Control method and system for high-precision tracking of landing glide line of unmanned aerial vehicle and unmanned aerial vehicle

Abstract

The invention relates to the field of flight control of aircrafts, and provides a control method and system for high-precision tracking of a landing glide line by an unmanned aerial vehicle, and the unmanned aerial vehicle. The control method comprises the steps that S1, a control structure for controlling the height of the elevator is determined, specifically, a double-ring cascade PID control structure is adopted, a pitch angle ring is a PID control structure, and a height ring is a PID control structure; a lag network is introduced between the pitch angle ring and the height ring; s2, an accelerator channel adopts a control structure that the air speed is controlled by an accelerator; s3, a landing height instruction and an air speed instruction are obtained, and the unmanned aerial vehicle is controlled to land along the designed glide line track through a control structure for controlling the height through an elevator and a control structure for controlling the air speed through an accelerator. The control system comprises a control module for controlling the height of the elevator, an accelerator control module and a landing glide control module. The method has the beneficial effects that the accuracy of tracking the landing glide track height by the unmanned aerial vehicle is effectively improved, and the safety of the unmanned aerial vehicle in the landing process is ensured.

Description

Technical Field

[0001] The present invention relates to the field of aircraft flight control, and particularly to a control method, system and unmanned aerial vehicle for high-precision tracking of the landing glide path of an unmanned aerial vehicle. Background Art

[0002] Since the birth of unmanned aerial vehicles (UAVs), they have been relatively maturely applied in many fields, and the development of flight control technology has played a crucial role in this process. Further, people hope to further broaden the usage scenarios of UAVs and improve the safety of autonomous control of UAVs. In terms of technical requirements, higher requirements are put forward for the longitudinal position accuracy, response speed and control robustness during the landing process of UAVs.

[0003] The conventional altitude control strategy is that the elevator controls the altitude by adjusting the pitch angle, changing the angle of attack, and indirectly changing the lift. However, the specific control structures are different. Different implementation methods of the control structure result in different control effects.

[0004] In the traditional landing control structure design of UAVs, a dual-loop structure (as shown in Figure 1 ) is often used. The altitude loop adopts an altitude PID control structure, and the pitch angle loop adopts a PD control. This control structure is easy to implement in engineering. However, when this structure is applied to landing and there are large disturbances, situations such as large altitude control errors, the UAV repeatedly crossing the glide path and landing with a large sinking rate often occur. Therefore, based on the existing altitude control strategy, how to improve the anti-interference ability of the UAV by optimizing the control structure implementation method, realize the precise tracking of the longitudinal glide trajectory of the UAV, and thus improve the safety of landing is the problem to be solved by the present invention. Summary of the Invention

[0005] The purpose of the present invention is to overcome the deficiencies of the prior art, and provide a control method, system and unmanned aerial vehicle for high-precision tracking of the landing glide path of an unmanned aerial vehicle. Based on the existing landing control strategy, by optimizing the implementation method of the control structure, the anti-interference ability of the UAV is improved, ensuring that the UAV stably tracks the glide path, guaranteeing the safety of the UAV landing, and improving the rapidity and control accuracy of the UAV altitude control.

[0006] The present invention adopts the following technical solutions:

[0007] On the one hand, the present invention provides a control method for high-precision tracking of the landing glide path of an unmanned aerial vehicle, including:

[0008] S1. Determine the control structure for elevator to control altitude: Adopt a double-loop cascade PID control structure. The inner loop is the pitch angle loop using the PID control structure, and the outer loop is the altitude loop using the PID control structure. A lag network is introduced between the pitch angle loop and the altitude loop. For a given landing altitude command, the pitch angle command is obtained through calculation in the altitude loop. The pitch angle command serves as the input to the lag network, and the output of the lag network and the landing trim pitch angle together serve as the input to the pitch angle loop. The elevator control command is obtained through calculation in the pitch angle loop.

[0009] S2. The throttle channel adopts a control structure for throttle to control airspeed: For a given airspeed command, the throttle control command is calculated.

[0010] S3. Obtain the landing altitude command and the airspeed command, and use the control structure for elevator to control altitude obtained in step S1 and the control structure for throttle to control airspeed obtained in step S2 to control the UAV to land along the designed glide path trajectory.

[0011] There is no sequence requirement for steps S1 and S2.

