Abstract:
It is desired to obtain a technique which enables turning of a compressor driven by a multi-shaft gas turbine. The multi-shaft gas turbine has a high-pressure side shaft and a low-pressure side shaft. A compressor drive device applies a drive force to a compressor connected to the low-pressure side shaft of the multi-shaft gas turbine. The compressor drive device includes: a motor which generates a drive force; and a control unit which controls the motor so as to generate an rpm when turning the compressor. If the torque generated by the gas turbine is insufficient, the control unit controls the motor so as to carry out a helper motor operation for increasing the torque.

Description:
TECHNICAL FIELD 
     The present invention relates to a turning of a compressor. The present application claims priority under the Convention based on Japanese patent application No. 2008-290391. Disclosed content of the Japanese patent application is incorporated herein by reference. 
     BACKGROUND ART 
     A multi-shaft type gas turbine having driving shafts of two or more is known. For example, a two shaft gas turbine has a high pressure side shaft arranged in an upstream side and a low pressure side shaft arranged in a downstream side. The low pressure side shaft is connected to, for example, a load like a compressor. 
     During the stop condition of a two shaft gas turbine, a turning operation which rotates the shaft at a low speed by a motor is carried out in order to suppress the thermal deformation of the shaft, and so on. The low pressure side shaft is, in general, not required to carry out turning, mainly because of the shortness of the shaft. 
     In Patent Document 1, a technique regarding the turning of a low pressure rotor of a gas turbine with two shafts is described. 
     Prior Art Documents 
     [Patent Document] 
     
         
         Patent Document 1: Japanese Patent Application 
         Publication JP-A-Showa, 59-90723 
       
    
     SUMMARY OF INVENTION 
     Recently, a multi-shaft gas turbine plant for driving a large-scale compressor has been required. In such a plant, a low pressure side shaft for driving the compressor is very long, so that the turning thereof is required. 
       FIG. 1  shows a plant of a reference technique for explaining the present invention. An example of a two shaft gas turbine and a compressor which is driven thereby is shown. The gas turbine  104  includes a compressor, a combustor and a turbine. The gas turbine  104  includes a high pressure side shaft  110  and a low pressure side shaft  112 . The high pressure side shaft  110  is connected to the motor  102 . The turning of the high pressure side shaft  110  is carried out by the motor  102 . 
     The low pressure side shaft  112  is connected to the compressor  114  and functions as a driving shaft of the compressor  114 . A gear of a pickup device for detecting a rotation speed is mounted on the low pressure side shaft  112 . The pickup device  120  is installed on a position corresponding to the gear  118 . 
       FIG. 2  shows an electromagnetic speed pickup (MPU, Magnetic Pickup) being an example of the pickup device  120 . The gear  118  rotates coaxially and at a same speed with the low pressure side shaft  112 . The head  120   a  of the pickup device  120  has a coil and a permanent magnet arranged therein. When the gear  118  rotates near the head  120   a , caused by the periodic concave and convex pattern (the wheel teeth) in the circumferential direction of the gear  118 , the direction between the head  120  and an edge of the gear  118  varies periodically in time series. According to this variation, a current flows in the coil of the head  120 . The detection value of the magnitude of the current in time series varies in synchronization with the rotation of the gear  118 . The control device  120   b  generates a rotation speed signal indicating the rotation speed of the gear  118  based on the variation of the current. 
     The motor  116  is connected to the compressor  114 . The motor  116  is driven by the variable frequency driving device  122  and the control device  124 . The motor  116  drives the low pressure side shaft  112  as a helper motor to assist an output when the output of the turbine  104  is insufficient to drive the compressor  114  under a desired driving condition. 
     The rotation speed signal generated by the pickup device  120  is inputted to the control device  124 . The control device  124  carries out a feedback control of the motor  116  based on the detected rotation speed of the low pressure side shaft  112  indicated by this signal. 
