Abstract:
A prime mover control system is provided that can prevent magnification of power fluctuation, included in a feedback signal, that occurs between a generator and a power system, and that enables stable operation of the prime mover to continue, without disturbing the power system. In the case where a deviation detection device ( 1   a ) that receives as input an output-power command value signal indicating a command value that is a target for the output power of a generator driven by a prime mover and an output-power signal indicating the present value of the output power, and that outputs a deviation signal indicating the deviation between the command value and the present value of the output power, and in the case where a control device ( 3   a ) that receives as an input the deviation signal and outputs a control output signal for controlling the output of the prime mover, a filtering device ( 2   a ) is provided that, in the output-power signal, the deviation signal, or the control output signal, attenuates or eliminates predetermined frequency components caused by periodic fluctuations, in the output power of a generator, that occur due to discrepancy between the output of the prime mover and the generator output power.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a prime mover output control system for a power-generating system in which, by means of a prime mover such as a water turbine, a steam turbine, a gas turbine, or an engine, a generator is rotated to generate electric power. 
     2. Description of the Related Art 
     In a conventional control system for prime mover output (mechanical) torque, there has been a problem in that, because a rotating speed detection signal includes white noise, such as sensor noise, and colored noise due to precession movement of a generator, whereby a signal is always outputted, a control system for prime mover output (mechanical) torque operates; therefore, in order to eliminate these types of noise, limitation of output, a dead band, and a band-pass filter are provided (e.g., Japanese Laid-Open Patent Publication No. 2002-233195, Paragraphs 0017 through 0025, FIG. 1). 
     In addition, there has been a conventional control system (e.g., Japanese Laid-Open Patent Publication No. 1996-266095, Paragraphs 0021 through 0028, FIG. 1) in which a dead-time function receives the deviation between a generator-output command signal and a generator-output signal, determines hunting status, and adds up a difference signal and the output of the dead-time function so as to make a control signal zero. 
     SUMMARY OF THE INVENTION 
     Because conventional prime mover control systems have been configured as described above, it has been possible to eliminate noise included in a rotating-speed detection signal and to prevent excessive fluctuations; however, the conventional prime mover control systems directly respond to power fluctuation components, other than those due to noise, that occur between a generator and a power system, thereby controlling the increase or decrease in prime mover output torque, there has been a case where, depending on a timing when the prime mover output torque fluctuates, the fluctuation is magnified rather than suppressed. Moreover, in a method in which a dead-time function is provided, there has been a problem in that, because actual hunting attenuates or increases its amplitude, thereby causing a difference between a past deviation outputted from the dead-time function and the present deviation, the control signal is not zero, whereby the hunting of the generator output can not be avoided due to the difference. 
     The present invention has been implemented in order to solve the foregoing problems; it is an object to provide a prime mover control system that can prevent magnification of power fluctuation, included in a feedback signal, that occurs between a generator and a power system, and that enables stable operation to continue, without disturbing the power system. 
     The present invention provides a prime mover output control system in which, in the case where a deviation detection device that receives as input an output-power command value signal indicating a command value that is a target for the output power of a generator driven by a prime mover and an output power signal indicating the present value of the output power, and that outputs a deviation signal indicating the deviation between the command value and the present value of the output power, and in the case where a control device that receives as an input the deviation signal and outputs a control output signal for controlling the output of the prime mover, a filtering device is incorporated that, in the output power signal, the deviation signal, or the control output signal, attenuates or eliminates predetermined frequency components caused by periodic fluctuations, in the output power of a generator, that occur due to discrepancy between the output of the prime mover and the generator output power. 
