Offshore wind turbine generator nonlinear variable pitch control method based on time disturbance observer

Abstract

The invention discloses an offshore wind turbine generator nonlinear variable pitch control method based on a time disturbance observer. The method comprises the following steps: firstly, considering a platform negative damping effect of the floating fan, and designing a rated generator rotating speed according to platform pitching motion; establishing a variable pitch dynamical model of the floating type wind turbine generator; performing input and output linearization on the established variable pitch dynamical model by utilizing a feedback linearization theory; using a pole assignment method to complete linearized model controller design; and a self-adaptive preset time sliding mode disturbance observer is designed for external uncertainty interference in the system for compensation. Compared with a traditional control method, the method can better stabilize the generation power of the wind turbine unit at the time-varying wind speed, and has better dynamic performance.

Description

Technical Field

[0001] The invention relates to the technical field of intelligent control of wind power generation pitch control, and in particular to a nonlinear pitch control method for offshore wind turbines based on a time disturbance observer. Background Art

[0002] Floating wind turbines are more susceptible to environmental influences such as wind and waves, and produce more platform motion, which will cause the wind turbine to bear more fatigue loads, and will also cause instability in output power, resulting in a decline in power generation performance and a reduction in the service life of the wind turbine system. The dynamic system of a floating wind turbine is very complex, with strong nonlinearity and strong coupling, and is affected by uncertainties such as system parameter perturbations and wind and wave disturbances. The change in the operating point makes the performance of the linearized model controller deteriorate, so it is particularly important to build a nonlinear robust control solution. Summary of the invention

[0003] Purpose of the invention: In order to overcome the above-mentioned defects of linear control, the present invention provides a nonlinear variable pitch control method for a floating wind turbine based on a time disturbance observer, which can achieve power stability under time-varying wind speed and better meet the variable pitch requirements of floating wind turbines.

[0004] Technical solution: The nonlinear variable pitch control method of a floating wind turbine generator system based on a time disturbance observer of the present invention comprises the following steps:

[0005] S1: Considering the negative damping effect of the floating wind turbine platform, the design is based on the rated generator speed of the platform pitch motion;

[0006] S2: Establish the variable pitch dynamics model of floating wind turbines;

[0007] S3: using feedback linearization theory, the pitch dynamics model established in step S2 is linearized in terms of input and output;

[0008] S4: Complete the model controller design of step S3 linearization using the pole placement method;

[0009] S5: Design an adaptive preset time sliding mode disturbance observer to compensate for the external uncertainty interference in the system.

[0010] Furthermore, the negative damping effect of the floating wind turbine platform is considered in step S1, and the rated generator speed is designed based on the pitch motion of the platform. , whose expression is: , Where 1173.7 is the rated setting value of the generator speed, in units of , i.e. the rated generator speed of the unified pitch controller; is the platform pitch speed, is the gear ratio; defining the platform pitch velocity positively as the downwind platform pitch, the slope in the equation is is negative.

[0011] Furthermore, the variable pitch dynamics model of the floating wind turbine generator set is established as follows:

[0012] Select rotor speed , high speed shaft speed , slip rate and pitch angle As the system state vector, the state vector Written as: , In the formula, the superscript Represents a transpose operation;

[0013] Take the pitch angle reference input As input, the state equation of the wind turbine is: , In the formula, The vector representation of the rotor speed is, Express Seeking guidance, The vector representation of the high-speed shaft speed is, Express Seeking guidance, The vector representation of the slip rate is, Express Seeking guidance, The vector representation of the pitch angle, Express Seeking guidance, Represents the mechanical power output of the wind turbine, represents the torsional damping of the transmission chain, Indicates the torsional stiffness of the transmission chain, represents the rotor inertia, represents the gear ratio, represents the generator inertia, represents the generator torque, Indicates the control amount, Indicates the output quantity, Indicates the pitch time constant.

