Model prediction control method for floating type wind and wave combined power generation system

Abstract

The invention relates to the technical field of ocean renewable energy power generation, and particularly discloses a floating type wind wave combined power generation system model prediction control method, which comprises the following steps: establishing a nonlinear mathematical model of a floating type wind wave combined power generation system; determining a steady-state working condition point of the system; carrying out linear processing on the nonlinear model; constructing a discrete time prediction model; designing a target function; defining a state and an input constraint condition; performing real-time rolling optimization solution; and dynamically feeding back a correction mechanism. Starting from a wind wave excitation mechanism, on one hand, response in a turbulent wind frequency band is reduced through fan variable pitch control, and on the other hand, response in a wave frequency band is reduced through wave energy power generation device PTO control, so that tower footing load is effectively reduced, and pitching motion of a platform is restrained. Global multi-objective optimization is realized by designing an objective function, defining constraint conditions and solving the objective function.

Description

Technical Field

[0001] The present invention relates to the technical field of marine renewable energy power generation, and uses a model predictive control strategy to optimize a combined power generation system. Specifically, it relates to a model predictive control method for a floating wind-wave combined power generation system. Background Art

[0002] A floating wind-wave combined power generation system in the complex deep-sea marine environment faces structural loads and dynamic response fluctuations brought by turbulent winds, ocean waves, and ocean currents, which pose great challenges to the control system. Although the concept of a floating wind-wave combined energy harvesting system has been proposed for many years, current research on its control technology still mainly focuses on the individual control of each part, such as the pitch control of floating wind turbines and the PTO (Power Take-Off) control of wave energy power generation devices.

[0003] Common control methods for floating wind turbines mainly include blade pitch control, variable speed control, yaw control, and structural control. Among them, blade pitch control includes two major categories: unified pitch control and independent pitch control. Unified pitch control often includes PI controllers and optimal controllers. PI controllers include feedback control and tuning gain, while optimal controllers mainly include LQR, H2, H∞, and MPC (Model Predictive Control). Wind turbine structural control is mainly divided into three categories: passive control devices, semi-active control devices, and active control devices. PTO control strategies mainly include passive control and reactive power control. Passive control realizes power control of the wave energy power generation device by changing the force related to the PTO system, usually including linear damping control, locking control, and clutch control. Reactive power control often sacrifices part of the power output to achieve the stability of the power output of the wave energy power generation device.

[0004] Currently, the research on the combined control technology for floating wind-wave combined power generation systems is relatively scarce.

[0005] 1) For example, Chinese Patent Application No. 202410080364.9 discloses an omnidirectional excitation pendulum-type wind-wave combined power generation platform energy harvesting and anti-rolling method, which absorbs the kinetic energy of the platform's pitching and rolling motions through the energy harvesting pendulum ball and damping mechanism, playing a dual role of energy harvesting and anti-rolling, and can improve the overall power generation and power generation stability.

[0006] 2) For example, Chinese Patent Application No. 202410615877.5 discloses a wind-wave combined power generation platform device and control method based on TMD vibration reduction. By using the wave energy power generation device as the mass component of the entire platform's TMD vibration reduction, vibration control of the platform under normal power generation conditions can be achieved without introducing external mass, thereby realizing vibration control of the overall structure.

[0007] However, the above technologies are mainly based on passive control technologies, and it is difficult to respond in a timely manner to changes in the wind and wave environment; the output power stability of the wave energy generation device is not considered; the influence of the turbulent wind frequency band on the structural response of the combined power generation system is not considered. Summary of the Invention

[0008] The object of the present invention is to overcome the deficiencies of the above-mentioned existing technologies, and provide a model predictive control method for a floating wind and wave combined power generation system. In the operating condition above the rated wind speed, this method can simultaneously reduce the structural response of the floating wind and wave combined power generation system in the turbulent wind frequency band and the wave frequency band, thereby effectively reducing the fluctuation of the tower base load, suppressing the fluctuation of the platform pitching motion, and at the same time improving the power output stability of the combined power generation system.

