Spatial optical communication tracking system servo control method based on active disturbance rejection

Abstract

The invention discloses a space optical communication tracking system servo control method based on active disturbance rejection, and belongs to the technical field of optical communication, and the method comprises the steps: simplifying a typical coarse-fine two-stage capture tracking structure, employing a first-stage tracking design, building a coarse tracking system model, analyzing the internal and external disturbance of a system, and simulating a satellite vibration signal; an improved active-disturbance-rejection controller is designed and applied to the space optical communication coarse tracking process, the controller suppresses and eliminates disturbance and noise on the basis of an improved extended state observer, and a nonlinear function with a better effect is adopted for construction; the feasibility of the control algorithm and the tracking performance of the tracking system are verified through a static tracking experiment.

Description

Technical Field

[0001] The invention relates to the technical field of optical communication, and in particular to a servo control method for a space optical communication tracking system based on self-disturbance rejection. Background Art

[0002] Space laser communication, also known as wireless optical communication, is a point-to-point communication technology that uses laser as a carrier and the atmosphere as a transmission medium. It can be used to transmit information data between fixed or mobile platforms. This communication technology has the advantages of large capacity, high speed, low power consumption, good confidentiality and strong anti-interference. It is widely used in satellite-to-satellite communication and communication between space platforms and aircraft, ships and other mobile or fixed terminal ground platforms in the atmosphere.

[0003] Although wireless optical communication has obvious advantages in many aspects, there are still some key issues to be solved. Since the laser beam is extremely narrow and often works in a complex environment, the two terminals of laser communication are far apart and often maintain a high-speed relative motion state. In order to achieve the stable establishment of the communication link between the two terminals of laser communication, a good control method is needed to improve the control accuracy of the system and thus improve the tracking performance of the system.

[0004] Active disturbance rejection control (ADRC) is a nonlinear control theory of active disturbance rejection proposed by Chinese scholar Han Jingqing. It can estimate and compensate for internal and external disturbances before they affect the system, so as to eliminate the impact on the system and improve the control effect of the system. Compared with other controllers, ADRC does not need to understand the mathematical model of the control object. It can estimate the disturbance of the system in real time only through the extended state observer of ADRC, and compensate the system according to the disturbance size, thereby improving the control performance of the system.

[0005] Therefore, we propose a servo control method for space optical communication tracking system based on self-disturbance rejection. Summary of the invention

[0006] The purpose of the present invention is to provide a servo control method for a space optical communication tracking system based on auto-disturbance rejection in order to solve the influence of input beam jitter and external environmental interference on the tracking accuracy of a space optical communication system.

[0007] To achieve the above objectives, this application provides the following technical solutions:

[0008] The present application provides a servo control method for a space optical communication tracking system based on auto-disturbance rejection, comprising:

[0009] Simplify the typical coarse and fine two-stage capture and tracking structure, use a one-stage tracking design, establish a coarse tracking system model, and analyze the internal and external disturbances of the system;

[0010] Design an improved active disturbance rejection controller according to the system model;

[0011] The designed controller is mounted on the optical communication tracking platform for static tracking experiments.

[0012] Furthermore, in the step of establishing the coarse tracking system model, the following steps are specifically included:

[0013] The overall open-loop transfer function of the control system is:

[0014] In the formula, is an integrator, It is the first-order inertia link simplified from the inner loop, T is the motor inertia time constant, K1 is the ratio of motor speed to input voltage, K2 is the value related to the deceleration ratio, and K3 is the number of camera pixels per unit radian.

[0015] Furthermore, the design of an improved active disturbance rejection controller for application in the coarse tracking process specifically includes the following steps:

[0016] Rewrite it into the state equation form according to the rough tracking model;

[0017] Select a more effective nonlinear function to design an extended state observer;

[0018] Design an active disturbance rejection controller based on an extended state observer.

[0019] Furthermore, in the step of rewriting the rough tracking model into a state equation form, specifically:

[0020] Transform equation (1) into the state equation:

[0021] Among them, x1 represents the position signal of the light spot, x2 represents the speed of the light spot at this time, d(t) represents the total disturbance, f0(x1,x2,t)+bu is the nominal part of the object, b is the gain of the control voltage, and t is the independent variable.

