Sliding mode variable structure speed control system based on nonlinear coupling mathematical model

Abstract

The invention discloses a sliding mode variable structure speed control system based on a nonlinear coupling mathematical model. In the propulsion system, a fuel delivery pump delivers fuel to an injection module. In the injection module, a high-pressure oil pump is connected to an injector through a fuel solenoid valve. The injector provides fuel to a main engine. The main engine drives a propeller through a reduction gearbox. The propeller drives the hull to sail. Sensors for detecting the speed, main engine speed and propeller speed are respectively provided on the hull, the main engine and the propeller. The control system receives the real-time feedback of the speed, main engine speed and propeller speed and maintains the three constant by controlling the opening of the fuel solenoid valve. The control system adopts a sliding mode variable structure algorithm, and regards the nonlinear coupling mathematical model of the speed, main engine speed and propeller speed in the propulsion system as a type of multi-input affine nonlinear model, and solves to obtain a sliding mode variable structure controller. The invention has fast response, small overshoot, good robustness, strong anti-interference ability, and good control effect.

Description

Technical Field

[0001] The invention belongs to the field of ship hull automatic control, and in particular relates to a sliding mode variable structure speed control system based on a nonlinear coupling mathematical model. Background Art

[0002] At present, most systems such as ship engine room cooling water temperature, water level, boiler steam pressure, fuel viscosity and steering gear rudder angle use traditional PID control methods. Some digital hosts also use fuzzy-PID methods to control their speed. The control of the overall ship's speed and heading basically uses PID algorithms. PID is a classic and universal control method that performs proportional, integral and differential operations on deviations, but it ignores the essential characteristics of the object and only adjusts the proportional band, integral time and differential time, which makes it difficult to achieve good control effects on complex objects. Summary of the invention

[0003] The purpose of the present invention is to provide a sliding mode variable structure speed control system based on a nonlinear coupling mathematical model, which has fast response, small overshoot, good robustness, strong anti-interference ability and good control effect.

[0004] The technical solution adopted by the present invention is:

[0005] A sliding mode variable structure ship speed control system based on a nonlinear coupling mathematical model comprises a propulsion system and a control system. In the propulsion system, a fuel delivery pump delivers fuel to an injection module. A high-pressure oil pump in the injection module is connected to an injector through a fuel solenoid valve. The injector provides fuel to a main engine. The main engine drives a propeller through a reduction gearbox. The propeller drives the hull to sail. Sensors for detecting the ship speed, the main engine speed and the propeller speed are respectively arranged on the hull, the main engine and the propeller. The control system receives real-time feedback of the ship speed, the main engine speed and the propeller speed and keeps the three constant by controlling the opening of the fuel solenoid valve. The control system adopts a sliding mode variable structure algorithm, and regards the nonlinear coupling mathematical model of the ship speed, the main engine speed and the propeller speed in the propulsion system as a type of multi-input affine nonlinear model, and solves and obtains a sliding mode variable structure controller.

[0006] The method of establishing the nonlinear coupling mathematical model of the ship speed, main engine speed and propeller speed in the propulsion system is as follows: the mathematical models of the hull-propeller subsystem, the propeller-main engine subsystem and the main engine-injection module subsystem are established respectively; the mathematical model of the hull-propeller subsystem is established according to the motion process of the propeller propelling the hull, so that the effective thrust of the propeller is balanced with the hull resistance and the uncertain environmental interference force to maintain the ship speed consistent with the set value; the mathematical model of the propeller-main engine subsystem is established according to the working process of the main engine transmitting torque to the propeller, so that the torque transmitted by the main engine is balanced with the torque load generated when the propeller rotates to maintain the propeller speed constant; the mathematical model of the main engine-injection module subsystem is established according to the mechanism of the influence of the injection amount on the main engine speed. The change of the main engine speed is determined by the difference between the main engine output torque and the propeller torque load. The main engine output torque is approximately proportional to the mean effective pressure. The mean effective pressure is the difference between the mean indicated pressure and the mean mechanical loss pressure. The mean indicated pressure changes by controlling the injection amount, thereby changing the main engine output torque to maintain the main engine speed stable.

