Method for determining wind energy utilization coefficient of semi-submersible fan

Abstract

The invention discloses a method for determining a wind energy utilization coefficient of a semi-submersible fan, which relates to the technical field of marine sciences, and is characterized by comprising the following steps of: (1) determining an actual wind speed at an infinitesimal point of a fan impeller according to a blade element plane and a flow velocity triangle of the infinitesimal point; (2) determining an inflow angle; (3) correcting an axial induction factor a and a radial induction factor b; (4) according to the six-degree-of-freedom motion relation of the floating platform, the factors of the wave load of the irregular waves for generating the substantial influence on the wind speed are surging, heaving and pitching, and then the wind speed is determined; (5) determining an effective tip speed ratio under the wind wave load coupling influence; and (6) the influence factors of the wind energy utilization coefficient (Cp) are decomposed into the tip speed ratio and the pitch angle, and therefore a correction formula of the Cp is obtained.

Description

Technical Field

[0001] This invention relates to the field of marine science and technology, and more specifically, to a method for determining the wind energy utilization coefficient of a semi-submersible wind turbine. Background Technology

[0002] The power output of offshore semi-submersible floating wind turbines is affected by the coupling of wind and wave loads, and a key factor in evaluating their output characteristics is the wind energy utilization factor (Cp). Existing methods for determining the Cp only consider wind load factors and do not address the impact of wave loads on Cp variations. This leads to a mismatch between the calculated wind power output and the actual output power, affecting the accuracy of downstream pitch control and grid-connected power system control strategies. Therefore, a method for determining the Cp of offshore floating wind turbines that considers the effects of both wind and wave loads is urgently needed. Summary of the Invention

[0003] In view of the shortcomings of the existing technology, the purpose of this invention is to provide a method for determining the wind energy utilization coefficient of a semi-submersible wind turbine, so as to overcome the limitation of the existing method when only wind load is considered in determining the wind energy utilization coefficient (Cp).

[0004] To achieve the above objectives, the present invention provides the following technical solution: a method for determining the wind energy utilization coefficient of a semi-submersible wind turbine, comprising:

[0005] (1) Based on the blade element plane and velocity triangle of the micro-element point, determine the actual wind speed at the micro-element point of the fan impeller, as shown below:

[0006] (1),

[0007] in, It is the actual wind speed at the impeller micro-element point. Here, a represents the ambient wind speed, a is the axial induction factor, and b is the radial induction factor. ω is the impeller deflection angular frequency, and r is the calculated distance from the root of the infinitesimal element.

[0008] (2) Determine the inflow angle as shown in the following formula:

[0009] (2),

[0010] in, It is the inflow angle. It's an attack angle. It is the torsion angle of the infinitesimal element. It is the propeller pitch angle. It is the ambient wind speed. ω is the impeller deflection angular frequency, and r is the distance from the root of the infinitesimal element.

[0011] (3) Correcting the axial induction factor a and the radial induction factor b;

[0012] (4) Based on the six-degree-of-freedom motion relationship of the floating platform, the factors that have a substantial impact on the wind speed of the irregular wave load are sway, heave, and pitch, and then the wind speed is determined.

[0013] (5) Determine the effective tip speed ratio under the combined effect of wind and wave loads ;

[0014] (6) The influencing factors of wind energy utilization coefficient (Cp) are decomposed into tip speed ratio and blade pitch angle, thus obtaining the corrected formula for Cp:

[0015] (6),

[0016] in, The wind energy utilization coefficient, Let be the tip speed ratio of the infinitesimal element located r away from the impeller root. It is the propeller pitch angle. For the effective tip speed ratio.

[0017] Furthermore, the axial induction factor a and the radial induction factor b are corrected according to the following formula:

[0018] (3),

[0019] Where a is the axial induction factor, b is the radial induction factor, and F is the Prandtl loss coefficient. Here, r is the calculated distance from the micro-element point to the root, and R is the blade length. Where N is the hub radius, C is the number of blades, and c is the wire diameter. and It is the drag coefficient of the blade airfoil. It is the normal force coefficient. It is the tangential force coefficient.

[0020] Furthermore, the wind speed corrected in step (4) is:

[0021] (4),

[0022] in, For the change in wind speed, The change in wind speed caused by oscillation. The change in wind speed caused by heave. The actual effective wind speed, The impeller longitudinal rocking angle, It refers to ambient wind speed.

[0023] Furthermore, in step (5), the effective tip speed ratio The method for determining it is as follows:

[0024] (5),

[0025] in, For an effective tip speed ratio, ω is the impeller deflection angular frequency, and r is the calculated distance from the root of the infinitesimal element. It is the ambient wind speed. Let a be the change in wind speed, and b be the axial induction factor and the radial induction factor.