     When turning of the low pressure side shaft  112  is carried out in such a plant, if an existing helper motor  116  and a rotation speed detection pickup  120  can be used, additional facilities are not required. However, in the electromagnetic speed pickup exemplified in  FIG. 2 , the voltage is low when the rotation speed of the gear  118  is small. Therefore, it is appropriate for the detection of the rotation speed under a normal operation, but not appropriate for a case where the rotation speed is small (about 100 rpm or less). The rotation speed range under the turning operation is about 10 to 20 rpm, so that the pickup device  120  is not able to generate the rotation speed signal under the turning, and the motor  116  is not able to be appropriately controlled. 
     An object of the present invention is to provide a technique which enables a turning of a compressor driven by a multi-shaft gas turbine. 
     According to an aspect of the present invention, a compressor driving device generates a driving power to drive a compressor connected to a low pressure side shaft of a multi-shaft gas turbine having a high pressure side shaft and the low pressure side shaft. The compressor driving device includes: a motor for generating the driving power; and a control section for controlling the motor to generate a turning rotation speed being a rotation speed of a turning of the compressor, and to control the motor to carry out a helper motor drive by which an assist torque is generated for assisting a torque of the gas turbine when a torque generated by the gas turbine is lacking. 
     According to another aspect of the present invention, a turning for the low pressure side shaft is carried out with the turning of the compressor. 
     According to further another aspect of the present invention, the compressor driving device further includes: a low speed pickup sensor for detecting a rotation speed of the low pressure side shaft when the turning of the compressor is carried out and output a detection signal for turning indicating the detected rotation speed. The control section controls the motor in accordance based on the detection signal for turning when the turning of the compressor is carried out. 
     According to further another aspect of the present invention, in the compressor driving device, a rotation speed detection member is arranged on the low pressure side shaft at a position corresponding to the low speed pickup. The low speed pickup has a head and generates the detection signal for turning in time series by detecting a distance between the head and a periodic convex and concave pattern formed on the rotation speed detection member. 
     According to further another aspect of the present invention, the compressor driving device further includes: a high speed pickup for detecting a rotation speed of the low pressure side shaft and output the detected rotation speed as a helper motor rotation speed signal when the helper motor drive is carried out. The control section controls the motor based on the helper motor rotation speed signal when the helper motor drive is carried out. 
     According to further another aspect of the present invention, in the compressor driving device according to claim  5 , the high speed pickup includes a coil and generates the helper motor rotation speed detection signal based on a periodic variation of a current flowing the coil generated by a moving of a periodic convex and concave pattern of a rotation speed detection member formed on the low pressure side shaft. 
     According to further another aspect of the present invention, in the compressor driving device, the control section includes a protection circuit for stopping the turning of the compressor when a rotation speed of the low pressure side shaft excesses a predetermined value. 
     According to an aspect of the present invention, a gas turbine plant includes: a multi-shaft gas turbine which includes a high pressure side shaft and a low pressure side shaft; a compressor connected to the low pressure side shaft; and a compressor driving device for generating a driving power of the compressor according to the present invention. 
     According to an aspect of the present invention, a driving method of a compressor being connected to a low pressure side shaft of a multi-shaft gas turbine including a high pressure side shaft and the low pressure side shaft includes: controlling the motor to generate a turning rotation speed being a rotation speed of a turning of the compressor; and controlling the motor to carry out a helper motor drive by which an assist torque is generated for assisting a torque of the gas turbine when a torque generated by the gas turbine is lacking. 
     According to the present invention, a technique which enables a turning of a compressor driven by a multi-shaft gas turbine is provided. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other objects, advantages and features of the present invention will be more apparent from the following description of certain preferred embodiments taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  shows a plant in a reference technique; 
         FIG. 2  shows an electromagnetic pickup; 
         FIG. 3  shows a gas turbine plant according to a first embodiment of the present invention; 
         FIG. 4  shows a control logic diagram according to the first embodiment of the present invention; 
         FIG. 5  shows a gas turbine plant according to a second embodiment of the present invention; and 
         FIG. 6  shows a control logic diagram according to the second embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Best embodiments for implementing the present invention will be explained below with reference to the drawings. 
