Parallel operation control system and method

Abstract

To provide a parallel operation control system suitable for controlling the parallel operation of a plurality of loads.SOLUTION: According to an embodiment, a parallel operation control system includes a determination unit that determines a critical output value of a steam turbine of a first generator and a critical output value of a steam turbine of a second generator during independent parallel operation of the first generator, which is a steam turbine generator, and the second generator, which is a diesel engine generator or a gas engine generator, without power supply from a commercial power supply; A control unit that performs control corresponding to a load, which is a facility to which power is supplied by each generator, on the other generator, wherein the determination unit re-determines the limit output value every time a predetermined time elapses.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a parallel operation control system and method suitable for controlling the parallel operation of, for example, a steam turbine generator with a diesel engine generator or a gas engine generator. [Background technology]

[0002] In recent years, an increasing number of plants are operating diesel engine generators (hereinafter referred to as "DG") or gas engine generators (hereinafter referred to as "GE") during long-term power outages, setting up equipment such as incinerators to operate steam turbine generators (hereinafter referred to as "STG"), and operating the DG or GE in parallel after the STG has started up.

[0003] Due to fuel reserves and other factors, DGs are often not operated for long periods of time and are then shut down after parallel operation, but some continue parallel operation until the STG stabilizes. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 9-195811 Summary of the Invention [Problem to be solved by the invention]

[0005] However, because STGs adjust the amount of fuel and water in boilers that generate steam and adjust the turbine output, there are cases where output control is not possible if there is not enough steam pressure, and normal equal load sharing control is not possible when the STG and DG are operating in independent parallel operation.Furthermore, when the STG is operating in independent parallel operation, automatic load transfer control of the DG is not possible.

[0006] In addition, if an abnormality occurs in the governor system other than the STG, the same phenomenon will occur.

[0007] In addition, in response to business continuity plans (hereinafter referred to as "BCP"), an increasing number of facilities are operating DG, GE, and gas turbine generators (hereinafter referred to as "GT") in parallel to supply power to loads during power outages.

[0008] There are also cases where a breakdown occurs due to an increase in load, such as a temperature rise (exhaust, lubricating oil, cooling water, bearings, stator windings, etc.) or large vibrations (shaft, bearings, etc.), resulting in a major breakdown and shutdown.

[0009] The parallel operation control system and method of the present invention have been made in consideration of the above circumstances, and an object of the present invention is to provide a parallel operation control system and method suitable for controlling parallel operation of a plurality of loads. [Means for solving the problem]

[0010] According to an embodiment, a parallel operation control system includes a determination unit that determines limit output values ​​of the steam turbines of a first unit, which is a steam turbine generator, and another unit, which is a diesel engine generator or a gas engine generator, during independent parallel operation in which the first unit is operating without power supply from a commercial power source, and a control unit that controls the first unit to maintain a constant output using the limit output value as a target output value, and controls the other units in accordance with the loads, which are facilities supplied with power by the generators, and the determination unit re-determines the limit output value every time a certain period of time has elapsed. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a block diagram showing an example of the configuration of a parallel operation control system to which the parallel operation control method of this embodiment is applied. [Figure 2] FIG. 2 is a system diagram showing an example of a state in which a parallel operation control system to which the parallel operation control method according to each embodiment of the present invention is applied is used. [Figure 3] FIG. 3 is a flowchart showing the operation of the parallel operation control in the conventional method. [Figure 4]FIG. 4 is a flowchart showing an example of the operation of the parallel operation control system when constant output control is performed. [Figure 5] FIG. 5 is a flowchart showing an example of operation of the parallel operation control system in the event of an abnormality when constant frequency control is performed. [Figure 6] FIG. 6 is a flowchart showing an example of the operation of the parallel operation control system under load sharing control. [Figure 7] FIG. 7 is a flowchart showing an example of the operation of the parallel operation control system when load sharing control is performed under the condition that the load is constant and the generator capacity is the same. [Figure 8] FIG. 8 is a flowchart showing an example of the operation of the parallel operation control system in the event of an abnormality when load sharing control is performed under the condition that the load is constant and the generator capacity is the same. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, each embodiment of the present invention will be described with reference to the drawings. The drawings are schematic or conceptual, and the relationship between the thickness and width of each part, the size ratio between parts, etc., are not necessarily the same as those in reality. Furthermore, even when the same part is shown, the dimensions and ratios may be different depending on the drawing. In this specification and each drawing, elements similar to those described above with reference to the previous drawings are designated by the same reference numerals, and detailed and redundant explanations will be omitted as appropriate.

