A method for maintaining altitude near the bottom of an underactuated underwater vehicle

Abstract

The present invention relates to the technical field of underactuated underwater vehicle control, and provides a near-bottom altitude control method for an underactuated underwater vehicle. The method converts the commanded altitude of the vehicle during near-bottom navigation into a commanded depth; obtains the deviation between the commanded altitude and the actual altitude of the vehicle; calculates the depth deviation based on the commanded depth and the altitude deviation to obtain the depth deviation of the vehicle during near-bottom altitude navigation; designs an angle of attack observer based on the depth deviation and nonlinear interference observation theory; combines the angle of attack observer with a line-of-sight navigation method to design a depth guidance algorithm to obtain a pitch command; obtains the rate of change of the pitch command through a differentiator; and adds the rate of change of the pitch command to the differential term of a PID controller to implement pitch tracking control. The present invention enables an underactuated underwater vehicle to accurately and stably track the seabed topography at a specified altitude, thereby ensuring the operational capability of the underactuated underwater vehicle and improving the safety of near-bottom operations.

Description

Technical Field

[0001] The present invention relates to the technical field of under-actuated underwater vehicle manipulation, and in particular to a near-bottom altitude constant control method for an under-actuated underwater vehicle. Background Art

[0002] Underwater vehicles are widely used in civilian applications such as marine rescue, salvage, marine resource surveys, and oil extraction, and can also undertake military missions such as minesweeping, reconnaissance, intelligence gathering, and ocean exploration. During topographic mapping, lost property recovery, and seabed resource exploration, underwater vehicles must navigate at a constant altitude near the bottom to provide a stable operating environment.

[0003] Underactuated underwater vehicles (UUVs) are simple in structure but difficult to control. Their biggest difference from traditional UUVs is that they lack an independent propulsion system, so they cannot directly generate control torque through thrust. Instead, they need to generate control force by adjusting the deflection angle of the underactuated rudder to change their direction of motion. Underactuated UUVs are affected by the complex ocean environment when navigating underwater. Because the seabed topography is not flat, maintaining an altitude near the bottom of an UUV is not a stable depth control process. The depth command converted from the near-bottom altitude must be tracked and controlled. Due to the underactuated nature of the UUV in the depth direction, control lags are prone to occur during depth tracking, which can easily cause the UUV to deviate from the predetermined near-bottom altitude, affecting its operational capability. In severe cases, the UUV can crash into the seabed, causing significant economic losses. Summary of the Invention

[0004] The present invention aims to address at least one of the technical problems existing in the related art. To this end, the present invention provides a method for controlling an underactuated underwater vehicle near the bottom, enabling the vehicle to accurately and stably track the seabed topography at a specified altitude, thereby ensuring the vehicle's operational capability and improving the safety of near-bottom operations.

[0005] The present invention provides a method for controlling an underactuated underwater vehicle at a constant altitude near the bottom, comprising:

[0006] S1: According to the correspondence between the near-bottom depth and the near-bottom height when the aircraft is navigating near the bottom, the command altitude of the aircraft during the near-bottom fixed altitude navigation is converted into the command depth;

[0007] S2: According to the correspondence between the near-bottom depth and the near-bottom height when the aircraft is navigating near the bottom, the height deviation between the commanded height and the actual height of the aircraft during the near-bottom fixed altitude navigation is obtained;

[0008] S3: Calculate the depth deviation based on the command depth and altitude deviation to obtain the depth deviation of the vehicle when navigating at a constant altitude near the bottom.

[0009] S4: Design an angle of attack observer based on depth deviation and nonlinear interference observation theory;

[0010] S5: Combine the angle of attack observer with the line-of-sight navigation method to design a depth guidance algorithm to obtain pitch commands;

[0011] S6: Processing the pitch command through the differentiator to obtain the pitch command change rate;

[0012] S7: Add the pitch command change rate to the differential term of the PID controller to obtain a lag-free pitch controller.

