Fixed time increment fault-tolerant control method for control surface hybrid fault aircraft

Abstract

The invention discloses a fixed time increment fault-tolerant control method for a control surface mixed fault aircraft. The method comprises the following steps: analyzing the fault type and performance of an aircraft control surface; modeling a control surface fault aircraft; improving the design of a tracking differentiator; designing an incremental dynamic inverse control law; and designing a fixed time increment dynamic inverse fault-tolerant controller. The control method provided by the embodiment of the invention is low in cost and simple in structure, can realize accurate acquisition of the angular acceleration signal and noise filtering, reduces hardware consumption of the angular acceleration sensor, and has a practical engineering application prospect; the robustness is high, and stable control and instruction tracking of the aircraft under the control surface mixed fault can be achieved; the method is high in convergence speed and good in steady-state performance, can guarantee that the faulty aircraft quickly recovers to be stable in a fixed time and accurately tracks the instruction, and effectively improves the flight performance of the faulty aircraft.

Description

A fixed-time incremental fault-tolerant control method for aircraft with mixed control surface failures Technical Field

[0001] This invention relates to the field of flight control technology, and in particular to a fixed-time incremental fault-tolerant control method for aircraft with mixed control surface failures. Background Technology

[0002] Control surface failures are a major safety hazard in aviation, encompassing three typical forms: jamming, damage, and loosening. These failures are characterized by uncertainty, asymmetry, and high destructiveness, severely threatening flight safety. After a failure occurs, fault-tolerant control is crucial for maintaining aircraft stability and ensuring a safe return, even enabling continued mission execution under fault conditions. It is a vital technical means for addressing control surface failures. Existing research on linear fault-tolerant control methods based on trim state point design can improve the flight performance of faulty aircraft, but when the aircraft state deviates from the controller's designed state point, the controller's performance degrades. Because aircraft typically exhibit complex nonlinearities and uncertain fault states after a control surface failure, linear fault-tolerant control methods cannot achieve stable control across the entire control envelope.

[0003] Nonlinear control methods can eliminate nonlinear terms in a system, achieving the desired dynamic characteristics and satisfying stable control across the entire control envelope. However, this method relies on accurate nonlinear coupling terms and control terms to eliminate the nonlinear components of the system. When uncertainties exist in the system model, the nonlinearity cannot be completely eliminated, reducing the system's robustness. Incremental nonlinear control methods, because they do not depend on the nonlinear coupling terms of the controlled object but only on sensor measurement information and the control performance matrix, have lower dependence on model accuracy and exhibit strong robustness, making them very suitable for the design of fault-tolerant control systems for aircraft with control surface failures.

[0004] Existing incremental nonlinear dynamic inverse control methods require feedback of the differential signal of the previous moment's state. Their robustness depends on this differential signal. However, in practical applications, aircraft are generally not equipped with angular acceleration sensors. The angular acceleration signal is usually obtained by differentially processing the angular velocity signal measured by a sensor. Sensor measurements inevitably suffer from noise interference, making it impossible to obtain an accurate angular acceleration signal and reducing the system's robustness. Furthermore, after a control surface failure, a fault-tolerant controller is needed to quickly compensate for the impact of the failure and restore the aircraft to a stable state. However, the convergence time of traditional incremental nonlinear dynamic inverse controllers is usually uncertain, and the convergence time of finite-time stable controllers is related to the initial state. Due to the uncertainty of control surface failures, the initial state is difficult to obtain in advance, and the convergence time increases with the severity of the failure, potentially causing the aircraft state to exceed the safety envelope.

[0005] Therefore, it is necessary to improve one or more of the problems existing in the above-mentioned related technical solutions.

[0006] It should be noted that this section is intended to provide background or context for the technical solutions of this disclosure as set forth in the claims. The description herein does not constitute an admission that it is prior art simply because it is included in this section. Summary of the Invention

[0007] The purpose of this invention is to provide a fixed-time incremental fault-tolerant control method for aircraft with mixed control surface failures, thereby overcoming, at least to some extent, one or more problems caused by the limitations and defects of related technologies.

