Patent Abstract:
A combustion turbine power generating system and method in which the system includes a permanent magnet type AC power generator, a combustion turbine that drives the AC power generator, a first converter enabling conversion between AC current and DC current and having an AC side connected to the AC power generator, a second converter enabling conversion between AC current and DC current and having a DC side connected to a DC output side of the first converter, a capacitor connected between the first and second converters, a generator-speed control unit that controls the first converter and a DC voltage control unit that controls a DC-side voltage of the second converter. The generator-speed control unit controls the first converter on the basis of a number of revolution command value.

Full Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This is a continuation of U.S. application Ser. No. 10/246,470, filed Sep. 19, 2002, now U.S. Pat. No. 6,684,639, the subject matter of which is incorporated by reference herein. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Filed of the Invention 
     The present invention relates to a combustion turbine power generating system that can realize high efficient and high reliable operation and method of controlling the same. 
     2. Description of Related Art 
     As disclosed in JP-A-09-289776, in a case of a conventional combustion turbine power generating system, a command value for number of revolutions is calculated from a load power to be outputted and the command value for the number of revolutions is inputted to a turbine controller to control the number of revolutions for a combustion turbine, thereby controlling the number of revolutions for a power generator. 
     In the above technique, the command value for the number of revolutions is calculated from the output power of the turbine on the basis of the knowledge that the output power of the turbine is proportional to its the number of revolutions. 
     The turbine controller adjusts a quantity of fuel to be fed on the basis of the command value for the number of revolutions calculated as above and controls the number of revolutions. However, since the efficiency of turbine is influenced by a temperature of suction air or the like, the turbine cannot be always operated at the number of revolutions that the highest efficiency and a low Nox (nitrogen oxide) are attained for a certain fuel quantity. Accordingly, it is difficult that the efficiency of the turbine is always kept to be high. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to make power generation at high efficient state of turbine by controlling the number of revolutions of a power generator. 
     According to an aspect of the present invention, in a combustion turbine power generating system for supplying an output of turbine to an electric power system through a power generator and a power converter capable of converting the power between AC current and DC current, the speed of power generator is always controlled by means of the power converter connected to the power generator. 
     Further, an optimum speed command is produced from state quantity of the turbine and the speed of power generator is controlled on the basis of the optimum speed command by means of the power converter connected to the power generator. 
     Moreover, when a fuel quantity is varied by adjustment of fuel or the like and a current of the power generator is greater than a predetermined value, the speed of power generator is increased temporarily. 
     Other objects, features and advantages of the invention will become apparent from the following description of the embodiments of the invention taken in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a block diagram schematically illustrating the whole of a main circuit and a control system of a combustion turbine power conversion system according to an embodiment of the present invention; 
     FIG. 2 is a block diagram schematically illustrating a generator-speed control unit according to an embodiment of the present invention in detail; 
     FIG. 3 is a block diagram schematically illustrating a DC voltage control unit according to an embodiment of the present invention in detail; 
     FIG. 4 is a block diagram schematically illustrating a turbine control unit according to an embodiment of the present invention in detail; 
     FIG. 5 is a diagram explaining an optimum speed calculation unit of a turbine control unit according to a second embodiment of the present invention; 
     FIG. 6 is a block diagram schematically illustrating a generator-speed control unit according to a second embodiment of the present invention in detail; 
     FIG. 7 is a block diagram schematically illustrating a speed command calculation unit according to a second embodiment of the present invention in detail; and 
     FIG. 8 is a block diagram schematically illustrating another speed command calculation unit according to a second embodiment of the present invention in detail. 
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     An embodiment of a combustion turbine power generating system to which the present invention is applied is now described with reference to the accompanying drawings. FIG. 1 is a block diagram schematically illustrating the combustion turbine power generating system. 
     Referring to FIG. 1, a rotation axis  12  of a turbine  10  is connected to a shaft that supports a rotor  16  of a permanent-magnet generator  14 . The side of a stator  18  of the permanent-magnet generator  14  is connected to an AC side  22  of a converter  20 . The permanent-magnet generator  14  supplies an output power itself to the converter  20  in power generating operation and receives electric power from the converter  20  in motor operation. 
