Power distribution method for unmanned surface vessels

Abstract

This invention proposes a power distribution method for unmanned surface vessels (USVs). It involves observing the interference values ​​of the USV's motors using an extended observer, and then distributing power to the motors according to preset rules based on these interference values ​​to obtain the target thrust. Water flow velocity parameters are acquired using a water flow velocity sensor, and the current thrust of the motors is calculated based on these parameters. The thrust loop of the motors is controlled based on the target thrust and the current thrust. Interference is compensated for by a tracking differentiator and the target motor speed. Compared to existing technologies, this invention uses the observed interference values ​​of the motors as reference parameters for power distribution. This not only enables motor speed control but also serves as a factor influencing both the motor speed controller and power distribution, preventing significant speed changes in the motors under strong interference. This results in more accurate thrust control and superior performance for the USV.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of unmanned ships, and particularly relates to a power distribution method for an unmanned ship. BACKGROUND

[0002] The new energy unmanned ship mainly relies on a motor to drive a propeller to generate thrust. In motor control, many electronic speed controllers currently adopt a six-step commutation control strategy (i.e., according to the sensor detection of the sector in which the motor rotor is located, the force of the corresponding sector is given according to the feedback of the sensor). At the same time, to realize bottom control, the acquisition of motor thrust is also crucial. At present, most of the motor thrusts are calibrated in advance by speed and thrust, and then in actual control, the speed of the motor is directly controlled to realize the control of the thrust.

[0003] However, the six-step commutation control strategy has a large torque pulse. Meanwhile, when driving in complex water areas or sea areas, the influence of water flow interference on the motor cannot be ignored. Through literature review, it is found that when the motor operates in complex water conditions, the thrust generated at the same speed will also have a significant difference, which significantly reduces the effect of offline calibration of motor speed and thrust. If a thrust sensor is used to acquire the thrust in real time, the complexity and cost of the mechanical structure of the propulsion system will be increased.

[0004] Therefore, there is an urgent need for a new power distribution method for an unmanned ship to solve the above problems. SUMMARY

[0005] The application provides a power distribution method for an unmanned ship, which aims to improve the robustness of unmanned ship control.

[0006] The application provides a power distribution method for an unmanned ship, which comprises the following steps:

[0007] S1, observing the disturbance value of the motor of the unmanned ship based on an extended observer, and distributing power to the motor according to the disturbance value through a preset rule to obtain the target thrust of the motor;

[0008] S2, acquiring the water flow speed parameter through a water flow speed sensor, calculating the current thrust of the motor according to the water flow speed parameter, and controlling the thrust loop of the motor based on the target thrust and the current thrust;

[0009] S3, calculating the target speed of the motor according to the target thrust and the current thrust, compensating the disturbance of the motor based on a tracking differentiator and the target speed of the motor, and establishing a sliding mode controller to control the speed loop of the motor according to the disturbance value;

[0010] S4, controlling a current loop of the motor based on the PI controller and the target rotating speed, to realize power distribution of the unmanned ship.

[0011] Preferably, in step S1, the preset rule is that the target thrust satisfies the following relationship and constraint condition:

[0012] Min 1 / 2[D r (F r(t) -F r_d(t) ) 2 +D l (F l(t) -F l_d(t) ) 2 ];

[0013] Wherein, F r(t) represents the current thrust generated by the right motor of the unmanned ship, F l(t)) represents the current thrust generated by the left motor of the unmanned ship, the target thrust of the right motor is F r_d(t) , and the target thrust of the left motor is F l_d(t) , D r and D l respectively represent the disturbance of the right motor and the disturbance of the left motor.

[0014] The constraint condition is:

[0015] T=L(F L(ω1) -F r(ω2) );

[0016] Wherein, L represents half of the distance between the left motor and the right motor, and T represents the target torque of the unmanned ship.

