Unmanned ship path tracking control method based on active disturbance rejection decentralized control

Abstract

The invention discloses an unmanned ship path tracking control method based on active disturbance rejection decentralized control, and belongs to the field of unmanned ship motion control. The method comprises the steps that an unmanned ship mathematical model in the disturbance environment is constructed, a steering torque model of a steering engine and a longitudinal thrust model of a propeller are considered compared with the technology, control input is changed into the rotating speed of the propeller and the steering angle of the steering engine, and three disturbances of wind, waves and flow in the environment are considered at the same time; aiming at the problem that the control precision is influenced by environmental interference, a linear expansion state observer is constructed to estimate internal disturbance and external disturbance; and finally, in combination with a decentralized control strategy and an active-disturbance-rejection control theory, constructing an active-disturbance-rejection decentralized controller, and performing real-time estimation compensation on a coupling part between subsystems in the unmanned ship model as external disturbance. According to the method, the accuracy and the safety of tracking the given path by the unmanned ship in the disturbance environment can be better ensured, and the robustness of the controller is improved.

Description

Technical Field

[0001] The present invention belongs to the field of unmanned ship motion control, and specifically relates to a path tracking control method for unmanned ships based on active disturbance rejection decentralized control. By controlling the propeller and rudder in a disturbed environment, the unmanned ship can track a given desired path. Background Art

[0002] Unmanned ships can autonomously perform complex tasks in waters with harsh environments, saving time and labor costs. Therefore, they are widely used in industries such as maritime search and capture, detection of illegal fishing, water quality monitoring, and water quality sampling. In the motion control of unmanned ships, the path tracking control of unmanned ships has become a research hotspot. Most of the existing path tracking methods do not consider the rudder steering torque model and the propeller longitudinal thrust model, directly select the steering torque and longitudinal thrust as control inputs, and do not comprehensively consider the types of environmental disturbances. There are too many coupling parts in the unmanned ship mathematical model. Applying conventional decoupling control methods requires a high precision of the mathematical model and the process is cumbersome; applying the feedback linearization method will lose the accuracy of the model, resulting in a large gap between the simulation effect and the actual situation. Therefore, finding a path tracking control method that does not rely on a high-precision mathematical model and can better resist external environmental disturbances is of great significance for the safety, accuracy, and efficiency of unmanned ships when performing tasks.

[0003] For the path tracking control method of unmanned ships, there are mainly sliding mode control, adaptive control, backstepping control, active disturbance rejection control, and so on. Active Disturbance Rejection Control (ADRC) can regard external disturbances, unmodeled dynamics of the model, etc. as total disturbances for real-time estimation and compensation, and has the advantages of strong anti-interference ability, simple structure, and not relying on the accuracy of the controlled object model. Decentralized Control is an efficient control strategy for solving coupled systems. Its idea is to regard the coupling part between subsystems as "external disturbances" for robust control processing, and make full use of the internal information of local subsystems to design relatively independent feedback controls, thereby controlling the entire system. Summary of the Invention

[0004] In view of the path tracking requirements of unmanned ships affected by environmental disturbances in the actual environment, the present invention proposes a path tracking control method for unmanned ships based on active disturbance rejection decentralized control, effectively solving the problem that the real disturbance environment affects the autonomous navigation of unmanned ships, and being able to better ensure the accuracy and safety of unmanned ships tracking a given path in a disturbed environment, and improving the robustness of the controller.

[0005] The path tracking control method for unmanned ships based on active disturbance rejection decentralized control provided by the present invention includes the following steps:

[0006] Step 1: Construct the mathematical model of the unmanned ship under the perturbed environment from the kinematic and dynamic perspectives successively. Consider the three perturbations of wind, wave and current in the environment to construct the mathematical model of the unmanned ship. At the same time, model the steering torque of the rudder and the longitudinal thrust of the propeller, and change the input of the path tracking control system of the unmanned ship to the propeller speed and the rudder angle of the rudder.