     [First Embodiment] 
     An embodiment of the present invention is explained below with reference to the drawings.  FIG. 3  shows a two shaft gas turbine plant according to a first embodiment. The gas turbine  4  includes a compressor, a combustor, and a turbine. The compressor takes in and compresses the air. The compressed air is supplied to the combustor. The compressed air and a fuel are combusted in the combustor to generate a combustion gas. The turbine is driven by the combustion gas. 
     The turbine upstream side  6  includes the combustor and high pressure side blades of the turbine. They are driven by the high pressure side shaft  10 . The turbine downstream side  8  includes low pressure side blades driven by the low pressure side shaft  12 . The high pressure side shaft  10  and the low pressure side shaft are arranged rotatably around a same axis by the respective bearings. The high pressure side shaft  10  and the low pressure side shaft are not connected structurally and are able to be rotated independently. The low pressure shaft  12  driven via the gas flow, namely, the low pressure side blades are driven by the combustion gas supplied from the high pressure side blades. 
     The compressor  14  is connected to the gas turbine  4  as a load. This compressor composes a part of another thermal cycle engine and so on which is not shown in the drawings. The compressor  14  of the present embodiment is driven by the low pressure side shaft  12  being a driving shaft. Therefore, as described later, the turning of the low pressure side shaft  12  of the gas turbine  4  is carried out simultaneously by the turning of the compressor  14 . The compressor driving device for driving the compressor  14  includes a motor  16  being an electric motor for supplying a torque to the low pressure side shaft  12  being a driving shaft of the compressor  14 , and a control unit which controls the motor. The control unit includes a variable frequency driving device  22  and a control device  24 . The compressor driving device further includes a gear  18  being a member for detecting the rotation speed of the low pressure side shaft  12  and a high speed pickup  20 . 
     The motor  16  is connected to the compressor  14 . The motor  16  is controlled by the variable frequency driving device  22  and the control device  24 . The gear  18  is mounted on the low pressure side shaft  12 . The gear  18  is rotationally symmetric around the central axis of the low pressure side shaft at a periodic angle, has teeth formed at a predetermined pitch in the circumferential direction, and rotates at a same angular velocity with the low pressure side shaft  12  around the same axis with the low pressure side shaft  12  as the center. The high speed pickup  20  has a head including a permanent magnet and a coil as explained with reference to  FIG. 2 . When the gear  18  rotates, a current flows in the coil of the head. The current or the voltage waveform of this current shows a waveform being in synchronization with the rotation (more correctly, increase and decrease of the distance with a tooth of the gear  18  near the head) of the gear  18 . The high speed pickup  20  generates a rotation speed signal which indicates the rotation speed (rpm) of the low pressure side shaft  12  based on this waveform. 
     The motor is operated as a helper motor to assist a lacking of the output of the gas turbine  4  to the load of the compressor  14 . The variable frequency driving device  22  and the control device  24  determines that the output of the gas turbine is lacking when, for example, with monitoring the detected value of the temperature of the exhaust gas of the gas turbine  4 , the increase of the temperature exceeds a predetermined criterion which is preliminary stored. The variable frequency driving device  22  and the control device  24  controls the motor  16  to increase the motor torque as required in response to the determination indicating the output lacking. 
       FIG. 4  is a control logic diagram showing the control carried out by the control device  24 . In the left side column of  FIG. 4 , the signals inputted to the control device  24  are indicated. These are inputted from a higher-level device which carries out setting of operation conditions of the turbine  4 , compressor  14  and so on. Or these signals are directly inputted from a detection device like the high speed pickup  20 . In the right side column of  FIG. 4 , the signals generated by the control device  24  in response to the inputted signals and used for control are indicated. 