[0026] Furthermore, it also includes the step of determining the trend of wind energy utilization coefficient change under the coupling effect of wind and wave loads, specifically: according to formulas (4), (5), and (6), input the actual wind load data and wave load data of the target wind turbine.

[0027] In summary, the present invention has the following beneficial effects: The present invention modifies the existing method for determining the wind energy utilization factor (Cp) and takes into account the influence of wind load and wave load. As a result, the wind power output power obtained is more in line with the actual power, thereby improving the accuracy of the back-end pitch control and grid-connected power system control implementation. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the blade element plane and velocity triangle at a micro-element point of the wind turbine impeller;

[0029] Figure 2 This is a schematic diagram of the six degrees of freedom motion of a floating platform;

[0030] Figure 3 The motion response of the floating platform under different working conditions is the sway velocity, heave velocity and pitch angle. Among them, (a) wind speed 11.4 m / s, significant wave height of irregular wave 2.35 m, average wave period 7.5 s; (b) wind speed 11.4 m / s, wave influence not considered.

[0031] Figure 4 This is a graph showing the relationship between the blade tip speed ratio and the wind energy utilization coefficient under the influence of wind and wave loads.

[0032] Figure 5 This is a waveform diagram showing the output power and error of a semi-submersible floating wind turbine. Detailed Implementation

[0033] In order to fully disclose the present invention, the technical solution of the present invention will be specifically described below with reference to the accompanying drawings and embodiments.

[0034] This invention provides a method for determining the wind energy utilization coefficient of a semi-submersible wind turbine, comprising the following steps:

[0035] (1) Based on the blade element plane and velocity triangle of the micro-element point, determine the actual wind speed at the micro-element point of the fan impeller, as shown below:

[0036] (1),

[0037] in, It is the actual wind speed at the impeller micro-element point. Here, a represents the ambient wind speed, a is the axial induction factor, and b is the radial induction factor. ω is the impeller deflection angular frequency, and r is the calculated distance from the root of the infinitesimal element.

[0038] (2) Determine the inflow angle as shown in the following formula:

[0039] (2),

[0040] in, It is the inflow angle. It's an attack angle. It is the torsion angle of the infinitesimal element. It is the propeller pitch angle. It is the ambient wind speed. ω is the impeller deflection angular frequency, and r is the distance from the root of the infinitesimal element.

[0041] (3) Correcting the axial induction factor a and the radial induction factor b;

[0042] Specifically, the correction method is as follows:

[0043] (3),

[0044] Where a is the axial induction factor, b is the radial induction factor, and F is the Prandtl loss coefficient. Here, r is the calculated distance from the micro-element point to the root, and R is the blade length. Where N is the hub radius, C is the number of blades, and c is the wire diameter. and It is the drag coefficient of the blade airfoil. It is the normal force coefficient. It is the tangential force coefficient.

[0045] (4) Based on the six-degree-of-freedom motion relationship of the floating platform, the factors that have a substantial impact on the wind speed of the irregular wave load are sway, heave, and pitch, and then the wind speed is determined.

[0046] Specifically, the corrected wind speed is:

[0047] (4),

[0048] in, For the change in wind speed, The change in wind speed caused by oscillation. The change in wind speed caused by heave. The actual effective wind speed, The impeller longitudinal rocking angle, It refers to ambient wind speed.

[0049] (5) Determine the effective tip speed ratio under the combined effect of wind and wave loads ;

[0050] Specifically, effective tip speed ratio The method for determining it is as follows:

[0051] (5),

[0052] in, For an effective tip speed ratio, ω is the impeller deflection angular frequency, and r is the calculated distance from the root of the infinitesimal element. It is the ambient wind speed. Let a be the change in wind speed, and b be the axial induction factor and the radial induction factor.

[0053] (6) The influencing factors of wind energy utilization coefficient (Cp) are decomposed into tip speed ratio and blade pitch angle, thus obtaining the corrected formula for Cp:

[0054] (6),

[0055] in, The wind energy utilization coefficient, Let be the tip speed ratio of the infinitesimal element located r away from the impeller root. It is the propeller pitch angle. For the effective tip speed ratio.

[0056] (7) It also includes the step of determining the trend of wind energy utilization coefficient under the coupling effect of wind and wave loads. Specifically, according to formulas (4), (5), and (6), the actual wind load data and wave load data of the target wind turbine can be input.

[0057] To verify the effect of wind and wave load coupling on the wind energy utilization coefficient of a semi-submersible floating wind turbine, this invention uses a 5MW semi-submersible floating wind turbine from a certain NREL standard for numerical verification, and sets up two sets of calculation examples:

[0058] (a) Wind speed 11.4 m / s, significant wave height of irregular wave 2.35 m, average wave period 7.5 s;

[0059] (b) Wind speed 11.4 m / s, wave effect not considered.

