Envelope protection method and system for low speed boundaries

Abstract

The application provides a method and system for envelope protection of low-speed boundary. The method comprises: obtaining an angle of attack instruction; determining a maximum angle of attack based on flight state parameters, wherein the maximum angle of attack satisfies both an angle of attack protection limit and an overload limit, and the maximum angle of attack is set as an upper limit of the angle of attack; determining a lower limit of the angle of attack based on at least one of the flight state parameters and the maximum angle of attack; limiting the angle of attack instruction with the upper limit and the lower limit of the angle of attack to obtain a limited angle of attack instruction; and superimposing the limited angle of attack instruction with an angle of attack pitch-down correction quantity associated with a pitch angle limit to generate an angle of attack control instruction.

Description

Technical Field

[0001] This invention relates to the field of aviation, and more specifically, to a method and system for envelope protection at low-speed boundaries. Background Technology

[0002] With the development of aviation technology, aircraft mission scenarios are constantly expanding towards more complex boundaries. Low-speed boundary flight, as a typical operating condition during the takeoff and landing phase of civil aircraft and the close maneuver phase of military aircraft, has always placed flight safety at the core of flight control system design. In low-speed boundary scenarios, the aerodynamic efficiency of an aircraft decreases rapidly with increasing angle of attack. Simultaneously, it is susceptible to the coupled effects of various uncertainties, such as large displacement inputs from the pilot, abrupt changes in engine thrust, low-altitude turbulence / gust interference, and single-engine failure. This greatly increases the risk of core state parameters such as angle of attack, pitch angle, overload, and flight speed exceeding the safety envelope. If the angle of attack exceeds the aerodynamic stall threshold, large-scale airflow separation will occur on the wing surface, triggering flutter, uncommanded pitch / roll / yaw movements, and in severe cases, even irreversible dangerous states such as stall spin. Furthermore, abnormal states such as large pitch attitude, high overload, and low dynamic pressure will significantly reduce the safety margin, further increasing the stall risk and directly threatening the safety of the personnel on board and the aircraft itself.

[0003] To reduce pilot workload in low-speed boundary scenarios and avoid safety accidents caused by human error, low-speed boundary envelope protection technology has become a standard feature of modern fly-by-wire flight control systems. Its core design goal is to automatically constrain the core state parameters within a safe envelope without limiting the aircraft's normal maneuverability, thereby achieving a balance between safety and maneuverability.

[0004] However, existing low-speed boundary protection schemes generally suffer from insufficient adaptability to complex operating conditions: some schemes can only achieve independent boundary limits for a single or a small number of flight parameters, failing to consider the cumulative impact of multi-parameter coupling on safety margins, making it difficult to cope with the risk of multiple parameters simultaneously exceeding limits in extreme scenarios such as gusts and malfunctions; other schemes, while covering the protection needs of multiple types of parameters, use mutually exclusive triggering or priority switching control logic for different protection functions, failing to achieve the coordinated effectiveness of multi-dimensional safety constraints, and easily leading to blind spots in protection. It is evident that these schemes are ill-suited to the multi-dimensional safety protection needs of complex low-speed boundary scenarios and still have room for improvement. Summary of the Invention

[0005] This summary is provided to introduce, in a simplified form, some concepts that will be further described in the following detailed description. This summary is not intended to identify key or essential features of the claimed subject matter, nor is it intended to help determine the scope of the claimed subject matter.

[0006] One objective of this invention is to provide a method and system for envelope protection at low-speed boundaries. By determining the shared constraint boundary for angle-of-attack protection and overload limitation using flight state parameters, adaptively limiting the input angle-of-attack command, and then superimposing a dynamic correction related to the pitch angle to generate a cooperative control command, which, upon activation, outputs control surface signals through a multi-feedback loop architecture. This achieves the coordinated effect of multi-dimensional boundary constraints such as angle of attack, pitch angle, overload, and speed, maximizing aircraft maneuverability while ensuring flight safety at low-speed boundaries and effectively reducing pilot workload.

[0007] According to one aspect of the present invention, an envelope protection method for low-speed boundaries is provided, the envelope protection method comprising: acquiring an angle-of-attack command; determining a maximum angle of attack based on flight state parameters, wherein the maximum angle of attack satisfies both an angle-of-attack protection limit and an overload limit, and setting the maximum angle of attack as an upper limit of angle of attack; determining a lower limit of angle of attack based on at least one of the flight state parameters and the maximum angle of attack, limiting the angle of attack command using the upper limit of angle of attack and the lower limit of angle of attack as boundaries to obtain a limited angle of attack command; and superimposing the limited angle of attack command with an angle-of-attack pitch correction amount associated with a pitch angle limit to generate an angle-of-attack control command.

[0008] In one embodiment of the present invention, determining the maximum angle of attack based on flight state parameters includes: determining a first angle of attack that satisfies the angle of attack protection limit based on the stall angle of attack, wherein the stall angle of attack is related to the flap and slat configuration, landing gear condition, and Mach number; determining a second angle of attack that satisfies the overload limit based on the lift coefficient that matches the overload limit, wherein the overload limit is related to the flap and slat configuration; and determining the smaller of the first angle of attack and the second angle of attack as the maximum angle of attack.

[0009] In one embodiment of the invention, the stall angle of attack is further related to icing conditions and sideslip angle parameters.

[0010] In one embodiment of the present invention, determining a second angle of attack that satisfies the overload limit based on a lift coefficient that matches the overload limit includes: determining the overload limit based on the flap configuration in the flight state parameters; determining the lift coefficient, wherein the lift coefficient is proportional to the overload limit and the current weight of the aircraft, and inversely proportional to the wing reference area and the current dynamic pressure corresponding to the corrected airspeed; and obtaining a second angle of attack corresponding to the lift coefficient based on the correspondence between the lift coefficient and the angle of attack, wherein the correspondence between the lift coefficient and the angle of attack is dynamically adjusted according to the flap configuration, landing gear status, and Mach number in the flight state parameters.

[0011] In one embodiment of the present invention, determining the lower limit of angle of attack based on at least one of flight state parameters and the maximum angle of attack of the aircraft includes: determining the lower limit of angle of attack based on the minimum operating speed obtained from the flight state parameters, wherein the minimum operating speed is related to the flap and slat configuration, landing gear status, Mach number and / or weight in the flight state parameters; and / or determining the lower limit of angle of attack based on the lower limit margin obtained by offsetting the maximum angle of attack downward.

