A flight envelope protection method for unmanned aerial vehicle

Abstract

The present invention provides a flight envelope protection method for an unmanned aerial vehicle, comprising the following steps: determining the flight dynamics equation of the restriction parameters of the unmanned aerial vehicle under dynamic balance conditions; determining the critical control margin vector of the restriction parameters under dynamic balance according to the flight equation; determining the control law of the control system according to the critical control margin, wherein the basic principle of the control law is: providing the system with negative feedback inversely proportional to the 2-norm of the control margin vector of the boundary, so that when the aircraft approaches the flight envelope, the control input gradually decreases. The present invention can ensure that the restriction parameters of the aircraft do not exceed the restriction boundary within the entire flight envelope, thereby effectively improving the safety and reliability of the flight.

Description

Technical Field

[0001] The invention belongs to the technical field of aircraft design, and in particular relates to a flight envelope protection method for an unmanned aircraft. Background Art

[0002] The flight performance of a helicopter is constrained by its structural and aerodynamic limitations, which define the flight envelope. Helicopter flight envelope protection is to ensure flight safety by limiting the state of the aircraft during flight so that each limit parameter does not exceed the limit, that is, to ensure that it always flies within the envelope. Helicopter envelope protection includes: speed protection (underspeed or angle of attack limit protection, overspeed protection), attitude limit (pitch angle limit, roll angle limit), attitude angular rate limit (angular rate limit, load factor limit), etc. So far, a variety of envelope protection systems have been developed. Some of them directly measure the limit parameters through simple equipment, or link the measured data with the limit parameters, and pass this information to the pilot through the cockpit display. At present, many fixed-wing aircraft achieve limit avoidance in the above way, such as stall warning. However, as the limit parameters increase, it becomes very difficult to notify the pilot in the above simple way. In addition, if the limit parameters and the control margin of the current flight state reaching the limit boundary are complex functions of the aircraft flight parameters, then the limit parameters cannot be represented by a simple functional relationship with real-time measured flight data. If one wishes to fully exploit the helicopter's maneuverability and enable it to perform maneuvers close to the flight envelope, the envelope protection system may need to respond as it begins to approach the limit, thereby providing a buffer time for the pilot to react. Summary of the invention

[0003] The purpose of the present invention is to overcome the deficiencies in the prior art and provide a method for protecting an aircraft flight envelope. The solution of the present invention can solve the problems existing in the above-mentioned prior art.

[0004] The technical solution of the present invention:

[0005] A method for protecting the flight envelope of an unmanned aerial vehicle comprises the following steps:

[0006] Determine the flight dynamics equations of the UAV's limiting parameters under dynamic balance conditions;

[0007] Determine the critical control margin vector of the limiting parameters in the dynamic balance state according to the flight equation;

[0008] The control law of the control system is determined according to the critical control margin. The basic principle of the control law is to provide the system with negative feedback inversely proportional to the 2-norm of the control margin vector of the boundary, so that when the aircraft approaches the flight envelope, the control input gradually decreases.

[0009] Furthermore, the flight dynamics equation is:

[0010] in: is the time derivative of the slow state quantity, function f s is the relationship between the slow state quantity and the manipulated quantity in dynamic balance, function f is the relationship between the slow state quantity and the manipulated quantity and the limiting parameter in dynamic balance, u is the manipulated quantity, y p is a restriction parameter.

[0011] Furthermore, the critical control margin vector: Δu = u * -u0

[0012] Among them: u0 is the current manipulated value, u * is the control value boundary corresponding to the limiting parameter, in is the limit value of this parameter.

[0013] Furthermore, the control law formula is:

[0014] Among them, vector v is the pilot's control input, u is the obtained control amount with limited feedback, K is the adjustable proportional coefficient, and the larger the K value, the more sensitive the control action.

[0015] The beneficial effects of the present invention compared with the prior art are as follows:

[0016] (1) The present invention obtains the critical control margin vector based on the dynamic response characteristics of the unmanned aerial vehicle's restriction parameters and the flight parameters measurable by sensors, and realizes restriction avoidance through feedback control, so that the restriction parameters of the aircraft do not exceed the restriction boundary in the entire flight envelope, effectively improving the safety and reliability of flight;

[0017] (2) The present invention is simple and fast in calculation and reduces control delay, thus meeting the requirements for application in practical engineering of unmanned aerial vehicles. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The included drawings are used to provide a further understanding of the embodiments of the present invention, which constitute a part of the specification, are used to illustrate the embodiments of the present invention, and together with the text description, explain the principles of the present invention. Obviously, the drawings in the following description are only some embodiments of the present invention, and for ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0019] Figure 1 A schematic diagram of the steps of a method for protecting the flight envelope of an unmanned aerial vehicle provided in an embodiment of the present invention is shown;

[0020] Figure 2 A schematic diagram of a critical control margin vector provided according to an embodiment of the present invention is shown.

