Patent Publication Number: US-2019195193-A1

Title: Rotor blade hub for a wind turbine, and wind turbine having same

Description:
BACKGROUND 
     Technical Field 
     The present invention relates to a rotor blade hub for a wind turbine, comprising a connecting portion for torque-transmitting coupling of the rotor blade hub to a main shaft of the wind turbine. The invention further relates to a wind turbine having such a rotor blade hub, a generator for generating electric power, wherein the generator has a generator rotor and a generator stator, and wherein the generator rotor and the rotor blade hub are coupled with a main shaft. 
     Description of the Related Art 
     Wind turbines of the above-indicated kind are generally known. On the one hand wind turbines have become established in the state of the art, in which the rotor blade hub is coupled to the generator by means of a frequently multi-stage transmission, wherein the multi-stage transmission implements a step-up of the drive movement which is predetermined by the rotor blade hub to a higher rotary speed. In high loading situations the transmissions known from the state of the art exhibit an increased susceptibility to faults and defects. Wind turbines with a drive train including a transmission usually have an asynchronous generator which by virtue of the principle involved needs high rotary speeds. Wind turbines with a transmission are typically designed in such a way that the hub is connected at the drive output side to the main shaft leading to the transmission. That main shaft transmits not only the drive moment of the wind turbine but also the loadings resulting from the wind, turbulence, the dynamics and the inherent weight of the hub. As a result, as the rotating component, the main shaft is subjected to considerable stress variations and is to be of appropriate dimensions. 
     In comparison transmission gear-less wind turbines have become established in the state of the art, in particular by the present applicant, such wind turbines using a slowly rotating, multi-pole synchronous generator. Gear-less installations are typically mounted directly within the hub on a stationary journal, whereby external loadings are diverted into the pylon by way of substantially stationary structural elements. 
     Slowly rotating multi-pole synchronous generators are maintenance-friendly and reliable, but they require a large generator diameter by virtue of the principle involved in order, because of the low rotary speeds, nonetheless to be able to ensure sufficient electric power generation. There is a need for improvement in that respect by virtue of the trend towards ever higher power classes markedly above 4 megawatts. 
     BRIEF SUMMARY 
     Improving a rotor blade hub is provided herein to permit use in combination with generators of smaller and lighter structure, while the advantages of the stationary drive train concept are retained to the best possible extent. In addition the efficiency in producing electric power should remain unaffected as much as possible. 
     In a rotor blade hub of the kind set forth in the opening part of this specification that object is attained by designing a hub. In particular, provided is a rotor blade hub having a single-stage transmission which is non-rotatably mounted to the rotor blade hub at the drive input side and has a connecting portion at the drive output side. Preferably a shaft/hub connection is provided in the connecting portion between the single-stage transmission and the main shaft. 
     A drive train of the wind turbine is provided. Placement of a single-stage transmission directly at the rotor blade hub makes it possible to have a hitherto unattained advantage in regard to maintenance and replacement of the transmission. The further drive train in the direction of the generator can remain unaltered, it is only necessary for the transmission to be arranged at the rotor blade hub. In addition a paradigm shift is possible by virtue of integration of a single-stage transmission in the rotor blade hub. Hitherto in particular slowly rotating synchronous generators were operated exclusively in a transmission gear-less structure. In the state of the art the provision of a transmission on wind turbines with a synchronous generator, in particular with a slowly rotating synchronous generator, has been even dismissed as a matter of principle, because that was not required. 
     It has however surprisingly been found that, by the selection of a merely single-stage transmission which entails a clear straightforward change in the transmission ratio it is possible to achieve an increase in efficiency in regard to the generation of electric power. In comparison with conventional wind turbines the rotor blade hub according to the disclosure makes it possible to operate smaller generators at a higher speed of rotation by virtue of the step-up transmission of the single-stage transmission. That means that, in comparison with the conventional installations in a given power class, generators of a smaller and significantly lighter structure can now be used for the same power class in the wind turbine while the advantages of the gear-less drive train are retained. 