[0022] Combining formula (1), we can get b = K1K2K3 / T,

[0023] Furthermore, in the step of selecting a nonlinear function with better effect, specifically:

[0024] The traditional nonlinear function fal function expression is as follows:

[0025]

[0026] In order to solve the problem that the fal function is continuous but not smooth, which will lead to poor control performance of the system, the traditional nonlinear function is optimized and recorded as fal *, which is expressed as follows:

[0027]

[0028] The designed extended state observer ESO is:

[0029]

[0030] Furthermore, in the step of designing an active disturbance rejection controller based on an extended state observer, specifically:

[0031] Use ESO (denoted as ESO1) to observe the disturbance of the system, and then use the observed results as known quantities and input them into another ESO (denoted as ESO2) to better analyze the changes in the system and more accurately measure the remaining disturbance. Finally, the overall observed disturbance is compensated to the output of the controller to suppress the disturbance.

[0032] The state equation of ESO1 is as follows:

[0033]

[0034] By converting the ESO1 observation z 12 Treat it as a known quantity and input it into ESO2 to obtain the expression of ESO2:

[0035]

[0036] In the formula, z 22 is the ESO2 observed disturbance.

[0037] Using proportional control as feedback control compensation, the final output of the controller can be obtained through the feedback output and the observer output:

[0038]

[0039] Furthermore, in the step of mounting the designed controller on the optical communication tracking platform for a static tracking experiment, the following are specifically performed:

[0040] A laser spot is projected onto a screen, and then the turntable is started to track the static light spot. The static tracking error is calculated by the deviation of the turntable from the static target.

[0041] The present application provides a servo control method for a space optical communication tracking system based on self-disturbance rejection, which has the following beneficial effects:

[0042] This application establishes a coarse tracking system model, simplifies the typical coarse-fine two-stage capture and tracking structure, designs an improved anti-disturbance controller, estimates the disturbance of the system and suppresses the external environmental noise, thereby eliminating the influence of the disturbance on the controller and improving the control performance of the anti-disturbance controller. It can effectively solve the influence of input beam jitter and external environmental interference on the tracking accuracy of the space optical communication system and improve the tracking accuracy of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for describing the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work. Among them:

[0044] Figure 1 It is a closed-loop cascade control block diagram of the space optical communication tracking system of the present invention.

[0045] Figure 2 This is a simplified rough tracking control structure block diagram after adding disturbance influence of the present invention.

[0046] Figure 3 The figure shows the comparison of the function curves of the improved nonlinear fal function of the present invention and the original function at the segmentation points.

[0047] Figure 4 This is a control block diagram of the active disturbance rejection controller based on the cascade extended state observer of the present invention.

[0048] Figure 5 This is a schematic diagram of the static tracking experiment of the present invention. DETAILED DESCRIPTION

[0049] In order to make the above-mentioned purposes, features and advantages of the present invention clearer and easier to understand, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0050] This embodiment provides a servo control method for a space optical communication tracking system based on auto-disturbance rejection. Figure 1 This is a closed-loop cascade control block diagram of a space optical communication tracking system, which is implemented in the following steps:

[0051] Step 1: Simplify the typical coarse-fine two-stage capture and tracking structure, use a one-stage tracking design, establish a coarse tracking system model, and analyze the internal and external disturbances of the system;

[0052] Specifically, a typical capture and tracking system is usually divided into two modules: coarse tracking and fine tracking. The coarse tracking module is used to complete initial positioning in a larger field of view, capture the position of the other party's communication terminal, and guide one's own communication terminal to position the light beam in the small field of view required for fine tracking; the fine tracking module improves the tracking accuracy of the system through small-range, high-frequency optical path correction, and realizes more accurate optical path tracking based on coarse tracking; the present invention chooses to use a first-level tracking design to improve the tracking accuracy of the coarse tracking system, and adopts coarse tracking to compensate for the deflection of fine tracking.