[0013] (Example of parallel operation control system configuration) FIG. 1 is a block diagram showing an example of the configuration of a parallel operation control system to which a parallel operation control method according to an embodiment of the present invention is applied.

[0014] The parallel operation control system 10 includes an input unit 12, an output unit 14, and a processor 20. The input unit 12 and the output unit 14 are hardware having a communication function. The processor 20 stores a program that implements a determination unit 22 and a control unit 24.

[0015] The input unit 12 receives operation data a from the devices controlled by the parallel operation control system 10 (for example, the own unit (e.g., Ga) and other units (e.g., Gb)). The input unit 12 outputs the input operation data a to the processor 20. Both the own unit and other units are either steam turbine generators, diesel engine generators, gas turbine generators, or gas engine generators.

[0016] The determination unit 22 determines the limit output values ​​b of the own unit Ga and the other unit Gb based on the operation data a output from the input unit 12 during autonomous parallel operation of the own unit Ga and the other unit Gb.

[0017] Independent parallel operation is an operation in which power is supplied to on-site loads using only multiple generators, such as the own unit Ga and other units Gb, without being connected to a commercial power source. Therefore, independent parallel operation of the own unit Ga and other units Gb means that power is supplied to on-site loads using multiple generators consisting of the own unit, which is either a steam turbine generator, diesel engine generator, gas turbine generator, or gas engine generator, and other units, which are either steam turbine generators, diesel engine generators, gas turbine generators, or gas engine generators, without being connected to a commercial power source. Note that the load refers to the equipment powered by the generators.

[0018] When determining the limit output value b, for example, if the deviation between the target output value c and the current output value d is greater than a predetermined value, the determination unit 22 determines that the current output value d is the limit output value b. Also, for example, if the current output value d of only one of the own unit Ga and the other unit Gb, which are under constant frequency control, increases, the determination unit 22 determines that the increased current output value d is the limit output value b.

[0019] Constant frequency control is a control to keep the frequency of the power generating device at the rated frequency in order to supply power to the load only by the generator.

[0020] The determination unit 22 can also determine the limit output value b from the active power of the own vehicle Ga at the time when a pre-alarm occurs in the own vehicle Ga.

[0021] A pre-alarm is not an alarm that issues a warning or shuts down equipment due to a malfunction, but an alarm that warns of a situation where output control is not being performed according to normal control. The pre-alarm setting value is, for example, approximately 90% of the setting value for a malfunction (major malfunction) that shuts down the power generating equipment. Active power (kW) refers to the power that is affected by the speed of the steam turbine, and is distinguished from reactive power (kVAR), which is power that is not affected by the speed of the steam turbine.

[0022] The determination unit 22 performs such a determination of the limit output value b at regular time intervals, such as every 8 seconds, and outputs the limit output value b to the control unit 24 each time (for example, every 8 seconds).

[0023] Each time the limit output value b is output from the determination unit 22, the control unit 24 generates an output command R for controlling the own machine Ga and other machine Gb, and outputs it to the output unit 14. Then, the output unit 14 outputs the output command R from the control unit 24 to the own machine Ga and other machine Gb, thereby controlling the own machine Ga and other machine Gb.

[0024] In the following, although not limited to, a specific example of the output command R generated by the control unit 24 will be described.

