Abstract:
The fluid power generator is provided. The fluid power generator includes: a first member that has multiple coils; a second member that is rotatable relative to the first member and that has multiple permanent magnets; a rotating member that is mechanically linked with either one of the first member and the second member to rotate by fluid force; and a clearance controller that moves at least one of the first member and the second member to thereby change a clearance between the first member and the second member, wherein the clearance controller changes the clearance in such a manner as to make the clearance smaller after a start of rotation of the rotating member than before the start of rotation of the rotating member.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application claims the priority based on Japanese Patent Application No. 2008-34324 filed on Feb. 15, 2008, the disclosure of which is hereby incorporated by reference in its entirety. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to control of a fluid power generator. 
         [0004]    2. Description of the Related Art 
         [0005]    For reduction of carbon dioxide, power generations by utilizing natural energies, such as wind power generation, hydraulic power generation, and photovoltaic power generation, have been attracting a great deal of attention. Enhancement of the efficiency of such natural energy power generations is of great importance to solve the environmental problems. 
         [0006]    A fluid power generator may be constructed, for example, with a brushless motor structure. One example of the brushless motor structure is disclosed in JP 2001-298982A. 
         [0007]    One typical example of the fluid power generator is a wind power generator. The wind power generator uses blades that receive the wind force to rotate. The blades are generally designed to have a large weight for the enhanced inertia of rotation. In the condition of low wind force, it is difficult to rotate the blades and start power generation. One proposed structure of the wind power generator uses a drive motor separate from the power generator to start rotation of the blades even in the condition of low wind force. 
         [0008]    This prior art structure, however, requires the separate drive motor for starting the power generator. This undesirably complicates the overall mechanism and increases the manufacturing cost. Such drawbacks are not characteristic of the wind power generator but are commonly found in various fluid power generators. 
       SUMMARY 
       [0009]    An object of the present invention is to provide technology that is able to ensure a start of power generation even in the condition of low flow rate. 
         [0010]    According to an aspect of the present invention, a fluid power generator is provided. The fluid power generator comprises: a first member that has multiple coils; a second member that is rotatable relative to the first member and that has multiple permanent magnets; a rotating member that is mechanically linked with either one of the first member and the second member to rotate by fluid force; and a clearance controller that moves at least one of the first member and the second member to thereby change a clearance between the first member and the second member, wherein the clearance controller changes the clearance in such a manner as to make the clearance smaller after a start of rotation of the rotating member than before the start of rotation of the rotating member. 
         [0011]    According to this configuration, there is a large clearance before a start of rotation of the rotating member. This arrangement decreases the load at a start of rotation of the rotating member and thus ensures a start of power generation even in the condition of low flow rate. 
         [0012]    The technique of the invention is not restricted to the power generator having any of the above arrangements but is also actualized by diversity of other applications, for example, a power generation method, a power generation system, integrated circuits for attaining the functions of the power generation method and the power generation system, computer programs for the same purpose, and recording media in which such computer programs are recorded. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]      FIGS. 1A and 1B  are sectional views illustrating the schematic configuration of a wind power generator  1000  in one embodiment of the invention; 
           [0014]      FIGS. 2A to 2C  are an explanatory views showing the structures of the rotor  30  and the two stators  10 A and  10 B; 
           [0015]      FIG. 3  is a graph showing a variation in clearance CL against wind speed Vc, together with a variation in rotation speed N of the blades  110  and a variation in generated output P; 
           [0016]      FIG. 4  illustrates the schematic structure of a wind power generator  1000   b  in a second embodiment of the invention; 
           [0017]      FIG. 5  is a flowchart showing a control method of the wind power generator  1000   b ; and 
           [0018]      FIG. 6  is a graph showing a variation in clearance CL against the wind speed Vc. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0019]    Next, aspects of the present invention will be described in the following order on the basis of embodiments: 
       A. First Embodiment: 
     B. Second Embodiment: 
     C. Modified Examples: 
     A. First Embodiment 
       [0020]      FIGS. 1A and 1B  are sectional views illustrating the schematic configuration of a wind power generator  1000  in one embodiment of the invention.  FIG. 1A  shows the state of the wind power generator  1000  in a low wind force condition, and  FIG. 1B  shows the state of the wind power generator  1000  in a high wind force condition. The wind power generator  1000  includes a main body assembly  100 , blades  110 , and a power generation control circuit  200 . The blades  110  are rotated by wind force to rotate a rotating shaft  112  of the main body assembly  100 . The main body assembly  100  has a rotor  30 , an A-phase stator  10 A, a B-phase stator  10 B, and a casing  20 . A bearing  114  is provided at a joint of the rotating shaft  112  with the casing  20 . The rotor  30  is fastened to the rotating shaft  112  and rotates with rotation of the rotating shaft  112 . The rotor  30  is a substantially disk-shaped member about the rotating shaft  112  and has a magnet array  34 M of multiple permanent magnets. The magnet array  34 M is magnetized in a vertical direction. The A-phase coil  10 A and the B-phase coil  10 B are substantially disk-shaped members and have coil arrays  14 A and  24 B formed on respective faces opposed to the rotor  30 . The coil arrays  14 A and  24 B generate induced voltage by rotation of the rotor  30 . The electric current generated by the coil arrays  14 A and  24 B runs through a cable  13   a  to a circuit board  13  and is supplied to the power generation control circuit  200  via a connector  14 . The generated electric current is subjected to rectification, smoothing, and control by the power generation control circuit  200 . The generated electric current is then accumulated in an accumulator (not shown). 
