Abstract:
An electric rotation machine for windmill power generation equipped with a stator slot structure having distributed windings and a rotor pole structure having permanent magnets, wherein the number of slots per pole per phase (Nspp) is undividable by 3 times P (where P is the number of poles), and pole width rate Pw obtained by dividing pole piece width Tp by pole pitch Tr at the outermost diameters of the adjoining poles of the rotor is satisfied any of Pw≦0.6, 0.67≦Pw≦0.71, and 0.78≦Pw. The distortion factors of induced voltages in a permanent magnet type electrical rotation machine, particularly for windmill power generation, can be reduced.

Description:
CLAIM OF PRIORITY 
   The present application claims priority from Japanese application serial no. 2005-70260, filed on Mar. 14, 2005, the content of which is hereby incorporated by reference into this application. 
   FIELD OF THE INVENTION 
   This invention relates to an electrical rotation machine and a wind turbine system. 
   BACKGROUND OF THE INVENTION 
   Recently, wind turbine systems have been installed dramatically and the world has demanded large-capacity wind turbine systems of permanent magnet type of 1 megawatt (MW) or more to improve the economical efficiency by increasing the capacity of a single unit. Japanese Patent Laid-Open No. 2001-069735 discloses an electrical rotation machine equipped with a stator having an armature winding on an iron core and a rotor having a permanent magnet on an iron core, wherein the stator and the rotor are arranged so that all torques between the stator and the rotor may be made by synthesizing a reluctance torque and a torque which generates due to the action between a current passing through the armature coil and the interlinking magnetic flux of the permanent magnet and the armature coil is wound around the stator core at a winding pitch of 40 to 80% of the pole pitch. 
   SUMMARY OF THE INVENTION 
   If a permanent magnets are applied to a large-capacity electric rotation machine, the connected electric power system is seriously influenced. In order to reduce the serious influence, an induced voltage waveform is thought as important and the distributed winding is adopted as the large-capacity electric rotation machine. 
   However, there are so many combinations of numbers of poles and numbers of windings. Some of them may have problems to distort induced voltage waveforms. To reduce cogging torques, some methods select combinations of numbers of poles and numbers of windings, but we find that these methods also have problems to distort induced voltage waveforms. 
   An object of this invention is to reduce distortion factors of induced voltages in an electrical rotation machine and a wind turbine system. 
   One of characteristics of this invention is that the electrical rotation machine is equipped with a stator on which coils are wound and a rotor which is supported to rotate, wherein a gap is provided between the rotor and the stator; the rotor is equipped with a permanent magnet; and pole width rate Pw obtained by dividing pole piece width Tp by pole pitch Tr at the outermost diameters of the adjoining poles of the rotor satisfies any of Pw≦0.6, 0.67≦Pw≦0.71, or 0.78≦Pw. 
   Another characteristic of this invention is that the electrical rotation machine is equipped with a stator on which coils are wound and a rotor which is supported to rotate, wherein a gap is provided between the rotor and the stator; the rotor is equipped with a permanent magnet and a pole piece made of a magnetic material on the outer side of the permanent magnet; the pole piece has an almost circular part on the outer side thereof; and the radius R 1  of the outermost periphery of the rotor is greater than the radius R 2  of the almost circular part of the pole piece. 
   The other characteristics of this invention will be explained using best modes for carrying out the invention 
   An electrical rotation machine and a wind turbine system in accordance with this invention can reduce distortion factors of induced voltage waveforms. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a drawing to explain an example of electric rotation machine of this invention (Embodiment 1). 
       FIG. 2  is a drawing to explain an example of electric rotation machine of this invention (Embodiment 2). 
       FIG. 3  is a drawing to explain an example of electric rotation machine of this invention (Embodiment 3). 
       FIG. 4  is a drawing to explain the effect of an example of this invention (Embodiment 1). 
       FIG. 5  is a drawing to explain the effect of an example of this invention (Embodiment 2). 
       FIG. 6  is a drawing to explain the effect of an example of this invention (Embodiment 3). 
       FIG. 7  is a supplemental drawing to explain an example of electric rotation machine of this invention (Embodiment 1). 
       FIG. 8  is a drawing to explain the effect of an example of this invention (Embodiment 1). 
