Abstract:
A cooling system and method for a wind power generator and a wind power generator set. The cooling system for a wind power generator includes air extraction pipelines and air discharge devices. The air extraction pipelines are located inside a generator case. A pipeline inlet in communication with a generator, a first pipeline outlet in communication with the outside of the generator case, and a second pipeline outlet in communication with the inside of the generator case are arranged on the air extraction pipelines, and the first and second pipeline outlets are provided with air doors. Therefore, the cooling efficiency of the generator set in a high temperature environment is enhanced, and the temperature of the generator case is kept in a low temperature environment. The cost is lowered and the consumed energy is reduced.

Description:
FIELD 
       [0001]    The present application relates to the field of wind power technology, and more particularly to a system and a method for cooling wind turbine generators, and a wind turbine generator system. 
       BACKGROUND 
       [0002]      FIG. 1  is a schematic view showing the structure of a wind turbine generator system in the conventional technology. As shown in  FIG. 1 , the wind turbine generator system includes a nacelle  11 , a generator  12 , a cooling device  13 , an air extraction pipe  14 , a base  15 , a tower  16 , a hub  17  and a blade  18 . The cooling device  13 , the air extraction pipe  14  and the base  15  are arranged in the nacelle  11 . The nacelle  11  is arranged on the tower  16  via the base  15 , and the tower  16  is used to support the nacelle  11 . The blade  18  is connected to the generator  12  via the hub  17 , and the blade  18  rotates to drive a rotor shaft of the generator  12  to rotate to produce electricity. The generator  12  is a major energy conversion component of the wind turbine generator system, but also a major heat generating component, that is, the generator  12  generates heat during operation. To ensure the normal operation of the generator  12 , a cooling system is required to cool the generator  12 . As shown in  FIG. 1 , the cooling device  13  and the air extraction pipe  14  are used to cool the generator  12 . The air extraction pipe  14  has one end connected to the generator  12  and another end connected to the cooling device  13 , and the air extraction pipe  14  is used to extract hot air generated by the generator  12  during operation and convey the hot air into the cooling device  13 . The hot air is cooled by external air flow flowing in a cooling air flow passage  19  arranged in the cooling device  13 , and the cooling device  13  conveys the obtained cold air back to the generator  12  to cool the generator  12 . The conventional cooling system for a wind turbine generator system is an air-air heat exchange system. 
         [0003]    When the wind turbine generator system is in a high-temperature environment, a temperature difference between the ambient temperature and the generator temperature is small, which leads to a poor cooling effect of the external air flow in the cooling air flow passage on the hot air generated by the generator, thereby reducing the cooling efficiency of the generator. 
         [0004]    When the wind turbine generator system is in a low-temperature environment, the temperature difference between the ambient temperature and the generator temperature is large, thus the system for cooling the wind turbine generator system may stop, and the hot air generated by the generator may dissipate into the environment due to the large temperature difference, thereby cooling the generator. In this case, if the wind turbine generator system stops, the temperature in the nacelle will be close to the ambient temperature, and before restarting the wind turbine generator system, the temperature in the nacelle needs to be raised to the normal operating temperature for various parts and components and electrical elements. Generally, to make the temperature in the nacelle reach the operating temperature for various components, multiple independent heating devices need to be provided for parts and components of the wind turbine generator system, which will increase the cost and energy consumption. 
       SUMMARY 
       [0005]    A system and a method for cooling wind turbine generators, and a wind turbine generator system are provided according to the present application to improve the cooling efficiency of the generator in a case that the wind turbine generator system is in a high-temperature environment and reduce the cost and energy consumption in a case that the wind turbine generator is in a low-temperature environment. 
         [0006]    To realize the above objects, a system for cooling wind turbine generators is provided according to the present application, which includes an air extraction pipe and an air exhaust device, wherein the air extraction pipe is located in a nacelle and is provided with a pipe inlet, a first pipe outlet and a second pipe outlet, the pipe inlet is in communication with a generator, the first pipe outlet is provided with a first pipe air damper, and the second pipe outlet is provided with a second pipe air damper; 
         [0007]    in a case that a temperature of the generator is higher than a first set temperature and a temperature of the nacelle is higher than a second set temperature, the first pipe air damper is configured to be opened to communicate the first pipe outlet with an outside of the nacelle; 
         [0008]    in a case that the temperature of the nacelle is lower than or equal to the second set temperature, the second pipe air damper is configured to be opened to communicate the second pipe outlet with an inside of the nacelle; and 
         [0009]    in a case that the temperature of the generator is higher than the first set temperature and the temperature of the nacelle is higher than the second set temperature, the air exhaust device is configured to extract hot air generated by the generator into the air extraction pipe through the pipe inlet and exhaust the hot air to the outside of the nacelle through the first pipe outlet; and in a case that the temperature of the nacelle is lower than or equal to the second set temperature, the air exhaust device is configured to extract the hot air generated by the generator into the air extraction pipe through the pipe inlet and exhaust the hot air to the inside of the nacelle through the second pipe outlet. 
