Power generation system and method for controlling the power generation system

Abstract

To provide a power generation system and a power generation system control method in which, in a case where a power system abnormality or an isolated operation is detected by an active method using a master machine, occurrence of a non-detection time period can be suppressed.SOLUTION: A power generation system according to the present embodiment includes a plurality of power generation devices interconnected to a power system, and a main control unit. The power generation system is interconnected to the power system. Each of the power generation devices includes an isolated-operation preventing unit capable of serving as both a mater machine that actively generates a disturbance in order to detect an abnormality in the power system, and a slave machine that operates in response to an output signal from the master machine. The main control unit causes one of the isolated-operation preventing units of the respective power generation devices, to operate as the master machine, and causes the remaining isolated-operation preventing units to operate as the slave machines in accordance with a prescribed determination standard using operation information about each of the power generation devices.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] Embodiments of the present invention relate to a power generation system and a control method for the power generation system.

Background Art

[0002] When connecting a power generation device to a power grid, a power conditioner is equipped with a single operation prevention device for preventing single operation. An active method is known as a method for detecting single operation of such a single operation prevention device. Further, when a plurality of power generation devices are operating in parallel, in order to suppress mutual interference of the active method, one of the plurality of power generation devices may be used as a master machine to detect single operation.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, when the master machine fails or the power generation device as the master machine stops power generation, etc., the detection of single operation may be delayed. The problem to be solved by the present invention is to provide a power generation system and a control method for the power generation system that can suppress the occurrence of undetected periods when detecting an abnormality in the power grid or single operation by an active method using a master machine.

Means for Solving the Problems

[0005] The power generation system according to this embodiment comprises a plurality of power generation devices connected to a power grid and a main control unit. The power generation system is connected to a power grid. Each of the plurality of power generation devices has an islanding prevention unit that can operate as either a master unit that actively generates disturbances to detect abnormalities in the power grid, or a slave unit that operates based on the output signal of the master unit. The main control unit, based on predetermined criteria using the operating information of each of the plurality of power generation devices, designates one of the plurality of power generation devices as the master unit and operates the other power generation devices as slave units. [Brief explanation of the drawing]

[0006] [Figure 1] A block diagram showing a schematic overall configuration example of the power generation system according to the first embodiment. [Figure 2] A block diagram showing a more detailed configuration example of a power generation system. [Figure 3] A block diagram showing an example of the control device configuration. [Figure 4] A flowchart illustrating an example of startup processing in a power generation system. [Figure 5] A flowchart illustrating an example of the process when the standalone operation prevention unit, which is the master unit, stops. [Figure 6] A flowchart illustrating an example of how to handle situations where the master machine unexpectedly shuts down. [Figure 7] A block diagram showing the configuration of a power generation system according to a modified example of the first embodiment. effect

[0007] When the master unit detects anomalies in the power system or islanding, it becomes possible to suppress the occurrence of periods of no detection. [Modes for carrying out the invention]

[0008] Hereinafter, a power generation system and a control method for the power generation system according to embodiments of the present invention will be described in detail with reference to the drawings. Note that the embodiments shown below are examples of embodiments of the present invention, and the present invention is not limited to these embodiments. Furthermore, in the drawings referenced in these embodiments, the same or similar reference numerals are used for identical parts or parts having similar functions, and repeated descriptions may be omitted. Also, the dimensional ratios in the drawings may differ from the actual ratios for illustrative purposes, and some components may be omitted from the drawings.

[0009] (First Embodiment) Figure 1 is a block diagram illustrating a schematic overall configuration example of a power generation system 1 according to the first embodiment. As shown in Figure 1, the power generation system 1 is a system that generates electricity using a plurality of power generation devices 10 and can supply power to the commercial power grid Pg via the distribution system ds. More specifically, this power generation system 1 comprises a plurality of power generation devices 10, a control device 20, a measuring instrument 30, and a higher-level control device 40. Each of these plurality of power generation devices 10 has an islanding detection function that can prevent islanding. A load 60 is also shown in Figure 1.

