WO2017174612A1

WO2017174612A1 - Wind power installation and method for operating a wind power installation

Info

Publication number: WO2017174612A1
Application number: PCT/EP2017/058037
Authority: WO
Inventors: Markus Becker
Original assignee: Windwise Gmbh
Priority date: 2016-04-08
Filing date: 2017-04-04
Publication date: 2017-10-12
Also published as: CN108779759A

Abstract

The present invention relates to a wind power installation (10) including a tower (12), a rotor (16) with rotor blades (20), a drive train (23) and a generator (22) driven by the rotor (16) via the drive train (23), wherein said rotor (16) has a rotor area (sweep area) A given by a rotor diameter D with A=π/4 D² and said generator (22) has a specific nominal power P, wherein the wind power installation (10) is adapted for an operation wherein the rotation frequency f of the rotor (16) in operation does not exceed a limit f_g, wherein the tower (12) is designed as a tubular steel tower (12) and the ratio of the nominal power per rotor area P/A of the wind power installation (10) is in the range of 80 W/m² ≤ P / a ≤ 180 W/m², preferably in the range of 100 W/m²≤ P/A ≤ 160 W/m², wherein the limit fg is lower than the first natural frequency of the wind power installation (10). The invention further relates to a method for operating a corresponding wind power installation (10).

Description

WIND POWER INSTALLATION AND METHOD FOR OPERATING A WIND POWER

INSTALLATION

The present invention relates to a wind power installation including a tower, a rotor with rotor blades, a drive train and a generator driven by the rotor via the drive train, said rotor having a rotor area (sweep area) A given by a rotor diameter D with A= π/4 D² and said generator having a specific nominal power P, wherein the wind power installation is adapted for an operation wherein the rotation frequency f of the rotor in operation does not exceed a limit f_g.

Since start of the real industrialization of the wind industry in the beginning of the early 90' s, wind turbine generators have been continuously growing. Average turbine sizes grew from rated power values of 150 kW (and even below) to 4 MW (onshore) and up to > 8 MW (offshore). Rotor diameters increased from 20 m up to 140 m (onshore) and 180 m (offshore). Hub heights of turbine are site specific but go up 160 m and even higher towers in onshore application are under consideration.

Today's turbine size and related dimensions of main components have led to significant cost steps in production but especially for onshore application to logistical constraints. Transport and installation of components in onshore projects have become very difficult. New technology for high tower solutions, split blades and sophisticated transport devices have been devel- oped but impact of the logistics, necessary for implementation or more wind power, has become a significant part of the overall turbine cost. Document US 2013/0177418 Al describes a wind turbine including a tower, a rotor with rotor blades and a generator driven by the rotor, said rotor having a rotor/sweep area A and said generator having a specific nominal power P, wherein the wind power installation is adapted for an operation wherein the rotational speed of the rotor in operation does not exceed a speed limit.

Nowadays regions with best wind conditions are largely supplied with wind power installations. These already installed wind power installations are designed in such way that they can also work at strong winds. FIG. 2 shows a characteristic curve, which represents the dimensioning of conventional wind power installations.

In order to be able to use also those regions with less strong winds (hereinafter referred to as "low-wind regions"), the dimensions of the wind turbines have so far been enlarged without noticeably deviating from this characteristic curve. The tower height has also increased constantly so that the wind speeds available at this altitude at corresponding heights are acceptable even in low- wind regions.

In the future, there will be a growing need for wind power installations suitable for low-wind regions which are working profitably in these regions.

It is the object of the invention to provide a cost-effective, low noise wind power installation for low- wind regions having operating parameters, which complements the existing types of wind power installations in regards to a constant and reliable overall power supply and to provide a corresponding operation method.

This object is achieved by the present invention as defined in the independent claims. The dependent claims detail advantageous embodiments of the invention. According to a plurality of embodiment of the invention the wind power installation (wind turbine) includes a tower, a rotor with rotor blades and a generator driven by the rotor via a drive train, and is adapted for an operation wherein the rotation frequency f of the rotor in operation does not exceed a limit f_g. The ratio of the nominal power per rotor area P/A of this wind power installation is in the range of 80 W/m² < P/A < 180 W/m², preferably in the range of 100 W/m² < P/A < 160 W/m². The absolute limit f_g is lower than the 1^st natural frequency of the wind power installation (in terms of the corresponding building including tower, nacelle and rotor on stiff foundation). Preferably, the absolute limit f_g is less than 90% of the 1^st natural frequency of the building.

