HYBRID SYSTEM, SYSTEM VOLTAGE STABILIZATION METHOD, AND PROGRAM

Abstract

To obtain a hybrid system capable of stabilizing voltage of a power system more than before.SOLUTION: A hybrid system 100 comprises: a synchronous phase modifier 4 suppressing voltage fluctuation of a power system; a control device 2 for the synchronous phase modifier; a power conversion device 6 which supplies effective power or reactive power to the power system, can suppress voltage fluctuation of the power system at response speed higher than that of the synchronous phase modifier 4, and can be operated in a high speed response mode or a low speed response mode; a control device 3 for the power conversion device which can change over a control mode of the power conversion device 6 to any one of the high speed response mode and the low speed response mode; and a hybrid control device 1 which on the basis of whether the synchronous phase modifier 4 is in an operating state or a stop state, determines that the control mode of the power conversion device 6 is the low speed response mode or the high speed response mode, and makes the control device 3 for the power conversion device control the power conversion device 6 in the determined control mode.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present application relates to a hybrid system, a system voltage stabilization method, and a program. [Background technology]

[0002] Conventionally, there is a technology for stabilizing a power transmission and distribution system by connecting a reactive power regulating device such as an SVC (Static Var Compensator) or an SVG (Static Var Generator) and a voltage regulator such as an SVR (Step Voltage Regulator) or an OLTC (On-Load Tap-Changers) to a power transmission and distribution system to be controlled and coordinating these multiple devices. (See, for example, Patent Document 1). That is, in the technology described in Patent Document 1, slow voltage fluctuations are compensated for by a voltage regulator such as an SVR, and fast voltage fluctuations are compensated for by a power conversion device such as an SVC. Usually, in such a technology, the voltage regulator and the voltage conversion device are each controlled only by a dedicated control device. For example, the SVC described in Patent Document 1 is operated based on the output of a voltage signal detection processing device, and is therefore controlled only by the voltage signal detection processing device. Also, the SVR or OLTC described in Patent Document 1 is said to perform voltage compensation by a known method. In general, a step voltage regulator such as an SVR is controlled by its own control device. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2004-266915 A Summary of the Invention [Problem to be solved by the invention]

[0004] The technology described in Patent Document 1 switches processing depending on the speed of voltage fluctuation, but as described above, the SVC and SVR are only controlled individually, and the operating states of the devices are not notified to each other. For this reason, if one of the devices stops for some reason, it is not possible to respond, and there is a risk that the voltage of the power system to be controlled will become unstable. For this reason, in a hybrid system in which high-speed voltage fluctuations in the power system are suppressed by a power conversion device that supplies active power or reactive power to the power system, and low-speed voltage fluctuations are suppressed by a synchronous phase modifier having inertia force, the voltage of the power system may become unstable when the synchronous phase modifier stops due to maintenance or a malfunction. This is because if the short-circuit capacity of the power system decreases due to the stop of the synchronous phase modifier, the operation of the power conversion device operating with high-speed response may become unstable, and the voltage of the power system may also become unstable.

[0005] The present application discloses technology for solving the above-mentioned problems, and aims to provide a hybrid system, a system voltage stabilization method, and a program that can stabilize the voltage of a power system more than conventional methods. [Means for solving the problem]

[0006] The hybrid system disclosed in the present application is a hybrid system connected to an electric power system, and includes a synchronous phase modifier that suppresses voltage fluctuations in the electric power system, a first control device that controls the synchronous phase modifier, a power conversion device that supplies active power or reactive power to the electric power system and is capable of suppressing voltage fluctuations in the electric power system with a faster response speed than the synchronous phase modifier and is operable in a high-speed response mode or a low-speed response mode having a slower response speed than the high-speed response mode, a second control device that controls the power conversion device and is capable of switching the control mode of the power conversion device to either the high-speed response mode or the low-speed response mode, and a control device that controls whether the synchronous phase modifier is in an operating state or a stopped state. and the power system information and a third control device that determines the control mode of the power conversion device to be a slow response mode or a fast response mode based on the determined control mode, and causes the second control device to control the power conversion device in the determined control mode.