[0010] The power generator 10 can supply power to the power grid Pg via the distribution system ds. The control device 20 is, for example, an EMS (Energy Management System) and is composed of a CPU (Central Processing Unit) and controls, for example, the total amount of power generated by the multiple power generators 10. The control device 20 outputs power command signals to the multiple power generators 10, for example, which include information on the total amount of power generated in the power generation system 1. The control device 20 can also set a master unit among the multiple power generators 10. Furthermore, it can set other power generators 10 among the multiple power generators 10 as slave units. That is, each of the multiple power generators 10 can operate as either a master unit that actively generates disturbances to detect abnormalities in the power grid Pg, or a slave unit that operates based on the output signal of the master unit. Based on predetermined criteria using the operating information of each of the multiple power generators 10, the control device 20 sets one of the multiple power generators 10 as the master unit and the other power generators 10 as slave units. In this embodiment, the control device 20 is configured outside of the multiple power generation devices 10, but this is not the only configuration. For example, the control device 20 can be configured within at least one of the multiple power generation devices 10.

[0011] The measuring instrument 30 measures, for example, the power supplied to the power grid Pg. The measured value from the measuring instrument 30 is then supplied to, for example, multiple power generation devices 10 and control devices 20.

[0012] The higher-level control device 40 is, for example, an EMS (Energy Management System) and is configured to include a CPU (Central Processing Unit), and is capable of controlling multiple control devices 20. For example, one control device 20 controls multiple power generation devices 10, and the higher-level control device 40 is configured to control each of the multiple control devices 20.

[0013] Figure 2 is a block diagram showing a more detailed configuration example of the power generation device 10 according to the first embodiment. The power generation device 10 includes a power generation unit 102, a power conditioner 104, a higher-level command transmission / reception unit 106, and a control unit 108. Furthermore, the power conditioner 104 includes an inverter circuit 104a, an islanding prevention unit 104b, and a disconnection unit 104c.

[0014] The power generation unit 102 generates electricity according to the control of the control unit 108. The power generation unit 102 is, for example, a fuel cell, which converts hydrogen into electrical energy. The power generation unit 102 outputs the generated electricity (DC power) to the power conditioner 104. In this embodiment, the power generation device 10 is a fuel cell, but it is not limited to this. The power generation unit 102 may be, for example, a storage battery, a solar cell, a wind power generation device, etc.

[0015] The power conditioner 104 has an islanding detection function and converts the power (DC power) generated by the power generation unit 102 into AC power. It then outputs the converted AC power to the power grid Pg. In other words, the inverter circuit 104a of the power conditioner 104 converts the DC power input from the power generation unit 102 into AC power synchronized with the power grid Pg, according to the control of the control unit 108. The islanding prevention unit 104b, acting as a master or slave unit, detects abnormalities such as power outages in the power grid Pg. Details of the islanding prevention unit 104b will be described later.

[0016] The disconnection unit 104c can disconnect the power generation device 10 from the power grid Pg through control by the islanding prevention unit 104b, the control unit 108, the control device 20, and others. The power generation device 10 may sometimes be referred to as a distributed power source.

[0017] The higher-level command transmission / reception unit 106 transmits and receives control signals and the like between the control device 20 and the control unit 108. The control unit 108 is configured to include, for example, a CPU (Central Processing Unit), and, via the higher-level command transmission / reception unit 106, controls the power generation unit 102 to generate a predetermined amount of power for each power generation device 10 in accordance with the total amount of power generated instructed by, for example, the control device 20.

[0018] The control unit 108 can control the disconnection unit 104c to electrically disconnect the power conditioner 104 from the power grid Pg. Further, the control unit 108 performs control to boost (or lower) the AC voltage output from the inverter circuit 104a of the power conditioner 104. Additionally, the control unit 108 can control the single-operation prevention unit 104b.

[0019] Here, the details of the single-operation prevention unit 104b will be described. As described above, the single-operation prevention unit 104b, acting as a master unit, detects abnormalities such as a power outage in the power grid Pg. The single-operation prevention unit 104b of the power generation device 10 operating as a master unit is operated as a master unit, and the single-operation prevention unit 104b of the power generation device 10 operating as a slave unit is operated as a slave unit. That is, the single-operation prevention unit 104b operated as a master unit is referred to as the master unit, and the single-operation prevention unit 104b operated as a slave unit is referred to as the slave unit.

