Model predictive control method suitable for continuously adjustable variable damping wave energy device

Abstract

A model prediction control method suitable for a continuously adjustable damping wave energy device comprises the following steps: analyzing damping force and current of a continuously adjustable damper, determining a constraint boundary of the damping force, and establishing a correlation function of relative speed, current and damping force; a binary variable is introduced to convert the nonlinear constraint of the continuously adjustable damper into a combination of a threshold condition and a logic condition; s3, carrying out stress analysis on the adjustable damping wave energy device, and constructing a stress dynamic equation of the hybrid logic power system; displacement parameters, speed parameters and external wave excitation parameters of the wave energy device are set as known conditions, and a continuous state space equation is obtained in combination with a motion equation of the system; establishing an objective function for maximizing the energy capturing efficiency of the wave energy device; and updating the state vector of the wave energy device and the external wave excitation parameters at the next moment, constructing an input hybrid system model, and completing an overall model prediction control process.

Description

Technical field:

[0001] The invention relates to a model predictive control method suitable for a continuously adjustable variable damping wave energy device. Background technology:

[0002] Wave energy has great potential as a renewable energy source. Its global theoretical annual power generation is 32,000 TWh. The development and utilization of wave energy resources can help reduce carbon dioxide emissions and optimize the energy structure. Control strategies play an important role in improving the technical performance level of wave energy devices. Specifically, an energy maximization control system can adjust wave energy devices to adapt to different wave conditions.

[0003] Mechanical energy conversion systems have the advantage of high energy conversion efficiency, but it is difficult to control wave energy devices with mechanical energy conversion systems. Using continuously adjustable variable dampers to adjust the oscillating buoy wave energy devices with mechanical energy conversion systems can effectively improve the energy capture efficiency.

[0004] The introduction of continuously adjustable variable dampers will cause the wave energy device to have nonlinear characteristics. Due to the change in speed direction, logical variables are added to the wave energy system, making the system present a mixed state of logical variables and continuous variables. Its constraint boundary also has a significant impact on the energy capture effect of the wave energy device. Therefore, predictive control of mixed models has been widely used in the energy capture process of wave energy devices. Most of the existing predictive control methods are aimed at linear systems, and the overall control process is too idealized. The control strategy for wave energy systems containing logical variables and continuous variables is still in a state of scarcity, resulting in low energy conversion efficiency of wave energy devices and cannot meet the actual application needs well. Summary of the invention:

[0005] The embodiment of the present invention provides a model predictive control method suitable for a continuously adjustable variable damping wave energy device. The method is reasonably designed and can ensure the safe operation of the wave energy device in a harsh marine environment under the premise of ensuring the constraints of the adjustable variable damper. At the same time, the system is constrained under extreme wave conditions, the energy conversion efficiency of the wave energy device is improved, the execution capability of the hybrid model predictive controller is enhanced, and the failure probability of the wave energy device is reduced, thereby improving the feasibility of the hybrid model predictive control in the actual operation process of the wave energy device. The state of the continuously adjustable variable damper can be adjusted in time in a dynamically changing wave environment, so that the device achieves the optimal energy capture effect, and solves the problems existing in the prior art.

[0006] The technical solution adopted by the present invention to solve the above technical problems is:

[0007] A model predictive control method applicable to a continuously adjustable variable damping wave energy device, the predictive control method comprising the following steps:

[0008] S1, analyze the damping force and current of the continuously variable damper, clarify the constraint boundary of the damping force, and establish the correlation function of relative speed, current and damping force;

[0009] S2, introduce binary variables to convert the nonlinear constraints of the continuously adjustable variable damper into a combination of threshold conditions and logical conditions, and convert the combination of threshold conditions and logical conditions into linear constraints involving logical variables, and introduce auxiliary continuous variables to convert the linear constraints of logical variables into integer linear inequalities;

[0010] S3, perform force analysis on the adjustable variable damping wave energy device and construct the force dynamic equation of the hybrid logic power system as the discrete state space model of the wave energy device;

[0011] S4, setting the displacement parameter, velocity parameter and external wave excitation parameter of the wave energy device as known conditions, wherein the external wave excitation parameter is obtained by prediction, and the state vector of the wave energy device is formed by the displacement parameter and the velocity parameter, and a continuous state space equation is obtained by combining the motion equation of the system;

[0012] S5, establish the objective function of maximizing the energy capture efficiency of the wave energy device, bring the state vector into the state space model and the maximization objective function, and propagate it in the prediction time domain to obtain the first value of the control force sequence as the optimal control force at the current moment;

[0013] S6, at the next moment, the state vector of the wave energy device and the external wave excitation parameters are updated, and the above step S5 is re-executed to construct the input hybrid system model and complete the overall model prediction control process.

