Patent Publication Number: US-2013229017-A1

Title: Downwind Rotor Type Wind Power Generation Device

Description:
TECHNICAL FIELD 
     The present invention relates to downwind rotor type wind power generation devices in which a rotor is positioned downwind of a nacelle. 
     CLAIM OF PRIORITY 
     The present application claims priority from Japanese Patent application serial No. 2012-47140, filed on Mar. 2, 2012, the content of which is hereby incorporated by reference into this application. 
     BACKGROUND ART 
     Efforts have been continued to develop so-called wind power generation devices which use wind as an inexhaustible source of energy available in nature and convert the wind energy into electric energy. A wind power generation device is a relatively large structure and the site where it can be installed is limited, so the amount of electricity generated per device is expected to increase so that a smaller number of devices generate as much electricity as desired. In order for a single wind power generation device to generate a larger amount of electricity, its generator and step-up gear must be larger and the heat generated by the generator and step-up gear (energy loss) will increase, so it is necessary to increase the capacity of its cooling unit. 
     As a solution, a technique which uses a fan to send air from the rear portion of a nacelle housing a generator and a step-up gear to its front portion to cool the inside of the nacelle is disclosed (for example, JP-A-2010-116925 (PTL 1)) and also a technique which uses cooling fans located in upper and rear portions of a nacelle is disclosed (for example, JP-A-2008-286115 (PTL 2)). 
     However, when the external air is forced to be taken in by a fan, a fan and power to drive the fan are needed and the reliability and maintainability of the fan must be considered. So, an upwind rotor type wind power generation device in which a radiator (heat exchanger) is located behind the rotor to cool the generator and step-up gear by heat exchange is disclosed (for example, JP-A-2011-112051 (PTL 3)). 
     CITATION LIST 
     Patent Literature 
     
         
         [PTL 1] JP-A-2010-116925 
         [PTL 2] JP-A-2008-286115 
         [PTL 3] JP-A-2011-112051 
       
    
     SUMMARY OF INVENTION 
     Technical Problem 
     The above wind power generation devices described in PTL 1 to 3 are so-called upwind rotor type wind power generation devices in which a rotor is positioned upwind of a nacelle fixed on a tower. In this type of wind power generation devices, in order to expose the heat exchanger to the external air, the heat exchanger must protrude outward from the periphery of the nacelle. However, under the road traffic law, a nacelle with a heat exchanger protruding like this is not permitted to be transported from the factory to the installation site. Therefore, it is necessary to remove the heat exchanger before transportation and attach it again at the installation site, resulting in increased transportation and installation costs. For this reason, in the technique described in PTL 3, the heat exchanger can turn so that at the time of transportation and installation it is retracted from the periphery of the nacelle so as not to protrude from the nacelle. However, this retraction structure requires a large-scale mechanism, which is a contributory factor for a rise in manufacturing cost and a decline in the freedom of nacelle design. 
     In addition, upwind rotor wind type power generation devices have a problem that since the heat exchanger must be located backward of the rotor, the rotor reduces the wind energy and the generator and step-up gear cannot be cooled sufficiently. 
     The present invention has been made in view of the above problem and has an object to provide a downwind rotor type wind power generation device which allows a nacelle to be transported and installed more conveniently without the need for troublesome detachment and reattachment of a heat exchanger and improves the efficiency in cooling a generator. 
     Solution to Problem 
     According to an aspect of the present invention, in order to solve the above problem, there is provided a downwind rotor type wind power generation device which includes a rotor having a hub and a plurality of blades extending radially from the hub, a nacelle having a generator for converting the rotational energy of the rotor into electric energy and a heat exchanger for exchanging heat with heat generated at least by the generator and supporting the rotor rotatably, and a tower supporting the nacelle rotatably around a vertical axis so that the rotor is positioned downwind. The heat exchanger is located on the opposite side of the rotor with respect to the vertical axis in the nacelle so as to be exposed. 
     With the heat exchanger located in the nacelle, external dimensions of the heat exchanger may be within peripheral dimensions of the nacelle. 
     The downwind rotor type wind power generation device may further include a front cover located on the opposite side of the rotor with respect to the vertical axis and over the heat exchanger to prevent light from entering the heat exchanger from above. 