[0020] The master unit of the single-operation prevention unit 104b can detect the single operation of the power generation device 10 by an active method (active type). This single-operation prevention unit 104b can, for example, stop the power supply to the power grid Pg when detecting an abnormality such as a power outage. For example, the master unit of the single-operation prevention unit 104b can control the disconnection unit 104c to disconnect the power conditioner 104 from the power grid Pg within, for example, 0.5 seconds or more and 1 second or less. That is, the single-operation prevention unit 104b can disconnect the power generation device 10 by the disconnection unit 104c when it enters a single-operation state. Note that the single-operation prevention unit 104b may be referred to as a single-operation prevention device.

[0021] As such an active detection method, for example, any of the frequency shift method, slip mode frequency shift method, reactive power fluctuation method, and QC mode frequency shift method can be used. That is, the islanding prevention unit 104b, acting as a master unit, has the function of actively generating disturbances in the distribution system ds. Islanding refers to a state in which the power generation unit 102 is not disconnected from the power system Pg and can continue to supply power when the power system Pg has stopped supplying power due to an abnormality such as a power outage, or when the switchgear of the power system Pg has been released. Furthermore, the active method is not limited to any of the frequency shift method, slip mode frequency shift method, reactive power fluctuation method, and QC mode frequency shift method, and other active methods may be used. In this embodiment, the islanding prevention unit 104b that detects abnormalities in the power system or islanding using an active method is the master unit described above. On the other hand, the islanding prevention unit 104b that operates according to the output signal of the master unit is the slave unit described above.

[0022] Furthermore, when operating as a slave unit, the islanding prevention unit 104b can control the disconnection unit 104c according to the output signal of the master unit to disconnect the power conditioner 104 from the power grid Pg. This islanding prevention unit 104b, acting as a slave unit, can also disconnect the power conditioner 104 from the power grid Pg within, for example, 0.5 seconds to 1 second if, for example, a power outage occurs and the unit enters an islanding state. Thus, the islanding prevention unit 104b can operate as either a master unit that actively generates disturbances to detect abnormalities in the power grid Pg, or a slave unit that operates based on the output signal of the master unit.

[0023] Figure 3 is a block diagram showing an example configuration of the control device 20. As shown in Figure 3, the control device 20 has a storage unit 200 and a main control unit 202.

[0024] The memory unit 200 is implemented by, for example, a semiconductor memory element such as RAM (Random Access Memory) or flash memory, or a hard disk. The memory unit 200 stores the operating status as operating information for each power generation device 10. This memory unit 200 stores the operating information for each power generation device 10, for example, via the higher-level command transmission / reception unit of the power generation device 10. Alternatively, a memory unit may be provided for each power generation device 10 to store the operating information for each power generation device 10. In this case, the main control unit 202 can sequentially acquire the operating information from the memory unit of each power generation device 10 and store it in the memory unit 200.

[0025] The main control unit 202 controls the entire power generation system 1 in cooperation with the higher-level control unit 40. The main control unit 202 stores the drive information of the power conditioner 104 in the storage unit 200 via the higher-level command transmission / reception unit 106 of the power generation device 10. More specifically, the main control unit 202 acquires information regarding the cumulative operating time, cumulative power generated, and fuel cell voltage for each power generation device 10, and stores this information in the storage unit 200 in association with each power generation device 10.

[0026] The main control unit 202 uses the operating information of each power generation device 10 to determine which power generation device 10 will be designated as the master unit from among the islanding prevention units 104b of each power generation device 10. Based on the determination information of the main control unit 202, the main control unit 202 sets one power generation device 10 as the master unit. The main control unit 202 then sets the remaining power generation devices 10 as slave units. The islanding prevention unit 104b of the power generation device 10 designated as the master unit operates as the master unit. On the other hand, the islanding prevention unit 104b of the power generation device 10 designated as a slave unit operates as a slave unit. Thus, in this embodiment, when a power generation device 10 is designated as the master unit, the islanding prevention unit 104b of the power generation device 10 designated as the master unit operates as the master unit. On the other hand, when a power generation device 10 is designated as a slave unit, the islanding prevention unit 104b of the power generation device 10 designated as a slave unit operates as a slave unit.