     DC terminals  24  and  26  of the converter  20  are connected to a DC side  32  of a converter  30  through a capacitor  28 . An AC output side  34  of the converter  30  is connected to a reactor  36  constituting an AC filter for eliminating harmonics. The converters  20  and  30  are constituted by well-known semiconductor switching elements and make conversion between AC current and DC current by turning a gate pulse on and off. 
     In this embodiment, in power generating operation, the converter  20  converts AC output power of the AC power generator  14  into DC power and the converter  30  converts DC output power from the converter  20  into AC power. Further, the converter  30  converts AC power from an electric power system  44  into DC power and supplies the DC power to the converter  20 . In motor operation, conversely, the converter  30  receives the AC power from the electric power system  44  and converts the AC power into DC power to supply the DC power to the converter  20 . The converter  20  converts the DC power into AC power and operates the AC power generator as an electric motor. 
     The reactor  36  is connected to a capacitor  38  and a reactor  40  constituting an AC filter. The two series-connected reactors  36  and  40  and the capacitor  38  connected to the junction thereof constitute a T-type AC filter. The reactor  40  is connected through a circuit breaker  42  to the electric power system  44 . 
     A DC voltage control unit  46  for the converter  30  is supplied with detection values S 1  and S 2 , a voltage detection value S 3  and a DC voltage command value S 4  to supply a gate signal S 5  to the converter  30 . 
     The detection values S 1 , S 2  and the voltage detection value S 3  are produced from a current detector  48  that detects a current flowing through the reactor  40 , a voltage detector  50  disposed on the side of the electric power system  44  of the reactor  40 , and a voltage detector  52  for the capacitor  28  disposed on the DC side of the converter  30 , respectively. 
     Further, a generator-speed control unit  54  connected to the converter  20  is supplied with a detection value S 6  and an optimum speed command value S 7  and supplies a gate signal S 8  to the converter  20 . The detection value S 6  and the optimum speed command value S 7  are produced from a current detector  56  for detecting a current produced by the permanent-magnet generator  14  and a turbine control unit  58 , respectively. 
     The turbine control unit  58  is supplied with a power detection value S 9 , a power command S 10  and state quantity S 11  such as temperature and pressure from the turbine  10  and supplies a fuel adjustment command S 12  to the turbine  10 . 
     A power detector  60  detects electric power from AC current S 1  and AC voltage S 2  and produces the power detection value S 9 . Further, the turbine control unit  58  supplies the optimum speed command value S 7  to the generator-speed control unit  54  connected to the power converter  20 . 
     FIG. 2 is a block diagram schematically illustrating the generator-speed control unit  54  connected to the converter  20  in detail. Referring to FIG. 2, the generator-speed control unit  54  is supplied with the optimum speed command value S 7  and the generator current detection value S 6 . The optimum speed command value S 7  is supplied to a subtracter  64 . 
     A phase detector  62  is supplied with output voltage command values S 13  and S 14  of a 2-phase/3-phase coordinate converter  68  and the generator-current detection value S 6  to calculate a phase signal Thg of an induced voltage from the power generator  14  by means of a sensor-less phase detection system. The phase signal is supplied to a 3-phase-to-2-phase coordinate converter  66 , the 2-phase-to-3-phase coordinate converter  68  and a speed calculation unit  70 . 
     The speed calculation unit  70  calculates a speed Omeg from the phase signal Thg of the induced voltage in accordance with the expression (1): 
     
       
         Omeg=Δθ/Δ t   (1) 
       
     
     Δθ: increment of the phase signal Thg 
     Δt: variation of time 
     The subtracter  64  calculates a deviation between the optimum speed command value S 7  and the calculated speed value Omeg to supply the deviation to a speed regulator  72 . The speed regulator  72  can be constituted by, for example, a proportional integral controller. The speed regulator  72  regulates a q-axis current command value (torque current command value) S 15  so that the speed deviation is reduced to zero and supplies the command value to a subtracter  74 . 