[0013] According to the present invention, a method for controlling an underactuated underwater vehicle at a constant altitude near the bottom further includes the following step S1: when the vehicle is navigating near the bottom, the corresponding relationship between the near-bottom depth and the near-bottom altitude is:

[0014]

[0015] in, is the height of the bottom of the vehicle shell from the seabed, is the distance between the water surface and the seabed, is the current depth of the vehicle, is the distance from the bottom of the hull to the center of gravity of the vehicle;

[0016] The expression for converting instruction height into instruction depth is:

[0017]

[0018] in, is the instruction depth converted from instruction height, Set the command altitude for the aircraft to navigate.

[0019] According to the present invention, a method for controlling an underactuated underwater vehicle at a constant altitude near the bottom further includes, in step S2, obtaining a deviation between a commanded altitude and an actual altitude of the vehicle when navigating at a constant altitude near the bottom based on a correspondence between a near-bottom depth and a near-bottom altitude when the vehicle is navigating near the bottom. The deviation between the commanded altitude and the actual altitude of the vehicle when navigating at a constant altitude near the bottom is calculated as follows:

[0020]

[0021] in, The command altitude for the aircraft to sail near the bottom. is the height of the bottom of the vehicle shell from the seabed, is the distance between the water surface and the seabed, is the current depth of the vehicle, is the distance from the bottom of the hull to the center of gravity of the vehicle; is the instruction depth converted from instruction height, .

[0022] According to the present invention, a method for controlling an underactuated underwater vehicle at a constant altitude near the bottom further includes the following step S3: the depth deviation calculation expression of the vehicle at a constant altitude near the bottom is:

[0023]

[0024] in, It is the depth deviation of the vehicle when navigating at a fixed altitude near the bottom. is the current depth of the vehicle, is the current command depth of the vehicle, is the actual depth, and by taking the derivative, we get the following formula:

[0025]

[0026] in, To find the derivative of the depth deviation of the vehicle when navigating at a constant altitude near the bottom, To find the derivative of the current depth of the spacecraft, is the longitudinal velocity of the spacecraft, is the vertical velocity of the spacecraft, is the pitch angle of the aircraft, It is the angle of attack caused by changes in depth and pitch when sailing underwater;

[0027] Simplified to the following form;

[0028]

[0029] in, is a parameter related to the angle of attack .

[0030] According to the present invention, a method for controlling an underactuated underwater vehicle at a constant altitude near the bottom further includes, in step S4, designing an angle of attack observer based on the depth deviation of the vehicle during near-bottom constant altitude navigation and the design principle of a nonlinear disturbance observer;

[0031] The interference estimation expression of the parameters related to the angle of attack is:

[0032]

[0033] in, for The estimated value of is a parameter related to the angle of attack, are the parameters of the nonlinear disturbance observer, is the auxiliary variable of the nonlinear disturbance observer, To derive the auxiliary variable of the nonlinear disturbance observer, is the pitch angle of the aircraft, is the longitudinal velocity of the spacecraft, The depth deviation of the vehicle when navigating at a fixed altitude near the bottom;

[0034] The calculation expression of interference observation error is:

[0035]

[0036] in, is the interference observation error;

[0037] Taking the derivative of the above formula, we can get:

[0038]

[0039] in, To find the derivative of the interference observation error, For Estimated value of Seek derivation, Taking the derivative of the parameters related to the angle of attack, To find the derivative of the depth deviation of the vehicle when navigating at a constant altitude near the bottom.

[0040] According to the present invention, a method for controlling an underactuated underwater vehicle at a constant altitude near the bottom further includes: in the step S5,

[0041] According to the interference observation results, the angle of attack observation value during navigation can be derived as follows:

[0042]

[0043] in, is the observed value of angle of attack;

[0044] The observed angle of attack is combined with the line-of-sight navigation algorithm to obtain the depth guidance law for generating the commanded pitch angle. The commanded pitch angle calculation expression is:

[0045]

[0046] in, is the commanded pitch angle, is the foresight distance of the line of sight navigation method.