[0025] For example, the control unit 24 sets the limit output value b as the target output value c, and controls the own unit Ga, for example automatically, to maintain a constant output, and generates an output command R for controlling the other unit Gb in accordance with the load.

[0026] Constant output control is an automatic control that keeps the output constant (for example, limit output value b). When a pre-alarm occurs as described above, the control unit 24 generates an output command R for the own unit Ga to perform control that does not increase the load, i.e., control that implements load restriction.

[0027] Then, the output unit 14 controls the own unit Ga in accordance with this output command R, thereby avoiding a stoppage due to a serious failure of the own unit Ga and enabling long-term parallel operation.

[0028] On the other hand, control that is appropriate for the load on the other unit Gb is, for example, the constant frequency control as described above. In this case, the control unit 24 generates an output command R for the constant frequency control for the other unit Gb.

[0029] Then, the output unit 14 controls the other unit Gb in accordance with this output command R, thereby making it possible to perform control on the other unit Gb in accordance with the load.

[0030] The control unit 24 can also calculate a target output value c for equalizing the load sharing so that the outputs of the own unit Ga and the other unit Gb are the same ratio during droop operation during independent parallel operation, and generate an output command R including this target output value c, or generate an output command R for controlling the limit output value b to be constant.

[0031] Droop operation refers to an operation in which the speed is controlled by utilizing the characteristic that the operating speed of a driving machine drops when the load increases.

[0032] Furthermore, the control unit 24 generates an output command R that sets the load sharing between the own machine Ga and the other machine Gb as equal load sharing, for the purpose of re-determination by the determination unit 22, and outputs the output command R to the output unit 14.

[0033] In this way, the parallel operation control system 10 controls the parallel operation of the own unit Ga and the other unit Gb by the input unit 12, output unit 14, and processor 20, which are hardware, and the determination unit 22 and the program for the control unit 24, which are software, operating in cooperation with each other.

[0034] (Example of application of parallel operation control system) Specific application examples of the parallel operation control system 10 according to this embodiment will be described below with reference to the drawings.

[0035] FIG. 2 is a system diagram showing a specific application example of the parallel operation control system according to the embodiment of the present invention.

[0036] The above-described parallel operation control system 10 is applied as a load sharing control calculator 1 in a control environment as shown in FIG.

[0037] The load sharing control calculator 1 receives the active power of each generator Ga, Gb as input, and outputs an output command R instructing the engines 3a, 3b of each generator Ga, Gb to increase or decrease their output so that the capacity of each generator Ga, Gb is shared proportionally.

[0038] Governors 2a and 2b are devices that maintain constant rotational speeds of engines 3a and 3b of generators Ga and Gb, respectively, and are responsible for load sharing. For example, if generator Ga is a type equipped with a steam turbine as its engine 3a, governor 2a corresponds to a steam control valve that adjusts the amount of fuel.

[0039] The power transducer (hereinafter referred to as "power TRD") 4 is a device that converts active power into DC 4 to 200 mA, 0 to 5 V, or the like.

[0040] The frequency transducer (hereinafter referred to as "frequency TRD") 5 is a device that converts a frequency into an effective frequency.

[0041] When the load sharing control calculator 1 applied as shown in FIG. 2 controls the parallel operation of two generators Ga and Gb in a conventional manner, it operates as shown in the flowchart of FIG.

[0042] First, the two generators Ga and Gb are started to operate in parallel, and the load is equally shared by the droop control (S1).

[0043] If the STG steam pressure is insufficient or there is no abnormality in the governor system (S2: No), step S1 continues.

[0044] On the other hand, if the STG steam pressure is insufficient due to the steam limit of the operating facility (e.g., generator Ga), or if there is an abnormality in the governor system due to a malfunction of the governor (e.g., governor 2a) on the engine (e.g., engine 3a) side (S2: Yes), proceed to step S3.