     The 3-phase-to-2-phase coordinate converter  66  calculates a d-axis current (excitation current component) Id and a q-axis current (torque current component) Iq from the inputted generator-current detection value S 6  and the phase signal Thg of the induced voltage in accordance with the expression (2). The d-axis current detection value Id is supplied to a subtracter  76  and the q-axis current detection value Iq is supplied to the subtracter  74 .                (         Id           Iq         )     =       (             Iu   ·     cos        (   0   )         +     Iv   ·     cos        (     2                   π   /   3       )         +     Iw   ·     cos        (     4        π   /   3       )                       Iu   ·     sin        (   0   )         +     Iv   ·     sin        (     2                   π   /   3       )         +     Iw   ·     sin        (     4        π   /   3       )                 )          (           cos        (   Thg   )             sin        (   Thg   )                 sin        (   Thg   )             -     cos        (   Thg   )               )               (   2   )                                
     The subtracter  74  calculates a deviation between the q-axis current command value S 15  and the q-axis current detection value Iq and supplies it to a current regulator  78 . The current regulator  78  regulates a q-axis voltage command value S 16  so that the deviation between the command value S 15  and the detection value Iq is reduced to zero and supplies the regulated value to the 2-phase-to-3-phase coordinate converter  68 . 
     Further, the subtracter  76  calculates a deviation between a d-axis current command value S 17  and the d-axis current detection value Id to thereby supply the deviation to a current regulator  80 . The current regulator  80  regulates a d-axis voltage command value S 18  which is an output thereof so that a deviation between the command value S 17  and the detection value Id is reduced to zero, and supplies the regulated value to the 2-phase-to-3-phase coordinate converter  68 . The current regulators  78  and  80  can be constituted by, for example, a proportional integration controller. 
     The 2-phase-to-3-phase coordinate converter  68  is supplied with the phase signal Thg, the d-axis voltage command value S 18  and the q-axis voltage command value S 16  to be thereby calculated voltage command values S 13 , S 14  and S 19  produced by the 2-phase-to-3-phase coordinate converter  68  in accordance with the expressions (3) and (4) to be supplied to a PWM calculation unit (pulse-width-modulation calculation unit)  82 .          (         Vagr           Vbgr         )     =       (           cos        (   Thg   )             sin        (   Thg   )                 sin        (   Thg   )             -     cos        (   Thg   )               )          (         Vdgr           Vqgr         )                 (         Vugr           Vvgr           Vwgr         )     =       (           cos        (   0   )             sin        (   0   )                 cos        (     2                   π   /   3       )             sin        (     2                   π   /   3       )                 cos        (     4                   π   /   3       )             sin        (     4                   π   /   3       )             )          (         Vagr           Vbgr         )                              
     The PWM calculation unit  82  calculates a gate signal S 8  on the basis of the inputted voltage commands S 13 , S 14  and S 19 . The signal S 8  is supplied to the converter  20  constituted by the pulse-width-modulation system to turn on and off semiconductor elements thereof. 
     An example of operation of FIG. 2 is now described. In the generator-speed control unit  54  of FIG. 2, it is defined that a torque current in motor operation of the generator  14  is positive and a torque current in power generating operation is negative. 
     When the optimum speed command value S 7  of the turbine control unit  58  is now increased, the input of the speed regulator  72  is increased. Accordingly, the output (a torque current command value S 15 ) of the speed regulator  72  is increased in the positive direction. 
     Since the torque current in power generating operation is defined to be negative, the fact that the torque current command value S 15  is increased in the positive direction means that the torque current is reduced. When the torque current command value S 15  is increased in the positive direction, the input of the current regulator  78  is increased. 
     In order to reduce the torque current, the current regulator  78  changes the q-axis voltage command value S 16  to delay the phase of the voltage produced by the converter  20 . Consequently, the phase difference between the voltage and the induced voltage of the generator  14  is made small and the torque current is reduced. 
