Power system and method for controlling power system

Abstract

To provide a power system capable of appropriately controlling the output power of a power plant.SOLUTION: A power system includes a power plant 40, a power transmission flow suppression unit 50 inserted between the power transmission flow suppression unit and a substation 70 via transmission lines 82, 84, and a control system 30. The control system 30 outputs a power transmission flow suppression signal CP to the power transmission flow suppression unit 50 indicating that the output power P of the power plant 40 is be suppressed, and the power transmission flow suppression unit 50 suppresses the output power P of the power plant 40, which is transmitted via the transmission lines 82, 84, on the basis of the power transmission flow suppression signal CP.SELECTED DRAWING: Figure 4

Description

Technical Field

[0001] The present invention relates to a power system and a control method for a power system.

Background Art

[0002] Towards the realization of a decarbonized society, the introduction of renewable energy is progressing globally. However, in power systems to which renewable energy is connected, various problems such as supply-demand imbalance, transmission capacity overage, voltage fluctuation, frequency fluctuation, and stability are expected to occur. This is because the suitable locations for introducing variable renewable energy such as solar power and wind power generation are unevenly distributed, the power transmission current from the power generation location to the demand location increases, and local transmission lines are prone to overload.

[0003] To address this type of problem, for example, in the summary of Patent Document 1 below, it is described that "the power system stabilizer includes a system data creation unit 103 that creates system data based on the collected information of the power system, a basic power control unit selection unit 104 that selects a target generator for power supply restriction to maintain the stability of the power system based on a predetermined rule, a frequency model creation unit 105 that creates a reference frequency model that simulates the response of the frequency in the power system under the condition that a predetermined time has elapsed since the power supply restriction, a frequency stability determination unit 106 that determines the frequency stability using the created model, a power control unit target change unit 107 that changes the target generator for power supply restriction selected by the basic power control unit based on the determination result, a storage unit 101 that stores the determined power control unit change information, and a control signal transmission unit 108 that transmits a control signal to the target generator for power supply restriction indicated by the power control unit change information when a system accident occurs." Also, Non-Patent Document 1 describes a technology related to STATCOM (Static Synchronous Compensator). The descriptions of these documents are incorporated as part of the present specification.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Non-Patent Document

[0005]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] By the way, in the above-described technology, there is a desire to more appropriately control the output power of the power plant. This invention has been made in view of the above circumstances, and an object thereof is to provide a power system and a control method for a power system that can appropriately control the output power of a power plant.

Means for Solving the Problems

[0007] To solve the above problems, the power system of the present invention includes a condenser, a turbine, a steam generation unit that generates steam, a turbine bypass valve that distributes the steam generated by the steam generation unit to the condenser and the turbine, a generator driven by the turbine, a power transmission current suppression unit inserted via a power transmission line between a power plant and a substation, and a control system. The control system outputs a power transmission current suppression signal indicating that the output power of the power plant should be suppressed to the power transmission current suppression unit, and the power transmission current suppression unit suppresses the output power of the power plant transmitted via the power transmission line based on the power transmission current suppression signal.

Effects of the Invention

[0008] According to the present invention, the output power of a power plant can be appropriately controlled.

Brief Description of the Drawings

[0009]

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MODE FOR CARRYING OUT THE INVENTION

[0010] [Premise of Embodiment] First, before explaining each embodiment, the technology that is the premise of each embodiment will be explained. FIG. 1 is a schematic diagram showing the configuration of a power plant 202 according to a comparative example. Power plant 202 is, for example, a thermal power plant, and includes a generator 210, a turbine 211, a turbine bypass valve 212, a boiler 214, and a condenser 215. The boiler 214 generates steam, and the generated steam is supplied to the turbine 211 via the turbine bypass valve 212 to rotate the turbine 211. The generator 210 is directly connected to the turbine 211 and rotates together with the turbine 211.

[0011] Power plant 202 may receive a turbine bypass adjustment signal CA from a control system 201 which is, for example, a central power supply command station. When receiving the turbine bypass adjustment signal CA, power plant 202 controls the opening degree of the turbine bypass valve 212 so as to suppress the amount of steam to the turbine 211. Thereby, the amount of steam from the boiler 214 sent to the turbine 211 is suppressed, and the suppressed amount of steam is sent to the condenser 215. As a result of the suppression of the amount of steam to the turbine 211, the output power of the generator 210 is suppressed.