[0007] Step 2: Represent the path tracking control system of the unmanned ship as a two-input two-output control system composed of a longitudinal position subsystem and a heading subsystem. The control inputs are the propeller speed n and the rudder angle δ of the rudder respectively u , and the corresponding control outputs are the longitudinal position x and the heading angle of the unmanned ship respectively Define the heading control error and the longitudinal position control error, and construct linear extended state observers for the longitudinal position subsystem and the heading subsystem respectively as follows:

[0008]

[0009]

[0010] Among them, is the observed value of the longitudinal position subsystem, is the observed value of the heading subsystem, k represents the kth moment; h is the sampling step; β 01 , β 02 , β 03 are the observer gains; the control quantities u1 and u2 are used to control the propeller speed n and the rudder angle δ of the rudder respectively u ; e1 and e2 are the tracking errors of the longitudinal position subsystem and the heading subsystem respectively; y1 and y2 correspond to the actual longitudinal position x and the heading angle of the unmanned ship respectively

[0011] Step 3: Combine the decentralized control strategy and the active disturbance rejection control theory to construct an active disturbance rejection decentralized controller, which includes a longitudinal position controller and a heading controller. The corresponding nonlinear active disturbance rejection control laws of the longitudinal position controller and the heading controller are as follows:

[0012]

[0013] Among them, b1 and b2 are the control gains of the longitudinal position subsystem and the heading subsystem respectively, and are the estimated total disturbances of the longitudinal position subsystem and the heading subsystem, corresponding to the generated by the linear extended state observer of the longitudinal position subsystem and the generated by the linear extended state observer of the heading subsystem respectively; and are the nonlinear error feedback control laws respectively.

[0014] Step 4: Obtain the actual longitudinal position, lateral position, heading angle, and drift angle of the unmanned ship in real time, and estimate the total disturbance in real time through the linear extended state observers of the longitudinal position subsystem and the heading subsystem and Then input the total disturbance into the longitudinal position controller and the heading controller, calculate the tracking errors of the longitudinal position subsystem and the heading subsystem, and generate a nonlinear active disturbance rejection control law for the path tracking control of the unmanned ship.

[0015] The advantages and positive effects of the present invention are as follows:

[0016] (1) The mathematical model of the unmanned ship in the disturbance environment constructed by the method of the present invention, compared with the existing model, additionally considers the steering torque model of the steering gear and the longitudinal thrust model of the propeller, making the control input change from the steering torque and the longitudinal thrust to the propeller speed and the steering angle of the steering gear, which makes it easier to be applied in practice; and the method of the present invention simultaneously considers three kinds of disturbances of wind, wave, and current in the environment, and the considered disturbance factors are more comprehensive, and the disturbance environment is closer to the actual situation.

[0017] (2) Aiming at the problem of mutual coupling between the heading and longitudinal position subsystems of the unmanned ship, the method of the present invention combines the decentralized control strategy and the active disturbance rejection control theory to construct an active disturbance rejection decentralized controller, and regards the coupling part between the subsystems in the unmanned ship model as an "external disturbance" for real-time estimation and compensation, which can improve the robustness of the controller and improve the control accuracy.

[0018] (3) The method of the present invention constructs a linear extended state observer to estimate the internal and external disturbances in real time, and compensates the estimated value in the control law in real time, solves the problem that the environmental interference affects the control accuracy, and can better ensure the accuracy and safety of the unmanned ship tracking the given path in the disturbance environment, and improves the robustness of the controller. Description of the Drawings

[0019] Fig. 1(a) is a schematic diagram of the longitudinal position controller constructed by the method of the present invention;

[0020] Fig. 1(b) is a schematic diagram of the heading controller constructed by the method of the present invention;

[0021] Figure 2 is the schematic diagram of the overall active disturbance rejection decentralized controller of the method of the present invention for path tracking control of the unmanned ship;

[0022] Fig. 3(a) is an example diagram of the tracking result of the straight path in the embodiment of the present invention;

[0023] Fig. 3(b) is an example diagram of the tracking result of the curved path in the embodiment of the present invention. Detailed Embodiment

[0024] The present invention will be described in detail below with reference to the accompanying drawings and embodiments.