[0012] In one embodiment of the invention, the pitch angle-of-attack (POA) correction associated with the pitch angle limit is generated as follows: when the aircraft's current pitch angle is greater than a first threshold and / or the current pitch rate is greater than a second threshold, a negative POA correction is generated, wherein the absolute value of the POA correction is positively correlated with the pitch angle overshoot and / or the pitch rate overshoot, and wherein the pitch angle overshoot is the difference between the current pitch angle and the first threshold, and the pitch rate overshoot is the difference between the current pitch rate and the second threshold; and when the aircraft's current pitch angle is not greater than the first threshold and the current pitch rate is not greater than the second threshold, the POA correction is 0.

[0013] In one embodiment of the present invention, the envelope protection method further includes: determining whether the aircraft state meets the activation conditions based on flight state parameters; if so, activating the angle of attack protection function, wherein the activation conditions include ground lift not activated, ground mode not activated, degraded mode not activated, and the current angle of attack being greater than the activation threshold.

[0014] In one embodiment of the present invention, the envelope protection method further includes: in response to the activation of the angle-of-attack protection function, generating an elevator control command by superimposing the output of the control loop based on the angle-of-attack control command, wherein the control loop includes an angle-of-attack command feedforward loop, an angle-of-attack feedback loop, a velocity feedback loop, and an attitude feedback loop, and the input of the angle-of-attack feedback loop includes the current angle of attack and the rate of change of angle of attack in the flight state parameters, the input of the velocity feedback loop includes the airspeed and / or the rate of change of airspeed in the flight state parameters, and the input of the attitude feedback loop includes the pitch angle and / or the pitch rate in the flight state parameters.

[0015] In one embodiment of the present invention, the gain parameters of the angle of attack command feedforward loop, angle of attack feedback loop, velocity feedback loop, and attitude feedback loop in the control loop are dynamically adjusted according to the airspeed, flap / slat configuration, and angle of attack in the flight state parameters, so that the amplitude margin and phase margin of the adjusted control loop meet the stability requirements.

[0016] According to another aspect of the present invention, an envelope protection system for low-speed boundaries is provided, the envelope protection system comprising: a command calculation module for executing the envelope protection method of the present invention and generating an angle-of-attack control command; a protection activation module for determining whether the aircraft state meets the activation conditions based on the flight state parameters, and outputting an angle-of-attack protection activation enable signal if the conditions are met, wherein the activation conditions include ground lift not activated, ground mode not activated, degraded mode not activated, and the current angle of attack being greater than an activation threshold; and a protection control module for generating an elevator control command by superimposing the output of a control loop on the angle-of-attack control command from the command calculation module in response to receiving the angle-of-attack protection activation enable signal.

[0017] In one embodiment of the present invention, the control loop includes: an angle-of-attack command feedforward loop, the input of which includes an angle-of-attack control command; an angle-of-attack feedback loop, the input of which includes the current angle of attack and the rate of change of angle of attack in the flight state parameters; a velocity feedback loop, the input of which includes the airspeed and / or the rate of change of airspeed in the flight state parameters; and an attitude feedback loop, the input of which includes the pitch angle and / or the pitch rate in the flight state parameters. The gain parameters of the angle-of-attack command feedforward loop, the angle-of-attack feedback loop, the velocity feedback loop, and the attitude feedback loop are dynamically adjusted according to the airspeed, flap / slat configuration, and angle of attack in the flight state parameters, so that the gain margin and phase margin of the adjusted control loop meet stability requirements.

[0018] According to another aspect of the present invention, a non-transient computer-readable medium is provided that stores computer-executable instructions that, when executed by an envelope protection system, perform the envelope protection method of the present invention for low-speed boundaries.

[0019] These and other features and advantages will become apparent from the following detailed description and with reference to the accompanying drawings. It should be understood that the foregoing general description and the following detailed description are illustrative only and do not limit the scope of the claims. Attached Figure Description

[0020] To gain a more detailed understanding of the manner in which the features of the present invention are described above, reference can be made to various embodiments to provide a more specific description of the above-briefly summarized aspects, some of which are illustrated in the accompanying drawings. However, it should be noted that the drawings illustrate only certain typical aspects of the invention and should not be considered as limiting its scope, as this description may allow for other equivalent and effective aspects.

[0021] Figure 1 This is a functional block diagram of an envelope protection system for low-speed boundaries according to an embodiment of the present invention.

[0022] Figure 2 This is a schematic diagram of an instruction calculation module in an envelope protection system according to an embodiment of the present invention.

[0023] Figure 3 This is a schematic diagram of a protection activation module in a wire envelope protection system according to an embodiment of the present invention.

[0024] Figure 4 This is a schematic diagram of the protection activation logic of a protection activation module according to an embodiment of the present invention.

[0025] Figure 5 This is a schematic diagram of a protection control module in a wire envelope protection system according to an embodiment of the present invention.

[0026] Figure 6 This is a flowchart of an envelope protection method for low-speed boundaries according to an embodiment of the present invention.

[0027] Figure 7 This is a hardware architecture diagram of an envelope protection system for low-speed boundaries according to an embodiment of the present invention.

[0028] The accompanying drawings are not drawn to scale. Detailed Implementation

[0029] Embodiments of this disclosure will now be described in more detail with reference to the accompanying drawings. While some embodiments of this disclosure are shown in the drawings, it should be understood that this disclosure can be implemented in various forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of this disclosure. It should be understood that the accompanying drawings and embodiments of this disclosure are for illustrative purposes only and are not intended to limit the scope of protection of this disclosure.

[0030] In the description of this disclosure, it should be noted that, unless otherwise stated, "a plurality of" means two or more (including two); the terms "upper," "lower," "left," "right," "inner," "outer," etc., indicating orientation or positional relationships are only for the convenience of describing this disclosure and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this disclosure. Furthermore, the terms "first," "second," "third," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance. "Vertical" is not vertical in the strict sense, but within the allowable tolerance range. "Parallel" is not parallel in the strict sense, but within the allowable tolerance range.

[0031] The directional terms used in the following description refer to the directions shown in the figures and are not intended to limit the specific structure of this disclosure. It should also be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "joining" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms in this disclosure based on the specific circumstances.

[0032] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this disclosure. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0033] In the description of the embodiments of this disclosure, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship.

[0034] Figure 1 A functional block diagram of an envelope protection system 100 for low-speed boundaries according to an embodiment of the present invention is shown. It should be noted that... Figure 1 The wire protection system 100 shown is merely exemplary and not limiting. The wire protection system of the present invention may include, but is not limited to, other types of wire protection systems. Figure 1 The wire protection system 100 shown has more or fewer components.