[0012] FIG. 2 is a diagram showing the cooperation relationship between the power plant and the external power grid in the comparative example. In FIG. 2, the power plant 202 is connected to a substation 203 via a transmission line 206. And the substation 203 is connected to the power grid 220. For example, when a transmission line 226 included in the power grid 220 is disconnected, it is necessary to eliminate a local overload of the power grid 220 by suppressing the power flow in the power grid 220. In that case, as described above, the control system 201 transmits a turbine bypass adjustment signal CA to the power plant 202 to suppress the output power of the generator 210 (see FIG. 1). Thereby, the power transmission current sent to the substation 203 through the transmission line 206 is suppressed.

[0013] FIG. 3 is a diagram showing an example of the output power P of the generator 210 in the comparative example. Note that the output power P is the active power output by the generator 210. Assume that at time t1, a turbine bypass adjustment signal CA is supplied to the power plant 202. The output power P before the supply of the turbine bypass adjustment signal CA is P12, and it is reduced to P14 after the supply.

[0014] Returning to FIG. 1, as described above, when the power plant 202 is a thermal power plant, the turbine bypass valve 212 can be adjusted according to the turbine bypass adjustment signal CA. Thereby, the output of the generator 210 can be suppressed, and the system stability when a system fault occurs in the power system 220 can be improved. However, when the power plant 202 is a nuclear power plant, there is a problem that a signal (such as the turbine bypass adjustment signal CA) for changing the operation pattern of the power plant 202 cannot be received from the control system 201. This is because in a nuclear power plant, the control sequence is configured so that the operation of the generator 210 is determined only within the power plant in order to eliminate external disturbances that may cause abnormalities in the operation of the nuclear reactor.

[0015] As an alternative means that does not receive a signal from the control system 201, power limitation for disconnecting the generator from the system on the system side is also considered. That is, it is conceivable to disconnect the power plant 202 and the transmission line 206 (see FIG. 2). However, in a nuclear power plant, when power limitation is executed, control rods are inserted into the nuclear reactor, and it takes several weeks until normal operation after that (after the release of power limitation).

[0016] Therefore, in the embodiments described later, the output of the generator is adjusted by operating the turbine bypass valve without directly inputting and outputting signals with the control system 201. Although the specific configuration will be described later, in each embodiment, a power transmission current suppression unit is installed between the power plant and the substation, and the power transmission current flowing through the transmission line is suppressed by a signal from the control system 201. In response to the suppression of the power transmission current, the power plant passively executes the opening and closing of the turbine bypass valve in the power plant. Thereby, it becomes possible to adjust the output of the generator by adjusting the turbine bypass valve of the generator without directly inputting and outputting signals with the control system 201.

[0017] [First Embodiment] <Configuration of the First Embodiment> FIG. 4 is a block diagram of a power system SYS1 according to the first embodiment. In FIG. 4, the power system SYS1 includes a nuclear power plant 40 (power plant), a substation 70, a transmission power flow suppression unit 50, transmission lines 82 and 84, and a control system 30. The transmission line 82 connects the nuclear power plant 40 and the transmission power flow suppression unit 50, and the transmission line 84 connects the transmission power flow suppression unit 50 and the substation 70.

[0018] The substation is connected to the power grid 80. A specific configuration example of the transmission power flow suppression unit 50 will be described in other embodiments (see FIGS. 12 to 14) described later. The transmission power flow suppression unit 50 is a device that equivalently inserts a capacitor or the like into the transmission lines 82 and 84, or disconnects the connection of the transmission lines 82 and 84 during a system fault. The control system 30 is provided with a plant control device 32.

[0019] The plant control device 32 formulates the operating state of generators including other power plants (not shown) such as thermal power and nuclear power in addition to the nuclear power plant 40. The plant control device 32 includes a computer 980 (see FIG. 5) described later, and realizes various functions by executing a control program (not shown).

