Abstract:
Because of the necessity of resolver for detecting a rotating position, which is very expensive, and noise suppression of the rotating position signal line on a doubly-fed machine, cost increase of the generator and reduced reliability due to possible failures are inevitable. In order to solve such problem, a generation system in the present invention is equipped with an exciter that estimates the slip frequency of the doubly-fed machine from each primary current I 1  and voltage V 1  and secondary current I 2  and voltage V 2  of the doubly-fed machine and excites the secondary of the doubly-fed machine at the estimated slip frequency.

Description:
CROSS-REFERENCE TO A RELATED APPLICATION 
   This application claims the benefit of the filing date of Japanese Patent Application Serial No. 2004-004900, filed on Jan. 13, 2004. 
   BACKGROUND OF THE INVENTION 
   The present invention relates to a rotating electrical machine control unit and power generation system, particular to a control unit and power generation system of a doubly-fed machine. 
   Doubly-fed machine has conventionally been used as the generator for an aerogeneration system. It is a generator-motor, equipped with 3-phase winding laid in slots provided at equal distance on the stator and rotor, that is operated at variable speed by applying variable-frequency alternating current power particularly to the secondary of the generator-motor. As disclosed in the Japanese Application Patent Laid-Open Publication No. Hei 05-284798 (hereinafter called the Patent Document 1), the doubly-fed machine like the above has a resolver for detecting a rotating position, slip frequency which is the differential between the primary frequency and secondary frequency is calculated, and the output is controlled by a power converter. 
   [Patent Document 1] 
   Japanese Application Patent Laid-Open Publication No. Hei 05-284798 
   SUMMARY OF THE INVENTION 
   According to the prior art, cost increase of the generator has been inevitable because of the necessity of resolver for detecting a rotating position, which is very expensive, and noise suppression of the rotating position signal line. In addition, the reliability is lower because of increased chances of failure. The present invention is capable of controlling a doubly-fed machine without using a rotor position sensor such as resolver, and accordingly cost increase due to the use of a rotor position sensor such as resolver in a doubly-fed machine can be prevented. 
   A characteristic of the present invention is to calculate a command value of the voltage to be applied to the rotor winding based on the voltage of the stator winding, current of the stator winding, and current of the rotor winding. 
   Another characteristic of the present invention is to calculate the information relating to the rotor position based on the voltage of the stator winding, current of the stator winding, and current of the rotor winding. 
   Other characteristics of the present invention are explained in detail hereunder. 
   According to the present invention, cost increase due to the use of a rotor position sensor such as resolver in a doubly-fed machine can be prevented. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a diagram showing a brief construction of an embodiment of the present invention. 
       FIG. 2  is a diagram showing an equivalent circuit of a doubly-fed machine. 
       FIG. 3  is a diagram showing vectors based on  FIG. 2 . 
       FIG. 4  is a diagram showing part of a rotor position detector. 
       FIG. 5  is a diagram showing an embodiment of the generation system according to the present invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   An embodiment of the present invention is described hereunder, using figures.  FIG. 1  is a diagram showing the overall construction of a doubly-fed machine drive system to which the present invention applies. 
   As shown in  FIG. 1 , a doubly-fed machine  4 , mechanically connected with a power source  2 , is a generator-motor, equipped with 3-phase winding laid in slots provided at equal distance on the stator and rotor, that is operated at variable speed by applying variable-frequency alternating current power particularly to the secondary of the generator-motor, that is, a generator-motor which is controlled by comparing the primary voltage with a control variable in the alternating voltage control  44  so as to adjust the secondary voltage. The stator winding  5  of the doubly-fed machine  4  is connected to the electrical power system  1  via a switch  101 . 
   The rotor winding  6  of the doubly-fed machine  4  is electrically connected with an exciter  7  and the rotor winding  6  is alternatingly excited by the exciter  7 . The exciter  7  comprises an indirect alternating current converter, consisting of converter  8  and inverter  9 , which once converts alternating current power to direct current power and then converts the direct current power to the alternating power of desired frequency. 
   The converter  8  is controlled by a converter controlling apparatus  30  that generates a gate signal based on the electric power system voltage V 1  detected by a system voltage detector  21 , output voltage of the converter  8  detected by a current detector  26 , and direct current voltage V dc  of the exciter  7 . 
   The inverter  9  is driven by a gate signal generated by a PWM modulator  50 . This gate signal is generated in the circuitry explained below. The secondary current I 2  of the doubly-fed machine (current through the stator winding) detected by an exciting current detector  25  is converted into I α  and I β  by a 3-phase/2-phase converter  41 , and the d-axis current and q-axis current exhibited on a dq-axis rotating coordinate when the rotor position θ s  obtained from a rotating position calculator  20  is transformed in terms of the coordinate by a rotating coordinate transformer  42  are called I d  and I q , respectively. When the rotor position θ s  is in the same phase as with the induced electromotive force due to slip, the d-axis current I d  represents the excitation component and the q-axis current I q  represents the torque component. 
   A practical manner for the above is to convert 3-phase secondary current I 2  (I 2u , I 2v , I 2w ) into (I α , I β , I 0 ) using Expression 1 below on the 2-phase winding (α, β, 0) of the rotor. 
   