[0007] The system voltage stabilization method disclosed in the present application is a system voltage stabilization method using a synchronous phase modifier that is connected to a power system and suppresses voltage fluctuations in the power system, and a power conversion device that supplies active power or reactive power to the power system and is capable of suppressing voltage fluctuations in the power system with a faster response speed than the synchronous phase modifier and is operable in a high-speed response mode or a low-speed response mode whose response speed is slower than that of the high-speed response mode, the method including the steps of: determining whether the synchronous phase modifier is in an operating state or in a stopped state; and the power system information The method includes a step of determining whether the power conversion device should be operated in a slow response mode or a fast response mode based on the control mode, and a step of controlling the power conversion device in the control mode selected by the determination.

[0008] The program disclosed in the present application is executed in a system including a synchronous phase modifier that is connected to a power system and suppresses voltage fluctuations in the power system, and a power conversion device that supplies active power or reactive power to the power system and is capable of suppressing voltage fluctuations in the power system with a faster response speed than the synchronous phase modifier and is operable in a high-speed response mode or a low-speed response mode having a slower response speed than the high-speed response mode, the program including a step of determining whether the synchronous phase modifier is in an operating state or in a stopped state, and and the power system information The present invention causes the processor to execute a step of determining whether the power conversion device should be operated in a slow response mode or a fast response mode based on the control mode, and a step of controlling the power conversion device in the control mode selected by the determination. Effect of the Invention

[0009] According to the hybrid system disclosed in the present application, the voltage of the power grid can be more stabilized than ever before. [Brief description of the drawings]

[0010] [Figure 1]1 is a schematic configuration diagram showing a hybrid system according to a first embodiment. [Diagram 2] 1 is a block diagram showing a hybrid control device according to a first embodiment; [Diagram 3] FIG. 2 is a diagram illustrating an example of a hardware configuration of each control device according to the first embodiment. [Figure 4] FIG. 4 is a flow diagram showing the operation of the hybrid system in the first embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Embodiment 1 A first embodiment will be described with reference to Figs. 1 to 4. Fig. 1 is a schematic diagram showing a hybrid system in the first embodiment. The hybrid system 100 is linked to a power system to be controlled, and includes a synchronous phase modifier 4 and a power converter 6, each of which is connected to an AC bus 7 of the power system, a synchronous phase modifier control device 2 for controlling the synchronous phase modifier 4, i.e., a first control device, a power converter control device 3 for controlling the power converter 6, i.e., a second control device, and a hybrid control device 1 connected to the synchronous phase modifier control device 2 and the power converter control device 3, i.e., a third control device. The synchronous phase modifier 4 is connected to the AC bus 7 via a circuit breaker 81 and a main transformer 82 as viewed from the AC bus 7. The power converter 6 is connected to the AC bus 7 via a circuit breaker 83 and a main transformer 84 as viewed from the AC bus 7. Although a power system generally has a plurality of AC buses 7, the synchronous phase modifier 4 and the power converter 6 in the first embodiment are connected to the same AC bus 7.

[0012] There are various methods for increasing the rotational speed of the synchronous phase modifier from zero (stationary state) to the rated rotational speed, such as using an induction motor, or using the synchronous phase modifier itself as an induction motor. Here, the method using an induction motor will be described as an example. A drive motor 5 and a synchronous phase modifier excitation device 10 are connected to the synchronous phase modifier 4. The drive motor 5 includes a pony motor and a VFD (Variable-Frequency Drive: variable voltage variable frequency power conversion device), both of which are omitted from the drawings. The pony motor is a starting motor, and its shaft is connected to the rotating shaft of the synchronous phase modifier 4. The pony motor is used when increasing the rotational speed of the synchronous phase modifier 4 from zero (stationary state) to the rated rotational speed. The pony motor is configured using, for example, an induction motor. The VFD controls the rotational speed of the induction motor that configures the pony motor.