[0020] The control system 30 is, for example, a central power supply command center, but may be provided at the substation 70 or the like. The control system 30 has a function of outputting an output adjustment signal of the generator and an operation instruction of the protection relay to other thermal power plants (not shown) and other substations (not shown) in the event of a fault in the power grid 80. And when the output power P of the nuclear power plant 40, that is, when the transmission line power flow should be suppressed, the control system 30 supplies a transmission power flow suppression signal CP including an instruction to execute the suppression of the transmission line power flow and the suppression amount of the transmission line power flow to the transmission power flow suppression unit 50.

[0021] The nuclear power plant 40 includes a turbine 405, a generator 406, a nuclear reactor 407 (steam generation section), a condenser 408, a turbine bypass valve 409, and a bypass opening control device 440. The nuclear reactor 407 generates steam, and the generated steam is supplied to the turbine 405 via the turbine bypass valve 409 to rotate the turbine 405. The generator 406 is directly connected to the turbine 405 and rotates together with the turbine 405.

[0022] The bypass opening control device 440 monitors the state of the generator 406, such as the output voltage, output current, and frequency of the generator 406. Then, according to the monitoring result, it increases or decreases the turbine bypass adjustment signal CB, thereby controlling the opening degree of the turbine bypass valve 409. That is, the bypass opening control device 440 controls the opening degree of the turbine bypass valve 409 so as to suppress the amount of steam to the turbine 405. As a result, the amount of steam from the nuclear reactor 407 sent to the turbine 405 is suppressed, and the suppressed steam is sent to the condenser 408. And as a result of suppressing the amount of steam to the turbine 405, the output power P, which is the active power output by the generator 406, is suppressed.

[0023] When the control system 30 outputs a power flow suppression signal CP to the power flow suppression unit 50, the state of the power flow suppression unit 50 as seen from the nuclear power plant 40 changes. As a result, the rotational speed of the generator 406 increases, and the output voltage also increases. In response to this change in the state of the generator 406, the bypass opening control device 440 outputs a turbine bypass adjustment signal CB to the turbine bypass valve 409 so as to suppress the amount of steam to the turbine 405.

[0024] FIG. 5 is a block diagram of a computer 980. The plant control device 32 and the bypass opening control device 440 shown in FIG. 4 both include one or more of the computers 980 shown in FIG. 5. In FIG. 5, computer 980 includes a CPU 981, a storage unit 982, a communication I / F (interface) 983, an input / output I / F 984, and a media I / F 985. Here, the storage unit 982 includes a RAM 982a, a ROM 982b, and an SSD (Solid State Drive) 982c. The communication I / F 983 is connected to a communication circuit 986. The input / output I / F 984 is connected to an input / output device 987. The media I / F 985 reads and writes data from and to a recording medium 988. The ROM 982b stores an IPL (Initial Program Loader) and the like to be executed by the CPU. The SSD 982c stores a control program, various data, and the like. The CPU 981 realizes various functions by executing the control program and the like read from the SSD 982c into the RAM 982a.

[0025] FIG. 6 is a diagram showing examples of the transmission line voltage V, output power P, and rotational speed M in the first embodiment. Hereinafter, with reference to FIG. 6, the principle by which the power flow is suppressed in the first embodiment will be described. The transmission line voltage V is the voltage of the transmission line 82 and is equal to the output voltage of the generator 406. The output power P is the active power output from the generator 406 via the transmission line 82. Also, the rotational speed M is the rotational speed of the generator 406. Before time t10, the transmission line voltage V is the voltage V1H. Then, at time t10, when the plant control device 32 outputs a power flow suppression signal CP (see FIG. 4), the power flow suppression unit 50 sets the transmission line voltage V to a voltage V1L, which is a value below a predetermined voltage level, based on the power flow suppression signal CP. For this reason, it is advisable to provide a reactance such as a reactor or a capacitor in the power flow suppression unit 50.

[0026] The output power P output via the power transmission line 82 has an upper limit set from the viewpoints of the heat capacity of the power transmission line 82 and synchronous stability. For example, the illustrated power P1H is this upper limit. Then, when the power flow suppression unit 50 receives the power flow suppression signal CP at time t10, it reduces the upper limit value of the output power P. The command for this reduced upper limit value is included in the power flow suppression signal CP. The reduced upper limit value is, for example, the illustrated power P1L. The change in the upper limit value of the output power P is realized by the fact that the power transmission line voltage V after the system fault drops below the voltage V1L before the system fault. Details of the specific power transmission line flow equipment and the method for setting the upper limit value will be described in other embodiments (see FIGS. 12 to 14) described later.