       FIG. 9  is a drawing to explain an example of electric rotation machine of this invention (Embodiment 1). 
       FIG. 10  is a supplemental drawing to explain an example of electric rotation machine of this invention (Embodiment 1). 
       FIG. 11  is a drawing to explain the effect of an example of this invention (Embodiment 1). 
       FIG. 12  is a supplemental drawing to explain an example of electric rotation machine of this invention (Embodiment 4). 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Next will be explained embodiments of this invention in reference with the accompanying drawings. In the following description, like parts are designated by like reference numbers throughout the drawings. 
   A large-capacity permanent magnet type electric rotation machine of 1 MW or more is hard to be subject to an actual load test because its capacity is very big. In future business transactions of such electric rotation machines, they may be tested according to their standards. Inevitably, the test items contain items to regulate higher harmonic voltages such as waveform distortion factors or form deviation rates. The large-capacity permanent magnet type electric rotation machine of 1 MW or more is most effective when it is used for wind power generation. 
   Embodiment 1 
     FIG. 1  is a sectional view of the end of a 6-pole 54-slot permanent magnet type electric rotation machine which is a first embodiment of this invention. This machine is better suited for a wind turbine system of a few megawatts (MW) which allows a speed of 1000 to 2000 rpm. Stator  1  is of a distributed winding type which distributionally winds coil  10  around stator teeth  12 . Coil  10  has windings of three phases (U, V, and W) which are disposed so that 6 poles are electrically formed by 54 slots. Each stator slot  13  between stator teeth  12  contains upper coil  8  and lower coil  9  as shown in the drawing. In Embodiment 1, coil  10  is wound in a so-called distributed winding manner to form 3-phase windings along the periphery. Rotor  2  is provided in the center of rotor  1  so as to rotate. On rotor  2 , permanent magnet  3  is provided between rotor core  5  and pole piece  4 . Further, rotor core  5  is coupled with shaft  6 . Pole retainer  7  is provided between two adjoining poles to prevent permanent magnet  3  from moving circumferentially. It is preferable that the pole retainer is made of a non-magnetic material such as aluminum or copper. 
   Embodiment 2 
     FIG. 2  is a sectional view of the end of a 6-pole 63-slot permanent magnet type electric rotation machine which is a second embodiment of this invention. In Embodiment 2 as well as Embodiment 1, coils  10  are wound distributionally around stator  21  in a so-called distributed winding manner to form 3-phase windings along the periphery. Rotor  2  is provided in the center of rotor  1  so as to rotate. On rotor  2 , permanent magnet  3  is provided between rotor core  5  and pole piece  4 . Further, rotor core  5  is coupled with shaft  6 . Pole retainer  7  is provided between two adjoining poles to prevent permanent magnet  3  from moving circumferentially. It is preferable that the pole retainer  7  is made of a non-magnetic material such as aluminum or copper. 
   Embodiment 3 
     FIG. 3  is a sectional view of the end of a 6-pole 45-slot permanent magnet type electric rotation machine which is a third embodiment of this invention. In Embodiment 3 as well as Embodiment 1, coils  10  are wound distributionally around stator  1  in a so-called distributed winding manner to form 3-phase windings along the periphery. Rotor  2  is provided in the center of stator  1  so as to rotate. On rotor  2 , permanent magnet  3  is provided between rotor core  5  and pole piece  4 . Further, rotor core  5  is coupled with shaft  6 . Pole retainer  7  is provided between two adjoining poles to prevent permanent magnet  3  from moving circumferentially. It is preferable that the pole retainer  7  is made of a non-magnetic material such as aluminum or copper. 
     FIG. 4  shows the result of analysis of harmonic components in the induced voltage waveform of Embodiment 1. As shown in  FIG. 4 , the induced voltage waveform contains 17th and 19th harmonic components more with respect to the first harmonic component (100%). It is necessary to reduce these harmonic components (except the fundamental wave) to almost 0 to reduce the waveform distortion factor. 
     FIG. 5  shows the result of analysis of harmonic components in the induced voltage waveform of Embodiment 2.  FIG. 6  shows the result of analysis of harmonic components in the induced voltage waveform of Embodiment 3. The contents of harmonic components can be reduced by selecting the numbers of slots as shown in Embodiments 2 and 3. Generally, this means that the quotient of the number of slots N 2  per pole per phase Nspp by the product of the number of poles P and the number of phases N is not an integer. 
   