     The control device  24  outputs a motor ON/OFF signal S 7  for turning on or off the motor  16  in response to the set signal S 1  for setting the motor ON/OFF from an outside when the set signal S 1  is inputted. When the speed control signal S 2  is inputted, the control device  24  generates the signal S 8  and is set to the speed control mode. In the speed control mode, the control device  24  controls the motor  16  so that the difference between the rotation speed of the compressor  14  (namely, the detection value of the rotation speed of the low pressure side shaft  12 ) and the speed set value S 5  given from an outside (more precisely, the speed set value S 1  after limited by the limiter L 3 ). The control device  24  generates the speed signal S 10  based on the rotation speed signal S 4  outputted by the high speed pickup  20  to use as the detection value of the rotation speed. 
     The control device  24  generates the signal S 9  and is set to the torque control mode when the set signal S 3  for setting to the torque control mode is inputted. At this time, the control signal S 9  is outputted under the condition that the set signal S 2  indicates that the speed control setting by the logic elements L 1 , L 2 . In the torque control mode, the control device  24  controls the motor  16  so that the difference between the detection value of the torque of the compressor  14  (namely, the torque of the low pressure side shaft  12 ) and the torque set value S 6  given from an outside becomes small. According to the above control, the motor  16  is controlled in a case of the start up of the plant and a case where the output of the gas turbine  4  is lacking to the load. 
     The turning device  26  is installed to be able to connect to the low pressure side shaft  12  of such a plant. The turning device  26  is connected to the low pressure side shaft  12  via a gear mechanism. This gear mechanism is detached from the low pressure side shaft when the turning is finished. Therefore, the load of the turning device  26  is not applied to the low pressure side shaft  12  under a normal operation. For this plant, the turning is carried out in a period where the normal operation of the gas turbine  4  is stopped. The turning of the high pressure side shaft  10  is carried out by the motor  2 . The turning of the low pressure side shaft  12  being a rotation shaft of the compressor  14  is carried out by the turning device  26 . By such turning operations, even for a plant which drives a large-size compressor, it is possible to solve problems like a deformation of the driving shaft of the compressor by turning. 
     [Second Embodiment] 
       FIG. 5  shows a configuration of a two shaft gas turbine plant according to a second embodiment of the present invention. The followings are same to the first embodiment: motor  2 ; gas turbine  4 ; high pressure side shaft  10 ; low pressure side shaft  12 ; compressor  14 ; motor  16 ; variable frequency driving device  22 ; high speed pickup  20 . 
     The plant according to this embodiment is different from that of the first embodiment in that the low speed pickup  28  is installed, and the control logic of the control device  24   a  is different. As a result of the difference, as explained below in detail, the turning device  26  of the second embodiment which is dedicated to the turning of the compressor is not required. 
     The low speed pickup  28  detects the rotation speed of the low pressure side shaft  12  using the gear  18  mounted on the low pressure side shaft  12 . The gear  18  may be the gear  18  of the high speed pickup  20  used in the normal operation, and also may be a gear dedicated to the low speed pickup  28 . 
     The low speed pickup is a detector being appropriate for detecting the rotation speed of the low pressure side shaft  12  during the turning operation of the compressor  14 . As an example of such a detector, there is a displacement sensor which detects the distance between a head of the detector and a target object in real time to generate a detection signal indicating the distance. By measuring the distance between the head and the convex-concave pattern which is formed by the teeth of the gear and is periodic in the circumferential direction in time series, the detection signal which varies periodically in synchronization with the timing of the teeth passing near the head in accordance with the gear rotation is obtained. The rotation speed of the low pressure side shaft  12  can be detected from the detection signal. 
     An example of the displacement sensor is explained below. The displacement sensor includes a coil in the head. By flowing a high frequency current in the coil of the head from a power source connected to the displacement sensor, a high frequency magnetic field is generated. By this high frequency magnetic field, an eddy current flows in a metallic target object near the head. By detecting the variation of the impedance of the coil caused by the flow of the eddy current, the distance between the head and the target object can be detected. 