[0008] This invention provides a fixed-time incremental fault-tolerant control method for aircraft with mixed control surface failures, comprising: S1, analysis of aircraft control surface failure types and performance: based on the impact of three types of control surface failures—jamming, loosening, and damage—on control surface performance, the performance degradation of the control surfaces under these three failure types is obtained; S2, modeling of aircraft with control surface failures: based on the relationship between the state variables in the angular rate differential equation and the control surfaces, combined with the control surface performance degradation, an affine nonlinear model of the angular rate loop of the aircraft with control surface failures is established; S3, improved tracking differentiator design: based on fixed-time stability theory, the tracking differentiator is improved to achieve the acquisition of angular acceleration signals and noise filtering; S4, incremental dynamic inverse control law design: the angular rate equation is expanded using a first-order Taylor series, ignoring higher-order terms, to obtain the incremental dynamic inverse control law; S5, design of a fixed-time incremental dynamic inverse fault-tolerant controller: introducing fixed-time stability theory, a fixed-time incremental dynamic inverse angular rate fault-tolerant controller is designed to achieve control of the aircraft with control surface failures within a fixed time period.

[0009] In this invention, in S1, when the aircraft control surface malfunctions into a control surface jamming, the output amount of the deflection angle of the malfunctioning control surface is... as follows:

[0010] in, Represents a constant, whose value is , The control surface jamming angle; when the aircraft control surface failure is due to control surface damage, the output of the deflection angle of the faulty control surface. as follows:

[0011] in, This represents the percentage of the damaged area. This is the input value for the control surface deflection angle command; when the aircraft control surface malfunctions (control surface slack), the output value is the deflection angle of the malfunctioning control surface. as follows:

[0012] in, For the deflection angle amplitude due to a control surface failure, For the deflection frequency due to a control surface failure, The initial phase of the deflection angle for a control surface fault.

[0013] In this invention, in S2, the affine nonlinear model of the aircraft angular rate loop in the control surface failure is as follows:

[0014] in, For aircraft state variables, p, q, and r represent the aircraft roll rate, pitch rate, and yaw rate, respectively. It is the control effectiveness matrix; To control the quantity, These represent the left inner elevon, right inner elevon, left outer elevon, right outer elevon, rudder, and canard, respectively. It is a nonlinear term that is independent of the control input; For aircraft output; This is the output matrix.

[0015] In this invention, in S3, the improved tracking differentiator is represented as follows:

[0016] in, It is the input signal The estimate, It is the input signal The differential; For sliding mode function; improve the parameters of the tracking differentiator: , , , , , , , , .

[0017] In this invention, in S4, the incremental dynamic inverse control law takes the following form:

[0018] in, This indicates the state of the control system at the previous sampling time. Indicates virtual control input; This represents the actual control output at the previous sampling time.

[0019] In this invention, in S5, the fixed-time incremental dynamic inverse angular rate fault-tolerant controller is represented as follows:

[0020] in, This refers to the fault-tolerant controller. Represents the error between the expected command and response for angular rate; matrix The elements in are defined as , The elements in are defined as Fault-tolerant controller parameters: , , , .

[0021] In this invention, in S5, the upper bound of the convergence time of the fault-tolerant controller is:

[0022] in, , .

[0023] The technical solution provided by this invention can include the following beneficial effects: The fixed-time incremental fault-tolerant control method for aircraft with mixed control surface failures in this invention is low in cost and simple in structure. It can accurately acquire angular acceleration signals and filter out noise, reducing the hardware consumption of angular acceleration sensors and has practical engineering application prospects. It is robust and can achieve stable control and command tracking of aircraft under mixed control surface failures. It has fast convergence speed and good steady-state performance, which can ensure that the faulty aircraft can quickly recover stability and accurately track commands within a fixed time, effectively improving the flight performance of the faulty aircraft. Attached Figure Description

[0024] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this disclosure and, together with the description, serve to explain the principles of this disclosure. It is obvious that the drawings described below are merely some embodiments of this disclosure, and those skilled in the art can obtain other drawings based on these drawings without any inventive effort.