[0012] For any of the above possible implementation manners, a further implementation manner is provided. In step S1, the control structure for elevator to control altitude is as follows:

[0013]

[0014] In the formula, H g is the landing altitude command, which is generated in real time by the landing guidance law; H is the real-time altitude of the UAV; is the change rate of the landing altitude command; is the landing elevator speed; θ trim is the landing trim pitch angle; θ g is the pitch angle command; θ is the real-time pitch angle of the UAV; q is the real-time pitch angle rate of the UAV; δ e is the elevator servo command; is the altitude control proportional coefficient; is the altitude control integral coefficient; is the altitude control differential coefficient; is the pitch angle control proportional coefficient; is the pitch angle integral coefficient; is the pitch angle control differential coefficient; s is the frequency in the frequency-domain system analysis; a and b are the coefficients of the lag network, where a > 0, b > 0, and a > b.

[0015] For any of the possible implementation manners described above, a further implementation manner is provided. When determining the control law, according to the UAV control requirements, for example: according to the requirements of flight quality for the time domain and frequency domain, first determine the control law parameters of the pitch angle loop, and then determine the parameters of the altitude loop and the lag network.

[0016] For any of the possible implementation manners described above, a further implementation manner is provided. The control structure of the throttle controlling the airspeed is as follows:

[0017]

[0018] In the formula, V g is the airspeed command for the deep glide and shallow glide segments; V is the real-time airspeed of the UAV; δ Ttrim is the landing trim throttle; δ T is the throttle command; is the airspeed proportional control coefficient; is the airspeed integral control coefficient.

[0019] For any of the possible implementation manners described above, a further implementation manner is provided. In step S3, the UAV glide path trajectory includes an approach level flight segment, a deep glide segment, a shallow glide segment, and a deceleration taxiing segment; according to the information of the deep glide angle γ D , shallow glide angle γ S and the remaining flight distance X from the ground contact point, the current UAV landing altitude command H g is calculated in real time.

[0020] For any of the possible implementation manners described above, a further implementation manner is provided. In the deep glide segment and the shallow glide segment, the calculation formula for the height of the glide path trajectory is as follows:

[0021]

[0022] In the formula, H D is the relative height of the UAV corresponding X coordinate point in the deep glide segment; H S is the relative height of the UAV corresponding X coordinate point in the shallow glide segment; X is the remaining flight distance of the UAV from the ground contact point; H f is the start height of the shallow glide segment; X1 is the distance between the start point of the shallow glide and the ground contact point; X t is the ground contact point; γ D is the deep glide angle; γ S is the shallow glide angle.

[0023] For any of the possible implementation manners described above, a further implementation manner is provided. In step S3, according to the UAV aerodynamic data and weight information, perform aerodynamic trimming in the UAV landing state to obtain the airspeed command V g of the UAV in the deep glide segment and the shallow glide segment.

[0024] On the other hand, the present invention also provides a control system for a drone to accurately track the landing glide path. The control system is used to implement the above control method, and the control system includes:

[0025] An elevator height control module, which adopts a double-loop cascade PID control structure. The double loop includes a pitch angle loop and a height loop. The pitch angle loop is a PID control structure, and the height loop is a PID control structure; a lag network is introduced between the pitch angle loop and the height loop;

[0026] A throttle control module, which controls the throttle channel by adopting a control structure of controlling the airspeed with the throttle;

[0027] A landing glide control module, which obtains a landing height command and an airspeed command, and uses the elevator height control module and the throttle control module to control the drone to land along the designed glide path trajectory.

[0028] On the other hand, the present invention also provides a drone, which controls the landing of the drone by adopting the above control method.

[0029] On the other hand, the present invention also provides a drone, which includes the above control system.

[0030] The beneficial effects of the present invention are as follows:

[0031] 1. The rapidity and control accuracy of height control are improved. The present invention designs a two-loop cascade PID, and at the same time introduces a lag network between the two loops. The introduction of lag correction does not affect the transient response characteristics of the original control in the high-frequency band, increases the open-loop gain of the system in the low-frequency band, and reduces the steady-state error. In short, a suitable correction network improves the steady-state characteristics of the system while ensuring the original transient response characteristics of the system, and can also ensure that the system has sufficient phase margin.

[0032] 2. The control structure principle of the present invention is clear, the software code is easy to implement, and it is convenient for engineering implementation.