[0009] To achieve the above object, the present invention adopts the following technical solutions: A model predictive control method for a floating wind and wave combined power generation system, comprising: 1) Establish a nonlinear mathematical model of the floating wind and wave combined power generation system; According to the model parameters of the floating wind and wave combined power generation system, the blade element momentum theory and the potential flow theory, establish its nonlinear mathematical model; it can be expressed as: (1), where x is the state variable, u c is the control input variable, u d is the environmental disturbance quantity, and y is the output variable; 2) Determine the steady-state operating point of the system; Establish a high-fidelity physical model of the floating wind and wave combined power generation system through numerical simulation methods. Within its operating condition range, select different environmental conditions, and conduct numerical simulation based on the established high-fidelity physical model. Determine the steady-state operating point of the floating wind and wave combined power generation system based on statistical values; The operating condition range is determined by the wind speed and wave height. The present invention is directed to the operating condition above the rated wind speed, that is, from the rated wind speed to the cut-out wind speed and from the rated wave height to the cut-out wave height. For example, 11.4 m / s to 25 m / s and 1 m to 6 m.

[0010] The method for determining the steady-state operating point, for example, take the wind speed as 15 m / s and the wave height as 3 m, conduct numerical simulation under the steady-state wind and regular wave conditions based on the established high-fidelity physical model, with a simulation duration of 2000 s, and select the simulation results from 1500 - 2000 s to statistically calculate the mean values of the state variables, control input variables, and output variables, so as to obtain the steady-state operating point.

[0011] 3) Linearize the nonlinear model; According to the above non - linear mathematical model, design the state - space expression of the corresponding floating combined wind - wave power generation system; at the steady - state operating point, linearize the non - linear model by using the first - order Taylor series expansion or parameter identification method to obtain a linear time - varying state - space model. The state - space expression is: (2), where, δ represents a small increment, A represents the state matrix, B c represents the control - input matrix, B d represents the environmental - disturbance input matrix, C represents the output matrix, the state variable , the control input , the environmental input , the state - space output , T represents the transpose of the matrix, ω r represents the wind - turbine rotational speed, d t represents the front - and - back displacement of the tower top of the floating combined wind - wave power generation system, β p represents the blade pitch angle, T g represents the generator electromagnetic torque, B p represents the damping force of the PTO system of the wave - energy power generation device, ω a represents the angular velocity at the hinge point of the wave - energy power generation device; β pr represents the reference value of the control signal of the blade pitch angle, T gr represents the reference value of the control signal of the generator electromagnetic torque, B pr represents the reference value of the control signal of the damping of the PTO system of the wave - energy power generation device, ω ar represents the reference value of the control signal of the angular velocity at the hinge point of the wave - energy power generation device; v w represents the wind speed, H s represents the wave height; P HS represents the generated power output by the floating combined wind - wave power generation system.

[0012] The linear time - varying state - space model is: (3), (4), wherein, δ represents a small increment, ω r represents the rotational speed of the wind turbine, B dd is the damping coefficient of the wind turbine drive shaft, β p represents the blade pitch angle, v w represents the wind speed, H s represents the wave height, N g is the transmission ratio of the wind turbine gearbox, T g represents the electromagnetic torque of the generator, J r and J g are the moments of inertia of the blade and the generator respectively, d t represents the front - rear displacement of the top of the floating wind - wave combined power generation system, β pr represents the reference value of the control signal of the blade pitch angle, is the inertia time constant of the blade pitch angle, T gr represents the reference value of the control signal of the electromagnetic torque of the generator, is the inertia time constant of the electromagnetic torque of the wind turbine generator, B pr represents the reference value of the control signal of the damping of the PTO system of the wave energy power generation device, B p represents the damping force of the PTO system of the wave energy power generation device, is the inertia time constant of the PTO system of the wave energy power generation device; ω a represents the angular velocity at the hinge point of the wave energy power generation device, P HS represents the generated power output by the floating wind - wave combined power generation system, η WT is the efficiency of the wind turbine generator, η WEC is the power generation efficiency of the PTO system of the wave energy power generation device, N WECs is the number of wave energy power generation devices in the floating wind - wave combined power generation system, ω rr is the rated rotational speed of the wind turbine, ω ar represents the reference value of the control signal of the angular velocity at the hinge point of the wave energy power generation device, i The value range of N WECs, M is the pitching moment of the tower base front and back, and the parameter a t , K T 、K M and K B are obtained through model identification.