     The single-stage transmission is preferably a step-up transmission with a transmission ratio in a range of 1:1.5 to 1:10. 
     Preferably the single-stage transmission is in the form of a planetary transmission having a sun gear, a planetary carrier having a number of planetary gears and a ring gear, wherein the planetary gears are in engagement with the sun gear and the ring gear. In a preferred configuration the sun gear of the planetary transmission is non-rotatably connected to the connecting portion at the drive output side or has said connecting portion. Planetary transmissions have the advantage that they are robust, take up a small amount of space, in particular in the axial direction, and involve more moderate friction losses. A deterioration in the overall level of efficiency in producing electric power by using a planetary transmission is compensated by the increase in power generation by virtue of the higher rotary speed. 
     There are various equally preferred options for driving the main shaft by means of the single-stage transmission. In accordance with a first preferred option the planetary carrier of the planetary transmission is non-rotatably connected to the rotor blade hub at the drive input side. Further preferably the connecting portion is a first connecting portion and the ring gear further has a second connecting portion for non-rotatable connection to a journal of the wind turbine. The journal is preferably used to mount the rotor blade hub in generally known fashion. That affords the advantage that all the forces due to weight and wind loads are guaranteed to be carried in known manner by the journal so that the single-stage transmission and the main shaft have to transmit exclusively the torque from the rotor blade hub to the generator. 
     In an alternative preferred embodiment the connecting portion is a first connecting portion and the planetary carrier has a second connecting portion for non-rotatable connection to a journal of the wind turbine. Further then the ring gear of the planetary transmission is non-rotatably connected to the rotor blade hub at the drive input side. 
     The foregoing considerations relate to a planetary transmission. A single-stage transmission can also be preferably implemented by means of a magnetic transmission. In a further preferred embodiment accordingly the single-stage transmission is in the form of a magnetic transmission which instead of the sun gear has an inner permanent-magnetic ring, instead of the planetary carrier it has a ferromagnetic intermediate ring, and instead of the ring gear it has an outer permanent-magnetic ring. Preferably the inner magnetic ring of the magnetic transmission is non-rotatably connected to the connecting portion at the drive output side. Further preferably the ferromagnetic ring of the magnetic transmission is non-rotatably connected to the rotor blade hub at the drive input side. The connecting portion is preferably a first connecting portion and the outer permanent-magnetic ring has a second connecting portion for non-rotatable connection to the journal of the wind turbine. As an alternative thereto the connecting portion is a first connecting portion and the ferromagnetic ring has a second connecting portion for non-rotatable connection to a journal of the wind turbine. Preferably then the outer permanent-magnetic ring of the magnetic transmission is non-rotatably connected to the rotor blade hub at the drive input side. 
     The invention has been described hereinbefore in relation to a first aspect with reference to the rotor blade hub. Provided is a wind turbine of the kind set forth in the opening part of this specification, in that the rotor blade hub is designed in accordance with one of the above-described preferred embodiments. The generator is particularly preferably a synchronous generator. Further preferably the synchronous generator is in the form of a slowly rotating, multi-pole synchronous generator. Particularly preferably it is a ring generator. 
     The term slowly rotating generator is used to mean a generator which rotates at a speed of revolution of 100 revolutions per minute or less. 
     The term multi-pole generator is used to denote a generator having at least 48, 96 and in particularly at least 192 rotor poles. 
     The term ring generator is used to mean that the magnetically active regions of the rotor and stator, more specifically in particular the lamination assemblies of the stator and rotor, are arranged in an annular region around the air gap separating the stator and rotor. In that respect the generator in an inner region of a radius of at least 50% of the mean air gap radius is free from the magnetically active region. 
     A ring generator can also be defined in that the radial thickness of the magnetically active parts, or, in other words, the magnetically active region, namely the radial thickness from the inner edge of the pole wheel to the outer edge of the stator, or from the inner edge of the stator to the outer edge of the rotor, in the case of an external rotor, is less than the air gap radius, and in particular the radial thickness of the magnetically active region of the generator is less than 30%, in particular less than 25% of the air gap radius. In addition or alternatively ring generators can be defined by specifying that the depth, namely the axial extent of the generator, is less than the air gap radius, and in particular the depth is less than 30%, in particular less than 25% of the air gap radius. 