[0021] Figure 3 A schematic diagram of a linear restriction boundary provided according to an embodiment of the present invention is shown;

[0022] Figure 4 A control law structure block diagram according to an embodiment of the present invention is shown. DETAILED DESCRIPTION

[0023] It should be noted that, in the absence of conflict, the embodiments in this application and the features in the embodiments can be combined with each other. 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. The following description of at least one exemplary embodiment is actually only illustrative and is by no means intended to limit the present invention and its application or use. Based on the embodiments in 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.

[0024] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, it indicates the presence of features, steps, operations, devices, components and / or combinations thereof.

[0025] Unless otherwise specifically stated, the relative arrangement of the parts and steps described in these embodiments, numerical expressions and numerical values ​​do not limit the scope of the present invention. At the same time, it should be understood that, for ease of description, the sizes of the various parts shown in the accompanying drawings are not drawn according to the actual proportional relationship. The technology, method and equipment known to ordinary technicians in the relevant field may not be discussed in detail, but in appropriate cases, the technology, method and equipment should be regarded as a part of the authorization specification. In all examples shown and discussed here, any specific value should be interpreted as being merely exemplary, rather than as a limitation. Therefore, other examples of exemplary embodiments may have different values. It should be noted that similar reference numerals and letters represent similar items in the following drawings, so once a certain item is defined in an accompanying drawing, it does not need to be further discussed in subsequent drawings.

[0026] like Figure 1 As shown, according to an embodiment of the present invention, a method for protecting the flight envelope of an unmanned aerial vehicle is provided, comprising the following steps:

[0027] Step 1: Determine the flight dynamics equation of the unmanned aerial vehicle under dynamic balance conditions.

[0028] In one embodiment, the nonlinear state equation describing the flight dynamics of the aircraft can be written as:

[0029]

[0030] Among them, x s is the slow state quantity, x f is the fast state quantity, y p is the limiting parameter, u is the manipulated variable, is the derivative of the slow state quantity, is the derivative of the fast state quantity, x is the state quantity, g s is the nonlinear slow state equation of UAV flight mechanics, g f is the nonlinear fast state equation of unmanned aerial vehicle flight mechanics, To represent the state space of n state quantities, To represent the state space of k slow state variables, To represent the state space of nk fast states, To represent the state space of m manipulated variables, is the state space representing l restriction parameters, n is the number of state parameters of the UAV, m is the number of control variables, and l is the number of restriction parameters.

[0031] According to the time scale separation principle, the state vector is divided into k slow states x s and nk fast states x f In this embodiment, the slow state refers to flight parameters that change slowly over time, such as forward flight speed, climb rate, Euler angles, and altitude. These parameters will not always maintain a stable value during maneuvering flight. The fast state refers to flight parameters that change quickly over time, such as attitude angular rate. These parameters quickly reach a steady state during normal maneuvers. Output vector y p Represents a set of limiting parameters that need to be constrained within the flight envelope.

[0032] In this embodiment, dynamic balance is defined as a quasi-steady-state maneuver with a zero rate of change of the fast state quantity. Assuming that the control variable u is known, the above system can be expressed as n+l equations with n+k+l unknowns. s The value of is used to eliminate k unknowns. And in dynamic balancing, the functional relationship between the value of the implicit limiting parameter and the manipulated variable and the measured state quantity is obtained, thus obtaining formula (2):

[0033]

[0034] Among them, ff is the functional relationship between the fast state quantity, slow state quantity and the manipulated quantity, and f is the relationship between the slow state quantity and the manipulated quantity and the limiting parameter in dynamic equilibrium. This function is highly nonlinear and can be represented by an analytical model or empirical model based on experimental data.

[0035] This gives the flight dynamics equation under dynamic equilibrium conditions:

[0036]

[0037] Step 2, determining the critical control margin vector of the limiting parameter in the dynamic balance state according to the flight equation;

[0038] When a limiting parameter is affected by multiple control variables, its over-limit will be caused by an infinite number of control variable combinations. For example, different combinations of helicopter longitudinal cyclic pitch and collective pitch control may cause the angle of attack to reach the limit value. To predict the control margin, the envelope limit can be mapped to the vector space of the control variable, and then the shortest control vector that makes the limiting parameter reach the envelope boundary in dynamic balancing is found. The shortest control vector is called the critical control margin vector, and each limiting parameter corresponds to a critical control margin vector.

[0039] Formula (3) transforms each restriction parameter y i , are all expressed as slow state x s And the function of the manipulated variable u. For the limiting parameters:

[0040]

[0041] u * is the manipulated variable boundary corresponding to the limiting parameter, where is the limit value of this parameter.

[0042] like Figure 1 As shown, the critical control margin vector Δu is:

[0043] Δu=u * -u0 (5)

[0044] In the above formula, u0 is the current control position.