[0013] 4) Construct a discrete-time prediction model Based on the linear time-varying state space model, formula (3) is discretized to construct a prediction model in the discrete-time domain for predicting the dynamic responses of the state variables and control inputs of the system within a future time window; The prediction model in the discrete-time domain is: (5), where x(k) and x(k + 1) represent the state variables of the system at discrete time steps k and k + 1 respectively, u(k) represents the input variable of the system at discrete time step k, y(k) represents the observed output variable of the system at discrete time step k, G is the state transition matrix describing the natural evolution law of the system state without external input; H is the input matrix quantifying the direct influence of the control input and environmental disturbance on the state change; C is the output matrix whose role is to map the system state x to the system output y.

[0014] 5) Design the objective function When the floating wind and wave combined power generation system operates above the rated wind speed, taking into account the power output on the fan side, load suppression, and platform stability requirements, design the optimization objective function of the floating wind and wave combined power generation system: (6); where, δy(k+i) represents the output deviation vector at the future k+i th moment, δu(k+i-1) represents the control input change amount vector at the k+i-1 th moment, N represents the prediction time domain; the weight matrix Q is used to quantify the influence of the output deviation vector on the system performance, and the weight matrix R is used to limit the drastic fluctuations of the control input.

[0015] 6) Define the state and input constraint conditions To ensure that during the optimization solution process of the control algorithm, the control actions of the floating wind and wave combined power generation system always meet the requirements of the system's own performance, necessary constraint settings are made for the control input as follows: (7), where, u(k) represents the control input variable of the system at discrete time step k,δu(k) denotes the change in the control input of the system at discrete time step k, u max is the constraint on the control input amplitude, δu max is the constraint on the rate of change of the control input.

[0016] 7) Real-time rolling optimization and solution Within each control period, the CasADi solver is used to quickly solve the constrained optimization problem, obtain the optimal control sequence at a certain moment, and extract the first-step control quantity to output to the wind turbine pitch actuator and the PTO system of the wave energy power generation device. The above steps are repeated at the next moment to achieve the dynamic regulation of the system.

[0017] 8) Dynamic feedback correction mechanism The state of the floating wind and wave combined power generation system is collected in real time through the state monitoring system composed of multiple sensors and compared with the output value of the prediction model. Dynamically correct the parameters of the prediction model or adjust the weight coefficients of the objective function to compensate for the errors caused by environmental disturbances such as sudden changes in wind speed or surges and model mismatches, and improve the robustness and adaptability of the control system.

[0018] The beneficial effects of the present invention are: The model predictive control method for the floating wind and wave combined power generation system proposed by the present invention, in the operating condition above the rated wind speed, for the problems of load fluctuations and platform pitching motion in the complex marine environment, through the wind turbine pitch control and the PTO control of the wave energy power generation device based on the model predictive control method, can simultaneously reduce the structural responses of the wind and wave combined power generation system in the turbulent wind frequency band and the wave frequency band, thereby effectively reducing the load fluctuations at the tower base, suppressing the fluctuations of the platform pitching motion, and at the same time improving the stability of the power output of the combined power generation system.

[0019] The present invention designs an objective function considering the total power of the combined power generation system for the problems of load fluctuations and platform pitching motion in the complex marine environment, defines the constraint conditions considering the pitching moment of the tower base before and after and the platform pitching motion, and based on solving the objective function using the CasADi solver, online optimizes the control parameters of the wind turbine pitch control and the PTO control parameters of the wave energy power generation device, thereby realizing the global multi-objective optimization. This method can start from the mechanism of wind and wave excitation. On the one hand, it reduces the response in the turbulent wind frequency band (0 - 0.10 Hz) through the wind turbine pitch control, and on the other hand, it reduces the response in the wave frequency band (0.10 - 0.60 Hz) through the PTO control of the wave energy power generation device, thereby effectively reducing the load fluctuations at the tower base, suppressing the fluctuations of the platform pitching motion, and at the same time improving the stability of the power output of the combined power generation system. Description of the drawings