[0027] Furthermore, the main control unit 202 uses the operating information of each power generation unit 10 to determine the priority order for each power generation unit 10 to be designated as the master unit. This determined order is the order in which the next power generation unit to be designated as the master unit will be used if the power generation unit 10 equipped with the islanding prevention unit 104b that is currently being used as the master unit stops. In other words, when the power generation unit 10 equipped with the islanding prevention unit 104b stops, the main control unit 202 sets the power generation unit 10 to be used as the next master unit according to this determined order. Also, even if the power generation unit 10 being used as the master unit stops for any reason beyond the control of the main control unit 202, the main control unit 202 sets the next power generation unit 10 to be used as the master unit according to this determined order. This makes it possible to change the master unit in a shorter amount of time.

[0028] The main control unit 202 has, for example, three criteria for determination. The main control unit 202 may make a determination based on each of the three criteria individually, or it may make a determination based on a combination of criteria.

[0029] The main control unit 202 determines which islanding prevention unit 104b will be designated as the master unit based on the cumulative operating time of the power generation unit 102 as its first criterion. For example, the main control unit 202 determines which power generation device 10 has the shortest cumulative operating time of the power generation unit 102 to be designated as the master unit. Since the power generation device 10 has the shortest cumulative operating time of the power generation unit 102 is least likely to fail, the islanding prevention unit 104b can be used more continuously and stably. This makes it possible to suppress the occurrence of periods of no detection when the master unit detects an abnormality in the power system.

[0030] Furthermore, the main control unit 202 determines which islanding prevention unit 104b will be designated as the master unit based on the cumulative power generated by the power generation unit 102, as a second criterion. For example, the main control unit 202 determines which power generation device 10 has the smallest cumulative power generated by the power generation unit 102 to be designated as the master unit. Since the power generation device 10 has the smallest cumulative power generated by the power generation unit 102 is most likely to have the longest lifespan, the islanding prevention unit 104b can be used more continuously and stably. This makes it possible to suppress the occurrence of periods of no detection when an abnormality in the power system is detected by the master unit.

[0031] Furthermore, the main control unit 202 determines the master islanding prevention unit 104b based on a third criterion: the voltage of the fuel cell, which is the power generation unit 102. For example, the main control unit 202 determines that the islanding prevention unit 104b of the power generation device 10 with the highest voltage among the power generation units 102 will be the master unit. The power generation device 10 with the highest voltage among the power generation units 102 has good power generation performance and is likely to have the longest lifespan, so the islanding prevention unit 104b can be used more continuously and stably. In this way, the main control unit 202 of the control device 20 sets the master islanding prevention unit 104b using the operating information of each power generation unit 102, making it possible to designate the islanding prevention unit 104b of a more stable power generation device 10 as the master unit. This makes it possible to suppress the occurrence of periods of no detection when the master unit detects an abnormality in the power system.

[0032] Figure 4 is a flowchart showing an example of startup processing in the power generation system 1 according to this embodiment. Here, we will explain the case where one of the three judgment criteria is set in advance.

[0033] As shown in Figure 4, first, the main control unit 202 acquires operating information for each power generator 10 from the storage unit 200 before startup (step S100). Next, the main control unit 202 determines which power generator 10 will be designated as the master unit from among the multiple power generators 10 according to the determination criteria (step S102). The master unit is selected from among the power generators 10 scheduled to operate.

[0034] Next, the main control unit 202, based on the determination information of the main control unit 202, sets one of the power generation devices 10 as a master unit and sets the islanding prevention unit 104b of the power generation device 10 designated as the master unit as the master unit. Subsequently, the main control unit 202 sets the remaining power generation devices 10 as slave units and sets the islanding prevention unit 104b of the power generation devices 10 designated as slave units as the slave units. (Step S104).

[0035] Next, the main control unit 202 starts detecting isolated operation by the master unit (step S106). In this way, the main control unit 202 of the control device 20 uses the operation information of each power generation unit 102 to set the power generation unit 10 to be the master unit, and also sets the isolated operation prevention unit 104b of the power generation unit 10 to be the master unit.

[0036] Next, we will explain an example of the process when stopping a power generation device 10 that has an islanding prevention unit 104b acting as a master unit. Figure 5 is a flowchart showing an example of the process when the islanding prevention unit 104b acting as a master unit is stopped.