[0027] The rotational speed M is maintained at a predetermined reference speed M1L before time t10. Then, at time t10, due to the change of the output power P to the power P1L, the power that can no longer be transmitted from the generator 406 to the substation 70 is consumed to accelerate the generator 406. As a result, after time t10 when the power flow suppression unit 50 receives the power flow suppression signal CP, the rotational speed M of the generator 406 gradually increases from the reference speed M1L. When the bypass opening control device 440 detects the above-described state change of the generator 406, it adjusts the turbine bypass adjustment signal CB supplied to the turbine bypass valve 409.

[0028] FIG. 7 is a schematic block diagram of the nuclear power plant 40 in the first embodiment. Referring to FIG. 7, the principle of output adjustment by the operation of the turbine bypass valve 409 will be described. As shown previously in FIG. 4, the nuclear power plant 40 includes a reactor 407, a turbine bypass valve 409, a turbine 405, a generator 406, and a condenser 408. Further, the nuclear power plant 40 includes a bleed valve 401. The steam generated from the reactor 407 is branched into two paths by the turbine bypass valve 409: one path flows through the turbine 405 and then into the condenser 408, and the other path flows directly into the condenser 408. In FIG. 7, a nuclear power plant 40 with a boiling water reactor 407 is illustrated as an example, but the same applies to a nuclear power plant 40 with a pressurized water reactor 407.

[0029] The bypass opening control device 440 has a control logic that automatically controls the turbine bypass valve 409 so that the rotational speed M of the generator 406 approaches (preferably coincides with) the reference speed M1L (see FIG. 6). Therefore, when the rotational speed M becomes higher than the reference speed M1L as after time t10 in FIG. 6, the bypass opening control device 440 controls the turbine bypass valve 409 to reduce the amount of steam flowing into the turbine 405.

[0030] FIG. 8 is a block diagram of the bypass opening control device 440. The bypass opening control device 440 includes a turbine bypass valve opening calculation unit 442. The bypass opening control device 440 determines the opening of the turbine bypass valve 409 according to the output of the generator 406. The current output power Pa of the generator 406 and the target output power Pb are input to the turbine bypass valve opening calculation unit 442. Here, the output power Pa is, for example, the output power P shown in FIG. 6, and the target output power Pb is, for example, the power P1H shown in FIG. 6.

[0031] The turbine bypass valve opening calculation unit 442 has a table 444 that defines the relationship among the output power Pa, the target output power Pb, and the turbine bypass adjustment signal CB. The turbine bypass valve opening calculation unit 442 uses this table 444 to obtain the opening of the turbine bypass valve 409 that realizes the target output power Pb, and outputs a turbine bypass adjustment signal CB that specifies the obtained opening.

[0032] FIG. 9 is a diagram showing an example of the rotational speed M and the output power P in the first embodiment. In FIG. 9, examples of the rotational speed M and the output power P when the power flow control signal CP is received from the control system 30 are shown. Assume that at time t10, the power flow control signal CP is output from the control system 30 to the power flow suppression unit 50. As a result, as described above with reference to FIG. 6, the output power P output from the generator 406 decreases from P1H to P1L at time t10. Also, the rotational speed M was the reference speed M1L before time t10, but gradually increases from time t10.

[0033] Since the output power P has decreased from the power P1H to the power P1L, the bypass opening control device 440 changes the turbine bypass adjustment signal CB at time t12. That is, the opening of the turbine bypass valve 409 (see FIG. 7) is adjusted to increase the amount of steam flowing to the condenser 408 without passing through the turbine 405. As a result, after time t12, the rotational speed M gradually returns to the reference speed M1L and is then maintained at the reference speed M1L. On the other hand, the output power P is maintained at the power P1L after time t10.

[0034] By the above algorithm, the nuclear power plant 40 can suppress the output power P output from the generator 406 without directly receiving the power flow control signal CP from the control system 30. That is, the power flow suppression unit 50 receives the power flow control signal CP from the control system 30 and can passively suppress the output power P of the generator 406 in reflection of the setting of the upper limit of the output power P.