[0033] 3. The drone landing test shows that the present invention can effectively improve the accuracy of the drone tracking the landing glide path height and ensure the safety of the drone landing process. Description of the Drawings

[0034] Figure 1 Shown is the height control structure (double loop) of a conventional drone.

[0035] Figure 2 Shown is the optimized high-precision drone height control structure in the embodiment of the present invention.

[0036] Figure 3The figure shows the schematic diagram of the longitudinal trajectory of the UAV landing in the embodiment.

[0037] Figure 4 The figure shows the tracking situation of the glide trajectory during a certain landing flight.

[0038] Figure 5 The figure shows the altitude deviation situation during a certain landing flight.

[0039] Figure 6 The figure shows the Bode diagram of the lag network in the embodiment. Detailed implementation manners

[0040] The specific embodiments of the present invention will be described in detail below with reference to the specific drawings. It should be noted that the technical features or combinations of technical features described in the following embodiments should not be considered isolated, and they can be combined with each other to achieve better technical effects.

[0041] As Figure 2 shown, a control method for a UAV to accurately track the glide line during landing in an embodiment of the present invention includes:

[0042] S1. Determine the control structure for controlling the altitude of the elevator: Adopt a double-loop cascade PID control structure. The inner loop is the pitch angle loop using the PID control structure, and the outer loop is the altitude loop using the PID control structure. A lag network is introduced between the pitch angle loop and the altitude loop. For a given landing altitude command, the pitch angle command is obtained through calculation in the altitude loop. The pitch angle command serves as the input of the lag network, and the output of the lag network and the landing trim pitch angle together serve as the input of the pitch angle loop, and the elevator control command is obtained through calculation in the pitch angle loop.

[0043] S2. The throttle channel adopts a control structure for controlling the airspeed with the throttle: For a given airspeed command, the throttle control command is calculated.

[0044] S3. Obtain the landing altitude command and the airspeed command, and use the control structure for controlling the altitude of the elevator obtained in step S1 and the control structure for controlling the airspeed with the throttle obtained in step S2 to control the UAV to land along the designed glide line trajectory.

[0045] There is no sequence for steps S1 and S2.

[0046] In a specific embodiment, the lag network is

[0047] In a specific embodiment, in step S1, the control structure for controlling the altitude of the elevator is as follows:

[0048]

[0049] In the formula, H gis the landing altitude command, which is generated in real time by the landing guidance law; H is the real-time altitude of the UAV; is the change rate of the landing altitude command; is the landing vertical speed of the UAV; θ trim is the landing trim pitch angle; θ g is the pitch angle command; θ is the real-time pitch angle of the UAV; q is the real-time pitch angle rate of the UAV; δ e is the elevator servo command; is the proportional coefficient of altitude control; is the integral coefficient of altitude control; is the derivative coefficient of altitude control; is the proportional coefficient of pitch angle control; is the integral coefficient of pitch angle; is the derivative coefficient of pitch angle control; s is the frequency in the frequency-domain system analysis; a and b are the coefficients of the lag network, where a > 0, b > 0, and a > b.

[0050] In a specific embodiment, when determining the control law, according to the requirements of flight quality for the time domain and frequency domain, first determine the control law parameters of the pitch angle loop, and then determine the parameters of the altitude loop and the lag network. Since the lag network is introduced, the control parameters of the altitude loop can be a bit larger than those of the conventional control structure.

[0051] In a specific embodiment, the control structure for the throttle to control the airspeed is as follows:

[0052]

[0053] In the formula, V g is the airspeed command for the deep glide and shallow glide segments; V is the real-time airspeed of the UAV; δ Ttrim is the landing trim throttle; δ T is the throttle command; is the proportional control coefficient of airspeed; is the integral control coefficient of airspeed.

[0054] In a specific embodiment, as Figure 3 shown, in step S3, the UAV glide path trajectory includes an approach level flight segment, a deep glide segment, a shallow glide segment, and a deceleration taxiing segment; according to the information of the deep glide angle γ D , shallow glide angle γ S and the remaining flight distance X from the touchdown point, the current UAV target altitude, i.e., the landing altitude command H g is calculated in real time.

[0055] In a specific embodiment, in the deep glide segment and the shallow glide segment, the calculation formula for the glide path trajectory altitude is as follows:

[0056]

[0057] Wherein, H D is the relative height of the UAV at the corresponding X coordinate point in the deep glide section; H S is the relative height of the UAV at the corresponding X coordinate point in the shallow glide section; X is the remaining flight distance of the UAV from the landing point; H f is the starting height of the shallow glide section; X1 is the distance between the starting point of the shallow glide and the landing point; X t is the landing point; γ D is the deep glide angle; γ S is the shallow glide angle.