[0020] Figure 1Schematic diagram of the floating wind-wave combined power generation system provided by the present invention; Figure 2 Flowchart of the model predictive control method for the floating wind-wave combined power generation system provided by the present invention; Figure 3 Block diagram of the model predictive control method for the floating wind-wave combined power generation system provided by the present invention; Figure 4 Comparison diagram of the time history curves of wind speed, wave height, pitch angle, wind turbine side power, nacelle horizontal acceleration, and tower base fore-aft pitching moment between the model predictive control method for the floating wind-wave combined power generation system provided by the present invention and the baseline controller; Figure 5 Comparison diagram of the time history curves of the six-degree-of-freedom response of the platform between the model predictive control method for the floating wind-wave combined power generation system provided by the present invention and the baseline controller; Figure 6 Power spectral density diagram of wind speed and wave height of the model predictive control method for the floating wind-wave combined power generation system provided by the present invention; Figure 7 Comparison diagram of the power spectral density of the tower base fore-aft pitching moment between the model predictive control method for the floating wind-wave combined power generation system provided by the present invention and the baseline controller; Figure 8 Comparison diagram of the power spectral density of the platform pitching motion between the model predictive control method for the floating wind-wave combined power generation system provided by the present invention and the baseline controller; Figure 9 Comparison diagram of the statistical values of the power generation power between the model predictive control method for the floating wind-wave combined power generation system provided by the present invention and the baseline controller; Wherein, 1. Wind, 2. Wave, 3. Seabed, 4. Blade, 5. Hub, 6. Nacelle, 7. Tower barrel, 8. Hinge point where the wave energy power generation device is connected to the platform, 9. Rocker arm of the wave energy power generation device, 10. Float of the wave energy power generation device, 11. Floating platform, 12. Anchor chain. Detailed implementation manners

[0021] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0022] The structures, proportions, sizes, etc. shown in the attached drawings of this specification are only used to match the content disclosed in the specification for those familiar with this technology to understand and read, and are not used to limit the conditions for the implementation of the present invention. Therefore, they do not have substantial technical significance. Any modification of the structure, change in the proportional relationship, or adjustment of the size, without affecting the effects that the present invention can produce and the purposes that can be achieved, should still fall within the scope covered by the technical content disclosed in the present invention. At the same time, the terms such as "upper", "lower", "left", "right", "middle", and "one" cited in this specification are only for the convenience of clear narration and are not used to limit the scope for the implementation of the present invention. The change or adjustment of their relative relationships, without substantial change in the technical content, should also be regarded as the scope for the implementation of the present invention.

[0023] As Figure 1 shown, the environmental conditions include wind 1, waves 2, and seabed 3. The floating combined wind and wave power generation system includes three blades 4, a hub 5, a nacelle 6, a tower 7, three hinge points 8 connecting the wave energy power generation devices to the platform, three rocker arms 9 of the wave energy power generation devices, three floats 10 of the wave energy power generation devices, a floating platform 11, and three anchor chains 12. Among them, the hinge point, rocker arm, and float of the third wave energy power generation device connected to the platform are not shown in the picture.

[0024] As Figures 2 - 3 shown, the model predictive control method for the floating combined wind and wave power generation system includes: 1) Establish a non - linear mathematical model of the floating combined wind and wave power generation system; According to the model parameters of the floating combined wind and wave power generation system, the blade element momentum theory, and the potential flow theory, establish its non - linear mathematical model; it can be expressed as: (1), where x is the state variable, u c is the control input variable, u d is the environmental disturbance quantity, and y is the output variable; 2) Determine the steady - state operating point of the system; Establish a high - fidelity physical model of the floating combined wind and wave power generation system through numerical simulation methods. Within its operating condition range, select different environmental conditions, conduct numerical simulation based on the established high - fidelity physical model, and determine the steady - state operating point of the floating combined wind and wave power generation system based on statistical values; The operating condition range is determined by the wind speed and wave height. The present invention is directed to the operating conditions above the rated wind speed, that is, from the rated wind speed to the cut - out wind speed and from the rated wave height to the cut - out wave height. For example, from 11.4 m / s to 25 m / s and from 1 m to 6 m.