[0013] The synchronous phase modifier exciter may be a brush device or a brushless exciter, but the brushless exciter will be used as an example. In this case, the synchronous phase modifier exciter 10 is an AVR (Automatic Voltage Regulator). The brushless exciter 9 has an AC exciter, a rotary rectifier, and a permanent magnet generator arranged on the same axis as the rotor of the synchronous phase modifier 4, and the armature winding of the AC exciter is connected to the field winding of the synchronous phase modifier 4 via the rotary rectifier. The synchronous phase modifier exciter 10 controls the voltage and current applied to the field of the synchronous phase modifier 4, and keeps the terminal voltage of the synchronous phase modifier 4 constant.

[0014] The synchronous phase modifier control device 2 controls the operation of the synchronous phase modifier 4. Specifically, the synchronous phase modifier control device 2 sends a control command to the synchronous phase modifier excitation device 10 and controls the synchronous phase modifier 4 through the control of the synchronous phase modifier excitation device 10. The synchronous phase modifier control device 2 is also connected to a current transformer (not shown) provided near the line side terminal and the neutral side terminal of the synchronous phase modifier 4, and is capable of acquiring the current value of the current output by the synchronous phase modifier 4 via this current transformer. During the control of the synchronous phase modifier 4, the synchronous phase modifier control device 2 acquires the current value of the current output by the synchronous phase modifier 4 and controls the synchronous phase modifier 4 according to this current value.

[0015] Furthermore, the synchronous phase modifier control device 2 determines whether the synchronous phase modifier 4 is in an operating state or in a stopped state based on whether the synchronous phase modifier 4 is connected to the AC bus 7. Whether the synchronous phase modifier 4 is connected to the AC bus 7 is determined from the open / closed state (closed or open) of the circuit breaker 81. The synchronous phase modifier control device 2 outputs information indicating whether the synchronous phase modifier 4 is in an operating state or in a stopped state to the hybrid control device 1 as synchronous phase modifier state information S.

[0016] The synchronous phase modifier 4 has an inertial force, and suppresses the voltage fluctuation of the voltage of the power system (hereinafter, referred to as system voltage) by using this inertial force. The synchronous phase modifier 4 also suppresses the fluctuation of the system voltage by supplying a short-circuit current to the AC bus 7.

[0017] The power conversion device 6 is a device that compensates for reactive power, such as a STATCOM (STATic synchronous COMpensator), and is capable of suppressing voltage fluctuations faster than those suppressed by the synchronous phase modifier 4. The power conversion device 6 can be operated in a high-speed response mode or a low-speed response mode. The low-speed response mode is a control mode in which the response speed is slower than that of the high-speed response mode. The response speed of the high-speed response mode is faster than that of the synchronous phase modifier 4, but is not particularly limited. As the power conversion device 6, a self-excited converter such as a converter that converts DC voltage and AC voltage, which is used in HVDC (High Voltage Direct Current), may be used. The circuit configuration of the power conversion device 6 is not particularly limited. In short, it is sufficient that the power conversion device supplies active power or reactive power to the power system so as to suppress high-speed fluctuations in the system voltage and is capable of changing the response speed.

[0018] The power conversion device control device 3 controls the operation of the power conversion device 6. The power conversion device control device 3 has a function of switching the control mode of the power conversion device 6 between a high-speed response mode and a low-speed response mode in response to a control mode command T described later. As the rest of the configuration is similar to known power conversion device control devices, a description thereof will be omitted.

[0019] The circuit breaker 81 includes an output unit (not shown) that outputs switching state information K, which is information indicating its own switching state, to the synchronous phase modifier control device 2, and notifies the synchronous phase modifier control device 2 of its own switching state.