[0035] The envelope protection system 100 can be mounted on the flight control computer of fly-by-wire aircraft and is compatible with existing airborne hardware resources such as cockpit side sticks / sticks, inertial rate sensors, air data sensors, landing gear control units, flap and slat position sensors, and actuation control electronics. The cockpit side sticks / sticks are used to output the pilot's longitudinal control inputs. The inertial rate sensors, air data sensors, landing gear control units, and flap and slat position sensors are used to collect flight status parameters such as pitch angle, pitch rate, airspeed, angle of attack, flap and slat configuration, landing gear status, and Mach number. The actuation control electronics are used to enable data interaction between the various sensors, control units, and the flight control computer, and to transmit control commands output by the flight control computer to the elevator actuators.

[0036] like Figure 1As shown, the envelope protection system 100 may include an instruction calculation module 120, a protection activation module 130, and a protection control module 140.

[0037] The command calculation module 120 receives the input angle of attack command 102 and generates an angle of attack control command 104 after multi-constraint boundary limiting and pitch angle correction. For example, the command calculation module 120 can receive the angle of attack command 102 input by the pilot, and flight status parameters 108 (such as flap configuration, landing gear status, Mach number, corrected airspeed, current aircraft weight, etc.) collected by airborne sensors 150 (such as the aforementioned inertial rate sensor, air data sensor, landing gear control unit, and / or flap and slat position sensor, etc.). The pitch angle / pitch rate can be input separately or as part of the flight status parameters 108. The output is an angle of attack control command 104 that has been subjected to overload, dual angle of attack limiting, and dynamic pitch angle correction.

[0038] The protection activation module 130 is used to determine whether the aircraft state meets the activation conditions based on the flight state parameter 108. If it does, it outputs an angle-of-attack protection activation enable signal. For example, the protection activation module 130 receives the flight state parameter 108, aircraft system mode signals (such as ground lift enable signal, ground mode enable signal, etc.) and control law mode signals 110 (such as degradation mode enable signal, etc.), and determines whether the angle-of-attack protection function is triggered based on the preset activation logic. If it is triggered, it outputs an angle-of-attack protection activation enable signal.

[0039] The protection control module 140 is used to respond to the angle-of-attack protection activation enable signal received from the protection activation module 130, and generate an elevator control command 106 by superimposing the output of the control loop on the angle-of-attack control command 104 from the command calculation module 120. For example, when the protection control module 140 receives the angle-of-attack protection activation enable signal, it calculates and generates the elevator control command 106 based on the angle-of-attack control command 104 and the multi-loop feedback signal of the control loop, and outputs it to the elevator actuator 170 (or outputs it to the actuation control electronics, which transmits the control command to the elevator actuator) to drive the elevator to deflect, thereby achieving low-speed boundary envelope protection control of the aircraft body 180.

[0040] When the aircraft enters the high angle of attack and low speed region, the envelope protection system 100 can replace the conventional control law to perform control. Through real-time acquisition of flight state parameters 108 and dynamic adaptation of multi-dimensional constraints, it simultaneously limits the angle of attack, overload, pitch angle, and speed within the safe envelope range. At the same time, it improves the long-cycle response characteristics through a multi-feedback loop architecture, avoiding stall caused by oscillation of the angle of attack at the limit boundary. This avoids the risk of envelope breach under large control inputs by the pilot (or pilot) and maximizes the preservation of aircraft maneuverability, reducing the pilot's control load during low-speed flight.

[0041] The following combination Figures 2 to 5 The specific implementation methods of the three modules will be explained in detail.

[0042] Figure 2 A schematic diagram of an instruction calculation module 120 in an envelope protection system according to an embodiment of the present invention is shown.

[0043] like Figure 2 As shown, the input signals of the command calculation module 120 include the angle of attack command 102 input by the pilot (or operator), flight status parameters 108 (such as flap configuration, landing gear status, Mach number, current aircraft weight, corrected airspeed, icing conditions, sideslip angle parameters, etc.), and the current pitch angle / pitch rate 202, and the output signal is the angle of attack control command 104 ( Figure 2 The middle also shows as cmd ). Figure 2 For ease of explanation, the inputs including the current pitch angle / pitch rate 202 are listed separately, but it can be understood that the current pitch angle / pitch rate 202 also belongs to flight status parameter 108.

[0044] The specific execution logic of the instruction calculation module 120 is as follows: (1) Obtaining Angle of Attack Command 102. Angle of attack command 102 is the target angle of attack value that the aircraft is expected to achieve. In normal flight scenarios, it can be obtained by converting the longitudinal control displacement of the pilot's cockpit side stick / stick panel through a preset gain mapping. In simulation testing, flight test verification, and other scenarios, it can also be a preset value directly input into the test system. For example, the pilot inputs the longitudinal control displacement through the cockpit side stick / stick panel, and the command calculation module 120 converts the displacement of the side stick / stick panel (such as the deflection range of 0°~18°) into the corresponding desired angle of attack value according to the preset control gain mapping relationship, which serves as the input basis for subsequent amplitude limiting and correction stages.

[0045] (2) The maximum angle of attack is determined based on the flight state parameter 108. The maximum angle of attack satisfies both the angle of attack protection limit 220 and the overload limit 230.

[0046] In one example, the first angle of attack that satisfies the angle of attack protection limit 220 can be determined based on the stall angle of attack in flight state parameter 108. Figure 2 The stall angle of attack (denoted as amax_AOA) can be related to the flap / slat configuration, landing gear status, and Mach number. Optionally, the stall angle of attack can also be corrected based on icing conditions, sideslip angle parameters, etc. In a non-limiting embodiment, the first angle of attack amax_AOA can be set to a certain safety margin (2-3 degrees in a non-limiting embodiment) offset downwards from the stall angle of attack to prevent the aircraft from entering the stall range.

[0047] In one example, the second angle of attack that satisfies the overload limit of 230 can be determined based on the lift coefficient matched with the overload limit. Figure 2 The limit overload (denoted as amax_nz) is related to the flap and slat configuration. Specifically, the limit overload can be determined based on the flap and slat configuration in flight state parameter 108 (in a non-limiting embodiment, the limit overload can be set to 2g when the flaps are deployed and 2.5g when the flaps are retracted, where g is the acceleration due to gravity). The lift coefficient is then calculated according to the relationship that the lift coefficient is proportional to the limit overload and the current weight of the aircraft, and inversely proportional to the wing reference area and the current dynamic pressure of the corresponding corrected airspeed. Then, based on the lift coefficient-angle of attack correspondence that is dynamically adjusted according to the flap and slat configuration, landing gear status, and Mach number, the second angle of attack amax_nz corresponding to the lift coefficient can be obtained by querying. The second angle of attack, amax_nz, determined based on the overload limit 230, is used to avoid the risk of excessive overload on the airframe structure under scenarios with large control inputs or gust disturbances. Especially during high-speed flight phases with flaps and slats retracted, or high-speed stick maneuvers, it can prevent the normal overload of the aircraft from exceeding the upper limit of the airframe structure's load-bearing capacity, thus preventing damage to the wing and fuselage structures.