[0045] It is difficult to directly calculate the nonlinear limit boundary in equation (4). In this embodiment, the critical control margin vector can be approximately calculated by linearizing the function in f. In one embodiment, Taylor expansion is performed on the limit parameter:

[0046]

[0047] The limiting boundary can be approximated by the following linearized equation:

[0048]

[0049] The Moore-Penrose inverse of M is used to calculate the minimum control vector Δu to reach the limit boundary:

[0050]

[0051] In the above formula, Δu is the control margin when the limiting parameter reaches the limiting boundary in the dynamic balance state.

[0052] In other embodiments, other linearization methods may be used to linearize formula (4), so as to calculate the control margin when the limiting parameter reaches the limiting boundary in a dynamic balance state.

[0053] The critical control margin vector is approximated by restricted boundary linearization, as Figure 2 The true limiting boundary is nonlinear, so the linearized model must be constantly updated in real time. The linearized boundary is not exact, but as the boundary is approached, it becomes a surface tangent to the true nonlinear boundary, so as the vehicle approaches the limit, the linear approximation can be considered accurate.

[0054] Step three, determine the control law of the control system based on the critical control margin. The basic principle of the control law is: provide the system with negative feedback inversely proportional to the 2-norm of the critical control margin vector, so that when the aircraft approaches the flight envelope, the control input gradually decreases.

[0055] Further in one embodiment, the control law of the control system is:

[0056]

[0057] The vector v is the pilot's control input, and u is the obtained control amount with limited feedback. K is the adjustable proportional coefficient. The larger the K value, the more sensitive the control effect. The control law structure block diagram is as follows: Figure 3 As shown, the effect of the control loop is that when the pilot's control input gradually increases, the input signal u gradually approaches the limit boundary but does not exceed the limit.

[0058] If the control limit boundary u * is a constant and can be determined, then the actual manipulated variable in equation (9) can be solved algebraically. In one implementation, in the case of a single control channel, the control law is approximately:

[0059]

[0060] Among them, k is an adjustable proportional coefficient, which is selected according to actual conditions.

[0061] A medium stores the unmanned aerial vehicle flight envelope protection method of the present invention.

[0062] An aircraft uses the unmanned aircraft flight envelope protection method of the present invention to perform flight envelope protection.

[0063] In summary, the flight envelope protection method of an unmanned aerial vehicle provided by the present invention has at least the following advantages over the prior art:

[0064] (1) The present invention obtains the critical control margin vector based on the dynamic response characteristics of the unmanned aerial vehicle's restriction parameters and the flight parameters measurable by sensors, and realizes restriction avoidance through feedback control, so that the restriction parameters of the aircraft do not exceed the restriction boundary in the entire flight envelope, effectively improving the safety and reliability of flight;

[0065] (2) The present invention is simple and fast in calculation and reduces control delay, thus meeting the requirements for application in practical engineering of unmanned aerial vehicles.

[0066] For ease of description, spatially relative terms such as "above", "above", "on the upper surface of", "above", etc. may be used here to describe the spatial positional relationship between a device or feature and other devices or features as shown in the figure. It should be understood that spatially relative terms are intended to include different orientations of the device in use or operation in addition to the orientation described in the figure. For example, if the device in the accompanying drawings is inverted, the device described as "above other devices or structures" or "above other devices or structures" will be positioned as "below other devices or structures" or "below other devices or structures". Thus, the exemplary term "above" can include both "above" and "below". The device can also be positioned in other different ways (rotated 90 degrees or in other orientations), and the spatially relative descriptions used here are interpreted accordingly.

[0067] In addition, it should be noted that the use of terms such as "first" and "second" to limit components is only for the convenience of distinguishing the corresponding components. If not otherwise stated, the above terms have no special meaning and therefore cannot be understood as limiting the scope of protection of the present invention.

[0068] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. 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 method for protecting the flight envelope of an unmanned aerial vehicle, characterized in that: The following steps are involved: Determine the flight dynamics equations of the unmanned aerial vehicle's limiting parameters under dynamic balance conditions, The flight dynamics equation is: in: is the time derivative of the slow state quantity, function f s is the relationship between the slow state quantity and the manipulated quantity in dynamic balance, function f is the relationship between the slow state quantity and the manipulated quantity and the limiting parameter in dynamic balance, u is the manipulated quantity, y p is the limiting parameter; Determine the critical control margin vector of the limiting parameters in the dynamic balance state according to the flight dynamics equation; The critical control margin vector: Δu = u * -u0 Among them: u0 is the current manipulated value, u * is the control value boundary corresponding to the limiting parameter, in is the limit value of the parameter; A control law of the control system is determined according to the critical control margin vector, wherein the basic principle of the control law is: providing the system with negative feedback inversely proportional to the 2-norm of the critical control margin vector, so that when the aircraft approaches the flight envelope, the control input is gradually reduced; The control law formula is: Among them, the vector v is the pilot control input, u is the obtained control amount with limited feedback, K is the adjustable proportional coefficient, and the larger the K value is, the more sensitive the control action is.

2. An aircraft, characterized in that: The flight envelope protection method of the unmanned aerial vehicle as claimed in claim 1 is used to perform flight envelope protection.

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