[0045] In step S3, the output of an operating facility (for example, generator Ga) reaches its limit, and the load on other generators (for example, generator Gb) increases (S3). In other words, under equal sharing control, each is controlled to reach its target output, but the STG reaches its output limit and does not reach its target output. As a result, although there is a difference in output between the STG and other generators, the load = output, and the frequency drops.

[0046] As the frequency drops, the output of other types of generators also increases. As a result, they are controlled to reach the target value, and the frequency is lowered while the load is shared equally.

[0047] Then, in step S4, an output command R to increase the power output of each generator Ga and Gb is issued under constant frequency control, but the STG does not follow this command, resulting in a difference in the power output from the two generators Ga and Gb (S4). In other words, equal load sharing is not possible when there is a shortage of steam pressure in the operating facility or when there is a governor abnormality.

[0048] In contrast to this, in the parallel operation control method according to the embodiment of the present application and the parallel operation control system to which the method is applied, when normal equal load sharing control is not successfully performed, the affected unit is operated at its limit output value, and output control is performed by the other units. In addition, the healthy unit is subjected to constant frequency control.

[0049] To achieve this, in the parallel operation control method according to the embodiment of the present application and the parallel operation control system to which the method is applied, each of the STG, DG, and GE is provided with a voltage transformer (hereinafter referred to as "VT"), a current transformer (hereinafter referred to as "CT"), and an active power transducer (hereinafter referred to as "W-TRD") for detecting the output (active power) of the generator, and is also provided with a VT and a frequency transducer (hereinafter referred to as "Hz-TRD") for detecting the frequency of the common bus, with the function of receiving and calculating the signals of these TRDs, and the function of outputting an increase / decrease signal to a device that controls the rotation of the power generation device.

[0050] Next, an example of the operation of the parallel operation control system 10 will be described.

[0051] FIG. 4 is a flowchart showing an example of the operation of the parallel operation control system when constant output control is performed.

[0052] First, the two generators Ga and Gb start operating in an independent parallel manner, with equal load sharing (S11).

[0053] Then, during independent parallel operation, if the deviation between the target output value and the current output value of each generator is greater than a predetermined value (S12: Yes), proceed to step S13; if not (S12: No), continue with step S11.

[0054] The deviation may be greater than the predetermined value due to steam limitations in the operating facility or a faulty governor on the engine side.

[0055] In step S13, the determination unit 22 determines the current output value of the own vehicle Ga as the limit output value. This is performed, for example, when a pre-alarm occurs in the own vehicle Ga. The current output value of another vehicle Gb in which a pre-alarm has occurred is also determined to be the limit output value (S13).

[0056] In addition, when constant frequency control is being performed, in the processing of steps S12 and S13, if the current output value of only one of the own unit Ga and the other unit Gb increases, the judgment unit 22 judges that the increased current output value is the limit output value.

[0057] Next, in step S14, the control unit 24 implements load restriction based on the limit output value. For example, the control unit 24 sets the limit output value as the target output value, and controls the output of the own unit Ga to be constant (S14). For example, if a pre-alarm occurs in the own unit Ga in step S13, the control unit 24 generates an output command R that controls the own unit Ga so as not to increase the load, and outputs this from the output unit 14 to the governor 2a of the own unit Ga. This prevents the own unit Ga from being shut down due to a serious failure, and enables long-term parallel operation.

[0058] The target output value is calculated by the control unit 24, for example, during independent parallel operation, so that the outputs of the own unit Ga and the other unit Gb are in the same ratio during droop operation.

[0059] On the other hand, the control unit 24 performs control on the other unit Gb in accordance with the load, such as increasing / decreasing the output (S15).

[0060] After that, when a certain period of time has elapsed (S16), the process returns to step S11. The certain period of time in step S16 can be set to twice the control period. Therefore, for example, if the control period is 4 seconds, the certain period of time is 8 seconds.

[0061] As a result, the limit power value is re-determined by the determination unit 22, and control by the control unit 24 is continued based on the re-determined limit power value. Note that, in order to re-determine the limit power value, the load sharing between the own unit Ga and the other unit Gb can be set to equal load sharing.