     
       
         
           
             
               
                 Nspp 
                 = 
                 
                   Ns 
                   
                     P 
                     · 
                     N 
                   
                 
               
             
             
               
                 ( 
                 1 
                 ) 
               
             
           
         
       
     
   
   For Embodiment 2, Nspp is 3.5 as Ns, N, and P are respectively 63, 3, and 6 in that order. For Embodiment 3, Nspp is 2.5 as Ns, N, and P are respectively 45, 3, and 6 in that order. As the result of analysis, the inventors found that the waveform distortion factor can be reduced when the Nspp value is not an integer. Specifically, when the Nspp value is 3.5 or 2.5 as shown in Embodiments 2 and 3, the distortion factor can be reduced effectively. Further, the distortion factor of an induced voltage can also be reduced by selecting an adequate width of pole piece of rotor  2  in Embodiment 1.  FIG. 7  is a supplemental drawing to explain Embodiment 1. 
   Additional lines  71  and  72  are drawn passing through the center of rotation and the center  73  of the outermost circle of each of the adjoining poles of rotor  2 . Reference item Tr is an arc between additional lines  71  and  72 . Pole width rate Pw is expressed by Tr and Tp (the width of each pole piece  4 ) as shown below. 
   
     
       
         
           
             
               
                 Pw 
                 = 
                 
                   Tp 
                   Tr 
                 
               
             
             
               
                 ( 
                 2 
                 ) 
               
             
           
         
       
     
   
     FIG. 8  shows a relationship between pole width rate Pw and induced voltage distortion factor. Curved line  81  varies as the pole width rate changes. The waveform distortion factor is required to be 10% or less by the JEC Standards. Therefore, it is preferable to select the width (Tp) of pole piece  4  at a pole width rate (Pw) which satisfies Pw≦0.6, 0.67≦Pw≦0.71,or 0.78≦Pw. From  FIG. 8 , it is apparent that Tp in the above range can reduce the distortion factor very effectively. As shown in  FIG. 9  it is also possible to provide dumper bars  91  on pole piece  4  to make the width (Tp) of pole piece  4  equal to that shown in  FIG. 8 . 
     FIG. 10  is a supplemental drawing to explain a curvature of pole piece  4  of Embodiment 1. Rotor  2  has outermost peripheral part  91  of radius R 1 . It is possible to reduce the induced voltage distortion factor by making radius R 2  of the outer periphery of pole piece  4  smaller than R 1 . 
     FIG. 11  shows a relationship between the waveform distortion factor and the quotient of radius R 2  of the outer periphery of pole piece  4  by radius R 1  of rotor R 2 . Curved line  101  indicates that the waveform distortion factor goes down as the R 2 /R 1  value becomes smaller. As the waveform distortion factor is required to be 10% or less by the JEC Standards, the R 2 /R 1  value should preferably be about 0.9 or less. 
     FIG. 12  shows an example of wind turbine system to which the electric rotation machine of this invention is applied. Electric rotation machine  121  of Embodiment 1 to Embodiment 3 is coupled with windmill  124  via speed-up gear  123  and housed in windmill nacelle  122 . Electric rotation machine  121  is connected to power system  126  via power converter  125  for power generation. It is also possible to connect windmill  122  directly to electric rotation machine  121 . Although this example uses winds as its energy source, other energy sources such as water mill, engine, and turbine can be used. Further, this embodiment is applicable to electric motors.