[0053] Furthermore, the coarse tracking system is mainly composed of a capture detector, a servo controller, a motor position sensor and a servo mechanism. The function of the servo controller is to control the servo mechanism to complete the specified command, that is, to guide the light beam to the target position through the rotation of the servo mechanism. The servo controller and servo mechanism are collectively referred to as a servo control system. The control accuracy affects whether the light beam can be introduced into the fine tracking field of view, which directly determines whether the communication link can be successfully established.

[0054] In this embodiment, the internal and external disturbances of the system are analyzed. According to the requirements of the system, the sources of disturbances can be divided into internal disturbances N1(s) caused by internal nonlinearity and model uncertainty and external disturbances N2(s) caused by the external environment. Disturbance N1(s) affects the change of internal parameters, and disturbance N2(s) affects the target signal position.

[0055] Based on the above analysis, the simplified coarse tracking control structure block diagram after adding disturbance influence is as follows: Figure 2 As shown. G is the position controller, is an integrator, It is the first-order inertia link simplified from the inner loop, K1 is the ratio of motor speed to input voltage, K2 is the value related to the deceleration ratio, and K3 is the number of camera pixels per unit radian. r is the given target signal, u is the control voltage signal, ω is the motor rotation speed, θ is the motor rotation angle, T is the motor inertia time constant, and y is the output of the spot in the camera field of view relative to the center of the field of view.

[0056] Therefore, the overall open-loop transfer function of the control system is:

[0057] Step 2: Design an improved anti-disturbance controller and apply it to the coarse tracking process of space optical communication. The controller suppresses and eliminates disturbances and noise based on an improved extended state observer and is constructed using a nonlinear function with better effects.

[0058] In this embodiment, the steps of designing the improved active disturbance rejection controller specifically include the following steps 2.1 to 2.3, and the implementation method of each step is described in detail below.

[0059] Step 2.1: Rewrite the coarse tracking model into the state equation form.

[0060] According to the coarse tracking model, the position of the light spot relative to the center of the camera field of view and the relative speed of the light spot at this time are defined as two state variables x1 and x2 respectively, and then the output y and the given control voltage signal input u are defined, and equation (1) is transformed into the state equation:

[0061]

[0062] Among them, x1 represents the position signal of the light spot, x2 represents the speed of the light spot at this time, d(t) represents the total disturbance, f0(x1,x2,t)+bu is the nominal part of the object, b is the gain of the control voltage, and t is the independent variable.

[0063] Combining formula (1), we can get b = K1K2K3 / T,

[0064] Step 2.2: Select a more effective nonlinear function to design the extended state observer.

[0065] The traditional nonlinear function fal function expression is as follows:

[0066]

[0067] In order to solve the problem that the fal function is continuous but not smooth, which will lead to poor control performance of the system, the traditional nonlinear function is optimized and recorded as fal * , which is expressed as follows:

[0068]

[0069] The improved function curve is compared with the original curve. Figure 3 As shown, it can be seen that the improved fal * The (e, α, δ) function is smoother than before, and is continuous and differentiable at |e| = δ. In addition, the influence of the δ value on the entire curve is reduced, and the mutation phenomenon is significantly weakened, which can effectively reduce the high-frequency chattering phenomenon caused by nonlinear functions.

[0070] The new optimal control function fal * Function replaces the fal function, and the designed extended state observer ESO is:

[0071]

[0072] Step 2.3: Design an active disturbance rejection controller based on the cascade extended state observer.

[0073] The design idea of ​​the cascade extended state observer is to use ESO (denoted as ESO1) to observe the disturbance of the system, and then use the observed result as a known quantity and input it into another ESO (denoted as ESO2) to better analyze the changes in the system and more accurately measure the remaining disturbance. Finally, the overall observed disturbance is compensated to the output of the controller to suppress the disturbance.

[0074] See also Figure 4 , which is a control block diagram of an active disturbance rejection controller based on a cascade extended state observer according to an embodiment of the present application.

[0075] The state equation of ESO1 is as follows:

[0076]

[0077] By converting the ESO1 observation z 12 Treat it as a known quantity and input it into ESO2 to obtain the expression of ESO2:

[0078]

[0079] In the formula, z 22 is the ESO2 observed disturbance.