         [0010]    Further, the air extraction pipe includes a main pipe and a branch pipe, one end of the main pipe is the pipe inlet and another end of the main pipe is the first pipe outlet, and one end of the branch pipe is in communication with the main pipe and another end of the branch pipe is the second pipe outlet. 
         [0011]    Further, the air exhaust device includes a first air exhaust unit and a second air exhaust unit, the first air exhaust unit is located near the first pipe outlet in the air extraction pipe, and the second air exhaust unit is located near the second pipe outlet in the air extraction pipe; 
         [0012]    in a case that the temperature of the generator is higher than the first set temperature and the temperature of the nacelle is higher than the second set temperature, the first air exhaust unit is configured to extract the hot air generated by the generator into the air extraction pipe through the pipe inlet and exhaust the hot air to the outside of the nacelle through the first pipe outlet; and 
         [0013]    in a case that the temperature of the nacelle is lower than or equal to the second set temperature, the second air exhaust unit is configured to extract the hot air generated by the generator into the air extraction pipe through the pipe inlet and exhaust the hot air to the inside of the nacelle through the second pipe outlet. 
         [0014]    Further, a rotational frequency of the first air exhaust unit is adjustable according to the temperature of the generator, and a rotational frequency of the second air exhaust unit is adjustable according to the temperature of the nacelle. 
         [0015]    Further, the main pipe includes a first pipe segment and a second pipe segment, the first pipe segment is starting from an intersection of the main pipe and the branch pipe to the first pipe outlet, the second pipe segment is starting from the intersection of the main pipe and the branch pipe to the pipe inlet, and the air exhaust device is located in the second pipe segment. 
         [0016]    To realize the above objects, a wind turbine generator system is provided according to the present application, which includes a generator, a nacelle, a hub, blades and a system for cooling a wind turbine generator. The blades are connected to the generator through the hub. 
         [0017]    Further, the wind turbine generator system includes a heating device arranged on the air extraction pipe; and 
         [0018]    the heating device is configured to heat the nacelle. 
         [0019]    Further, the wind turbine generator system includes a base and a tower, the base is arranged in the nacelle, the nacelle is arranged on the tower via the base, and the tower is configured to support the nacelle. 
         [0020]    Further, a sealing cover is arranged above the base, the sealing cover is mounted on the base via a sealing gasket and is provided with an air filter apparatus, and the air filter apparatus is configured to filter air entering the nacelle from the tower. 
         [0021]    To realize the above objects, a method for cooling wind turbine generators is provided according to the present application based on the system for cooling wind turbine generators, wherein the system for cooling wind turbine generators includes an air extraction pipe and an air exhaust device, the air extraction pipe is located in a nacelle and is provided with a pipe inlet, a first pipe outlet and a second pipe outlet, the pipe inlet is in communication with a generator, the first pipe outlet is provided with a first pipe air damper, and the second pipe outlet is provided with a second pipe air damper; 
         [0022]    the method includes: 
         [0023]    monitoring a temperature of the generator and a temperature of the nacelle; 
         [0024]    in a case that the temperature of the generator is higher than a first set temperature and the temperature of the nacelle is higher than a second set temperature, opening the first pipe air damper to communicate the first pipe outlet with an outside of the nacelle; and extracting, by the air exhaust device, hot air generated by the generator into the air extraction pipe through the pipe inlet and exhausting, by the air exhaust device, the hot air to the outside of the nacelle through the first pipe outlet; and 
         [0025]    in a case that the temperature of the nacelle is lower than or equal to the second set temperature, opening the second pipe air damper to communicate the second pipe outlet with an inside of the nacelle; and extracting, by the air exhaust device, hot air generated by the generator into the air extraction pipe through the pipe inlet and exhausting, by the air exhaust device, the hot air to the inside of the nacelle through the second pipe outlet. 