         [0021]    Weights  17  and rods  18  are provided between the rotor  30  and the A-phase stator  10 A as well as between the rotor  30  and the B-phase stator  10 B. The weights  17  are linked to the rotor  30  by means of the rods  18 . With rotation of the rotor  30  induced by rotation of the blades  110 , the weights  17  rotate about the rotating shaft  112 . The rotation of the blades  110  applies the centrifugal force onto the weights  17 , so that the weights  17  start moving outward from the rotating shaft  112 . As the weights  17  move outward from the rotating shaft  112 , the two stators  10 A and  10 B are drawn by the rods  18  to be closer to the rotor  30  (see  FIG. 1B ). This results in decreasing a clearance CL between the rotor  30  and the stator  10 A and a clearance CL between the rotor  30  and the stator  10 B. 
         [0022]    Springs  19  are provided between the rotor  30  and the A-phase stator  10 A as well as between the rotor  30  and the B-phase stator  10 B. As the rotation speed of the blades  110  decreases to reduce the centrifugal force applied onto the weights  17 , the springs  19  work to respectively move the A-phase stator  10 A and the B-phase stator  10 B away from the rotor  30  and thereby increase the respective clearances CL. 
         [0023]      FIGS. 2A to 2C  are an explanatory views showing the structures of the rotor  30  and the two stators  10 A and  10 B. In this illustrated example, the A phase-coil array  14 A and the B-phase coil array  24 B respectively have six coils, while the magnet array  34 M has six permanent magnets. The number of the coils in each coil array and the number of the magnets in the magnet array are, however, not restricted to this number but may be set arbitrarily. 
         [0024]      FIG. 3  is a graph showing a variation in clearance CL against wind speed Vc, together with a variation in rotation speed N of the blades  110  and a variation in generated output P. These variations CL, N, and P are drawn as linear lines in the graph of  FIG. 3  for the simplicity of explanation and may be curved lines in the actual state. This is also applied to the graph of  FIG. 6  discussed later. The wind power generator  1000  has three options of operation mode according to the rotation speed N of the blades  110 , ‘power generation start mode’, ‘power generation control mode’, and ‘stable power generation mode’. 
         [0025]    When the wind speed Vc is in a range of 0 to Vc 1 , the blades  110  are not rotated to have the rotation speed N equal to 0. This activates the power generation start mode. In the power generation start mode, the weights  17  receive no centrifugal force, so that the clearance CL is set to a maximum clearance CLmax. The maximum clearance CLmax results in the minimum intensity of a magnetic field produced by the magnet array  34 M and applied to the coil arrays  14 A and  24 B. The coil arrays  14 A and  24 B accordingly generate only small electric power but have lowest rotational load. In the power generation start mode, because of the lowest rotational load, the rotation of the blades  110  is readily started even at the low wind speed Vc. 