[0014] Furthermore, the specific method of step S3 is as follows:

[0015] First, the variable pitch dynamics model established in step S2 is converted into the standard form of an affine nonlinear system: , in, and is the n-dimensional vector field in the state space, represents a scalar function of x;

[0016] The specific steps to linearize the input and output of the affine nonlinear system are as follows:

[0017] S2.1. Relative order determination: For the affine nonlinear system model, calculate the Lie derivative until the relative order is found , so that ,in express Pair vector field The Lie derivative of express Pair vector field The Lie derivative of

[0018] S2.2. Dynamic separation: decomposing the system into linear subsystems and internal dynamics by coordinate transformation; , represents the coordinate transformation function of the fan system; z represents the new state variable of the fan system after the coordinate transformation; represents the external state variable, and its dimension is equal to the relative order of the system; subscript Represents the internal state variable, and its dimension is equal to the system dimension minus the relative order of the system;

[0019] S2.3. Feedback linearization control rate design: Design control quantity To cancel the nonlinear term, the virtual input Achieving linear relationship , It means to find the r-order derivative of the output y; , in express Pair vector field and The Lie derivative of express Pair vector field The second-order Lie derivative of ;

[0020] S2.4.Zero dynamic stability analysis: Select the following Lyapunov function to prove the zero dynamic stability of the system; , In the formula, Indicates internal state 1, express The derivative of Indicates internal state 2, express The derivative of .

[0021] Furthermore, the specific method of step S4 is as follows:

[0022] The linear controller is obtained by pole placement: , In the formula, represents the control gain 1, Indicates external state 1, express The reference value of represents the control gain 2, Indicates external state 2, express Reference value of

[0023] The linear controller obtained by placing the poles Substitution , and the nonlinear control rate is obtained: .

[0024] Furthermore, the specific steps of step S5 are as follows:

[0025] S5.1. Assume nonlinear terms in the controller , System input gain When both are unknown and the input wind is time-varying, define a disturbance Represent nonlinear terms and time-varying disturbances in the system: , In the formula, represents constant gain;

[0026] Introducing auxiliary variables The definition is as follows: , In the formula is the perturbed observation value, so there exists the following formula: , In the formula represents the perturbation observation error, express The second derivative of

[0027] S5.2. The designed preset time-integrated sliding surface is as follows: , In the formula, is the adaptive gain, satisfying , To preset time parameters, , represents the sliding surface, represents the constant 3.14;

[0028] S5.3. Based on the sliding surface, the differential form of the adaptive preset time disturbance observer is constructed as follows: , In the formula, is an adaptive parameter, satisfying , It is the preset time parameter, a positive number satisfy ; represents the inverse of the perturbed observation, represents a symbolic function;

[0029] Through the sliding mode disturbance observer, the disturbance in the wind turbine system Ability to set time Precise observation within.

[0030] The present invention discloses a nonlinear variable pitch control method for a wind turbine generator set based on a time disturbance observer, and the specific beneficial effects are as follows:

[0031] Traditional wind turbine pitch control methods are often based on onshore wind turbines, without considering the impact of platform motion on wind turbine operation. At the same time, traditional control methods are often based on linear control methods. The dynamic system of a floating wind turbine is very complex, with strong nonlinearity and strong coupling, and is affected by uncertainties such as system parameter perturbations and wind and wave disturbances. Changes in the operating point cause the performance of the linearized model controller to deteriorate. The nonlinear pitch control method for a wind turbine based on a time disturbance observer provided by the present invention considers platform motion to correct the rated speed of the wind turbine, and can effectively suppress platform motion. The feedback linearization theory is used to linearize the nonlinear part of the system, and an adaptive preset time disturbance observer is designed to compensate for the uncertainty of external interference in the system. The proposed control strategy does not require an accurate system model, and can achieve power stability under time-varying wind speeds, which is more in line with the pitch requirements of floating wind turbines. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 is a flow chart of the method of the present invention;

[0033] Figure 2 It is a graph of wind speed and wave height;