[0025] Method for determining the steady-state operating point. For example, take the wind speed as 15 m / s and the wave height as 3 m, and conduct numerical simulations under steady-state wind and regular wave conditions based on the established high-fidelity physical model. The simulation duration is 2000 s. Select the simulation results from 1500 - 2000 s to statistically calculate the means of the state variables, control input variables, and output variables, thereby obtaining the steady-state operating point.

[0026] Identify the key parameters at the equilibrium state (such as the wind turbine rotor speed, generator speed, pitch angle, and the angular velocity of the hinge point of the wave energy power generation device), provide a reference operating condition for the subsequent control strategy design, and ensure the applicability of the model under typical sea conditions.

[0027] 3) Linearize the non-linear model; According to the above non-linear mathematical model, design the state space expression of the corresponding floating wind and wave combined power generation system; at the steady-state operating point, linearize the non-linear model using the first-order Taylor series expansion or parameter identification method to obtain a linear time-varying state space model; The state space expression is: (2), where, δ represents a small increment, A represents the state matrix, B c represents the control input matrix, B d represents the environmental disturbance input matrix, C represents the output matrix, the state variable the control input the environmental input the state space output T represents the transpose of the matrix, ω r represents the wind turbine rotor speed, d t represents the front and back displacement of the top of the floating wind and wave combined power generation system, β p represents the blade pitch angle, T g represents the generator electromagnetic torque, B p represents the damping force of the PTO system of the wave energy power generation device, ω a represents the angular velocity at the hinge point of the wave energy power generation device; β pr represents the control signal reference value of the blade pitch angle, T gr represents the control signal reference value of the generator electromagnetic torque, B prThe reference value of the control signal representing the damping of the PTO system of the wave energy power generation device ω ar The reference value of the control signal representing the angular velocity at the hinge point of the wave energy power generation device; v w Represents the wind speed, H s Represents the wave height; P HS Represents the generated power output by the floating wind-wave combined power generation system.

[0028] The linear time-varying state space model is: (3), (4), where δ represents a small increment, ω r Represents the rotational speed of the wind turbine, B dd Is the damping coefficient of the wind turbine drive shaft, β p Represents the blade pitch angle, v w Represents the wind speed, H s Represents the wave height, N g Is the transmission ratio of the wind turbine gearbox, T g Represents the electromagnetic torque of the generator, J r And J g Are the moments of inertia of the blade and the generator respectively, d t Represents the front-back displacement of the top of the floating wind-wave combined power generation system, β pr Represents the reference value of the control signal of the blade pitch angle, Is the inertia time constant of the blade pitch angle, T gr Represents the reference value of the control signal of the generator electromagnetic torque, Is the inertia time constant of the wind turbine generator electromagnetic torque, B pr Represents the reference value of the control signal of the damping of the PTO system of the wave energy power generation device, B p Represents the damping force of the PTO system of the wave energy power generation device, Is the inertia time constant of the PTO system of the wave energy power generation device; ω a Represents the angular velocity at the hinge point of the wave energy power generation device, P HSrepresents the generated power output of the floating wind-wave combined power generation system, η WT is the efficiency of the wind turbine generator, η WEC is the power generation efficiency of the PTO system of the wave energy power generation device, N WECs is the number of wave energy power generation devices in the floating wind-wave combined power generation system, ω rr is the rated rotational speed of the wind turbine, ω ar represents the reference value of the control signal for the angular velocity at the hinge point of the wave energy power generation device, i The value range of is 1 to N WECs , M is the pitching moment of the tower base in the front and back directions, and the parameter a t , K T 、K M and K B are obtained through model identification.

[0029] 4) Construct a discrete-time prediction model Based on the linear time-varying state-space model, formula (3) is discretized to construct a prediction model in the discrete-time domain, which is used to predict the dynamic responses of the state variables and control inputs of the system within the future time window; The prediction model in the discrete-time domain is: (5), Among them, x(k) and x(k + 1) represent the state variables of the system at discrete time steps k and k + 1 respectively, u(k) represents the input variable of the system at discrete time step k, y(k) represents the observed output variable of the system at discrete time step k, G is the state transition matrix, which describes the natural evolution law of the system state without external input; H is the input matrix, which quantifies the direct influence of the control input and environmental disturbance on the state change; C is the output matrix, and its function is to map the system state x to the system output y.

