CN111650947A - A non-linear control method for stratospheric airship height - Google Patents

Abstract

The invention discloses a non-linear control method for the height of a stratospheric airship, belonging to the field of airship flight control. It only needs to measure the height signal and compare it with the desired height command to form the height error signal. At the same time, nonlinear transformation and integration are used to form terminal sliding mode signal. At the same time, a differential dislocation device is constructed to obtain the differential dislocation signal of the terminal sliding mode signal, which provides damping for the system. Then a disturbance observer is constructed to observe and estimate the nonlinear term and uncertainty of the altitude channel. Finally, the final desired signal of airship pitch angle is formed by the terminal sliding mode signal, disturbance observation signal and differential dislocation signal, which is carried out by the airship attitude stabilization system. Tracking, and finally achieve highly precise and stable control of the stratospheric airship. The advantage of this method is that it has good adaptability to both high-altitude signals and small-altitude signals, and at the same time, the altitude control is stable, and the dynamic characteristics of the transition process are good, which is very suitable for the altitude control of stratospheric airships.

Description

A non-linear control method for stratospheric airship height

technical field

The invention belongs to the field of aircraft flight guidance, in particular to a highly nonlinear control method of a stratospheric airship.

Background technique

The stratospheric airship has the characteristics of low flight speed and large flight aerodynamic shape, which leads to large control delay and slow attitude response. At the same time, the mission platform of the airship generally requires that the climbing process of the aircraft is very stable, which is conducive to the safety of its cargo. Take the altitude control of general aircraft as an example to ensure that the altitude control has sufficient stability margin and smoothness. Generally, it is necessary to measure the differential of the altitude signal, which increases the control cost. At the same time, the altitude control scheme of the high-speed moving aircraft cannot be directly copied to the control of the stratospheric airship. The main reason is that its speed is too fast, and the altitude control cannot be guaranteed under the action of the differential signal.

Based on the above background technology, the present invention adopts a nonlinear control method based on terminal sliding mode, which only needs to measure the height signal, provide damping signal through the dislocation difference method, and use the interference observation method to provide strong adaptive ability, so that the final height The control has good robustness, and the height control effect also has good dynamic characteristics.

It should be noted that the information disclosed in the above Background section is only for enhancing understanding of the background of the invention, and therefore may include information that does not form the prior art known to a person of ordinary skill in the art.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a non-linear control method for the height of a stratospheric airship, thereby at least to a certain extent overcome the problems of insufficient stability and robustness of the height control of the stratospheric airship caused by the traditional height control method.

The invention provides a non-linear control method for the height of a stratospheric airship, comprising the following steps:

Step S10: using an altimeter to measure the flight altitude of the stratospheric airship, setting a desired altitude command according to the control task, and comparing to obtain the altitude error;

Step S20: Design a terminal nonlinear term according to the height error signal, and perform integration to obtain a nonlinear integrated signal, and then form a terminal sliding mode signal;

Step S30: designing a differential dislocation device according to the terminal sliding mode signal to obtain a differential dislocation signal of the terminal sliding mode signal;

Step S40: Design an altitude channel interference observer according to the altitude error signal to obtain an interference observation signal;

Step S50: Design the final expected signal of the pitch angle of the stratospheric airship according to the terminal sliding mode signal, the differential dislocation signal and the interference observation signal, and send it to the airship attitude control system to realize altitude control.

In an exemplary embodiment of the present invention, the terminal type nonlinear term is designed and integrated to obtain a nonlinear integral signal, and then forming a terminal sliding mode signal includes:

e _h =hh ^d ;

s _ef =∫e _f1 dt;

s ₁ =c ₅ e _h +c ₆ s _ef ;

where e _h is the height error signal, h ^d is the desired height command set according to the flight mission of the stratospheric airship, h is the actual height of the stratospheric airship, e _f1 is the terminal nonlinear term, c ₁ , c ₂ , c ₃ , c ₄ is a constant value parameter, and its detailed design is shown in the following case implementation. s _ef is the integral of the terminal nonlinear term, s ₁ is the terminal sliding mode signal, and c ₅ and c ₆ are constant value parameters. The detailed design is shown in the following case implementation.