[0048] At frame 240, the smaller of the first and second angles of attack is determined as the maximum angle of attack. By taking the smaller of the two, both aerodynamic stall and structural overload risks can be covered simultaneously, achieving coordinated adaptation of multiple constraints.

[0049] (3) At frame 250, the angle of attack command is limited to obtain a limited angle of attack command. Specifically, the maximum angle of attack obtained at frame 240 can be set as the upper limit of the angle of attack ( Figure 2 (shown as amax), the lower limit of the angle of attack is determined based on at least one of the flight state parameters and the maximum angle of attack. Figure 2 The angle of attack command 102 input by the driver is limited by the upper limit of angle of attack (amax) and the lower limit of angle of attack (aprot), and the angle of attack command with limited amplitude is output. This not only avoids angle of attack overshoot stall, but also ensures the control continuity of the protection activation range.

[0050] In one example, the lower limit of the angle of attack can be determined using any one or a combination of the following methods: (1) The minimum operating speed can be calculated based on the flight status parameters, and the lower limit of the angle of attack can be determined based on the minimum operating speed. The minimum operating speed generally refers to the minimum speed of the aircraft's operating speed envelope, which is related to the flap and slat configuration, landing gear status, Mach number and / or weight in the flight status parameters. This lower limit is used to ensure that the aircraft still has the required maneuverability under the current flight status. (2) The maximum angle of attack can be offset downward by a lower limit margin to obtain the lower limit of the angle of attack (i.e., the high angle of attack protection start angle of attack). The lower limit margin can be a fixed value or a preset value, or it can be dynamically adjusted according to flight state parameters (such as airspeed, flap and slat configuration). In a non-limiting embodiment, the lower limit margin is 2-3 degrees.

[0051] In this step, the upper boundary limiting can directly prevent the angle of attack from exceeding the stall threshold or the overload from exceeding the structural bearing capacity, thus preventing stall or structural damage; the lower boundary limiting can match the activation threshold of the high angle of attack protection, avoiding frequent activation of the angle of attack protection during normal operation, ensuring that the control logic of the protection activation range is continuous and smooth, without the problem of repeated switching in and out of the control system.

[0052] (4) Generate an angle-of-attack control command by superimposing a pitch angle limit of 260° on the angle-of-attack command that has been limited. cmd 104.

[0053] In one example, the following operation can be used to generate the pitch angle limit 260° nose-down correction: when the aircraft's current pitch angle is greater than a first threshold and / or the current pitch rate is greater than a second threshold, a negative nose-down correction is generated, and the absolute value of the correction is positively correlated with the pitch overshoot (the difference between the current pitch angle and the first threshold) and / or the pitch rate overshoot (the difference between the current pitch rate and the second threshold); when the aircraft's current pitch angle is not greater than the first threshold and the current pitch rate is not greater than the second threshold, the nose-down correction is 0. This can be understood, but other positively correlated calculation methods can also be used according to actual control requirements.

[0054] The correction steps for the superimposed pitch angle limit are a supplementary constraint to the dual limit logic of angle of attack and overload, which can fill the protection blind spot of the existing single parameter limit: when the aircraft is in a high angle of attack state but the pitch angle / pitch rate exceeds the preset threshold, the target angle of attack value is actively reduced by a negative pitch angle correction amount, so as to avoid the risk of attitude loss of control caused by further pitch angle increase in extreme scenarios such as strong gust disturbances and single engine failure; in addition, the correction is only applied when the pitch angle or pitch rate exceeds the limit, and the correction amount is 0 in normal flight scenarios, which will not interfere with the pilot's normal control response, taking into account both the safety of boundary protection and the degree of freedom of control.

[0055] It is understood that the process in this embodiment is merely exemplary and can be adjusted, modified, added, and / or deleted according to actual needs.

[0056] The command calculation module 120 has been described above. It is evident that the command calculation module 120 can achieve dynamic collaborative adaptation of multiple constraint boundaries. Specifically, by synchronously acquiring flight state parameters 108, the maximum angle of attack that simultaneously satisfies both aerodynamic stall and structural overload limitations is calculated. Based on this, the bidirectional limiting boundary of the angle of attack command 102 is set, and then the dynamic correction amount associated with the pitch angle is superimposed. This synchronously constrains the three core parameters—angle of attack, overload, and pitch angle—within the safety envelope, fundamentally avoiding the risks of stall, structural damage, and attitude loss caused by single parameter exceeding limits. It also provides compliant angle of attack target inputs for the closed-loop control of subsequent protection and control modules, ensuring the consistency and effectiveness of the overall protection logic.

[0057] Figure 3 A schematic diagram of a protection activation module 130 in a wire protection system according to an embodiment of the present invention is shown. Figure 4 A schematic diagram of the protection activation logic 400 of the protection activation module 130 according to an embodiment of the present invention is shown.

[0058] like Figure 3 As shown, the input signals to the protection activation module 130 include the current angle of attack in the flight status parameters 108. )302, and the ground lift enable signal 304, ground mode enable signal 306, and degrade mode enable signal 308 of the aircraft system and control law mode signal 110, with the output signal being the protection activation enable signal 310.

[0059] In one example, such as Figure 4 As shown, the protection activation module 130 can use multi-condition AND logic to determine whether to activate the angle-of-attack protection function. When all activation conditions are met simultaneously, it outputs the angle-of-attack protection activation enable signal 310. If any condition is not met, the judgment is terminated directly, and the protection function is not activated. However, it can be understood that the priority of conditions and the combination of logic can be adjusted according to the actual scenario.

[0060] In this example, the specific execution operation of the protection activation logic 400 is as follows: If the input signal of the protection activation module 130 also includes the control law mode signal 110, the system determines whether the current control law mode allows switching to the angle of attack protection mode based on the control law mode signal 110. If it allows, the system proceeds to the next determination step; otherwise, it proceeds to block 412 and does not activate the angle of attack protection. Figure 4 (Not shown in the image).