[0030] 5) Design the objective function When the floating wind-wave combined power generation system operates above the rated wind speed, the wind turbine side needs to adjust the generator speed to keep the output power of the wind turbine side stable near the rated power. At the same time, in order to reduce the fatigue load of the wind turbine pitch actuator, the actions of the pitch angle and generator torque should not be too frequent; the wave energy power generation device side needs to adjust the angular velocity at the hinge point to be stable to keep the output power of the PTO system stable. At the same time, the damping force of the PTO system of the wave energy power generation device should not act too frequently. Considering the above factors, the optimization objective function of the floating wind-wave combined power generation system is designed as follows: (6); Among them, δy(k+i) represents the output deviation vector at the k+i -th future moment, δu(k+i-1) represents the control input change vector at the k+i-1 -th moment, N represents the prediction horizon; the weight matrix Q is used to quantify the influence of the output deviation vector on the system performance, and the weight matrix R is used to limit the violent fluctuations of the control input.

[0031] 6) Define the state and input constraint conditions To ensure that during the optimization solution process of the control algorithm, the control actions of the floating wind-wave combined power generation system always meet the requirements of the system's own performance, taking into account the total output power and stability requirements of the system, necessary constraint settings are made for the control input as follows: (7), Among them, u(k) represents the control input variable of the system at the discrete time step k, δu(k) represents the control input change of the system at the discrete time step k, u max is the control input amplitude constraint, δu max is the control input rate of change constraint.

[0032] 7) Real-time rolling optimization solution In each control period, the CasADi solver is used to quickly solve the constrained optimization problem, obtain the optimal control sequence at a certain moment, and extract the first-step control quantity to output to the wind turbine pitch actuator and the PTO system of the wave energy power generation device. Repeat the above steps at the next moment to achieve the dynamic adjustment of the system.

[0033] 8) Dynamic feedback correction mechanism The state of the floating wind-wave combined power generation system is real-time collected through the state monitoring system composed of multiple sensors, and compared with the output value of the prediction model. Dynamically correct the parameters of the prediction model or adjust the weight coefficients of the objective function to compensate for the errors caused by environmental disturbances such as sudden changes in wind speed or surges and model mismatches, and improve the robustness and adaptability of the control system.

[0034] As Figure 4 shown, under the conditions of turbulent wind (average wind speed 15 m / s) and irregular waves (significant wave height 3 m, spectral peak period 6 s), compared with the use of the baseline controller, the fluctuations of the wind turbine side power, nacelle horizontal acceleration, and tower base pitch moment of the floating wind-wave combined power generation system using the control method of the present invention are smaller.

[0035] As Figure 5 shown, under the same working conditions, compared with the baseline controller, the fluctuations of the surge motion and heave motion of the platform of the floating wind-wave combined power generation system using the control method of the present invention slightly increase, while the fluctuations of the pitch motion of the platform significantly decrease, and the changes in the sway motion, roll motion and yaw motion of the platform are not obvious. The pitch motion of the platform is the most important parameter affecting the power generation performance on the wind turbine side and the platform stability of the floating wind-wave combined power generation system. Therefore, the control method of the present invention can effectively improve the platform stability.

[0036] As Figure 6 shown, the power spectral densities of the environmental wind speed and wave height present different distribution laws. Among them, the energy of the turbulent wind is mainly concentrated in the higher frequency band, between 0 and 0.10 Hz, while the energy of the wave is mainly concentrated in the higher frequency band, between 0.10 and 0.60 Hz. This indicates that the environmental excitation received by the floating wind-wave combined power generation system has obvious broadband characteristics.

[0037] As Figure 7 shown, compared with the baseline controller, using the control method of the present invention can effectively reduce the response of the pitching moment before and after the tower base of the floating wind-wave combined power generation system in the turbulent wind frequency band (0 - 0.10 Hz), and can also significantly reduce the response of the pitching moment of the tower base in the wave frequency band (0.10 - 0.60 Hz). This shows that the method of the present invention has great potential in reducing the structural fatigue load of the floating wind-wave combined power generation system.