         [0026]    The present application has the following advantageous effects: 
         [0027]    In the technical solutions of the system and method for cooling wind turbine generators and the wind turbine generator system provided in the present application, in a case that the temperature of the generator is higher than the first set temperature and the temperature of the nacelle is higher than the second set temperature, the first pipe air damper is opened, and the air exhaust device extracts the hot air generated by the generator into the air extraction pipe through the pipe inlet and exhausts the hot air to the outside of the nacelle through the first pipe outlet, thereby improving the cooling efficiency of the generator when the wind turbine generator system is in a high-temperature environment. In a case that the temperature of the nacelle is lower than or equal to the second set temperature, the second pipe air damper is opened, and the air exhaust device extracts the hot air generated by the generator into the air extraction pipe through the pipe inlet and exhausts the hot air to the inside of the nacelle through the second pipe outlet, so as to raise the temperature in the nacelle to a set temperature or keeping the temperature in the nacelle at the set temperature when the wind turbine generator system is in a low-temperature environment, thereby avoiding the need for providing multiple independent heating devices for parts and components of the wind turbine generator system, and reducing the cost and energy consumption. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0028]      FIG. 1  is a schematic view showing the structure of a wind turbine generator system in the conventional technology; 
           [0029]      FIG. 2  is a schematic view showing the structure of a system for cooling wind turbine generators according to a first embodiment of the present application; 
           [0030]      FIG. 3  is an operation schematic diagram of the system for cooling wind turbine generators in the first embodiment; 
           [0031]      FIG. 4  is another operation schematic diagram of the system for cooling wind turbine generators in the first embodiment; 
           [0032]      FIG. 5  is a schematic view showing the structure of a system for cooling wind turbine generators according to a second embodiment of the present application; 
           [0033]      FIG. 6  is a schematic view showing the structure of a wind turbine generator system according to a third embodiment of the present application; 
           [0034]      FIG. 7  is an operation schematic diagram of a system for cooling wind turbine generators in the third embodiment; and 
           [0035]      FIG. 8  is another operation schematic diagram of the system for cooling wind turbine generators in the third embodiment. 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0036]    To make the person skilled in the art better understand the technical solutions of the present application, a system and a method for cooling wind turbine generators and a wind turbine generator system provided in the present application will be described in detail in conjunction with the accompanying drawings. 
         [0037]      FIG. 2  is a schematic view showing the structure of a system for cooling wind turbine generators according to a first embodiment of the present application. As shown in  FIG. 2 , the system for cooling wind turbine generators includes an air extraction pipe and an air exhaust device. The air extraction pipe is located in a nacelle, and is provided with a pipe inlet  21 , a first pipe outlet  22  and a second pipe outlet  23 . The pipe inlet  21  is in communication with a generator, the first pipe outlet  22  is provided with a first pipe air damper  24 , and the second pipe outlet  23  is provided with a second pipe air damper  25 . In a case that a temperature of the generator is higher than a first set temperature and a temperature of the nacelle is higher than a second set temperature, the first pipe air damper  24  is opened to communicate the first pipe outlet  22  with the outside of the nacelle. In a case that the temperature of the nacelle is lower than or equal to the second set temperature, the second pipe air damper  25  is opened to communicate the second pipe outlet  23  with the inside of the nacelle. In a case that the temperature of the generator is higher than the first set temperature and the temperature of the nacelle is higher than the second set temperature, the air exhaust device extracts hot air generated by the generator into the air extraction pipe through the pipe inlet  21  and exhausts the hot air to the outside of the nacelle through the first pipe outlet  22 ; and in a case that the temperature of the nacelle is lower than or equal to the second set temperature, the air exhaust device extracts the hot air generated by the generator into the air extraction pipe through the pipe inlet  21  and exhausts the hot air to the inside of the nacelle through the second pipe outlet  23 . 
         [0038]    In this embodiment, the air extraction pipe includes a main pipe  28  and a branch pipe  29 . The main pipe  28  has one end functioning as the pipe inlet  21  and another end functioning as the first pipe outlet  22 . The branch pipe  29  has one end in communication with the main pipe  28  and another end functioning as the second pipe outlet  23 . In practical application, the air extraction pipe may be in other structures which are not detailed here. 