Decreasing number of potential sites with very good wind conditions and increasing penetration of wind power in the grid, especially in these regions, lead to power evacuation issues and limitations for further wind power installation. Subsequently wind projects are moving into regions with lower average wind speeds and less distance to the big consumers. These sites have been less attractive in the past but technology improvement and turbine adaptation have had positive impact on cost development and make these sites commercially viable. This is especially the case when the real project and grid infrastructure cost are taken into account and the technical and commercial advantages of distributed wind power generation with op- timised technology for reduction of power volatility is used.

The nominal power per rotor area ratio P/A according to the above mentioned embodiments of the invention is based on a comprehensive approach of new combination of the range of rotor speed, rated power and tower frequency leading to a significant lighter structure of the main components, improved energy yield and reduced noise emission.

The energy capture of a turbine according to this new approach is focused on times and wind speeds with statistically higher occurrence probability. Energy capture shall be improved by increase of tower height and in parallel reduction of rated rotor speed and rated power. The potential energy capture at higher wind speeds is neglected.

The wind power installation based on the mentioned specific operational and design parame- ters optimising the interfering effects of rotor speed ranges and natural frequencies of main components like e.g. the tower. This leads to a structure-wise, production-wise and noise- emission- wise optimised wind power installation (turbine) concept serving in a first glance the demand of low- wind- speed sites. The wind power installation with a maximum rotor speed given by the frequency limit f_g allows the realization of so called soft-stiff tower structures (first natural frequency above rated speed frequency) with natural frequencies below 0.2 Hz.

Consequently, the tower is designed as a tower of so such a soft-stiff tower structure, namely a tubular steel tower. A tubular steel tower is much more cost-effective than a comparable concrete tower, whereby, on the other hand, the individual segments of such a tubular steel tower must be portable on public roads.

According to a preferred embodiment of the invention, the wind power installation comprises a control and/or regulation device (control device) adapted for limiting the rotation frequency f of the rotor. The control and/or regulation device is configured for limiting the rotation frequency f of the rotor in operation in such way that the rotation frequency f does not exceed the limit f_g (which is lower than the 1^st natural frequency of the wind power installation). According to another preferred embodiment of the invention, the torque of the drive train is adjustable for limiting the rotation frequency f of the rotor. According to yet another preferred embodiment of the invention, the rotor diameter D is in the range of 120 m < D < 150 m.

According to another preferred embodiment of the invention, the ratio of hub height H to ro- tor diameter D is in the range of 0.7 < H/D < 1.3, preferably at H/D ~ 1. In case the rotor diameter D is in the range of 120 m < D < 150 m, the hub height H would be in the same range, namely 120 m < H < 150 m.

According to yet another preferred embodiment of the invention, the ratio of torque N to rota- tional frequency f is in the range of 9600 kNms < N/f < 13000 kNms. This range is equivalent to a rotational speed range of 160 kNm/RPM < N/n < 217 kNm/RPM (with 1 RPM = 1/60 Hz).

According to yet another preferred embodiment of the invention, the wind power installation is designed as an onshore wind power installation.

The invention further relates to a method for operating a wind power installation, which installation includes a tower designed as a tubular steel tower, a rotor with rotor blades and a generator driven by the rotor, said rotor having a rotor area (sweep area) A given by a rotor diameter D with A= π/4 D² and said generator having a specific nominal power P, wherein the ratio of the nominal power per rotor area P/A of the wind power installation is in the range of 80 W/m² < P / a < 180 W/m², preferably in the range 100 W/m² < P/A < 160 W/m² and wherein the wind power installation is operated in such way that the rotation frequency f of the rotor in operation does not exceed a limit f_g.

According to yet another preferred embodiment of the invention, the torque of the drive train is adjusted for limiting the rotation frequency f of the rotor. These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.

In the drawings:

FIG. 1 shows a schematic representation of a wind power installation 10 according to a preferred embodiment of the invention; and

FIG. 2 shows a diagram depicting the ratio or the rated torque /the rated rotational speed ver- sus the rotor diameter D for known wind power installations and the wind power installation according to a preferred embodiment of the invention.

