CN111506086A - An improved LOS guidance law combined with fuzzy PID path tracking control method for unmanned ship - Google Patents

Abstract

The invention discloses a control method for unmanned ship path tracking, which belongs to the field of unmanned ship motion control. The invention proposes to use the improved LOS guidance law combined with the fuzzy PID control method to realize the path tracking control of the unmanned ship. The path tracking control system of the unmanned ship is divided into a guidance subsystem and a control subsystem. The guidance subsystem adopts the improved LOS guidance law, and the variable speed control law is added to the variable foresight distance LOS guidance law, so that it can provide the desired heading and desired speed at the same time. , in order to realize the self-tuning of the speed of the unmanned ship during the path tracking process and reduce the influence of the speed. Considering the complex and changeable marine environment, the control layer uses fuzzy PID to design the course and speed controller to improve the adaptability and robustness of the controller, to achieve precise tracking control of the desired course and desired speed, and to ensure that the unmanned ship can effectively Stay on the desired path. The method effectively reduces the influence of the speed on the path tracking control of the unmanned ship, and improves the speed and accuracy of the path tracking of the unmanned ship.

Description

An improved LOS guidance law combined with fuzzy PID path tracking control method for unmanned ship

technical field

The invention relates to the field of unmanned ship motion control, in particular to an unmanned ship path tracking control method with improved LOS guidance law and fuzzy PID.

Background technique

With the rapid development of unmanned ships, it is urgent for unmanned ships to improve the accuracy and speed of path tracking control to ensure their good maritime autonomous operation capabilities and navigation safety. However, the complex sea environment seriously affects the path tracking control effect of the unmanned ship. In addition, the control system of the unmanned ship has the characteristics of nonlinearity, model uncertainty, input constraints, etc., which also increases the control difficulty to a certain extent.

The existing control technology usually optimizes and improves the controller according to the environmental disturbance and the control characteristics of the unmanned ship itself, aiming at improving the robustness of the controller and improving the path tracking control effect of the unmanned ship under the disturbance of the marine environment. However, this kind of method ignores the influence of the speed on the path tracking control of the unmanned ship, and has the disadvantages of complicated controller design and low engineering practicability.

SUMMARY OF THE INVENTION

In order to solve the problems existing in the prior art, the present invention provides an improved LOS guidance law combined with fuzzy PID path tracking control method for the unmanned ship. On the basis of considering the influence of the speed of the unmanned ship on the path tracking control, the influence of the speed on the path tracking is reduced by improving the LOS guidance law. Secondly, considering the adaptability and practicability of the marine environment disturbance, the fuzzy PID control is designed. device. Under the cooperation of LOS guidance law and fuzzy PID controller, the path tracking of unmanned ship is realized.

The concrete technical scheme adopted in the present invention is:

The path tracking control of the unmanned ship is divided into two parts: the guidance layer and the control layer. The improved LOS guidance law is adopted in the guidance layer, and the variable-speed control law is added on the basis of the LOS guidance law of variable foresight distance. The improved LOS guidance law can be During the path tracking process of the unmanned ship, the desired heading and desired speed are adjusted according to the geometric relationship between the position of the unmanned ship and the desired path, so as to reduce the influence of the speed on the path tracking of the unmanned ship and improve the flexibility and stability of the guidance law. .

In the control layer, fuzzy PID is used to design the course and speed controller of the unmanned ship. The fuzzy PID control algorithm can realize the self-tuning of the PID parameters according to the deviation and the deviation change rate by combining the PID control and the fuzzy algorithm, and control the tracking of the unmanned ship more quickly and accurately. The desired speed and desired heading given by the guidance layer ensure that the unmanned ship travels along the desired path.

Compared with the prior art, the present invention considers the influence of the speed on the path tracking control of the unmanned ship, and further adds a reasonable and feasible variable speed control law on the basis of the existing LOS guidance law of variable foresight distance, thereby improving the path tracking. speed and stability. Secondly, the fuzzy PID control method is used to design the course and speed controller of the unmanned ship, which takes into account the practicability and good robustness. With the cooperation of the improved LOS guidance law and the fuzzy PID controller, the influence of the speed of the unmanned ship on the path tracking is reduced, the path tracking accuracy of the unmanned ship is improved, and a good foundation for the autonomous operation of the unmanned ship is laid.