In an exemplary embodiment of the present invention, designing a differential dislocation device to obtain the differential dislocation signal of the terminal sliding mode signal includes:

s _d1 =(s ₁ -y ₁ )/T ₁ ;

When n≥1, y ₁ (n+1)=y ₁ (n)+s _d1 T;

s _d2 =(s ₁ -y ₂ )/T ₂ ;

When n≥1, y ₂ (n+1)=y ₂ (n)+s _d2 T;

s ₁ is the terminal sliding mode signal, y ₁ and y ₂ are the output signals of the first and second differentiators respectively, and their initial values are both 0, y ₁ (1)=0, y ₂ (1 )=0. s _d1 and s _d2 are the growth signals of the first and second differentiators, respectively, and T ₁ and T ₂ are time constants. The detailed design is shown in the following case implementation. y ₁ (n) is the nth data of the output signal y ₁ of the first differentiator, and T is the time interval between the data. The detailed design is shown in the following case implementation. y ₂ (n) is the n-th data of the output signal y ₂ of the second differentiator. s _d is the required differential dislocation signal.

In an exemplary embodiment of the present invention, designing a height channel interference observer, and obtaining the interference observation signal includes:

为干扰观测信号为，k₁、k₂、k₆为常值参数，其详细设计见后文案例实施，θ^d为俯仰角指令信号，其详细设计见下一步设计，其初始值可以选取为0，即θ^d(1)＝0。其中T为数据间的时间间隔，与差分器的设置相同即可。Among them, z is the state variable of the disturbance observer, and its initial value is zero, that is, z(1)=0.

In order to interfere with the observation signal, k ₁ , k ₂ , and k ₆ are constant value parameters, and the detailed design is shown in the following case implementation, θ ^d is the pitch angle command signal, and the detailed design is shown in the next design. 0, that is, θ ^d (1)=0. Among them, T is the time interval between data, which is the same as the setting of the differentiator.

In an exemplary embodiment of the present invention, according to the terminal sliding mode signal, the differential dislocation signal and the interference observation signal, designing the final desired signal of the pitch angle of the stratospheric airship includes:

为干扰观测信号，θ^d为最终的平流层飞艇俯仰角期望信号，其初始值选为0，k₃、k₄、k₅、k₇为常值参数，其详细设置见后文案例实施。where s ₁ is the terminal sliding mode signal, s _d is the differential dislocation signal,

In order to interfere with the observation signal, θ ^d is the final expected signal of the pitch angle of the stratospheric airship, and its initial value is selected as 0, and k ₃ , k ₄ , k ₅ , and k ₇ are constant parameters.

On this basis, let the aircraft attitude control system track the final desired signal of the pitch angle of the stratospheric airship, which can eliminate the altitude control error and realize the altitude control of the stratospheric airship.

beneficial effect

The present invention provides a non-linear control method for the height of a stratospheric airship. One of its advantages lies in that a new type of terminal sliding mode is used to combine the height error signals, so that the final height control method has very good effects on both large and small signals. good adaptability. At the same time, a disturbance observer is used to estimate the nonlinearity and uncertainty of the triangular variation between the height signal and the pitch angle signal in the height channel, so that the final height nonlinear control method has good robustness. Finally, this highly nonlinear method only needs to measure the height signal, and uses the dislocation differential method to provide damping, but does not need to measure the velocity signal to provide damping, so it has the characteristics of clear physical meaning, simple implementation, and smooth signal, and finally makes the height change very gentle. , which is very suitable for the practical application needs of stratospheric airships.

It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention.

Description of drawings

The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the invention and together with the description serve to explain the principles of the invention. Obviously, the drawings in the following description are only some embodiments of the present invention, and for those of ordinary skill in the art, other drawings can also be obtained from these drawings without creative effort.

Fig. 1 is the design implementation flow chart of a kind of stratospheric airship height nonlinear control method provided by the present invention;

Fig. 2 is the flight height curve (unit: meter) of the stratospheric airship of the method provided by the embodiment of the present invention;

3 is a nonlinear integral signal curve (unitless) of a method provided by an embodiment of the present invention;

4 is a terminal sliding mode signal (unitless) of a method provided by an embodiment of the present invention;

5 is a differential misalignment signal curve (unitless) of a method provided by an embodiment of the present invention;

Fig. 6 is the interference observation signal curve (unitless) of the method provided by the embodiment of the present invention;

FIG. 7 is a desired signal of the pitch angle of the stratospheric airship (unit: degree) of the method provided by the embodiment of the present invention;