     
       
         
           
             
               
                 
                   ( 
                   
                     
                       
                         
                           I 
                           α 
                         
                       
                     
                     
                       
                         
                           I 
                           β 
                         
                       
                     
                     
                       
                         
                           I 
                           0 
                         
                       
                     
                   
                   ) 
                 
                 = 
                 
                   
                     
                       2 
                       3 
                     
                   
                   ⁢ 
                   
                     ( 
                     
                       
                         
                           1 
                         
                         
                           
                             
                               - 
                               1 
                             
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                             2 
                           
                         
                         
                           
                             
                               - 
                               1 
                             
                             / 
                             2 
                           
                         
                       
                       
                         
                           0 
                         
                         
                           
                             
                               3 
                             
                             / 
                             2 
                           
                         
                         
                           
                             
                               - 
                               
                                 3 
                               
                             
                             / 
                             2 
                           
                         
                       
                       
                         
                           
                             1 
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                               2 
                             
                           
                         
                         
                           
                             1 
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                             1 
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                     ) 
                   
                   ⁢ 
                   
                     ( 
                     
                       
                         
                           
                             I 
                             u 
                           
                         
                       
                       
                         
                           
                             I 
                             v 
                           
                         
                       
                       
                         
                           
                             I 
                             w 
                           
                         
                       
                     
                     ) 
                   
                 
               
             
             
               
                 [ 
                 
                   Expression 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   1 
                 
                 ] 
               
             
           
         
       
     
   
   Next, based on Expression 2, (I α , I β , I 0 ) is transformed into a rotating coordinate (I d , I q , I 0 ) using the rotor position θ s . This is nothing but the definition of a general dq transformation. 
   
     
       
         
           
             
               
                 
                   ( 
                   
                     
                       
                         
                           I 
                           d 
                         
                       
                     
                     
                       
                         
                           I 
                           q 
                         
                       
                     
                     
                       
                         
                           I 
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                   ) 
                 
                 = 
                 
                   
                     
                       2 
                       3 
                     
                   
                   ⁢ 
                   
                     ( 
                     
                       
                         
                           
                             cos 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             θs 
                           
                         
                         
                           
                             
                               - 
                               sin 
                             
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             θs 
                           
                         
                         
                           0 
                         
                       
                       
                         
                           
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                             ⁢ 
                             
                                 
                             
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                             θs 
                           
                         
                         
                           
                             
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                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             θs 
                           
                         
                         
                           0 
                         
                       
                       
                         
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                           0 
                         
                         
                           1 
                         
                       
                     
                     ) 
                   
                   ⁢ 
                   
                     ( 
                     
                       
                         
                           
                             I 
                             α 
                           
                         
                       
                       
                         
                           
                             I 
                             β 
                           
                         
                       
                       
                         
                           
                             I 
                             0 
                           
                         
                       
                     
                     ) 
                   
                 
               
             
             
               
                 [ 
                 
                   Expression 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   2 
                 
                 ] 
               
             
           
         
       
     
   
   The electric power system voltage V 1  detected by the system voltage detector  21  is changed into scalar V by a system voltage detector  43 , and the deviation between the voltage control command value V* and V is inputted into an alternating-current voltage controller  44  so as to obtain a d-axis current command value I d *. The alternating-current voltage controller  44  shall preferably be an ordinary PI controller. 
   The primary current I 1  of the doubly-fed machine  4  (current through the stator winding) detected by a primary current detector  22  and the electric power system voltage V 1  are changed into scalar power P by an effective power detector  45 , and the deviation between the power control command value P* and P* is inputted into an effective power controller  46  so as to obtain a q-axis current command value I q *. The effective power controller  46  shall preferably be an ordinal PI controller. 
   Each deviation between the d-axis current I d  and d-axis current command value I d * and between the q-axis current I q  and q-axis current command value I q * are inputted into a current controller  47  so as to obtain a d-axis voltage command value V d * and q-axis voltage command value V q *, respectively. The current controller  47  shall preferably be an ordinary PI controller. 
   From these voltage command values and rotating position θ s  obtained from the rotating position calculator  20 , 2-phase voltage command values V α * and V β * are obtained respectively using an rotating coordinate inverse transformer  48 , and also 3-phase voltage command values V u *, V v *, and V w * are obtained respectively using a 2-phase/3-phase converter. To be concrete, an inverse transformation in Expression 1 and Expression 2 is performed, and then a dq transformation is performed. 
   The inverter  9  is controlled using these 3-phase voltage command values and gate signal generated by the PWM modulator  50 . 
   Description about the rotating position calculator  20  is given below, using  FIG. 2 ,  FIG. 3  and  FIG. 4 . In these figures, the same symbol is given to the same component/part as in  FIG. 1 .  FIG. 2  is an equivalent circuit of the doubly-fed machine  4 . The voltage equation of this equivalent circuit is expressed as in Expressions 3, 4, 5, and 6. 
   