[0025] Figure 1 shows a schematic diagram of a fixed-time incremental fault-tolerant control method for an aircraft with mixed control surface failures in an exemplary embodiment of the present disclosure; Figure 2 shows the time-domain simulation results of the improved tracking differentiator in an exemplary embodiment of the present disclosure, where (a) is the step command signal and the tracking signal, and (b) is the step numerical derivative and the differential signal extracted by the tracking differentiator; Figure 3 shows the frequency-domain simulation results of the improved tracking differentiator in an exemplary embodiment of the present disclosure, where (a) is the sinusoidal command signal and the tracking signal, and (b) is the sinusoidal numerical derivative and the differential signal extracted by the tracking differentiator. Differential signal; Figure 4 shows the digital simulation results under different input commands in the exemplary embodiments of this disclosure, wherein (a) is the roll rate command and response, (b) is the pitch rate command and response, (c) is the yaw rate command and response, and (d) is the aircraft control surface deflection; Figure 5 shows the digital simulation results under the mixed failure condition of control surfaces in the exemplary embodiments of this disclosure, wherein (a) is the roll rate command and response, (b) is the pitch rate command and response, (c) is the yaw rate command and response, and (d) is the aircraft control surface deflection. Detailed Implementation

[0026] Exemplary embodiments will now be described more fully with reference to the accompanying drawings. However, these exemplary embodiments can be implemented in many forms and should not be construed as limited to the examples set forth herein; rather, they are provided so that this disclosure will be more comprehensive and complete, and will fully convey the concept of the exemplary embodiments to those skilled in the art. The described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments.

[0027] Furthermore, the accompanying drawings are merely illustrative diagrams of embodiments of this disclosure and are not necessarily drawn to scale. The same reference numerals in the drawings denote the same or similar parts, and therefore repeated descriptions of them will be omitted. Some block diagrams shown in the drawings are functional entities and do not necessarily correspond to physically or logically independent entities.

[0028] This example implementation provides a fixed-time incremental fault-tolerant control method for an aircraft with mixed control surface failures. The method includes S1-S5, specifically as follows: S1, Analysis of aircraft control surface failure types and performance: Based on the impact of three types of control surface failures—jamming, loosening, and damage—on control surface performance, the performance degradation under these three failure types is obtained; S2, Modeling of aircraft with control surface failures: Based on the relationship between the state variables in the angular rate differential equation and the control surface, and combined with the control surface performance degradation, an affine nonlinear model of the angular rate loop for the aircraft with control surface failures is established; S3, Improved tracking differentiator design: Based on fixed-time stability theory, the tracking differentiator is improved to achieve angular acceleration signal acquisition and noise filtering; S4, Incremental dynamic inverse control law design: The angular rate equation is expanded using a first-order Taylor series, ignoring higher-order terms, to obtain the incremental dynamic inverse control law; S5, Design of a fixed-time incremental dynamic inverse fault-tolerant controller: Introducing fixed-time stability theory, a fixed-time incremental dynamic inverse angular rate fault-tolerant controller is designed to achieve control of the aircraft with control surface failures within a fixed time period.

[0029] The fixed-time incremental fault-tolerant control method in this embodiment is low-cost and simple in structure. It can accurately acquire angular acceleration signals and filter out noise, reducing the hardware consumption of angular acceleration sensors and showing promise for practical engineering applications. It is also robust, enabling stable control and command tracking of aircraft under mixed control surface faults. Furthermore, it has fast convergence speed and good steady-state performance, ensuring that the faulty aircraft can quickly recover stability and accurately track commands within a fixed time, effectively improving the flight performance of the faulty aircraft.

[0030] Please refer to Figure 1. The specific process of each step in the above embodiments will be explained below.

[0031] In S1, when the aircraft control surface malfunctions into a control surface jam, the aircraft's structure and control surface layout remain unchanged, and the aircraft's aerodynamic characteristics are consistent with normal conditions. When the control surface is jammed... At that time, the output of the deflection angle of the faulty control surface The value remains constant due to a freeze, as shown below: (1) Among them, Represents a constant, whose value is .

[0032] When an aircraft control surface malfunctions, specifically when the control surface is damaged, the effective area and control derivative of the damaged control surface change, resulting in a degraded control surface output effectiveness. When the damaged area... At that time, the actual control effect of the control surface is only... Faulty control surface deflection angle output as follows: (2) Among them, This is the input value for the control surface deflection angle command, i.e., the deflection angle value under the control surface deflection command.