8 is a pitch rudder declination signal curve (unit: degree) of a stratospheric airship according to a method provided by an embodiment of the present invention;

Fig. 9 pitch angle signal curve (unit: degree) of the stratospheric airship according to the method provided by the embodiment of the present invention;

Detailed ways

Example embodiments will now be described more fully with reference to the accompanying drawings. Example embodiments, however, can be embodied in various forms and should not be construed as limited to the examples set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the concept of example embodiments to those skilled in the art. The described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. In the following description, numerous specific details are provided in order to give a thorough understanding of the embodiments of the present invention. However, those skilled in the art will appreciate that the technical solutions of the present invention may be practiced without one or more of the specific details, or other methods, components, devices, steps, etc. may be employed. In other instances, well-known solutions have not been shown or described in detail to avoid obscuring aspects of the present invention.

The present invention is a non-linear control method for the height of a stratospheric airship, which mainly forms a terminal sliding mode signal by nonlinear integration of the height error signal, and at the same time adopts a differential dislocation method to obtain the dislocation difference of the terminal sliding mode signal, thereby providing a damping signal for the system. Then, according to the disturbance observer, the nonlinearity and uncertainty of the height channel inconvenient to measure and calculate are estimated and observed, and the final height nonlinear control method is formed. Due to the strong robustness brought by the terminal sliding mode and the adaptive capability brought by the disturbance observer, it is especially suitable for the altitude control of stratospheric airships.

Hereinafter, a method for nonlinear control of the height of a stratospheric airship mentioned in the example embodiments of the present invention will be explained and described with reference to the accompanying drawings. Referring to Figure 1, a method for nonlinear control of the height of a stratospheric airship may include the following steps:

Step S10: Measure the flight height of the stratospheric airship by using an altimeter, set a desired height command according to the control task, and compare to obtain the height error.

Specifically, first, according to the flight mission of the stratospheric airship, a desired altitude command is set, denoted as h ^d . Next, measure the height of the stratospheric airship through an altimeter or other height measuring device, denoted as h. Finally, the height error signal is obtained by comparison, denoted as e _h . It is defined as: e _h =hh ^d .

Step S20: Design a terminal type nonlinear term according to the height error signal, and perform integration to obtain a nonlinear integral signal, and then form a terminal sliding mode signal.

Specifically, first, according to the height error signal, the following terminal nonlinear term is designed, denoted as e _f1 , and its calculation method is as follows:

Among them, c ₁ , c ₂ , c ₃ , and c ₄ are constant value parameters, and the detailed design is shown in the following case implementation.

Secondly, perform integration according to the terminal nonlinear term to obtain the terminal integration signal, denoted as s _ef , and the integration operation is as follows:

s _ef =∫e _f1 dt;

Finally, according to the height error signal and the terminal integral signal, a terminal sliding mode signal is combined into a terminal sliding mode signal, denoted as s ₁ , and its calculation method is as follows:

s ₁ =c ₅ e _h +c ₆ s _ef ;

Among them, c ₅ and c ₆ are constant value parameters, and the detailed design is shown in the following case implementation.

Step S30: Design a differential dislocation device according to the terminal sliding mode signal to obtain a differential dislocation signal of the terminal sliding mode signal.

Specifically, first, build a first differentiator according to the terminal sliding mode signal s ₁ , set the output signal of the first differentiator as y ₁ , and set its initial value to 0, that is, y ₁ (1)=0 , find the growth signal of the first differentiator as s _d1 , the calculation method is:

s _d1 =(s ₁ -y ₁ )/T ₁ ;

Among them, T ₁ is the time constant, and its detailed design is shown in the following case implementation. Then calculate the nth data y ₁ (n) of the output signal y ₁ of the first differentiator according to the following recursive formula

When n≥1, y ₁ (n+1)=y ₁ (n)+s _d1 T;

Among them, T is the time interval between data, and its detailed design is shown in the implementation of the following case.

Secondly, first, build a second differentiator according to the terminal sliding mode signal s ₁ , set the output signal of the second differentiator as y ₂ , and set its initial value to 0, that is, y ₂ (1)=0, Find the growth signal of the second differentiator as s _d2 , which is calculated as:

s _d2 =(s ₁ -y ₂ )/T ₂ ;

Among them, T ₂ is the time constant, and its detailed design is shown in the following case implementation. Then calculate the nth data y ₂ (n) of the output signal y ₂ of the second differentiator according to the following recursive formula

When n≥1, y ₂ (n+1)=y ₂ (n)+s _d2 T;

Where T is the time interval between data, which is the same as the setting of the first differentiator.