[0007] When building a mathematical model of the hull-propeller subsystem:

[0008] In order to balance the effective thrust of the propeller with the hull resistance and the uncertain environmental interference force, the relationship is obtained:

[0009] Where n P is the propeller speed; V S is the ship speed; w is the wake coefficient, estimated by the empirical formula; λ P is the advance coefficient, which is the propeller hydrodynamic characteristic parameter; D is the propeller diameter;

[0010] The mechanical relationship between the propeller rotation and the hull linear motion conforms to Newton's second law, and the hull motion equation is obtained

[0011]

[0012] In the formula

[0013] T P =F P (1-t p ) (3)

[0014]

[0015]

[0016] Where, T P is the effective thrust of the propeller; R is the hull resistance; γ S is the attached water coefficient of the hull; M is the hull mass; F Pis the thrust generated by the propeller; t P K is the percentage of hull thrust reduction, that is, the movement of the propeller and the hull causes an increase in hull resistance or a reduction in propeller thrust, estimated by an empirical formula; F is the propeller thrust coefficient, and the advance coefficient λ P It is related to the propeller characteristic curve, which is determined by the propeller characteristic curve; ρ is the seawater density; β is the resistance coefficient of the hull; the value of m is determined according to the navigation area;

[0017] In the formula, h(t) is the uncertain environmental interference force. The ship is assumed to be in a normal navigation environment, that is, the wind speed is less than 3m / s, the wave height is less than 0.3m, and the water flow speed is less than 1m / s. According to the measurement of the ship in the normal navigation environment, the uncertain environmental interference force is equivalent to a multiple of the hull resistance, and then

[0018] h(t)=0.3RsinV S (6).

[0019] When establishing the mathematical model of the propeller-main engine subsystem:

[0020] In order to balance the torque transmitted by the main engine with the torque load generated by the propeller rotation, the relationship is obtained:

[0021]

[0022] In the formula, γ P is the additional water coefficient of the propeller; I is the moment of inertia of the rotating part of the propulsion system; M l M is the instantaneous effective torque of the main engine, which is related to the propeller characteristics of the main engine and is set as a function of the main engine speed n; P is the torque load of the propeller; K M is the torque coefficient of the propeller, and the advance coefficient λ P Related, determined by the propeller characteristic curve map.

[0023] When establishing the mathematical model of the host-injection module subsystem:

[0024] According to the D'Alembert principle, the output torque M of the main engine d and load torque, i.e. the torque load M of the propeller P , the difference determines the change of the main engine speed, so the motion equation is

[0025]

[0026] Where, J is the equivalent moment of inertia of the host and its driven mechanical parts; ω is the angular velocity of the host;

[0027] Output torque of the main engine Md With the mean effective pressure P e The average effective pressure P is approximately proportional to e is the average indicated pressure P i and the average mechanical loss pressure P f The difference between the two values; measure the value of the cyclic injection amount q corresponding to different main engine speeds n, and then calculate the indicated power according to the main engine's measured power diagram, and calculate the average indicated pressure P from the indicated power i , the average indicated pressure P of the main engine when the speed is constant i It is linearly related to the cycle injection amount q; according to the measured main engine speed n and output torque M d Calculate the effective work, and then calculate the average effective pressure P from the effective work e ; Considering the output torque M of the main engine at different main engine speeds n d The relationship between the cycle injection amount q is no longer linear. Using the quadratic polynomial fitting method, the nonlinear mathematical model of the main engine speed n is obtained as follows:

[0028]

[0029] Where n is the main engine speed; q is the cyclic injection amount; a1, a2, a3, a4, a5, and a6 are parameters related to the main engine.