[0034] Figure 3 It is the curve diagram of wind turbine pitch angle variation;

[0035] Figure 4 It is the wind turbine rotor speed curve diagram;

[0036] Figure 5 It is the power curve of wind turbine engine;

[0037] Figure 6 is the standard deviation of wind turbine platform motion;

[0038] Figure 7 is the maximum absolute value of the wind turbine platform movement. DETAILED DESCRIPTION

[0039] This specific implementation method discloses a nonlinear pitch control method for a wind turbine based on a time disturbance observer. Figure 1 , the specific implementation method is as follows:

[0040] S1: Considering the negative damping effect of the floating wind turbine platform, the design is based on the rated generator speed of the platform pitch motion;

[0041] S2: Establish the variable pitch dynamics model of floating wind turbines;

[0042] S3: using feedback linearization theory, the pitch dynamics model established in step S2 is linearized in terms of input and output;

[0043] S4: Complete the model controller design of step S3 linearization using the pole placement method;

[0044] S5: Design an adaptive preset time sliding mode disturbance observer to compensate for the external uncertainty interference in the system.

[0045] In step S1, the rated generator speed of the wind turbine is corrected by taking into account the platform motion. In order to solve the negative damping effect of the platform,

[0046] Design based on the rated generator speed of the platform pitch motion , whose expression is: , Where 1173.7 is the rated setting value of the generator speed, in units of , i.e. the rated generator speed of the unified pitch controller; is the platform pitch speed, is the gear ratio. Define the platform pitch velocity positively as the downwind platform pitch, so the slope in the equation is When the rotor is pitched upwind, more energy is extracted from the wind by increasing the rated rotor speed, thereby suppressing the platform motion; when the rotor is pitched downwind, less energy is extracted because the rated rotor speed is reduced and the motion is suppressed again. Therefore, the effect of suppressing the platform motion is achieved by tracking the rated rotor speed with the actual rotor speed.

[0047] The variable pitch dynamics model of the floating wind turbine generator system established in step S2 is as follows:

[0048] Select rotor speed , high speed shaft speed , slip rate and pitch angle As the system state vector, the state vector Written as: , In the formula, the superscript Represents a transpose operation;

[0049] Take the pitch angle reference input As input, the state equation of the wind turbine is: , In the formula, The vector representation of the rotor speed is, Express Seeking guidance, The vector representation of the high-speed shaft speed is, Express Seeking guidance, The vector representation of the slip rate is, Express Seeking guidance, The vector representation of the pitch angle, Express Seeking guidance, Represents the mechanical power output of the wind turbine, represents the torsional damping of the transmission chain, Indicates the torsional stiffness of the transmission chain, represents the rotor inertia, represents the gear ratio, represents the generator inertia, represents the generator torque, Indicates the control amount, Indicates the output quantity, Indicates the pitch time constant.

[0050] Input-output linearization in step S3 is a method in control theory, which is used to transform a nonlinear system into a linear system through state feedback, thereby simplifying the control design. The core idea is to make the relationship between the input and output of the system linear through appropriate coordinate transformation and feedback control. The present invention considers using feedback linearization to transform the nonlinear floating wind turbine model into a linear model. The specific method of step S3 is as follows:

[0051] First, the variable pitch dynamics model established in step S2 is converted into the standard form of an affine nonlinear system: , in, and is the n-dimensional vector field in the state space, represents a scalar function of x;

[0052] The specific steps to linearize the input and output of the affine nonlinear system are as follows:

[0053] S2.1. Relative order determination: For the affine nonlinear system model, calculate the Lie derivative until the relative order is found , so that ,in express Pair vector field The Lie derivative of express Pair vector field The Lie derivative of

[0054] S2.2. Dynamic separation: decomposing the system into linear subsystems and internal dynamics by coordinate transformation; , represents the coordinate transformation function of the fan system; z represents the new state variable of the fan system after the coordinate transformation; represents the external state variable, and its dimension is equal to the relative order of the system; subscript Represents the internal state variable, and its dimension is equal to the system dimension minus the relative order of the system;

[0055] S2.3. Feedback linearization control rate design: Design control quantity To cancel the nonlinear term, the virtual input Achieving linear relationship , It means to find the r-order derivative of the output y; , in express Pair vector field and The Lie derivative of express Pair vector field The second-order Lie derivative of ;

[0056] S2.4. Zero dynamic stability analysis: Select the following Lyapunov function to prove that the system is zero dynamic stable.