[0020] The hybrid control device 1 controls the control mode to suppress the fluctuation of the grid voltage according to the state of the hybrid system 100. Fig. 2 is a block diagram showing the hybrid control device according to the first embodiment. The hybrid control device 1 includes a state information acquisition unit 11 that acquires synchronous phase modifier state information S from the synchronous phase modifier control device 2, a system short-circuit capacity acquisition unit 12 that acquires a system short-circuit capacity C that is a short-circuit capacity of the power grid, a control mode determination unit 13 that determines the control mode of the power conversion device 6 based on the synchronous phase modifier state information S and the system short-circuit capacity C, a threshold storage unit 14 that stores a threshold Cth of the system short-circuit capacity C described later, and a control mode command output unit 15 that outputs a control mode command T to the power conversion device control device 3 to instruct the power conversion device 6 to be controlled in the control mode determined by the control mode determination unit 13.

[0021] When the synchronous phase modifier state information S indicates that the synchronous phase modifier 4 is in a stopped state, the control mode determination unit 13 compares the grid short-circuit capacity C with a threshold value Cth, and when the grid short-circuit capacity C is smaller than the threshold value Cth, the control mode determination unit 13 determines the control mode of the power conversion device 6 to be the "slow response mode". When the grid short-circuit capacity C is equal to or greater than the threshold value Cth, the control mode determination unit 13 determines the control mode of the power conversion device 6 to be the "fast response mode". When the synchronous phase modifier state information S indicates that the synchronous phase modifier 4 is in an operating state, the control mode determination unit 13 determines the control mode of the power conversion device 6 to be the "fast response mode". That is, when the synchronous phase modifier 4 is in a stopped state and the grid short-circuit capacity C is smaller than the threshold value Cth, the control mode determination unit 13 determines the control mode of the power conversion device 6 to be the "slow response mode", and otherwise determines the control mode of the power conversion device 6 to be the "fast response mode".

[0022] In the first embodiment, it is determined whether the synchronous phase modifier 4 is in an operating state or in a stopped state based on the open / closed state of the circuit breaker 81. However, since it may be known in advance that the synchronous phase modifier 4 will be stopped due to maintenance or the like, the synchronous phase modifier status information S may be configured to be input from the outside to the hybrid control device 1, and when the synchronous phase modifier 4 is stopped before the start of maintenance, the user may input the synchronous phase modifier status information S indicating the stopped state to the hybrid control device 1, and when the synchronous phase modifier 4 is started after the completion of maintenance, the user may input the synchronous phase modifier status information S indicating the operating state to the hybrid control device 1. Furthermore, in the first embodiment, the synchronous phase modifier control device 2 determines whether the synchronous phase modifier 4 is in an operating state or a stopped state, but the synchronous phase modifier control device 2 may be configured to determine only the connection state between the synchronous phase modifier 4 and the AC bus 7 and output the determination result of this connection state to the hybrid control device 1. In this case, based on the connection state between the synchronous phase modifier 4 and the AC bus 7, the hybrid control device 1 determines whether the synchronous phase modifier 4 is in an operating state or a stopped state.

[0023] The grid short circuit capacity C may be obtained, for example, by a notification from a power transmission and distribution company. The threshold value Cth is determined in advance by obtaining, by a simulation or the like, the range of the grid short circuit capacity C in which the power conversion device 6 operates stably.

[0024] Next, an example of the hardware configuration of each control device of the first embodiment, that is, the hybrid control device 1, the synchronous phase modifier control device 2, and the power conversion device control device 3 will be described. FIG. 3 is a diagram showing an example of the hardware configuration of each control device according to the first embodiment. Here, the hybrid control device 1 will be described, but the synchronous phase modifier control device 2 and the power conversion device control device 3 are similar. The hybrid control device 1 is mainly composed of a processor 91, a memory 92 as a main storage device, and an auxiliary storage device 93. The processor 91 is composed of, for example, a central processing unit (CPU), an application specific integrated circuit (ASIC), a digital signal processor (DSP), a field programmable gate array (FPGA), etc. The memory 92 is composed of a volatile storage device such as a random access memory, and the auxiliary storage device 93 is composed of a nonvolatile storage device such as a flash memory or a hard disk. A predetermined program executed by the processor 91 is stored in the auxiliary storage device 93, and the processor 91 appropriately reads and executes this program to perform various arithmetic processing. At this time, the predetermined program is temporarily saved from the auxiliary storage device 93 to the memory 92, and the processor 91 reads the program from the memory 92. The arithmetic processing by each functional unit shown in Fig. 1 is realized by the processor 91 executing the predetermined program as described above. The results of the arithmetic processing by the processor 91 are temporarily stored in the memory 92, and are then stored in the auxiliary storage device 93 according to the purpose of the executed arithmetic processing.