[0037] As shown in Figure 5, first, the main control unit 202 determines whether the power generation device 10 having the isolated operation prevention unit 104b designated as the master unit is scheduled to stop (step S200). If it is determined that it will not stop (NO in step S200), the main control unit 202 continues to determine the priority order of the master unit from among the multiple power generation devices 10 according to the determination criteria (step S202).

[0038] On the other hand, if the main control unit 202 determines that it should stop (YES in step S200), the main control unit 202 sets the next master unit from among the multiple power generation units 10 according to the priority order of the master units (step S204). Subsequently, the main control unit 202 causes the islanding prevention unit 104b of the next master unit to start detecting islanding (step S206), and stops detecting islanding for the original master unit (step S208). In addition, the main control unit 202 can temporarily suspend the determination of the master unit if multiple islanding prevention units 104b are operating simultaneously as master units. In this way, the main control unit 202 replaces the master unit according to the priority order using the operating information of each power generation unit 102, so that islanding prevention units 104b can be replaced in a shorter time and with greater stability. As a result, when the master unit detects an abnormality in the power system, the occurrence of periods of no detection can be suppressed.

[0039] Next, we will explain an example of processing when the master power generator 10 unexpectedly stops. Figure 6 is a flowchart showing an example of processing when the master power generator 10 unexpectedly stops. Here, we will explain the case where the islanding prevention unit 104b of the master power generator 10 periodically outputs a continuation signal to the islanding prevention unit 104b of the slave power generator 10.

[0040] As shown in Figure 6, first, the main control unit 202 sets a priority order for each power generation device 10 via the main control unit 202 (step S300). For example, the main control unit 202 sets information indicating that the islanding prevention unit 104b of the power generation device 10 with the second priority order has the second priority order. Similarly, it sets information indicating that the islanding prevention unit 104b of the power generation device 10 with the third priority order has the third priority order. Each islanding prevention unit 104b stores its own priority order.

[0041] Next, the islanding prevention unit 104b in the power generation unit 10, which has the highest priority and is designated as the master unit, starts detecting islanding and periodically outputs a continuation signal containing information about the continuation of operation (step S302). The islanding prevention unit 104b in the power generation unit 10 designated as a slave unit determines whether or not the power generation unit 10 designated as the master unit is running (step S304). Each islanding prevention unit 104b designated as a slave unit determines that the master unit is not stopped if it has received a continuation signal within a predetermined time (NO in step S304).

[0042] On the other hand, each islanding prevention unit 104b, which is a slave unit, determines that the master unit has stopped if it has not received a continuous signal within a predetermined time (YES in step S304). In this case, the islanding prevention unit 104b, which has information indicating that it is the second highest priority unit, immediately starts detecting islanding as the master unit (step S306). In this way, the slave units are informed that the master unit has stopped via a hardwired signal without going through the control of the control device 20, and the unit with the predetermined priority autonomously becomes the master unit, so that the operation can be immediately changed to a different master unit. This makes it possible to suppress the occurrence of periods of no detection when the master unit detects an abnormality in the power system.

[0043] As described above, according to this embodiment, each of the multiple islanding prevention units 104b corresponds to one of the multiple power generation devices 10 and is configured to operate as either a master unit that actively generates disturbances to detect abnormalities in the power system Pg, or a slave unit that operates according to the output signal of the master unit. Based on predetermined criteria using the operating information of each of the multiple power generation devices 10, one of the multiple power generation devices 10 is designated as the master unit, and the other power generation devices 10 are operated as slave units. This allows for the selection of a slave unit that reflects the state of the multiple power generation devices 10, making it possible to designate the islanding prevention unit 104b of a more stable power generation device 10 as the master unit.

[0044] (Modification of the first embodiment) The power generation system 1a according to a modification of the first embodiment differs from the power generation system 1 according to the first embodiment in that the control unit 108a also has the function of the control device 20. The differences from the power generation system 1 according to the first embodiment will be explained below.

[0045] Figure 7 is a block diagram showing the configuration of a power generation system 1a according to a modified example of the first embodiment. The control unit 108a of each power generation device 10 is capable of performing the same control as the control device 20. That is, the control unit 108a has a main control unit 202, a storage unit 200, and a main control unit 202.