[0014] The constraint boundary and correlation function of the damping force are expressed as:

[0015]

[0016] Where u represents the control force, α and β are the constraint boundary coefficients, v represents the relative motion speed of the float and the floating body of the wave energy device, i is the driving current of the continuously adjustable damper, and F d represents the control force, and f is the correlation function of relative speed, current and damping force.

[0017] The combination of the threshold condition and the logic condition is:

[0018]

[0019] Among them, the conjunction It means "if and only if";

[0020] The logical variable δ vThe linear constraints are:

[0021]

[0022] Among them, v l and v u is the lower and upper limits of the relative motion speed v of the float and the floating body of the wave energy device; ε>0 is the tolerance, usually the computer precision;

[0023] Furthermore, the linear constraint of the damping force can be expressed as:

[0024]

[0025] Among them, z 1 、z 2 and z 3 All belong to the set of real numbers, are auxiliary continuous variables, and have constraints:

[0026] z 1 , z 2 , z 3 >0

[0027] The general "if-then-else" can be expressed as:

[0028] IFδTHEN z=a 1 x+b 1 u+f 1

[0029] ELSE z=a 2 x+b 2 u+f 2

[0030] Among them, δ∈{0,1},z∈R,u∈R,a 1 , a 2 , b 1 , b 2 , f 1 and f 2 is a constant with appropriate dimension;

[0031] The integer linear inequality is:

[0032] (f 2 -F 1 )δ+z≤a 2 x+b 2 u+c 2

[0033] (f 1 -F 2 )δ-z≤-a 2 xb 2 uc 2

[0034] (f 1 -F 2 )(1-δ)+z≤a 1 x+b 1 u+c 1

[0035] (f 2 -F 1 )(1-δ)-z≤-a 1 xb 1 uc 1

[0036] Among them, f i and F i They are respectively i x+b i u+c i , the lower and upper bounds of i∈{1,2}.

[0037] The dynamic force equation is:

[0038]

[0039] Where, “1” and “2” represent the float and the floating body respectively; m is the mass; x is the displacement relative to the equilibrium position; F exc Represents the wave excitation force; F radij is the radiation force exerted on structure i due to the motion of structure j; F b F is the hydrostatic restoring force; pto is the PTO force; F u For control;

[0040] The discrete state space model is:

[0041] p(k+1)=A d p(k)-B du F d (k)+B dδ δ v (k)+B dz z(k)+B de F exc

[0042] E 2 δ v (k)+E 3 z(k)≤E 1 F d (k)+E 4 p(k)+E 5

[0043] Among them, p∈R is the state vector, F d∈R is the control input, A d , B du and B de is the discrete system matrix in the discrete state space equation; B dδ and B dz are all zero matrices; E 1 , E 2 , E 3 , E 4 and E 5 are matrices of suitable dimensions.

[0044] The wave excitation force includes regular wave excitation force and irregular wave excitation force. The regular wave excitation force is:

[0045]

[0046] Where R represents the real part; H is the wave height; F exc (ω) is the frequency-dependent complex amplitude of the wave excitation;

[0047] The irregular wave excitation force can be obtained by superposition of regular wave excitation within a certain frequency range, which is:

[0048]

[0049] Among them, A j is the frequency ω j The wave amplitude, φ j is the random initial phase, N is the frequency bandwidth;

[0050] The radiation force is:

[0051]

[0052] Among them, μ ij is the additional mass of infinite frequency, K rij is the radiation impulse response function;

[0053] The convolution part of the radiation force is expressed in the form of state-space equations:

[0054]

[0055] Where q is the state vector of the system;

[0056] The hydrostatic restoring force is:

[0057] F b =-ρgSx =-K H ·x

[0058] Where ρ is the seawater density, g is the neutral acceleration, S is the seawater contact area of ​​the structure, and KH is the hydrostatic stiffness coefficient;

[0059] The PTO is a linear mass-spring-damper energy conversion system, and the PTO force is:

[0060]

[0061] Among them, m PTO is the PTO force equivalent mass; c pto is the PTO system damping; k PTO is the stiffness of the PTO system.

[0062] The convolution state space of the radiation force can be expressed as:

[0063]

[0064] Among them, F c rad1 and F c rad2 are the radiation forces acting on the float and the floating body, namely:

[0065]

[0066] Then the equation of motion of the system is obtained as:

[0067]

[0068] in,

[0069]

[0070] The state vector is represented as:

[0071]

[0072] The continuous state space equation is:

[0073]

[0074] The continuous state space equation is discretized by using the zero-order hold method, and the discrete state space equation is obtained as follows:

[0075] p(k+1)=A d p(k)+B de F exc (k)+B du F u (k) = A d p(k)+B de F exc (k)-B du F d (k)

[0076] The sampling period is T s ;

[0077] in,

[0078] A d =e AT s

[0079]

[0080] The maximization objective function is:

[0081]

[0082] Among them, N P To optimize the time domain length, the Q matrix is:

[0083] Q=N T N

[0084] N=[0 0 1 -1 0 T ]

[0085] The hybrid system model predictive control can be established as:

[0086]

[0087] Among them, p∈R is the state vector, F d ∈R is the control input, F exc is the wave excitation vector, A d , B du and B de is the discrete system matrix in the discrete state space equation; B dδ and B dz are all zero matrices; E 1 , E 2 , E 3 , E 4 and E 5 are matrices of suitable dimensions.