[0025] The present invention discloses an unmanned ship path tracking control method based on active disturbance rejection decentralized control. First, a mathematical model of the unmanned ship in a disturbance environment is constructed. Compared with the existing models, the steering torque model of the steering gear and the longitudinal thrust model of the propeller are considered, so that the control input changes from the steering torque and the longitudinal thrust to the propeller speed and the steering angle of the steering gear. At the same time, the present invention considers three kinds of disturbances of wind, wave and current in the environment. Then, aiming at the problem that environmental disturbances affect the control accuracy, the present invention constructs a linear extended state observer to estimate the internal and external disturbances. Finally, aiming at the problem of mutual coupling between the heading and longitudinal position subsystems of the unmanned ship, the present invention combines the decentralized control strategy and the active disturbance rejection control theory to construct an active disturbance rejection decentralized controller, and regards the coupling part between the subsystems in the unmanned ship model as "external disturbance" for real-time estimation and compensation. The present invention can better ensure the accuracy and safety of the unmanned ship tracking the given path in a disturbance environment and improve the robustness of the controller.

[0026] The unmanned ship path tracking control method based on active disturbance rejection decentralized control according to the embodiment of the present invention includes the following steps 1 to 4.

[0027] Step 1: Construct a mathematical model of the unmanned ship in a disturbance environment from the kinematic and dynamic perspectives in turn, and at the same time model the steering torque of the steering gear and the longitudinal thrust of the propeller, and set the inputs of the unmanned ship path tracking control to the propeller speed and the steering angle of the steering gear. The specific steps are as follows 101 to 106:

[0028] Step 101: The embodiment of the present invention constructs a 3-degree-of-freedom kinematic model of the unmanned ship in the hull coordinate system as follows:

[0029]

[0030] where: x and y respectively represent the longitudinal and lateral coordinate positions of the unmanned ship, u r and v r respectively represent the surge velocity and sway velocity of the unmanned ship relative to the water flow in the hull coordinate system, and r respectively represent the heading angle and angular velocity of the ship, V c is the flow velocity of the environmental flow, is the flow direction angle, is the angle between the oncoming flow direction and the o0x0 axis of the hull coordinate system, and the clockwise direction is the positive direction.

[0031] The components of the flow velocity V c on the hull coordinate axes can be expressed as:

[0032]

[0033] Among them, u c , v c respectively represent the longitudinal velocity and the lateral velocity of the flow relative to the earth.

[0034] Assume that the velocity components of the unmanned ship relative to the ground in the hull coordinate system are the surge velocity u and the sway velocity v respectively. Then, the acceleration components of the unmanned ship's motion relative to the water can be expressed as:

[0035]

[0036] Step 102: Further construct the dynamic model of the 3 degrees of freedom of the unmanned ship as follows:

[0037]

[0038] Among them, considering the action of the uniform flow, the angular velocity of the unmanned ship's yaw relative to the ground and the water flow is equal, both are r; X p is the longitudinal thrust generated by the propeller, X wind , Y wind are the average pressures acting on the ship by the wind in the x-direction and y-direction of the hull coordinate system, N wind is the moment acting on the ship by the wind about the z-direction of the hull coordinate system; X wave , Y wave are the average pressures acting on the ship by the wave in the x-direction and y-direction of the hull coordinate system, N wave is the moment acting on the ship by the wave about the z-direction of the hull coordinate system; m 11 , m 22 , m 33 respectively represent the components of the ship's inertia matrix on the three coordinate axes of the hull coordinate system, d 11 , d 22 , d 33 respectively represent the components of the ship's damping matrix on the three coordinate axes of the hull coordinate system; N R represents the steering torque of the steering gear.

[0039] Step 103: Establish a longitudinal thrust model of the propeller. The specific calculation formula for the propeller thrust X p is:

[0040]

[0041] Among them, t p is the thrust deduction coefficient, ρ is the water density, n is the propeller speed, D p is the propeller diameter, K T is the thrust coefficient of the propeller, J p is the advance coefficient of the propeller.

[0042] Step 104: Establish the steering torque model of the servo, and the steering torque N of the servo R The specific calculation formula is as follows:

[0043]

[0044] Among them, δ is the actual rudder angle, and δ u is the commanded rudder angle, T E is the time constant of the servo, x R is the longitudinal distance from the center of the rudder force to the center of gravity of the ship, a H is the ratio of the additional lateral force of the hull caused by steering to the lateral force of the rudder, x H is the distance from the center of the lateral force induced by steering to the center of gravity of the ship, F N is the normal pressure of the rudder, A R is the rudder area, U R is the effective oncoming flow velocity of the rudder, is the drift angle at the servo, f a is the slope of the lift coefficient of the rudder.