     Fluctuation components, in the output power of a generator, that do not require control of a prime mover, and if unnecessarily controlled, rather deteriorates stability of the power system, are attenuated or eliminated by means of a filtering device; therefore, it is possible to prevent the output of the prime mover from unnecessarily responding to fluctuations in output power of the generator, thereby magnifying the fluctuation in the output power. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram illustrating a control method for a prime mover control system of a power-generating system, according to Embodiment 1 of the present invention; 
         FIG. 2  is a diagram illustrating a model for a single machine infinite bus system; 
         FIG. 3  is a set of charts representing behavior of the power fluctuation between a generator and a power system; 
         FIG. 4  is a block diagram illustrating a control method for a prime mover control system according to Embodiment 2 of the present invention; 
         FIG. 5  is a block diagram illustrating a control method for a prime mover control system according to Embodiment 3 of the present invention; 
         FIG. 6  is a block diagram illustrating a control method for a prime mover control system according to Embodiment 4 of the present invention; 
         FIG. 7  is a block diagram illustrating a control method for a prime mover control system according to Embodiment 5 of the present invention; 
         FIG. 8  is a block diagram illustrating a control method for a prime mover control system according to Embodiment 5 of the present invention; 
         FIG. 9  is a block diagram illustrating a control method for a prime mover control system according to Embodiment 5 of the present invention; 
         FIG. 10  is a block diagram illustrating a control method for a prime mover control system according to Embodiment 5 of the present invention; 
         FIG. 11  is a block diagram illustrating a control method for a prime mover control system according to Embodiment 6 of the present invention; 
         FIG. 12  is a diagram illustrating a relationship between the rotating-speed and the frequency in a single machine infinite bus system; 
         FIG. 13  is a block diagram illustrating a control method for a prime mover control system according to Embodiment 7 of the present invention; 
         FIG. 14  is a block diagram illustrating a control method for a prime mover control system according to Embodiment 8 of the present invention; and 
         FIG. 15  is a block diagram illustrating a computing method for a feedback signal, according to Embodiment 9 of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Embodiment 1 
       FIG. 1  is a block diagram illustrating a control method for a prime mover control system, of a power-generating system, according to Embodiment 1 of the present invention. In  FIG. 1 , an electric-power command value, which is forwarded in accordance with a demand/supply plan to the power-generating system and is a command value as a target for output power, is inputted to a difference detection device  1   a ; an output-power signal, which is utilized as a feedback signal and indicates the present value of output power of a generator (unillustrated), is also inputted by way of a filtering device  2   a  to the deviation detection device  1   a . The deviation detection device  1   a  obtains the difference between the electric-power command value and the filtered output-power signal and outputs a difference signal. Based on the difference signal outputted by the deviation detection device  1   a , a PI circuit  3 , which is an example of a control device for adjusting responsiveness and stability of a control system and implements proportion/integration control, outputs a control output signal for adjusting output of a prime mover. In the case of a water turbine, the control output signal is forwarded to a control system for opening a guide-vane; in the case of a steam turbine, to a boiler control system or to a control system for opening a steam adjusting valve; and in the case of a gas turbine, to a prime mover output adjusting unit such as a combustion control system. 
     The filtering device  2   a  is configured of a filter for, through an average-value computation during a specific time period, attenuating or eliminating fluctuating components that are not required to be responded to, a low-pass filter for transmitting low-frequency components (attenuating or eliminating high-frequency components), a notch filter for attenuating or eliminating a specific frequency components, and the like. 
     Next, the operation of the prime mover control system, of a generator, according to Embodiment 1 of the present invention will be explained. 
     With regard to a single machine infinite bus system briefly illustrated in  FIG. 2 , the output power P e  in the case where a generator is connected with a power system is given by Equation 1: 
     