Finally, the differential dislocation signal is solved according to the output signal y ₁ of the first differentiator and the output signal y ₂ of the second differentiator, denoted as s _d , and the calculation method is as follows:

Step S40: Design an altitude channel interference observer according to the altitude error signal to obtain an interference observation signal.

其计算方式如下：Specifically, first, the initial value of the disturbance observer state variable z is set to zero, that is, z(1)=0. Second, set the interference observation signal as

It is calculated as follows:

Finally, the state variable z of the disturbance observer is calculated recursively according to the following disturbance observer:

Among them, k ₁ , k ₂ , and k ₆ are constant value parameters, and the detailed ^design is shown in the implementation of the following ^case . (1)=0. Among them, T is the time interval between data, which is the same as the setting of the differentiator.

Step S50: Design the final expected signal of the pitch angle of the stratospheric airship according to the terminal sliding mode signal, the differential dislocation signal and the interference observation signal, and send it to the airship attitude control system to realize altitude control.

设计最终的平流层飞艇俯仰角期望信号，记作θ^d，其初始值选为0，后续计算如下：Specifically, according to the terminal sliding mode signal s ₁ , the differential dislocation signal s _d and the interference observation signal

The final expected signal of the pitch angle of the stratospheric airship is designed, denoted as θ ^d , and its initial value is selected as 0, and the subsequent calculation is as follows:

Among them, k ₃ , k ₄ , k ₅ , and k ₇ are constant value parameters, and the detailed settings are shown in the following case implementation.

Then, the desired pitch angle signal is sent to the pitch channel attitude control system of the stratospheric airship, and attitude control is performed, so that the actual pitch angle of the stratospheric airship tracks the desired pitch angle command θ ^d , so that the height of the stratospheric airship can be adjusted. Among them, the stratospheric airship attitude control system is relatively complex, and there are corresponding disclosed design methods, and the content not protected by this patent will not be repeated here.

Case implementation and analysis of computer simulation results

In order to verify the effectiveness of the method provided by the example of the present invention, the following case simulation is carried out.

采用高度表测量平流层飞艇的飞行高度如图2所示。In step S10, a desired height command is set, denoted as

Using an altimeter to measure the flight height of the stratospheric airship is shown in Figure 2.

In step S20, c ₁ =0.01, c ₂ =0.01, c ₃ =0.01, and c ₄ =3 are selected to obtain a nonlinear integral signal as shown in FIG. 3 . Finally, c ₅ =0.08 and c ₆ =0.5 are selected to form a terminal sliding mode signal as shown in FIG. 4 .

In step S30, T ₁ =10, T ₂ =20, and T = 0.2 are selected, and the differential dislocation signal of the terminal sliding mode signal is obtained as shown in FIG. 5 .

In step S40, k ₁ =0.05, k ₂ =0.01, k ₃ =0.02 are selected to design a height channel interference observer, and the interference observation signal is obtained as shown in FIG. 6 .

In step S50, k ₃ =15, k ₇ =200, k ₄ =0.02, and k ₅ =0.02 are selected to obtain the final desired signal of the pitch angle of the stratospheric airship as shown in FIG. 7 . The final pitch angle of the stratospheric airship is shown in Figure 8, and the pitch angle of the stratospheric airship is shown in Figure 9.

It can be seen from Figure 2 that the altitude control of the final stratospheric airship can well complete the tracking control task of the size and altitude commands, and the flight is stable. Before 800 seconds, it is a low-altitude flight mission, and after 800 seconds, it is a high-altitude flight mission. It can be seen from Figure 7 and Figure 9 that the pitch angle of the airship can smoothly track the pitch angle command task. At the same time, it can be seen from Figure 8 that the maximum pitch angle command of the airship is not greater than 30 degrees, so it can meet the needs of engineering control. It can be seen from Figure 4, Figure 5 and Figure 6 that the magnitude of the interference observation signal is relatively consistent with the sliding mode signal and the differential error signal. At the same time, because the signal itself is relatively large, the corresponding control parameters are also relatively small. reasonable. To sum up, it can be seen that the method provided by the example of the present invention has reasonable signal matching, clear physical meaning, and at the same time, the stratospheric airship has the characteristics of relatively stable and accurate tracking of both height and size signals, so it has high practical value.

