Unmanned aerial vehicle false attack angle stability augmentation control method

Abstract

The invention discloses an unmanned aerial vehicle false attack angle stability augmentation control method, belongs to the technical field of unmanned aerial vehicle flight control, and introduces a pitch angle rate signal and a false attack angle stability augmentation control strategy into an elevator control channel to improve the dynamic response characteristic of an unmanned aerial vehicle. A pitch angle rate signal collected by a sensor is used as feedback, a transfer function from a pitch angle rate to a pseudo attack angle is deduced through flight mechanics related theories, pseudo attack angle feedback is added into an angular rate stability augmentation loop, and longitudinal static stability is widened through pseudo attack angle stability augmentation; through comparison simulation verification in a six-degree-of-freedom simulation model, the rise time, steady-state error and overshoot of the system fed back by the pseudo-angle-of-attack stability augmentation loop are superior to those of the system with static stability not relaxed.

Description

Technical Field

[0001] The invention belongs to the technical field of unmanned aerial vehicle flight control, and in particular relates to a pseudo angle of attack stabilization control method for unmanned aerial vehicle. Background Art

[0002] As mission requirements become increasingly diverse and complex, the requirements for UAV maneuverability continue to increase. For example, in some special mission scenarios, UAVs need to quickly change their flight attitude and trajectory to adapt to complex environments or complete specific mission objectives. However, the traditional UAV design with high static stability limits its maneuverability to a certain extent. For a given UAV flight speed and aerodynamic layout, achieving high maneuverability often requires a larger angle of attack, but in conventional designs, the allowable rudder deflection angle is usually limited, which leads to difficulties in pursuing maneuverability. In order to solve the above problems, pseudo angle of attack feedback technology came into being.

[0003] The pseudo angle of attack feedback technology can achieve the stabilization of statically unstable drones or the destabilization of statically overstable drones and stabilize their control ratio by building an angle of attack feedback loop around the drone body to form an artificial restoring torque. For example, in some missile designs, the introduction of pseudo angle of attack feedback can improve robustness while ensuring a high control ratio. For example, when the angle of attack requirement is large, the steady-state rudder deflection angle requirement can be reduced, while balancing the dynamic response requirements to a certain extent.

[0004] In practical applications, it is necessary to determine the parameters of the pseudo angle of attack feedback loop more accurately to better adapt to different flight conditions and mission requirements. At the same time, further research is needed on how to better deal with the relationship between rudder angle limitation, flight stability and maneuverability.

[0005] When the drone body exhibits low static stability, it is a divergent system. This often happens in the initial powered flight stage of some tactical missiles. At this time, without the assistance of the autopilot, it is difficult for the drone to achieve stable flight. Taking missile control as an example, the transfer function of the rear-controlled missile has a right half plane zero point, which belongs to a non-minimum phase system. In the initial stage of control, the acceleration output direction is opposite to the expected direction. The expected acceleration direction will not appear until the lift generated by the angle of attack is large enough, which undoubtedly affects the accuracy and efficiency of control. In addition, the traditional autopilot has poor robustness when facing changes in the body gain. Once the center of gravity and the center of pressure position change, causing the missile body gain to change significantly, the autopilot design is very likely to fail the robustness evaluation.

[0006] In traditional designs, to ensure flight safety and stability, drones are often designed to have high static stability, which makes it difficult for them to quickly change their attitude and trajectory during flight. For example, in scenarios where agile maneuvers are required to avoid obstacles or quickly track targets, drones with high static stability cannot quickly respond to commands to adjust their flight status due to their aerodynamic layout and control characteristics. Existing control methods are difficult to achieve effective relaxation of static stability operations on drones with high static stability. On the one hand, conventional control strategies lack targeted mechanisms to actively adjust the static stability of drones. In actual flight, when faced with complex and changing mission requirements, such as the need to quickly turn in a small space or maintain an accurate flight trajectory under strong airflow interference, existing control methods cannot dynamically reduce the static stability of drones to obtain higher maneuverability; on the other hand, traditional control methods are prone to cause fluctuations in other flight performance when trying to adjust static stability. For example, it may cause problems such as unstable flight attitude and increased difficulty in controlling flight speed, thereby affecting the overall flight performance and mission execution effect. Therefore, there is an urgent need for a control method that can effectively relax static stability and ensure stable flight performance to meet the needs of modern drones in diverse mission scenarios. Summary of the invention