[0047] According to the present invention, a method for controlling an underactuated underwater vehicle at a constant altitude near the bottom further includes the following steps:

[0048] The linear tracking differentiator is used to process the pitch command to obtain the pitch command change rate. The calculation expression of the pitch command change rate is:

[0049]

[0050] in, is the pitch command tracking value output by the differentiator, is the tracking value of the pitch command change rate output by the differentiator, To derive the pitch command tracking value output by the differentiator, To find the derivative of the tracking value of the pitch command change rate output by the differentiator, is the speed factor of the tracking differentiator, is the commanded pitch angle.

[0051] According to the present invention, a method for controlling an underactuated underwater vehicle at a constant altitude near the bottom further includes, in step S6, using a traditional PID controller to design a pitch controller, and the pitch controller calculation expression is:

[0052]

[0053] in, is the command rudder angle of the stern horizontal rudder of the aircraft, is the proportional parameter of the controller, is the pitch angle of the aircraft, is the integral parameter of the controller, is the differential parameter of the controller, is the cumulative term of the longitudinal deviation, is the pitch angular velocity term.

[0054] According to the present invention, a method for controlling an underactuated underwater vehicle at a constant altitude near the bottom further includes, in step S7, adding the pitch command change rate to the differential term of the PID controller to obtain a hysteresis-free pitch controller. The calculation expression of the hysteresis-free pitch controller is:

[0055]

[0056] will track the output of the differentiator Instead of commanded pitch rate , the final calculation expression of the hysteresis-free pitch controller is obtained:

[0057]

[0058] in, is the commanded pitch rate of change, It is a hysteresis-free pitch controller.

[0059] According to the present invention, a method for controlling an underactuated underwater vehicle at a constant altitude near the bottom further includes accurately controlling the pitch of the vehicle to a pitch instruction using a pitch controller. The depth guidance law yields:

[0060]

[0061] Introducing the above formula into the depth deviation equation yields:

[0062]

[0063] in, .

[0064] The above one or more technical solutions in the embodiments of the present invention have at least one of the following technical effects:

[0065] The present invention proposes a command conversion method for near-bottom altitude-fixed navigation. This method converts near-bottom altitude-fixed altitude commands into depth commands for the vehicle based on the relationship between the vehicle's depth below the seabed and its height above the bottom. This simplifies the design process of the altitude-fixed controller and improves the feasibility of near-bottom altitude-fixed control.

[0066] The present invention uses a pitch guidance algorithm to accurately observe the angle of attack of a vehicle in an interference environment, and compensates the observed angle of attack to form a pitch guidance law in the line-of-sight navigation method, thus realizing the depth control capability of an underactuated underwater vehicle when the seawater density changes.

[0067] The present invention proposes a depth guidance algorithm based on a nonlinear disturbance observer, which can accurately observe the angle of attack generated by changes in the depth and pitch of an underactuated vehicle. It also combines the line-of-sight navigation algorithm to design a depth guidance law, providing correct pitch guidance instructions for depth tracking control during constant-altitude navigation.

[0068] The present invention adds a tracking differentiator to the design of the pitch controller, adds the pitch command change rate solved by the differentiator to the differential term of the PID controller, and controls the pitch and its change rate at the same time to achieve hysteresis-free control of depth tracking.

[0069] The present invention enables an under-actuated underwater vehicle to accurately and stably track the seabed topography at a specified altitude, thereby ensuring the operational capability of the under-actuated underwater vehicle and improving the safety of near-bottom operations.

[0070] Additional aspects and advantages of the present invention will be set forth in part in the description which follows and, in part, will be obvious from the description which follows, or may be learned by practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0071] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0072] Figure 1 The present invention provides a flow chart of a method for controlling an underactuated underwater vehicle at a constant altitude near the bottom.