[0030] The method for solving the sliding mode variable structure controller is: 1) Integrate the mathematical models of the hull-propeller subsystem, the propeller-main engine subsystem, and the main engine-injection module subsystem to obtain a nonlinear coupling mathematical model with the ship speed, main engine speed and propeller speed as state variables, convert the nonlinear coupling mathematical model into a system state equation, and use the cyclic injection amount as the control input. Under normal sea conditions with less external wind and water flow interference, the fluctuations of the ship speed, propeller speed and main engine speed are small, and the three state variables are maintained stable. For a fixed-pitch propeller hull, a small range of fluctuations in propeller speed is suitable for normal sea conditions. For a controllable pitch propeller hull, although the propeller thrust can be changed by changing the pitch of the adjustable propeller, thereby maintaining the stability of the propeller speed, the propeller advance speed under normal sea conditions is The coefficient maintains a stable value; 2) the system state equation is written as a standard form of a class of affine multi-input nonlinear systems, and the switching function of the sliding mode variable structure control is taken to obtain the sliding mode motion equation; 3) the constant speed approach rate is taken, the sliding mode variable structure control is solved, and the control rate is solved. When the speed control analysis under large disturbance state is carried out, on the basis of the original sliding mode variable structure controller, for the adjustable propeller hull, the propeller advance coefficient and the injection amount are selected as two control inputs to maintain the three state variables of speed, propeller speed and main engine speed constant; for the fixed pitch propeller hull, the transmission ratio and the injection amount of the propeller speed are selected as two control inputs to maintain the two state variables of speed and main engine speed constant; 4) the reliability of the sliding mode variable structure controller is verified through simulation analysis and calculation.

[0031] Sensors for detecting the ship speed, main engine speed and propeller speed are respectively connected to display screens for displaying the ship speed, main engine speed and propeller speed. A flow meter is provided between the fuel delivery pump and the injection module, and a hydraulic dynamometer is provided at the main engine output end.

[0032] The beneficial effects of the present invention are:

[0033] The difficulty in performing constant value control on the ship speed, propeller speed and main engine speed is that when the ship speed is controlled, the propeller speed and the main engine speed change, and when the propeller speed and the main engine speed are controlled, the ship speed deviates from the given value, so this is a highly coupled complex nonlinear system. The present invention targets the nonlinear mathematical model of ship-engine-propeller and uses a sliding mode variable structure control algorithm to perform constant value control on the ship speed, propeller speed and main engine speed, which has fast response, small overshoot, good robustness, strong anti-interference ability and good control effect; the present invention only treats the propulsion system as a type of affine nonlinear system to carry out sliding mode control research, and the propeller speed can also be used as a control input variable in the future, and the propulsion system can be studied as a multi-input-multi-output nonlinear system, providing a reference for the research of today's drones and underwater robots. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1It is a structural schematic diagram of a sliding mode variable structure speed control system based on a nonlinear coupling mathematical model in an embodiment of the present invention.

[0035] Figure 2 It is the simulation result of sliding mode control of ship speed in the embodiment of the present invention.

[0036] Figure 3 It is the simulation result of sliding mode control of propeller speed in the embodiment of the present invention.

[0037] Figure 4 It is the sliding mode control simulation result of the main engine speed in the embodiment of the present invention.

[0038] Figure 5 It is the simulation result of sliding mode control of ship speed under parameter perturbation in the embodiment of the present invention.

[0039] In the figure: 1-hull; 2-navigation speed sensor; 3-speed display screen; 4-reduction gearbox; 5-propeller; 6-propeller speed sensor; 7-propeller speed display screen; 8-fuel delivery pump; 9-flow meter; 10-main engine; 11-injection module; 12-hydraulic dynamometer; 13-main engine speed sensor; 14-main engine speed display screen; 15-high-pressure oil pump; 16-fuel solenoid valve; 17-injector; 18-control system. DETAILED DESCRIPTION

[0040] The present invention is further described in detail below with reference to the accompanying drawings and embodiments.

[0041] like Figure 1 As shown, a sliding mode variable structure speed control system based on a nonlinear coupling mathematical model includes a propulsion system and a control system 18; in the propulsion system, a fuel delivery pump 8 delivers fuel to an injection module 11, a high-pressure oil pump 15 in the injection module 11 is connected to an injector 17 through a fuel solenoid valve 16, and the injector 17 provides fuel to a main engine 10, the main engine 10 drives a propeller 5 through a reduction gearbox 4, and the propeller 5 drives a hull 1 to sail, and sensors (2, 13, 6) for detecting the speed, the main engine speed and the propeller speed are respectively provided on the hull 1, the main engine 10 and the propeller 5; the control system receives real-time feedback of the speed, the main engine speed and the propeller speed and maintains the three constant by controlling the opening of the fuel solenoid valve 16, and the control system 18 adopts a sliding mode variable structure algorithm, and regards the nonlinear coupling mathematical model of the speed, the main engine speed and the propeller speed in the propulsion system as a type of multi-input affine nonlinear model, and solves and obtains a sliding mode variable structure controller.