[0035] [Second Embodiment] Next, the power system according to the second embodiment will be described. The overall configuration of the power system according to the second embodiment is the same as that of the first embodiment (see FIG. 4). In the following description, parts corresponding to the respective parts of the first embodiment described above may be denoted by the same reference numerals, and the description thereof may be omitted.

[0036] Similar to the first embodiment described above, in this embodiment as well, the control system 30 transmits a power flow suppression signal CP to the power flow suppression unit 50 as necessary. Here, from the perspective of the system stability of the power system 80 when the power flow suppression signal CP is output, it is considered more preferable to determine the necessity of outputting the power flow suppression signal CP and the upper limit value of the power flow to be suppressed. Thereby, it can be expected that supplying the power flow suppression signal CP to the power flow suppression unit 50 will be effective for improving system stability. Therefore, in this embodiment, the plant control device 32 provided in the control system 30 is configured to display a screen as shown in FIG. 10.

[0037] FIG. 10 is a diagram showing an example of the system stability evaluation screen 34 displayed by the plant control device 32 of the second embodiment. The system stability evaluation screen 34 includes a system diagram display column 36 and an evaluation result display unit 38. The system diagram display column 36 displays the connection states of synchronous generators, renewable energy power sources, loads, transformers, buses, lines, etc.

[0038] Further, the evaluation result display unit 38 displays the stability evaluation results in the power system 80 for various assumed faults (assumed fault cases C1 to C5). Here, "fault" targets power line disconnections, generator dropouts, and other power system faults.

[0039] The evaluation result display unit 38 shows the output power of the generator, the phase angle of the generator, the output voltage of the generator, and the output frequency of the generator as stability indicators when the assumed fault cases C1 to C5 occur. In the figure, "○" means stable and "×" means unstable. In the example of FIG. 10, when the assumed fault C3 occurs, it is shown that there is a problem that the phase angle difference of the generator becomes unstable (×).

[0040] FIG. 11 is a diagram showing another example of the system stability evaluation screen 34. In the assumed failure C3 of the evaluation result display unit 38 in FIG. 11, it is shown that the output power P of the "generator A1" is suppressed from 500 [MW] to 200 [MW]. Further, as a result, it is shown that the phase angle difference of the generator changes from "unstable (×)" to "stable (○)", and the problem with respect to the phase angle of the generator has been resolved. Note that "500 [MW]" in the figure corresponds to the power P1H in FIG. 6, and "200 [MW]" corresponds to the power P1L. Also, "P1H - P1L" is referred to as the "suppression amount ΔP" of the output power P. Referring to the analysis results as described above, the control system 30 determines whether to output the power flow suppression signal CP to the power flow suppression unit 50, and if it outputs, determines the suppression amount ΔP of the output power P.

[0041] [Third Embodiment] Next, the power system according to the third embodiment will be described. The overall configuration of the power system according to the third embodiment is the same as that of the first embodiment (see FIG. 4). Also, the point that the plant control device 32 displays the power system stability evaluation screen 34 (see FIG. 10) is the same as that of the second embodiment. In the following description, parts corresponding to those of the other above-described embodiments may be denoted by the same reference numerals, and the description thereof may be omitted.

[0042] In the second embodiment, the plant control device 32 determined the suppression amount ΔP of the output power P from the viewpoint of the stability of the power system 80. However, if the suppression amount ΔP in the nuclear power plant 40 is too large, even if the amount of steam flowing from the turbine bypass valve 409 to the condenser 408 is maximized, there is a possibility that the output cannot be suppressed to the target generator output. In this case, in order to prevent the acceleration of the generator 406, a scram may occur in the nuclear power plant 40, and the nuclear reactor 407 may stop.

[0043] To solve this problem, in the present embodiment, the upper limit value of the suppression amount ΔP determined by the plant control device 32 is calculated in advance from the opening degree of the turbine bypass valve 409. In other words, the plant control device 32 sets the upper limit value A of the suppression amount ΔP to a value corresponding to the configuration of the nuclear power plant 40. Specifically, taking the upper limit value of the suppression amount ΔP as A [MW], the rated output of the generator 406 as B [MW], and the maximum throttle amount of the turbine bypass valve 409 as C [%], based on the following formula (1), the upper limit value A of the suppression amount ΔP is calculated. A [MW]=B [MW]×C [%] … Formula (1)

[0044] Here, the maximum throttle amount C may be set according to the turbine bypass valve 409 provided in the existing and newly installed nuclear power plants 40, such as 33 [%] or 70 [%]. Also, in order to ensure a certain margin, the control system 30 may set the upper limit value A to a value less than or equal to "B [MW]×C [%]".