         [0039]    In this embodiment, the air exhaust device may further include a first air exhaust unit  26  and a second air exhaust unit  27 . The first air exhaust unit  26  is located near the first pipe outlet  22  in the air extraction pipe, and the second air exhaust unit  27  is located near the second pipe outlet  23  in the air extraction pipe. In a case that the temperature of the generator is higher than the first set temperature and the temperature of the nacelle is higher than the second set temperature, the first air exhaust unit  26  is used to extract the hot air generated by the generator into the air extraction pipe through the pipe inlet  21  and exhaust the hot air to the outside of the nacelle through the first pipe outlet  22 . In a case that the temperature of the nacelle is lower than or equal to the second set temperature, the second air exhaust unit  27  is used to extract the hot air generated by the generator into the air extraction pipe through the pipe inlet  21  and exhaust the hot air to the inside of the nacelle through the second pipe outlet  23 . In this embodiment, one or more of the first air exhaust units  26  may be provided, and one or more of the second air exhaust units  27  may be provided. The first air exhaust unit  26  and the second air exhaust unit  27  may each be an exhaust fan. 
         [0040]    In this embodiment, a temperature sensor may be used to monitor the temperature of the generator and the temperature of the nacelle. A central processing unit of the wind turbine generator system may be used to open or close the first air exhaust unit  26  and the first pipe air damper  24 , or open or close the second air exhaust unit  27  and the second pipe air damper  25 . 
         [0041]    The operating principles of the system for cooling wind turbine generators in this embodiment will be described in detail in conjunction with  FIGS. 3 and 4 . 
         [0042]      FIG. 3  is an operation schematic diagram of the system for cooling wind turbine generators in the first embodiment. As shown in  FIG. 3 , after the generator  31  is started, in a case that the temperature of the generator  31  is higher than the first set temperature and the temperature of the nacelle  30  is higher than the second set temperature, the first air exhaust unit  26  is started and the first pipe air damper  24  is opened, thus the first pipe outlet  22  is communicated with the outside of the nacelle  30 . The first air exhaust unit  26  extracts the hot air generated by the generator  31  into the air extraction pipe through the pipe inlet  21  and exhausts the hot air to the outside of the nacelle  30  through the first pipe outlet  22 . At this time, the second air exhaust unit  27  is shut and the second pipe air damper  25  is closed. A rotational frequency of the first air exhaust unit  26  may be adjusted according to the temperature of the generator  31 , so as to realize an object of controlling the flow rate of the hot air according to the temperature of the generator  31 , thus two objects of improving the cooling efficiency of the generator  31  and reducing the energy consumption of the first air exhaust unit  26  may be balanced. In detail, when the temperature of the generator  31  rises, the rotational frequency of the first air exhaust unit  26  is increased to speed up the flow rate of the hot air, so as to exhaust the hot air faster to the outside of the nacelle  30  through the first pipe outlet  22 , thereby improving the cooling effect of the generator  31 . When the temperature of the generator  31  drops, the rotational frequency of the first air exhaust unit  26  is decreased to slow down the flow rate of the hot air, thereby reducing the energy consumption of the first air exhaust unit  26  during operation while ensuring the cooling effect of the generator  31 .  FIG. 3  may be an operating status of the system for cooling wind turbine generators when the wind turbine generator system is in a high-temperature environment. 
         [0043]      FIG. 4  is another operation schematic diagram of the system for cooling wind turbine generators in the first embodiment. As shown in  FIG. 4 , after the generator  31  is started, in a case that the temperature of the nacelle  30  is lower than or equal to the second set temperature, the second air exhaust unit  27  is started and the second pipe air damper  25  is opened, thus the second pipe outlet  23  is communicated with the inside of the nacelle  30 . The second air exhaust unit  27  extracts the hot air generated by the generator  31  into the air extraction pipe through the pipe inlet  21  and exhausts the hot air to the inside of the nacelle  30  through the second pipe outlet  23 , which raises the temperature in the nacelle  30 , thereby realizing the heat preservation of the nacelle  30 . At this time, the first air exhaust unit  26  is shut and the first pipe air damper  24  is closed. A rotational frequency of the second air exhaust unit  27  may be adjusted according to the temperature of the nacelle  30 , so as to realize an object of controlling the flow rate of the hot air according to the temperature of the nacelle  30 , thus two objects of ensuring the heat preservation of the nacelle  30  and reducing the energy consumption of the second air exhaust unit  27  may be balanced. In detail, when the temperature of the nacelle  30  drops, the rotational frequency of the second air exhaust unit  27  is increased to speed up the flow rate of the hot air, so as to exhaust the hot air faster to the inside of the nacelle  30  through the second pipe outlet  23 , thereby improving the heat preservation in the nacelle  30 . When the temperature in the nacelle  30  rises, the rotational frequency of the second air exhaust unit  27  is decreased to slow down the flow rate of the hot air, thereby reducing the energy consumption of the second air exhaust unit  27  during operation while ensuring the heat preservation of the nacelle  30 .  FIG. 4  may be an operating status of the system for cooling wind turbine generators when the wind turbine generator system is in a low-temperature environment. 