[0042] like Figure 1As shown, in this embodiment, sensors (2, 13, 6) for detecting the ship speed, the main engine speed and the propeller speed are respectively connected to display screens (3, 14, 7) for displaying the ship speed, the main engine speed and the propeller speed, a flow meter 9 is provided between the fuel delivery pump 8 and the injection module 11, and a hydraulic dynamometer 12 is provided at the output end of the main engine 10.

[0043] In this embodiment, when solving the nonlinear coupling mathematical model of the ship speed, the main engine speed and the propeller speed to obtain the sliding mode variable structure controller, the following steps are included:

[0044] 1. Establish a nonlinear coupling mathematical model of ship speed, main engine speed and propeller speed

[0045] The method of establishing the nonlinear coupling mathematical model of the ship speed, main engine speed and propeller speed in the propulsion system is to respectively establish the mathematical models of the hull-propeller subsystem, the propeller-main engine subsystem and the main engine-injection module subsystem.

[0046] (1) Establishing a mathematical model of the hull-propeller subsystem

[0047] The mathematical model of the hull-propeller subsystem is established according to the motion process of the hull. Specifically, the propeller 5 rotates to generate thrust, which is transmitted through the thrust bearing to push the hull 1 forward, and the water flow generated by the forward movement of the hull 1 will affect the rotation of the propeller 5. When the control system 18 balances the effective thrust generated by the propeller 5 with the resistance of the hull 1 and the uncertain environmental interference force, the actual sailing speed of the hull 1 can be maintained consistent with the set value. The following relationship can be obtained:

[0048]

[0049] Where n P is the propeller speed, r / min; V S is the ship speed, kn; w is the wake coefficient, for a single-screw ship, the value is estimated by Taylor's formula to be 0.3277; λ P is the advance coefficient, which is the hydrodynamic characteristic parameter of the propeller; D is the propeller diameter, m.

[0050] The mechanical relationship between the rotational motion of the propeller 5 and the linear motion of the hull 1 conforms to Newton's second law, and the following motion equation of the hull 1 can be determined:

[0051]

[0052] Where:

[0053] T P =F P (1-t p ) (3)

[0054]

[0055]

[0056] Where, T P is the effective thrust generated by the propeller, N; R is the hull resistance, N; γ S is the attached water coefficient of the hull, which is 1.08; M is the hull mass, which is taken as 1.0×10 8 kg; F P is the thrust generated by the propeller, N; t P K is the percentage of hull thrust reduction, that is, the movement of the propeller and the hull causes an increase in hull resistance or a reduction in propeller thrust. For the single-propeller hull involved in this patent, it is estimated to be 0.3441 by the empirical formula of Hankscher or Shanghe; F is the propeller thrust coefficient, and the advance coefficient λ P Its value is determined by the propeller characteristic curve; ρ is the seawater density, usually 1.025×10 3 kg / m 3 ; β is the resistance coefficient of the hull; the value of m is related to the navigation area, and this patent takes it as 2 in coastal navigation areas.

[0057] h(t) is the uncertain environmental interference force, N. Specifically, considering the influence of wind, waves and tides on the speed, if the hull is in a normal navigation environment, the wind speed is less than 3m / s, the wave height is less than 0.3m, and the water speed is less than 1m / s, then h(t) can be assumed to be an uncertain interference quantity with a known upper limit value. According to the measurement during the navigation process under normal working conditions of the hull, the uncertain interference force can be equivalent to a multiple of the hull resistance R, then:

[0058] h(t)=0.3RsinV S (6)

[0059] (2) Establishing a mathematical model of the propeller-main engine subsystem

[0060] The propeller 5 transmits the power of the main engine 10 to the hull, that is, converts the rotational motion of the main engine 10 into the linear motion of the hull 1. Therefore, a mathematical model of the propeller-main engine subsystem can be established based on this working process. Specifically, as the propeller 5 that propels the hull 1, its rotational kinetic energy comes from the effective torque transmitted by the main engine 10 through the tail shaft. When the control system 18 balances the torque transmitted by the main engine 10 with the torque load generated by the rotation of the propeller 5, the rotation speed of the propeller 5 can remain unchanged. From this, the following relationship can be obtained:

[0061]

[0062]

[0063] In the formula, γ P is the coefficient of additional water of the propeller; I is the moment of inertia of the rotating part of the propulsion system kg·㎡; M l is the instantaneous effective torque of the main engine, which is related to the propeller characteristics of the main engine. This patent can be set as a function of the main engine speed n, that is, αn 3 , N·m; M P is the torque load of the propeller, N·m; K M is the torque coefficient of the propeller, and the advance coefficient λ P The value of the propeller is determined by the propeller characteristic curve.