[0088] The wave energy device comprises a ball screw, a screw nut, a gear box, a generator, a battery pack, a float, a continuously adjustable damper, a buoy, a damping plate, an energy conversion system and a floating body that are arranged in coordination with each other;

[0089] The energy conversion system includes a ball screw, a screw nut, a gear box, a generator and a battery pack. The continuously adjustable variable damper is installed on the float and the floating body in parallel with the energy conversion system. The relative movement between the float and the floating body drives the screw nut to move up and down, driving the rotation of the ball screw to amplify the speed through the gear box and drive the generator to generate electricity and store the electrical energy in the battery pack.

[0090] The present invention adopts the above method, analyzes the damping force and current of the continuously adjustable variable damper, clarifies the constraint boundary of the damping force, and establishes the correlation function of the relative speed, current and damping force; converts the nonlinear constraint of the continuously adjustable variable damper into a combination of threshold conditions and logical conditions by introducing binary variables, and converts the combination of threshold conditions and logical conditions into linear constraints involving logical variables; constructs the force dynamic equation of the hybrid logic power system as a discrete state space model of the wave energy device by performing force analysis on the adjustable variable damping wave energy device; establishes the objective function of maximizing the energy capture efficiency of the wave energy device, brings the state vector into the state space model and the maximization objective function, and propagates it in the prediction time domain, and obtains the first value of the control force sequence as the optimal control force at the current moment; by improving the simple linear model predictive control method, the logical state conversion of the system is also taken into account, and the execution capability of the hybrid model predictive controller is enhanced, which can handle more complex wave energy devices and has the advantages of accuracy, efficiency, practicality and reliability. Description of the drawings:

[0091] Figure 1 It is a schematic structural diagram of the wave energy device of the present invention.

[0092] Figure 2 The figure is a damping force-current relationship diagram of the continuously adjustable variable damper of the present invention.

[0093] Figure 3 It is a chart of average output power in different predicted time domains under irregular waves of the present invention.

[0094] In the figure, 1. ball screw; 2. screw nut; 3. gear box; 4. generator; 5. battery pack; 6. float; 7. continuously adjustable damper; 8. buoy; 9. damping plate; 10. energy conversion system; 11. float. Specific implementation method:

[0095] In order to clearly illustrate the technical features of the present solution, the present invention is described in detail below through specific implementation methods and in conjunction with the accompanying drawings.

[0096] like Figure 1-3 As shown in , a model predictive control method applicable to a continuously adjustable variable damping wave energy device comprises the following steps:

[0097] S1, analyze the damping force and current of the continuously variable damper, clarify the constraint boundary of the damping force, and establish the correlation function of relative speed, current and damping force;

[0098] S2, introduce binary variables to convert the nonlinear constraints of the continuously adjustable variable damper into a combination of threshold conditions and logical conditions, and convert the combination of threshold conditions and logical conditions into linear constraints involving logical variables, and introduce auxiliary continuous variables to convert the linear constraints of logical variables into integer linear inequalities;

[0099] S3, perform force analysis on the adjustable variable damping wave energy device and construct the force dynamic equation of the hybrid logic power system as the discrete state space model of the wave energy device;

[0100] S4, setting the displacement parameter, velocity parameter and external wave excitation parameter of the wave energy device as known conditions, wherein the external wave excitation parameter is obtained by prediction, and the state vector of the wave energy device is formed by the displacement parameter and the velocity parameter, and a continuous state space equation is obtained by combining the motion equation of the system;

[0101] S5, establish the objective function of maximizing the energy capture efficiency of the wave energy device, bring the state vector into the state space model and the maximization objective function, and propagate it in the prediction time domain to obtain the first value of the control force sequence as the optimal control force at the current moment;

[0102] S6, at the next moment, the state vector of the wave energy device and the external wave excitation parameters are updated, and the above step S5 is re-executed to construct the input hybrid system model and complete the overall model prediction control process.

[0103] The constraint boundary and correlation function of the damping force are expressed as:

[0104]

[0105] Where u represents the control force, α and β are the constraint boundary coefficients, v represents the relative motion speed of the float and the floating body of the wave energy device, i is the driving current of the continuously adjustable damper, and F d represents the control force, and f is the correlation function of relative speed, current and damping force.