     The downwind rotor type wind power generation device may further include a side cover which is located on the opposite side of the rotor with respect to the heat exchanger and extends in the axial direction of the rotor. 
     The downwind rotor type wind power generation device may further include a lifting device which is located over the heat exchanger and can lift and lower the heat exchanger. 
     Advantageous Effects of Invention 
     According to the present invention, the nacelle can be transported and installed more conveniently without the need for troublesome detachment and reattachment of the heat exchanger and the efficiency in cooling the generator can be improved. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is an external view showing an appearance of a downwind rotor type wind power generation device; 
         FIG. 2  is a functional block diagram illustrating the general functionality of the downwind rotor type wind power generation device; 
         FIG. 3  is a perspective view of a nacelle as seen from below; 
         FIG. 4  is a perspective view of the nacelle as seen from below; 
         FIGS. 5A and 5B  are bottom views illustrating how the side covers work, in which  FIG. 5A  shows the side covers turned so as to decrease the area of an opening and  FIG. 5B  shows the side covers turned so as to increase the area of the opening; 
         FIG. 6  illustrates the location and position of the heat exchanger; and 
         FIG. 7  is a graph which explains the rotation speed of an impeller. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Next, the preferred embodiment of the present invention will be described in detail referring to the accompanying drawings. The dimensions, materials, specific numerical values and other details given below in the description of the preferred embodiment are just illustrative examples for the better understanding of the invention and do not limit the invention. In this specification and the drawings, elements with virtually identical functions or structures are designated by like reference numerals and repeated descriptions of such elements are omitted. Also, elements which are not directly associated with the present invention are omitted in the drawings. 
     (Downwind Rotor Type Wind Power Generation Device  100 ) 
       FIG. 1  is an external view showing an appearance of a downwind rotor type wind power generation device  100  and FIG.  2  is a functional block diagram illustrating the general functionality of the downwind rotor type wind power generation device  100 . Hereinafter the terms “frontward” and “backward” (as shown in  FIG. 2 ) are sometimes used in the explanation of positional relationship of components of the downwind rotor type wind power generation device  100 . Since the downwind rotor type wind power generation device  100  is so designed that its tip portion is oriented upwind, it may be thought that “frontward” corresponds to upwind and “backward” corresponds to downwind. 
     As shown in  FIG. 1 , the downwind rotor type wind power generation device  100  includes a rotor  102 , a nacelle  104 , and a tower  106 . 
     As shown in  FIG. 2 , the rotor  102  includes a hub  112 , a plurality of blades  114  extending radially from the hub  112 , and a rotor shaft  116  coupled to the hub  112 , extending perpendicularly to a plane formed by the blades  114 . As the wind hits the blades  114 , due to its lift force the rotor  102  rotates around the rotor shaft  116 . 
     The nacelle  104  includes a nacelle frame  120 , a step-up gear  122 , a generator  124 , and a control board  126 . The nacelle frame  120  includes a platform or structure to bear the weight load on the nacelle  104 . The step-up gear  122  and the generator  124  are supported by the platform or structure of the nacelle frame  120 . The step-up gear  122  is pivotally supports the rotor shaft  116  and increases the rotation speed of the rotor shaft  116  to rotate another rotating shaft  122   a . The step-up gear  122  and nacelle frame  120  rotatably support the rotor  102  in this way. The generator  124  is coupled to the rotating shaft  122   a  whose speed is increased by the step-up gear  122 , so that the rotational energy of the rotor  102  is converted into electric energy. The control board  126  performs pitch control of the rotor  102  and electric power control of the generator  124 . 
     In the process that the downwind rotor type wind power generation device  100  converts the wind energy into electric energy, heat is generated by energy loss of the generator  124  and step-up gear  122 . In recent years, as the demand for increase in the amount of electricity generated has been growing, the amount of heat generated in the electricity generation process has been increasing. For this reason, a cooling unit  130  is required in order to prevent the electricity generating efficiency from declining due to heat generation. 