[0073] Figure 2 The present invention provides a schematic diagram of the corresponding relationship between the depth and altitude of an underwater vehicle in a method for controlling an underactuated underwater vehicle at a constant altitude near the bottom.

[0074] Figure 3 The present invention provides a schematic diagram of the depth control of an underwater vehicle according to a method for controlling the near-bottom constant altitude of an underactuated underwater vehicle.

[0075] Figure 4 This is a curve showing the change in depth of the underwater vehicle and the seabed depth in a near-bottom constant altitude control method for an underactuated underwater vehicle provided by the present invention.

[0076] Figure 5 The present invention provides a near-bottom height variation curve of an underwater vehicle in accordance with a near-bottom height-fixed control method for an underactuated underwater vehicle. DETAILED DESCRIPTION

[0077] To make the purpose, technical solutions and advantages of the present invention clearer, the technical solutions in the present invention will be clearly and completely described below. Obviously, the embodiments described are part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention. The following embodiments are used to illustrate the present invention, but are not used to limit the scope of the present invention.

[0078] In the description of this specification, the reference terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" mean that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the embodiment of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art can combine and combine different embodiments or examples described in this specification and features of different embodiments or examples without contradiction.

[0079] In related technologies, due to the under-actuated characteristics of underwater vehicles in the depth direction, control lag is prone to occur in the vehicle during depth tracking, which can easily cause the vehicle to deviate from the predetermined near-bottom altitude, thereby affecting its operational capability. In severe cases, the vehicle may crash into the seabed, causing huge economic losses. In order to solve this problem, a near-bottom fixed-altitude control method for an under-actuated underwater vehicle is used to ensure that the underwater vehicle accurately and stably tracks the seabed terrain at a specified altitude, thereby ensuring the vehicle's operational capability and improving the safety of near-bottom operations.

[0080] The following combination Figures 1 to 5 The present invention describes a method for controlling an underactuated underwater vehicle at a constant altitude near the bottom.

[0081] like Figure 1 As shown, a method for controlling an underactuated underwater vehicle at a constant altitude near the bottom includes: S1: converting a commanded altitude for the vehicle to sail at a constant altitude near the bottom into a commanded depth according to a correspondence between a near-bottom depth and a near-bottom altitude when the vehicle is sailing near the bottom;

[0082] S2: According to the correspondence between the near-bottom depth and the near-bottom height when the aircraft is navigating near the bottom, the height deviation between the commanded height and the actual height of the aircraft during the near-bottom fixed altitude navigation is obtained;

[0083] S3: Calculate the depth deviation based on the command depth and altitude deviation to obtain the depth deviation of the vehicle when navigating at a constant altitude near the bottom.

[0084] S4: Design an angle of attack observer based on depth deviation and nonlinear interference observation theory;

[0085] S5: Combine the angle of attack observer with the line-of-sight navigation method to design a depth guidance algorithm to obtain pitch commands;

[0086] S6: Processing the pitch command through the differentiator to obtain the pitch command change rate;

[0087] S7: Add the pitch command change rate to the differential term of the PID controller to obtain a lag-free pitch controller.

[0088] Specifically, S1: converting the commanded altitude of the aircraft near the bottom into the commanded depth according to the corresponding relationship between the depth and the height near the bottom when the aircraft is near the bottom;

[0089] like Figure 2 As shown in the figure, the corresponding relationship between the height of the vehicle shell from the seabed and the depth is calculated as follows:

[0090]

[0091] in, is the height of the bottom of the vehicle shell from the seabed, is the distance between the water surface and the seabed, is the current depth of the vehicle, is the distance from the bottom of the hull to the center of gravity of the vehicle;

[0092] The expression for converting height instruction into depth instruction is:

[0093]

[0094] in, is the instruction depth converted from instruction height, Set the command altitude for the aircraft to navigate.

[0095] In some embodiments of the present invention, the height command of the near-bottom altitude control is converted into the depth command of the aircraft to simplify the design process of the altitude control controller and improve the feasibility of the near-bottom altitude control.