         [0026]    The rotation speed N of the blades  110  gradually increases with an increase in wind speed Vc over Vc 1  and reaches a stable rotation speed Nth at the wind speed Vc to Vc 2 . The ‘stable rotation speed Nth’ represents the rotation speed N of the blade  110  at the clearance CL equal to a minimum clearance CLmin. The minimum clearance CLmin is a minimum possible value of the clearance CL in the structure of the main body assembly  100  (see  FIG. 1B ). At the rotation speed N of higher than 0 but not higher than the stable rotation speed Nth, the operation mode shifts to the power generation control mode. In the power generation control mode, as the blades  110  receive the wind of the wind speed Vc 1  and start rotation, the centrifugal force is applied to the weights  17  to gradually decrease the clearance CL. The gradual decrease of the clearance CL with an increase in rotation speed N gradually increases the intensity of the magnetic field produced by the magnet array  34 M and applied to the coil arrays  14 A and  24 B. Namely the rotational load increases with an increase in rotation speed N in the power generation control mode. This enhances the power generation efficiency per rotation speed. As mentioned above, when the blades  110  receive the wind of the wind speed Vc 2  and their rotation speed N reaches the stable rotation speed Nth, the clearance CL is decreases to the minimum clearance CLmin. Even when the rotation speed N of the blades  110  exceeds the stable rotation speed Nth, the structure of the main body assembly  100  ( FIG. 1B ) restricts the clearance CL to the minimum clearance CLmin. 
         [0027]    In the power generation control mode, with a decrease in wind speed Vc, the centrifugal force applied to the weights  17  is reduced, and the clearance CL is increased by the force of the spring  19 . The increased clearance CL results in decreasing the intensity of the magnetic field produced by the magnet array  34 M and applied to the coil arrays  14 A and  24 B. In the power generation control mode, even when the rotation speed N is decreased with a decrease in wind speed Vc, the reduced rotational load allows the blades  110  to keep their rotation. Namely even in the event of a variation in wind speed Vc, the clearance changes according to the rotation speed N to vary the rotational load, thus ensuring continuation of power generation. The operation mode shifts to the stable power generation mode when the wind speed Vc increases to or over Vc 2  and the rotation speed N of the blades  110  exceeds the stable rotation speed Nth. In the stable power generation mode, the clearance CL is fixed to the minimum clearance CLmin and gives the highest rotational load. In the stable power generation mode, the load of power generation may be changed for efficient power generation by the power generation control circuit  200  connecting with the connector  14  (see  FIG. 1A ) in a certain range of the rotation speed N that is not lower than the stable rotation speed Nth. The graph of  FIG. 3  shows the rotation speed N under the condition of a fixed power generation load. 
         [0028]    In the wind power generator  1000  of the first embodiment, the clearance CL is set to the maximum clearance CLmax until the rotation of the blades  110  is started, so as to minimize the rotational load applied onto the blades  110 . This arrangement ensures a start of power generation even in the condition of low flow rate. 
       B. Second Embodiment 
       [0029]      FIG. 4  illustrates the schematic structure of a wind power generator  1000   b  in a second embodiment of the invention. The differences of the second embodiment from the first embodiment are a wind gauge  120 , actuators  15  provided in place of the weights  17  and the springs  19 , and selection of the operation mode according to the wind speed Vc instead of the rotation speed N. Otherwise the wind power generator  1000   b  of the second embodiment has the same structure as that of the wind power generator  1000  of the first embodiment. 
         [0030]    The wind gauge  120  is used to measure the wind speed Vc. The actuators  15  move the stators  10 A and  10 B in the vertical direction according to the wind speed Vc measured by the wind gauge  120  to change the clearances CL. 
         [0031]      FIG. 5  is a flowchart showing a control method of the wind power generator  1000   b . At step S 10 , the wind speed Vc is measured by the wind gauge  120 . At step S 20 , the actuator  15  compares the observed wind speed Vc with two reference wind speeds Vth 1  and Vth 2  and selects one of the three options discussed above as the operation mode based on the result of the comparison. The two reference wind speeds Vth 1  and Vth 2  satisfy a relation of Vth 1 &lt;Vth 2 . 
         [0032]    If the wind speed Vc is lower than the first reference wind speed Vth 1 , the power generation start mode is selected as the operation mode, and the clearance CL is set to the maximum clearance CLmax. This arrangement ensures a start of power generation even in the condition of the low wind speed Vc. 
         [0033]    If the wind speed Vc is not lower than the first reference wind speed Vth 1  but lower than the second reference wind speed Vth 2 , the power generation control mode is selected as the operation mode, and the clearance CL is set according to the wind speed Vc. The clearance CL is changed responsive to variation of the wind speed Vc to vary the rotational load. This arrangement desirably enhances the power generation efficiency and ensures continuation of power generation even in the state of the decreased wind speed Vc. 