     In the cooling unit  130 , refrigerant (gas or liquid) is pressurized by a circulating pump  132  and introduced into the generator  124  and step-up gear  122  to collect the heat generated by the generator  124  and step-up gear  122  before being conveyed to a heat exchanger  134  such as a radiator. In the heat exchanger  134 , heat exchange between the hot refrigerant and the external air takes place and the refrigerant cooled by heat exchange is returned to the circulating pump  132 . This circulation of refrigerant cools the generator  124  and step-up gear  122 . 
     The cooling unit  130  includes an impeller  136 , a step-up gear  138 , and a cooling fan  140 . The impeller  136  is rotatably supported by the nacelle  104 . The step-up gear  138  increases the rotation speed of the impeller  136  to rotate another rotating shaft and directly drives the circulating pump  132  (gives pressure directly to the refrigerant by rotational energy). The cooling fan  140  is fixed on the rotating shaft of the impeller  136  or step-up gear  138  and rotates in a way to follow the rotation of the impeller  136  to stir the air inside the nacelle  104  and homogenize the atmospheric temperature in the nacelle  104 . The cooling unit  130  will be described in more detail later. 
     A vane anemometer  152  which measures the direction and speed of the wind received by the downwind rotor type wind power generation device  100  is provided on a nacelle cover  150  which serves as an exterior of the nacelle  104 . 
     The tower  106  is coupled virtually to the center of gravity of the rotor  102  and nacelle  104  and supports the nacelle  104  rotatably around a vertical axis  160 . The rotor  102  is coupled to the nacelle  104  and as the blades  114  of the rotor  102  receive the wind, the nacelle  104  turns so that the rotor  102  is positioned downwind of the tower  106 . Thus, in the downwind rotor type wind power generation device  100 , the wind energy is utilized to make the virtual plane formed by the blades  114  of the rotor  102  perpendicular to the direction in which the wind flows so that the wind energy can be captured efficiently. 
     (Cooling Unit  130 ) 
       FIG. 3  is a perspective view of the nacelle  104  as seen from below. The heat exchanger  134  is located on the opposite side of the rotor  102  (front portion of the nacelle  104 ) with respect to the vertical axis  160  and in a lower portion of the nacelle  104  and exposed to the external air. In this embodiment, the heat exchanger  134  is inclined so that a lower portion thereof has a shorter distance from the vertical axis  160 . However the way the heat exchanger  134  is positioned in relation to the nacelle  104  is not limited thereto and it may be positioned vertically upright or in other various ways. 
     For not only the downwind rotor type wind power generation device  100  but also other types of wind power generation devices, it is desirable to use large blades  114  in order to capture the wind energy efficiently, which means that the external dimensions of the nacelle  104  should be large enough. For example, if the external dimensions of the nacelle  104  are close to the size limit for transportation under the road traffic law (for example, 4.5 m in height×4.5 m in width), the size limit would be exceeded by a protruding body attached to the periphery to the nacelle  104 . In that case, it is necessary to once detach the heat exchanger as a protruding body from the nacelle after operation check of the nacelle and reattach it at the installation site of the wind power generation device. In particular, since the heat exchanger  134  is required to exchange heat with the external air directly, it must be exposed to the external air outside the nacelle  104 , but if it is simply reattached to the periphery of the nacelle  104 , transportation and installation costs would rise. In addition, its reattachment at the installation site might cause quality deterioration. 
     In this embodiment, the heat exchanger  134  is located on the upwind side tip of the nacelle  104 , taking advantage of the special feature of the downwind rotor type wind power generation device  100  that the rotor  102  is located on the downwind side. When the heat exchanger  134  is located on the upwind side tip of the nacelle  104  in this way, the external dimensions of the heat exchanger  134  is within the peripheral dimensions of the nacelle  104  and the dimensions (width and height) of the periphery of the nacelle  104  (in the circumferential direction of the rotor shaft  116 ) remain unchanged regardless of whether or not the heat exchanger  134  is attached. In other words, the peripheral dimensions of the nacelle  104  are kept within the legal size limit even when the heat exchanger  134  is not detached. Therefore, the nacelle  104  can be transported with the heat exchanger  134  attached thereto and there is no need for detachment and reattachment of the heat exchanger  134  at the time of transportation and installation. This resolves the problems of increased installation cost and quality deterioration. 