       
         
           
             
               
                 
                   
                     P 
                     e 
                   
                   = 
                   
                     
                       
                         
                           E 
                           fd 
                         
                         · 
                         
                           V 
                           b 
                         
                       
                       X 
                     
                     ⁢ 
                     sin 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     δ 
                   
                 
               
               
                 
                   Eq 
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                   1 
                 
               
             
           
         
       
     
     In addition, in  FIG. 2 , Reference characters E fd , V b , X, and δ denote a voltage behind transient reactance, the voltage on an infinite bus  4 , reactance between a generator  5  and the infinite bus  4 , and the phase angle of the generator  5 , respectively. 
       FIG. 3  is a set of charts representing the behavior of power fluctuation between the generator and the power system; in  FIG. 3 , a characteristic chart in which, with the abscissa indicating the phase angle δ and the ordinate indicating the output power P e , the output power P e in Equation 1 is represented, and behavior charts representing the behavior in the case of change in the output of a prime mover that drives the generator are added. 
     The characteristic chart consists of two p—δ curves that, in the case where, due to opening of one line, or the like, the reactance X of the power transmission line increases, represent a before-change characteristic and an after-change characteristic, of the output power; the temporal fluctuation in the output power P e , in the case where, due to the change, the output of the prime mover changes, is represented at the right-hand side of the characteristic chart, and the temporal fluctuation in the phase angle δ is represented below the characteristic chart. 
     In the steady state, the generator is operated at a cross point a between a line representing an output P m0  of the prime mover and the characteristic curve representing the output power P e  of the generator, i.e., at the phase angle of δ 0 . 
     In the case where, due to opening of one line, or the like, the reactance X of the power transmission line increases, the output power of the generator changes, thereby causing the following fluctuation: 
     (1) The operating point changes from Point a to Point b. In this case, the output power P e  changes; however, the phase angle δ does not change. 
     (2) Because the P e  becomes smaller than the output P m0  of the prime mover, the generator is accelerated. The generator is accelerated in such a way as to exceed Point c where the output power P e  coincides with the output P m0  of the prime mover. In the case where a rotational loss in the generator and a resistance loss can be neglected, the generator is accelerated to Point d where the areas of triangles Δabc and Δcde are equal. 
     (3) When reaching Point d, the output power P e  is larger than the output P m0  of the prime mover, whereby the generator is decelerated. In the case where the losses are zero, the generator is decelerated Point b. 
     (4) If the losses are zero, the fluctuation from Point b to Point d, of the output power P e , continues; however, in effect, there are various kinds of losses that act in such a way as to suppress the fluctuation of the output power P e ; therefore, the output power P e  eventually converges on Point c (P e  =P m0 , δ=δ s ). In addition, the fluctuation period of the output power P e  is determined by synchronizing torque that is determined by the characteristics of a power system and a generator, and by the total inertial constant of the rotating part of the generator, the prime mover and so on. 
     Meanwhile, because the prime mover control system that implements control in such a way that the deviation between the electric-power command value and the output power P e  becomes zero operates so as to suppress the fluctuation of the output power P e , the output of prime mover changes. 
     The change in the output of the prime mover depends on the characteristics of the prime mover; if, in the case (1) where the operating point changes to Point b, the output of the prime mover increases, the area of the triangle Δabc, i.e., the acceleration energy is magnified, whereby the change is accelerated until the output power P e  exceeds Point d that is a transient point in the case where the output of the prime mover does not change. 
     Next, if, in the case (3) where the operating point changes to Point d, the output of the prime mover decreases, the area of the triangle Δcde, i.e., the deceleration energy is magnified, whereby the generator is decelerated until the output power P e  becomes smaller than Point b that is a transient point in the case where the output of the prime mover does not change. The repetition of the foregoing operation magnifies the oscillation of the change. 
     In Embodiment 1, as described above, after fluctuation components, in the output power of a generator, that does not require control by a prime mover and, if unnecessarily controlled, rather deteriorates stability are attenuated or eliminated, by making the output-power signal from the generator pass through the filtering device  2   a , the deviation between a electric-power command value and a generator-output value is obtained in the deviation detection device  1   a ; therefore, unnecessary fluctuation components are attenuated in or eliminated from the control output signal based on a deviation signal outputted from the deviation detection device  1   a . Accordingly, the output of a prime mover is prevented from unnecessarily responding to the fluctuation in the output power of a generator, thereby magnifying the power fluctuation. 
     In addition, with regard to adjustment of components to be eliminated by the filtering device  2   a , in addition to the method implemented based on the fact that the frequency of the fluctuation components is determined, as described above, by synchronizing torque and the inertial constant of a rotating part, a method, e.g., adjustment of an actual apparatus, with conditions being varied, is conceivable. 
     Heretofore, the local-mode components in a single machine infinite bus system model has been explained; the fluctuation components, which may be caused by the configuration and operation, of a power system, and by the constants of a generator, and which does not require control by a prime mover and, if unnecessarily controlled, rather deteriorates stability, also include other components, such as generator-to-generator-mode components, power system-to-power system-mode components, that occur in a multiple machine system; however, those other components can also be attenuated or eliminated by the filtering device  2   a.    
     Moreover, in  FIG. 1 , an example is illustrated in which the filtering device  2   a  is arranged before the deviation detection device  1   a . The configuration as described above demonstrates the following advantages: however, wherever after the deviation detection device  1   a  (including the prime mover) the filtering device  2   a  is arranged, the same effect of suppressing fluctuation can be obtained. 