[0096] S2: Obtain the deviation between the aircraft's commanded altitude and actual altitude based on the corresponding relationship between the aircraft's depth and altitude near the bottom when the aircraft is navigating near the bottom;

[0097] According to the corresponding relationship between altitude and depth, the deviation between the aircraft's command altitude and actual altitude is obtained as follows:

[0098]

[0099] in, Set the altitude command for the aircraft to sail. is the height of the bottom of the vehicle shell from the seabed, is the distance between the water surface and the seabed, is the current depth of the vehicle, is the distance from the bottom of the shell to the center of gravity of the spacecraft, is the instruction depth converted from instruction height, .

[0100] In some embodiments of the present invention, the command depth converted from the command altitude is determined by three quantities: the seabed depth, the distance from the bottom of the shell to the center of gravity of the vehicle, and the command altitude. Therefore, when performing near-bottom constant altitude navigation, it is necessary to know in advance or measure in real time the seabed depth information of one's own position.

[0101] S3: Calculate the depth deviation based on the command depth and altitude deviation to obtain the depth deviation of the vehicle when navigating at a constant altitude near the bottom.

[0102] like Figure 3 As shown, the positive direction of the x coordinate is the forward direction of the aircraft, and the z coordinate is the opposite direction of the aircraft's depth. The depth deviation of the aircraft in the current coordinate system is shown as follows:

[0103]

[0104] in, is the vehicle depth deviation, is the current depth of the vehicle, is the current command depth of the vehicle, is the actual depth, and by taking the derivative, we get the following formula:

[0105]

[0106] in, is the longitudinal velocity of the spacecraft, is the vertical velocity, is the pitch angle, It is the angle of attack caused by changes in depth and pitch when sailing underwater;

[0107] Simplified to the following form;

[0108]

[0109] in, is the depth deviation of the aircraft on the vertical plane, is a parameter related to the angle of attack .

[0110] In some embodiments of the present invention, an angle of attack observer is designed based on a depth deviation model on the vertical plane of the vehicle and nonlinear interference observation theory to compensate for the angle of attack caused by depth and pitch changes during depth tracking.

[0111] S4: Design an angle of attack observer based on the depth deviation of the vehicle near the bottom and the nonlinear interference observation theory;

[0112] According to the design principle of nonlinear disturbance observer, the angle of attack observer is designed, and the disturbance estimation expression of the parameters related to the angle of attack is:

[0113]

[0114] in, for The estimated value of is a parameter related to the angle of attack, are the parameters of the nonlinear disturbance observer, is the auxiliary variable of the nonlinear disturbance observer, To derive the auxiliary variable of the nonlinear disturbance observer, is the pitch angle of the aircraft, is the longitudinal velocity of the spacecraft, The depth deviation of the vehicle when navigating at a fixed altitude near the bottom;

[0115] The interference observation error is shown as follows:

[0116]

[0117] in, is the interference observation error;

[0118] Taking the derivative of the above formula, we can get:

[0119]

[0120] in, To find the derivative of the interference observation error, For Estimated value of Seek derivation, Taking the derivative of the parameters related to the angle of attack, To find the derivative of the depth deviation of the vehicle when navigating at a constant altitude near the bottom.

[0121] In some embodiments of the present invention, when the aircraft is sailing close to the bottom, the angle of attack of the aircraft changes very slowly and the amplitude of the change is negligible, so it can be assumed that , then the above formula can be simplified to , it can be seen that the nonlinear disturbance observer of the angle of attack converges gradually, and it is reasonable to increase the parameter It can accelerate the convergence speed of nonlinear disturbance observer.

[0122] According to the design principle of nonlinear disturbance observer, an angle of attack observer is designed, which can accurately observe the angle of attack generated by the changes in depth and pitch of the under-actuated vehicle.