[0045] Thus, according to the present embodiment, the suppression amount ΔP can be set within the range below the upper limit value A shown in formula (1). Thereby, within the normal operation range of the nuclear power plant 40, it is possible to determine the suppression amount ΔP for the output power P of the generator 406 without directly receiving signals from an external system such as the control system 30.

[0046] "Unstable (×)" in the evaluation result display unit 38 indicates that the system stability SA (not shown) corresponding to various assumed faults is less than a predetermined lower limit value SB (not shown). On the other hand, "stable (○)" indicates that the system stability SA is greater than or equal to the lower limit value SB. Here, assuming the upper limit value of the system stability SA is SC, the control system 30 sets the upper limit value A of the suppression amount ΔP so as to satisfy "SB < SA < SC".

[0047] Here, as an index of the system stability SA, in the examples shown in FIGS. 10 and 11, all of the output power of the generator, the phase angle of the generator, the output voltage of the generator, and the output frequency of the generator were included. However, it is not always necessary to include all of these items as the system stability SA. That is, at least one of the output power of the generator, the phase angle of the generator, the voltage, or the frequency may be included as an index of the system stability SA.

[0048] [Fourth Embodiment] Next, the fourth embodiment will be described. FIG. 12 is a block diagram of a power system SYS4 according to the fourth embodiment. In the following description, parts corresponding to those of the other embodiments described above may be denoted by the same reference numerals, and the description thereof may be omitted. The power system SYS4 includes a nuclear power plant 40, a substation 70, a transmission power flow suppression unit 50, transmission lines 82 and 84, and a control system 30, similar to the power system SYS1 (see FIG. 4). These functions are the same as those of the first embodiment.

[0049] However, the transmission power flow suppression unit 50 of the present embodiment includes a reactor 52 inserted between the transmission lines 82 and 84. Further, the transmission power flow suppression unit 50 may include reactances such as other reactors and capacitors 54. Thereby, similar to the first embodiment, the transmission power flow suppression unit 50 can suppress the output power P of the generator 406 based on the transmission power flow suppression signal CP.

[0050] [Fifth Embodiment] Next, the fifth embodiment will be described. FIG. 13 is a block diagram of a power system SYS5 according to the fifth embodiment. In the following description, parts corresponding to those of the other embodiments described above may be denoted by the same reference numerals, and the description thereof may be omitted. The power system SYS4 includes a nuclear power plant 40, a substation 70, transmission lines 82 and 84, and a control system 30, similar to the power system SYS1 (see FIG. 4). These functions are the same as those of the first embodiment.

[0051] Further, in the present embodiment, instead of the power flow suppression unit 50 in the first embodiment, a power flow suppression unit 60 is provided. The power flow suppression unit 60 includes a reactor 62 and an inverter 64. In the power flow suppression unit 60, the power transmission lines 82 and 84 are directly connected. And a reactor 62 is inserted between the direct connection point and the inverter 64. That is, the reactor 62 is connected to the power transmission lines 82 and 84 and is used to change the power transmission line voltage V.

[0052] The power flow suppression unit 60 has a configuration similar to that of the STATCOM (Static Synchronous Compensator) shown in Non-Patent Document 1 described above. That is, the power flow suppression unit 60 suppresses the output power P of the generator 406 by supplying reactive current to the power transmission lines 82 and 84 according to the power flow suppression signal CP.

[0053] Assuming that the output voltage of the inverter 64 is Vi, the power transmission line voltage of the power transmission lines 82 and 84 is V, the reactance value of the reactor 62 is X, and the current flowing through the power transmission lines 82 and 84 is I, the following equation holds. V = Vi + jXI … Equation (2) The above Equation (2) is also a common relational expression when a capacitor (not shown) is applied instead of the reactor 62. By changing the output voltage Vi of the inverter 64 and the reactance value X, it is possible to change the power transmission line voltage V.