[0080] Using proportional control as feedback control compensation, the final output of the controller can be obtained through the feedback output and the observer output:

[0081]

[0082] Step 3: Mount the designed controller on the optical communication tracking platform to conduct a static tracking experiment to verify the feasibility of the control algorithm and the tracking performance of the tracking system.

[0083] Specifically, a laser spot is projected onto a screen, and then a turntable is started to track the static light spot. The static tracking error is calculated through the deviation of the turntable from the static target.

[0084] See also Figure 5 , which is a schematic diagram of the static tracking experiment principle of an embodiment of the present application.

[0085] In this embodiment, a projection screen dedicated to the projector is used as a beacon laser receiving target surface, and a movable two-dimensional turntable equipped with a laser is placed at a distance. By adjusting the direction of the turntable, the laser irradiates the laser spot to the center of the projection screen, forming a laser spot as a target.

[0086] At the beginning of the experiment, the turntable's tracking function is activated to capture the laser target aimed at the center of the screen. During the tracking process, the direction and trajectory of the target can be controlled by adjusting the direction of the optical turntable to test the tracking performance of the system.

[0087] Among them, x1 is the horizontal angle of the beacon laser, y1 is the pitch angle of the beacon laser, x2 is the horizontal angle of the turntable, y2 is the pitch angle of the turntable, s1 is the vertical distance between the laser and the curtain, and s2 is the vertical distance between the turntable and the curtain. x1 and y1 can be read directly through the encoder, s1 and s2 can be obtained by measurement, and x2 and y2 are theoretical values ​​calculated. The actual horizontal and pitch angles can be obtained through the encoder of the turntable, and the static tracking error can be obtained by comparing with the theoretical value.

[0088] where x2 and y2 are calculated as follows:

[0089]

[0090] The above-mentioned servo control method of the space optical communication tracking system based on auto-disturbance rejection establishes a coarse tracking system model, simplifies the typical coarse-fine two-stage capture and tracking structure, designs an improved auto-disturbance rejection controller, estimates the disturbance of the system and suppresses the external environmental noise, thereby eliminating the influence of the disturbance on the controller and improving the control performance of the auto-disturbance rejection controller. It can effectively solve the influence of input beam jitter and external environmental interference on the tracking accuracy of the space optical communication system and improve the tracking accuracy of the system.

[0091] Finally, it should be noted that the above description is only used to illustrate the technical solution of the present invention, rather than to limit it; although the present invention has been described in detail with reference to the aforementioned embodiments, it is still possible for a person skilled in the art to modify the technical solutions described in the aforementioned embodiments, or to replace some of the technical features therein by equivalents. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A servo control method for a space optical communication tracking system based on auto-disturbance rejection, characterized in that: The following steps are involved: Step 1: Simplify the typical coarse-fine two-stage capture and tracking structure, use a one-stage tracking design, establish a coarse tracking system model, and analyze the internal and external disturbances of the system; Step 2, design an improved anti-disturbance controller and apply it to the rough tracking process of space optical communication. The controller suppresses and eliminates disturbances and noise based on an improved extended state observer and is constructed using a nonlinear function with better effect. Step 3: Mount the designed controller on the optical communication tracking platform to conduct a static tracking experiment to verify the feasibility of the control algorithm and the tracking performance of the tracking system.

2. According to claim 1, a servo control method for a space optical communication tracking system based on auto-disturbance rejection is characterized in that: In the steps of simplifying the typical coarse-fine two-stage capture and tracking structure, specifically: A typical capture and tracking system is usually divided into two modules: coarse tracking and fine tracking. The coarse tracking module is used to complete the initial positioning in a larger field of view, capture the position of the other party's communication terminal, and guide the own communication terminal to position the light beam in the small field of view required for fine tracking; the fine tracking module improves the tracking accuracy of the system through small-range, high-frequency optical path correction, and realizes more accurate optical path tracking on the basis of coarse tracking. The typical coarse-fine two-stage capture and tracking structure is simplified, a one-stage tracking design is used, the tracking accuracy of the coarse tracking system is improved, and coarse tracking is used to compensate for the fine tracking deflection.