         [0034]    If the wind speed Vc is not lower than the second reference wind speed Vth 2 , the stable power generation mode is selected as the operation mode, and the clearance CL is set to the minimum clearance CLmin. In the stable power generation mode, the load of power generation is changed according to the wind speed Vc at step S 30 . This further enhances the power generation efficiency. 
         [0035]    After setting the clearance CL in the selected operation mode, the control method goes back to step S 10  to measure the wind speed Vc and to step S 20  to select the operation mode. The processing of step S 30  may be omitted when not required. 
         [0036]      FIG. 6  is a graph showing a variation in clearance CL against the wind speed Vc. In the graph of  FIG. 6 , the power generation start mode is selected as the operation mode until an increase of the wind speed Vc to or over the first reference wind speed Vth 1  even at the rotation speed N exceeding 0. Such setting of the first reference wind speed Vth 1  keeps the operation mode to the power generation start mode until stable rotation of the blades  110  with the stable wind force. 
         [0037]    In the stable power generation mode, the power generation control circuit  200  changes the load of power generation, in order to keep the rotation speed N of the blades  110  to a preset rotation speed Ns. The rotation speed N is thus substantially fixed to the preset rotation speed Ns even in the state of the increased wind speed Vc. 
         [0038]    The system of changing the clearance CL according to the wind speed Vc ensures a start of power generation even in the condition of the low wind speed Vc, as in the first embodiment. 
       C. Modified Examples 
       [0039]    The embodiments discussed above are to be considered in all aspects as illustrative and not restrictive. There may be many modifications, changes, and alterations without departing from the scope or spirit of the main characteristics of the present invention. Some examples of possible modification are given below. 
       C1. Modified Example 1 
       [0040]    In the embodiments discussed above, the clearance CL is changed according to either one of the rotation speed N and the wind speed Vc. The clearance CL may alternatively be changed according to both the rotation speed N and the wind speed Vc. The actuators  15  provided in the wind power generator  1000   b  of the second embodiment may be arranged to measure the rotation speed N of the blades  110  and change the clearance CL according to the observed rotation speed N. 
       C2. Modified Example 2 
       [0041]    In the wind power generators  1000  and  1000   b  of the above embodiments, the stators  10 A and  10 B are moved in the vertical direction to change the clearances CL between the respective stators  10 A and  10 B and the rotor  30 . The rotor  30  may be moved, instead of the stators  10 A and  10 B, in the vertical direction to change the clearances CL. Otherwise both the stators  10 A and  10 B and the rotor  30  may be moved in the vertical direction to change the clearances CL. Any of these techniques is adoptable to ensure relative motion of the stators  10 A and  10 B to the rotor  30 . 
       C3. Modified Example 3 
       [0042]    In the wind power generators  1000  and  1000   b  of the above embodiments, the member (rotor  30 ) equipped with the magnet array  34 M is linked with the blades  110 . The members (stators  10 A and  10 B) equipped with the coil arrays  14 A and  24 B may alternatively be linked with the blades  110 . 
       C4. Modified Example 4 
       [0043]    The above embodiments describe application of the invention to the wind power generators  1000  and  1000   b . The technique of the invention is, however, not restricted to such wind power generators but may be applied to various fluid power generators, such as a water power generator. 
       C5. Modified Example 5 
       [0044]    In the wind power generators  1000  and  1000   b  of the above embodiments, the main body assembly  100  has the two phase coil arrays  14 A and  24 B. The coils arrays are, however, not restricted to the two phases but the main body assembly  100  may have only one phase coil array or three or greater number of phase coil arrays. 
       C6. Modified Example 6 
       [0045]    In the wind power generators  1000  and  1000   b  of the above embodiments, the power generation control circuit  200  changes the load of power generation in the stable power generation mode. The load of power generation may also be changed according to the wind speed Vc or according to the rotation speed N in the power generation control mode. For example, in the power generation control mode, as the clearance CL increases with a decrease in wind speed Vc or a decrease in rotation speed N, the intensity of the magnetic field produced by the magnet array  34 M and applied to the coil arrays  14 A and  24 B is lowered to decrease the generated output P. The power generation control circuit  200  controls the amount of generated current according to the decrease of the generated output P, thus decreasing the load of power generation. The decreasing load of power generation increases the rotation speed N of the blades  100  in the wind power generator  1000  or  1000   b . In the power generation control mode, the control procedure may change the load of power generation with the control of the clearance CL to ensure adequate power generation according to the wind speed Vc or the rotation speed N.