[0064] (3) Establishing the mathematical model of the host-injection module subsystem

[0065] The control system 18 calculates the effective work according to the actual speed of the main engine 10 and the output torque measured by the hydraulic dynamometer 12, and then calculates the average effective pressure from the effective work, and the output torque of the main engine is approximately proportional to the average effective pressure. Because the difference between the output torque and the load torque, that is, the torque load of the propeller 5, determines the change of the main engine speed, when the control system 18 controls the main engine injection amount, the average indicated pressure changes, the average effective pressure (the difference between the average indicated pressure and the average mechanical loss pressure) changes, and finally the output torque of the main engine 10 changes to maintain the stability of the main engine speed.

[0066] Specifically: According to the D'Alembert principle, the output torque M d and load torque, i.e. the torque load M of the propeller P , the difference determines the change of the main engine speed, and the following motion equation is obtained:

[0067]

[0068] Where, J is the equivalent moment of inertia of the host and its driven mechanical parts; ω is the angular velocity of the host, rad / s.

[0069] Output torque M d With the mean effective pressure P e (kPa) are approximately proportional to each other, and the average effective pressure P e The average indicated pressure P i (kPa) and average mechanical loss pressure P f The value of the cyclic injection amount q(g) corresponding to the different speeds n(rpm) of the specific type of host is measured, and then the indicated power is calculated according to the actual measured power diagram of the host, and the average indicated pressure P is calculated from the indicated power. iIt can be seen that when the speed is constant, the average indicated pressure of the main engine and the injection amount are linearly related. The effective work is calculated based on the actual speed and the output torque measured by the hydraulic dynamometer, and then the average effective pressure P is calculated from the effective work. e Considering that the output torque and the cyclic injection amount are no longer in a linear relationship at different speeds, the nonlinear mathematical model of the main engine speed can be obtained by using the fitting method of quadratic polynomial:

[0070]

[0071] Wherein: n is the main engine speed, r / min; q is the cyclic injection amount, g; as an example of this patent, the 8190ZLC1 main engine of the 8303 ship of China Shipping Container Lines, a1=-0.00153, a2=0.0000213, a3=4.39, a4=-0.0756, a5=3102.34, a6=-60.05.

[0072] 2. Solve to obtain the sliding mode variable structure controller

[0073] Sliding mode variable structure control is a control strategy developed on the basis of variable structure control. Its basic idea is that the system's movement first reaches a certain switching surface, and then gradually approaches the origin in this subspace in a sliding mode. Sliding mode control has a relatively mature theory for linear systems, but nonlinear systems must select a suitable solution method based on the characteristics of the mathematical model.

[0074] (1) Obtain a nonlinear coupling mathematical model with ship speed, main engine speed and propeller speed as state variables, and convert the nonlinear coupling mathematical model into the system state equation

[0075] The mathematical models of the hull-propeller subsystem, propeller-main engine subsystem, and main engine-injection module subsystem can obtain a set of differential equations with propeller speed, ship speed, and main engine speed as state variables:

[0076]

[0077] Obviously, formula (11) is a highly coupled complex nonlinear system with square and trigonometric function terms, but considering the injection amount q as the control input, it has the following characteristics of the affine nonlinear state equation:

[0078]

[0079] In the formula, f(x) and g(x) are both function vectors:

[0080]

[0081] Among them, f i (x) = fi (x1,…,x n ), g i (x) = g i (x1,…,x n ), and i = 1,…,n, that is, it is linear with respect to the control input u.