[0025] In addition, although not shown in the figure, the hybrid control device 1 is equipped with an input circuit that accepts various inputs from the outside, such as synchronous modifier status information S and system short-circuit capacity C, and an output circuit that outputs a control mode command T and the like to the outside.

[0026] Next, the operation of the hybrid system 100, that is, the system voltage stabilization method in the first embodiment, will be described. Fig. 4 is a flow diagram showing the operation of the hybrid system in the first embodiment. First, the state of the synchronous phase modifier 4, that is, whether the synchronous phase modifier 4 is in an operating state or a stopped state, is determined from the open / closed state of the circuit breaker 81 (step ST101). If the synchronous phase modifier 4 is in a stopped state, the process proceeds to step ST103, and if the synchronous phase modifier 4 is in an operating state, the process proceeds to step ST105 (step ST102).

[0027] When the synchronous phase modifier 4 is in a stopped state, the system short-circuit capacity C, which is the short-circuit capacity of the power system, is compared with the threshold value Cth, and if the system short-circuit capacity C is smaller than the threshold value Cth, the process proceeds to step ST104. If the system short-circuit capacity C is equal to or larger than the threshold value Cth, the process proceeds to step ST105 (step ST103).

[0028] When the synchronous phase modifier 4 is in a stopped state and the system short-circuit capacity C is smaller than the threshold value Cth, the control mode of the power conversion device 6 is determined to be the "slow response mode" (step ST104).

[0029] When the synchronous phase modifier 4 is in operation, or even when it is in a stopped state, the system short-circuit capacity C is equal to or greater than the threshold value Cth, the control mode of the power conversion device 6 is determined to be the "fast response mode" (step ST105).

[0030] The power conversion device 6 is controlled in the control mode determined in step ST104 or step ST105 (step ST106). If the determined control mode is the same as the current control mode, the current control mode is continued, and if the determined control mode is different from the current control mode, the control mode is switched.

[0031] The timing for performing the series of operations from step ST101 to step ST106 described above is not particularly limited, but it is conceivable to detect a change in the state of the synchronous phase modifier 4, i.e., a change from an operating state to a stopped state, or a change from a stopped state to an operating state, and perform the above operations at the timing when the change is detected. In the first embodiment, since the state of the synchronous phase modifier 4 is determined based on the open / closed state of the circuit breaker 81, it can also be considered that the state of the synchronous phase modifier 4 has changed when a change in the open / closed state of the circuit breaker 81, i.e., a change in the connection state between the AC bus 7 and the synchronous phase modifier 4, is detected.

[0032] It is also possible to set the response speed of the slow response mode of the power conversion device 6 according to the system short circuit capacity C. By setting the response speed of the slow response mode according to the system short circuit capacity C, for example, by setting the response speed of the slow response mode slower as the system short circuit capacity C becomes smaller, it is possible to more reliably prevent divergence caused by the control of the system voltage by the power conversion device 6 and cause the system to become unstable. Furthermore, if the system short circuit capacity C is relatively large, the response speed of the slow response mode can also be set faster, making it possible to more effectively suppress fluctuations in the system voltage.

[0033] In the first embodiment, the control mode of the power conversion device 6 is not always set to the slow response mode even when the synchronous phase modifier 4 is in a stopped state, but the slow response mode or the fast operation mode is determined according to the magnitude of the grid short-circuit capacity C. However, it is also possible to immediately set the control mode of the power conversion device 6 to the slow response mode when it is determined that the synchronous phase modifier 4 is in a stopped state, regardless of the magnitude of the grid short-circuit capacity C. In this case, the slow operation mode may be set even when it is not necessarily required, but the process of step ST103 can be omitted, so that the configuration is simplified. Such a configuration is effective when it is clear that the grid short-circuit capacity C is small and it is clear that the slow operation mode is required without even having to be compared with the threshold value Cth.

