Fly-by-wire aircraft two-step flight control mode switching instruction desalting device design method

Abstract

The invention provides a fly-by-wire aircraft two-step flight control mode switching instruction desalination device design method, which comprises the following steps: detecting a flight control mode trigger signal; calculating the difference between control instructions of an elevator control surface at the current moment and the last moment in real time; keeping the difference DU between the two control instructions during flight control mode switching; a first-level instruction DU1 needing to be desalted is obtained; second-stage desalination treatment is carried out, and a second-stage instruction DU2 needing desalination is obtained; generating a starting signal SWFADER of the single-step instruction desalting device; judging whether a single-step type instruction desalination device or a two-step type desalination device needs to be started or not; when a starting signal SWFADER of the single-step type instruction desalination device is equal to 1, starting the single-step type instruction desalination device; and when the SWFADER is equal to 0, the difference DU of the two control instructions indicating the switching of the flight control mode is greater than the threshold value for starting the second-stage desalination, and the two-step desalination device is started. According to the instruction desalting device design method, the transition time is optimized and the transient response is reduced, so that the performance of the flight control system is remarkably improved.

Description

Technical Field

[0001] The invention relates to the technical field of control laws of fly-by-wire aircraft, and in particular to a design method for a two-step flight control mode switching instruction desalter of a fly-by-wire aircraft. Background Art

[0002] Generally, civil transport fly-by-wire aircraft, in addition to setting the normal mode control law with all control functions, also set the direct link working mode. When a specific fault occurs, the flight control system will switch the control law from the normal mode control law to the direct link mode control law to ensure that the aircraft still has the appropriate flight quality capability after the fault occurs, thereby ensuring flight safety. The direct link mode control law is generally a simple control law configuration with consistent stick and rudder, that is, the stick displacement is in the neutral position and the rudder surface is also in the neutral position. In order to ensure the responsive horizontal tail when switching from the normal mode to the direct link mode, general civil transport fly-by-wire aircraft (A320, A350, etc.) all adopt a movable horizontal tail design. When the aircraft is flying stably, the elevator trim amount is unloaded through the movable horizontal tail so that the elevator can return to the neutral position. When the flight control mode is switched, since the elevators in the normal mode and the direct link mode are basically at zero position, the command difference is small, and the response of the transition process will be relatively small. For fly-by-wire aircraft with a fixed horizontal tail, the elevator trim amount cannot be offset by the movable horizontal tail.

[0003] At certain state points, there is a large elevator trim amount. When the flight control mode is switched, the elevator needs to fade from the normal control law trim position to zero in a short time, causing the aircraft to produce a large transient. At most state points in normal flight, the trim amount is small and will not produce excessive transients. Directly increasing the fade time can reduce transients, but it will cause the transition time of state points that do not require a long command transition to be too long, and a long command transition time will lead to uncontrollable risks. Summary of the invention

[0004] In order to solve the problems existing in the traditional fly-by-wire aircraft control law, the purpose of the present invention is to provide a design method for a two-step flight control mode switching command desalter for fly-by-wire aircraft, which can improve flight safety, enhance system reliability, improve control accuracy, simplify operation procedures and improve flexibility, and can ensure that the mode switching command transition time is short in most states, and can also ensure that the transient response is not too large in some special state points.

[0005] The present invention achieves the above-mentioned purpose through the following technical solutions:

[0006] A design method for a two-step flight control mode switching instruction desalter for a fly-by-wire aircraft, the method comprising the following steps:

[0007] Detect flight control mode trigger signal;

[0008] Calculate in real time the difference between the elevator control instructions at the current moment and the previous moment;

[0009] Keep the difference DU between the two control instructions when the flight control mode is switched;

[0010] Perform the first-level fading process to obtain the first-level fading instruction DU1;

[0011] Perform second-level fading processing to obtain the second-level fading instruction DU2;

[0012] Generate a single-step command fader start signal SW_FADER;

[0013] Determine whether to start a single-step instruction fader or a two-step fader:

[0014] When the single-step instruction fader start signal SW_FADER=1, the single-step instruction fader is started;

[0015] When SW_FADER=0, it means that the difference DU of the two control instructions for switching the flight control mode is greater than the threshold value for starting the second-level fade, and the two-step fader is started.