[0106] The combination of the threshold condition and the logic condition is:

[0107]

[0108] Among them, the conjunction It means "if and only if";

[0109] The logical variable δ v The linear constraints are:

[0110]

[0111] Among them, v l and v uis the lower and upper limits of the relative motion speed v of the float and the floating body of the wave energy device; ε>0 is the tolerance, usually the computer precision;

[0112] Furthermore, the linear constraint of the damping force can be expressed as:

[0113]

[0114] Among them, z 1 、z 2 and z 3 All belong to the real number set, are auxiliary continuous variables, and have constraints:

[0115] z 1 , z 2 , z 3 >0

[0116] The general "if-then-else" can be expressed as:

[0117] IFδTHEN z=a 1 x+b 1 u+f 1

[0118] ELSE z=a 2 x+b 2 u+f 2

[0119] Among them, δ∈{0,1},z∈R,u∈R,a 1 , a 2 , b 1 , b 2 , f 1 and f 2 is a constant with appropriate dimension;

[0120] The integer linear inequality is:

[0121] (f 2 -F 1 )δ+z≤a 2 x+b 2 u+c 2

[0122] (f 1 -F 2 )δ-z≤-a 2 xb 2 uc 2

[0123] (f 1 -F 2 )(1-δ)+z≤a 1 x+b 1 u+c1

[0124] (f 2 -F 1 )(1-δ)-z≤-a 1 xb 1 uc 1

[0125] Among them, f i and F i They are respectively i x+b i u+c i , the lower and upper bounds of i∈{1,2}.

[0126] The dynamic force equation is:

[0127]

[0128] Where, “1” and “2” represent the float and the floating body respectively; m is the mass; x is the displacement relative to the equilibrium position; F exc Represents the wave excitation force; F radij is the radiation force exerted on structure i due to the motion of structure j; F b F is the hydrostatic restoring force; pto is the PTO force; F u For control;

[0129] The discrete state space model is:

[0130] p(k+1)=A d p(k)-B du F d (k)+B dδ δ v (k)+B dz z(k)+B de F exc

[0131] E 2 δ v (k)+E 3 z(k)≤E 1 F d (k)+E 4 p(k)+E 5

[0132] Among them, p∈R is the state vector, F d ∈R is the control input, A d , B du and B de is the discrete system matrix in the discrete state space equation; B dδ and B dz are all zero matrices; E1 , E 2 , E 3 , E 4 and E 5 are matrices of suitable dimensions.

[0133] The wave excitation force includes regular wave excitation force and irregular wave excitation force. The regular wave excitation force is:

[0134]

[0135] Where R represents the real part; H is the wave height; F exc (ω) is the frequency-dependent complex amplitude of the wave excitation;

[0136] The irregular wave excitation force can be obtained by superposition of regular wave excitation within a certain frequency range, which is:

[0137]

[0138] Among them, A j is the frequency ω j The wave amplitude, φ j is the random initial phase, N is the frequency bandwidth;

[0139] The radiation force is:

[0140]

[0141] Among them, μ ij is the additional mass of infinite frequency, K rij is the radiation impulse response function;

[0142] The convolution part of the radiation force is expressed in the form of state-space equations:

[0143]

[0144] Where q is the state vector of the system;

[0145] The hydrostatic restoring force is:

[0146] F b =-ρgSx =-K H ·x

[0147] Where ρ is the seawater density, g is the neutral acceleration, S is the seawater contact area of ​​the structure, and K H is the hydrostatic stiffness coefficient;

[0148] The PTO is a linear mass-spring-damper energy conversion system, and the PTO force is:

[0149]

[0150] Among them, m PTO is the PTO force equivalent mass; c pto is the PTO system damping; k PTO is the stiffness of the PTO system.

[0151] The convolution state space of the radiation force can be expressed as:

[0152]

[0153] Among them, F c rad1 and F c rad2 are the radiation forces acting on the float and the floating body, namely:

[0154]

[0155] Then the equation of motion of the system is obtained as:

[0156]

[0157] in,

[0158]

[0159] The state vector is represented as:

[0160]

[0161] The continuous state space equation is:

[0162]

[0163] The continuous state space equation is discretized by using the zero-order hold method, and the discrete state space equation is obtained as follows:

[0164] p(k+1)=A d p(k)+B de F exc (k)+B du F u (k) = A d p(k)+B de F exc (k)-B du F d (k)

[0165] The sampling period is T s ;

[0166] in,

[0167] Ad =e AT s

[0168]

[0169] The maximization objective function is:

[0170]

[0171] Among them, N P To optimize the time domain length, the Q matrix is:

[0172] Q=N T N

[0173] N=[0 0 1 -1 0 T ]

[0174] The hybrid system model predictive control can be established as:

[0175]

[0176] Among them, p∈R is the state vector, F d ∈R is the control input, F exc is the wave excitation vector, A d , B du and B de is the discrete system matrix in the discrete state space equation; B dδ and B dz are all zero matrices; E 1 , E 2 , E 3 , E 4 and E 5 are matrices of suitable dimensions.