     (1) Unnecessary response in stages after the deviation detection device  1   a  can be avoided. 
     (2) Errors and nonlinearization that are caused by a limiter or through saturation can be prevented. 
     (3) In the case of control-mode switching, switching through the deviation signal is easy. 
     Embodiment 2 
     In Embodiment 1, a method has been described in which the magnification of power fluctuation is prevented by attenuating or eliminating fluctuation components that does not require response; however, in Embodiment 2, a control method will be described in which the unnecessary fluctuation is positively suppressed. 
       FIG. 4  is a block diagram illustrating a control method for a prime mover control system according to Embodiment 2 of the present invention. In  FIG. 4 , in place of the filtering device  2   a  in  FIG. 1 , a phase adjustment device  6   a  configured of a lag-lead network (1+T 1 ·s)/(1+T 2 ·s) and the like is arranged before the PI circuit  3 . The adjustment of the phase is similar to that in Embodiment 1, and eventually implemented on the basis of an actual apparatus. 
     In the phase adjustment device  6   a , by changing increase and decrease, in the output of the prime mover, for the fluctuation of the output power P e  of the generator in such a way as to occur at the following timing, thereby making the following behavior to be repeated, the oscillation of the change can be converged: 
     (1) When the output power Pe changes to Point b, the output of the prime mover is reduced. The area of Δabc, i.e., the acceleration energy becomes small, whereby the output power P e  is not accelerated up to as high as Point d that is a transient point in the case where the output of the prime mover does not change. 
     (2) Next, the output at Point d, of the prime mover, is increased. The area of Δcde, i.e., the deceleration energy becomes small, whereby the output power P e  is not decelerated down to as low as Point b that is a transient point in the case where the output of the prime mover does not change. 
     In addition, in  FIG. 4 , an example has been illustrated in which the phase adjustment device  6   a  is arranged between the deviation detection device  1   a  and the PI circuit  3 ; however, also in the case where, as is the case with Embodiment 1, the phase adjustment device  6   a  is provided in the deviation detection device  1   a  and receives the output-power signal, or in the case where the phase adjustment device  6   a  is provided after the PI circuit  3 , the same effect is demonstrated. 
     Moreover, even when the characteristics of the prime mover, which includes a servo system to which the control output signal is outputted and the output-power adjusting unit for implementing output-power adjustment such as combustion control, changes depending on an operational condition, the change in the characteristics of the prime mover can be coped with, by providing multiple phase adjustment device  6   a  and switching them, depending on an operational condition, or by adding a changing device for changing the constant of the phase adjustment device  6   a , depending on an operational condition. 
     Embodiment 3 
     In Embodiment 2, a method has been described in which, in order to adjust the timing at which the output of the prime mover is increased or decreased, the phase adjustment device  6   a  is arranged in series with a control device; however, in Embodiment 3, a method will be described in which, by adding a circuit that responds only to fluctuation components in the output power of the generator, thereby positively increasing or decreasing the output of the prime mover, the fluctuation in the output power of the generator is suppressed. 
       FIG. 5  is a block diagram illustrating a control method for a prime mover control system according to Embodiment 3 of the present invention. The configuration in  FIG. 5  is obtained by, to the configuration in  FIG. 1 , adding a change detection device  7   a  for detecting changing components in the output-power signal, a phase adjustment device  8   a , and a addition device  9   a  for adding up the output of the PI circuit  3  and the output of the phase adjustment device  8   a  and creating the control output signal. 
     The change detection device  7   a  is configured of a differentiation circuit for extracting only fluctuation components, a band-pass filter circuit for transmitting only a component having a predetermined fluctuation frequency, and the like; the phase adjustment device  8   a  is configured of the lag-lead network (1+T 1 ·s)/(1+T 2 ·s) and the like, as is the case with the phase adjustment device  6   a . The adjustment of the phase is implemented in the same manner as that in Embodiment 2. 
     In the configuration in  FIG. 5 , in the case where the output power of the generator fluctuates, a signal corresponding to the fluctuation components only is extracted by the change detection device  7   a , the phase of the signal is adjusted by the phase adjustment device  8   a  in such a way that the output of the prime mover increases or decreases at the same timing for suppressing the fluctuation as described in Embodiment 2, and the signal as the control output signal increases or decreases the output of the prime mover, through the addition device  9   a ; therefore, as is the case with Embodiment 2, the fluctuation in the output power of the generator can be suppressed. 
     Moreover, in Embodiment 3, as a configuration in which a separate circuit is added that responds only to fluctuation components of the output-power signal, a control system is employed in which ordinary power control and fluctuation control can separately be implemented; therefore, each function can be adjusted to an optimal condition. 
     In addition, in  FIG. 5 , a configuration has been illustrated in which the filtering device  2   a  is provided that separates power control in response to the electric-power command value from fluctuation-component suppression control; however, by, in place of the filtering device  2   a , adding the change detection device  7   a  and the phase adjustment device  8   a  and adjusting the phase adjustment device  8   a , the same effect can be obtained. 
     Similarly, by, to a method in which, as described in Embodiment 2, the phase adjustment device  6   a  is provided for implementing power control in response to the electric-power command value, adding the change detection device  7   a  and the phase adjustment device  8   a  and adjusting the phase adjustment devices  6   a  and  8   a , the same effect can be obtained. 
     In addition, it should be understood that, by forwarding the output of the phase adjustment device  8   a  directly to the servo system and the prime mover output adjusting unit for combustion control or the like, to which the control output signal is outputted, the same effect can be obtained. 
     Embodiment 4 
     Letting Tm, Te, M. and Δω denote the output torque of a prime mover, the output torque of a generator, the inertial constant of a rotating part, the rotating-speed deviation, respectively, these factors are in the following relationship: In addition, Reference Character s denotes a Laplace operator. 
     