     When a detection device which can detect the rotation speed in a range including both of the rotation speed of the motor  16  in use as the helper motor and the rotation speed under the turning, both function of the high speed pickup  20  and the low speed pickup  28  can be realized by such a detection device. When it is difficult to prepare such a detection device, by preparing the detection devices which are dedicated to the high speed rotation and low speed rotation respectively as shown in  FIG. 5 , the control under the turning can be realized at low cost. 
       FIG. 6  is a control logic diagram showing a control carried out by the control device  24   a . In the left side column of  FIG. 6 , signals inputted to the control device  24   a  are indicated. These are inputted form a higher-level device which carries out setting of operation conditions of the turbine  4 , compressor  14  and so on. Or these signals are directly inputted from a detection device like the high speed pickup  20  or the low speed pickup  28 . In the right side column of  FIG. 6 , the signals generated by the control device  24   a  in response to the inputted signals are indicated. In the following description of the various ON/OFF controls in this control logic, the ON and OFF are represented by the value 1 and 0, respectively. 
     The control device  24   a  includes a protection circuit L 11 . The protection circuit L 11  outputs the motor ON/OFF signal S 30  which indicates that the motor is turned ON only in a case where a predetermined condition is satisfied when the value 1 indicating that the motor is turned ON is inputted as the set signal S 21  for setting the motor ON/OFF. When the condition is not satisfied, the protection operation is carried out by outputting the motor ON/OFF signal S 30  for turning off the motor. 
     The protection circuit L 11  includes a comparator L 12 . The comparator L 12  inputs the signal S 26  which indicates the rotation speed of the low pressure side shaft  12  detected by the low speed pickup  28 . When the inputted rotation speed is a predetermined value or less, the comparator L 12  outputs the value 0. When the inputted rotation speed excesses the predetermined value, the comparator L 12  outputs the value 1. 
     The OR element L 13  inputs an output of the comparator L 12  and the signal S 29  which indicates the regeneration operation (being the value 1 when the regeneration operation is carried out and the value 0 when it is not carried out) and is outputted from the control device  24   a . The AND element L 14  inputs the output of the OR element and the set signal S 22  (being the value 1 when the turning is carried out and the value 0 when the turning is not carried out) of the turning mode of the motor  16 . The output value of the AND element L 14  is inverted by the inverter L 15  and inputted to a terminal of the AND element L 16 . The set signal S 21  of the motor ON/OFF is inputted to another terminal of the AND element L 16 . 
     By such a protection circuit L 11 , the motor ON/OFF signal S 30  takes the value 1 and the control device  24   a  drives the motor  16  only when the set signal S 21  of the motor ON/OFF is the value 1, and the following conditions are satisfied.
     (1) The motor  16  does not carry out the turning operation of the compressor  14  (the set signal S 22  takes the value 0).   (2) The motor  16  is carrying out the turning operation of the compressor  14 , the rotation speed of the low pressure side shaft  12  detected by the low speed pickup  28  does not exceed a predetermined value, and the motor  16  is not in the regeneration operation.   

     By such a protection circuit, it is possible to automatically stop the turning during the output of the set signal S 22  to carry out the turning operation of the compressor  14  when the rotation speed of the low pressure side shaft  12  increases to more than a predetermined criterion or when an abnormal event, for example a control to start the regeneration operation of the motor  16  starts, occurs. 
     Next, the switching of the operation mode (either one of the turning mode, speed control mode, and torque control mode) when the motor drives the low pressure side shaft  12  will be explained. When the value 1 is inputted as the set signal S 22  of the turning, the signal S 36  indicating to set the control of the motor  16  to the turning is generated. Further, the set signal S 22  is inputted to the OR element L 23 . When the value of the set signal S 22  is 1, the output of the OR element L 23  is 1, and based on the output of the OR element, the signal S 31  to set the speed control is generated. Further, based on the value of the output of the OR element L 23  inverted by the inverter L 24 , the signal S 32  to set the torque control is generated. As a result, when the set signal S 22  being value 1 is inputted, the signal S 31  being value 1 and the signal S 32  being value 0 are outputted. Namely, by such a control, when a signal to set to the turning mode is inputted, the torque control is automatically released and the feedback control of the speed is set. 