         [0044]    In the system for cooling wind turbine generators of this embodiment, in a case that the temperature of the generator is higher than the first set temperature and the temperature of the nacelle is higher than the second set temperature, the first pipe air damper is opened, and the air exhaust device extracts the hot air generated by the generator into the air extraction pipe through the pipe inlet and exhausts the hot air to the outside of the nacelle through the first pipe outlet, thereby improving the cooling efficiency of the generator when the wind turbine generator system is in a high-temperature environment. In a case that the temperature of the nacelle is lower than or equal to the second set temperature, the second pipe air damper is opened, and the air exhaust device extracts the hot air generated by the generator into the air extraction pipe through the pipe inlet and exhausts the hot air to the inside of the nacelle through the second pipe outlet, so as to raise the temperature in the nacelle to a set temperature (such as the second set temperature) or keeping the temperature in the nacelle at the set temperature when the wind turbine generator system is in a low-temperature environment, thereby avoiding the need for providing multiple independent heating devices for parts and components of the wind turbine generator system, and reducing the cost and energy consumption. Compared with the conventional technology, the system for cooling wind turbine generators in this embodiment does not require a cooling device, thereby further saving the cost. The air extraction pipe in the system for cooling wind turbine generators in this embodiment may adopt a dual-pipe structure, which may actively control the heat exchange between the air inside and outside the nacelle, thereby not only cooling the generator, but also regulating the temperature in the nacelle. The hot air generated by the generator is recycled to raise the temperature in the nacelle. 
         [0045]      FIG. 5  is a schematic view showing the structure of a system for cooling wind turbine generators according to a second embodiment of the present application. Unlike the first embodiment, in this embodiment as shown in  FIG. 5 , the main pipe  28  includes a first pipe segment and a second pipe segment, the first pipe segment is a segment of the main pipe  28  which starts from an intersection of the main pipe  28  and the branch pipe  29  to the first pipe outlet  22 , the second pipe segment is a segment of the main pipe  28  which starts from the intersection of the main pipe  28  and the branch pipe  29  to the pipe inlet  21 , and the air exhaust device  32  is located in the second pipe segment. In this embodiment, one or more of the air exhaust devices  32  may be provided, and the air exhaust device  32  may be an exhaust fan. Compared with the technical solutions in the first embodiment, the technical solutions in this embodiment may reduce the number of the air exhaust devices, thereby saving the cost. 
         [0046]      FIG. 6  a schematic view showing the structure of a wind turbine generator system according to a third embodiment of the present application. As shown in  FIG. 6 , the wind turbine generator system includes a generator  31 , a nacelle  30 , a hub  34 , a blade  35  and a system for cooling the wind turbine generator. The blade  35  is connected to the generator  31  via the hub  34 . The blade  35  rotates to drive a rotor shaft of the generator  31  to rotate to produce electricity. The generator  31  is connected to the nacelle  30 , and the generator  31  and the nacelle  30  are enclosed. Air circulation between the generator  31  and the nacelle  30  is achieved by an air extraction pipe and an air inlet, and more particularly, the hot air generated by the generator  31  may be extracted by the air extraction pipe, and the air in the nacelle  30  may be sucked into the generator  31  through the air inlet after being filtered by a filter. The generator  31  may be located outside or inside the nacelle  30 . In this embodiment, preferably, the generator  31  is located outside the nacelle  30 . 
         [0047]    The system for cooling wind turbine generators includes an air extraction pipe and an air exhaust device. The air extraction pipe is located in the nacelle  30  and is provided with a pipe inlet  21 , a first pipe outlet  22  and a second pipe outlet  23 . The first pipe inlet  21  is in communication with the generator, the first pipe outlet  22  is provided with a first pipe air damper  24 , and the second pipe outlet  23  is provided with a second pipe air damper  25 . In a case that the temperature of the generator  31  is higher than the first set temperature and the temperature of the nacelle  30  is higher than the second set temperature, the first pipe air damper  24  is opened to communicate the first pipe outlet  22  with the outside of the nacelle  30 . In a case that the temperature of the nacelle  30  is lower than or equal to the second set temperature, the second pipe air damper  25  is opened to communicate the second pipe outlet  23  with the inside of the nacelle  30 . In a case that the temperature of the generator  31  is higher than the first set temperature and the temperature of the nacelle  30  is higher than the second set temperature, the air exhaust device is used to extract the hot air generated by the generator into the air extraction pipe through the pipe inlet  21  and exhaust the hot air to the outside of the nacelle  30  through the first pipe outlet  22 ; and in a case that the temperature of the nacelle  30  is lower than or equal to the second set temperature, the air exhaust device is used to extract the hot air generated by the generator  31  into the air extraction pipe through the pipe inlet  21  and exhaust the hot air to the inside of the nacelle  30  through the second pipe outlet  23 . 