       
         
           
             
               
                 
                   
                     Δ 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     ω 
                   
                   = 
                   
                     
                       ( 
                       
                         
                           T 
                           m 
                         
                         - 
                         
                           T 
                           e 
                         
                       
                       ) 
                     
                     · 
                     
                       1 
                       
                         M 
                         · 
                         s 
                       
                     
                   
                 
               
               
                 
                   Eq 
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                   2 
                 
               
             
           
         
       
     
     In Embodiment 3, a method has been described in which the output-power signal, from the generator, that is utilized for controlling the output of the prime mover is added by the addition device  9   a , by way of the change detection device  7   a  and the phase adjustment device  8   a ; however, because the relationship among the rotating-speed ω, the output torque of a prime mover, and the output torque of a generator is given by Equation 2, the same effect can be obtained, by, as illustrated in  FIG. 6 , adding the rotating-speed ω, by way of the change detection device  7   b  and the phase adjustment device  8   b.    
     Embodiment 5 
     Embodiments 1 through 3 relate to electric-power control in which the output power of a generator is controlled to be the electric-power command value as a target; however, with regard to the control of the prime mover, a rotating-speed control function is also provided in which the output of the prime mover is increased or decreased in response to the change in the rotating-speed. Embodiment 5 relates to the control of the rotating-speed of the prime mover. 
       FIGS. 7 through 9  illustrate configuration examples of Embodiment 5; with regard to the configurations illustrated in  FIGS. 1 ,  4  , and  5 , the electric-power command value, the output power, of the generator, that is a feedback signal, the PI circuit  3  as a control device are replaced by a rotating-speed command value (normally, a rated rotating-speed), a rotating-speed signal, and a speed drop rate  10   b , respectively. In addition, the rotating-speed signal is detected through a gear or the like mounted on the shaft of the prime mover; the speed drop rate  10   b  is a ratio of the amount of change in the output of the prime mover to the change in the rotating-speed. 
     By being accelerated or decelerated in accordance with the difference between the output of the prime mover and the output power of the generator, the rotating-speed of the prime mover changes. Therefore, when fluctuation in the output power of the generator occurs, the rotating-speed signal fluctuates, and the control output signal changes in accordance with the speed drop rate  10   b , whereby the output of the prime mover is changed. Also in rotating-speed control, depending on the timing at which the output of the prime mover fluctuates, magnification of the fluctuation in the output power of the generator is caused by the same action as that described in Embodiment 1. 
     In consequence, by configuring the control systems as illustrated in  FIGS. 7 through 9 , the same effect as that in electric-power control can be demonstrated also in rotating-speed control, through actions similar to those in Embodiments 1 through 3. 
     In addition, in the configuration in  FIG. 9 , a method has been described in which the rotating-speed signal utilized for rotating-speed control is added to the addition device  9   b , by way of the change detection device  7   b  and the phase adjustment device  8   b ; however, because the relationship between the rotating-speed and the output power of a generator is given by Equation 2, the same effect can be obtained, by, as illustrated in  FIG. 10 , configuring the control system in which the output power of the generator is added, by way of the change detection device  7   a  and the phase adjustment device  8   a.    
     Embodiment 6 
       FIG. 11  illustrates a configuration example of Embodiment 6. In the deviation detection device  1   c  in  FIG. 11 , the deviation between the reference frequency (normally, 50 Hz or 60 Hz) and a frequency signal, as a feedback signal, at an electric-generator terminal or at the power-system side is obtained, converted in accordance with the speed drop rate  10   c  into a controlling variable, and outputted as the control output signal. By forwarding the control output signal to the prime mover output adjusting unit, frequency fluctuation at the electric-generator terminal or at the power-system side is suppressed. 