[0016] According to a design method of a two-step flight control mode switching command desalter for a fly-by-wire aircraft provided by the present invention, when detecting a flight control mode trigger signal, when the flight control mode trigger signal SW_MODE=1, the flight control mode is switched from a normal control law to a first control law, which is a relatively simpler and more reliable control law (a control law that uses fewer input parameters to ensure basic flight safety of the aircraft, such as rod displacement=transmission ratio*rudder deflection), and the elevator rudder control command ELE_CMD is switched from command A (normal control law) to command B (simple control law), which is expressed as the following formula:

[0017] ELE_CMD = SW_MODE*Command B – (SW_MODE-1)*Command A

[0018] According to a design method of a two-step flight control mode switching instruction fader for a fly-by-wire aircraft provided by the present invention, the calculation of the difference between the elevator control surface control instructions at the current moment and the previous moment includes:

[0019] The elevator control surface control instruction ELE_CMD at the previous moment is subtracted in real time from the elevator control surface control instruction ELE_CMD at the current moment (-1) to obtain the elevator control instruction difference DU0 between the current moment and the previous moment.

[0020] According to a design method of a two-step flight control mode switching instruction fader for a fly-by-wire aircraft provided by the present invention, the difference DU of two control instructions when the flight control mode is switched is maintained, comprising:

[0021] When the flight control mode trigger signal SW_MODE=1, the trigger holder works and keeps outputting the elevator control command difference DU between the current moment and the previous moment, that is, the difference between the two control commands when the flight control mode is switched, which is expressed as the following formula:

[0022] DU = instruction B - instruction A

[0023] According to a design method of a two-step flight control mode switching instruction desalter for a fly-by-wire aircraft provided by the present invention, the first-level instruction DU1 to be desalinated is obtained, comprising:

[0024] The difference DU of the two control instructions when the flight control mode is switched is passed through the instruction limiter to obtain the first-level instruction DU1 that needs to be diluted. That is, when the instruction difference DU is less than the limit range, the output DU1 = DU value, and when the instruction difference DU is greater than the limit range, the output DU1 is equal to the limit value, which is expressed as the following formula:

[0025]

[0026] The command limit is a signal threshold value set in advance for starting the second-level fade.

[0027] According to a design method of a two-step flight control mode switching instruction desalter for a fly-by-wire aircraft provided by the present invention, the second-level instruction DU2 to be desalinated is obtained, comprising:

[0028] The instruction difference DU is subtracted from the instruction DU1 that needs to be faded at the first level to obtain the instruction DU2 that needs to be faded at the second level, which is expressed as the following formula:

[0029] DU2=DU-DU1

[0031] According to a design method of a two-step flight control mode switching command fader for a fly-by-wire aircraft provided by the present invention, the generating of a single-step command fader start signal SW_FADER comprises:

[0032] When the second-stage fade instruction DU2 passes through the state judgment module, the single-step instruction fader start signal SW_FADER is obtained, that is, when DU2=0, SW_FADER=1, it indicates that the mode switching instruction difference DU is less than the threshold value for starting the second-stage fade, that is, there is no need to start the two-step fader, and the rudder instruction output is connected to the single-step instruction fader.

[0033] According to a design method for a two-step flight control mode switching command fader for a fly-by-wire aircraft provided by the present invention, the single-step command fader is a linear fader, that is, the command DU1 is linearly faded to 0 within a specified time FadeTime1, and the control command ELE_CMD of the current step length is superimposed on the real-time fade command DU_F to obtain the control surface command, which is expressed as the following formula:

[0034] Rudder command = ELE_CMD-DU_F

[0035] According to a design method for a two-step flight control mode switching command fader for a fly-by-wire aircraft provided by the present invention, when the signal SW_FADER=0, it indicates that the command difference DU for mode switching is greater than the threshold value for starting the second-level fade, that is, the two-step fader needs to be started, and the control surface command output connects to the two-step command fader.