     The reduction of the torque current corresponds to reduction of electric energy taken out from the generator  14 . The generator  14  increases rotational energy by the reduction of the taken-out energy, so that the rotational speed thereof is increased. 
     This can be explained from the equation of motion of the generator given by the expression (5). In the expression (5), when energy of the generator  14  received from the turbine  10  is T and energy taken out by the converter  20  from the generator  14  is Ti, T&gt;Ti represents acceleration, T=Ti fixed speed and T&lt;Ti deceleration. 
     
       
           T−Ti=j·dω/dt   (5) 
       
     
     Conversely, when the speed command value S 7  is reduced in power generating operation, the positive-direction input of the speed regulator  72  is reduced. Accordingly, the output (torque current command value S 15 ) of the speed regulator  72  is increased in the negative direction. 
     Since the torque current in power generating operation is defined to be negative, change of the torque current command value S 15  in the negative direction means that the torque current is increased. In order to increase the torque current, the current regulator  78  reduces the q-axis voltage command value S 16  and advances the phase of the voltage produced by the converter  20 . Thus, a phase difference between the voltage and the induced voltage of the generator  1  is increased. 
     The increase of the torque current corresponds to increase of electric energy taken out from the generator  14 . The generator  14  reduces the rotational energy by the increase of the taken-out energy, so that the rotational speed thereof is reduced. 
     In this case, the relation of the energy T inputted to the generator  14  from the turbine  10  and the energy Ti taken out from the generator  14  by the converter  20  is T&lt;Ti, so that the generator is decelerated. 
     FIG. 3 is a block diagram schematically illustrating the DC voltage control unit  46  for the converter  30  in detail. In FIG. 3, the DC voltage control unit  46  is supplied with the current detection value S 1 , the voltage detection value S 2 , the DC voltage detection value S 3  and the DC voltage command value S 4 . 
     The AC voltage detection value S 2  is supplied to a phase detector  84  and a 3-phase-to-2-phase coordinate converter  86 . The phase detector  84  calculates a phase signal Thn following the voltage of the electric power system  44  by means of the phase-locked loop (PLL) system, for example, and supplies the phase signal Thn to 3-phase-to-2-phase coordinate converters  88  and  86  and a 2-phase-to-3-phase coordinate converter  90 . 
     The DC voltage command value S 4  and the DC voltage detection value S 3  are inputted to a subtracter  92 , which supplies a deviation between the DC voltage command value S 4  and the DC voltage detection value S 3  to a voltage regulator  94 . 
     The voltage regulator  94  can be constituted by, for example, a proportional integration controller. The DC voltage regulator  94  regulates a d-axis current command value (effective current command value) S 22  produced therefrom so that the inputted deviation is reduced to zero and supplies the command value to a subtracter  96 . 
     The 3-phase-to-2-phase coordinate converter  88  calculates a d-axis current detection value Idn (effective current) and a q-axis current detection value Iqn (reactive current) from the inputted current S 1  in accordance with the conversion equation given by the expression (2) and supplies the d-axis current detection value Idn and the q-axis current detection value Iqn to the subtracter  96  and a subtracter  98 , respectively. 
     The subtracter  96  calculates a deviation between the d-axis current command value S 22  and the d-axis current detection value Idn and supplies the deviation to a current regulator  100 . The current regulator  100  regulates a d-axis voltage command value S 23  so that the deviation between the command value S 22  and the detection value Idn is reduced to zero and supplies the command value to an adder  103 . 
     Similarly, the subtracter  98  calculates a deviation between a q-axis current command value S 24  and the q-axis current detection value Iqn and supplies the deviation to a current regulator  102 . The current regulator  102  regulates a q-axis voltage command value S 25  so that a deviation between the inputted command value and the detection value is reduced to zero and supplies the command value to an adder  104 . The current regulators  100  and  102  can be constituted by, for example, a proportional integration controller. 
     The 3-phase-to-2-phase coordinate converter  86  calculates a d-axis voltage detection value (phase component coincident with system voltage  44 ) and-a q-axis voltage detection value (component orthogonal to the d-axis voltage detection value) Vqn from the inputted voltage S 2  in accordance with the conversion equation given by the equation (2) and supplies the values Vdn and Vqn to the adders  103  and  104 , respectively. 