FIG. 1 shows a schematic representation of a wind power installation 10. The wind power installation 10 has a tower 12, a nacelle 14 and a rotor 16 with a rotor shaft 18 and a plurality (normally three) of rotor blades 20, of which only two are shown in FIG. 1. The blade angles of the rotor blades 20 are adjustable. The blade angle is also normally called the pitch angle. The adjustment is normally performed by electric or hydraulic motors i.e. at least one motor per rotor blade 20, which are not shown in FIG. 1. Two or more motors can also be provided per rotor blade 20 for the adjustment of the blade angle. The adjustment of the blade angle 20 serves to optimally tap power, which is provided by the wind on the wind power plant, through the rotor blade 20. Moreover, the blade angle adjustment serves to reduce power draw and thus also the load on the wind power installation 10 in the case of high wind speeds.

The wind power is converted to a rotation of the rotor 16 via the rotor blades 20. A generator 22 is driven by the rotor 16 via a drive train 23 including a gear box 24, which is passed to an electrical connection at the bottom of the tower 12 (not shown) via a power cable, which is fed through the tower 12. A transformation to a high voltage, which is then fed to a network, takes place there. The tower 12 is a tubular steel tower 12 built on a foundation 26. The tubu- lar steel tower 12 is build of a number of tubular elements (not shown explicitly). In the upper area the tower 12 carries the nacelle 14, which has the corresponding provided components. A wind power installation 10 can also be provided without a gear box 24. Furthermore, a rotor brake (not shown) is normally also provided on the fast shaft between gear box 24 and gen- erator 22.

The generator 22 has a specific nominal power P of about 2 MW. A control device, which regulates and/or controls the wind power installation 10, is also provided in the nacelle 14 (not shown). The control device is (inter alia) adapted for limiting the rotation frequency f of the rotor 16 to an absolute limit f_g. This absolute limit f_g is significantly lower than the 1^st natural frequency of the wind power installation 10 (tower including nacelle and rotor on stiff foundation). The control device adjusts the pitch angle of the rotor blades 20 for limiting the rotation frequency f of said rotor blades 20. The wind power installation 10 shown in FIG. 1 has a ratio of hub height H (rotor 20 over ground 28) to rotor diameter D, which is about H/D ~ 1. Both, hub high H and rotor diameter D are about 140m in the shown example.

The rotor 16 has a rotor area/sweep area A given by the rotor diameter D with A= π/4 D². The ratio of the nominal power (of the generator 22) per rotor area (of the rotor 16) P/A of the wind power installation 10 is about 130 W/m², which is in the range of 100 W/m² < P/A < 160 W/m². The ratio of nominal power per rotor area P/A of "state of the art"-wind power installations is substantially higher. The main design drivers for the power conversion system are (a) the rated mechanical torque born by the rotor of the turbine. This is independent if the drive train is consisting of a high or medium speed generator + gearbox and power conversion system or direct drive systems con- sisting of ring generator + power conversion system and (b) the rated rotation frequency f or rotor speed.

Targeting for an increase of rated power of a wind power installation 10 leads consequently either to increase of the rated torque or rated speed of the rotor or to increase of both.

As noise emission of wind power installations 10, which is critical to design, is mainly born out of the tip speed of the rotor blade 20, maximum tip speeds of modern wind turbines in the multi MW size are limited today in a range between 74m/s to 80m/s. Consequently the in- crease of the rotor diameter D leads to reduction of rotor speed when the tip speed should be kept below the mentioned limits. If rated turbine power is planned to be constant the rated torque of the drive train 23 has to grow approximately proportionally to the increase of rotor diameter D. In case the rated power shall increase in addition to the rotor diameter D for achievement of objected performance targets the rated torque has to increase further. As rated power is also proportional to rated torque, as consequence the growth of the overall rated torque of the drive train 23 is proportional to the "rotor diameter times rated power output" of the turbine: rated drive train torque = f(rated power, rated speed, rotor diameter).

Main design drivers for the tower (in particular tubular steel tower) 12:

(a) Structural loading out of extreme and fatigue situations: The relation between wind conditions, rotor aerodynamics and dynamic behaviour of the complete wind power installations 10 is complex, especially as a big variety of design driving load cases and other conditions have to be taken into account. Nevertheless it can be assumed that the majority of design driving wind conditions of a pitch controlled variable speed wind turbine occur in the range of rated wind speed before real pitch activity for power curtailment starts. Another main factor is for sure the rotor size and aerodynamics. Based on these assumptions it is assumed that the design driving tower thrust, loading the tower structure, is roughly proportional to the rotor area and the square of the rated wind speed (when the turbine reaches rated power). (b) Transport dimensions for onshore tower systems: The most cost-effective tower system is the tubular steel tower design. Transport of tower segments on the street is limited my maximum weight and maximum diameter (normally 4.3m to 4.4m).