[0123] S5: Combine the angle of attack observer with the line-of-sight navigation method to design a depth guidance algorithm to obtain pitch commands;

[0124] According to the interference observation results, the angle of attack observation value during navigation can be derived as follows:

[0125]

[0126] in, is the observed value of angle of attack;

[0127] Combining the observed angle of attack with the line-of-sight navigation algorithm, we obtain the depth guidance law that generates the commanded pitch angle. The commanded pitch angle calculation expression is:

[0128]

[0129] in, is the commanded pitch angle, is the foresight distance of the line of sight navigation method.

[0130] In some embodiments of the present invention, an angle of attack observer is combined with a line of sight navigation method to design a depth guidance algorithm to provide correct pitch guidance instructions for depth tracking control during constant altitude navigation.

[0131] The pitch controller is used to accurately control the pitch of the vehicle to the pitch command, and the depth guidance law can be obtained:

[0132]

[0133] Introducing the above formula into the depth deviation equation yields:

[0134]

[0135] in, .

[0136] In some embodiments of the present invention, during navigation, the pitch motion range of the aircraft is within ±30°, so , so we can know , the depth deviation can converge to 0 asymptotically.

[0137] S6: obtain the rate of change of the pitch command through the differentiator;

[0138] A linear tracking differentiator is used to obtain the commanded pitch change rate, as shown in the following equation:

[0139]

[0140] in, is the pitch command tracking value output by the differentiator, is the tracking value of the pitch command change rate output by the differentiator, To derive the pitch command tracking value output by the differentiator, To find the derivative of the tracking value of the pitch command change rate output by the differentiator, is the speed factor of the tracking differentiator, is the commanded pitch angle.

[0141] S7: Add the pitch command change rate to the differential term of the PID controller to achieve pitch tracking control.

[0142] The pitch controller is designed using a traditional PID controller, as shown below:

[0143]

[0144] in, is the command rudder angle of the stern horizontal rudder of the aircraft, is the proportional parameter of the controller, is the commanded pitch angle, is the pitch angle, is the integral parameter of the controller, is the differential parameter of the controller, is the cumulative term of the longitudinal deviation, is the pitch angular velocity term. The purpose of the PID controller is to stabilize the pitch to the commanded pitch and the pitch angular velocity to 0. However, when the commanded pitch changes continuously, the control goal of stabilizing the pitch angular velocity to 0 will affect the pitch tracking control, causing the pitch tracking control to lag, which in turn affects the altitude control of the aircraft. The pitch command change rate is added to the differential term of the PID controller to obtain a lag-free pitch controller. The calculation expression of the lag-free pitch controller is:

[0145]

[0146] To track the output of the differentiator Instead of commanded pitch rate The final form of the pitch tracking controller is shown as follows:

[0147]

[0148] in, is the commanded pitch rate of change, It is a hysteresis-free pitch controller.

[0149] In some embodiments of the present invention, pitch tracking control is achieved by a hysteresis-free pitch controller.

[0150] In some embodiments of the present invention, in order to verify the effectiveness of the control algorithm proposed in the present invention, a simulation experiment is carried out with the autonomous underwater vehicle AUV Remus 100 as the controlled object. The simulation conditions are set as follows: the initial depth of the autonomous underwater vehicle AUV Remus 100 is 30m, the heading is 0°, and the seabed depth is set to continuously change along the forward direction of the vehicle. The change function is , the underwater autonomous underwater vehicle AUV Remus 100 is set to the near-bottom directional and fixed-altitude control mode, and the command altitude is set to 2m.

[0151] The simulation results are as follows Figure 4 and Figure 5 As shown in FIG, it can be seen that the underwater vehicle can follow the seabed topography at a specified height from the bottom, proving that the near-bottom fixed-altitude control algorithm proposed in the present invention can enable the vehicle to complete the near-bottom fixed-altitude navigation task; Figure 5It can be seen from the curve of the aircraft's height change from the bottom that, except for the height adjustment process at the beginning of the mission, the aircraft's height deviation has been maintained within ±1m. After statistical calculation of the mean square error, the aircraft's altitude control accuracy in this simulation is 0.05m, proving that the improved near-bottom altitude control algorithm of the present invention has very high altitude control accuracy.