[0017] Preferably, in step S2, the motor calculates the propeller ratio according to the water flow speed parameter, and calculates the current thrust according to the propeller ratio; the propeller ratio satisfies the following rule:

[0018]

[0019] Wherein, u a represents the water flow speed parameter, ω represents the rotating speed of the motor, D represents the diameter of the propeller of the motor, and J represents the propeller ratio.

[0020] Preferably, in step S3, the compensation value of the tracking differentiator to the disturbance of the motor satisfies the following rule:

[0021] v1(k+1)=v1(k)+hfst[v1(k)-v0(k),v1(k),r,h0];

[0022] wherein v1(k) represents a target speed of the motor, v1(k+1) represents a compensation value of the tracking differentiator, h represents a sampling period, fst represents a fastest control synthesis function, v0(k) represents an input of the tracking differentiator, r represents a speed factor, and h0 represents a filter factor.

[0023] Preferably, in step S3, the sliding mode controller controls a speed loop of the motor according to the disturbance value, and the following rule is satisfied:

[0024]

[0025] wherein u represents an output of the sliding mode controller, D is p n represents a number of pole pairs of the motor, ψ f represents a flux constant of the motor, J represents a moment of inertia of the motor, x2 represents a state variable of the motor, sat(s) represents a saturation function, c and q represent sliding mode controller parameters, and s represents a sliding surface function.

[0026] Preferably, the q value satisfies the following rule:

[0027]

[0028] wherein K q represents a maximum preset value of q, D0 represents a preset threshold value, and D m represents a preset critical value. Preferably, in step S4, a PI controller is used to control a current loop of the motor, and the following rule is satisfied:

[0029]

[0030] wherein K P represents a proportional gain coefficient, K i represents an integral gain coefficient, ω curr represents a bandwidth of the PI controller of the current loop, R represents a phase resistance of the motor, and L d represents a phase inductance of the motor.

[0031] Compared with the prior art, the present application observes the interference value of the motor of the unmanned ship based on an extended observer, distributes power to the motor according to the interference value through a preset rule to obtain the target thrust of the motor, obtains the current flow speed parameter through a flow speed sensor, calculates the current thrust of the motor according to the current flow speed parameter, controls the thrust loop of the motor based on the target thrust and the current thrust, calculates the target rotating speed of the motor according to the target thrust and the current thrust, compensates the interference of the motor based on a tracking differentiator and the target rotating speed of the motor, establishes a sliding mode controller, controls the speed loop of the motor according to the interference value, controls the current loop of the motor based on a PI controller and the target rotating speed, and realizes power distribution of the unmanned ship. The interference value observed by the motor is used as a reference parameter for power distribution of the motor, is not only used for realizing motor rotating speed control, but also used as an influencing factor for motor rotating speed controller and power distribution, so that the motor is prevented from changing the rotating speed greatly in the case of strong interference. The thrust control of the unmanned ship is more accurate and the performance is better. BRIEF DESCRIPTION OF DRAWINGS

[0032] The present application will be described in detail below with reference to the drawings. The above or other aspects of the present application will become more apparent and more readily appreciated through detailed description, taken in conjunction with the following drawings, in which:

[0033] Figure 1 is a flow block diagram of the power distribution method of the unmanned ship provided by the embodiment of the present application. DETAILED DESCRIPTION

[0034] In order to make the objectives, technical solutions and advantages of the present application clearer, the present application will be further described in detail below with reference to the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and not used to limit the present application.

[0035] Please refer to Figure 1 The present application provides a power distribution method of an unmanned ship, which comprises the following steps:

[0036] S1, observing the interference value of the motor of the unmanned ship based on an extended observer, and distributing power to the motor according to the interference value through a preset rule to obtain the target thrust of the motor;

[0037] In the embodiment of the present application, when the upper control algorithm of the unmanned ship calculates the torque required to realize the current trajectory tracking, the torque is transmitted to the bottom control system. Since the power of the unmanned ship used in the present application is derived from the two motors at the tail, the torque is provided by the thrust difference of the left and right motors. When the target thrust is obtained, the motor can be controlled to realize different torques, i.e. formula (1)

[0038] T=L(FL(t) -F r(t) ); (1)

[0039] Wherein, the right motor generated thrust, the left motor generated thrust, L is the distance of two motor 1 / 2.