[0082] Under normal sea conditions with less external wind and current interference, the fluctuations of ship speed, propeller speed and main engine speed are small, so the stability of the three state variables in formula (11) must be maintained, and the control input is selected as the main engine's fuel injection amount. For fixed-pitch propeller hulls, small fluctuations in propeller speed are suitable for normal sea conditions; for controllable pitch propeller hulls, although the propeller thrust can be changed by changing the pitch of the adjustable propeller, thereby maintaining the stability of the propeller speed, the propeller advance coefficient maintains a stable value under normal sea conditions.

[0083] (2) Write the system state equation as a standard form of an affine multi-input nonlinear system, take the switching function of the sliding mode variable structure control, and obtain the sliding mode motion equation

[0084] Get state variables The speed control model can be written as:

[0085]

[0086] in

[0087]

[0088]

[0089] u=q (17)

[0090] The equivalent control and sliding mode motion of the affine nonlinear speed control system are required, and the following switching function is taken:

[0091]

[0092] Then we have:

[0093]

[0094] Let F(x,u)=0, as long as hour, Equivalent control must have a solution

[0095]

[0096] (3) Take the constant velocity approach rate, solve the sliding mode variable structure control, and solve the control rate

[0097] Take the constant velocity approach rate:

[0098]

[0099] The control input u can be solved:

[0100]

[0101] If speed control analysis under large disturbance conditions is to be performed, then based on the mathematical model established above, the state variables and control inputs should be selected for the adjustable propeller and fixed-pitch propeller hulls. For the adjustable propeller hull, the propeller advance coefficient and the main engine fuel injection amount can be selected as two control inputs to maintain the three state variables of speed, propeller and main engine speed constant; for the fixed-pitch propeller hull, the transmission ratio of the propeller speed control and the main engine fuel injection amount should be selected as two control inputs to maintain the two state variables of speed and main engine speed constant.

[0102] (4) The reliability of the sliding mode variable structure controller is verified through simulation analysis and calculation.

[0103] In order to verify whether the mathematical model of the established nonlinear speed system is correct and whether the designed affine nonlinear sliding mode variable structure control algorithm is scientific, simulation analysis is carried out. MATLAB is a powerful computing software, especially for the calculation of matrices, differential equations and other systems with complex solution processes. The hull speed is set to 10kn, the propeller stable speed is 500r / min, and the set speed of the four-stroke main engine under stable working conditions is 1000r / min. The ambient wind speed, periodic wave height and water flow speed in normal sea conditions during navigation are equivalent to the uncertain interference quantity with known upper bound values ​​in formula (6). According to the solution process of sliding mode variable structure control, the three state variable control results calculated on the MATLAB software platform are as follows: Figure 2-4 As shown:

[0104] From the above simulation results, it can be seen that the sliding mode variable structure control strategy can stabilize the ship speed, propeller and main engine speed at the same time, and the stabilization time is about 650s. If the external environmental interference is increased, the wind speed of the navigation environment is considered to be 5-9m / s, the periodic wave height is 0.3-0.6m, and the water flow rate is 2m / s, the upper limit of the uncertain interference in formula (6) can be adjusted to 0.9R, and the calculation is re-calculated on the MATLAB software platform. The displayed results are consistent with Figure 2-4 Basically no changes.

[0105] If the fixed parameters in the programming language are set to interval perturbations, such as the moment wake coefficient is perturbed between [0.20, 0.30], the displacement is perturbed between [5557.2, 5559.2], the thrust reduction coefficient is perturbed between [0.18, 0.25], and the propeller diameter is perturbed between [4.103, 4.303], the output response of each state variable will change significantly, but the control results can be stable. Taking the speed as an example, the simulation calculation results of the parameter perturbation are as follows: Figure 5 As shown:

[0106] It can be seen that the nonlinear mathematical model of speed established in the present invention is correct, the sliding mode variable structure control strategy based on the affine nonlinear analysis method is feasible, and the results of simulation calculations also verify that the sliding mode variable structure control still has good robustness when the disturbance increases and the parameters are perturbed.