[0045] Step 105: Establish the calculation models of the average wind pressure and torque acting on the ship as follows:

[0046]

[0047] Among them, ρ a is the air density, U R is the relative wind speed, α R is the wind chord angle, that is, the angle between the wind direction and the bow direction of the ship, A f 、A s are the orthographic projection area and side projection area of the hull above the waterline respectively, C wx 、C wy are the longitudinal wind pressure coefficient and lateral wind pressure coefficient of the unmanned ship respectively, C wn (α R ) is the turning moment coefficient.

[0048] Step 106: Establish the calculation formulas for the wave drift force and torque:

[0049]

[0050] Among them, g is the acceleration due to gravity, ζ D is the average wave amplitude, C XD (λ), C YD (λ) and C ND (λ) are the wave drift moment coefficients in the x direction, y direction and around the z direction in the hull coordinate system respectively, λ is the wavelength, χ is the wave encounter angle, and L is the ship length.

[0051] Step 2: Regarding the problem that environmental interference affects control accuracy, construct a linear extended state observer to estimate and compensate for internal and external disturbances. The specific steps are as follows 201-205:

[0052] Step 201: On the basis of Step 1, the path tracking control system of the unmanned ship can be reduced to the following two-input two-output control system composed of a longitudinal position subsystem and a heading subsystem:

[0053]

[0054] Among them, each channel is a second-order system, and the control inputs are the propeller speed n and the rudder angle δ of the rudder u , the control gains of the two channels are b1 and b2 respectively, f1 and f2 are the total disturbances in the two channels respectively; y1 and y2 are the outputs of the two channels, corresponding to the actual longitudinal position x and the heading angle of the unmanned ship respectively

[0055] Step 202: Use the nonlinear combination form of the lateral position deviation y e =y - y d , the drift angle β and the heading angle as the new object of the path tracking control system of the unmanned ship, and the nonlinear combination expression of the controlled object z is:

[0056]

[0057] Among them, a0 and a1 are two coefficients greater than 0. a0 is used to compress the coordinates, and a1 is used to limit the amplitude. y d represents the desired lateral position, and y represents the actual lateral position.

[0058] Step 203: At this time, stabilize z, then there is The desired heading can be obtained as follows:

[0059]

[0060] Step 204: Define the heading control error and the longitudinal position control error x e as follows:

[0061]

[0062] Among them, x d is the lateral coordinate of the desired path, and x represents the actual lateral position.

[0063] Step 205: On the basis of the obtained two-input two-output control system composed of a longitudinal position subsystem and a heading subsystem, design the following linear extended state observer:

[0064]

[0065]

[0066] Among them, is the observation value of the longitudinal position subsystem, is the observation value of the heading subsystem, k represents the k-th moment; h is the sampling step; β 01 and β 02 and β 03 are the observer gains; e1 and e2 are the tracking errors of the longitudinal position subsystem and the heading subsystem respectively; u1 and u2 are two control variables, corresponding to the control of the propeller speed n and the rudder angle δ u .

[0067] Step 3: On the basis of Step 2, combine the decentralized control strategy and the active disturbance rejection control theory to construct an active disturbance rejection decentralized controller, which includes a longitudinal position controller and a heading controller. As shown in Figure 1(a), construct a longitudinal position controller, and as shown in Figure 1(b), construct a heading controller. The specific steps are as follows 301 to 305:

[0068] Step 301: Define the tracking errors of the two subsystems as follows:

[0069]

[0070]

[0071] Among them, are the two tracking errors of the longitudinal position subsystem, are the two tracking errors of the heading subsystem; is the observation value of the longitudinal position subsystem at the current moment, is the observation value of the heading subsystem at the current moment.

[0072] Step 302: Design the active disturbance rejection control laws for the longitudinal position deviation and the heading deviation as follows:

[0073]

[0074] Among them, k 1,1 and k 2,1 and k 1,2 and k 2,2 are all error feedback control gain parameters greater than zero, is the estimated value of the total disturbance generated by the linear extended state observer of the longitudinal position subsystem is the estimated value of the total disturbance generated by the linear extended state observer of the heading subsystem

[0075] Step 303: The PD (Proportional-Derivative) form error feedback control laws u 01 and u 02 for the two subsystems are as follows:

[0076]

[0077] where k 1,j and k 2,j (j = 1, 2) are parameters greater than zero, k 1,j represents the time constant, and k 2,j is used to adjust the system response speed.