[0007] The invention provides a pseudo angle of attack stabilization control method for an unmanned aerial vehicle, which introduces a pitch angle rate signal and a pseudo angle of attack stabilization control strategy into an elevator control channel to improve the dynamic response characteristics of the unmanned aerial vehicle.

[0008] To achieve the above objectives, the present invention adopts the following technical solutions:

[0009] A pseudo angle of attack stabilization control method for unmanned aerial vehicles mainly introduces a pitch rate signal into an elevator control channel to improve the dynamic response characteristics of the unmanned aerial vehicle, and specifically includes the following steps:

[0010] The pitch rate signal collected by the sensor is used as feedback, and the transfer function from pitch rate to pseudo angle of attack is derived through relevant flight mechanics theories. Pseudo angle of attack feedback is added to the angular rate augmentation loop, and the longitudinal static stability is relaxed through pseudo angle of attack augmentation.

[0011] The transfer function expression from pitch angle rate to pseudo angle of attack is: , in is the pitch angle rate signal measured by the sensor, is the complex variable in the Laplace transform, is the pseudo angle of attack, is the dynamic derivative: the longitudinal force caused by the change in angle of attack.

[0012] The stabilization control law of the pitch channel based on classical feedback control is: , in, is the elevator command for the stability augmentation loop, is the elevator command of the pseudo angle of attack stabilization loop, is the elevator command of the original angular rate augmentation loop, is the pseudo angle of attack stabilization control gain, Pitch rate stabilization control gain.

[0013] Beneficial effect: The present invention provides a pseudo angle of attack stabilization control method for unmanned aerial vehicles. The pitch rate signal is introduced into the elevator control channel to improve the dynamic response characteristics of the unmanned aerial vehicle. The pitch rate signal obtained by the sensor is used as feedback, and the transfer function from the pitch rate to the pseudo angle of attack is derived through the relevant theory of flight mechanics. The pseudo angle of attack feedback is added to the angular rate stabilization loop, and the longitudinal static stability is relaxed through pseudo angle of attack stabilization. A six-degree-of-freedom flight simulation is performed at an altitude of 4km, an indicated speed of 130m / s, and half the fuel consumption. Given From the pitch angle step response and time domain simulation, it can be seen that the rise time, steady-state error and overshoot of the system with pseudo angle of attack stabilization loop feedback added in the present invention are better than those of the system without relaxing static stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 This is a block diagram of pseudo angle of attack calculation in an embodiment of the present invention;

[0015] Figure 2 This is a block diagram of a pseudo angle of attack stabilization loop in an embodiment of the present invention;

[0016] Figure 3 is a diagram of angle of attack-elevator root locus in an embodiment of the present invention;

[0017] Figure 4 Graph showing attitude response in an embodiment of the present invention. DETAILED DESCRIPTION

[0018] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments:

[0019] In the initial stage of the longitudinal motion of the UAV, the short period is dominant. In order to improve the damping characteristics and stability of the aircraft, the pitch channel stabilization system generally uses the pitch angle rate signal feedback, but this loop will reduce the static maneuverability of the aircraft. The state space equation of the short period mode is obtained by linearizing the nonlinear mathematical model: , , , Choose a balance point: , , , , ,in, ,in, Represents the flight speed, Represents the flight altitude, represents the angle of attack, represents the pitch angular rate, represents the elevator command, Represents throttle and rudder commands.