[0058] In a specific embodiment, in step S3, according to the aerodynamic data and weight information of the UAV, aerodynamic trim is performed in the landing state of the UAV to obtain the airspeed commands V of the UAV in the deep glide section and the shallow glide section g .

[0059] A control system for a UAV to accurately track the landing glide path according to an embodiment of the present invention, the control system is used to implement the above control method, and the control system includes:

[0060] A control module for controlling the height of the elevator, adopting a double-loop cascade PID control structure. The double loop includes a pitch angle loop and a height loop. The pitch angle loop is a PID control structure, and the height loop is a PID control structure; a lag network is introduced between the pitch angle loop and the height loop;

[0061] A throttle control module, which controls the throttle channel by adopting a control structure of controlling the airspeed with the throttle;

[0062] A landing glide control module, which obtains the landing height command and the airspeed command, and uses the control module for controlling the height of the elevator and the throttle control module to control the UAV to land along the designed glide path trajectory.

[0063] A UAV according to an embodiment of the present invention controls the landing of the UAV by adopting the above control method.

[0064] A UAV according to an embodiment of the present invention, the UAV includes the control system as described above.

[0065] A lag network is introduced between the pitch angle loop and the height loop of the present invention, and a lag link is connected in series on the basis of the original control structure and a proportional link greater than 1 (this proportional link is reflected in the optimized high-precision UAV height control structure in ), and its greatest function is to reduce the steady-state error of the system. On this basis, the original system characteristics in the middle frequency band are maintained, and the anti-high-frequency interference ability of the system is improved.

[0066] In a specific embodiment, asFigure 6 As shown in the logarithmic amplitude-phase-frequency characteristic curve, the upper figure shows the relationship between the system amplitude and frequency, and the lower figure shows the relationship between the system phase angle and frequency. The amplitude in the low-frequency band is greater than 0 dB. Therefore, when connected in series to the original system, it can significantly reduce the steady-state error of the system. The amplitude in the middle-frequency band decreases with a slope of -20 dB / dec, and the phase-frequency characteristic also attenuates here. Therefore, the cut-off frequency of the original system decreases. The original system has more phase angle reserves at the new cut-off frequency than at the previous cut-off frequency. Therefore, the phase margin of the system attenuates here but still meets the engineering requirements. The amplitude in the high-frequency band is less than 0 dB. Therefore, the decibel value in the high-frequency band of the system is reduced compared to the original system, and the anti-high-frequency interference ability of the system is also improved.

[0067] In the present invention, a proportional link greater than 1 is connected in series. Therefore, the control parameters of the altitude loop are larger than those of the conventional control structure. Since the time-domain indexes such as the adjustment time and overshoot of the system become worse than before, the differential link coefficient and integral link coefficient are also larger than before.

[0068] The control structure of the present invention is used in actual landing tests. The results of multiple tests show that this control scheme can achieve precise longitudinal altitude control of the UAV during landing, ensure that the UAV stably tracks the glide path, and guarantee the safety of the UAV landing. As Figure 4 、 Figure 5 shown, the situation of a certain test is as follows: when gliding from a relative altitude of 150 m to 0 m and using the control structure proposed in the present invention, the altitude deviation is within ±1.5 m, and the altitude tracking is fast and stable.

[0069] Based on the actual situation that the UAV needs to lock the glide path during landing and combining the characteristics of the compensation network in the automatic control theory, the present invention proposes a control structure for the UAV to accurately track the glide path. This control structure improves the accuracy of the UAV altitude control and enhances the anti-interference ability of the UAV.

[0070] Although several embodiments of the present invention have been given in this article, those skilled in the art should understand that the embodiments in this article can be changed without departing from the spirit of the present invention. The above embodiments are only exemplary and should not be used as a limitation of the scope of the rights of the present invention.