[0062] FIG. 5 is a flowchart showing an example of operation of the parallel operation control system in the event of an abnormality when constant frequency control is performed.

[0063] For example, if the own unit Ga is a unit set to the output limit value (S21) and the other unit Gb is not (S22), the own unit Ga is controlled to a constant output (S23).

[0064] If a load fluctuation occurs in this state (S24), the own unit Ga is controlled to maintain a constant output (S25), and the other unit Gb is controlled to bear the load of the fluctuation (S26) by constant frequency control (S27). For a specific example of constant frequency control, see FIG. 7, which will be described later.

[0065] FIG. 6 is a flowchart showing an example of the operation of the parallel operation control system under load sharing control.

[0066] First, the determination unit 22 reads the active power from the operation data input from the own unit Ga and the other units Gb to the input unit 12 (S31). Furthermore, the determination unit 22 sets a target value so that the total active power is proportionally shared (S32).

[0067] Next, the control unit 24 determines the deviation ΔP by subtracting the current output value from the target output value (deviation ΔP=target output value−current output value) (S33), and further calculates the control pulse width (S34).

[0068] Thereafter, an output command R is generated based on the calculation result of step S34 and is output to each of the units Ga and Gb from the output unit 14. The output command R is an output command R that instructs the governor 2a to increase (or decrease) the output (S35), or an output command R that instructs the governor 2b to decrease (or increase) the output (S36).

[0069] FIG. 7 is a flowchart showing an example of the operation of the parallel operation control system when load sharing control is performed under the condition that the load is constant and the generator capacity is the same.

[0070] For example, from the operating data of the own unit Ga and the other unit Gb, the judgment unit 22 determines that the active power of the own unit Ga is 20% (S41) and that the active power of the other unit Gb is 80% (S42).

[0071] In this case, the target values ​​of the respective units Ga and Gb calculated by the control unit 24 are as follows (S43):

[0072] 20% (own unit Ga) + 80% (other units Gb) = 100% (total) 100% / 2=50% (equal load sharing).

[0073] Therefore, the control unit 24 further calculates the deviation ΔP relative to the own car Ga as 50%-20%=30% (S44), and calculates the deviation ΔP relative to the other car Gb as 50%-80%=-30% (S45).

[0074] The control unit 24 further generates an output command R that instructs the governor 2a to increase the output by 30% based on the calculation result of step S44 (S46), and generates an output command R that instructs the governor 2b to decrease the output by 30% based on the calculation result of step S45 (S47).

[0075] In this case, if the increase and decrease are equal, the amount of fuel also remains the same (+30%-30%=0), so there is no change in frequency.

[0076] FIG. 8 is a flowchart showing an example of the operation of the parallel operation control system in the event of an abnormality when load sharing control is performed under the condition that the load is constant and the generator capacity is the same.

[0077] In Fig. 8, the same step numbers are used for the same processing steps as in Fig. 7 to avoid redundant explanation. That is, in the flowchart shown in Fig. 8, steps S41 to S47 are the same as in the flowchart shown in Fig. 7, but steps S48 and onwards are different.

[0078] In step S46, an output command R is output to the governor 2a to instruct it to increase the output by 30%, and in step S47, an output command R is output to the governor 2b to instruct it to decrease the output by 30%.

[0079] However, in the event of an abnormality when the load is constant and the generator capacity is the same and load sharing control is performed, only the output command R for output reduction is valid. Therefore, in accordance with the output command R in step S47, the output of the governor 2b is reduced, and the fuel of the other unit Gb is also reduced (S50).

[0080] On the other hand, the output command R in step S46 is not validated, and the output of the governor 2a remains unchanged. As a result, a shortage of STG steam pressure or a governor abnormality occurs in the host unit Ga (S48). Thus, even if an output command R to increase the governor's output is issued, the fuel is not increased (S49).