     In preferred configurations arising out of the foregoing description concerning the first aspect relating to the rotor blade hub the rotor blade hub is torque-transmittingly coupled to the main shaft of the wind turbine by means of a connecting portion, insofar as the rotor blade hub has a single-stage transmission which is non-rotatably mounted to the rotor blade hub at the drive input side and is non-rotatably connected to the main shaft at the drive output side. Preferably the wind turbine has a journal. Further preferably the journal is non-rotatably connected to the planetary carrier or ring gear of the planetary transmission, or non-rotatably connected to the ferromagnetic ring or the outer permanent-magnetic ring of a magnetic transmission. 
     The wind turbine preferably has a machine carrier, wherein the rotor blade hub is arranged on a first side of the machine carrier, the generator is arranged on the opposite second side of the machine carrier, and the main shaft which is preferably a hollow shaft is passed through the machine carrier and is non-rotatably connected to the generator rotor. The oppositely disposed arrangement of the rotor blade hub and the generator compensate for the tilting moments which are exerted by the two units and which act on the machine carrier, whereby overall this permits a further saving in weight by virtue of the use of smaller bearings. 
     In an alternative configuration the wind turbine has a machine carrier and a journal, wherein the generator is mounted in the form of a generator module directly to the machine carrier, the journal is mounted to the generator module or to the machine carrier, and the rotor blade hub is mounted rotatably on the journal. In that case the main shaft is also passed through the journal. This configuration retains the conventional arrangement of generator and rotor blade hub on the same side in relation to the machine carrier. It is considered to be advantageous that it is possible to have recourse to the tried-and-tested mounting concepts in regard to the journal, the rotor blade hub and the mounting of the rotor blade hub. 
     In a further preferred embodiment the single-stage transmission of the rotor blade hub is in the form of an ancillary attachment transmission and is mounted to a side of the rotor blade hub, that is remote from the machine carrier. By virtue of this configuration the single-stage transmission is disposed at the front end of the rotor blade hub. This further facilitates access to the single-stage transmission from the outside in order to maintain it, repair it or replace it. In addition changing the single-stage transmission and replacing it by a single-stage transmission with a different transmission ratio with the generator unchanged for adaptation of the power class of the wind turbine is structurally easier. That leads to a greater number of identical components over various power classes of wind turbines and affords power advantages in regard to costs, production and stock-keeping. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       The invention is described in greater detail hereinafter with reference to the accompanying Figures by means of preferred embodiments by way of example. In the Figures: 
         FIG. 1  shows a diagrammatic perspective view of a wind turbine, 
         FIG. 2  shows a diagrammatic cross-sectional view through a pod of the wind turbine of  FIG. 1  in a first embodiment, and 
         FIG. 3  shows a diagrammatic cross-sectional view through the pod of the wind turbine as shown in  FIG. 1  in a second embodiment. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows a diagrammatic view of a wind turbine  100 . The wind turbine  100  has a pylon  102  and a pod  104  on the pylon  102 . Provided on the pod  104  is an aerodynamic rotor  106  having three rotor blades  108  and a spinner  110 . In operation of the wind turbine  100  the aerodynamic rotor  106  is caused to rotate by the wind and thus also rotates the generator rotor or rotor member  115  ( FIG. 2 ) of a generator  113  ( FIG. 2 ) directly or indirectly coupled to the aerodynamic rotor  106 . The electric generator  113  is disposed in the pod  104  and generates electric power. 
       FIG. 2  shows the internal structure of the pod  104  according to a first embodiment. The rotor blades  108  shown in  FIG. 1  are connected to a rotor blade hub  1 . The rotor blade hub  1  is mounted rotatably on a journal  112 . The rotor blade hub  1  has a single-stage transmission connected to the rotor blade hub  1  by way of a corresponding connection  5 . At the drive output side the single-stage transmission  3  has a connecting portion  7 , at which the single-stage transmission  3  is non-rotatably coupled to a main shaft  111  of the wind turbine  104 . The main shaft  111  constitutes the drive train to the generator  113 . 