[0054] [Sixth Embodiment] Next, the sixth embodiment will be described. The overall configuration of the power system according to the sixth embodiment is the same as that of the first embodiment (see FIG. 4). In the following description, parts corresponding to the respective parts of the first embodiment described above may be denoted by the same reference numerals, and the description thereof may be omitted. FIG. 14 is a block diagram of the power flow suppression unit 50 in the sixth embodiment. The power transmission current suppression unit 50 in this embodiment includes a low-pass filter unit 102, a rectifier circuit 104, an ignition angle control unit 106, a capacitor 108, and an inverter 110.

[0055] The low-pass filter unit 102 includes a reactor (not shown) connected in series to the transmission line 82 and a capacitor (not shown) connected between the three phases of the transmission line 82. Thereby, the low-pass filter unit 102 suppresses the harmonic components of the current flowing through the transmission line 82. The rectifier circuit 104 is formed by connecting six thyristors (not shown) in a bridge shape, rectifies the alternating current input through the low-pass filter unit 102, and charges the capacitor 108. The ignition angle control unit 106 controls the ignition angle of the thyristors in the rectifier circuit 104 based on the power transmission current suppression signal CP. That is, when the power transmission current suppression signal CP is not supplied, the ignition angle is set to "0°", and the ignition angle increases as the suppression amount included in the power transmission current suppression signal CP increases.

[0056] As the ignition angle increases, the impedance of the power transmission current suppression unit 50 as seen from the generator 406 (see FIG. 4) increases, so the current output from the generator 406 is suppressed. The inverter 110 modulates the terminal voltage of the capacitor 108, generates an alternating voltage of the system frequency, and outputs an alternating current through the transmission line 84. Thereby, similar to the first embodiment, the power transmission current suppression unit 50 can suppress the output power P of the generator 406 based on the power transmission current suppression signal CP.

[0057] [Effects of the Embodiment] According to the embodiment described above as described above, the control system 30 outputs a power transmission current suppression signal CP indicating that the output power P of the power plant (40) should be suppressed to the power transmission current suppression unit 50, and the power transmission current suppression unit 50 suppresses the output power P of the power plant (40) transmitted through the transmission lines 82 and 84 based on the power transmission current suppression signal CP. Thereby, the output power P of the power plant (40) can be appropriately controlled.

[0058] Furthermore, it is more preferable that the control system 30 sets the upper limit value A of the suppression amount ΔP of the output power P suppressed by the power transmission current suppression signal CP to a value corresponding to the configuration of the power plant (40). Thereby, since the upper limit value A of the suppression amount ΔP can be set according to the configuration of the power plant (40), the output power P of the power plant (40) can be controlled more appropriately.

[0059] In addition, the substation 70 is connected to the power grid 80. The control system 30 sets the system stability SA of the power grid 80 when suppressing the output power P of the power plant (40), sets the lower limit value of the system stability SA as SB, and sets the upper limit value of the system stability SA as SC. It is more preferable that the control system 30 sets the upper limit value A of the suppression amount ΔP of the output power P so as to satisfy "SB < SA < SC". Thereby, the system stability SA can be set to be between the lower limit value SB and the upper limit value SC, and the output power P of the power plant (40) can be controlled more appropriately.

[0060] Moreover, as an index of the system stability SA, it is more preferable to include at least one of the phase angle of the generators included in the power grid 80, the voltage in the power grid 80, and the frequency in the power grid 80. Thereby, based on an appropriate index, the output power P of the power plant (40) can be controlled more appropriately.

[0061] Furthermore, when the control system 30 sets the maximum throttle value C of the turbine bypass valve 409 as C[%] and the rated output B of the power plant (40) as B, it is more preferable to set the upper limit value A of the suppression amount ΔP to a value less than or equal to "B × C". Thereby, the suppression amount ΔP can be set to a value achievable by the turbine bypass valve 409, and the output power P of the power plant (40) can be controlled more appropriately.

[0062] In addition, it is more preferable that the power transmission current suppression unit 50 includes a reactor 52. Thereby, by utilizing the characteristics of the reactor 52, the output power P of the power plant (40) can be controlled more appropriately.

[0063] Moreover, it is more preferable that the power transmission current suppression unit 50 includes a capacitor 54. Thereby, by utilizing the characteristics of the capacitor 54, the output power P of the power plant (40) can be controlled more appropriately.