[0060] like Figure 3 The figure shows the motion response of the floating platform under two operating conditions, (a) and (b). The irregular wave was measured using the JONSWAP wind wave spectrum, with a sampling step size of 0.1 s and a total sampling time of 4000 s. It can be seen that, compared to the influence of wind load alone, under the influence of irregular waves, the floating platform's sway velocity can reach 0.3 m / s, its heave velocity can reach 0.15 m / s, and its pitch angle can reach 3.9°.

[0061] Combining equations (4), (5), and (6), the relationship between the tip speed ratio and the wind energy utilization coefficient under the influence of wind and wave loads can be calculated. Figure 4 It can be seen that wave load can change the tip speed ratio by up to 3%, and reduce the wind energy utilization coefficient from 0.48 to about 0.427.

[0062] This invention verifies the actual output power of the target semi-submersible floating wind turbine, the output power calculated according to this invention, and the relationship between the error values ​​of the two. The numerical calculation uses actual wind and wave loads and power generation data of a certain semi-submersible floating wind turbine, with a total duration of 480 hours. The results are as follows: Figure 5 As shown, the output power of the semi-submersible floating wind turbine obtained by the wind energy utilization coefficient relationship determined by the method of this invention closely matches the actual output power. Except for the high-frequency fluctuation of wind speed, the error value does not exceed 4% in other cases, proving that the determination method proposed in this invention is effective and accurate.

[0063] This specific embodiment is merely an explanation of the present invention and is not intended to limit the invention. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they are within the scope of the claims of the present invention.

Claims

1. A method for determining the wind energy utilization coefficient of a semi-submersible wind turbine, characterized in that, include: (1) Based on the blade element plane and velocity triangle of the micro-element point, determine the actual wind speed at the micro-element point of the fan impeller, as shown below: （1）， in, It is the actual wind speed at the impeller micro-element point. Here, a represents the ambient wind speed, a is the axial induction factor, and b is the radial induction factor. ω is the impeller deflection angular frequency, and r is the calculated distance from the root of the infinitesimal element. (2) Determine the inflow angle as shown in the following formula: （2）， in, It is the inflow angle. It's an attack angle. It is the torsion angle of the infinitesimal element. It is the propeller pitch angle. It is the ambient wind speed. ω is the impeller deflection angular frequency, and r is the distance from the root of the infinitesimal element. (3) Correcting the axial induction factor a and the radial induction factor b; (4) Based on the six-degree-of-freedom motion relationship of the floating platform, the factors that have a substantial impact on the wind speed of the irregular wave load are sway, heave, and pitch, and then the wind speed is determined. (5) Determine the effective tip speed ratio under the combined effect of wind and wave loads ; (6) The influencing factors of wind energy utilization coefficient (Cp) are decomposed into tip speed ratio and blade pitch angle, thus obtaining the corrected formula for Cp: （6）， in, The wind energy utilization coefficient, Let be the tip speed ratio of the infinitesimal element located r away from the impeller root. It is the propeller pitch angle. For the effective tip speed ratio.

2. The method for determining the wind energy utilization coefficient of a semi-submersible wind turbine according to claim 1, characterized in that... The axial induction factor a and the radial induction factor b are corrected according to the following formula: （3）， Where a is the axial induction factor, b is the radial induction factor, and F is the Prandtl loss coefficient. Here, r is the calculated distance from the micro-element point to the root, and R is the blade length. Where N is the hub radius, C is the number of blades, and c is the wire diameter. and It is the drag coefficient of the blade airfoil. It is the normal force coefficient. It is the tangential force coefficient.

3. The method for determining the wind energy utilization coefficient of a semi-submersible wind turbine according to claim 1, characterized in that, The corrected wind speed in step (4) is: （4）， in, For the change in wind speed, The change in wind speed caused by oscillation. The change in wind speed caused by heave. The actual effective wind speed, The impeller longitudinal rocking angle, It refers to ambient wind speed.

4. The method for determining the wind energy utilization coefficient of a semi-submersible wind turbine according to claim 1, characterized in that, Effective tip speed ratio in step (5) The method for determining it is as follows: （5）， in, For an effective tip speed ratio, ω is the impeller deflection angular frequency, and r is the calculated distance from the root of the infinitesimal element. It is the ambient wind speed. Let a be the change in wind speed, and b be the axial induction factor and the radial induction factor.

5. The method for determining the wind energy utilization coefficient of a semi-submersible wind turbine according to claim 1, characterized in that, It also includes the step of determining the trend of wind energy utilization coefficient under the influence of wind and wave load coupling, specifically: according to formulas (4), (5), and (6), input the actual wind load data and wave load data of the target wind turbine.

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