     The single-stage transmission  3  has a ring gear  9 . A planetary carrier  11  is moved relative to the ring gear  9  by means of a number of planetary gears  13  which are in engagement with the ring gear. As a result a sun gear  15  of the single-stage transmission  3  which has the connecting portion to the main shaft  111  is driven in a stepped-up ratio. Preferably the ratio of the single-stage transmission is in the range of 1:2.5 to 1:5. 
     The main shaft  111  is passed through the journal  112  and a machine carrier  114  of the wind turbine  100  and non-rotatably connected to the generator rotor  115  of the generator  113 . The generator rotor  115  is driven in rotation relative to a stator  117  by means of the hub  1 , in which case the single-stage transmission  3  brings about a moderate step-up transmission effect and an increase in the rotary speed of the generator rotor  115  relative to the rotor blade hub  1 . 
     In the embodiment shown in  FIG. 2  the generator  113  is arranged in opposite relationship to the rotor blade hub  1 , relative to the machine carrier  114 . The generator  113  is fixed to the machine carrier  114  by means of a first connecting flange  119  while the journal  112  supporting the rotor blade hub  1  is connected to the machine carrier  114  at an oppositely disposed second connecting flange  118 . The machine carrier  114  is connected to the pylon  102 , preferably by means of a rotary connection (not shown). Reference A identifies the axis of rotation of the rotor blade hub  1  and the generator  115 . 
     In the embodiment of  FIG. 2  the single-stage transmission is connected to the main shaft at the sun gear  15  by means of a first connecting portion  7  and the sun gear  9  is non-rotatably connected to the journal  112  by means of a second connecting portion so that the sun gear  9  does not rotate about the axis A. By virtue of the connection at the connection  5  the planetary carrier  11  rotates at the same speed of rotation as the rotor blades connected to the rotor blade hub  1 , about the axis A. A transmission step-up ratio acts on the sun gear  15  by means of the planetary gears  13 . 
       FIG. 3  is structurally similar to the embodiment of  FIG. 2 , in particular in regard to the arrangement of the generator  113  relative to the rotor blade hub  1  on different sides of the machine carrier  114 . What distinguishes the embodiment of  FIG. 3  from the embodiment of  FIG. 2  is the connection of the single-stage transmission  3 . In the  FIG. 3  embodiment the ring gear  9  is connected directly to the rotor blade hub  1  by means of the connecting portion  5  and is synchronized therewith while the planetary carrier  11  is connected to the journal  112  by means of the second connecting portion  17  and is thus fixed. In this variant by way of a rotational movement of the ring gear  9  and a rotational movement of the otherwise stationary planetary gears  13  there is a step-up transmission action on the sun gear  15  which drives the main shaft  111  at an increased speed in comparison with the speed of rotation of the rotor blades  108 . 
     In both embodiments shown in  FIG. 2  and  FIG. 3  the single-stage transmission  3  is arranged in the form of an attachment transmission  10  at the front end on the rotor blade hub  1  and is thus accessible from the end at any time without influencing the rest of the drive train. 
     As was described in detail hereinbefore the use of the single-stage transmission  3 , in particular in its configuration in the form of the attachment transmission  10 , permits uncomplicated adaptation of the respectively required transmission ratio to the installation conditions and the desired power class of the wind turbine  100 , wherein different step-up transmission ratios in conjunction with always the same generator  113  can lead to different power yields. In comparison with a direct drive without transmission smaller generators can be used for the same power class, which affords massive savings in regard to the costs and the weight of the wind turbine  100 , in particular the pod  104 . The assembly costs, in particular in conjunction with the cranes required for that purpose and the assembly time, are also reduced by virtue of using the single-stage transmission  3  as smaller loads have to be conveyed up to the pod  104  of the wind turbine  100 .