[0020] Short-period natural frequency , , the natural frequency is higher, and the root locus of the angle of attack to the elevator is as follows Figure 3 As shown, as the open-loop gain increases slightly, the closed-loop pole falls into the real axis, becoming an over-damped system, and the frequency is too large, reflecting that the system has a tendency to return to stability too quickly and the system stability is too large, so the static stability needs to be relaxed.

[0021] The following provides a pseudo angle of attack stabilization control method for a UAV with relaxed static stability, which specifically includes the following steps:

[0022] This gives the natural form of the equation for the longitudinal small perturbation: , in, is the mass of the aircraft, For engine mounting angle, is the angle of attack under the reference motion, is the engine thrust under reference motion, is the track inclination angle under the reference motion, is the speed under the reference motion, is the change in angle of attack, is the pitch angle change, is the change of track inclination angle under the reference motion, is the height change, is the speed change, is the elevator change, is the throttle lever change, is the drag caused by the change in angle of attack, is the resistance caused by the speed change, is the resistance caused by the height change, is the drag caused by elevator deflection, is the lift caused by the change in angle of attack, is the lift caused by the rate of change of angle of attack, is the lift caused by the speed change, is the lift caused by the change in pitch rate, is the lift caused by the altitude change, is the lift caused by the deflection of the elevator, is the pitching moment caused by the change in angle of attack, is the pitching moment caused by the rate of change of angle of attack, is the pitching moment caused by the speed change, is the pitch moment caused by the change of pitch angle rate, is the pitching moment caused by the altitude change, is the pitching moment caused by the elevator deflection, is the engine thrust caused by the speed change, is the engine thrust caused by the altitude change, The engine thrust caused by the change of throttle lever.

[0023] For the analysis of aircraft stability and maneuverability, the influence of altitude changes on external forces and moments can generally be ignored, and the reference motion is assumed to be horizontal steady straight flight, which can be simplified to: , The state vector , manipulate the vector ; Ignoring the tangential force equation, we obtain the approximate equations for the initial stage of the main reaction disturbance recovery:

[0024] .

[0025] The pitch rate signal obtained by the sensor is used as feedback, and the transfer function from pitch rate to pseudo angle of attack is derived through the above-mentioned flight mechanics related theory. The pseudo angle of attack feedback is added to the angular rate augmentation loop, and the longitudinal static stability is relaxed through pseudo angle of attack augmentation.

[0026] The transfer function expression from pitch angle rate to pseudo angle of attack is: , in is the pitch angle rate signal measured by the sensor, is the complex variable in the Laplace transform, is the pseudo angle of attack, is the dynamic derivative: the longitudinal force caused by the change in angle of attack.

[0027] The transfer function from pitch rate to pseudo angle of attack is discretized in the simulink module and is as follows: , The calculation frame of the pseudo angle of attack can be obtained as Figure 1 shown.

[0028] like Figure 2As shown, the pitch sensor acquires the pitch angle rate As feedback, the pseudo angle of attack is obtained through the transfer function from pitch rate to pseudo angle of attack , and then through the dynamic equation and proportional term, the transfer function from pseudo angle of attack to elevator can be obtained: , as the compensation part of pseudo angle of attack stabilization / relaxed stabilization, plus the original pitch angle rate stabilization feedback, we can get the pitch channel stabilization control law based on classical feedback control: , in, is the elevator command of the pseudo angle of attack stabilization loop, is the pseudo angle of attack stabilization control gain, is the dynamic derivative: the pitching moment caused by the change in angle of attack, The dynamic pressure is obtained for the atmospheric machine. is the wing area, is the mean geometric chord length, is the moment of inertia around the y-axis of the body; is the elevator command for the stability augmentation loop, is the elevator command of the original angular rate augmentation loop, Pitch rate stabilization control gain.

[0029] Comparative simulation verification was carried out in the six-degree-of-freedom simulation model. A six-degree-of-freedom flight simulation was carried out at an altitude of 4km, an indicated speed of 130m / s, and half the fuel consumption. Pitch angle step response, time domain simulation results are as follows Figure 4 As shown, it can be seen that the rise time, steady-state error and overshoot of the system with pseudo angle of attack stabilization loop feedback are better than those of the system without relaxing static stability, indicating that the above method effectively improves the dynamic response characteristics of the UAV.