[0078] Step 304: To improve the feedback efficiency and the accuracy of the control system, design the nonlinear error feedback control laws and for the two subsystems based on the PD form error feedback control laws as follows:

[0079]

[0080] In Fig. 1, NLSEF1 and NLSEF2 respectively represent the longitudinal position nonlinear error feedback control law and the heading nonlinear error feedback control law established based on the active disturbance rejection decentralized controller.

[0081] Step 305: Obtain the nonlinear active disturbance rejection control law:

[0082]

[0083] Step 4: As shown in Figure 2 , obtain the actual lateral position y and longitudinal position x of the unmanned ship, the actual heading angle and the drift angle β in real time, and combine with the desired lateral position y d to obtain the desired heading Input x into the linear extended state observer of the longitudinal position subsystem, calculate the longitudinal position control error, and estimate the observed value Input into the linear extended state observer of the heading subsystem, calculate the heading control error, and estimate the observed value In the two linear extended state observers, regard the coupling part between the heading subsystem and the longitudinal position subsystem, the external environmental disturbance, and the system unmodeled dynamics as the total disturbance, and estimate the total disturbance estimated value in real time and Input them into the longitudinal position controller and the heading controller respectively, adjust the parameters of the heading controller and the longitudinal position controller, and use the total disturbance estimated value and Compensation is carried out in real time in the control law, and finally the whole system is reduced to an integral series type, and the path tracking control of the unmanned ship is realized through active disturbance rejection decentralized control.

[0084] As shown in Fig. 3(a), it is an experimental result of using the method of the present invention to track a straight path of an unmanned ship; as shown in Fig. 3(b), it is an experimental result of using the method of the present invention to track a curved path of an unmanned ship. It can be seen from the tracking results that the method of the present invention realizes the accuracy of the unmanned ship tracking a given path in a disturbed environment, and has a high tracking accuracy. The unmanned ship path tracking controller realized by using the method of the present invention has high robustness and high control precision, and can better ensure the accuracy and safety of the unmanned ship tracking a given path in a disturbed environment.

[0085] Except for the technical features described in the specification, they are all well-known technologies to those skilled in the art. The present invention omits the description of well-known components and well-known technologies to avoid redundancy and unnecessary limitation of the present invention. The embodiments described in the above embodiments do not represent all embodiments consistent with the present application. Based on the technical solution of the present invention, various modifications or deformations that can be made by those skilled in the art without creative labor are still within the protection scope of the present invention.

Claims

1. An unmanned ship path tracking control method based on active disturbance rejection decentralized control, characterized in that It includes the following steps: Step 1: Construct a mathematical model of an unmanned boat in a perturbed environment from the perspectives of kinematics and dynamics. At the same time, model the steering torque of the rudder and the longitudinal thrust of the propeller, and set the inputs of the unmanned boat path tracking control system as the propeller speed and the rudder angle of the rudder. Step 2: Represent the unmanned ship path tracking control system as a two-input two-output control system consisting of a longitudinal position subsystem and a heading subsystem. The control inputs are the propeller speed n and the rudder angle δ of the rudder servo respectively u , and the corresponding control outputs are the longitudinal position x and the heading angle of the unmanned ship respectively Define the longitudinal position control error and the heading control error, and construct linear extended state observers for the longitudinal position subsystem and the heading subsystem respectively. In the two linear extended state observers, the coupling part between the longitudinal position subsystem and the heading subsystem, the external environmental disturbance, and the system unmodeled dynamics are regarded as disturbances to generate the observed values of the total disturbance and Step 3: Construct an active disturbance rejection decentralized controller, including a longitudinal position controller and a heading controller. The nonlinear active disturbance rejection control laws corresponding to the two controllers are as follows: where \(b_1\) and \(b_2\) are the control gains of the longitudinal position subsystem and the heading subsystem, respectively; and are the estimated total disturbances of the longitudinal position subsystem and the heading subsystem, corresponding to the observed values generated by the linear extended state observer of the longitudinal position subsystem and the observed values generated by the linear extended state observer of the heading subsystem obtained; and are the nonlinear error feedback control laws of the longitudinal position subsystem and the heading subsystem, respectively; Step 4: Obtain the actual longitudinal position, lateral position, heading angle, and drift angle of the unmanned ship in real time, and estimate the total disturbance in real time through the linear extended state observers of the longitudinal position subsystem and the heading subsystem. and Then input the total disturbance into the longitudinal position controller and the heading controller, calculate the tracking errors of the longitudinal position subsystem and the heading subsystem, and generate a nonlinear active disturbance rejection control law for the path tracking control of the unmanned ship.