[0036] According to a design method of a two-step flight control mode switching instruction desalter for a fly-by-wire aircraft provided by the present invention, the two-step desalter is formed by superimposing two desalters, which are started in sequence according to time;

[0037] Among them, the first-stage desalination device is a single-step desalination device, and the command value to be desalinated is the threshold value of the limiter module. It is linearly desalinated to 0 within the specified time FadeTime1, and the real-time desalination command generated is DU_F1; the second-stage desalination device DU2 first goes through a delayed start link, and starts to start desalination device B after the time FadeTime1. Desalination device B is a linear desalination device, that is, the command difference DU2 is linearly desalinated to 0 within the specified time FadeTime2, and the real-time desalination command generated is DU_F2; the control command ELE_CMD of the current step length is superimposed on the real-time desalination commands DU_F1 and DU_F2 to obtain the rudder command, which is expressed as the following formula:

[0038] Rudder command = ELE_CMD-DU_F1-DU_F2.

[0039] In the present invention, the real-time fading adopts linear fading logic. Assuming the fading time is ΔT, the real-time fading instruction calculation formula is as follows:

[0040] Fade real-time instruction = required fade instruction value * f(t)

[0041] In the formula, function f(t) is the fade function, and the specific formula is as follows:

[0042]

[0043] Wherein, t is the real time starting from the fade start time t=0.

[0044] It can be seen that the present invention has the following beneficial effects:

[0045] 1. The present invention uses a two-step fading process to ensure that the elevator control surface control command can smoothly transition when the flight control mode is switched, avoiding flight instability and dangerous situations that may be caused by sudden changes in the command. During the switching process, the present invention effectively prevents overload on the aircraft structure or system caused by excessive control commands through command limiting and gradual fading, thereby protecting the safety of the aircraft.

[0046] 2. The present invention designs a command limit and two-stage desalination mechanism, which can maintain the stable operation of the system through redundancy and gradual adjustment even when some sensors or systems fail. The present invention prevents system failures caused by command errors or mutations by real-time monitoring and judging the command difference and timely starting the corresponding desalination device.

[0047] 3. The present invention gradually fades the instruction difference to 0 through a linear fader, thereby achieving precise adjustment of the control instruction and improving the accuracy and stability of flight control. The present invention flexibly selects a single-step or two-step fader according to the size and characteristics of the instruction difference, ensuring on-demand adjustment and optimization of the control instruction.

[0048] 4. The present invention realizes the automatic desalination processing of the flight control mode switching instruction, reduces the operating burden of the pilot and improves the operating efficiency. The method is based on a linear desalter and simple logical judgment, and is easy to implement and integrate in the existing flight control system.

[0049] 5. The method of the present invention is not only applicable to the switching of flight control modes, but can also be extended to other control scenarios that require smooth transition, such as engine thrust adjustment, flight attitude adjustment, etc. Parameters such as fade time and limit value can be configured and adjusted according to actual needs to adapt to different flight missions and conditions.

[0050] The present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Figure 1 The present invention is a flow chart of an embodiment of a design method of a two-step flight control mode switching instruction desalter for a fly-by-wire aircraft.

[0052] Figure 2 The present invention is a logic principle diagram of a two-step flight control mode desalter in an embodiment of a design method for a two-step flight control mode switching instruction desalter for a fly-by-wire aircraft.

[0053] Figure 3 The present invention is a schematic diagram of the use effect of a two-step flight control mode desalter in an embodiment of a design method for a two-step flight control mode switching instruction desalter for a fly-by-wire aircraft. DETAILED DESCRIPTION

[0054] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be clearly and completely described below in conjunction with the drawings of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0055] Reference to "embodiments" herein means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment of the present application. The appearance of the phrase in various locations in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0056] See also Figure 1 and Figure 2 The present invention provides a design method for a two-step flight control mode switching instruction desalter for a fly-by-wire aircraft, the method comprising the following steps:

[0057] Step S1, detecting a flight control mode trigger signal;

[0058] Step S2, calculating in real time the difference between the elevator control surface control instructions at the current moment and the previous moment;

[0059] Step S3, maintaining the difference DU of the two control instructions when the flight control mode is switched;

[0060] Step S4, performing a first-level fading process to obtain a first-level fading instruction DU1;

[0061] Step S5, performing second-level fading processing to obtain the second-level fading instruction DU2;

[0062] Step S6, generating a single-step instruction fader start signal SW_FADER;

[0063] Step S7, determining whether it is necessary to start a single-step instruction desalter or a two-step desalter:

[0064] Step S8, when the single-step instruction fader start signal SW_FADER=1, start the single-step instruction fader;

[0065] Step S9, when SW_FADER=0, it means that the difference DU of the two control instructions for switching the flight control mode is greater than the threshold value for starting the second-level fade, and the two-step fader is started.