[0061] At frame 402, the activation of ground lift is determined based on the ground lift enable signal 304. If ground lift is not activated, proceed to frame 404; if ground lift is activated, proceed to frame 412 without activating angle of attack protection. This step excludes scenarios where the lift function is active during the ground taxiing phase, avoiding false triggering of protection during the ground phase.

[0062] At box 404, the activation of ground mode is determined based on ground mode enable signal 306. If ground mode is not activated, proceed to box 406; if ground mode is activated, proceed to box 412 without activating angle of attack protection. This step confirms that the aircraft is in flight and activates angle of attack protection only in flight scenarios.

[0063] At box 406, the degraded mode enable signal 308 is used to determine whether the degraded mode is activated. If the degraded mode is not activated, proceed to box 408; if the degraded mode is activated, proceed to box 412 and do not activate the angle of attack protection. This step eliminates the possibility that the flight control system is in a degraded operation state, avoiding the introduction of additional risks by the protection logic under fault conditions. At box 408, the current angle of attack 302 is used to determine if it exceeds the activation threshold. If the current angle of attack exceeds the activation threshold, proceed to box 410; if the current angle of attack does not exceed the activation threshold, proceed to box 412 and do not activate the angle of attack protection. This step confirms that the aircraft has entered the preset high angle of attack protection zone, ensuring that the protection function is triggered only when necessary and does not interfere with the control response during normal flight.

[0064] At box 410, output protection activation enable signal 310. This step activates the angle-of-attack protection function when the aircraft status meets the above activation conditions, and the protection control module 140 takes over the control logic.

[0065] It is understood that the process in this embodiment is merely exemplary and can be adjusted, modified, added, and / or deleted according to actual needs.

[0066] The protection activation module 130 has been described above. As can be seen, the protection activation module 130 can effectively avoid false triggering and missed triggering of the protection function through the above-mentioned multi-condition protection activation logic 400. The four types of conditions correspond to judgment dimensions such as scenario compliance, operational security, and functional necessity. Protection is only activated when all dimensions are met simultaneously, balancing the security of low-speed boundary protection with the smoothness of normal operation.

[0067] Figure 5 A schematic diagram of a protection control module 140 in an envelope protection system according to an embodiment of the present invention is shown.

[0068] like Figure 5As shown, the input signals of the protection control module 140 include angle-of-attack protection activation enable signal 310, angle-of-attack control command 104, current angle of attack 302, angle of attack change rate 502, airspeed / airspeed change rate 504, and pitch angle / pitch rate 202. Among these, the current angle of attack 302, angle of attack change rate 502, airspeed / airspeed change rate 504, and pitch angle / pitch rate 202 are all components of the flight status parameters 108. In this embodiment, to clarify the input source of each feedback loop, they are listed separately. The output signal of the protection control module 140 is elevator control command 106.

[0069] In one example, the specific execution logic of the protection control module 140 is as follows: When the protection activation enable signal 310 is received from the protection activation module 130, the protection control module 140 generates the elevator control command 106 by superimposing the outputs of the angle of attack command feedforward loop 520, angle of attack feedback loop 530, speed feedback loop 540, and attitude feedback loop 550, and outputs it to the elevator actuator 170 to drive the control surface deflection.

[0070] Specifically, the angle-of-attack command feedforward loop 520 takes the angle-of-attack control command 104 as its input and outputs a feedforward control quantity through a forward gain to achieve a fast response to the command and reduce control lag. The angle-of-attack feedback loop 530 takes the current angle of attack 302 and the rate of change of angle of attack 502 as its inputs and may include proportional, derivative, and integral branches. It outputs an angle-of-attack feedback control quantity through an angle-of-attack feedback gain to achieve closed-loop tracking of the angle of attack and reduce the steady-state error and overshoot of the angle of attack. The speed feedback loop 540 takes the airspeed and / or the rate of change of airspeed 504 as its inputs and outputs a speed feedback control quantity through a speed feedback gain to suppress long-period oscillations of the aircraft and avoid excessive speed decay. The attitude feedback loop 550 takes the pitch angle and / or the pitch rate 202 as its inputs and outputs an attitude feedback control quantity through an attitude feedback gain to further stabilize the aircraft attitude and improve the control robustness at high angles of attack.

[0071] The output control quantities of the above four loops are superimposed to obtain the candidate elevator control quantity, which is then input to the switch 560. Another input of the switch 560 is the angle-of-attack protection activation enable signal 310. Its output logic is as follows: when the angle-of-attack protection activation enable signal 310 is valid, the switch outputs the above candidate elevator control quantity as the final elevator control command 106, which is output to the elevator actuator to drive the control surface deflection; when the angle-of-attack protection activation enable signal 310 is invalid, the switch outputs the elevator command generated by the conventional control law of the flight control system, maintaining the conventional control response, and the envelope protection system of this invention does not intervene in the current control.

[0072] In a further example, the gain parameters of the four loops mentioned above are dynamically adjusted according to the airspeed, flap / slat configuration, and angle of attack in flight state parameters 108, so that the adjusted control loops meet the preset stability margin requirements. In a non-limiting embodiment, the stability margin that the adjusted control loops need to meet is an amplitude margin ≥ 6 dB and a phase margin ≥ 45°. The margin requirements can also be adjusted according to the aircraft's safety level, thereby ensuring control stability under different flight states and avoiding stall caused by oscillations at the limit angle of attack.

[0073] It is understood that the process in this embodiment is merely exemplary and can be adjusted, modified, added, and / or deleted according to actual needs.

[0074] The protection control module 140 has been described above. It can be seen that the protection control module 140 achieves seamless switching between the conventional control law and the protection control law through the switcher 560, without interrupting the control link and avoiding control surface jumps during mode switching. Simultaneously, through the coordinated control of multiple feedback loops, it can simultaneously achieve multi-dimensional stable control of angle of attack, speed, and attitude during the protection activation phase. This ensures both the response speed and accuracy of angle of attack tracking, and improves the long-period response characteristics in high angle-of-attack scenarios, avoiding the risk of angle-of-attack boundary oscillations and stall caused by long-period modal oscillations when only angle-of-attack feedback is used.

[0075] It is understood that the process in this embodiment is merely exemplary and can be adjusted, modified, added, and / or deleted according to actual needs.