     Furthermore, in an upwind rotor type wind power generation device, even if a heat exchanger is used, the heat exchanger must be positioned downwind of the rotor and due to interference by the rotor, it can only receive, for example, about 50% of the wind energy received by the rotor, so it cannot provide sufficient cooling efficiency. By contrast, in the downwind rotor wind type power generation device  100 , the heat exchanger  134  receives the wind energy on the most upwind side of the nacelle  104 , so the wind energy is not attenuated and a higher cooling efficiency is achieved. 
     The heat exchanger  134 , exposed from the nacelle  104 , passively receives the external air and does not require a means to take in the external air forcedly, such as a fan, thereby contributing to cost reduction, decrease in the number of components, and improvement in design freedom. 
     In the above structure, the rotor  102  is positioned downwind of the heat exchanger  134 . However, as mentioned above, the heat exchanger  134  does not protrude from the periphery of the nacelle  104  and the wind energy which the rotor  102  receives is not attenuated. Even if the wind energy is attenuated by the heat exchanger  134 , the point at which the wind force is applied is outside the rotation of the blades  114 , so the amount of wind energy in the rotation center scarcely affects the amount of electricity generated. For this reason, there is no problem with the structure in which the rotor  102  is positioned downwind of the heat exchanger  134 . 
     (Front Cover  150   a ) 
     In an upwind rotor type wind power generation device, the heat exchanger must be located over the nacelle and in a fine weather it is easily affected by the sunlight and due to the sunlight heat it cannot provide sufficient cooling efficiency. On the other hand, in the downwind rotor type wind power generation device  100 , as shown in  FIG. 3 , a front cover  150   a  as a constituent part of the nacelle cover  150  is located in a forward position of the nacelle  104  (on the opposite side of the rotor  102  with respect to the vertical axis  160 ) and over the heat exchanger  134  to prevent the sunlight from entering the heat exchanger  134  from above. Therefore, the heat exchanger  134  can efficiently receive the wind from forward of the nacelle  104  and provide a higher cooling efficiency while avoiding the influence of the sunlight from above. 
     Generally in wind power generation devices, a vane anemometer is provided to ensure that electricity is stably generated with high efficiency. In order to detect the direction of the wind and its speed accurately, it is desirable that the vane anemometer be located on the periphery of the nacelle  104  and over the nacelle  104 . However, when the heat exchanger  134  is provided simply on the upwind side of the nacelle  104 , the heat exchanger  134  might make the wind flow over the nacelle  104  turbulent at the tip portion of the nacelle  104 . In this embodiment, the front cover  150   a  has a curved surface whose curvature radius changes gradually, so that the wind from forward is rectified and disturbance in the direction and speed of the wind over the tip portion of the nacelle  104  is minimized. As a consequence, the vane anemometer  152  can ensure high accuracy in measurement. 
     (Side Covers  150   b ) 
       FIG. 4  is a perspective view of the nacelle  104  as seen from below and  FIGS. 5A and 5B  are bottom views illustrating how side covers  150   b  work. In this embodiment, the side covers  150   b  extending in the direction of the rotor shaft  116  may be provided in a lower part of the tip portion of the nacelle  104  (on the opposite side of the rotor with respect to the heat exchanger  134 ) and upwind of the heat exchanger  134 . Each of these side covers  150   b  is fixed on the nacelle  104  or attached rotatably around a vertically extending rotation axis  150   c  to regulate the air volume. 
     For example, if the force of wind is too strong, the side covers  150   b  are turned around the rotation axes  150   c  as shown in  FIG. 5A  so as to decrease the area of the upwind side opening and produce a reducer effect to decrease the speed of the wind received by the heat exchanger  134  and alleviate the wind load on the heat exchanger  134  in the strong wind. 
     Conversely, the side covers  150   b  are turned around the rotation axes  150   c  as shown in  FIG. 5B  to increase the area of the upwind side opening so that the wind forward of the nacelle  104  is collected as indicated by arrows in  FIG. 5B  and the introduced air is led into the heat exchanger  134  without leakage. Therefore, even in a weak wind, the heat exchanger  134  can provide a higher cooling efficiency. 