[0034] According to the first embodiment, the voltage of the power system can be stabilized more than in the past. More specifically, the power system includes a synchronous phase modifier that suppresses fluctuations in the system voltage, a control device for the synchronous phase modifier that controls the synchronous phase modifier, a power conversion device that supplies active power or reactive power to the power system and is capable of suppressing fluctuations in the system voltage at a faster response speed than the synchronous phase modifier and is operable in a fast response mode or a slow response mode that is slower in response speed than the fast response mode, a control device for the power conversion device that controls the power conversion device and is capable of switching the control mode of the power conversion device to either the fast response mode or the slow response mode, and a hybrid control device that determines the control mode of the power conversion device to the slow response mode or the fast response mode based on whether the synchronous phase modifier is in an operating state or a stopped state, and causes the control device for the power conversion device to control the power conversion device in the determined control mode. As a result, when the synchronous phase modifier is in an operating state, slow voltage fluctuations can be suppressed by the synchronous phase modifier while fast voltage fluctuations can be suppressed by the power conversion device, and a wide range of voltage fluctuations can be handled by the cooperation of the synchronous phase modifier and the power conversion device. On the other hand, when the synchronous phase modifier is stopped, the control mode of the power conversion device is switched to a slow response mode to slow down the response speed, so that the operation of the power conversion device does not become unstable even if the short-circuit capacity of the power system is small. Therefore, it is possible to stabilize the voltage of the power system even when the synchronous phase modifier is stopped, which previously caused the voltage of the power system to become unstable.

[0035] In addition, even if the synchronous modifier is stopped, the control mode of the power conversion device is set to the slow response mode only when the short-circuit capacity of the power grid is smaller than a predetermined threshold value. Therefore, the control mode of the power conversion device is not switched to the slow response mode even when control is possible in the fast response mode, and it is possible to respond to voltage fluctuations as fast as possible.

[0036] Moreover, the determination of whether the synchronous phase modifier is in an operating state or in a stopped state is made based on the connection state of the synchronous phase modifier and the AC bus of the power system. As described above, in the first embodiment, the circuit breaker provided between the synchronous phase modifier and the AC bus includes an output unit that outputs its own open / closed state, but it is a general configuration for a circuit breaker to have a function of outputting its own open / closed state, and no additional configuration is required to determine the state of the synchronous phase modifier.

[0037] Furthermore, when a change in the state of the synchronous phase modifier is detected based on a change in the connection state between the AC busbar of the power system and the synchronous phase modifier, and a process of determining the control mode of the power conversion device is performed at the timing when the change in the state of the synchronous phase modifier is detected, the process from detecting a change in the open / close state of the circuit breaker to switching the control mode of the power conversion device can be performed automatically, and the control mode of the power conversion device can be switched at an appropriate time. For example, when the synchronous phase modifier is switched to a stopped state, the control mode of the power conversion device can be automatically switched to a slow response mode, and when the synchronous phase modifier is switched to an operating state (when operation is resumed), the control mode of the power conversion device can be automatically switched to a fast response mode.

[0038] In addition, in a configuration in which the user inputs whether the synchronous phase modifier is in an operating state or a stopped state into the hybrid control device, if the stop time of the synchronous phase modifier is known in advance, for example, for maintenance, it is also possible to switch the control mode of the power conversion device to the slow response mode before the synchronous phase modifier stops.