Description of drawings

Fig. 1 is the control principle diagram of the present invention;

Figure 2 is a schematic diagram of the LOS guidance law;

Figure 3 is a schematic diagram of fuzzy PID control;

Figure 4 is a schematic diagram of the design of the fuzzy controller;

Fig. 5 is the simulation result diagram of unmanned ship path tracking;

Fig. 6 is a comparison simulation result diagram of the unmanned ship PID and fuzzy PID course tracking controller;

Figure 7 shows the changes of self-tuning PID parameters under fuzzy rules

Detailed ways

The invention discloses an unmanned ship path tracking control method with improved LOS guidance law and fuzzy PID, belonging to the field of unmanned ship motion control. The invention realizes the path tracking control of the unmanned ship by improving the LOS guidance law and designing the fuzzy PID controller. This method effectively reduces the impact of speed on the path tracking control of the unmanned ship, improves the speed and accuracy of the path tracking of the unmanned ship, and lays a foundation for the autonomous and intelligent development of the unmanned ship.

In the following, by introducing the specific implementation steps of the present invention, a further detailed description is made in conjunction with the accompanying drawings. According to the following description, the content, features, advantages and effects of the present invention will become more clear.

Fig. 1 is the overall control principle block diagram of the present invention, and the specific implementation steps are as follows:

Step 101: The input of the control system is the desired path set artificially, and then the actual position information (x, y) of the unmanned ship is obtained by the GPS equipped on the unmanned ship. The expected speed _ud and the expected course of the human-vessel path tracking

后，利用无人船配备的传感系统得到无人船实际的航速u和航向

两者比较后得到航速误差、航向误差。然后依据误差的大小利用模糊PID控制器进行相应的调节作用，控制无人船航向、航速的实际值与期望值保持一致，从而实现无人船路径跟踪控制。Step 102: Obtain the desired speed _ud and desired heading

Then, use the sensor system equipped with the unmanned ship to obtain the actual speed u and heading of the unmanned ship

After comparing the two, the speed error and heading error are obtained. Then, according to the size of the error, the fuzzy PID controller is used for corresponding adjustment, and the actual value of the course and speed of the unmanned ship is controlled to be consistent with the expected value, so as to realize the path tracking control of the unmanned ship.

Fig. 2 is the LOS guiding law principle diagram of the present invention, and the concrete implementation steps are as follows:

Step 201: According to the position (x, y) of the unmanned ship, the forward-looking distance Δ, and the path points (x _k , y _k ) and (x _k+1 , y _k+1 ) of the unmanned ship, the solution is solved by the LOS guidance law The desired course of the unmanned ship

Step 201.1: Calculate the size of the angle α between the current expected path (D) of the unmanned ship and the true north direction (Y axis), and the calculation formula is as follows:

Step 201.2: Calculate the size of the included angle β between the straight line formed by the actual position (x, y) of the unmanned ship and the path point (x _k+1 , y _k+1 ) and the true north direction. The calculation formula is as follows:

Step 201.3: Calculate the distance d between the actual position (x, y) of the unmanned ship and the waypoint (x _k+1 , y _k+1 ), and the calculation formula is as follows:

Step 201.4: Calculate the tracking error y _e between the unmanned ship and the desired path, the calculation formula is as follows:

y _e =d*sin(α-β) (4)

Step 201.5: Design the forward-looking distance variation law in the LOS guidance law. Since the forward-looking distance Δ affects the speed of path tracking convergence to a certain extent, in order to improve the control effect of the path tracking, the forward-looking distance Δ is designed as follows: when the unmanned ship deviates from the path with a large error, the forward-looking distance at this time is expected. The distance is small, so that the unmanned ship can quickly return to the desired path; as the tracking error gradually decreases, it is expected that the forward-looking distance at this time is large, and the desired path can be tracked more smoothly, reducing overshoot and oscillation. In order to meet the above characteristics, the exponential function is used to design the change law of the foresight distance, as shown in the following formula:

In the formula, k is a constant value parameter strictly greater than zero; _Δmin is the minimum value of the foresight distance Δ; _Δc is the maximum increment of the foresight distance.