[0177] The wave energy device comprises a ball screw, a screw nut, a gear box, a generator, a battery pack, a float, a continuously adjustable damper, a buoy, a damping plate, an energy conversion system and a floating body that are arranged in coordination with each other;

[0178] The energy conversion system includes a ball screw, a screw nut, a gear box, a generator and a battery pack. The continuously adjustable variable damper is installed on the float and the floating body in parallel with the energy conversion system. The relative movement between the float and the floating body drives the screw nut to move up and down, driving the rotation of the ball screw to amplify the speed through the gear box and drive the generator to generate electricity and store the electrical energy in the battery pack.

[0179] The working principle of the model predictive control method applicable to the continuously adjustable variable damping wave energy device in the embodiment of the present invention is: based on a variety of operation models and algorithm formulas, it can ensure the safe operation of the wave energy device in a harsh marine environment under the premise of ensuring the constraints of the adjustable variable damper, and at the same time constrain the system under extreme wave conditions, thereby improving the energy conversion efficiency of the wave energy device, enhancing the execution capability of the hybrid model predictive controller, and reducing the failure probability of the wave energy device, thereby improving the feasibility of the hybrid model predictive control in the actual operation process of the wave energy device, and can timely adjust the state of the continuously adjustable variable damper in a dynamically changing wave environment, so that the device can achieve the optimal energy capture effect.

[0180] Furthermore, the present application can construct a hybrid system model containing logical variables and continuous variables by analyzing the characteristics of the wave energy device, and realize variable damping regulation to maximize the energy capture efficiency of the wave energy device while considering the maximum limiting force constraint of the continuously adjustable variable damper; at the same time, a prediction model and energy maximization objective function of the hybrid system wave energy device are constructed, and dynamic response to complex wave environments is achieved through the regulation of the continuously adjustable variable damper.

[0181] In the overall scheme, the predictive control method includes the following steps: analyzing the damping force and current of the continuously adjustable variable damper, clarifying the constraint boundary of the damping force, and establishing the correlation function of the relative speed, current and damping force; introducing binary variables to convert the nonlinear constraints of the continuously adjustable variable damper into a combination of threshold conditions and logical conditions, and converting the combination of threshold conditions and logical conditions into linear constraints involving logical variables, and introducing auxiliary continuous variables to convert the linear constraints of logical variables into integer linear inequalities; performing force analysis on the adjustable variable damping wave energy device, constructing the force dynamic equation of the hybrid logical power system as a discrete state space model of the wave energy device; and converting the wave energy device into a discrete state space model of the wave energy device. The displacement parameters, velocity parameters and external wave excitation parameters are set as known conditions, the external wave excitation parameters are obtained by prediction, and the state vector of the wave energy device is composed of the displacement parameters and the velocity parameters. Combined with the motion equation of the system, a continuous state space equation is obtained; an objective function for maximizing the energy capture efficiency of the wave energy device is established, the state vector is brought into the state space model and the maximization objective function, and propagated in the prediction time domain, and the first value of the control force sequence is obtained as the optimal control force at the current moment; at the next moment, the state vector and the external wave excitation parameters of the wave energy device are updated, and the above step S5 is re-executed to construct the input hybrid system model to complete the overall model prediction control process.

[0182] Specifically, since the nonlinear damping force depends on the relative speed and current between the hydraulic cylinder and the piston rod, a bounded region can be formed by five straight lines. Therefore, the constraint boundary and correlation function of the damping force are respectively expressed as:

[0183]

[0184]

[0185] Where u represents the control force, α and β are the constraint boundary coefficients, v represents the relative motion speed of the float and the floating body of the wave energy device, i is the driving current of the continuously adjustable damper, and F d represents the control force, and f is the correlation function of relative speed, current and damping force.

[0186] Preferably, the combination of the threshold condition and the logic condition is:

[0187]

[0188] Among them, the conjunction It means "if and only if";

[0189] The logical variable δ v The linear constraints are:

[0190]

[0191] Among them, v l and v u is the lower and upper limits of the relative motion speed v of the float and the floating body of the wave energy device; ε>0 is the tolerance, usually the computer precision;

[0192] Furthermore, the linear constraint of the damping force can be expressed as:

[0193]

[0194] Among them, z 1 、z 2 and z 3 All belong to the set of real numbers, are auxiliary continuous variables, and have constraints:

[0195] z 1 , z 2 , z 3 >0

[0196] The general "if-then-else" can be expressed as:

[0197] IFδTHEN z=a 1 x+b 1 u+f 1

[0198] ELSE z=a 2 x+b 2 u+f 2

[0199] Among them, δ∈{0,1},z∈R,u∈R,a 1 , a 2 , b 1 , b 2 , f 1 and f 2 is a constant with appropriate dimension;