[0076] The envelope protection system 100 has been described above. It can be seen that through the collaborative architecture of the above three-level modules, multi-parameter synchronous constraint protection in low-speed boundary scenarios can be achieved: the command calculation module 120 synchronously covers three types of safety boundaries—angle of attack, overload, and pitch angle—from the command source; the protection activation module 130 avoids false and missed triggering of protection through multi-dimensional judgment logic; and the protection control module 140 ensures control stability at high angles of attack through dynamic gain scheduling of multiple feedback loops. Together, these three modules achieve end-to-end low-speed boundary protection of "command generation-activation judgment-closed-loop control." Compared to single-parameter limitation or switching protection schemes, this approach can simultaneously maximize flight safety, handling smoothness, and maneuverability.

[0077] Figure 6 A flowchart of a low-speed boundary envelope protection method 600 according to an embodiment of the present invention is shown. The envelope protection method 600 corresponds to the execution logic of the envelope protection system 100 described above, and the same implementation logic as that described in the following embodiments will not be repeated.

[0078] like Figure 6 As shown, the envelope protection method 600 may include the following steps: In step 602, the angle of attack command can be obtained. This step can be performed by the command calculation module 120 in the envelope protection system 100.

[0079] In step 604, the maximum angle of attack can be determined based on flight state parameters, wherein the maximum angle of attack satisfies both the angle of attack protection limit and the overload limit, and the maximum angle of attack is set as the upper limit of angle of attack, amax. This step can be executed by the command calculation module 120 in the envelope protection system 100.

[0080] In one example, referencing... Figure 2 The maximum angle of attack can be determined using the following methods: (1) Determine the first angle of attack (amax_AOA) that meets the angle of attack protection limit based on the stall angle of attack. In a non-limiting embodiment, amax_AOA is set as a safety margin of 2 to 3 degrees downward offset from the stall angle of attack. The stall angle of attack varies with the flap and slat configuration (the smaller the slats and the larger the flaps, the smaller the stall angle of attack), landing gear status (the smaller the stall angle of attack when the landing gear is down), and Mach number (the larger the Mach number, the smaller the stall angle of attack). It can also be corrected by combining icing conditions and sideslip angle.

[0081] (2) Determine the second angle of attack (amax_nz) that meets the overload limit based on the lift coefficient matching the overload limit: First, determine the overload limit according to the flap-slat configuration, and then calculate the lift coefficient corresponding to the overload limit value using the following formula: (1) in, This is the overload limit value, which can be a preset value that varies with the flaps and slats; mg is the current weight of the aircraft, which can be collected by the flight control system or estimated by weight. The current dynamic pressure corresponding to the corrected airspeed can be obtained from the atmospheric data system; S is the wing reference area, which is an inherent parameter of the aircraft.

[0082] Finally, based on the lift coefficient-angle of attack correspondence dynamically adjusted according to flap and slat configuration, landing gear status, and Mach number, the second angle of attack amax_nz corresponding to this CL is obtained by querying.

[0083] (3) Take the smaller value of the first angle of attack amax_AOA and the second angle of attack amax_nz as the maximum angle of attack.

[0084] In step 606, the lower angle of attack (APROT) can be determined based on at least one of the flight state parameters and the maximum angle of attack. The angle of attack command is then limited using the upper angle of attack (AMAX) and the lower angle of attack (APROT) as boundaries to obtain a limited angle of attack command. This step can be performed by the command calculation module 120 in the envelope protection system 100.

[0085] In one example, the lower angle of attack (aprot) can be determined based on the minimum operating speed obtained from flight state parameters, where the minimum operating speed is related to the flap / slat configuration, landing gear condition, Mach number, and / or weight in the flight state parameters; and / or the lower angle of attack (aprot) can be determined based on a lower margin obtained by offsetting the maximum angle of attack downwards.

[0086] In step 608, the angle of attack command, which has been limited, can be superimposed with the angle of attack pitch correction associated with the pitch angle limit to generate an angle of attack control command 104. This step can be executed by the command calculation module 120 in the envelope protection system 100.

[0087] In one example, the following steps can be used to generate the pitch angle correction related to the pitch limit: (1) When the current pitch angle of the aircraft is greater than the first threshold and / or the current pitch rate is greater than the second threshold, a negative pitch angle-of-attack correction is generated. The absolute value of the pitch angle-of-attack correction is positively correlated with the pitch angle overshoot and / or the pitch rate overshoot, where the pitch angle overshoot is the difference between the current pitch angle and the first threshold, and the pitch rate overshoot is the difference between the current pitch rate and the second threshold. For example, when only the pitch angle exceeds the limit, the pitch angle-of-attack correction can be directly taken as the pitch angle overshoot; when only the pitch rate exceeds the limit, the pitch angle-of-attack correction can be directly taken as the pitch rate overshoot; when both exceed the limit, the sum of the two can be directly taken.

[0088] (2) When the current pitch angle of the aircraft is not greater than the first threshold and the current pitch rate is not greater than the second threshold, the pitch angle correction is 0.

[0089] In one example, the envelope protection method 600 may further include an activation determination step. Specifically, it is determined whether the aircraft state meets the activation conditions based on flight state parameters. If all conditions are met, the angle-of-attack protection function is activated; otherwise, it is not activated. This step can be performed by the protection activation module 130 in the envelope protection system 100.

[0090] In a further example, the envelope protection method may also include a closed-loop control step. Specifically, in response to the activation of the angle-of-attack protection function, an elevator control command is generated by superimposing the output of the control loop based on the angle-of-attack control command. If the angle-of-attack protection function is not activated, the elevator command is maintained and output in response to driver input. This step can be performed by the protection control module 140 in the envelope protection system 100.

[0091] In a non-limiting embodiment, reference back Figure 5 The control loop may include an angle-of-attack feedback loop 530. The angle-of-attack feedback loop 530 may include proportional, derivative, and integral branches, with the output being the corresponding elevator control component. The calculation formula is as follows: (2) Among them, K p For proportional gain, K d For differential gain, K i For integral gain, all three are gain parameters that dynamically change with aircraft airspeed, flaps and slats, and angle of attack; This is the current angle of attack, measured by the angle of attack sensor; The rate of change of angle of attack is obtained by filtering and differentiating the angle of attack signal. Angle of attack control command 104.

[0092] When angle-of-attack protection is activated, the final elevator command is given. 106 is obtained by superimposing the outputs of multiple loops, as shown in the following formula: (3) in, K1 is the forward gain, K2 is the velocity feedback gain, and K3 is the attitude feedback gain. All three are gain parameters that dynamically change with the aircraft airspeed, flap and slat configuration, and angle of attack. Angle of attack control command 104; The elevator control component output by the angle of attack feedback loop 530 obtained from equation (2); CAS is the current corrected airspeed, which is collected by the air data system. θ is the airspeed rate of change, obtained by filtering and differentiating the airspeed signal; θ is the current pitch angle, obtained by the inertial navigation system. The pitch angle change rate is obtained from the inertial navigation system.