[0040] In the present application, the thrust of the motor is the motor speed as the independent variable, so formula (1) can be converted to formula (2)

[0041] T=L(F L(ω1) -F r(ω2)) ; (2)

[0042] Where ω1 and ω2 are the speed of the left and right motor.

[0043] In the open water, there are various forms of water flow, such as: vortex, turbulence and so on. These non-stationary water flow, the influence degree of two propulsion motor of the unmanned ship tail is also different, the water flow influence big side, the motor maintains stable operation and fast response difficulty is bigger. At the same time, considering the longitudinal speed and lateral speed of the unmanned ship is coupled with each other. Therefore, the motor torque fluctuation should not be too large, combined with the motor disturbance big side, should be smaller than the interference side, torque change is smaller. This is converted into a multi variable coupling optimization problem, obviously a nonlinear programming problem, here using quadratic programming to find the optimal solution, namely step S1, the preset rule is to make the target thrust satisfy the following relationship and constraint condition:

[0044] Min 1 / 2[D r (F r(t) -F r_d(t) ) 2 +D l (F l(t) -F l_d(t) ) 2 ]; (3)

[0045] Wherein, F r(t) represent the current right motor of the unmanned ship generated thrust, F l(t)) represent the current left motor of the unmanned ship generated thrust, the target thrust of the right motor is F r_d(t) , the target thrust of the left motor is F l_d(t) , D r , D l represent the disturbance of the right motor and the left motor respectively;

[0046] The constraint condition is:

[0047] T=L(F L(ω1) -F r(ω2) ); (4)

[0048] Wherein, L represents half of the distance between the left motor and the right motor, and T represents the target torque of the unmanned ship.

[0049] S2, the water flow speed parameter is acquired by a water flow speed sensor, the current thrust of the motor is calculated according to the water flow speed parameter, and the thrust ring of the motor is controlled based on the target thrust and the current thrust.

[0050] In the embodiment of the application, the motor calculates the propulsion ratio according to the water flow speed parameter, and calculates the current thrust according to the propulsion ratio; the speed of the motor and the torque of the motor are obtained by looking up the table to obtain the propulsion ratio, and then the real-time thrust of the motor is obtained.

[0051] The mapping relationship between the speed of the motor, the torque of the motor and the thrust of the motor has good effect in static water area, since the method is based on complex water conditions, the method is not applicable, the application adopts a water flow speed sensor near the motor propeller to approximately obtain the propulsion ratio of the motor. The propulsion ratio satisfies the following rules:

[0052]

[0053] Wherein, u a represents the water flow speed parameter, ω represents the speed of the motor, D represents the diameter of the propeller of the motor, and J represents the propulsion ratio.

[0054] The speed of the motor can be measured by a position sensor or obtained by an inductance control algorithm of the motor, the application obtains the speed of the motor by an encoder, and has:

[0055] T p = T e G QT (J) (6)

[0056] Since the unmanned ship targeted by the application is a motor directly driving a propeller, the torque of the motor is represented in the application. The torque of the motor can be obtained by formula (6):

[0057] T e = 2 / 3P n ψ f i q (7)

[0058] Wherein, P n is the number of pole pairs of the motor, ψ f is the rotor flux of the motor, and i q is the current of the q-axis of the motor. Wherein, P n and ψ f are known, and i qAlso can be measured by motor drive board three-phase current and by Clark and Park transformation calculation.

