV) mission planning path is as follows: Assuming the task planning path is in and The path segment equations between are ,make The original equation is transformed into: ， in, These are the parameter values ​​for the parametric equation. =0 indicates the starting point of the path. =1 indicates the end point of the path.

4. The low-speed, high-precision tracking control method for an unmanned surface vessel according to claim 1, characterized in that, The guidance point coordinates are obtained by adding the forward-looking distance and the projection point parameter value, and then substituting the guidance point parameter value into the parametrically expressed task planning path to obtain the guidance point coordinates; the guidance point parameter value is specifically the parameter value corresponding to the projection point on the parametrically expressed task planning path.

5. The low-speed, high-precision tracking control method for an unmanned surface vessel according to claim 1, characterized in that, The specific calculation method for the expected heading value is as follows: ， in, and This indicates the current coordinates of the unmanned surface vessel. and This represents the coordinates of the current position of the unmanned surface vessel within the coordinates of the mission planning path expressed in parametric equations.

6. The low-speed, high-precision tracking control method for an unmanned surface vessel according to claim 1, characterized in that, The specific calculation method for speed and heading control rate is as follows: ， in, , , Indicates the value of the control parameter. This indicates the speed error value. This represents the speed error value at the previous time step.

7. The low-speed, high-precision tracking control method for an unmanned surface vessel according to claim 4, characterized in that, The selection of the unmanned surface vessel's projection point on the path is constrained by the following constraints: The unmanned surface vessel initially uses the starting point of the mission-planned path as its projection point; When the difference between the guidance point parameter value at a certain moment and the previous moment exceeds a certain threshold, the cost function value at that moment is recorded. Modify the starting point of the optimization and start the optimization process again to obtain the cost function value after the optimization. ,like and If the difference is less than a certain threshold, then the points of the re-optimized task planning path will be used as projection points.

8. The low-speed, high-precision tracking control method for an unmanned surface vessel according to claim 4, characterized in that, The guidance point coordinate calculation is optimized using the look-ahead distance (LOS) method. Specifically, when the calculated look-ahead distance is greater than a certain threshold, the portion of the look-ahead distance exceeding the threshold is converted into the look-ahead distance calculation for the next task planning path.

9. A computer storage medium, characterized in that, It contains a computer program that can be executed by a processor, which performs a low-speed, high-precision tracking control method for an unmanned surface vessel according to any one of claims 1-8.

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