[0033] When the aircraft control surface malfunctions into a loose control surface, the malfunctioning control surface is not controlled by the control signal, does not generate any force or torque, and floats with the aircraft. The output of the malfunctioning control surface deflection angle is... as follows: (3) Among them, For the deflection angle amplitude due to a control surface failure, For the deflection frequency due to a control surface failure, The initial phase of the deflection angle for a control surface fault.

[0034] Based on the above analysis, the aerodynamic characteristics, dynamics, and kinematic equations of the aircraft remain unchanged before and after the control surface jamming and loosening failures, and are the same as those of a normal aircraft model. After a control surface damage failure, the change in structural shape will alter the aircraft's mass, control derivatives, etc. However, since the weight of the control surface is much smaller than the weight of the entire aircraft, and the aerodynamic coefficients are minimally affected by control surface damage, it is assumed that the aircraft's equations of motion remain unchanged before and after the damage; only the control derivatives of the damaged control surfaces are affected, resulting in a degraded control surface output rudder effectiveness.

[0035] S2. Considering the relationship between the state variables in the angular rate differential equation and the control surfaces, and taking into account the control surface performance degradation, an affine nonlinear model of the angular rate loop for an aircraft with control surface failure is established. Under the condition of control surface failure, the actual control surface deflection... It can be represented as: (4) In the formula, For the control surface deflection command matrix; It is a 6th-order identity matrix; a diagonal matrix. Indicates the control surface malfunction, its elements , This indicates a normal situation. Indicates the first One control surface malfunction; The output of the deflection angle of the fault control surface is shown in the aforementioned formulas (1), (2) and (3).

[0036] Control surface position constraints It is expressed as follows: (5) In the formula, Indicates the first Each control surface takes into account the deflection command value after a fault. and They represent the first The minimum and maximum deflection values ​​of each control surface.

[0037] Since the effect of aircraft control surface deflection is reflected in torque, directly affecting the three-axis angular rates, control surface failures have a more significant impact on the aircraft angular rate loop. The affine nonlinear model of the aircraft angular rate loop in the case of control surface failure is as follows: (6) In the formula, For the controlled system (aircraft) state variables, p, q, and r represent the aircraft roll rate, pitch rate, and yaw rate, respectively. It is the control effectiveness matrix; To control the quantity, These represent the left inner elevon, right inner elevon, left outer elevon, right outer elevon, rudder, and canard, respectively. It is a nonlinear term that is independent of the control input; For aircraft output; This is the output matrix.

[0038] and The specific expression is as follows:

[0039]

[0040] in, , and These represent the roll, pitch, and yaw moments, which are independent of the control surfaces. , , , , , , , , , , For the aircraft to orbit in the body coordinate system Moment of inertia of the shaft, about Moment of inertia of the shaft, about Moment of inertia and product of inertia of the shaft; For dynamic pressure, For wing area, For the average aerodynamic chord length, For the exhibition length, , and They represent the first The roll, pitch, and yaw moment coefficients generated by each control surface.

[0041] S3. To address the difficulties and low accuracy in acquiring angular acceleration signals, a nonlinear control system as shown in equation (7) is defined based on fixed-time stability theory: In equation (7), yes The differential, It is the input signal The estimate, It is the input signal The differential; Sliding mode function; Nonlinear control system parameters: , , , , , , , The above parameters have no specific physical meaning. This nonlinear control system is globally fixed-time stable, and the upper bound of the convergence time is: (8) The improved tracking differentiator derived from system (7) is shown in equation (9): In equation (9), It is the input signal The estimate, It is the input signal The differential; For sliding mode function; improve the parameters of the tracking differentiator: , , , , , , , , The above parameters have no specific physical meaning.

[0042] It should be noted that fixed-time stability control is an extension of finite-time stability control. Its upper limit of convergence time is independent of the initial state and depends only on the controller parameters. Finite-time system stability under any initial conditions can be achieved through the design of system parameters.

[0043] S4, during the sampling time interval Next, performing a first-order Taylor series expansion on equation (6), we obtain the following equation: In formula (10), , These represent the control system state and control input respectively within a sampling time interval. Increment within; It represents a higher-order infinitesimal term.