[0064] [Modification Example] The present invention is not limited to the above-described embodiments, and various modifications are possible. The above-described embodiments are exemplified for easy understanding and explanation of the present invention, and are not necessarily limited to those having all the configurations described. Also, a part of the configuration of one embodiment can be replaced with the configuration of another embodiment, and the configuration of another embodiment can be added to the configuration of one embodiment. Further, a part of the configuration of each embodiment can be deleted, or addition or replacement with other configurations is possible. Also, the control lines and information lines shown in the figures indicate those considered necessary for explanation, and do not necessarily show all the control lines and information lines required in the product. In practice, it may be considered that almost all the configurations are interconnected. Possible modifications to the above embodiments are, for example, as follows.

[0065] (1) Since the hardware of the plant control device 32 in the above embodiment can be realized by a general computer, a program or the like for executing the various processes described above may be stored in a storage medium (a computer-readable recording medium on which the program is recorded) or distributed via a transmission path.

[0066] (2) The various processes described above were explained as software processes using a program in the above embodiment, but a part or all of them may be replaced with hardware processes using an ASIC (Application Specific Integrated Circuit) or an FPGA (Field Programmable Gate Array).

Explanation of Reference Numerals

[0067] 30 Control system 40 Nuclear power plant (power plant) 50 Power Transmission Current Suppression Unit 52 Reactor 54 Capacitor 70 Substation 80 Power System 82 Transmission Line 82,84 Transmission Lines 84 Transmission Line 405 Turbine 406 Generator 407 Reactor (Steam Generation Section) 408 Condenser 409 Turbine Bypass Valve A Upper Limit Value B Rated Output C Maximum Throttle Quantity P Output Power CP Power Transmission Current Suppression Signal SA System Stability SB Lower Limit Value SC Upper Limit Value ΔP Suppression Quantity SYS1, SYS4, SYS5 Power Systems

Claims

1. A power system comprising: a condenser; a turbine; a steam generation unit that generates steam; a turbine bypass valve that distributes the steam generated by the steam generation unit to the condenser and the turbine; a generator driven by the turbine; a power transmission current suppression unit inserted via a power transmission line between the power plant and a substation; and a control system, wherein the control system outputs a power transmission current suppression signal to the power transmission current suppression unit, indicating that the output power of the power plant should be suppressed; and the power transmission current suppression unit suppresses the output power of the power plant transmitted via the power transmission line based on the power transmission current suppression signal. A power system characterized by the above.

2. The control system sets an upper limit value of the suppression amount of the output power suppressed by the power transmission current suppression signal to a value corresponding to the configuration of the power plant. The power system according to claim 1, characterized by the above.

3. The substation is connected to the power grid. The control system sets the power grid stability of the power grid when suppressing the output power of the power plant as SA, sets the lower limit value of the grid stability as SB, and sets the upper limit value of the grid stability as SC. The control system sets the upper limit value of the suppression amount of the output power so as to satisfy "SB < SA < SC". The power system according to claim 2, characterized by the above.

4. As an index of the grid stability, it includes at least one of the phase angle of the generator included in the power grid, the voltage in the power grid, and the frequency in the power grid. The power system according to claim 3, characterized by the above.

5. When the control system sets the maximum throttle amount of the turbine bypass valve as C [%] and the rated output of the power plant as B, the control system sets the upper limit value of the suppression amount to a value less than or equal to "B × C". The power system according to claim 2, characterized by the above.

6. The power transmission current suppression unit includes a reactor. The power system according to claim 1, characterized by the above.

7. The power transmission current suppression unit includes a capacitor. The power system according to claim 1, characterized by the above.

8. A power system comprising: a condenser; a turbine; a steam generation unit that generates steam; a turbine bypass valve that distributes the steam generated by the steam generation unit to the condenser and the turbine; a generator driven by the turbine; a power transmission current suppression unit inserted via a power transmission line between the power plant and a substation; A control method for a power system including a control system, comprising: a process in which the control system outputs a power flow suppression signal to the power flow suppression unit, indicating that the output power of the power plant should be suppressed; a process in which the power flow suppression unit suppresses the output power of the power plant transmitted through the transmission line based on the power flow suppression signal. A control method for a power system, characterized by the above.

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