A design method for a two-step flight control mode switching command de-escalator for fly-by-wire aircraft

Abstract

The present invention provides a design method for a two-step flight control mode switching command fader for fly-by-wire aircraft, comprising detecting a flight control mode trigger signal; calculating in real time the difference between the elevator control commands at the current moment and the previous moment; maintaining the difference DU of the two control commands during flight control mode switching; performing a first-level fade process to obtain a first-level fade command DU1; performing a second-level fade process to obtain a second-level fade command DU2; generating a single-step command fader start signal SW_FADER; and determining whether to activate the single-step command fader or the two-step fader: when the single-step command fader start signal SW_FADER = 1, the single-step command fader is activated; when SW_FADER = 0, indicating that the difference DU of the two control commands for flight control mode switching is greater than a threshold for activating the second-level fade, the two-step fader is activated. The command fader design method of the present invention significantly improves the performance of the flight control system by optimizing transition time and reducing transient response.

Description

Technical Field

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

[0002] Typically, civil transport fly-by-wire aircraft employ a direct-link mode in addition to the normal mode control law, which encompasses all control functions. Upon the occurrence of a specific fault, the flight control system switches from the normal mode control law to the direct-link mode control law to ensure the aircraft maintains adequate flight qualities and flight safety even after the fault. The direct-link mode control law typically employs a simple control law configuration where the stick and rudder are aligned, meaning that when the stick is in a neutral position, the rudder surfaces are also in a neutral position. To ensure a responsive horizontal tail during the transition from normal mode to direct-link mode, civil transport fly-by-wire aircraft (such as the A320 and A350) typically utilize a movable horizontal tail. When the aircraft is in stable flight, the movable horizontal tail unloads the elevator trim, allowing the elevator to return to its neutral position. When the flight control mode transition occurs, since the elevators are essentially at zero position in both normal and direct-link modes, the command difference is minimal, resulting in a relatively slow transition response. However, for fly-by-wire aircraft with a fixed horizontal tail, the elevator trim cannot be offset by the movable horizontal tail.

[0003] At certain states, the elevator trim amount is large. When switching flight control modes, the elevator must quickly fade from the normal control law trim position to zero, resulting in significant transients. During normal flight, the trim amount is small at most states, and significant transients are not expected. Simply increasing the fade time can reduce transients, but this can result in extended transition times at states where a long transition is not necessary. This can 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 de-escalator for fly-by-wire aircraft. This method can improve flight safety, enhance system reliability, improve control accuracy, simplify operation procedures and increase flexibility. It can ensure that the mode switching command transition time is short in most states and that the transient response is not excessive 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 the difference between the elevator control instructions at the current moment and the previous moment in real time;

[0009] Maintain the difference DU between the two control commands when switching the flight control mode;

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

[0011] Perform the second-level desalination process to obtain the second-level desalination instruction DU2;

[0012] Generate a single-step instruction 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 indicates that the difference DU between the two control instructions for switching the flight control mode is greater than the threshold value for starting the second-stage fader, and the two-step fader is started.

[0016] According to the present invention, a design method for a two-step flight control mode switching command de-escalator for a fly-by-wire aircraft is provided. When a 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. This control law is a relatively simpler and more reliable control law (using fewer input parameters to ensure basic flight safety of the aircraft, such as stick displacement = transmission ratio * control surface deflection). The elevator 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 for a two-step flight control mode switching command desalter for a fly-by-wire aircraft provided by the present invention, the step of calculating the difference between the elevator control command at the current moment and the elevator control command at the previous moment includes:

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

[0020] According to the present invention, a design method for a two-step flight control mode switching instruction desalter for a fly-by-wire aircraft is provided, wherein the method maintains the difference DU of two control instructions during flight control mode switching, including:

[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 for a two-step flight control mode switching instruction desalter for a fly-by-wire aircraft provided by the present invention, obtaining the first-level instruction DU1 that needs to be desalted includes:

[0024] The difference DU of the two control commands when switching the flight control mode is subjected to command clipping to obtain the first-level command DU1 that needs to be diluted. That is, when the command difference DU is less than the clipping range, the output DU1 = DU value; when the command difference DU is greater than the clipping range, the output DU1 is equal to the clipping value, which can be 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 for a two-step flight control mode switching instruction desalter for a fly-by-wire aircraft provided by the present invention, obtaining the second-level instruction DU2 that needs to be desalted includes:

[0028] Subtract the first-level de-emphasized instruction DU1 from the instruction difference DU to obtain the second-level de-emphasized instruction DU2, which can be expressed as the following formula:

[0029] DU2=DU-DU1

[0030] 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, generating a single-step command fader start signal SW_FADER includes:

[0031] When the second-stage fade instruction DU2 passes through the status judgment module, the single-step instruction fader start signal SW_FADER is obtained. That is, when DU2=0 and 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.