     (Nacelle Frame  120 ) 
       FIG. 6  illustrates the location and position of the heat exchanger  134 . As shown in  FIG. 6 , the nacelle frame  120  is located inside the nacelle  104 . In this embodiment, the heat exchanger  134  is fixed on the nacelle frame  120  directly or indirectly through a bracket or the like so that the heat exchanger  134  is supported firmly. 
     (Lifting Device  170 ) 
     The heat exchanger  134  is connected to various circuits of the cooling unit  130  such as the circulating pump  132  through joints and can be detached for maintenance or replacement of the heat exchanger  134 . As shown in  FIG. 6 , a lifting device  170  which can lift and lower the heat exchanger  134  while supporting it in a tensioned state is provided over the heat exchanger  134  inside the nacelle  104 , so that the heat exchanger  134  can be vertically lifted or lowered directly without being moved horizontally from the tip portion of the nacelle  104 . 
     (Impeller  136 ) 
     In the cooling unit  130 , the circulating pump  132  circulates the refrigerant between the generator  124  and step-up gear  122  and the heat exchanger  134 . A large amount of electricity is required to drive the circulating pump  132 . In this embodiment, electricity is not supplied to the circulating pump  132  and instead the circulating pump  132  is driven directly by the torque of the impeller  136 . 
     In this embodiment, the impeller  136  is located at a lower part of the tip portion of the nacelle  104  and downwind of the heat exchanger  134  as shown in  FIG. 3 . Like the heat exchanger  134 , the impeller  136  is located at the tip portion of the nacelle  104  so that it can directly receive the wind energy not attenuated and thus the circulation efficiency of the circulating pump  132  (cooling efficiency of the cooling unit  130 ) can be improved. 
     Since the nacelle frame  120  is located in a lower portion of the nacelle  104  as shown in  FIG. 6 , the impeller  136  can be supported rotatably without the need for a special fixing member. This means that the nacelle  104  can be constructed at low cost and light in weight. It may be possible that the impeller  136  is located not at the lower portion of the nacelle  104  but at a lateral side of it, but if that is the case, depending on the orientation (rotation angle) of the nacelle  104 , the lateral side of the nacelle  104  would become an obstacle and the air volume (force of wind) which the impeller  136  receives would vary. If the impeller  136  is located at a upper portion of the nacelle  104 , it might make the wind flow over the nacelle  104  turbulent, resulting in deterioration in the measuring accuracy of the vane anemometer  152 . If the impeller  136  is located downwind of the vane anemometer  152 , the wind energy would be attenuated by interference by the vane anemometer  152  and sufficient cooling efficiency might not be achieved. Therefore, it is desirable that the impeller  136  be located at a lower portion of the nacelle  104 . 
       FIG. 7  is a graph which explains the rotation speed of the impeller  136 . This embodiment uses a drag type impeller  136 . It is known that when the drag type impeller  136  is used, the rotation speed  210  relative to the wind energy is somewhat higher than the rotation speed  212  of a lift type impeller while the wind energy is small. This means that even when the wind is weak, the circulating pump  132  can be driven and a desired cooling capacity can be obtained. 
     When the rotor  102  is rotating at high speed (high load), namely when the wind is strong, the impeller  136  is also rotating at high speed, so the circulation efficiency of the circulating pump  132  is higher and the generator  124  and step-up gear  122  are cooled at a higher cooling efficiency. Therefore, in this embodiment, the cooling efficiency varies according to the amount of electricity generated by the downwind rotor type wind power generation device  100 , so the cooling unit  130  works effectively without a special cooling control means. Also the cooling fan  140  rotates in a way to follow the rotation of the impeller  136 , so the air inside the nacelle  104  can be properly stirred according to the amount of electricity generated by the downwind rotor type wind power generation device  100 . 
     Furthermore, in its principle the drag type impeller  136  cannot attain a higher rotation speed than the wind speed. As shown in  FIG. 7 , after the wind energy exceeds a given level, the rotation speed does not increase in a similar pattern. Taking advantage of the drag type impeller&#39;s feature that the rotation speed cannot be high even when the wind energy is high, this embodiment prevents an excessive load from being applied to the impeller  136  even in a strong wind such as a typhoon and ensures safety without a special means to suppress the rotation speed and drives the circulating pump  132  stably. 