[0057] , In the formula, Indicates internal state 1, express The derivative of Indicates internal state 2, express The derivative of .

[0058] Feedback linearization eliminates nonlinear coupling through global feedback, transforms the nonlinear system into a linear system, simplifies the controller design, and improves the stability of the system.

[0059] The pole configuration method in step S4 dynamically adjusts the position of the closed-loop poles of the system and combines feedback control to achieve stability optimization and precise adjustment of dynamic response, which is suitable for the robustness design of the system. The specific method of step S4 is as follows:

[0060] The linear controller is obtained by pole placement: , In the formula, represents the control gain 1, Indicates external state 1, express The reference value of represents the control gain 2, Indicates external state 2, express Reference value of

[0061] The linear controller obtained by placing the poles Substitution , and the nonlinear control rate is obtained: .

[0062] The present invention adopts an adaptive preset time sliding mode disturbance observer to compensate for external unknown disturbances. Its advantages are: the upper limit of the convergence time of the adaptive preset time sliding mode disturbance observer is used as an independent observer parameter, which is convenient for direct design and more intuitive, and also avoids the problem of too many parameters of the traditional fixed time sliding mode disturbance observer. The adaptive gain is introduced into the sliding mode disturbance observer to replace the fixed gain in the traditional sliding mode control to achieve preset time convergence, which further improves the robustness of the observer to the initial value of the disturbance. The specific steps of step S5 are as follows:

[0063] S5.1. Assume nonlinear terms in the controller , System input gain When both are unknown and the input wind is time-varying, define a disturbance Represent nonlinear terms and time-varying disturbances in the system: , In the formula, represents constant gain; Introducing auxiliary variables The definition is as follows: , In the formula is the perturbed observation value, so there exists the following formula: , In the formula represents the perturbation observation error, express The second derivative of

[0064] S5.2. The designed preset time-integrated sliding surface is as follows: , In the formula, is the adaptive gain, satisfying , To preset time parameters, , represents the sliding surface, represents the constant 3.14;

[0065] S5.3. Based on the sliding surface, the differential form of the adaptive preset time disturbance observer is constructed as follows: , In the formula, is an adaptive parameter, satisfying , It is the preset time parameter, a positive number satisfy ; represents the inverse of the perturbed observation, represents a symbolic function;

[0066] Through the sliding mode disturbance observer, the disturbance in the wind turbine system Ability to set time Precise observation within.

[0067] Simulation examples and calculation parameters

[0068] The effectiveness of the present invention is verified by using a variable pitch control system based on FAST and Matlab / Simulink platform. The NREL 5MW floating offshore wind turbine is used, the fixed step size is 0.0125s, and the simulation running time is 600s. Considering the actual physical application of wind turbines, the operating range of the blade pitch angle is set to ( ), the pitch rate limit is The simulation environment is set to the constant power stage, that is, the operation stage between the rated wind speed and the cut-out wind speed. The rated wind speed and cut-out wind speed of the NREL-5MW wind turbine are 11.4m / s and 25m / s respectively. According to the IEC standard, Figure 2 As shown in the figure, the wind speed model uses turbulent wind with an average wind speed of 18m / s generated by Turbsim, and the effective wave height is 3m. In order to verify the superiority of the control method (SMDOF) of the present invention, the variable gain PI controller (GSPI) of FAST is compared for simulation. The control scheme parameters are set according to experience as , , , the disturbance observer control parameters are set empirically as , , ,The performance and effectiveness of this application are evaluated by analyzing the ,simulation results.