[0081] In this way, since only the output command R for reducing the output is enabled, the amount of fuel decreases (in this example, 0-30=-30%) and the frequency decreases.

[0082] As described above, the parallel operation control system to which the parallel operation control method of this embodiment is applied, due to the above-mentioned effects, when performing parallel operation, does not simply control the effective power sharing equally, but rather determines the operating status of the power generation units and automatically performs constant output control or constant frequency control on the other model generator side, thereby making it possible to automatically perform optimal parallel operation control.

[0083] If it is determined that the load cannot be controlled evenly based on the capacity ratio, the output of the steam turbine at that time will be the limit output depending on the amount of steam, and will not be able to reach the target value of conventional control, resulting in a drop in output. However, according to the parallel operation control system 10, by performing constant frequency control, which is control that matches the load on the other unit Gb, even if the output of the generator drops, the load will consume the necessary power, so it is possible to detect a drop in speed (frequency) and recognize the output at that time as the limit value.

[0084] Furthermore, if the parallel operation control system 10 does not set a limit output value, the speed of the unit in question will increase (or decrease) and the speed of the other units will decrease (or increase), and the unit on the limit output side will not increase or decrease its fuel, resulting in frequency fluctuations. However, according to this embodiment, frequency changes can also be avoided.

[0085] Furthermore, according to this embodiment, it is possible to prevent engine overload tripping by detecting the limit output value in the operating state of the power generation device, monitoring the information, and limiting the load.

[0086] For example, by providing a pre-alarm to warn of a fault and limiting the output of the power generating device in which the alarm occurs to prevent a major fault from shutting down, it becomes possible to operate the power generating device in parallel for a long period of time.

[0087] Although several embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included within the scope and spirit of the invention, as well as within the scope of the invention described in the claims and their equivalents. [Explanation of symbols]

[0088] 1 Load sharing control calculation section 2a Governor 2b Governor 3a Institution 3b Institution 4 Power Transducers 5 Frequency Transducers 10 Parallel operation control system 12 Input section 14 Output section 20 processors 22 Judgment section 24 Control Unit a. Operation data b. Limit power value c Target output value d Current output value Ga generator (self-numbered unit) Gb generator (other units) R output command

Claims

1. a determination unit that determines the limit output values ​​of the steam turbines of the own unit, which is a steam turbine generator, and the other unit, which is a diesel engine generator or a gas engine generator, during independent parallel operation in which the own unit and the other unit are operated without power supply from a commercial power source; a control unit that controls the output of the own unit to a constant level using the limit output value as a target output value, and controls the other units in accordance with the loads that are facilities to which power is supplied by each generator, The determination unit re-determines the limit output value every time a certain period of time elapses. Parallel operation control system.

2. the determination unit determines that the current output value is the limit output value when a deviation between the target output value and the current output value is greater than a predetermined value.

2. The parallel operation control system according to claim 1.

3. When the current output value of only one of the steam turbine of the own unit and the steam turbine of the other unit, which are subjected to constant frequency control, increases, the determination unit determines that the increased current output value is the limit output value, The constant frequency control is a control in which the frequency is set to a predetermined value because the load is supplied with power only by each generator.

2. The parallel operation control system according to claim 1.

4. the control unit calculates the target output value in droop operation during the independent parallel operation so that the outputs of the own unit and the other unit are in the same ratio, The droop operation is an operation in which the speed is limited by utilizing the characteristic that the operating speed drops when the load increases.

4. The parallel operation control system according to claim 2 or 3.

5. the control unit controls the limit output value to be constant by droop operation during the independent parallel operation, The droop operation is an operation in which the speed is limited by utilizing the characteristic that the operating speed drops when the load increases.

4. The parallel operation control system according to claim 2 or 3.

6. The control appropriate for the load is constant frequency control, The constant frequency control is a control in which the frequency is set to a predetermined value because the load is supplied with power only by each generator.

2. The parallel operation control system according to claim 1.

7. The control unit sets the load sharing between the own machine and the other machine to equal load sharing for the re-determination.