     In general, because, in prime movers, respective rotating-speed detectors are provided that accurately detect the rotating-speed in order to control the prime mover rotating-speed, the prime mover rotating-speed is utilized as a feedback signal for rotating-speed control. The relationship between the rotating-speed (angular velocity ω=2πf, f is frequency) and the phase angle δ is given by ω=dδ/dt; considering the single machine infinite bus system illustrated in  FIG. 2 , change in the phase angle δ, i.e., change in the frequency, at infinitive point, is zero. The relationship can be illustrated as in  FIG. 12 ; the closer to the infinitive point the subject point is, the smaller the frequency change becomes. In general, because the inner reactance of a generator is large, the generator terminal is considered an approximately infinitive point and the frequency change becomes small. In contrast, in the case of an independent power system that is separated from a large-scale power system, the system frequency is determined by the demand/supply condition within the independent power system; the system frequency is approximately equivalent to the rotating-speed of the prime mover. 
     When a generator is connected with the power system, it is an object of rotating-speed control that, when the frequency changes due to a change in the demand/supply condition in the entire power system, the output of the prime mover is increased or decreased in accordance with a speed drop rate, in order to restore the changed frequency to the original one. Therefore, rotating-speed control through the rotating-speed signal when the generator is connected with the power system is excessive control, whereby power fluctuation is magnified. 
     By, as described in Embodiment 6, employing as a feedback signal the frequency at the terminal of the generator or at the power system, thereby suppressing excessive change in the output of the prime mover, the magnification of fluctuation in the output power of the generator can be prevented. It should be understood that, with the generator disconnected from the power system, frequency fluctuation and rotating-speed fluctuation are, as described above, equivalent to each other, the same control as those in conventional control systems can be maintained. 
     The configuration in  FIG. 11  is obtained by, with regard to the configuration in  FIG. 7 , replacing the rotating-speed command value and the rotating-speed signal by the reference frequency and the frequency signal, respectively and removing the filtering device  2   b ; however, by, with regard to the configuration in  FIG. 11 , adding as in  FIGS. 7 through 10  the filtering device  2   b  and the phase adjustment device  8   b , the same effect as that in Embodiment 5 can be obtained. 
     Embodiment 7 
     In Embodiment 6, a method has been described in which, as a signal for rotating-speed control, a rotating-speed signal is utilized; however, in the case of a no-load condition in which the generator is not connected with the power system, or in the case of an independent power system, the method according to Embodiment 6 is inferior to a method utilizing a rotating-speed signal, in terms of accuracy and sensitivity of the control. Embodiment 7 solves the inferiority. 
       FIG. 13  illustrates a configuration example of Embodiment 7. In  FIG. 13 , a switching device  11  switches between the frequency signal and the rotating-speed signal after determining, based on the input of an independent power system/no-load signal, which signal to be utilized. The independent power system/no-load signal is a status signal to be transferred from the breaker being in its operation mode and from a substation or the like in the case of an independent system; in the case of an independent power system or in the case of a no-load condition, the independent power system/no-load signal is “1”, and in other cases, i.e., in the case of a normal operation condition, the independent power system/no-load signal is “0”; the switching device  11  switches inputs to the speed drop rate  10   d  in such a way that C is A in the case where the independent power system/no-load signal is “0”, and C is B in the case where the independent power system/no-load signal is “1”. 
     With the control system being configured as described above, in the case of a normal operation in which the generator is connected with power system, a deviation signal A that is the deviation between the reference frequency and the frequency signal is selected, converted in the speed drop rate  10   d  into the prime mover output control signal, and outputted as the control output signal; in contrast, in the case of an independent power system or in the case of a no-load condition, a deviation signal B that is the deviation between the rotating-speed command value and the rotating-speed signal is selected, converted in the speed drop rate  10   d  into the prime mover output control signal, and outputted as the control output signal; therefore, in both cases, rotating-speed fluctuation can be suppressed with high accuracy and sensitivity. 
     In addition, in  FIG. 13 , an example has been illustrated in which the switching device  11  is arranged before the speed drop rate  10   d ; however, by employing a configuration in which respective speed drop rate  10   d  are provided for the frequency and the rotating-speed and the respective speed drop rates  10   d  are switched later, or by employing a method in which setting values for the speed drop rate are switched concurrently with the switching of the signals, the same effect can be obtained. Moreover, because the frequency and the rotating-speed are each compared with their reference values, a configuration may be employed in which, without providing the separated deviation detection devices, the frequency and the rotating-speed are switched before the deviation detection device. 