[0030] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A pseudo angle of attack stabilization control method for an unmanned aerial vehicle, characterized in that: The following steps are involved: S1: The natural form of the longitudinal small perturbation equation is given, and the approximate equation for the initial stage of the main reaction disturbance recovery is obtained; S2: The pitch rate signal collected by the sensor is used as feedback, and the transfer function from the pitch rate to the pseudo angle of attack is derived through the flight mechanics theory in S1, and the pseudo angle of attack is obtained through the transfer function from the pitch rate to the pseudo angle of attack; S3: The transfer function from the pseudo angle of attack to the elevator is used as the compensation part of the pseudo angle of attack stabilization / relaxed stabilization, and the original pitch angle rate stabilization feedback is added to obtain the pitch channel stabilization control law based on classical feedback control.

2. The pseudo angle of attack stabilization control method for unmanned aerial vehicles according to claim 1, characterized in that: The natural form of the longitudinal small perturbation equation is: in, is the mass of the aircraft, For engine mounting angle, is the angle of attack under the reference motion, is the engine thrust under reference motion, is the track inclination angle under the reference motion, is the speed under the reference motion, is the change in angle of attack, is the pitch angle change, is the change of track inclination angle under the reference motion, is the height change, is the speed change, is the elevator change, is the throttle lever change, is the drag caused by the change in angle of attack, is the resistance caused by the speed change, is the resistance caused by the height change, is the drag caused by elevator deflection, is the lift caused by the change in angle of attack, is the lift caused by the rate of change of angle of attack, is the lift caused by the speed change, is the lift caused by the change in pitch rate, is the lift caused by the altitude change, is the lift caused by the deflection of the elevator, is the pitching moment caused by the change in angle of attack, is the pitching moment caused by the rate of change of angle of attack, is the pitching moment caused by the speed change, is the pitch moment caused by the change of pitch angle rate, is the pitching moment caused by the altitude change, is the pitching moment caused by the elevator deflection, is the engine thrust caused by the speed change, is the engine thrust caused by the altitude change, The engine thrust caused by the change of throttle lever.

3. The pseudo angle of attack stabilization control method for unmanned aerial vehicles according to claim 2, characterized in that: For the analysis of aircraft stability and maneuverability, the influence of altitude change on external forces and moments is ignored, and the reference motion is assumed to be horizontal steady straight flight, which is simplified to: The state vector , manipulate the vector .

4. The pseudo angle of attack stabilization control method for unmanned aerial vehicles according to claim 3, characterized in that: Ignoring the tangential force equation, the approximate equation for the initial stage of the main reaction disturbance recovery is obtained: 。 5. The UAV pseudo angle of attack stabilization control method according to claim 1 or 3, characterized in that: The transfer function expression from the pitch angle rate to the pseudo angle of attack is: ， in is the pitch angle rate signal measured by the sensor, is the complex variable in the Laplace transform, is the pseudo angle of attack, is the longitudinal force caused by the change in angle of attack.

6. The pseudo angle of attack stabilization control method for unmanned aerial vehicles according to claim 1, characterized in that: The transfer function of the pseudo angle of attack to the elevator is: , in, is the elevator command of the pseudo angle of attack stabilization loop, is the pseudo angle of attack stabilization control gain, is the pitching moment caused by the change in angle of attack, The dynamic pressure is obtained for the atmospheric machine. is the wing area, is the mean geometric chord length, is the moment of inertia about the y-axis of the machine body.

7. The UAV pseudo angle of attack stabilization control method according to claim 1 or 6, characterized in that: Pitch channel stabilization control law based on classical feedback control: ， in, is the elevator command for the stability augmentation loop, is the elevator command of the pseudo angle of attack stabilization loop, is the elevator command of the original angular rate augmentation loop, is the pseudo angle of attack stabilization control gain, Pitch rate stabilization control gain.

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