[0066] In the above step S1, when the flight control mode trigger signal is detected, when the flight control mode trigger signal SW_MODE=1, the flight control mode is switched from the normal control law to the first control law, which is a relatively simpler and more reliable control law (a control law that uses fewer input parameters to ensure the basic flight safety of the aircraft, such as rod displacement=transmission ratio*rudder deflection), and the elevator control surface control instruction ELE_CMD is switched from instruction A (normal control law) to instruction B (simple control law), which is expressed as the following formula:

[0067] ELE_CMD = SW_MODE*Command B – (SW_MODE-1)*Command A

[0068] In the above step S2, the difference between the elevator control surface control instructions at the current moment and the previous moment is calculated, including:

[0069] The elevator control surface control command ELE_CMD(-1) at the previous moment is subtracted from the current moment elevator control surface control command ELE CMD in real time to obtain the elevator control command difference DU0 between the current moment and the previous moment.

[0070] In the above step S3, the difference DU of the two control instructions when the flight control mode is switched is maintained, including:

[0071] When the flight control mode trigger signal SW_MODE=1, the trigger holder works and keeps outputting the elevator control command difference DU between the current moment and the previous moment, that is, the difference between the two control commands when the flight control mode is switched, which is expressed as the following formula:

[0072] DU = instruction B - instruction A

[0073] In the above step S4, the first level instruction DU1 to be faded is obtained, including:

[0074] The difference DU of the two control instructions when the flight control mode is switched is passed through the instruction limiter to obtain the first-level instruction DU1 that needs to be diluted. That is, when the instruction difference DU is less than the limit range, the output DU1 = DU value, and when the instruction difference DU is greater than the limit range, the output DU1 is equal to the limit value, which is expressed as the following formula:

[0075]

[0076] The command limit is a signal threshold value set in advance to start the second-level fade. In this embodiment, the limit threshold value is ±5 degrees.

[0077] In the above step S5, the second level instruction DU2 that needs to be faded is obtained, including:

[0078] The instruction difference DU is subtracted from the instruction DU1 that needs to be faded at the first level to obtain the instruction DU2 that needs to be faded at the second level, which is expressed as the following formula:

[0079] DU2=DU-DU1

[0081] In the above step S6, the generating of the single-step instruction fader start signal SW_FADER includes:

[0082] When the second-stage fade instruction DU2 passes through the state judgment module, the single-step instruction fader start signal SW_FADER is obtained, that is, when DU2=0, SW_FADER=1, it indicates that the mode switching instruction difference DU is less than the threshold value for starting the second-stage fade, that is, there is no need to start the two-step fader, and the rudder instruction output is connected to the single-step instruction fader.

[0083] In this embodiment, the single-step instruction fader is a linear fader, that is, the instruction DU1 is linearly faded to 0 within the specified time FadeTime1, and the control instruction ELE_CMD of the current step length is superimposed on the real-time fade instruction DU_F to obtain the rudder instruction, which is expressed as the following formula:

[0084] Rudder command = ELE_CMD-DU_F

[0085] In the present invention, the real-time fading adopts linear fading logic. Assuming the fading time is ΔT, the real-time fading instruction calculation formula is as follows:

[0086] Fade real-time instruction = required fade instruction value * f(t)

[0087] In the formula, function f(t) is the fade function, and the specific formula is as follows:

[0088]

[0089] Wherein, t is the real time starting from the fade start time t=0.

[0090] In the above step S9, when the signal SW_FADER=0, it means that the command difference DU of the mode switching is greater than the threshold value for starting the second-level fade, that is, the two-step fader needs to be started, and the control surface command output connects the two-step command fader.

[0091] In this embodiment, the two-step desalination device is composed of two desalination devices stacked together, which are started in sequence according to time;

[0092] Among them, the first-stage desalination device is a single-step desalination device, and the command value to be desalinated is the threshold value of the limiter module. It is linearly desalinated to 0 within the specified time FadeTime1, and the real-time desalination command generated is DU_F1; the second-stage desalination device DU2 first goes through a delayed start link, and starts to start desalination device B after the time FadeTime1. Desalination device B is a linear desalination device, that is, the command difference DU2 is linearly desalinated to 0 within the specified time FadeTime2, and the real-time desalination command generated is DU_F2; the control command ELE_CMD of the current step length is superimposed on the real-time desalination commands DU_F1 and DU_F2 to obtain the rudder command, which is expressed as the following formula:

[0093] Rudder command = ELE_CMD–DU_F1–DU_F2.