[0093] The aforementioned gain parameters are functions of dynamic adjustment based on airspeed, flap / slat configuration, angle of attack, etc. After adjustment, the control loop must meet stability margins to ensure control stability under different flight conditions. By appropriately selecting the gain parameters, when the pilot pulls the side stick to its maximum displacement, the aircraft's angle of attack can be stabilized at the maximum angle of attack (i.e., the limiting angle of attack), maximizing the aircraft's low-speed boundary maneuverability without exceeding the safety envelope.

[0094] It is understood that the process in this embodiment is merely exemplary and can be adjusted, modified, added, and / or deleted according to actual needs.

[0095] The envelope protection method 600 has been described above. It can be seen that through a progressive process of "command generation - activation judgment - closed-loop control," multi-parameter coordinated protection of angle of attack, overload, pitch angle, and speed can be achieved. Specifically, on the one hand, the coordinated limiting of the three types of constraints avoids the risk of a single parameter exceeding the limit; on the other hand, the speed and pitch angle feedback loops improve long-period response characteristics, preventing stall caused by oscillations at the limit boundary of the angle of attack, while simultaneously maximizing flight safety, handling smoothness, and maneuverability.

[0096] Figure 7 A hardware architecture diagram of an envelope protection system for low-speed boundaries according to an embodiment of the present invention is shown. The system illustrates a general hardware environment in which the invention can be applied according to exemplary embodiments. This hardware architecture corresponds to the embedded operating environment of an airborne flight control computer mounted on a fly-by-wire aircraft, and is compatible with existing airborne hardware resources such as cockpit side sticks / sticks, inertial rate sensors, atmospheric data sensors, landing gear control units, flap / slat position sensors, and actuation control electronics.

[0097] The system may include components that are connected to or communicate with the bus 720. For example, the system may include the bus 720, a processor 705, and one or more memories 710, etc.

[0098] Processor 705 can be any type of processor and may include, but is not limited to, general-purpose processors and / or special-purpose processors (e.g., special processing chips), intelligent hardware devices (e.g., general-purpose processors, DSPs, CPUs, microcontrollers, ASICs, FPGAs, programmable logic devices, discrete gate or transistor logic components, discrete hardware components, or any combination thereof). In some cases, processor 705 may be configured to use a memory controller to operate the memory array. In other cases, a memory controller (not shown) may be integrated into processor 705. Processor 705 may be responsible for managing bus 720 and general processing, including executing software 715 stored on memory 710. Processor 705 may also be configured to perform various functions described herein related to envelope protection methods for low-speed boundaries. For example, processor 705 may be configured to: acquire angle of attack command; determine the maximum angle of attack based on flight state parameters, wherein the maximum angle of attack satisfies both angle of attack protection limits and overload limits, and set the maximum angle of attack as the upper limit of angle of attack; determine the lower limit of angle of attack based on at least one of the flight state parameters and the maximum angle of attack, limit the angle of attack command using the upper and lower limits of angle of attack as boundaries to obtain a limited angle of attack command; and superimpose the limited angle of attack command with an angle of attack pitch correction associated with pitch limits to generate an angle of attack control command.

[0099] Memory 710 can be any storage device capable of storing data. Memory 710 may include, but is not limited to, disk drives, optical storage devices, solid-state storage, floppy disks, hard disks, magnetic tapes or any other magnetic media, optical discs or any other optical media, ROM (Read-Only Memory), RAM (Random Access Memory), cache memory and / or any other memory chip or cartridge, and / or any other medium from which a computer can read data, instructions and / or code. Memory 710 may store computer-executable software 715 including computer-readable instructions that, when executed, cause a processor to perform the various functions described herein. Memory 710 may have various data / instructions / code for implementing the various functions described herein related to the design of an envelope protection system for low-speed boundaries. In one example, memory 710 may also store preset parameters such as a stall angle of attack correspondence table, a lift coefficient-angle of attack correspondence table, a gain scheduling table for each feedback loop, a protection activation threshold, and a pitch angle / pitch rate threshold.

[0100] Software 715 may be stored in memory 710 and includes, but is not limited to, an operating system, one or more application programs, drivers, and / or other data and code. Instructions for performing the various functions described herein may be included in one or more application programs, and the components of the system may be implemented by processor 705 reading and executing the instructions of one or more application programs. In some cases, software 715 may not be directly executable by the processor, but may (e.g., when compiled and executed) enable the computer to perform the various functions described herein related to the envelope protection method for low-speed boundaries.

[0101] It is understood that the above hardware architecture is merely exemplary. In practical applications, the configuration and connection relationship of hardware components can be adjusted according to the airborne safety level and performance requirements, as long as the envelope protection function for low-speed boundaries described in this invention can be achieved.

[0102] The envelope protection scheme for low-speed boundaries described in this invention has at least the following two technical advantages compared to existing similar technologies: (1) During the command generation stage, the coordinated logic of dual limiting of angle of attack and overload and dynamic correction of pitch angle can simultaneously constrain the three core parameters of angle of attack, overload and pitch angle within the safe envelope range, and achieve synchronous coverage of multi-dimensional boundaries without switching different protection logics. Thus, it avoids the risk of attitude loss of control caused by extreme conditions such as strong gusts and single engine failure in scenarios with large angle of attack and excessive pitch angle when only angle of attack and overload limiting are used. It also avoids the problem of overload exceeding the standard or angle of attack overshoot stall in high speed stick scenarios. At the same time, it does not require switching between different protection functions, ensuring the continuity of operation response.

[0103] (2) In the closed-loop control stage, by introducing a speed feedback loop and a pitch angle attitude feedback loop, the short-cycle and long-cycle response modes of the aircraft can be stabilized simultaneously, thereby improving the robustness of high angle-of-attack protection. For example, the scheme that only uses angle-of-attack feedback can only stabilize the short-cycle mode, and the aircraft is prone to long-cycle oscillations of about 60 s, which causes the angle of attack to oscillate repeatedly at the limit boundary, resulting in a stall risk. In contrast, this scheme, by introducing speed and pitch angle feedback, can suppress long-cycle oscillations, ensure that the angle of attack is stable within the control range, and simultaneously constrain the flight speed within the safety envelope, thereby achieving multi-parameter coordinated protection.