[0059] The mapping relationship between the propulsion ratio J and G QT The mapping relationship between the propulsion ratio J and G is obtained by the premise design experiment. When the unmanned ship is actually running, J is calculated by the flowmeter and the rotating speed of the motor, and G is obtained by looking up the table QT The value of J, and the torque of the motor is multiplied to obtain the real-time thrust of the motor.

[0060] As shown in formula (8):

[0061]

[0062] S3, the target speed of the motor is calculated according to the target thrust and the current thrust, the disturbance of the motor is compensated based on a tracking differentiator and the target speed of the motor, and a sliding mode controller is established, the sliding mode controller controls the speed loop of the motor according to the disturbance value;

[0063] In the embodiment of the application, when the unmanned ship faces a sharp turn, sometimes the left and right motors need to change the speed greatly to produce the target torque difference. However, when the error between the target value and the current feedback value is large, the ordinary PI controller will have serious overshoot. The application uses a first-order tracking differentiator to smooth the target signal, and the compensation value of the tracking differentiator to the disturbance of the motor satisfies the following rules:

[0064] v1(k+1)=v1(k)+hfst[v1(k)-v0(k),v1(k),r,h0];

[0065] Wherein, v1(k) represents the target speed of the motor, v1(k+1) represents the compensation value of the tracking differentiator, h represents the sampling period, fst represents the fastest control synthesis function, v0(k) represents the input (reference speed) of the tracking differentiator, r represents the speed factor (determines the speed of tracking), and h0 represents the filtering factor.

[0066] Specifically, the motor used by the unmanned ship of the application is a surface-mounted permanent magnet synchronous motor, and the motion equation of the motor can be represented by formula (10):

[0067]

[0068] Combined with formula (7), the following can be obtained:

[0069]

[0070] Wherein The internal disturbance of the speed loop, The compensation coefficient of the speed loop.

[0071] The external disturbance of the control system of the unmanned ship is defined as f o , the internal disturbance of the system is known as f, and the total disturbance of the speed loop control system can be defined as: D = f o +f, let x1 = ω Ref , y is the input of the extended observer, and is the feedback speed. The state equation of the speed loop control system can be designed as:

[0072]

[0073] According to the above formula, the observation equation of the second-order linear extended observer can be designed as:

[0074]

[0075] Wherein z1 is the estimated value of the motor speed, z2 is the estimated value of the total disturbance D of the system, ω fdk is the actual speed returned by the encoder of the motor and converted into electrical angular velocity. In order to ensure the stability of the observer, let ω0 be the bandwidth of the system, then let β1 = 2ω0,

[0076] When e1 converges, that is, the estimated value of the speed is equal to the actual feedback value, then the z2 at this time, that is, the estimated value of the total disturbance of the system, is also accurate. This observed disturbance value can be used in the quadratic programming mentioned at the beginning of the method, which needs to use the disturbance, and the next subsection needs to use the disturbance to adaptively adjust the parameters of the sliding mode controller, and is used for compensation of the feedback rate output.

[0077] In ADRC, the nonlinear error feedback control rate is equivalent to the proportional controller of a PID controller, and too large deviation will reduce the stability of the system, and the parameter setting in NLSEF is difficult, which has great influence on the speed regulation performance. Therefore, the adaptive sliding mode control is used in the application, and the robustness of the sliding mode to external disturbance is fully utilized. At the same time, according to the disturbance value observed by the extended observer in ADRC, the parameters of the exponential reaching law in the sliding mode controller are changed in real time.