[0069] Depend on Figure 3 As described above, compared with the traditional GSPI control, under the nonlinear variable pitch control strategy of the floating wind turbine based on the time disturbance observer proposed in the present invention, the blade pitch angle fluctuation of the offshore floating wind turbine is large, but due to the addition of pitch angle rate and angle limit in the control, the fluctuation of the variable pitch actuator is acceptable at this time.

[0070] Figure 4 and Figure 5 The following are the comparisons of the wind rotor speed and output power under the two types of control. It can be seen that under the nonlinear control strategy, the response to changes in wind speed is faster and the overshoot is smaller. The change amplitude and fluctuation of the wind rotor speed under nonlinear control are also smaller. The power generation capacity of the variable gain PI controller and nonlinear control can be stabilized at around 5MW. Compared with the variable gain PI control, the output power under nonlinear control is more stable.

[0071] The detailed data comparison of wind rotor speed and power generation is shown in Table 1:

[0072] Table 1: Control effect parameters under different controllers

[0073] From Table 1, we can see that the nonlinear control has smaller fluctuations in wind wheel speed and engine power.

[0074] When a floating wind turbine encounters the combined effects of wind and wave loads, it will produce six degrees of freedom motion, including translation and rotation. Translation includes sway, swing and heave; rotation includes pitch, roll and bow. Suppressing the motion of the platform can effectively improve the stability of the floating wind turbine.

[0075] Depend on Figure 6 and Figure 7It can be seen that compared with the traditional GSPI controller, the present invention has less impact on the pitch and sway of the platform, and has a certain degree of deterioration in the roll motion, but the amplitude is low. The standard deviations of the platform's pitch, sway, and heave are reduced by 7.6%, 38%, and 5.1%, respectively, and the maximum value of the platform motion is significantly suppressed.

[0076] In summary, the present invention proposes a nonlinear variable pitch control method for a floating wind turbine based on a time disturbance observer. A wind turbine generator model is established according to the relevant models and parameters of the wind turbine generator; secondly, based on the feedback linearization theory, this paper designs a feedback linearization variable pitch controller, and uses a time disturbance observer to compensate for the uncertainties in the controller. The present invention proposes a nonlinear variable pitch control method for a floating wind turbine based on a time disturbance observer, and proposes a nonlinear variable pitch method that is more in line with the mechanism of wind turbine operation, which can provide a reference for studying wind turbine pitch control.

[0077] The above embodiments are only for illustrating the technical idea of ​​the present invention, and cannot be used to limit the protection scope of the present invention. Any changes made on the basis of the technical solution in accordance with the technical idea proposed by the present invention shall fall within the protection scope of the present invention; any technology not involved in the present invention can be realized by existing technologies.

Claims

1. A nonlinear variable pitch control method for offshore wind turbines based on a time disturbance observer, characterized in that: The method comprises the following steps: S1: Considering the negative damping effect of the floating wind turbine platform, the design is based on the rated generator speed of the platform pitch motion; S2: Establish the variable pitch dynamics model of floating wind turbines; S3: using feedback linearization theory, the pitch dynamics model established in step S2 is linearized in terms of input and output; S4: Complete the model controller design of step S3 linearization using the pole placement method; S5: Design an adaptive preset time sliding mode disturbance observer to compensate for the external uncertainty interference in the system.

2. The nonlinear variable pitch control method for offshore wind turbines based on a time disturbance observer according to claim 1 is characterized in that: Considering the negative damping effect of the floating wind turbine platform described in step S1, the rated generator speed based on the pitch motion of the platform is designed. , whose expression is: ， Where 1173.7 is the rated setting value of the generator speed, in units of , i.e. the rated generator speed of the unified pitch controller; is the platform pitch speed, is the gear ratio; the positive platform pitch velocity is defined as the downwind platform pitch, so the slope in the equation is negative.