[0038] As Figure 8 shown, compared with the baseline controller, using the control method of the present invention can significantly reduce the response of the pitch motion of the platform of the floating wind-wave combined power generation system in the turbulent wind frequency band (0 - 0.10 Hz), and can also slightly reduce the response of the pitch motion of the platform in the wave frequency band (0.10 - 0.60 Hz). This shows that the method of the present invention has certain potential in improving the platform stability of the floating wind-wave combined power generation system.

[0039] As Figure 9 shown, compared with the baseline controller, using the control method of the present invention can effectively reduce the fluctuation of the power generation power on the wind turbine side of the floating wind-wave combined power generation system, and does not affect the average value of the power generation power on the wind turbine side. In addition, the wave energy power generation device side of the floating wind-wave combined power generation system can also output about 300 kW of power generation power, accounting for about 6% of the power generation power on the wind turbine side. This shows that the method of the present invention is beneficial to improving the stability of the power generation power output of the floating wind-wave combined power generation system.

[0040] Although the specific embodiments of the present invention have been described above in conjunction with the accompanying drawings, it is not a limitation on the protection scope of the present invention. Those skilled in the art should understand that various modifications or deformations that can be made without creative efforts on the basis of the technical solution of the present invention are still within the protection scope of the present invention.

Claims

1. A model predictive control method for a floating combined wind and wave power generation system, characterized in that, Including: (1) Establish a nonlinear mathematical model of the floating wind-wave combined power generation system; expressed as: （1）， where x is the state variable, u c is the control input variable, u d is the environmental disturbance quantity, and y is the output variable; (2) Determine the steady-state operating point of the system; (3) Linearize the nonlinear model; according to the nonlinear mathematical model in step (1), design the state-space expression of the corresponding floating wind-wave combined power generation system; at the steady-state operating point, linearize the nonlinear model by using the first-order Taylor series expansion or parameter identification method to obtain a linear time-varying state-space model; (4) Construct a discrete-time prediction model; Based on the linear time-varying state-space model, discretize the state-space expression to construct a prediction model in the discrete-time domain for predicting the dynamic responses of the state variables and control inputs of the system within a future time window; (5) Design the objective function; When the floating wind-wave combined power generation system operates above the rated wind speed, taking into account the requirements of power output on the fan side, load suppression, and platform stability, design the optimization objective function of the floating wind-wave combined power generation system; (6) Define the state and input constraint conditions; To ensure that during the optimization solution process of the control algorithm, the control actions of the floating wind-wave combined power generation system always meet the requirements of the system's own performance, necessary constraint settings are made for the control inputs; (7) Real-time rolling optimization solution; In each control period, use the CasADi solver to quickly solve the constrained optimization problem to obtain the optimal control sequence at a certain moment, and extract the first-step control quantity to output to the fan pitch actuator and the PTO system of the wave energy power generation device. Repeat the above steps at the next moment to achieve the dynamic regulation of the system; (8) Dynamic feedback correction mechanism; Real-time collect the system state through the state monitoring system of the floating wind-wave combined power generation system and compare it with the output value of the prediction model; dynamically correct the parameters of the prediction model or adjust the weight coefficients of the objective function to compensate for the errors caused by sudden changes in wind speed or surge environmental disturbances and model mismatches, and improve the robustness and adaptability of the control system.

2. The model predictive control method for the floating combined wind and wave power generation system according to claim 1, characterized in that, In step (2) above, a high-fidelity physical model of the floating wind-wave combined power generation system is established by numerical simulation method. Within its operating condition range, different environmental conditions are selected, and numerical simulation is carried out based on the established high-fidelity physical model. The steady-state operating point of the floating wind-wave combined power generation system is determined based on statistical values; The method for determining the steady-state operating point is to carry out numerical simulation under steady-state wind and regular wave conditions based on the established high-fidelity physical model. The simulation results are the means of statistical state variables, control input variables, and output variables, so as to obtain the steady-state operating point.