[0200] The integer linear inequality is:

[0201] (f 2 -F 1 )δ+z≤a 2 x+b 2 u+c 2

[0202] (f 1 -F 2 )δ-z≤-a 2 xb 2 uc 2

[0203] (f 1 -F 2 )(1-δ)+z≤a 1 x+b 1 u+c 1

[0204] (f 2 -F 1 )(1-δ)-z≤-a 1 xb 1 uc 1

[0205] Among them, f i and F i They are respectively i x+b i u+c i , the lower and upper bounds of i∈{1,2}, each “if-then-else” equation can be transformed into four linear inequality constraints, which is convenient for data calculation and aggregation.

[0206] The force analysis of the float of the wave energy device is carried out. The hydrodynamic effects considered include hydrostatic restoring force, radiation force, wave excitation force, PTO force and control force. Combined with Newton's second law, the dynamic force equation of the wave energy device can be obtained as follows:

[0207]

[0208] Where, “1” and “2” represent the float and the floating body respectively; m is the mass; x is the displacement relative to the equilibrium position; F exc Represents the wave excitation force; Fradij is the radiation force exerted on structure i due to the motion of structure j; F b F is the hydrostatic restoring force; pto is the PTO force; F u For control.

[0209] Specifically, the wave excitation force includes regular wave excitation force and irregular wave excitation force, and the regular wave excitation force is:

[0210]

[0211] Where R represents the real part; H is the wave height; F exc (ω) is the frequency-dependent complex amplitude of the wave excitation;

[0212] The irregular wave excitation force can be obtained by superposition of regular wave excitation within a certain frequency range, which is:

[0213]

[0214] Among them, A j is the frequency ω j The wave amplitude, φ j is the random initial phase, N is the frequency bandwidth;

[0215] The radiation force is:

[0216]

[0217] Among them, μ ij is the additional mass of infinite frequency, K rij is the radiation impulse response function;

[0218] The convolution part of the radiation force is expressed in the form of state-space equations:

[0219]

[0220] Where q is the state vector of the system;

[0221] The hydrostatic restoring force is:

[0222] F b =-ρgSx=-K H ·x

[0223] Where ρ is the seawater density, g is the neutral acceleration, S is the seawater contact area of ​​the structure, and K H is the hydrostatic stiffness coefficient;

[0224] The PTO is a linear mass-spring-damper energy conversion system, and the PTO force is:

[0225]

[0226] Among them, m PTO is the PTO force equivalent mass; c pto is the PTO system damping; k PTO is the stiffness of the PTO system.

[0227] According to the above calculation results, the discrete state space model is obtained as follows:

[0228] p(k+1)=A d p(k)-B du F d (k)+B dδ δ v (k)+B dz z(k)+B de F exc

[0229] E 2 δ v (k)+E 3 z(k)≤E 1 F d (k)+E 4 p(k)+E 5

[0230] Among them, p∈R is the state vector, F d ∈R is the control input, A d , B du and B de is the discrete system matrix in the discrete state space equation; B dδ and B dz are all zero matrices; E 1 , E 2 , E 3 , E 4 and E 5 are matrices of suitable dimensions.

[0231] In order to facilitate calculation and improve calculation accuracy, the radiation force is expressed in the form of convolution. The convolution state space of the radiation force can be expressed as:

[0232]

[0233] Among them, F c rad1 and F c rad2 are the radiation forces acting on the float and the floating body, namely:

[0234]

[0235] Then the equation of motion of the system is obtained as:

[0236]

[0237] in,

[0238]

[0239] The state vector is represented as:

[0240]

[0241] The continuous state space equation is:

[0242]

[0243] The continuous state space equation is discretized by using the zero-order hold method, and the discrete state space equation is obtained as follows:

[0244] p(k+1)=A d p(k)+B de F exc (k)+B du F u (k) = A d p(k)+B de F exc (k)-B du F d (k)

[0245] The sampling period is T s ;

[0246] in,

[0247] A d =e AT s

[0248]

[0249] Furthermore, the displacement parameters, velocity parameters and external wave excitation parameters of the wave energy device are set as known conditions, and the state vector of the wave energy device is constructed by combining the displacement parameters and velocity parameters. Through the equation of motion, the continuous state space equation is obtained. Then, the objective function of maximizing the energy capture efficiency of the wave energy device is established, and the state vector is brought into the state space model and the maximization objective function, and propagated in the prediction time domain, and the first value of the control force sequence is obtained as the optimal control force at the current moment.