[0044] When the sampling frequency is high enough, within a very small sampling time interval Internal control input The change is faster than the state quantity Therefore, state variables The value will be very close to the previous beat, and And higher-order terms This can be ignored, and the above formula can be further simplified to: (11) The incremental dynamic inverse control law can be obtained as follows: In formula (12), This indicates a virtual control input.

[0045] S5. To improve the convergence speed of the closed-loop system, the following fixed-time incremental dynamic inverse angular rate fault-tolerant controller is designed: In equation (13), This refers to the fault-tolerant controller. Represents the error between the expected command and response for angular rate; matrix The elements in are defined as , The elements in are defined as Fault-tolerant controller parameters: , , , The above parameters have no specific physical meaning.

[0046] definition , The designed fault-tolerant controller is semi-global, fixed-time, consistent, and eventually bounded, with an upper bound on the convergence time: (14) Combining the above steps, rapid and stable control of the aircraft under mixed control surface failures can be achieved.

[0047] Figure 2 shows the time-domain simulation results of the improved tracking differentiator, with the input command signal being a step signal containing Gaussian noise (variance 0.004). As can be seen from Figure 2(a), the improved tracking differentiator has a good filtering effect and can stably track the input command signal while suppressing noise; as can be seen from Figure 2(b), the improved tracking differentiator can accurately describe the differentiated signal and has good anti-interference ability.

[0048] Figure 3 shows the frequency domain simulation results of the improved tracking differentiator, with the input command signal being a sinusoidal signal containing Gaussian noise (variance 0.004). As can be seen from Figure 3(a), the improved tracking differentiator exhibits excellent tracking performance when tracking the sinusoidal response, with the tracked signal almost overlapping with the input command signal; as can be seen from Figure 3(b), the improved tracking differentiator can effectively eliminate noise interference and accurately describe the differentiated signal.

[0049] Figure 4 shows the input commands set to... and Simulation results of the time-tolerant controller; the balance point is selected as... , The angle of attack and angle of pitch are adjusted as follows: The upper bound of the convergence time can be set by parameters. As can be seen from Figure 4, under different input commands, the aircraft's roll rate, pitch rate, and yaw rate responses can all track the desired command within a fixed time, and the convergence time is consistent and unaffected by the initial state.

[0050] Figure 5 shows the simulation results of the fault-tolerant controller when a mixed failure occurs on the aircraft control surfaces. Considering the uncertainties such as noise in the acquisition of angular rate signals under actual conditions, Gaussian noise with a variance of 0.0025 is introduced into the improved tracking differentiator. The aircraft experiences left outer aileron jamming at 3, 7, and 10 seconds, respectively. The right outer aileron suffered 42% damage and the right inner aileron was loose. For mixed fault scenarios, the upper bound of the convergence time can be set by parameters. As can be seen from Figure 5, after the jamming fault occurred in the 3rd second, the roll rate response increased by approximately The jitter, under the action of the fault-tolerant controller After recovering to a stable state and continuing to track commands, the pitch and yaw rate responses were less affected by the left outer aileron jamming fault. Under the fault-tolerant controller, the effects of the fault were quickly eliminated, and command tracking resumed. After the right outer aileron was damaged in the 7th second... The rudder effectiveness decreased by 42%, and the rudder extension of the right inner aileron increased to compensate for the torque loss due to the damaged control surfaces. At this time, the three-axis angular rate responses were able to accurately track the commands. After the right inner aileron detached at the 10th second, the roll rate fluctuated significantly as the severity of the fault increased, but it could still maintain a fixed time under the action of the fault-tolerant controller. Once the pitch and yaw rates return to a stable state, they can also quickly return to a stable state and accurately track the desired commands.

[0051] In summary, the fixed-time-increment dynamic inverse fault-tolerant control method proposed in this invention is effective. It enables aircraft with mixed control surface failures to quickly recover to a stable state and achieve good command tracking, thereby improving the robustness and control performance of aircraft after mixed control surface failures.

[0052] It should be noted that although several modules of the system for executing actions are mentioned in the detailed description above, this division is not mandatory. In fact, according to embodiments of the present invention, the features and functions of two or more modules described above can be embodied in one module. Conversely, the features and functions of one module described above can be further divided into multiple modules for embodiment. Components shown as modules may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the modules can be selected to achieve the purpose of the present invention according to actual needs. Those skilled in the art can understand and implement this without any inventive effort.