3. The model predictive control method for the floating combined wind and wave power generation system according to claim 1, characterized in that, In step (3) above, the state-space expression is: （2）， where, δ represents a small increment, A represents the state matrix, B c represents the control input matrix, B d represents the environmental disturbance input matrix, C represents the output matrix, and the state variables , the control input , the environmental input , the state space output , where, T represents the transpose of the matrix, ω r represents the wind turbine rotational speed, d t represents the front - rear displacement of the top of the floating wind - wave combined power generation system, β p represents the blade pitch angle, T g represents the generator electromagnetic torque, B p represents the damping force of the PTO system of the wave energy power generation device, ω a represents the angular velocity at the hinge point of the wave energy power generation device; β pr represents the reference value of the control signal of the blade pitch angle, T gr represents the reference value of the control signal of the generator electromagnetic torque, B pr represents the reference value of the control signal of the damping of the PTO system of the wave energy power generation device, ω ar represents the reference value of the control signal of the angular velocity at the hinge point of the wave energy power generation device; v w represents the wind speed, H s represents the wave height; P HS represents the generated power output by the floating wind - wave combined power generation system.

4. The model predictive control method for the floating wind and wave combined power generation system according to claim 1, characterized in that, In step (3) above, the linear time-varying state-space model is: （3）， （4）， Among them, δ represents a small increment, ω r represents the wind turbine rotor speed, B dd is the damping coefficient of the wind turbine drive shaft, β p represents the blade pitch angle, v w represents the wind speed, H s represents the wave height, N g is the transmission ratio of the wind turbine gearbox, T g represents the electromagnetic torque of the generator, J r and J g are the moments of inertia of the blade and the generator respectively, d t represents the front - rear displacement of the top of the floating wind - wave combined power generation system, β pr represents the reference value of the control signal for the blade pitch angle, is the inertia time constant of the blade pitch angle, T gr represents the reference value of the control signal for the electromagnetic torque of the generator, is the inertia time constant of the electromagnetic torque of the wind turbine generator, B pr represents the reference value of the control signal for the damping of the PTO system of the wave energy power generation device, B p represents the damping force of the PTO system of the wave energy power generation device, is the inertia time constant of the PTO system of the wave energy power generation device; ω a represents the angular velocity at the hinge point of the wave energy power generation device, P HS represents the generated power output by the floating wind - wave combined power generation system, η WT is the efficiency of the wind turbine generator, η WEC is the power generation efficiency of the PTO system of the wave energy power generation device, N WECs is the number of wave energy power generation devices in the floating wind - wave combined power generation system, ω rr is the rated speed of the wind turbine rotor, ω ar represents the reference value of the control signal for the angular velocity at the hinge point of the wave energy power generation device, i The value range of N WECs , M is the pitching moment of the tower base before and after, and the parameter a t , K T 、K M and K B are obtained through model identification.

5. The model predictive control method for the floating wind-wave combined power generation system according to claim 1, characterized in that, In step (4) above, the prediction model in the discrete-time domain is: （5）， Among them, x(k) and x(k + 1) respectively represent the state variables of the system at discrete time steps k and k + 1, u(k) represents the input variable of the system at discrete time step k, y(k) represents the observed output variable of the system at discrete time step k, G is the state transition matrix, which describes the natural evolution law of the system state without external input; H is the input matrix, which quantifies the direct impact of control input and environmental disturbance on the state change; C is the output matrix, whose function is to map the system state x to the system output y.

6. The model predictive control method for the floating combined wind and wave power generation system according to claim 1, characterized in that, In the said step (5), the optimization objective function of the floating wind and wave combined power generation system is: （6)， Among them, δy(k + i) represents the output deviation vector at the k + i th future time instant, δu(k + i - 1) represents the change amount vector of the control input at the k + i - 1 th time instant, N represents the prediction horizon; the weight matrix Q is used to quantify the impact of the output deviation vector on the system performance, and the weight matrix R is used to limit the drastic fluctuations of the control input.

7. The model predictive control method for the floating wind and wave combined power generation system according to claim 1, characterized in that, In the said step (6), necessary constraints are set for the control input as follows: （7）， Among them, u(k) represents the control input variable of the system at discrete time step k, δu(k) represents the change in the control input of the system at discrete time step k, u max is the control input amplitude constraint, δu max is the control input rate of change constraint.

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