[0107] The difficulty in performing constant value control on the ship speed, propeller speed and main engine speed is that when the ship speed is controlled, the propeller speed and the main engine speed change, and when the propeller speed and the main engine speed are controlled, the ship speed deviates from the given value, so this is a highly coupled complex nonlinear system. The present invention targets the nonlinear mathematical model of ship-engine-propeller and uses a sliding mode variable structure control algorithm to perform constant value control on the ship speed, propeller speed and main engine speed, which has fast response, small overshoot, good robustness, strong anti-interference ability and good control effect; the present invention only treats the propulsion system as a type of affine nonlinear system to carry out sliding mode control research, and the propeller speed can also be used as a control input variable in the future, and the propulsion system can be studied as a multi-input-multi-output nonlinear system, providing a reference for the research of today's drones and underwater robots.

[0108] It should be understood that those skilled in the art can make improvements or changes based on the above description, and all these improvements and changes should fall within the scope of protection of the appended claims of the present invention.

Claims

1. A sliding mode variable structure speed control system based on a nonlinear coupling mathematical model, characterized by: It includes a propulsion system and a control system; in the propulsion system, a fuel delivery pump delivers fuel to an injection module, a high-pressure oil pump in the injection module is connected to an injector through a fuel solenoid valve, the injector provides fuel to the main engine, the main engine drives the propeller through a reduction gearbox, the propeller drives the hull to sail, and sensors for detecting the ship speed, the main engine speed and the propeller speed are respectively provided on the hull, the main engine and the propeller; the control system receives real-time feedback of the ship speed, the main engine speed and the propeller speed and maintains the three constant by controlling the opening of the fuel solenoid valve, the control system adopts a sliding mode variable structure algorithm, and regards the nonlinear coupling mathematical model of the ship speed, the main engine speed and the propeller speed in the propulsion system as a type of multi-input affine nonlinear model, and solves and obtains a sliding mode variable structure controller; The method of establishing the nonlinear coupling mathematical model of the ship speed, main engine speed and propeller speed in the propulsion system is to respectively establish the mathematical models of the hull-propeller subsystem, the propeller-main engine subsystem and the main engine-injection module subsystem; the mathematical model of the hull-propeller subsystem is established according to the motion process of the propeller propelling the hull, so that the effective thrust of the propeller is balanced with the hull resistance and the uncertain environmental interference force to maintain the ship speed consistent with the set value; The mathematical model of the propeller-host subsystem is established based on the working process of the host transmitting torque to the propeller, so that the torque transmitted by the host is balanced with the torque load generated when the propeller rotates to maintain the propeller speed constant; The mathematical model of the main engine-injection module subsystem is established according to the mechanism of the influence of the injection amount on the main engine speed. The change of the main engine speed is determined by the difference between the main engine output torque and the propeller torque load. The main engine output torque is approximately proportional to the mean effective pressure. The mean effective pressure is the difference between the mean indicated pressure and the mean mechanical loss pressure. The mean indicated pressure changes by controlling the injection amount, thereby changing the main engine output torque to maintain the main engine speed stable.

2. The sliding mode variable structure ship speed control system based on the nonlinear coupling mathematical model according to claim 1, characterized in that: When establishing the mathematical model of the hull-propeller subsystem, In order to balance the effective thrust of the propeller with the hull resistance and the uncertain environmental interference force, the relationship is obtained: (1) In the formula, n P is the propeller speed; V S is the speed; is the wake coefficient, estimated by the empirical formula; is the advance coefficient, which is the propeller hydrodynamic characteristic parameter; D is the propeller diameter; The mechanical relationship between the propeller rotation and the hull linear motion conforms to Newton's second law, and the hull motion equation is obtained (2) In the formula (3) (4) (5) In the formula, T P is the effective thrust of the propeller; R is the hull resistance; is the attached water coefficient of the hull; M is the hull mass; F P is the thrust generated by the propeller; t P is the percentage of hull thrust reduction, that is, the movement of the propeller and the hull causes an increase in hull resistance or a reduction in propeller thrust, estimated by an empirical formula; K F is the propeller thrust coefficient, and the advance coefficient Related, determined by the propeller characteristic curve map; is the density of seawater; is the resistance coefficient of the hull; m The value of is determined according to the navigation area; In the formula, h(t) For uncertain environmental interference forces, the ship is assumed to be in a normal navigation environment, that is, the wind speed is less than 3 m / s , wave height is less than 0.3 m , water flow velocity is less than 1 m / s According to the calculation of the ship in the normal navigation environment, the uncertain environmental interference force is equivalent to the multiple of the hull resistance, then (6)。 3. The sliding mode variable structure ship speed control system based on the nonlinear coupling mathematical model according to claim 1, characterized in that: When establishing the mathematical model of the propeller-main engine subsystem, In order to balance the torque transmitted by the main engine with the torque load generated by the propeller rotation, the relationship is obtained: (7) (8) In the formula, is the additional water coefficient of the propeller; I is the moment of inertia of the rotating parts of the propulsion system; M l It is the instantaneous effective torque of the main engine, which is related to the propeller characteristics of the main engine and is set to the main engine speed. n Function of M P is the torque load of the propeller; K M is the torque coefficient of the propeller, and the advance coefficient Related, determined by the propeller characteristic curve map.