[0032] 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:

[0033] Control surface command = ELE_CMD-DU_F

[0034] According to a design method for a two-step flight control mode switching command desalter for 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 desalination, that is, the two-step desalination needs to be activated, and the control surface command output is connected to the two-step command desalination.

[0035] 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, the two-step desalter is composed of two superimposed desalters, which are started in sequence according to time;

[0036] The first-stage desalination device is a single-step desalination device. 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 generated real-time desalination command is DU_F1. The second-stage desalination device DU2 first goes through a delayed start link. After the time FadeTime1, desalination device B is started. Desalination device B is a linear desalination device. That is, the command difference DU2 is linearly desalinated to 0 within the specified time FadeTime2. The generated real-time desalination command 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:

[0037] Rudder command = ELE_CMD-DU_F1-DU_F2.

[0038] In the present invention, real-time fading adopts linear fading logic. Assuming that the fading time is ΔT, the real-time fading instruction calculation formula is as follows:

[0039] Fade real-time instruction = required fade instruction value * f(t)

[0040] In the formula, function f(t) is the fade function, and the specific formula is as follows

[0041]

[0042] Wherein, t is the real time starting from the fade start time t=0.

[0043] It can be seen that the present invention has the following beneficial effects:

[0044] 1. The present invention utilizes a two-step fade process to ensure a smooth transition of elevator control commands during flight control mode switching, avoiding flight instability and hazards that could result from sudden command changes. During the switching process, the present invention utilizes command limiting and gradual fade-out to effectively prevent overloads on the aircraft structure or systems caused by excessive control commands, thereby ensuring aircraft safety.

[0045] 2. This invention incorporates command limiting and a two-stage desalination mechanism. This mechanism maintains stable system operation through redundancy and gradual adjustments, even in the event of sensor or system failures. By monitoring and determining command variances in real time and activating the appropriate desalination device promptly, this invention prevents system failures caused by command errors or sudden changes.

[0046] 3. This invention uses a linear desalination device to gradually desalinate the command differential to zero, achieving precise adjustment of control commands and improving flight control accuracy and stability. This invention flexibly selects a single-step or two-step desalination device based on the size and characteristics of the command differential, ensuring on-demand adjustment and optimization of control commands.

[0047] 4. This invention implements automated desalination processing of flight control mode switching instructions, reducing the pilot's operational burden and improving operational efficiency. Based on a linear desalination device and simple logical judgment, this method is easy to implement and integrate into existing flight control systems.

[0048] 5. The method of this invention is not only applicable to flight control mode switching but can also be extended to other control scenarios requiring smooth transitions, such as engine thrust adjustment and flight attitude adjustment. 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.

[0049] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Figure 1 The present invention is a flow chart of an embodiment of a method for designing a two-step flight control mode switching instruction desalter for a fly-by-wire aircraft.

[0051] 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.

[0052] Figure 3 The present invention is a schematic diagram of the use effect of a two-step flight control mode switching instruction 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

[0053] To make the objectives, technical solutions, and advantages of the present invention more clear, the technical solutions of the present invention will be clearly and completely described below in conjunction with the accompanying drawings. Obviously, the embodiments described are only some of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts shall fall within the scope of protection of the present invention.