[0094] Preferably, the fade times FadeTime1 and FadeTime2 in this embodiment are both 8 seconds.

[0095] Specifically, when applying the design method of a two-step flight control mode switching instruction desalter for a fly-by-wire aircraft provided in this embodiment, it includes:

[0096] Record the instruction difference DU0 between the normal mode control instruction A and the direct link mode control instruction B in real time;

[0097] When the flight control mode switching signal SW_FCMMODE is triggered, the command difference DU0 at the triggering moment is recorded;

[0098] The command difference DU0 is judged. When DU0 is less than the preset threshold value, the single-step fader is started to fade the command, so as to ensure that when the mode switching command is small, the normal mode control command can be quickly switched to the direct chain control command without generating excessive transient response.

[0099] When the instruction difference DU0 is greater than the preset threshold value, the two-step fader is started to fade the instruction. First, the first-level instruction fade is started to fade the given instruction difference within the specified time FadeTime1, thereby quickly releasing a part of the control surface authority to ensure more flight safety margin under the direct link control law; secondly, after the first-level fader is executed, the second-level instruction fade is started to reduce the transient state during mode switching.

[0100] like Figure 3 As shown, Figure 3 This is a comparison chart of the usage effects of a two-step flight control mode fader and a single-step fader. Figure 3The comparison simulation results of two-step and single-step desalination are given in the paper. The two-step desalination first desalinates part of the control surface command difference within 8 seconds to ensure that the remaining control surface can maintain safe flight, and then further desalinates the remaining control surface to reduce transient response. Figure 3 It can be seen that the normal overload response of the aircraft is significantly downgraded, and the effect is significant.

[0101] In summary, the present invention uses a two-step fading process to enable a smooth transition of the elevator control command when the flight control mode is switched, thereby avoiding flight instability and dangerous situations that may be caused by sudden changes in the command. During the switching process, the present invention effectively prevents overload on the aircraft structure or system caused by excessive control commands through command limiting and gradual fading, thereby protecting the safety of the aircraft.

[0102] The present invention designs a command limit and a two-stage desalination mechanism, which can maintain the stable operation of the system through redundancy and gradual adjustment even when some sensors or systems fail. The present invention prevents system failures caused by command errors or mutations by real-time monitoring and judging the command difference and timely starting the corresponding desalination device.

[0103] The present invention gradually fades the instruction difference to 0 through a linear fader, thereby achieving accurate adjustment of the control instruction and improving the accuracy and stability of flight control. The present invention flexibly selects a single-step or two-step fader according to the size and characteristics of the instruction difference, ensuring on-demand adjustment and optimization of the control instruction.

[0104] The present invention realizes the automatic desalination processing of the flight control mode switching instruction, reduces the operation burden of the pilot, and improves the operation efficiency. The method is based on a linear desalter and simple logical judgment, and is easy to implement and integrate in the existing flight control system.

[0105] The present invention is not only applicable to the switching of flight control modes, but can also be extended to other control scenarios that require smooth transition, such as engine thrust adjustment, flight attitude adjustment, etc. Parameters such as fade time and limit value can be configured and adjusted according to actual needs to adapt to different flight missions and conditions.

[0106] The present invention can be applied to a fly-by-wire aircraft with an excessively large transient response when switching flight control modes. The invention has a simple structure and can be extended to be applied to all fly-by-wire aircraft with an excessively large transient response when switching flight control modes.

[0107] The technical features of the above embodiments may be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0108] The above-mentioned embodiments are only preferred embodiments of the present invention and cannot be used to limit the scope of protection of the present invention. Any non-substantial changes and substitutions made by technicians in this field on the basis of the present invention shall fall within the scope of protection required by the present invention.