3. The servo control method of a space optical communication tracking system based on auto-disturbance rejection according to claim 2 is characterized in that: The coarse tracking system is mainly composed of a capture detector, a servo controller, a motor position sensor and a servo mechanism; The function of the servo controller is to control the servo mechanism to complete the specified command, that is, to guide the light beam to the target position through the rotation of the servo mechanism. The servo controller and servo mechanism are collectively referred to as a servo control system. The control accuracy affects whether the light beam can be introduced into the precision tracking field of view, which directly determines whether the communication link can be successfully established.

4. The servo control method of a space optical communication tracking system based on auto-disturbance rejection according to claim 1, characterized in that: The steps of establishing a rough tracking system model specifically include the following steps: According to the system requirements, the sources of disturbance can be divided into internal disturbance N1(s) caused by internal nonlinearity and model uncertainty and external disturbance N2(s) caused by the external environment; disturbance N1(s) affects the change of internal parameters, and disturbance N2(s) affects the target signal position; based on the above analysis, the coarse tracking control structure is simplified after adding the disturbance effect, and the total open-loop transfer function of the control system is obtained as follows: In the formula, is an integrator, It is the first-order inertia link simplified from the inner loop, T is the motor inertia time constant, K1 is the ratio of motor speed to input voltage, K2 is the value related to the deceleration ratio, and K3 is the number of camera pixels per unit radian.

5. The servo control method of a space optical communication tracking system based on auto-disturbance rejection according to claim 1, characterized in that: Designing an improved active disturbance rejection controller and applying it to the coarse tracking process includes the following steps: Rewrite it into the state equation form according to the rough tracking model; Select a more effective nonlinear function to design an extended state observer; Design an active disturbance rejection controller based on an extended state observer.

6. The servo control method of a space optical communication tracking system based on auto-disturbance rejection according to claim 5, characterized in that: Rewrite the rough tracking model into the state equation form, which specifically includes the following steps: According to the coarse tracking model, the position of the light spot relative to the center of the camera field of view and the relative speed of the light spot at this time are defined as two state variables x1 and x2 respectively, and then the output y and the given control voltage signal input u are defined, and equation (1) is transformed into the state equation: Among them, x1 represents the position signal of the light spot, x2 represents the speed of the light spot at this time, d(t) represents the total disturbance, f0(x1,x2,t)+bu is the nominal part of the object, b is the gain of the control voltage, and t is the independent variable; It is concluded that b = K1K2K3 / T, 7. The servo control method of a space optical communication tracking system based on auto-disturbance rejection according to claim 5, characterized in that: A more effective nonlinear function is selected to construct an extended state observer, specifically: The traditional nonlinear function fal function expression is as follows: In order to solve the problem that the fal function is continuous but not smooth, which will lead to poor control performance of the system, the traditional nonlinear function is optimized and recorded as fal * , which is expressed as follows: The designed extended state observer ESO is:

8. The servo control method of a space optical communication tracking system based on auto-disturbance rejection according to claim 5, characterized in that: Design an active disturbance rejection controller based on a cascade extended state observer, specifically: Use ESO (denoted as ESO1) to observe the disturbance of the system, and then use the observed results as known quantities and input them into another ESO (denoted as ESO2) to better analyze the changes in the system and more accurately measure the remaining disturbance. Finally, the overall observed disturbance is compensated to the output of the controller to suppress the disturbance. The state equation of ESO1 is as follows: By converting the ESO1 observation z 12 Treat it as a known quantity and input it into ESO2 to obtain the expression of ESO2: In the formula, z 22 is the ESO2 observation disturbance; Using proportional control as feedback control compensation, the final output of the controller can be obtained through the feedback output and the observer output:

9. The servo control method of a space optical communication tracking system based on auto-disturbance rejection according to claim 1, characterized in that: The controller is mounted on the optical communication platform to conduct static tracking experiments, specifically: A laser spot is projected onto a screen, and then the turntable is started to track the static light spot. The static tracking error is calculated by the deviation of the turntable from the static target.

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