     The adder  103  adds the d-axis voltage command value S 23  and the d-axis voltage detection value Vdn and supplies its sum to the 2-phase-to-3-phase coordinate converter  90 . Similarly, the adder  104  adds the q-axis voltage command value S 25  and the q-axis voltage detection value Vqn and supplies its sum to the 2-phase-to-3-phase coordinate converter  90 . 
     The 2-phase-to-3-phase coordinate converter  90  is supplied with the phase signal Thn and the results of the adders  104  and  103  and calculates voltage command values S 26 , S 27  and S 28  produced therefrom in accordance with the conversion expressions (3) and (4) to supplies them to the PWM calculation unit  106 . 
     The PWM calculation unit  106  calculates the gate signal S 5  from the inputted voltage commands S 26 , S 27  and S 28 . In order to control to turn on and off the semiconductor elements of the converter  30  constituted by the pulse width modulation system, the gate signal S 5  is supplied to the converter  30 . 
     FIG. 4 is a block diagram schematically illustrating the turbine control unit  58  in detail. In FIG. 4, the turbine control unit  58  is supplied to the power command value S 10 , the power detection value S 9  and the state quantity S 11 . 
     A subtracter  108  calculates a deviation between the power command value S 10  and the power detection value S 9  and supplies the deviation to an AC power regulator  110 . The AC power regulator  110  can be constituted by, for example, a proportional integration controller. The AC power regulator  110  produces a power command value S 30  which is the power command value S 10  corrected so that the deviation between the command value and the detection value is reduced to zero. 
     The corrected power command value S 30  is supplied to a fuel conversion unit  112 . The fuel conversion unit  112  calculates the fuel adjustment command value S 12  from the power and outputs the command value. 
     Further, the corrected power command value  30  is also supplied to an optimum speed calculation unit  114 . The optimum speed calculation unit  114  is supplied with the corrected power command value S 30  and the state quantity S 11  and refers to optimum operation conditions in previously set states to produce the optimum speed command value S 7  for satisfactory turbine efficiency. 
     Referring now to FIG. 5, operation of the optimum speed calculation unit  114  is described. The graph shown in (a) of FIG. 5 shows a relation of the number of revolutions of the generator  14  and a temperature at an outlet of the turbine  10 . Further, the graph shown in (b) of FIG. 5 shows a relation of the power generation efficiency and the temperature at the outlet of the turbine  10 . 
     When the temperature at the outlet of the turbine, for example, is used as the state quantity S 11  of the turbine  10 , the optimum speed command S 7  is decided from the optimum number of revolutions (shown in the graph of (a) in FIG. 5) for operation at the highest power generation efficiency. 
     When the optimum number of revolutions is tabulated for each output power, for example, which is a certain power output condition from the graphs shown in FIG. 5, the optimum speed calculation unit  114  can always produce the optimum speed command value S 7 . 
     Further, in addition to the tabulation, the optimum speed command value S 7  can be obtained even by reducing the speed when the outlet temperature of the turbine is low and by increasing the speed when the outlet temperature of the turbine is high so that the temperature of the turbine is equal to the permissible maximum temperature Tmax. 
     In the above description, the outlet temperature of the turbine is used, while even the state quantity corresponding to the outlet temperature of the turbine is used to attain the same function. Further, the efficiency of the general combustion turbine as described above is varied depending on the number of revolutions and even the combustion turbine utilizing high-humidity air can attain the same effects. 
     According to the embodiment, since the speed of the generator can be always controlled by the converter  20  connected to the generator  14  even in power generating operation, its control is simplified as compared with the case where control is once stopped and rectification by diodes is made. 
     Further, the optimum speed command S 7  is prepared from the state quantity S 11  of the turbine  10  and the speed of the generator is controlled by the converter  20  connected to the generator  14  on the basis of the optimum speed command S 7 , so that the generator  14  can be operated at the speed of the satisfactory turbine efficiency. 