(c) Natural frequency of the tower 12: The tower frequency has significant impact on the tur- bine dynamics. For avoidance of dynamic interference of tower dynamics and speed range of the turbine the tower design aims for a stiff structure with a first natural frequency above the exciting frequency out of the rated rotor speed. Transport of tower segments is, as described, restricted by maximum dimensions/ diameters. These restriction (minimum first natural frequency and maximum tower bottom diameter) have to be taken into account, when going for higher towers. This leads consequently to a maximum tower height (mainly tubular steel towers) depending on operational parameters of the turbine: Max tower height = f(wind speed, rotor diameter, rated rotor speed).

In the following, two main characteristics of the wind power installation 10 are mentioned again:

• Wind power installation 10 with a maximum rotor speed allowing realisation of so called soft-stiff tower structures (first natural frequency above rated speed frequency) with natural frequencies below 0.2Hz; and

· Wind power installation 10 with limited rated power in a way that rated power is reached at low wind speeds with the intention to keep structural loading on a level that allows design of tubular steel towers with standard transport dimensions (max diameter of tubular steel segment < 4,5m) and natural frequencies below 0,2Hz and hub heights > 110 m. FIG. 2 shows a diagram depicting the ratio or the rated torque /the rated rotational speed versus the rotor diameter D for known wind power installations and the wind power installation 10 according to one embodiment.

The ratio of rated torque to rated speed is continuously growing since introduction of the 1.5 MW class (graph 30) as limitation of max tip speed requires massive growth of drive train torque for realisation of higher power output combined with rotor growth. The wind power installation 10 would be roughly 40% below market average (area 32).

While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive; the invention is not limited to the disclosed embodiments.

Other variations to be disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting scope.

LIST OF REFERENCES

10 wind power installation

12 tower

14 nacelle

16 rotor

18 rotor shaft

20 rotor blade

22 generator

23 drive train

24 gear box

26 foundation

28 ground

30 graph

32 area

Claims

1. A wind power installation (10) including a tower (12), a rotor (16) with rotor blades (20), a drive train (23) and a generator (22) driven by the rotor (16) via the drive train (23), wherein said rotor (16) has a rotor area A given by a rotor diameter D with A= π/4 D² and said generator (22) has a specific nominal power P, wherein the wind power installation (10) is adapted for an operation wherein the rotation frequency f of the rotor (16) in operation does not exceed a limit f_g, wherein the tower (12) is designed as a tubular steel tower (12) and the ratio of the nominal power per rotor area P/A of the wind power installation (10) is in the range of 80 W/m² < P / a < 180 W/m², preferably in the range of 100 W/m² < P/A < 160 W/m², wherein the limit f_g is lower than the first natural frequency of the wind power installation (10).

2. The wind power installation according to claim 1, wherein the torque of the drive train (23) is adjustable for limiting the rotation frequency f of the rotor (16).

3. The wind power installation according to claim 1 or 2, wherein the rotor diameter D of the rotor (20) is in the range of 120 m < D < 150 m.

4. The wind power installation according to one of claims 1 to 3, wherein the ratio of hub height H of the rotor (20) to rotor diameter D is in the range of 0.7 < H/D < 1.3, preferably at H/D ~ 1.

5. The wind power installation according to one of claims 1 to 4, wherein the ratio of torque N to rotational frequency f is in the range of 9600 kNms < N/f < 13000 kNms.

6. The wind power installation according to one of claims 1 to 5, wherein the wind power installation (10) is designed as an onshore wind power installation.

7. A method for operating a wind power installation (10), which installation includes a tower (12) designed as a tubular steel tower (12), a rotor (16) with rotor blades (20) and a generator (22) driven by the rotor (16), said rotor (16) having a rotor area A given by a rotor diameter D with A= π/4 D² and said generator (22) having a specific nominal power P, wherein the ratio of the nominal power per rotor area P/A of the wind power installation (10) is in the range of 80 W/m² < P / a < 180 W/m², preferably in the range 100 W/m² < P/A < 160 W/m² and wherein the wind power installation (10) is operated in such way that the rotation frequency f of the rotor (16) in operation does not exceed a frequency limit f_g, which is lower than the first natural frequency of the wind power installation (10).

8. The method according to claim 7, wherein the torque of the drive train (23) is adjusted for limiting the rotation frequency f of the rotor blades of the rotor (16).