2. The parallel operation control system according to claim 1.

8. The control unit implements a load limit on the own unit based on the limit output value.

2. The parallel operation control system according to claim 1.

9. the determination unit determines the limit output value from the active power of the own vehicle at the time when a pre-alarm occurs in the own vehicle, The pre-alarm is an alarm that indicates a situation in which output control is not performed according to normal control, The active power is the power affected by the speed of the steam turbine.

2. The parallel operation control system according to claim 1.

10. The control unit automatically performs constant output control at the limit output value, or performs constant frequency control on the other units, The constant frequency control is a control in which the frequency is set to a predetermined value because the load is supplied with power only by each generator.

2. The parallel operation control system according to claim 1.

11. When a pre-alarm occurs in the own unit, the control unit controls the own unit so as not to increase the load on the own unit, thereby avoiding a serious failure stop of the own unit and enabling long-term parallel operation, The pre-alarm is an alarm that indicates a situation in which output control is not performed according to normal control.

2. The parallel operation control system according to claim 1.

12. The processor of the parallel operation control system During independent parallel operation in which a self-unit which is a steam turbine generator and another unit which is a diesel engine generator or a gas engine generator are operated without power supply from a commercial power source, the limit output values ​​of the steam turbines of the self-unit and the other unit are determined, The limit output value is set as a target output value, and the output of the own unit is controlled to a constant value. Controlling the other generators in accordance with the loads that are the equipment supplied with power by each generator, The limit output value is re-determined every certain time period. Parallel operation control method.

13. The processor further comprises: If the deviation between the target output value and the current output value is greater than a predetermined value, the current output value is determined to be the limit output value. The parallel operation control method according to claim 12.

14. The processor further comprises: When the current output value of only one of the steam turbine of the own unit and the steam turbine of the other unit, which are under constant frequency control, increases, the increased current output value is determined to be the limit output value, The constant frequency control is a control in which the frequency is set to a predetermined value because the load is supplied with power only by each generator. The parallel operation control method according to claim 12.

15. The processor further comprises: During the independent parallel operation, the target output value is calculated so that the output of the own unit and the other unit is the same ratio during droop operation, The droop operation is an operation in which the speed is limited by utilizing the characteristic that the operating speed drops when the load increases. The parallel operation control method according to claim 13 or 14.

16. The processor further comprises: During the independent parallel operation, the limit output value is controlled to be constant by droop operation, The droop operation is an operation in which the speed is limited by utilizing the characteristic that the operating speed drops when the load increases. The parallel operation control method according to claim 13 or 14.

17. The control appropriate for the load is constant frequency control, The constant frequency control is a control in which the frequency is set to a predetermined value because the load is supplied with power only by each generator. The parallel operation control method according to claim 12.

18. The processor further comprises: For the purpose of re-determining the limit output value, the load sharing between the own unit and the other unit is set to equal load sharing. The parallel operation control method according to claim 12.

19. The processor further comprises: Implementing load shedding based on the critical output value. The parallel operation control method according to claim 12.

20. The processor further comprises: The limit output value is determined based on the active power of the own unit at the time when a pre-alarm occurs in the own unit, The pre-alarm is an alarm that indicates a situation in which output control is not performed according to normal control, The active power is the power affected by the speed of the steam turbine. The parallel operation control method according to claim 12.

21. The processor further comprises: At the limit output value, automatic constant output control is performed, or constant frequency control is performed for the other units, The constant frequency control is a control in which the frequency is set to a predetermined value because the load is supplied with power only by each generator. The parallel operation control method according to claim 12.

22. The processor further comprises: When a pre-alarm occurs in the own unit, control is performed so as not to increase the load on the own unit, thereby avoiding a serious failure and shutdown of the own unit and enabling long-term parallel operation, The pre-alarm is an alarm that indicates a situation in which output control is not performed according to normal control. The parallel operation control method according to claim 12.

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