Other embodiments of the invention will readily occur to those skilled in the art upon consideration of the specification and practice of the invention disclosed herein. This application is intended to cover any variations, uses or adaptations of the invention which follow the general principles of the invention and which include common knowledge or conventional techniques in the art to which the invention is not invented . The specification and examples are to be regarded as exemplary only, with the true scope and spirit of the invention being indicated by the claims.

Claims (5)

1. a stratospheric airship height nonlinear control method, is characterized in that, comprises the following steps: Step S10: using an altimeter to measure the flight altitude of the stratospheric airship, setting a desired altitude command according to the control task, and comparing to obtain the altitude error; Step S20: Design a terminal nonlinear term according to the height error signal, and perform integration to obtain a nonlinear integrated signal, and then form a terminal sliding mode signal; Step S30: designing a differential dislocation device according to the terminal sliding mode signal to obtain a differential dislocation signal of the terminal sliding mode signal; Step S40: Design an altitude channel interference observer according to the altitude error signal to obtain an interference observation signal; Step S50: Design the final expected signal of the pitch angle of the stratospheric airship according to the terminal sliding mode signal, the differential dislocation signal and the interference observation signal, and send it to the airship attitude control system to realize altitude control. 2 . The method for nonlinear control of stratospheric airship height according to claim 1 , wherein a terminal type nonlinear term is designed and integrated to obtain a nonlinear integral signal, and then a terminal sliding mode signal is formed. 3 . include: e _h =hh ^d ;

s _ef =∫e _f1 dt; s ₁ =c ₅ e _h +c ₆ s _ef ; where e _h is the height error signal, h ^d is the desired height command set according to the flight mission of the stratospheric airship, h is the actual height of the stratospheric airship, e _f1 is the terminal nonlinear term, c ₁ , c ₂ , c ₃ , c ₄ , c ₅ , and c ₆ are constant value parameters. s _ef is the integral of the terminal nonlinear term, and s ₁ is the terminal sliding mode signal. 3. the described a kind of stratospheric airship height nonlinear control method according to claim 1, is characterized in that, designing differential dislocation device, the differential dislocation signal that obtains terminal sliding mode signal comprises: s _d1 =(s ₁ -y ₁ )/T ₁ ; When n≥1, y ₁ (n+1)=y ₁ (n)+s _d1 T; s _d2 =(s ₁ -y ₂ )/T ₂ ; When n≥1, y ₂ (n+1)=y ₂ (n)+s _d2 T;

s ₁ is the terminal sliding mode signal, y ₁ and y ₂ are the output signals of the first and second differentiators respectively, and their initial values are both 0, y ₁ (1)=0, y ₂ (1 )=0. s _d1 and s _d2 are the increasing signals of the first and second differentiators, respectively, and T ₁ and T ₂ are time constants. y ₁ (n) is the nth data of the output signal y ₁ of the first differentiator, and T is the time interval between the data. y ₂ (n) is the n-th data of the output signal y ₂ of the second differentiator. s _d is the required differential dislocation signal. 4. the described a kind of stratospheric airship height nonlinear control method according to claim 1, is characterized in that, designing height channel disturbance observer, obtains disturbance observation signal comprises:

Among them, z is the state variable of the disturbance observer, and its initial value is zero, that is, z(1)=0.

In order to interfere with the observation signal, k ₁ , k ₂ , and k ₆ are constant parameters, and θ ^d is the pitch angle command signal. For the detailed design, see the next design. The initial value can be selected as 0, that is, θ ^d (1)= 0. Among them, T is the time interval between data, which is the same as the setting of the differentiator. 5. the described a kind of stratospheric airship height nonlinear control method according to claim 1, is characterized in that, according to terminal sliding mode signal and differential dislocation signal and interference observation signal, design final stratospheric airship pitch angle expectation Signals include:

where s ₁ is the terminal sliding mode signal, s _d is the differential dislocation signal,

In order to interfere with the observation signal, θ ^d is the final expected signal of the pitch angle of the stratospheric airship, and its initial value is selected as 0. k ₃ , k ₄ , k ₅ , and k ₇ are constant value parameters.

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