4. The sliding mode variable structure ship speed control system based on the nonlinear coupling mathematical model according to claim 1, characterized in that: When establishing the mathematical model of the host-injection module subsystem, According to the D'Alembert principle, the output torque of the main engine M d and load torque, i.e. the torque load of the propeller M P , the difference determines the change of the main engine speed, so the motion equation is (9) In the formula, J is the equivalent moment of inertia of the host and its driven mechanical parts; is the angular velocity of the host; Output torque of the main engine M d Mean effective pressure P e The average effective pressure is approximately proportional to P e The average indicated pressure P i and average mechanical loss pressure P f The difference between the two; measuring different host speeds n Corresponding cycle injection amount q The indicated power is calculated based on the actual power diagram of the main engine, and the average indicated pressure is calculated from the indicated power. P i , the average indicated pressure of the main engine at a certain speed P i Cycle injection amount q There is a linear relationship between them; according to the measured host speed n and output torque M d Calculate the effective work, and then calculate the average effective pressure from the effective work P e ; Considering different host speeds n Under this condition, the output torque of the main engine M d Cycle injection amount q The relationship is no longer linear, so the main engine speed is obtained by using the quadratic polynomial fitting method. n The nonlinear mathematical model is (10) In the formula, n is the host speed; q is the cycle injection amount; a 1. a 2. a 3. a 4. a 5. a 6 is the parameters related to the host.

5. The sliding mode variable structure ship speed control system based on the nonlinear coupling mathematical model according to claim 1, characterized in that: The method to solve the sliding mode variable structure controller is: 1) The mathematical models of the hull-propeller subsystem, propeller-main engine subsystem, and main engine-injection module subsystem are integrated to obtain a nonlinear coupling mathematical model with the ship speed, main engine speed, and propeller speed as state variables. The nonlinear coupling mathematical model is converted into a system state equation, and the cyclic injection amount is used as the control input. Under normal sea conditions with less external wind and water flow interference, the fluctuations of the ship speed, propeller speed, and main engine speed are small, and the three state variables are maintained stable. For fixed-pitch propeller hulls, small fluctuations in propeller speed are suitable for normal sea conditions. For controllable pitch propeller hulls, although the propeller thrust can be changed by changing the pitch of the adjustable propeller, thereby maintaining the stability of the propeller speed, the propeller speed is stable under normal sea conditions. The propeller advance coefficient maintains a stable value; 2) the system state equation is written as a standard form of a class of affine multi-input nonlinear systems, the switching function of the sliding mode variable structure control is taken, and the sliding mode motion equation is obtained; 3) the constant speed approach rate is taken, the sliding mode variable structure control is solved, and the control rate is solved. When the speed control analysis under the large disturbance state is carried out, on the basis of the original sliding mode variable structure controller, for the adjustable propeller hull, the propeller advance coefficient and the injection amount are selected as two control inputs to maintain the three state variables of the ship speed, the propeller speed and the main engine speed constant. For the fixed pitch propeller hull, the transmission ratio and the injection amount of the propeller speed are selected as two control inputs to maintain the two state variables of the ship speed and the main engine speed constant; 4) Verify the reliability of the sliding mode variable structure controller through simulation analysis and calculation.

6. The sliding mode variable structure ship speed control system based on the nonlinear coupling mathematical model according to claim 1, characterized in that: Sensors for detecting the ship speed, main engine speed and propeller speed are respectively connected to display screens for displaying the ship speed, main engine speed and propeller speed. A flow meter is provided between the fuel delivery pump and the injection module, and a hydraulic dynamometer is provided at the main engine output end.

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