     In addition, in  FIG. 13 , a configuration has been illustrated in which, as a signal for switching the control signals, an operation status signal, such as an operation status of the breaker, is employed; however, by utilizing the characteristics that, as described above, in the case where the generator is connected with the power system, a large difference between the rotating-speed and the frequency at the terminal of the generator or at the power system occurs, but in the case of a no-load condition or in the case of the independent power system, the difference becomes small, and by providing a circuit that determines that, when the difference between the frequency and the rotating-speed becomes small, the generator is in a no-load condition, or in an independent-power-system condition, the control signals may be switched by a signal derived from the determination. 
     Moreover, in  FIG. 13 , a configuration has been explained in which a filter and the like are not provided; however, the switching device  11  can be applied to  FIGS. 7 through 10  in Embodiments 5. Therefore, with a configuration in which a filter, a phase adjustment device, or a change detection device and a phase adjustment device are utilized, it is also possible that, in stead of control based only on the rotating-speed, the control is implemented in which, based on the operation status, the rotating-speed signal and the frequency signal are switchably utilized. 
     Embodiment 8 
     In Embodiment 7, a method has been described in which the rotating-speed signal and the frequency signal are switched in accordance with a operation status; however, in this case, two detection units, i.e., a rotating-speed detection unit and a frequency detection unit are required to be provided. 
     Meanwhile, as illustrated in  FIG. 12 , the relationship between rotating-speed fluctuation and frequency fluctuation at an arbitrary point is determined by the reactance X corresponding to the distance of the arbitrary point; in the case of the terminal of the generator, the rotating-speed fluctuation can be converted into a level equivalent to that of the frequency signal at a terminal  12  of the generator, by multiplying the rotating-speed fluctuation by X e /(X d +X e ) (referred to as a sensitivity adjustment ratio, hereinafter). 
     Embodiment 8 is enabled to demonstrate the same effect as that in  FIG. 7 , through the foregoing principle and with a single detector;  FIG. 14  illustrates a configuration example of Embodiment 8. In  FIG. 14 , the rotating-speed signal is converted, through a sensitivity adjustment rate  13  as a conversion device, into frequency fluctuation sensitivity at a point the power fluctuation at which is requested to be suppressed. 
     By configuring the control system in such a way as described above, also in a single-input-signal control system utilizing as an input signal only the rotating-speed signal, control in accordance with an operation condition can be realized, by selecting through the switching device  11  the input of the speed drop rate  10   d  in such a way that, as is the case with Embodiment 7, C is A in the case where the independent power system/no-load signal is “0”, and C is B in the case where the independent power system/no-load signal is “1”. 
     In addition, by switching the speed drop rates  10   d  between a conventional speed drop rate and a speed drop rate compensated through the sensitivity adjustment rate, the same effect can be obtained. 
     As is the case with Embodiment 7, a configuration in which, by employing the switching device  11 , the rotating-speed signal in Embodiment 8 and a signal obtained by converting the rotating-speed signal into frequency-fluctuation sensitivity are switched in accordance with operation status can also be applied to the configurations in  FIGS. 7 through 10  in Embodiment 5. 
     Embodiment 9 
     With regard to a prime mover control system that carries out control so that the output-power of a generator is equal to an electric-power command value, in Embodiments 1 through 4, a fact has been described that, in the case where the prime mover carries out the control in response to fluctuation of the output power of the generator, the fluctuation of the output power of the generator may be magnified, depending on the timing of the output from the prime mover, and methods of suppressing the magnification of fluctuation have been described. 
     As illustrated in  FIG. 2 , in the steady state, the output of the prime mover and the output power of the generator are equal; however, in a fluctuating condition, they are not equal. In other words, because the prime mover carries out the control by utilizing as a feedback signal the output power of the generator that is different from the output of the prime mover, the prime mover may respond to fluctuation, which is, in terms of genuine output-power control by the prime mover, not required to be responded, to change the output of the prime mover, thereby magnifying the fluctuation of the output power of the generator. 
     Embodiment 9 relates to a method in which, by obtaining through computation a signal having a nature similar to the output of the prime mover and employing the signal as a feedback signal, thereby suppressing unnecessary response by the prime mover control system, the magnification of fluctuation in the output power of the generator can be prevented. 
       FIG. 15  is a block diagram illustrating an example of a computing method for a feedback signal. In  FIG. 15 , a rotating-speed deviation signal that represents the deviation between the rated rotating-speed and an actual rotating-speed, of the generator, is inputted to a differentiation device  14 , the output-power signal from the generator and the output of the differentiation device  14  are added up in an addition device  15 , and a prime mover output corresponding signal is outputted that is employed for controlling the output of the prime mover. 
     It assumed that fluctuation in the rotating-speed is minute and the generator and the prime mover are operated approximately at the rated
 