Claims

1. A control method for a drone to accurately track the landing glide path, characterized in that, The control method includes: S1. Determine the control structure for controlling the elevator height: Adopt a double-loop cascade PID control structure. The inner loop is the pitch angle loop using the PID control structure, and the outer loop is the height loop using the PID control structure. A lag network is introduced between the pitch angle loop and the height loop. For a given landing height command, the pitch angle command is obtained through calculation in the height loop. The pitch angle command serves as the input of the lag network, and the output of the lag network and the landing trim pitch angle together serve as the input of the pitch angle loop. The elevator control command is obtained through calculation in the pitch angle loop. S2. The throttle channel adopts a control structure for controlling the airspeed with the throttle: For a given airspeed command, the throttle control command is calculated. S3. Obtain the real-time landing height command and the real-time airspeed command, and use the control structure for controlling the elevator height obtained in step S1 and the control structure for controlling the airspeed with the throttle obtained in step S2 to control the UAV to land along the designed glide path trajectory. There is no sequence for steps S1 and S2.

2. The control method for the high-precision tracking of the landing glide path of the unmanned aerial vehicle according to claim 1, characterized in that, In step S1, the control structure for controlling the elevator height is as follows: where, H g is the landing altitude command, which is generated in real time by the landing guidance law; H is the real-time altitude of the UAV; is the change rate of the landing altitude command; is the landing lift-off speed of the UAV; θ trim is the landing trim pitch angle; θ g is the pitch angle command; θ is the real-time pitch angle of the UAV; q is the real-time pitch rate of the UAV; δ e is the elevator servo command; is the altitude control proportional coefficient; is the altitude control integral coefficient; is the altitude control derivative coefficient; is the pitch angle control proportional coefficient; is the pitch angle integral coefficient; is the pitch angle control derivative coefficient; s is the frequency in the frequency-domain system analysis; a and b are the coefficients of the lag network, where a > 0, b > 0, and a > b.

3. The control method for the high-precision tracking of the landing glide path of the drone according to claim 2, characterized in that, When determining the control law, according to the control requirements of the UAV, first determine the control law parameters of the pitch angle loop Then determine the parameters a and b of the lag network and the control law parameters of the altitude loop 4. The control method for a drone to accurately track the landing glide path according to claim 1, characterized in that, The control structure for controlling the airspeed with the throttle is as follows: Where, V g is the airspeed command for the deep and shallow glide segments; V is the real-time airspeed of the UAV; δ Ttrim is the landing trim throttle; δ T is the throttle command; is the airspeed proportional control coefficient; is the airspeed integral control coefficient.

5. The control method for a drone to accurately track the landing glide path as described in claim 1, characterized in that, In step S3, the glide path of the UAV includes an approach level flight segment, a deep glide segment, a shallow glide segment, and a decelerating taxiing segment; according to the deep glide angle γ D and the shallow glide angle γ S of the UAV at landing and the information of the remaining flight distance X from the touchdown point, the current landing altitude command H of the UAV is calculated in real time g .

6. The control method for the high-precision tracking of the landing glide path of the drone according to claim 5, characterized in that, In the deep glide section and the shallow glide section, the calculation formula for the glide path trajectory height is as follows: Where, H D is the relative height of the UAV at the corresponding X coordinate point in the deep glide segment; H S is the relative height of the UAV at the corresponding X coordinate point in the shallow glide segment; X is the remaining flight distance of the UAV from the touchdown point; H f is the starting height of the shallow glide segment; X1 is the distance between the starting point of the shallow glide and the touchdown point; X t is the touchdown point; γ D is the deep glide angle; γ S is the shallow glide angle.

7. The control method for the high-precision tracking of the landing glide path of the drone according to claim 1, characterized in that, In step S3, according to the aerodynamic data and weight information of the UAV, aerodynamic trimming is performed in the landing state of the UAV to obtain the airspeed command V of the UAV in the deep glide segment and the shallow glide segment g .

8. A control system for a drone to accurately track the landing glide path, characterized in that, The control system is used to implement the control method according to any one of claims 1-7. The control system includes: An elevator height control module, which adopts a double-loop cascade PID control structure. The double loop includes a pitch angle loop and a height loop. The pitch angle loop is a PID control structure, and the height loop is a PID control structure. A lag network is introduced between the pitch angle loop and the height loop. A throttle control module, which controls the throttle channel by adopting a control structure for controlling the airspeed with the throttle. A landing glide control module, which obtains the landing height command and the airspeed command, and uses the elevator height control module and the throttle control module to control the UAV to land along the designed glide path trajectory.

9. A drone, characterized in that, The UAV adopts the control method according to any one of claims 1-7 to control the UAV landing.

10. A drone, characterized in that, The UAV includes the control system according to claim 8.

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