[0053] The embodiments of the present invention have been described above with reference to the accompanying drawings. However, the present invention is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of the present invention without departing from the spirit and scope of the claims. All of these forms are within the protection scope of the present invention.

Claims

1. A fixed-time incremental fault-tolerant control method for an aircraft with mixed control surface failures, characterized in that, include: S1. Fault Types and Performance Analysis of Aircraft Control Surfaces: Based on the impact of three types of faults—jamming, loosening, and damage—on control surface performance, the performance degradation under these three fault types is obtained. S2. Aircraft Modeling with Control Surface Faults: Based on the relationship between the state variables in the angular rate differential equation and the control surfaces, and considering the performance degradation, an affine nonlinear model of the angular rate loop for aircraft with control surface faults is established. S3. Improved Tracking Differentiator Design: The tracking differentiator is improved based on fixed-time stability theory to achieve angular acceleration signal acquisition and noise filtering. S4. Incremental Dynamic Inverse Control Law Design: The angular rate equation is expanded using a first-order Taylor series, ignoring higher-order terms, to obtain the incremental dynamic inverse control law. S5. Fixed-Time Incremental Dynamic Inverse Fault-Tolerant Controller Design: Introducing fixed-time stability theory, a fixed-time incremental dynamic inverse angular rate fault-tolerant controller is designed to achieve control of the aircraft with control surface faults within a fixed time period.

2. The fixed-time incremental fault-tolerant control method for aircraft with mixed control surface failures according to claim 1, characterized in that, In S1, when the aircraft control surface malfunction is control surface jamming, the output of the deflection angle of the malfunctioning control surface is... as follows: in, Represents a constant, whose value is ， The control surface jamming angle; when the aircraft control surface failure is due to control surface damage, the output of the deflection angle of the faulty control surface. as follows: in, This represents the percentage of the damaged area. This is the input value for the control surface deflection angle command; when the aircraft control surface malfunctions (control surface slack), the output value is the deflection angle of the malfunctioning control surface. as follows: in, For the deflection angle amplitude due to a control surface failure, For the deflection frequency due to a control surface failure, The initial phase of the deflection angle for a control surface fault.

3. The fixed-time incremental fault-tolerant control method for aircraft with mixed control surface failures according to claim 1, characterized in that, In S2, the affine nonlinear model of the aircraft angular rate loop in the control surface failure is as follows: in, For aircraft state variables, p, q, and r represent the aircraft roll rate, pitch rate, and yaw rate, respectively. It is the control effectiveness matrix; To control the quantity, These represent the left inner elevon, right inner elevon, left outer elevon, right outer elevon, rudder, and canard, respectively. It is a nonlinear term that is independent of the control input; For aircraft output; This is the output matrix.

4. The fixed-time incremental fault-tolerant control method for aircraft with mixed control surface failures according to claim 3, characterized in that, In S3, the improved tracking differentiator is represented as follows: in, It is the input signal The estimate, It is the input signal The differential; For sliding mode function; improve the parameters of the tracking differentiator: ， ， ， ， ， ， ， ， 。 5. The fixed-time incremental fault-tolerant control method for aircraft with mixed control surface failures according to claim 4, characterized in that, In S4, the incremental dynamic inverse control law takes the following form: in, This indicates the state of the control system at the previous sampling time. Indicates virtual control input; This represents the actual control output at the previous sampling time.

6. The fixed-time incremental fault-tolerant control method for aircraft with mixed control surface failures according to claim 5, characterized in that, In S5, the fixed-time incremental dynamic inverse angular rate fault-tolerant controller is represented as follows: in, This refers to the fault-tolerant controller. Represents the error between the expected command and response for angular rate; matrix The elements in are defined as ， The elements in are defined as Fault-tolerant controller parameters: ， ， ， 。 7. The fixed-time-increment fault-tolerant control method for aircraft with mixed control surface failures according to claim 6, characterized in that, In S5, the upper bound of the convergence time of the fault-tolerant controller is: in, ， 。

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