[0078] The sliding mode controller is established. First, the mathematical model of the motor in d-q coordinate system is established. In d-q coordinate system, the torque and current of the actual permanent magnet synchronous motor can be decoupled. The motor digital model is shown in formula (14):

[0079]

[0080] Wherein L sFor stator inductance, for SPMSM, there is no reluctance torque, so the control strategy of id=0 is adopted, at this time, formula (14) can be changed into:

[0081]

[0082] Define the state variable of the sliding mode control system:

[0083]

[0084] According to formula (15) and formula (16), the following formula can be obtained:

[0085]

[0086] Definition: Combined with the extended observer Then formula (17) can be changed into:

[0087]

[0088] Define the sliding surface function as:

[0089] s=cx1+x2 (19);

[0090] Derivation of the sliding surface can be obtained:

[0091]

[0092] The control effect of the sliding mode controller depends largely on the selection of the reaching law, the exponential reaching law is selected in the application, which can quickly reach and maintain on the sliding surface when facing a large error. At the same time, considering that the sign function will cause motor chattering, the sign function is replaced by the saturation function. Then the sliding mode controller can control the speed loop of the motor according to the disturbance value, and satisfy the following rules:

[0093]

[0094] Wherein, u represents the output of the sliding film controller, D represents p n represents the number of pole pairs of the motor, ψ f represents the flux constant of the motor, J represents the moment of inertia of the motor, x2 represents the state variable (derivative of speed error) of the motor, sat(s) represents the saturation function, c and q represent the parameters of the sliding mode controller, and s represents the sliding surface function.

[0095] In the two embodiments of the present application, when q is increased, the stability of the rotating speed of the motor will be greatly improved, but the overshoot will also be too large, so q cannot be set at a large value all the time, but depends on the specific situation. Therefore, the present application designs a saturation function, that is, the q value satisfies the following rules:

[0096]

[0097] wherein K q represents the maximum preset value of q, D0 represents the preset threshold, and D m represents the preset critical value. Specifically, K q represents the maximum value of the acceptable value range of q, D0 represents that if the interference value exceeds D0, the value of q will not change, and will be maintained at K q , and D m represents a critical value, when the interference is greater than the value, q will change with the change of the interference.

[0098] Specifically, K q represents the maximum value of the acceptable value range of q, D m is positioned as a critical value that the value of q needs to be adaptively changed, when the value exceeds the value, the value of q will change with the change of the interference, if the interference is greater than D0, the value of q will not change, and if the value range of q is not limited, it may cause serious overshoot.

[0099] The limitation of Dm is to prevent the overshoot from being too large, in the linear region, the value of the parameter q linearly changes with the interference observed by the extended observer, reasonably avoids the flow interference, and ensures the stable operation of the motor.

[0100] S4, control the current loop of the motor based on the PI controller and the target rotating speed, to realize the power distribution of the unmanned ship.

[0101] In the embodiments of the present application, the current loop is the innermost loop of the motor control system, directly controls the torque of the motor, the PI controller is adopted, the PI controller can achieve good effect in complex water conditions, and the PI controller of the current loop is easy to adjust parameters, and most of them can be calculated through the resistance and inductance of the motor and the bandwidth of the current loop. The PI controller is used to control the current loop of the motor, and satisfies the following rules:

[0102]

[0103] wherein K P represents a proportional gain coefficient, K i represents an integral gain coefficient, and ω currdenotes a bandwidth of a PI controller of the current loop, R denotes a phase resistance of the motor, L d denotes a phase inductance of the motor.

[0104] Compared with the prior art, the present application observes the interference value of the motor of the unmanned ship based on an extended observer, distributes power to the motor according to the interference value through a preset rule to obtain a target thrust of the motor, obtains a water flow speed parameter through a water flow speed sensor, calculates a current thrust of the motor according to the water flow speed parameter, controls the thrust loop of the motor based on the target thrust and the current thrust, calculates a target rotating speed of the motor according to the target thrust and the current thrust, compensates for the interference of the motor based on a tracking differentiator and the target rotating speed of the motor, establishes a sliding mode controller, controls the speed loop of the motor according to the interference value by the sliding mode controller, controls the current loop of the motor based on a PI controller and the target rotating speed, and realizes power distribution of the unmanned ship. The interference value observed by the motor is used as a reference parameter for power distribution of the motor, is not only used for realizing motor rotating speed control, but also used as an influencing factor for motor rotating speed control and power distribution, so that the motor is prevented from changing the rotating speed greatly in the case of strong interference. The thrust control of the unmanned ship is more accurate and the performance is better.