[0039] Although the present application describes exemplary embodiments, the various features, aspects, and functions described in the embodiments are not limited to application to a particular embodiment, but may be applied to the embodiments alone or in various combinations. Therefore, countless modifications not illustrated are expected within the scope of the technology disclosed in this application, including, for example, modifying, adding, or omitting at least one component. [Explanation of symbols]

[0040] 1 Hybrid control device, 2 Synchronous phase condenser control device, 3 Power conversion device control device, 4 Synchronous phase condenser, 6 Power conversion device, 7 AC bus, 11 Status information acquisition unit, 12 System short circuit capacity acquisition unit, 13 Control mode determination unit, 14 Threshold value storage unit, 15 Control mode command output unit, 100 Hybrid system, C System short circuit capacity, Cth Threshold value, S Synchronous phase condenser status information, T Control mode command

Claims

1. A hybrid system connected to an electric power grid, A synchronous phase modifier for suppressing voltage fluctuations in the power grid; A first control device that controls the synchronous phase modifier; a power conversion device that supplies active power or reactive power to the power system, is capable of suppressing voltage fluctuations in the power system at a faster response speed than the synchronous phase modifier, and is operable in a high-speed response mode or a low-speed response mode having a slower response speed than the high-speed response mode; a second control device that controls the power conversion device and is capable of switching a control mode of the power conversion device to either the high-speed response mode or the low-speed response mode; a third control device that determines the control mode of the power conversion device to be the slow response mode or the fast response mode based on information on whether the synchronous phase modifier is in an operating state or a stopped state and information on the power system, and causes the second control device to control the power conversion device in the determined control mode; A hybrid system comprising:

2. 2. The hybrid system according to claim 1, wherein the third control device causes the second control device to control the power conversion device in the slow response mode when the synchronous phase modifier is in a stopped state and when a short-circuit capacity of the power system, which is information about the power system, is smaller than a predetermined threshold value.

3. 3. The hybrid system according to claim 1, wherein the third control device causes the second control device to control the power conversion device in the high-speed response mode when the synchronous phase modifier is in an operating state.

4. 4. The hybrid system according to claim 1, wherein the synchronous phase modifier determines whether the synchronous phase modifier is in an operating state or in a stopped state based on whether the synchronous phase modifier is connected to an AC bus of the power system.

5. 5. The hybrid system according to claim 4, wherein a change in a state of the synchronous phase modifier from an operating state to a stopped state or from a stopped state to an operating state is detected from a change in a connection state between the synchronous phase modifier and the AC bus, and the control mode is determined by the third control device at the timing of the detection.

6. 4. The hybrid system according to claim 1, wherein information on whether the synchronous phase modifier is in an operating state or in a stopped state is obtained through an input from a user.

7. The hybrid system according to claim 1 , wherein the synchronous modifier and the power conversion device are connected to the same AC bus of the power system.

8. 8. The hybrid system according to claim 1, wherein a response speed of the slow response mode is set according to a short-circuit capacity of the power grid.

9. A system voltage stabilization method using a synchronous phase modifier that is connected to an electric power system and suppresses voltage fluctuations in the electric power system, and a power conversion device that supplies active power or reactive power to the electric power system, is capable of suppressing voltage fluctuations in the electric power system with a faster response speed than the synchronous phase modifier, and is operable in a high-speed response mode or a low-speed response mode having a slower response speed than the high-speed response mode, determining whether the synchronous phase modifier is in an operating state or in a stopped state; determining whether the power conversion device is to be operated in the slow response mode or the fast response mode based on the result of the determination and information on the power system; controlling the power converter in a control mode selected by the determination; A system voltage stabilization method comprising:

10. A program executed in a system including a synchronous phase modifier that is connected to an electric power system and suppresses voltage fluctuations in the electric power system, and a power conversion device that supplies active power or reactive power to the electric power system, is capable of suppressing voltage fluctuations in the electric power system with a faster response speed than the synchronous phase modifier, and is operable in a high-speed response mode or a low-speed response mode having a slower response speed than the high-speed response mode, determining whether the synchronous phase modifier is in an operating state or in a stopped state; determining whether the power conversion device is to be operated in the slow response mode or the fast response mode based on the result of the determination and information on the power system; controlling the power converter in a control mode selected by the determination; A program characterized by causing a processor to execute the above.

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