[0104] The foregoing description includes examples of various aspects of the claimed subject matter. It is certainly impossible to describe every conceivable combination of components or methods for the purpose of depicting the claimed subject matter, but those skilled in the art will recognize that many further combinations and arrangements of the claimed subject matter are possible. Thus, the disclosed subject matter is intended to cover all such changes, modifications, and variations that fall within the spirit and scope of the appended claims.

Claims

1. A method for envelope protection at low-speed boundaries, characterized in that, The envelope protection method includes: Obtain angle of attack command; The maximum angle of attack is determined based on real-time flight status parameters, wherein the maximum angle of attack satisfies both the angle of attack protection limit and the overload limit, and the maximum angle of attack is set as the upper limit of the angle of attack; The lower limit of the angle of attack is determined based on at least one of the real-time flight state parameters and the maximum angle of attack. The angle of attack command is then limited using the upper and lower limits of the angle of attack as boundaries to obtain a limited angle of attack command. The angle-of-attack command, after being limited, is superimposed with the pitch-down correction associated with the pitch angle limit to generate the angle-of-attack control command. The pitch angle correction related to the pitch angle limit is generated using the following operation: When the aircraft's current pitch angle is greater than a first threshold and / or the current pitch rate is greater than a second threshold, a negative pitch-down correction is generated. The absolute value of this pitch-down correction is positively correlated with the pitch overshoot and / or pitch rate overshoot, where the pitch overshoot is the difference between the current pitch angle and the first threshold, and the pitch rate overshoot is the difference between the current pitch rate and the second threshold. When the aircraft’s current pitch angle is not greater than the first threshold and the current pitch rate is not greater than the second threshold, the angle of attack pitch correction is 0.

2. The method for protecting the envelope according to claim 1, characterized in that, Determining the maximum angle of attack based on flight state parameters includes: The first angle of attack that satisfies the angle of attack protection limit is determined based on the stall angle of attack, wherein the stall angle of attack is related to the flap and slat configuration, landing gear condition, and Mach number; A second angle of attack is determined based on a lift coefficient that matches the overload limit, wherein the overload limit is related to the flap / slat configuration; and The smaller of the first angle of attack and the second angle of attack is determined as the maximum angle of attack.

3. The method for protecting the wire envelope according to claim 2, characterized in that, The stall angle of attack is further related to icing conditions and sideslip angle parameters.

4. The method for protecting the envelope according to claim 2, characterized in that, Determining the second angle of attack that satisfies the overload limit based on the lift coefficient that matches the overload limit includes: The overload limitation is determined based on the flap-slat configuration in the flight status parameters. Determine the lift coefficient, wherein the lift coefficient is proportional to the limit overload and the current weight of the aircraft, and inversely proportional to the wing reference area and the current dynamic pressure corresponding to the corrected airspeed; and The second angle of attack corresponding to the lift coefficient is obtained based on the relationship between the lift coefficient and the angle of attack. The relationship between the lift coefficient and the angle of attack is dynamically adjusted according to the flap and slat configuration, landing gear status, and Mach number in the flight state parameters.

5. The method for protecting the envelope according to claim 1, characterized in that, Determining the lower limit of the angle of attack based on at least one of the flight state parameters and the maximum angle of attack includes: The lower limit of the angle of attack is determined based on the minimum operating speed obtained from the flight status parameters, wherein the minimum operating speed is related to the flap / slat configuration, landing gear configuration, Mach number, and / or weight in the flight status parameters; and / or The lower limit of the angle of attack is determined based on the lower limit margin obtained by downward offset of the maximum angle of attack.

6. The method for protecting the envelope according to claim 1, characterized in that, The envelope protection method further includes: The flight status parameters are used to determine whether the aircraft status meets the activation conditions. If it does, the angle of attack protection function is activated. The activation conditions include ground lift not activated, ground mode not activated, degraded mode not activated, and the current angle of attack being greater than the activation threshold.

7. The method for protecting the envelope according to claim 6, characterized in that, The envelope protection method further includes: In response to the activation of the angle-of-attack protection function, an elevator control command is generated by superimposing the output of the control loop based on the angle-of-attack control command. The control loop includes an angle-of-attack command feedforward loop, an angle-of-attack feedback loop, a velocity feedback loop, and an attitude feedback loop. The input of the angle-of-attack feedback loop includes the current angle of attack and the rate of change of angle of attack among the flight state parameters. The input of the velocity feedback loop includes the airspeed and / or the rate of change of airspeed among the flight state parameters. The input of the attitude feedback loop includes the pitch angle and / or the pitch rate among the flight state parameters.

8. The method for protecting the envelope according to claim 7, characterized in that, The gain parameters of the angle of attack command feedforward loop, the angle of attack feedback loop, the velocity feedback loop, and the attitude feedback loop in the control loop are dynamically adjusted according to the airspeed, flap / slat configuration, and angle of attack in the flight state parameters, so that the amplitude margin and phase margin of the adjusted control loop meet the stability requirements.

9. A envelope protection system for low-speed boundaries, characterized in that, The envelope protection system includes: The instruction calculation module is used to execute the envelope protection method as described in any one of claims 1 to 5 and generate angle of attack control instructions; The protection activation module is used to determine whether the aircraft state meets the activation conditions based on the flight state parameters. If the conditions are met, it outputs an angle-of-attack protection activation enable signal. The activation conditions include: ground lift not activated, ground mode not activated, degraded mode not activated, and the current angle of attack greater than the activation threshold. The protection control module is used to generate an elevator control command by superimposing the output of the control loop on the angle-of-attack protection activation enable signal received from the command calculation module.

10. The envelope protection system according to claim 9, characterized in that, The control loop includes: Angle of attack command feedforward loop, wherein the input of the angle of attack command feedforward loop includes the angle of attack control command; Angle of attack feedback loop, wherein the input of the angle of attack feedback loop includes the current angle of attack and the rate of change of angle of attack in the flight state parameters; A speed feedback loop, the input of which includes airspeed and / or airspeed rate of change among the flight state parameters; and An attitude feedback loop, wherein the inputs to the attitude feedback loop include the pitch angle and / or pitch rate from the flight state parameters. The gain parameters of the angle of attack command feedforward loop, the angle of attack feedback loop, the velocity feedback loop, and the attitude feedback loop are dynamically adjusted according to the airspeed, flap / slat configuration, and angle of attack in the flight state parameters, so that the amplitude margin and phase margin of the adjusted control loop meet the stability requirements.

11. A non-transient computer-readable medium storing computer-executable instructions that, when executed by an envelope protection system, perform the envelope protection method for low-speed boundaries as described in any one of claims 1 to 8.

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