3. The nonlinear variable pitch control method for offshore wind turbines based on a time disturbance observer according to claim 2 is characterized in that: The variable pitch dynamics model of the floating wind turbine generator set is established in step S2 as follows: Select rotor speed , high speed shaft speed , slip rate and pitch angle As the system state vector, the state vector Written as: ， In the formula, the superscript Represents a transpose operation; Take the pitch angle reference input As input, the state equation of the wind turbine is: ， In the formula, The vector representation of the rotor speed is, Express Seeking guidance, The vector representation of the high-speed shaft speed is, Express Seeking guidance, The vector representation of the slip rate is, Express Seeking guidance, The vector representation of the pitch angle, Express Seeking guidance, Represents the mechanical power output of the wind turbine, represents the torsional damping of the transmission chain, Indicates the torsional stiffness of the transmission chain, represents the rotor inertia, represents the gear ratio, represents the generator inertia, represents the generator torque, Indicates the control amount, Indicates the output quantity, Indicates the pitch time constant.

4. The nonlinear variable pitch control method for offshore wind turbines based on a time disturbance observer according to claim 3 is characterized in that: The specific method of step S3 is as follows: First, the variable pitch dynamics model established in step S2 is converted into the standard form of an affine nonlinear system: ， in, and is the n-dimensional vector field in the state space, represents a scalar function of x; The specific steps to linearize the input and output of the affine nonlinear system are as follows: S2.

1. Relative order determination: For the affine nonlinear system model, calculate the Lie derivative until the relative order is found , so that ,in express Pair vector field The Lie derivative of express Pair vector field The Lie derivative of S2.

2. Dynamic separation: decomposing the system into linear subsystems and internal dynamics by coordinate transformation; ， represents the coordinate transformation function of the fan system; z represents the new state variable of the fan system after the coordinate transformation; represents the external state variable, and its dimension is equal to the relative order of the system; Represents the internal state variable, and its dimension is equal to the system dimension minus the relative order of the system; S2.

3. Feedback linearization control rate design: Design control quantity To cancel the nonlinear term, the virtual input Achieving linearization , It means to find the r-order derivative of the output y; ， in express Pair vector field and The Lie derivative of express Pair vector field The second-order Lie derivative of ; S2.4.Zero dynamic stability analysis: Select the following Lyapunov function to prove the zero dynamic stability of the system; ， In the formula, Indicates internal state 1, express The derivative of Indicates internal state 2, express The derivative of .

5. The nonlinear variable pitch control method for offshore wind turbines based on a time disturbance observer according to claim 4 is characterized in that: The specific method of step S4 is as follows: The linear controller is obtained by pole placement: ， In the formula, represents the control gain 1, Indicates external state 1, express The reference value of represents the control gain 2, Indicates external state 2, express Reference value of The linear controller obtained by placing the poles Substitution , and the nonlinear control rate is obtained: 。 6. The nonlinear variable pitch control method for offshore wind turbines based on a time disturbance observer according to claim 5 is characterized in that: The specific steps of step S5 are as follows: S5.

1. Assume nonlinear terms in the controller , System input gain When both are unknown and the input wind is time-varying, define a disturbance Represent nonlinear terms and time-varying disturbances in the system: ， In the formula, represents constant gain; Introducing auxiliary variables The definition is as follows: ， In the formula is the perturbed observation value, so there exists the following formula: ， In the formula represents the perturbation observation error, express The second derivative of S5.

2. The designed preset time-integrated sliding surface is as follows: ， In the formula, is the adaptive gain, satisfying , To preset time parameters, , represents the sliding surface, represents the constant 3.14; S5.

3. Based on the sliding surface, the differential form of the adaptive preset time disturbance observer is constructed as follows: ， In the formula, is an adaptive parameter, satisfying , It is the preset time parameter, a positive number satisfy ; represents the inverse of the perturbed observation, represents a symbolic function; Through the sliding mode disturbance observer, the disturbance in the wind turbine system Ability to set time Precise observation within.

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