         [0048]    In this embodiment, the air extraction pipe includes a main pipe  28  and a branch pipe  29 . The main pipe  28  has one end functioning as the pipe inlet  21  and another end functioning as the first pipe outlet  22 . The branch pipe  29  has one end in communication with the main pipe  28  and another end functioning as the second pipe outlet  23 . In practical application, the air extraction pipe may be in other structures which are not detailed here. 
         [0049]    In this embodiment, the air exhaust device may include a first air exhaust unit  26  and a second air exhaust unit  27 . The first air exhaust unit  26  is located near the first pipe outlet  22  in the air extraction pipe, and the second air exhaust unit  27  is located near the second pipe outlet  23  in the air extraction pipe. In a case that the temperature of the generator  31  is higher than the first set temperature and the temperature of the nacelle  30  is higher than the second set temperature, the first air exhaust unit  26  is used to extract the hot air generated by the generator  31  into the air extraction pipe through the pipe inlet  21  and exhaust the hot air to the outside of the nacelle  30  through the first pipe outlet  22 . In a case that the temperature of the nacelle  30  is lower than or equal to the second set temperature, the second air exhaust unit  27  is used to extract the hot air generated by the generator  31  into the air extraction pipe through the pipe inlet  21  and exhaust the hot air to the inside of the nacelle  30  through the second pipe outlet  23 . In this embodiment, one or more of the first air exhaust units  26  may be provided, and one or more of the second air exhaust units  27  may be provided. The first air exhaust unit  26  and the second air exhaust unit  27  may each be an exhaust fan. 
         [0050]    In this embodiment, a temperature sensor may be used to monitor the temperature of the generator and the temperature of the nacelle. A central processing unit of the wind turbine generator system may be used to open or close the first air exhaust unit  26  and the first pipe air damper  24 , or open or close the second air exhaust unit  27  and the second pipe air damper  25 . 
         [0051]    The operating principles of the system for cooling wind turbine generators in this embodiment will be described in detail in conjunction with  FIGS. 7 and 8 . 
         [0052]      FIG. 7  is an operation schematic diagram of a system for cooling wind turbine generators in the third embodiment. As shown in  FIG. 7 , when the generator  31  is in operation, in a case that the temperature of the generator  31  is higher than the first set temperature and the temperature of the nacelle  30  is higher than the second set temperature, the first air exhaust unit  26  is started and the first pipe air damper  24  is opened, thus the first pipe outlet  22  is communicated with the outside of the nacelle  30 . The first air exhaust unit  26  extracts the hot air generated by the generator  31  into the air extraction pipe through the pipe inlet  21  and exhausts the hot air to the outside of the nacelle  30  through the first pipe outlet  22 . At this time, the second air exhaust unit  27  is shut and the second pipe air damper  25  is closed. A rotational frequency of the first air exhaust unit  26  may be adjusted according to the temperature of the generator  31 , so as to realize an object of controlling the flow rate of the hot air according to the temperature of the generator  31 , thus two objects of improving the cooling efficiency of the generator  31  and reducing the energy consumption of the first air exhaust unit  26  may be balanced. In detail, when the temperature of the generator  31  rises, the rotational frequency of the first air exhaust unit  26  is increased to speed up the flow rate of the hot air, so as to exhaust the hot air faster to the outside of the nacelle  30  through the first pipe outlet  22 , thereby improving the cooling effect of the generator  31 . When the temperature of the generator  31  drops, the rotational frequency of the first air exhaust unit  26  is decreased to slow down the flow rate of the hot air, thereby reducing the energy consumption of the first air exhaust unit  26  during operation while ensuring the cooling effect of the generator  31 .  FIG. 7  may be an operating status of the system for cooling wind turbine generators when the wind turbine generator system is in a high-temperature environment. 