[0250] For the maximization objective function, it is specifically:

[0251]

[0252] Among them, N P To optimize the time domain length, the Q matrix is:

[0253] Q=N T N

[0254] N=[0 0 1 -1 0 T ]

[0255] The hybrid system model predictive control can be established as:

[0256]

[0257] Among them, p∈R is the state vector, F d ∈R is the control input, F exc is the wave excitation vector, A d , B du and B de is the discrete system matrix in the discrete state space equation; B dδ and B dz are all zero matrices; E 1 , E 2 , E 3 , E 4 and E 5 are matrices of suitable dimensions.

[0258] When the next moment is reached, the system state of the wave energy device and the external wave excitation sequence are updated, the hybrid system model is input, and the above steps are executed again.

[0259] In actual use, the present invention takes into account the introduction of system logical variables, enhances the model predictive controller's ability to regulate the system, and can timely adjust the state of the continuously adjustable damper in a dynamically changing wave environment, so that the system can achieve the optimal energy capture effect.

[0260] Specifically, through the attached Figure 3 The data comparison in can verify the effectiveness of the present invention. It can be seen that under most wave conditions, the predictive control method of the present application can effectively improve the energy capture effect of the wave energy device.

[0261] It is particularly noted that the wave energy device of the present application includes a ball screw, a screw nut, a gear box, a generator, a battery pack, a float, a continuously adjustable variable damper, a buoy, a damping plate, an energy conversion system and a floating body that are arranged in coordination with each other; the energy conversion system includes a ball screw, a screw nut, a gear box, a generator and a battery pack, and the continuously adjustable variable damper is installed in parallel with the energy conversion system on the float and the floating body, and the screw nut is pushed up and down through the relative movement between the float and the floating body, driving the rotation of the ball screw to amplify the speed through the gear box and drive the generator to generate electricity and store the electrical energy in the battery pack.

[0262] To sum up, the model predictive control method suitable for the continuously adjustable variable damping wave energy device in the embodiment of the present invention is based on a variety of operation models and algorithm formulas. It can ensure the safe operation of the wave energy device in a harsh marine environment under the premise of ensuring the constraints of the adjustable variable damper. At the same time, it can constrain the system under extreme wave conditions, improve the energy conversion efficiency of the wave energy device, enhance the execution capability of the hybrid model predictive controller, and reduce the failure probability of the wave energy device, thereby improving the feasibility of the hybrid model predictive control in the actual operation process of the wave energy device, and can timely adjust the state of the continuously adjustable variable damper in a dynamically changing wave environment, so that the device can achieve the optimal energy capture effect.

[0263] The above specific implementation manner cannot be used as a limitation on the protection scope of the present invention. For those skilled in the art, any substitution, improvement or change made to the implementation manner of the present invention falls within the protection scope of the present invention.

[0264] The matters not described in detail in the present invention are all known technologies to those skilled in the art.

Claims

1. A model predictive control method for a continuously adjustable variable damping wave energy device, characterized in that: The predictive control method The following steps are involved: S1, analyze the damping force and current of the continuously variable damper, clarify the constraint boundary of the damping force, and establish the correlation function of relative speed, current and damping force; S2, introduce binary variables to convert the nonlinear constraints of the continuously adjustable variable damper into a combination of threshold conditions and logical conditions, and convert the combination of threshold conditions and logical conditions into linear constraints involving logical variables, and introduce auxiliary continuous variables to convert the linear constraints of logical variables into integer linear inequalities; S3, perform force analysis on the adjustable variable damping wave energy device and construct the force dynamic equation of the hybrid logic power system as the discrete state space model of the wave energy device; S4, setting the displacement parameter, velocity parameter and external wave excitation parameter of the wave energy device as known conditions, wherein the external wave excitation parameter is obtained by prediction, and forming a state vector of the wave energy device by the displacement parameter and the velocity parameter, and combining the motion equation of the system to obtain a continuous state space equation; S5, establish the objective function of maximizing the energy capture efficiency of the wave energy device, bring the state vector into the state space model and the maximization objective function, and propagate it in the prediction time domain to obtain the first value of the control force sequence as the optimal control force at the current moment; S6, at the next moment, the state vector of the wave energy device and the external wave excitation parameters are updated, and the above step S5 is re-executed to construct the input hybrid system model and complete the overall model predictive control process.

2. The model predictive control method for a continuously adjustable variable damping wave energy device according to claim 1, characterized in that: The constraint boundary and correlation function of the damping force are expressed as: Where u represents the control force, α and β are the constraint boundary coefficients, v represents the relative motion speed of the float and the floating body of the wave energy device, i is the driving current of the continuously adjustable damper, and F d represents the control force, and f is the correlation function of relative speed, current and damping force.