[0046] Each power generation device 10 is assigned a priority order to become the control device 20. The control unit 108a of the power generation device 10 with the highest priority performs the same control as the control device 20 during startup. In this embodiment, all control units 108a have the functions of the control device 20, but this is not limited to this. For example, at least one control unit 108a may be configured to have the functions of the control device 20. In this case, the operation of the control unit 108a having the functions of the control device 20 can be operated independently of the control of the power generation device 10.

[0047] Next, after the power generation system 1a is started, a master unit is set according to the same priority order as in the power generation system 1 of the first embodiment. The control unit 108a of the power generation device 10, which has become the master unit, controls as the control device 20. In this way, the CPU of the control unit 108a of the power generation device 10 can also be used as the control device 20. This eliminates the need for the control device 20, making it possible to further miniaturize the configuration of the power generation system 1a.

[0048] Although several embodiments of the present invention have been described above, these embodiments are presented as examples only and are not intended to limit the scope of the invention. These novel 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 variations are included in the scope and spirit of the invention, as well as in the claims of the invention and its equivalents. [Explanation of symbols]

[0049] 1, 1a: Power generation system, 10: Power generation device, 20: Control device, 30: Measuring instrument, 102: Power generation unit, 104b: Islanding prevention unit, 108, 108a: Control unit, 200: Memory unit, 202: Main control unit, 204: Judgment unit, Pg: Power system.

Claims

1. Multiple power generation devices connected to the power grid, It comprises a main control unit and, Each of the aforementioned multiple power generation devices has an islanding prevention unit that can operate as either a master unit that actively generates disturbances to detect abnormalities in the power system, or a slave unit that operates based on the output signal of the master unit. The main control unit sets a priority order for each of the multiple power generators based on at least one of the cumulative operating time, cumulative power generated, and the voltage of the power generation section of each power generator, prioritizing those that will have a longer lifespan or a lower probability of failure. The first power generator with the highest priority is designated as the master unit, and the second power generator with the next highest priority is designated as the slave unit. The islanding prevention unit acting as the master unit outputs a predetermined signal to other islanding prevention units acting as slave units, and the islanding prevention unit of the second power generation unit acting as a slave unit autonomously becomes the next master unit when the predetermined signal stops, in a power generation system.

2. The power generation system according to claim 1, wherein the main control unit, in a control that prioritizes power generation of power generation devices with shorter cumulative operating times, sets the power generation device with the shortest cumulative operating time among the plurality of power generation devices as the master device.

3. The power generation system according to claim 1, wherein the main control unit, in a control that prioritizes power generation of power generation devices with low cumulative power generation, sets the power generation device with the lowest cumulative power generation among the plurality of power generation devices as the master device.

4. Each of the aforementioned multiple power generation devices has a fuel cell as a power generation unit. The power generation system according to claim 3, wherein the main control unit, in a control that prioritizes power generation to power generators with high fuel cell voltages, sets the power generator with the highest fuel cell voltage as the master unit.

5. The power generation system according to claim 1, wherein the main control unit, when the master unit stops, designates the second power generation device as the next master unit before stopping.

6. The power generation system according to claim 1, wherein if the master unit stops without control by the main control unit, the second power generation device becomes the next master unit.

7. The main control unit is configured in at least one of the plurality of power generation devices, Each of the aforementioned multiple power generation devices is Furthermore, it has a power generation unit that generates electricity, The power generation system according to claim 1, wherein the power supply from the power generation unit to the power grid is stopped in accordance with the output signal of the isolated operation prevention unit.

8. A control method for a power generation system comprising multiple power generation devices connected to a power grid and a main control unit, Each of the aforementioned multiple power generation devices has an islanding prevention unit that can operate as either a master unit that actively generates disturbances to detect abnormalities in the power system, or a slave unit that operates based on the output signal of the master unit. The main control unit sets a priority order for each of the multiple power generators based on at least one of the cumulative operating time, cumulative power generated, and the voltage of the power generation section of each power generator, prioritizing those that will have a longer lifespan or a lower probability of failure. The first power generator with the highest priority is designated as the master unit, and the second power generator with the next highest priority is designated as the slave unit. A method for controlling a power generation system, wherein the islanding prevention unit acting as the master unit outputs a predetermined signal to other islanding prevention units acting as slave units, and the islanding prevention unit of the second power generation unit acting as a slave unit autonomously becomes the next master unit when the predetermined signal stops.

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