         [0053]      FIG. 8  is another operation schematic diagram of the system for cooling wind turbine generators in the third embodiment. As shown in  FIG. 8 , when the generator  31  is in operation, in a case that the temperature of the nacelle  30  is lower than or equal to the second set temperature, the second air exhaust unit  27  is started and the second pipe air damper  25  is opened, thus the second pipe outlet  23  is communicated with the inside of the nacelle  30 . The second air exhaust unit  27  extracts the hot air generated by the generator  31  into the air extraction pipe through the pipe inlet  21  and exhausts the hot air to the inside of the nacelle  30  through the second pipe outlet  23 , which raises the temperature in the nacelle  30 , thereby realizing the heat preservation of the nacelle  30 . At this time, the first air exhaust unit  26  is shut and the first pipe air damper  24  is closed. A rotational frequency of the second air exhaust unit  27  may be adjusted according to the temperature of the nacelle  30 , so as to realize an object of controlling the flow rate of the hot air according to the temperature of the nacelle  30 , thus two objects of ensuring the heat preservation of the nacelle  30  and reducing the energy consumption of the second air exhaust unit  27  may be balanced. In detail, when the temperature of the nacelle  30  drops, the rotational frequency of the second air exhaust unit  27  is increased to speed up the flow rate of the hot air, so as to exhaust the hot air faster to the inside of the nacelle  30  through the second pipe outlet  23 , thereby improving the heat preservation in the nacelle  30 . When the temperature in the nacelle  30  rises, the rotational frequency of the second air exhaust unit  27  is decreased to slow down the flow rate of the hot air, thereby reducing the energy consumption of the second air exhaust unit  27  during operation while ensuring the heat preservation of the nacelle  30 .  FIG. 8  may be an operating status of the system for cooling wind turbine generators when the wind turbine generator system is in a low-temperature environment. 
         [0054]    Optionally, the wind turbine generator system may further include a heating device  33  arranged in the nacelle  30 , and the heating device  33  is used for heating the nacelle  30 . Preferably, the heating device  33  is arranged on the air extraction pipe. As shown in  FIG. 8 , when the wind turbine generator system is in a low-temperature environment, the temperature in the nacelle  30  fails to meet the normal operating temperature for various parts and components and electrical elements. In this case, if the generator  31  is out of service for a long time and needs to restart, the heating device  33  may be started for heating the nacelle  30  to raise the temperature in the nacelle  30  to the normal operating temperature for various parts and components and electrical elements. When the heating device  33  is in operation, the first air exhaust unit  26  is shut and the first pipe outlet  22  is closed, and the second air exhaust unit  27  is started and the second pipe outlet  23  is opened. By arranging the heating device  33  on the air extraction pipe, the second air exhaust unit  27  in operation may convey the hot air generated by the heating device  33  to the inside of the nacelle  30 , thereby raising the temperature in the nacelle  30  faster and more efficiently. 
         [0055]    Further, the wind turbine generator system may include a base  36  and a tower  37 . The base  36  is arranged in the nacelle  30 , the nacelle  30  is arranged on the tower  37  via the base  36 , and the tower  37  is used to support the nacelle  30 . A sealing cover  38  is arranged above the base  36 . The sealing cover  38  may be arranged above the base  36  via a sealing gasket  39 . The sealing cover  38  is provided with an air filter apparatus  40  which may be used to filter the air entering the nacelle  30  from the tower  37 . The air filter apparatus  40  may be a protruding mesh cover on the sealing cover  38 . Further, a handle, which is not shown in the figures, may be provided on the sealing cover  38  for the operator to open the sealing cover  38 . 
         [0056]    The nacelle  30  in this embodiment is an enclosed structure, which may increase the cleanliness in the wind turbine generator system, thereby improving the insulation capacity and protection capacity of the generator. To seal the nacelle  30 , the wind turbine generator system may further include a sealing structure, which may be a peripheral sealing structure arranged at the junction of a yaw system, a root of the blade  35 , a cover of the nacelle  30 , a rotor and a stator of the generator  31  and other components. 
         [0057]    Optionally, the system for cooling wind turbine generators in the wind turbine generator system in this embodiment may adopt the system for cooling wind turbine generators according to the second embodiment as shown in  FIG. 2  and will not be specifically described herein. 