     In order to use the drag type impeller  136 , this embodiment adopts a vertical-axis wind turbine (Savonius or cross-flow type) in which the rotating shaft of the impeller is perpendicular to the direction of the wind. Here, the rotating shaft of the impeller  136  is disposed on a horizontal plane of the nacelle  104  along the width direction of the nacelle  104 . Therefore, the rotating shaft of the impeller  136  is orthogonal to the rotor shaft  116 . 
     Generally, if the impeller  136  whose rotating shaft is perpendicular to the direction of the wind as in a vertical-axis wind turbine is located with its rotating shaft horizontal, the vertical-axis wind turbine&#39;s advantage that it does not depend on the direction of the wind would be lost. However, in the downwind rotor type wind power generation device  100 , as the blades  114  of the rotor  102  receives the wind, the rotor  102  turns in a way that it is positioned downwind of the tower  106  and thus the nacelle  104  copes with change in the direction of the wind so that sufficient wind energy is supplied to the impeller  136 . 
     In this embodiment, since the rotating shaft of the impeller  136  is disposed along the width direction of the nacelle  104  horizontally, both ends of the rotating shaft can be supported rotatably by the nacelle frame  120  as shown in  FIG. 6 . Therefore, the impeller  136  can be securely fixed and the cooling unit  130  can ensure high reliability and high stability. 
     When the ends of the rotating shaft of the impeller  136  are supported as mentioned above, the upper half of the impeller  136  is covered by the nacelle cover  150 . In this case, when the impeller  136  rotates, the upper half of the impeller  136  does not receive the wind while turning back toward the upwind direction. In other words, the wind hits only the impeller portion whose rotation direction is the same as the direction of the wind and does not hit the impeller portion whose rotation direction is reverse to the direction of the wind. This contributes to improvement in cooling efficiency. 
     In this embodiment, since the heat exchanger  134  is positioned in an inclined state as shown in  FIG. 3 , the wind is easily led to the impeller  136  and the cooling efficiency is improved. 
     According to the downwind rotor type wind power generation device  100  as mentioned above, the nacelle  104  can be transported and installed conveniently without the need for troublesome detachment and reattachment of the heat exchanger  134  and also the efficiency in cooling the generator  124  and step-up gear  122  can be improved. 
     Furthermore, the cooling unit  130  saves the electricity to drive the circulating pump  132  for circulating the refrigerant and properly cools the generator  124  and step-up gear  122  at a cooling efficiency depending on the amount of electricity generated by the downwind rotor type wind power generation device  100 . 
     So far the preferred embodiment of the present embodiment has been described referring to the accompanying drawings, but obviously the invention is not limited thereto. It is apparent that a person skilled in the art can conceive of various changes and modifications thereto within the scope of the appended claims and such changes and modifications are interpreted to fall within the technical scope of the present invention. 
     For example, although the impeller  136  includes the step-up gear  138  in the above embodiment, the invention is not limited thereto. The step-up gear  138  can be omitted. 
     Furthermore, the above embodiment includes the step-up gear  122  but the invention is not limited thereto. Another embodiment of the invention may not include the step-up gear  122 , or may include a hydraulic gearbox instead of the step-up gear  122 , or may include both the step-up gear  122  and a hydraulic gearbox. 
     INDUSTRIAL APPLICABILITY 
     The present invention can be applied to a downwind rotor wind power generation device in which a rotor is positioned downwind of a nacelle. 
     REFERENCE SIGNS LIST 
     
         
           100  . . . Downwind rotor type wind power generation device 
           102  . . . Rotor 
           104  . . . Nacelle 
           106  . . . Tower 
           112  . . . Hub 
           114  . . . Blade 
           116  . . . Rotor shaft 
           120  . . . Nacelle frame 
           122  . . . Step-up gear 
           124  . . . Generator 
           134  . . . Heat exchanger 
           136  . . . Impeller 
           138  . . . Step-up gear 
           140  . . . Cooling fan 
           150  . . . Nacelle cover 
           150   a  . . . Front cover 
           150   b  . . . Side cover 
           170  . . . Lifting device