[0105] It should be noted that in this document, the terms "comprise", "comprising", or any other variant thereof are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements in the list, but can also include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without more limitations, an element defined by the phrase "comprising a" does not exclude the existence of additional identical elements in the process, method, article, or apparatus that includes the element.

[0106] The embodiments of the present application are described above in conjunction with the drawings, and the disclosed are only the preferred embodiments of the present application, but the present application is not limited to the above specific embodiments, and the above specific embodiments are only illustrative, but not restrictive, and those skilled in the art can make many equivalent changes without departing from the purpose of the present application and the scope of the claims, which are all within the protection of the present application.

Claims

1. A power distribution method for an unmanned surface vessel, characterized in that, The method comprises the following steps: S1, observing the disturbance value of the motor of the unmanned ship based on an extended observer, and distributing power to the motor according to the disturbance value through a preset rule to obtain a target thrust of the motor; S2, obtaining a water flow speed parameter through a water flow speed sensor, calculating a current thrust of the motor according to the water flow speed parameter, and controlling a thrust loop of the motor based on the target thrust and the current thrust; S3, calculating a target rotating speed of the motor according to the target thrust and the current thrust, and compensating the disturbance of the motor based on a tracking differentiator and the target rotating speed of the motor; establishing a sliding mode controller, which controls a speed loop of the motor according to the disturbance value; S4, controlling a current loop of the motor based on a PI controller and the target rotating speed to realize power distribution of the unmanned ship; In step S1, the preset rule is to make the target thrust satisfy the following relationship and constraint condition: Min 1 / 2 ; wherein, represents the current thrust generated by the right motor of the unmanned boat, represents the current thrust generated by the left motor of the unmanned boat, the target thrust of the right motor is , and the target thrust of the left motor is , respectively represent the disturbance of the right motor and the disturbance of the left motor. The constraint condition is: T= ； wherein, L denotes half of the distance between the left motor and the right motor, and T denotes a target torque of the unmanned surface vehicle.

2. The method of claim 1, wherein, In step S2, the motor calculates a propelling ratio according to the water flow speed parameter, and calculates the current thrust according to the propelling ratio; the propelling ratio satisfies the following rule: ； wherein, represents the water flow speed parameter, represents the rotation speed of the electric machine, D1 represents the diameter of the propeller of the electric machine, and J represents the propulsion ratio.

3. The method of claim 1, wherein, In step S3, the compensation value of the disturbance of the motor satisfies the following rule: ； wherein denotes the output of the tracking differentiator at the previous time instant, denotes the output of the tracking differentiator at the current time instant, h denotes the sampling period, denotes the fastest control synthesis function, denotes the input of the tracking differentiator, denotes the speed factor, denotes the filter factor.

4. The method of claim 1, wherein, In step S3, the sliding mode controller controls the speed loop of the motor according to the disturbance value, which satisfies the following rule: ； wherein represents an output of the sliding mode controller, is , represents a number of pole pairs of the electric machine, represents a flux constant of the electric machine, J1 represents a moment of inertia of the electric machine, represents a state variable of the electric machine, represents a saturation function, c and represents a sliding mode controller parameter, represents a sliding surface function.

5. The power distribution method for an unmanned surface vehicle of claim 4, wherein, The sliding mode controller parameters q satisfy the following rules: ； wherein represents q a maximum preset value of represents a preset threshold value, represents a preset critical value.

6. The method of claim 1, wherein, In step S4, the control of the current loop of the motor based on the PI controller satisfies the following rule: ； wherein, represents a proportional gain coefficient, represents an integral gain coefficient, represents a bandwidth of a PI controller of the current loop, R represents a phase resistance of the motor, represents a phase inductance of the motor.

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