         [0058]    In the wind turbine generator system provided in this embodiment, in a case that the temperature of the generator is higher than the first set temperature and the temperature of the nacelle is higher than the second set temperature, the first pipe air damper is opened, and the air exhaust device extracts the hot air generated by the generator into the air extraction pipe through the pipe inlet and exhausts the hot air to the outside of the nacelle through the first pipe outlet, thereby improving the cooling efficiency of the generator when the wind turbine generator system is in a high-temperature environment. In a case that the temperature of the nacelle is lower than or equal to the second set temperature, the second pipe air damper is opened, and the air exhaust device extracts the hot air generated by the generator into the air extraction pipe through the pipe inlet and exhausts the hot air to the inside of the nacelle through the second pipe outlet, so as to raise the temperature in the nacelle for heat preservation when the wind turbine generator system is in a low-temperature environment, thereby avoiding the need for providing multiple independent heating devices for parts and components of the wind turbine generator system, and reducing the cost and energy consumption. Compared with the conventional technology, the system for cooling wind turbine generators in this embodiment does not require a cooling device, thereby further saving the cost. The air extraction pipe in the wind turbine generator system in this embodiment may adopt a dual-pipe structure, which may actively control the heat exchange between the air inside and outside the nacelle, thereby not only cooling the generator, but also regulating the temperature in the nacelle. The hot air generated by the generator is recycled to raise the temperature in the nacelle. 
         [0059]    A method for cooling wind turbine generators is provided according to a fourth embodiment of the present application based on the system for cooling wind turbine generators. The system for cooling wind turbine generators includes an air extraction pipe and an air exhaust device. The air extraction pipe is located in a nacelle and is provided with a pipe inlet, a first pipe outlet and a second pipe outlet. The pipe inlet is in communication with a generator, the first pipe outlet is provided with a first pipe air damper, and the second pipe outlet is provided with a second pipe air damper. 
         [0060]    The method for cooling wind turbine generators may includes the following steps. 
         [0061]    Step  101  may include monitoring a temperature of the generator and a temperature of the nacelle, and proceeding to Step  102  in a case that the temperature of the generator is higher than a first set temperature and the temperature of the nacelle is higher than a second set temperature; and proceeding to Step  103  in a case that the temperature of the nacelle is lower than or equal to the second set temperature. 
         [0062]    Step  102  may include opening the first pipe air damper to communicate the first pipe outlet with an outside of the nacelle; and extracting, by the air exhaust device, hot air generated by the generator into the air extraction pipe through the pipe inlet and exhausting, by the air exhaust device, the hot air to the outside of the nacelle through the first pipe outlet. 
         [0063]    Step  103  may include opening the second pipe air damper to communicate the second pipe outlet with an inside of the nacelle; and extracting, by the air exhaust device, hot air generated by the generator into the air extraction pipe through the pipe inlet and exhausting, by the air exhaust device, the hot air to the inside of the nacelle through the second pipe outlet. 
         [0064]    In the technical solutions of the method for cooling wind turbine generators provided in this embodiment, in a case that the temperature of the generator is higher than the first set temperature and the temperature of the nacelle is higher than the second set temperature, the first pipe air damper is opened, and the air exhaust device extracts the hot air generated by the generator into the air extraction pipe through the pipe inlet and exhausts the hot air to the outside of the nacelle through the first pipe outlet, thereby improving the cooling efficiency of the generator when the wind turbine generator system is in a high-temperature environment. In a case that the temperature of the nacelle is lower than or equal to the second set temperature, the second pipe air damper is opened, and the air exhaust device extracts the hot air generated by the generator into the air extraction pipe through the pipe inlet and exhausts the hot air to the inside of the nacelle through the second pipe outlet, so as to raise the temperature in the nacelle for heat preservation when the wind turbine generator system is in a low-temperature environment, thereby avoiding the need for providing multiple independent heating devices for parts and components of the wind turbine generator system, and reducing the cost and energy consumption. The method for cooling wind turbine generators provided in this embodiment may actively control the heat exchange between the air inside and outside the nacelle, thereby not only cooling the generator, but also regulating the temperature in the nacelle. The hot air generated by the generator is recycled to raise the temperature in the nacelle. 
         [0065]    It can be understood that, the first set temperature and the second set temperature are each a temperature threshold value which is pre-set according to the practical operation of the wind turbine. In determining the temperature threshold value, the following factors are generally required to be considered, for example, the environment of the wind turbine, a generator operation temperature range required for ensuring the normal operation of the generator, and a nacelle operation temperature range required for ensuring the normal operation of various parts and components and electrical elements in the nacelle. The value of the first set temperature is required to be in the generator operation temperature range required for ensuring the normal operation of the generator, and the value of the second set temperature is required to be in the nacelle operation temperature range required for ensuring the normal operation of various parts and components and electrical elements in the nacelle. 
         [0066]    It can be understood that, the above embodiments are merely exemplary embodiments used to illustrate the principles of the present application, and the present application is not limited to this. For person skilled in the art, various changes and modifications may be made without departing front the spirit and essence of the present application, and these changes and modifications are deemed to fall into the scope of the present application.