2. The method according to claim 1, characterized in that, In step 2 mentioned above, linear extended state observers are constructed for the longitudinal position subsystem and the heading subsystem respectively as follows: Among them, is the observation value of the longitudinal position subsystem, is the observation value of the heading subsystem, k represents the k-th moment; h is the sampling step; β 01 , β 02 , β 03 are the observer gains; the control variables u1 and u2 are used to control the propeller speed n and the rudder angle δ u respectively; e1 and e2 are the tracking errors of the longitudinal position subsystem and the heading subsystem respectively; y1 and y2 correspond to the actual longitudinal position x and the heading angle of the unmanned ship 3. The method according to claim 2, characterized in that, Step 2 includes: Step 2.1: Construct a two-input two-output control system as follows: Among them, the two channels correspond to the longitudinal position subsystem and the heading subsystem respectively. Both channels are second-order systems, and f1 and f2 are the total disturbances of the two systems respectively. Step 202: Adopt the lateral position deviation y of the unmanned ship e = y - y d , the drift angle β, and the heading angle The nonlinear combination of is used as the new controlled object z of the unmanned ship path tracking control system and is expressed as follows: where a0 and a1 are two coefficients greater than 0, a0 is used to compress coordinates, a1 is used to limit the amplitude, y d represents the desired lateral position, and y represents the actual lateral position; Step 203: Stabilize the controlled object z, then there is Obtain the desired course as follows: Step 204: Define the heading control error and the longitudinal position control error x e as follows: where x d is the lateral coordinate of the desired path, and x represents the actual lateral position, is the actual heading angle; Step 205: Construct linear extended state observers for the longitudinal position subsystem and the heading subsystem respectively.

4. The method according to claim 1 or 2, characterized in that, In step 3 mentioned above, combining the decentralized control strategy and the active disturbance rejection control theory, construct a longitudinal position controller and a heading controller, including: Step 301: Define the tracking errors of the longitudinal position subsystem and the heading subsystem respectively as follows: Among them, are two tracking errors of the longitudinal position subsystem, are two tracking errors of the course subsystem; is the observed value of the longitudinal position subsystem at the current moment, is the observed value of the course subsystem at the current moment; x d is the lateral coordinate of the desired path, is the desired course; Step 302: Design the active disturbance rejection control laws for the longitudinal position deviation and the heading deviation respectively as: where k 1,1 , k 1,2 , k 2,1 , k 2,2 are all error feedback control gain parameters greater than zero, k 1,1 , k 1,2 represents the time constant, k 2,1 , k 2,2 is used to adjust the system response speed; is the estimated value of the total disturbance generated by the linear extended state observer of the longitudinal position subsystem is the estimated value of the total disturbance generated by the linear extended state observer of the heading subsystem Step 303: Obtain the PD-form error feedback control laws u of the longitudinal position subsystem and the heading subsystem 01 and u 02 as follows: Step 304: Further obtain the nonlinear error feedback control laws of the longitudinal position subsystem and the heading subsystem and are as follows: Step 305: Determine the nonlinear active disturbance rejection control laws of the longitudinal position controller and the heading controller.

5. The method according to claim 1, wherein In step 1 mentioned above, first consider the environmental flow to construct a kinematic model of the 3-degree-of-freedom unmanned boat in the hull coordinate system, then consider the wind and wave disturbances to construct a dynamic model of the 3-degree-of-freedom unmanned boat, and then establish a longitudinal thrust model of the propeller and a steering torque model of the rudder, establish a calculation model of the average wind pressure and torque acting on the boat, and a calculation model of the wave drift force and torque.

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