其计算公式如下：Step 201.6: Calculate the desired heading of the unmanned ship

Its calculation formula is as follows:

Step 202: A variable speed control law is proposed for the influence of the speed on the path tracking control. According to the length D _k between the adjacent desired path points (x _k , y _k ) and (x _k+1 , y _k+1 ) The distance d from the actual position (x, y) of the unmanned ship to the next waypoint (x _k+1 , y _k+1 ), and the variable speed control law of the unmanned ship is designed on the basis of the LOS guidance law. The basic form of the control law is as follows:

速度越接近最低航速；越远离路径点，

越接近最大航速。In the formula, d is the distance between the actual position of the unmanned ship and the next desired waypoint; _Dk is the distance between the current waypoint and the previous waypoint; δ is the adjustment factor, and the speed control law can be adjusted to achieve more good control effect. As the unmanned ship gradually approaches the next waypoint, the speed of the unmanned ship can be adjusted autonomously according to the distance from the next waypoint under the action of the variable speed control law: the closer to the waypoint, the

The closer the speed is to the minimum speed; the further away from the waypoint,

closer to the maximum speed.

Step 203: The desired path point of the current unmanned ship is P _k =(x _k+1 , y _k+1 ). In order to achieve smoother steering, the path point switching radius is designed, that is, when the unmanned ship enters the desired path point P When _k is within a certain range, it is necessary to automatically give up tracking the desired path point, and switch to tracking the next desired path point. Its judging conditions are as follows:

(x _k+1 -x) ² +(y _k+1 -y) ² ≤R ₀ ² (8)

Fig. 3 is the fuzzy PID controller design principle diagram of the present invention, and the concrete implementation steps are as follows:

Step 301: Determine the initial PID parameters through simulation or real ship test, and pay attention to the accumulation of experience in the process of parameter adjustment, and finally obtain a set of PID parameters that can initially achieve the control requirements.

Step 302: Fig. 4 is a flowchart of designing a fuzzy controller, the controller input is the error e and the error rate of change ec, after fuzzification, fuzzy reasoning, and clarity, the output PID parameter changes Δk _p , Δk _i , Δk _d

Step 301.1: Fuzzy variables, first determine the basic universe of error e and error rate of change ec, and then convert the clarity in the basic universe into the fuzzy universe represented by fuzzy language through quantization factors, and give each The fuzzy linguistic variables specify their respective membership functions.

Step 301.2: Perform fuzzy mathematics inference operation on the fuzzified variables, where fuzzy rules are the core of fuzzy reasoning, and the formulation of fuzzy rules should be based on experience in the operation process. Here is based on the relationship between k _p , k _i , k _d and error e and error rate of change ec, the following fuzzy rules are formulated:

Table 1. Δk _p fuzzy tuning rules

Table 2. Δk _i fuzzy tuning rules

Table 3. Δk _d fuzzy tuning rules

Step 302.3: After fuzzy reasoning, the membership degrees of PID parameter changes Δk _p , Δk _i , and Δk _d in the fuzzy universe are obtained, and the conversion from the fuzzy universe to the basic universe can be completed by clarifying them. Get an exact Δk _p , _Δki , Δk _d .

Step 303: Next, according to the error e(t) at the current moment, through the actions of proportional (K _p +ΔK _p ), integral (K _i +ΔK _i ), and differential (K _d +ΔK _d ), the fuzzy PID controller is obtained: output u(t)

Figures 5-7 are the simulation results of the path tracking control of the unmanned ship according to the present invention, and Figure 5 verifies the effectiveness of the path tracking control method of the unmanned ship with improved LOS guidance law and fuzzy PID, with small overshoot and tracking accuracy. Figure 6 further illustrates the effectiveness of the fuzzy PID controller by comparing the PID heading controller, the fuzzy PID is better than the PID control, the overshoot is smaller, and the adjustment time is shorter; and Figure 7 reflects the fuzzy PID controller According to the change of error, the PID parameters can be adjusted in time, so as to optimize the control effect under complex environmental disturbance.