     In the embodiment, sensor-less control is used for control of the converter of the generator  14 , while even in the case where a position detector connected to the rotation axis  12  of the generator  14  is used to detect a phase, the same effects can be attained. 
     Another embodiment of the present invention is now described. Like constituent elements are designated by like reference numerals throughout the drawings and detailed description thereof is omitted. 
     [Embodiment 2] 
     FIGS. 6 to  8  schematically illustrate another embodiment for realizing a combustion turbine power converting apparatus and a control method of the present invention. The generator-speed control unit  118  of FIG. 6 is different in partial configuration from the generator-speed control unit  54  of the embodiment 1. 
     The optimum speed command value S 7  inputted from the turbine control unit  58  is supplied to a speed command calculation unit  116  and an output of the speed command calculation unit  116  is used as the speed command value. The generator-speed control unit  54  of FIG. 1 can be replaced by the generator-speed control unit  118 . Other configuration shown in FIG. 6 is the same as FIG.  2  and accordingly detailed description thereof is omitted. 
     FIG. 7 is a block diagram schematically illustrating the speed command calculation unit  116  shown in FIG.  6 . The speed command calculation unit  116  is supplied with the d-axis current detection value Id (exciting current component), the q-axis current detection value Iq (torque current component) and the optimum speed command value S 7 . 
     The d-axis current detection value Id and the q-axis current detection value Iq are inputted to an amplitude calculation unit  119 , which calculates an amplitude Is of the current in accordance with the expression (6) and supplies it to a dead-band limiter  120 . 
     
       
           Is=√{square root over (Id 2   +Iq   2 )}   (6) 
       
     
     The dead-band limiter  120  outputs the input value Is when the input value Is exceeds a set value. The output value of the dead-band limiter  120  is supplied to a gain multiplier  122 , which multiplies the output value by a predetermined gain and supplies its result to an adder  124 . 
     The adder  124  is supplied with the multiplication result and the optimum speed command value S 7  and supplies its addition result to a limiter  126  for preventing over-speed exceeding the command value. The limiter  126  produces a limit value when the input value exceeds the limit value and produces the input value when the input value is smaller than or equal to the limit value. 
     According to the embodiment, in addition to the advantages of the embodiment 1, the speed of the generator is temporarily increased to absorb or discharge energy produced by inertial energy upon transient variation that fuel is varied by adjustment of fuel fed to the turbine and the current of the converter  20  is larger than a predetermined value. 
     More particularly, since variation of mechanical input can be absorbed by mechanical energy of the rotating body to suppress electrical variation, there can be realized the reliable system that can prevent the over-current of the converter  20 . 
     Further, in the embodiment, the system using the amplitude of the current has been described, while even a speed command calculation unit  128  using the q-axis current (torque current) detection value as shown in FIG. 8 can attain the same effects. 
     As described above, in the embodiment, since the speed is always controlled by the converter connected to the generator even in power generating operation, the control is simplified as compared with the case where control is once stopped and rectification by diodes is made. 
     Further, the optimum speed command is prepared from the state quantity of the turbine and the speed of the generator is controlled by the converter connected to the generator on the basis of the optimum speed command, so that the generator can be operated at speed of the satisfactory turbine efficiency. 
     Moreover, since the speed of the generator is increased temporarily to absorb or discharge energy produced by inertial energy upon transient variation that fuel is varied by adjustment of fuel and the current of the converter is larger than a predetermined value, there can be realized the reliable system that can prevent the over-current of the converter. 
     When the current of the converter is increased, the speed is controlled to be increased temporarily and accordingly there can be realized the reliable system that can prevent the over-current of the converter. 
     According to the present invention, since the speed is always controlled by the converter connected to the generator even in power generating operation, the control is simplified as compared with the case where control is once stopped and rectification by diodes is made. 
     It should be further understood by those skilled in the art that although the foregoing description has been made on embodiments of the invention, the invention is not limited thereto and various changes and modifications may be made without departing from the spirit of the invention and the scope of the appended claims.

Technology Classification (CPC): 5