     The set signal S 22  is further inputted to an input terminal of the AND element L 19  via the inverter L 17 . The set signal S 23  of the speed control mode is inputted to another input terminal of the AND element L 19 . In accordance with the output signal of the AND element L 19 , the signal S 37  which instructs to set the control of the motor  16  to the speed control mode is generated. By this control, the set signal S 22  of value 1 which instructs to set to the turning mode functions as the disable signal to the set signal S 23  of the speed control mode. As a result, it can be prevented that the speed control mode is erroneously set when the set signal S 22  of the turning mode is inputted. 
     The rotation speed signal generated by the high speed pickup  28  for the normal operation is inputted to the control device  24   a  as the normal rotation speed signal S 25 . This normal rotation speed signal S 25  is treated as a detection value of the rotation speed. 
     The rotation speed signal generated by the low speed pickup  28  for the turning is inputted to the control device  24   a  as the turning detection signal S 26 . The normal detection signal S 25  and the turning detection signal S 26  are inputted to the switch L 26 . The switch L 26  selects and outputs the normal rotation speed signal S 25  when the turning set signal S 22  has value 0. The switch L 26  selects and outputs the turning detection signal S 26  when the turning set signal S 22  has value 1. The output of the switch L 26  is used for the speed control of the motor  16  as the speed detection signal S 33 . 
     The upper limit of the speed set value S 27  is limited by the high value limiter L 27  and the low value limiter L 28 . The high value limiter L 27  limits the rotation speed of the low pressure side shaft  12  during the normal operation (for example, the upper limit 5000rpm). The low value limiter limits the rotation speed of the low pressure side shaft  12  during the turning (for example, the upper limit 20rpm). The switch L 29  selects and outputs the output of the high value limiter L 27  when the turning set signal S 22  has value 0. The switch L 29  selects and outputs the low value limiter L 28  when the turning set signal S 22  has value 1. 
     The switch L 30  selects a signal in response to the output of the AND element L 14 . Under a normal regular operation or turning, the output of the AND element L 14  is value 0. In this case, the switch L 30  selects the output of the switch L 29  and output it as the speed set value S 34 . The speed set value S 34  is used as the set value of the rotation speed of the low pressure side shaft  12  under the speed control mode. 
     The output of the AND element L 14  is value 1 in the following cases.
     (1) A case where the turning set signal S 22  has value 1, and the motor regeneration signal S 29  has value 1.   (2) A case where the turning set signal S 22  has value 1 and the comparator L 12  outputs the value 1. Namely, a case where the rotation speed of the low pressure side shaft  12  exceeds a predetermined value during the turning operation.   

     In a case where these abnormal events occur, the selector L 30  outputs the value 0.0 generated by the signal generator L 31  as the speed set value S 34 . By this control, in a case where an abnormal event occurs during the turning, the setting of the undesirable speed set value can be avoided. 
     The torque set value S 28  is used for a control as the set value of the torque generated by the low pressure side shaft  12  under the torque control mode. In this case, the motor  16  undertakes a part of the torque as a helper motor which assists the load. 
     In the above description, some embodiments of the present invention are explained by taking an example of the two shaft gas turbine. However, also in a case of three or more shaft gas turbine, same operations and effects can be obtained. In such a case, the shaft which is driven as a common shaft with a compressor among the three or more shafts corresponds to the low pressure side shaft, and other shafts correspond to the high pressure side shaft. 
     In the above, the present invention is explained by referring to some embodiments. However, these embodiments are exemplified only for explaining the invention, and it is obvious for those skilled in the art that they are not to be referred to limit the meaning of the claims of the present invention.