It can be seen from the above process that the present invention provides an improved LOS guidance law combined with a fuzzy PID path tracking control method for an unmanned ship, which can calculate the appropriate desired heading and desired speed according to the improved LOS guidance law, and then control the heading and speed through the fuzzy PID. The device realizes the tracking of the expected value of the unmanned ship, and then completes the path tracking control. This method effectively reduces the influence of the speed on the path tracking of the unmanned ship, takes into account the practicability and robustness of the controller, and improves the ability to resist the disturbance of the marine environment to a certain extent.

Claims (6)

1. An improved L OS guide law and fuzzy PID combined unmanned ship path tracking control method is characterized in that an unmanned ship path tracking control system is divided into a guidance subsystem and a control subsystem, the guidance subsystem adopts an improved L OS guide law, a variable speed control law is added to a variable foresight distance L OS guide law, an expected course and an expected speed are provided at the same time, so that the speed self-tuning of an unmanned ship in the path tracking process is realized, the influence of the speed is further reduced, in consideration of a complex and changeable marine environment, a control layer adopts fuzzy PID to design a course speed controller, the adaptivity and the robustness of the controller are improved, the accurate tracking control of the expected course and the expected speed is realized, and the unmanned ship is effectively kept on an expected path.

2. The improved L OS guidance law unmanned ship path tracking control method combined with fuzzy PID as claimed in claim 1, wherein the desired path of the unmanned ship is composed of a series of waypoints in geodetic coordinate system, the unmanned ship path tracking requires USV to reach the desired path from any departure point and to navigate along the desired path with the smallest tracking error at the desired speed, and the desired tracking control target is formulated as follows:

in the formula, y_eThe transverse error between the unmanned ship and the expected path under the ship body coordinate system is obtained;

is the desired heading angle; u. of_dThe desired speed is the longitudinal direction of the unmanned ship.

3. The improved L OS guidance law and fuzzy PID combined unmanned ship path tracking control method according to claim 1, wherein firstly, aiming at the contradiction between rapidity and stability existing in the traditional L OS guidance law, a foresight distance variation law is designed, so that the foresight distance can be adjusted according to the tracking error of an unmanned ship, the adaptivity of the L OS guidance law is improved, secondly, the speed variation law is increased on the basis of the variable foresight distance L OS guidance law, the speed is divided into a fixed part and a variable part, the speed self-tuning capability is increased, and the influence of the speed on the unmanned ship path tracking control is reduced.

4. The improved L OS guidance law combined with fuzzy PID unmanned ship path tracking control method according to claim 3, wherein a variable speed control law is designed and divided into a fixed navigational speed part and a variable navigational speed part to realize a navigational speed self-tuning function of the unmanned ship in the path tracking process, thereby reducing the influence of the navigational speed on the path tracking control and improving the path tracking accuracy and quality, the variable speed control law is formulated as follows:

u_d＝u₁+u₂μ(d) (2)

in the formula: u. of_dRepresenting the desired longitudinal speed, u, of the unmanned ship₁Representing a fixed minimum speed; u. of₂A maximum value representing a variable speed portion; μ (d) is an adjustment factor, ranging between (0,1), for adjusting the variable speed portion.

5. The design of the adjustment factor μ (d) in the variable speed control law according to claim 4, characterized in that: when the unmanned ship approaches the next expected path point, the speed is reduced to reduce the overshoot during steering and complete smooth steering control; and when the maximum navigational speed is kept between two path points, the rapidity of path tracking is improved, the Sigmoid function is adopted to determine mu (d) according to the requirements, and the formula is expressed as follows:

in the formula, d is the distance between the actual position of the unmanned ship and the next path point; d_kBetween adjacent desired path pointsA distance; is a regulatory factor.

6. The unmanned ship path tracking control method based on the improved L OS guidance law according to claim 1, wherein a fuzzy PID course speed controller is designed, and a fuzzy rule is formulated according to PID parameter setting experience, so that PID parameters have self-setting capability, thereby improving the rapidity of the controller and the robustness to environmental disturbance.

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