Claims

1. A design method for a two-step flight control mode switching instruction desalter for a fly-by-wire aircraft, characterized in that: The following steps are involved: Detect flight control mode trigger signal; Calculate the difference DU0 between the elevator control command at the current moment and the previous moment in real time; Keep the difference DU between the two control instructions when the flight control mode is switched; Perform the first-level fading process to obtain the first-level fading instruction DU1; Perform second-level fading processing to obtain the second-level fading instruction DU2; Generate a single-step command fader start signal SW_FADER; Determine whether to start a single-step instruction fader or a two-step fader: When the single-step instruction fader start signal SW_FADER=1, the single-step instruction fader is started; When SW_FADER=0, it means that the difference DU of the two control instructions for switching the flight control mode is greater than the threshold value for starting the second-level fade, and the two-step fader is started.

2. The method according to claim 1, characterized in that: When detecting the flight control mode trigger signal, when the flight control mode trigger signal SW_MODE=1, the flight control mode is switched from the normal control law to the first control law, and the elevator control command ELE_CMD is switched from command A to command B, which is expressed as the following formula: ELE_CMD = SW_MODE*command B – (SW_MODE-1)*command A.

3. The method according to claim 1, characterized in that The step of calculating the difference between the elevator control surface control instructions at the current moment and the previous moment includes: The elevator control surface control instruction ELE_CMD at the previous moment is subtracted in real time from the elevator control surface control instruction ELE_CMD at the current moment (-1) to obtain the elevator control instruction difference DU0 between the current moment and the previous moment.

4. The method according to claim 1, characterized in that The difference DU of the two control instructions when maintaining the flight control mode switching includes: When the flight control mode trigger signal SW_MODE=1, the trigger holder works and keeps outputting the elevator control command difference DU between the current moment and the previous moment, that is, the difference between the two control commands when the flight control mode is switched, which is expressed as the following formula: DU=instruction B-instruction A.

5. The method according to claim 1, characterized in that The step of obtaining the first level instruction DU1 that needs to be faded includes: The difference DU of the two control instructions when the flight control mode is switched can be obtained after the instruction limiter to obtain the first-level instruction DU1 that needs to be faded, that is, when the instruction difference DU is less than the limit range, the output DU1=DU value, when the instruction difference DU is greater than the limit range, the output DU1 is equal to the limit value; wherein the instruction limit module is the signal threshold value set in advance to start the second-level fade, which is expressed as the following formula:

6. The method according to claim 1, characterized in that The step of obtaining the second level instruction DU2 that needs to be faded includes: The instruction difference DU is subtracted from the instruction DU1 that needs to be faded at the first level to obtain the instruction DU2 that needs to be faded at the second level, which is expressed as the following formula: DU2=DU-DU1.

7. The method according to claim 1, characterized in that The generating of the single-step instruction fader start signal SW_FADER comprises: When the second-stage fade instruction DU2 passes through the state judgment module, the single-step instruction fader start signal SW_FADER is obtained, that is, when DU2=0, SW_FADER=1, it indicates that the mode switching instruction difference DU is less than the threshold value for starting the second-stage fade, that is, there is no need to start the two-step fader, and the rudder instruction output is connected to the single-step instruction fader.

8. The method according to claim 1, characterized in that: The single-step command fader is a linear fader, that is, the command DU1 is linearly faded to 0 within the specified time FadeTime1. The control command ELE_CMD of the current step length is superimposed on the real-time fade command DU_F to obtain the rudder command, which is expressed as the following formula: Rudder command = ELE_CMD-DU_F.

9. The method according to any one of claims 1 to 8, characterized in that: When the signal SW_FADER=0, it indicates that the command difference DU of the mode switching is greater than the threshold value for starting the second-level fade, that is, the two-step fader needs to be started, and the control surface command output connects the two-step command fader.

10. The method according to claim 9, characterized in that: The two-step desalination device is composed of two desalination devices stacked together, which are started in sequence according to time; Among them, the first-stage desalination device is a single-step desalination device, and the command value to be desalinated is the threshold value of the limiter module. It is linearly desalinated to 0 within the specified time FadeTime1, and the real-time desalination command generated is DU_F1; the second-stage desalination device DU2 first goes through a delayed start link, and starts to start desalination device B after the time FadeTime1. Desalination device B is a linear desalination device, that is, the command difference DU2 is linearly desalinated to 0 within the specified time FadeTime2, and the real-time desalination command generated is DU_F2; the control command ELE_CMD of the current step length is superimposed on the real-time desalination commands DU_F1 and DU_F2 to obtain the rudder command, which is expressed as the following formula: Rudder command = ELE_CMD-DU_F1-DU_F2.

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