[0152] The beneficial effects of the present invention are as follows: the present invention proposes a command conversion method for near-bottom altitude-fixed navigation, which can convert the near-bottom altitude-fixed altitude command into the depth command of the vehicle based on the relationship between the depth of the vehicle below the seabed and its height from the bottom, thereby simplifying the design process of the altitude-fixed controller and improving the feasibility of near-bottom altitude-fixed control;

[0153] The present invention uses a pitch guidance algorithm to accurately observe the angle of attack of a vehicle in an interference environment, and compensates the observed angle of attack to form a pitch guidance law in the line-of-sight navigation method, thus realizing the depth control capability of an underactuated underwater vehicle when the seawater density changes.

[0154] The present invention proposes a depth guidance algorithm based on a nonlinear disturbance observer, which can accurately observe the angle of attack generated by changes in the depth and pitch of an underactuated vehicle. It also combines the line-of-sight navigation algorithm to design a depth guidance law, providing correct pitch guidance instructions for depth tracking control during constant-altitude navigation.

[0155] The present invention adds a tracking differentiator to the design of the pitch controller, adds the pitch command change rate solved by the differentiator to the differential term of the PID controller, and controls the pitch and its change rate at the same time to achieve hysteresis-free control of depth tracking.

[0156] The present invention enables an under-actuated underwater vehicle to accurately and stably track the seabed topography at a specified altitude, thereby ensuring the operational capability of the under-actuated underwater vehicle and improving the safety of near-bottom operations.

[0157] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A method for controlling an underactuated underwater vehicle at a constant altitude near the bottom, characterized in that: include: S1: According to the correspondence between the near-bottom depth and the near-bottom height when the aircraft is navigating near the bottom, the command altitude of the aircraft during the near-bottom fixed altitude navigation is converted into the command depth; S2: According to the correspondence between the near-bottom depth and the near-bottom height when the aircraft is navigating near the bottom, the height deviation between the commanded height and the actual height of the aircraft during the near-bottom fixed altitude navigation is obtained; S3: Calculate the depth deviation based on the command depth and altitude deviation to obtain the depth deviation of the vehicle when navigating at a constant altitude near the bottom. S4: Design an angle of attack observer based on depth deviation and nonlinear interference observation theory; According to the depth deviation of the vehicle sailing at constant altitude near the bottom and the design principle of nonlinear disturbance observer, the angle of attack observer is designed. The interference estimation expression of the parameters related to the angle of attack is: in, for The estimated value of is a parameter related to the angle of attack, are the parameters of the nonlinear disturbance observer, is the auxiliary variable of the nonlinear disturbance observer, To derive the auxiliary variable of the nonlinear disturbance observer, is the pitch angle of the aircraft, is the longitudinal velocity of the spacecraft, The depth deviation of the vehicle when navigating at a fixed altitude near the bottom; The calculation expression of interference observation error is: in, is the interference observation error; Taking the derivative of the above formula, we can get: in, To find the derivative of the interference observation error, For Estimated value of Seek derivation, Taking the derivative of the parameters related to the angle of attack, To find the derivative of the depth deviation of the vehicle when it is navigating at a constant altitude near the bottom; S5: Combine the angle of attack observer with the line-of-sight navigation method to design a depth guidance algorithm to obtain pitch commands; According to the interference observation results, the angle of attack observation value during navigation can be derived as follows: in, is the observed value of angle of attack; The observed angle of attack is combined with the line-of-sight navigation algorithm to obtain the depth guidance law for generating the commanded pitch angle. The commanded pitch angle calculation expression is: in, is the commanded pitch angle, The forward sight distance of the line of sight navigation method; S6: Processing the pitch command through the differentiator to obtain the pitch command change rate; S7: Add the pitch command change rate to the differential term of the PID controller to obtain a lag-free pitch controller.