[0054] References herein to "embodiments" mean that a particular feature, structure, or characteristic described in connection with the embodiments may be included in at least one embodiment of the present application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor does it constitute an independent or alternative embodiment that is mutually exclusive of other embodiments. It is understood, both explicitly and implicitly, by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0055] 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:

[0056] Step S1, detecting a flight control mode trigger signal;

[0057] Step S2, calculating in real time the difference between the elevator control instructions at the current moment and the previous moment;

[0058] Step S3, maintaining the difference DU between the two control instructions when the flight control mode is switched;

[0059] Step S4, performing the first-level desalination process to obtain the first-level desalination instruction DU1;

[0060] Step S5, performing a second-level desalination process to obtain a second-level desalination instruction DU2;

[0061] Step S6, generating a single-step instruction fader start signal SW_FADER;

[0062] Step S7, determining whether it is necessary to start a single-step instruction desalter or a two-step desalter:

[0063] Step S8, when the single-step instruction fader start signal SW_FADER=1, start the single-step instruction fader;

[0064] Step S9: when SW_FADER=0, indicating that the difference DU between the two control instructions for switching the flight control mode is greater than the threshold for starting the second-stage fader, the two-step fader is started.

[0065] 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 (using fewer input parameters to ensure basic flight safety of the aircraft, such as stick displacement=transmission ratio*control surface deflection), and the elevator 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:

[0066] ELE_CMD = SW_MODE*Command B – (SW_MODE-1)*Command A

[0067] 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:

[0068] 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.

[0069] In the above step S3, the difference DU between the two control instructions when the flight control mode is switched is maintained, including:

[0070] 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:

[0071] DU = instruction B - instruction A

[0072] In the above step S4, obtaining the first-level instruction DU1 that needs to be faded includes:

[0073] The difference DU of the two control commands when switching the flight control mode is subjected to command clipping to obtain the first-level command DU1 that needs to be diluted. That is, when the command difference DU is less than the clipping range, the output DU1 = DU value; when the command difference DU is greater than the clipping range, the output DU1 is equal to the clipping value, which can be expressed as the following formula:

[0074]

[0075] 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.

[0076] In the above step S5, obtaining the second-level fade instruction DU2 includes:

[0077] Subtract the first-level de-emphasized instruction DU1 from the instruction difference DU to obtain the second-level de-emphasized instruction DU2, which can be expressed as the following formula:

[0078] DU2=DU-DU1

[0079] In the above step S6, the generating of the single-step instruction fader start signal SW_FADER includes:

[0080] When the second-stage fade instruction DU2 passes through the status judgment module, the single-step instruction fader start signal SW_FADER is obtained. That is, when DU2=0 and 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.

[0081] 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. 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:

[0082] Control surface command = ELE_CMD-DU_F

[0083] In the present invention, real-time fading adopts linear fading logic. Assuming that the fading time is ΔT, the real-time fading instruction calculation formula is as follows:

[0084] Fade real-time instruction = required fade instruction value * f(t)

[0085] In the formula, function f(t) is the fade function, and the specific formula is as follows

[0086]

[0087] Wherein, t is the real time starting from the fade start time t=0.

[0088] In the above step S9, when the signal SW_FADER=0, it indicates that the mode switching command difference DU is greater than the threshold value for starting the second stage fade, that is, the two-step fader needs to be started, and the control surface command output connects to the two-step command fader.

[0089] In this embodiment, the two-step desalination device is composed of two superimposed desalination devices, which are activated in sequence according to time;

[0090] The first-stage desalination device is a single-step desalination device. 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 generated real-time desalination command is DU_F1. The second-stage desalination device DU2 first goes through a delayed start link. After the time FadeTime1, desalination device B is started. Desalination device B is a linear desalination device. That is, the command difference DU2 is linearly desalinated to 0 within the specified time FadeTime2. The generated real-time desalination command 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:

[0091] Rudder command = ELE_CMD–DU_F1–DU_F2.

[0092] Preferably, the fade time FadeTime1 and FadeTime2 in this embodiment are both 8 seconds.

[0093] 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, the method includes:

[0094] Record the instruction difference DU0 between the normal mode control instruction A and the direct link mode control instruction B in real time;

[0095] When the flight control mode switching signal SW_FCMMODE is triggered, the command difference DU0 at the triggering moment is recorded;

[0096] The command difference DU0 is judged. When DU0 is less than the preset threshold value, the single-step desalination device is activated to desalinate the command 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.

[0097] When the command difference DU0 is greater than the preset threshold value, the two-step fader is activated to perform command fade. First, the first-level command fader is activated to fade the given command difference within the specified time FadeTime1, thereby quickly releasing some 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 command fader is activated to reduce the transient state during mode switching.

[0098] 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 degraded, and the effect is significant.