     
       
         
           
             
               
                 
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                 = 
                 
                   
                     
                       ( 
                       
                         
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                   Expression 
                   ⁢ 
                   
                       
                   
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                 = 
                 
                   
                     
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                   4 
                 
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                       ⁢ 
                       
                           
                       
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                     1 
                   
                 
               
             
             
               
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                   6 
                 
                 ] 
               
             
           
         
       
     
   
   A symbol marked with dot “{dot over ( )}” on its top is a scalar and marked with dash “′” is a primary conversion value. In the expressions, j is an imaginary unit, L 1  is inductance, R 1  is primary resistance, L 2  is secondary leak inductance, R 2  is secondary resistance, R M  is no-load loss resistance, L M  is excitation inductance, e 0  is induced electromotive force, I 0  is excitation current, ω is output frequency, and ω s  is slip frequency.  FIG. 3  shows the vector diagram of the equivalent circuit. Finding the slip frequency ω s  enables to estimate the rotor position. The slip frequency ω s  is obtained from Expressions 3 to 6 and expressed as in Expression 7. 
   [Expression 7] 
   
     
       
         
           
             
               
                 
                   ω 
                   S 
                 
                 = 
                 
                   
                     
                       
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                         M 
                       
                       ⁢ 
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                       ⁢ 
                       
                           
                       
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                       ⁢ 
                       
                           
                       
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                         M 
                       
                     
                     
                       
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                         ⁢ 
                         
                             
                         
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                         ′ 
                       
                     
                   
                   
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                 [ 
                 
                   Expression 
                   ⁢ 
                   
                       
                   
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                   7 
                 
                 ] 
               
             
           
         
       
     
   
   Accordingly, the slip frequency ω s  can be obtained by inputting the detected electric power system voltage V 1 , primary current I 1 , secondary excitation voltage V 2 , secondary current I 2  and system frequency ω into the rotating position calculator  20 . When R&lt;&lt;L applies in Expressions 3 to 7, the primary resistance and secondary resistance can be neglected. A way for finding the slip frequency ω s  using the secondary excitation voltage V 2  has been explained herein, but the voltage command values V u *, V v * and V w * can be used instead of the secondary excitation voltage V 2 . 
   In order to decide the initial value of the slip frequency ω s  at the rotor position θ s  in case the switch  101  is open, the transformation shown in  FIG. 4  is performed. Firstly, position information is set to θ s0  by a time multiplier  201 . Then, from the electric power system voltage V 1 , voltage phase θ 1  is obtained by a phase detector  202 . The generator voltage V g  is then converted into V α  and V β  by a 3-phase/2-phase converter  203  and, from these V α  and V β  and the voltage phase θ 1 , the d-axis voltage V d  and q-axis voltage V q  are obtained by a rotating coordinate transformer  204 . Since the q-axis voltage V q  becomes zero if the electric power system voltage V 1  and generator voltage V g  are at the same phase, it is compared with zero and the difference is inputted into a phase adjuster  205 . By adding/subtracting its output to/from the position information θ s0 , the phase of the rotor position θ s  is adjusted and accordingly, as the electric power system voltage V 1  and generator voltage V g  at the switch  101  become equal, the initial phase of the position information θ s0  is decided. Then, when the switch  101  is closed, the output from the phase adjuster becomes zero because of V 1 =V g  and accordingly the routine for deciding the initial phase does not work in the normal generation mode. θ s  is decided as above. 
     FIG. 5  shows an embodiment wherein a windmill  501  is employed as the power source of the present invention. Power source of the invention may include wind power, hydraulic power, engine and turbine, but greater effect of the invention is expected in the case of aerogeneration system of which number of revolutions is very much variable. 
   According to the above embodiment of the present invention, wherein a doubly-fed machine is controlled without using a rotor position sensor such as resolver, it becomes possible to efficiently control the generator without using a rotor position sensor such as resolver on the doubly-fed machine, and accordingly cost increase of a rotating machine can be prevented. In addition, any noise suppression means is not necessary for the rotor position sensor.