2. The method for controlling an underactuated underwater vehicle at a constant altitude near the bottom according to claim 1, characterized in that: In step S1, the corresponding relationship between the near-bottom depth and the near-bottom height when the aircraft is navigating near the bottom is: in, is the height of the bottom of the vehicle shell from the seabed, is the distance between the water surface and the seabed, is the current depth of the vehicle, is the distance from the bottom of the hull to the center of gravity of the vehicle; The expression for converting instruction height into instruction depth is: in, is the instruction depth converted from instruction height, Set the command altitude for the aircraft to navigate.

3. The method for controlling an underactuated underwater vehicle at a constant altitude near the bottom according to claim 1, characterized in that: In step S2, the deviation between the commanded altitude and the actual altitude of the aircraft during near-bottom navigation is obtained based on the corresponding relationship between the near-bottom depth and the near-bottom altitude when the aircraft is navigating near the bottom. The calculation expression for the deviation between the commanded altitude and the actual altitude of the aircraft during near-bottom navigation at a constant altitude is: in, The command altitude for the aircraft to sail near the bottom. is the height of the bottom of the vehicle shell from the seabed, is the distance between the water surface and the seabed, is the current depth of the vehicle, is the distance from the bottom of the hull to the center of gravity of the vehicle; is the instruction depth converted from instruction height, .

4. The method for controlling an underactuated underwater vehicle at a constant altitude near the bottom according to claim 1, characterized in that: In step S3, the depth deviation calculation expression of the aircraft near the bottom and constant altitude navigation is: in, It is the depth deviation of the vehicle when navigating at a fixed altitude near the bottom. is the current depth of the vehicle, is the current command depth of the vehicle, is the actual depth, and by taking the derivative, we get the following formula: in, To find the derivative of the depth deviation of the vehicle when navigating at a constant altitude near the bottom, To find the derivative of the current depth of the spacecraft, is the longitudinal velocity of the spacecraft, is the vertical velocity of the spacecraft, is the pitch angle of the aircraft, It is the angle of attack caused by changes in depth and pitch when sailing underwater; Simplified to the following form; in, is a parameter related to the angle of attack .

5. The method for controlling an underactuated underwater vehicle at a constant altitude near the bottom according to claim 1, characterized in that: In the step S6, The linear tracking differentiator is used to process the pitch command to obtain the pitch command change rate. The calculation expression of the pitch command change rate is: in, is the pitch command tracking value output by the differentiator, is the tracking value of the pitch command change rate output by the differentiator, To derive the pitch command tracking value output by the differentiator, To find the derivative of the tracking value of the pitch command change rate output by the differentiator, is the speed factor of the tracking differentiator, is the commanded pitch angle.

6. The method for controlling an underactuated underwater vehicle at a constant altitude near the bottom according to claim 5, characterized in that: In step S6, a traditional PID controller is used to design the pitch controller, and the pitch controller calculation expression is: in, is the command rudder angle of the stern horizontal rudder of the aircraft, is the proportional parameter of the controller, is the pitch angle of the aircraft, is the integral parameter of the controller, is the differential parameter of the controller, is the cumulative term of the longitudinal deviation, is the pitch angular velocity term.

7. The method for controlling an underactuated underwater vehicle at a constant altitude near the bottom according to claim 6, characterized in that: In step S7, the pitch command change rate is added to the differential term of the PID controller to obtain a hysteresis-free pitch controller. The calculation expression of the hysteresis-free pitch controller is: will track the output of the differentiator Instead of commanded pitch rate , the final calculation expression of the hysteresis-free pitch controller is obtained: in, is the commanded pitch rate of change, It is a hysteresis-free pitch controller.

8. The method for controlling an underactuated underwater vehicle at a constant altitude near the bottom according to claim 1, characterized in that: The pitch controller is used to accurately control the pitch of the vehicle to the pitch command, and the depth guidance law can be obtained: Introducing the above formula into the depth deviation equation yields: in, .

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