[0099] In summary, the present invention utilizes a two-step de-escalation process to ensure a smooth transition of elevator control commands during flight control mode switching, avoiding flight instability and dangerous situations that could result from sudden command changes. During the switching process, the present invention utilizes command limiting and gradual de-escalation to effectively prevent overloads on the aircraft structure or systems caused by excessive control commands, thereby protecting aircraft safety.

[0100] This invention incorporates command limiting and a two-stage desalination mechanism. This allows for redundancy and gradual adjustments to maintain stable system operation even in the event of sensor or system failures. By monitoring and determining command variances in real time and activating the appropriate desalination units promptly, this invention prevents system failures caused by command errors or sudden changes.

[0101] The present invention uses a linear desalination device to gradually desalinate the command difference to zero, achieving precise adjustment of control commands and improving flight control accuracy and stability. The present invention flexibly selects a single-step or two-step desalination device based on the size and characteristics of the command difference, ensuring on-demand adjustment and optimization of control commands.

[0102] The present invention realizes the automatic desalination processing of flight control mode switching instructions, reduces the operating burden of the pilot and improves the operating efficiency. The method is based on a linear desalination device and simple logical judgment and is easy to implement and integrate into the existing flight control system.

[0103] This invention is not only applicable to flight control mode switching, but can also be extended to other control scenarios that require smooth transitions, such as engine thrust adjustment and flight attitude adjustment. 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.

[0104] The present invention can be applied to fly-by-wire aircraft with excessively large transient response when switching flight control modes. It has a simple structure and can be extended to all fly-by-wire aircraft with excessively large transient response when switching flight control modes.

[0105] The technical features of the above embodiments can 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.

[0106] The above 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 replacements made by technicians in this field on the basis of the present invention 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 in real time the difference DU0 between the elevator control commands at the current moment and the previous moment; Maintain the difference DU between the two control commands when switching the flight control mode; Perform the first-level desalination process to obtain the first-level desalination instruction DU1; Perform the second-level desalination process to obtain the second-level desalination instruction DU2; Generate a single-step instruction 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 between the two control instructions for switching the flight control mode is greater than the threshold value for starting the second-stage fade, and the two-step fader is started; Among them, the single-step command fader is a linear fader, that is, the command DU1 is linearly faded to 0 within the specified time FadeTime1, and the current step control command ELE_CMD is superimposed on the real-time fade command DU_F to obtain the first rudder command; Among them, the two-step desalination device is composed of two superimposed desalination devices, which are started in sequence according to time; the first-stage desalination device of the two-step desalination device is a single-step desalination device, and the instruction value to be desalinated is the threshold value of the limiting module. It is linearly faded to 0 within the specified time FadeTime1, and the real-time desalination instruction generated is DU_F1; the second-stage desalination device of the two-step desalination device is used to linearly fade the instruction difference DU2 to 0 within the specified time FadeTime2, and the real-time desalination instruction generated is DU_F2.

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

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

4. The method according to claim 1, wherein The difference DU between 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, wherein The step of obtaining the first-level instruction DU1 that needs to be faded includes: The difference DU between the two control commands when switching the flight control mode can be subjected to command clipping to obtain the first-level de-fading command DU1. That is, when the command difference DU is less than the clipping range, the output DU1 = DU value; when the command difference DU is greater than the clipping range, the output DU1 is equal to the clipping value. Among them, the command clipping module is the signal threshold value set in advance to start the second-level de-fading, 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: Subtract the first-level de-emphasized instruction DU1 from the instruction difference DU to obtain the second-level de-emphasized instruction DU2, which can be 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 status judgment module, the single-step instruction fader start signal SW_FADER is obtained. That is, when DU2=0 and 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, wherein: The first control surface instruction 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 means that the command difference DU for mode switching is greater than the threshold value for starting the second-stage desalination, that is, the two-step desalination device needs to be started, and the control surface command output connects the two-step desalination device.

10. The method according to claim 9, characterized in that: The second-stage desalination device of the two-step desalination device first goes through a delayed start-up phase. That is, desalination device B starts to start after the time FadeTime1. Desalination device B is a linear desalination device. The control instruction ELE_CMD of the current step length is superimposed on the real-time desalination instructions DU_F1 and DU_F2 to obtain the second control surface instruction, which is expressed as the following formula: Rudder command = ELE_CMD – DU_F1 – DU_F2.

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