 P   m   =P   e   +Δω·M·s   Eq.3
 
rotating-speed; in Equation 2, the output torque T m  of the prime mover is equal to the output P m  of the prime mover, and the output torque T e  of the generator is equal to the output power P e  of the generator; therefore, the output of the prime mover is given by Equation 3:
 
       FIG. 15  is a block diagram illustrating the concept of Equation 3. In other words, when the output power P e  of the generator fluctuates, the generator is accelerated or decelerated, due to the deviation between the output power P e  and the output P m  of the prime mover, to change its rotating-speed; therefore, by adding the fluctuation components to the output power P e  of the generator, thereby obtaining through computation the output P m  of the prime mover to be utilized as the prime mover output corresponding signal. Accordingly, in the case where only the output power P e  of the generator changes, the prime mover output corresponding signal does not fluctuates; therefore, unnecessary response of the prime mover control system can be prevented. 
     In addition, the function of differentiation device  14  may be a genuine differential function or an inexact differential function; in the case of a digital control system, a method of computing the difference between the immediately previous value and the present value can demonstrate the same effect. 
     In Embodiment 9, a method has been described in which unnecessary fluctuation, in the output of the prime mover, that occurs when only the output power of the generator fluctuates can be avoided; however, due to inherent fluctuation in the output of the prime mover, or, e.g., due to a computing error in detecting the output power of the generator, fluctuation in the output of the prime mover may occur, and the control through that fluctuation may be implemented at the timing that results in magnification of the fluctuation in the output power of the generator. 
     Thus, by, also in Embodiment 9, employing the methods according to Embodiments 1 through 4, an effect can be obtained in which magnification of fluctuation in the output power of the generator is prevented.