3. The model predictive control method for a continuously adjustable variable damping wave energy device according to claim 1, characterized in that: The combination of the threshold condition and the logic condition is: Among them, the conjunction It means "if and only if"; The logical variable δ v The linear constraints are: Among them, v l and v u is the lower and upper limits of the relative motion speed v of the float and the floating body of the wave energy device; ε>0 is the tolerance, usually the computer precision; Furthermore, the linear constraint of the damping force can be expressed as: Among them, z1, z2 and z3 all belong to the real number set, are auxiliary continuous variables, and have constraints: z1,z2,z3>0 The general "if-then-else" can be expressed as: IFδTHEN z=a1x+b1u+f1 ELSE z=a2x+b2u+f2 Where δ∈{0,1}, z∈R, u∈R, a1, a2, b1, b2, f1 and f2 are constants with appropriate dimensions; The integer linear inequality is: (f2-F1)δ+z≤a2x+b2u+c2 (f1-F2)δ-z≤-a2x-b2u-c2 (f1-F2)(1-δ)+z≤a1x+b1u+c1 (f2-F1)(1-δ)-z≤-a1x-b1u-c1 Among them, f i and F i They are respectively i x+b i u+c i , the lower and upper bounds of i∈{1,2}.

4. The model predictive control method for a continuously adjustable variable damping wave energy device according to claim 1, characterized in that: The dynamic force equation is: Where "1" and "2" represent the float and the floating body respectively; m is the mass; x is the displacement relative to the equilibrium position; F exc Represents the wave excitation force; F radij is the radiation force exerted on structure i due to the motion of structure j; F b F is the hydrostatic restoring force; pto is the PTO force; F u For control; The discrete state space model is: p(k+1)=A d p(k)-B du F d (k)+B dδ δ v (k)+B dz z(k)+B de F exc E2δ v (k)+E3z(k)≤E1F d (k)+E4p(k)+E5 Among them, p∈R is the state vector, F d ∈R is the control input, A d , B du and B de is the discrete system matrix in the discrete state space equation; B dδ and B dz are all zero matrices; E1, E2, E3, E4 and E5 are all matrices of appropriate dimensions.

5. The model predictive control method for a continuously adjustable variable damping wave energy device according to claim 4, characterized in that: The wave excitation force includes regular wave excitation force and irregular wave excitation force. The regular wave excitation force is: Where R represents the real part; H is the wave height; F exc (ω) is the frequency-dependent complex amplitude of the wave excitation; The irregular wave excitation force can be obtained by superposition of regular wave excitation within a certain frequency range, which is: Among them, A j is the frequency ω j The wave amplitude, φ j is the random initial phase, N is the frequency bandwidth; The radiation force is: Among them, μ ij is the additional mass of infinite frequency, K rij is the radiation impulse response function; The convolution part of the radiation force is expressed in the form of state-space equations: Where q is the state vector of the system; The hydrostatic restoring force is: F b =-ρgSx=-K H ·x Where ρ is the seawater density, g is the neutral acceleration, S is the seawater contact area of ​​the structure, and K H is the hydrostatic stiffness coefficient; The PTO is a linear mass-spring-damper energy conversion system, and the PTO force is: Among them, m PTO is the PTO force equivalent mass; c pto is the PTO system damping; k PTO is the stiffness of the PTO system.

6. The model predictive control method for a continuously adjustable variable damping wave energy device according to claim 5, characterized in that: The convolution state space of the radiation force can be expressed as: Among them, F c rad1 and F c rad2 are the radiation forces acting on the float and the floating body, namely: Then the equation of motion of the system is obtained as: in, The state vector is represented as: The continuous state space equation is: The continuous state space equation is discretized by using the zero-order hold method, and the discrete state space equation is obtained as follows: p(k+1)=A d p(k)+B de F exc (k)+B du F u (k)=A d p(k)+B de F exc (k)-B du F d (k) The sampling period is T s ; in, 7. The model predictive control method for a continuously adjustable variable damping wave energy device according to claim 1, characterized in that: The maximization objective function is: Among them, N P To optimize the time domain length, the Q matrix is: Q=N T N N＝[0 0 1 -1 0 T ] The hybrid system model predictive control can be established as: Among them, p∈R is the state vector, F d ∈R is the control input, F exc is the wave excitation vector, A d , B du and B de is the discrete system matrix in the discrete state space equation; B dδ and B dz are all zero matrices; E1, E2, E3, E4 and E5 are all matrices of appropriate dimensions.

8. The model predictive control method for a continuously adjustable variable damping wave energy device according to claim 1, characterized in that: The wave energy device comprises a ball screw, a screw nut, a gear box, a generator, a battery pack, a float, a continuously adjustable damper, a buoy, a damping plate, an energy conversion system and a floating body that are arranged in coordination with each other; The energy conversion system includes a ball screw, a screw nut, a gear box, a generator and a battery pack. The continuously adjustable variable damper is installed on the float and the floating body in parallel with the energy conversion system. The relative movement between the float and the floating body drives the screw nut to move up and down, driving the rotation of the ball screw to amplify the speed through the gear box and drive the generator to generate electricity and store the electrical energy in the battery pack.

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