JP4670864B2 - DC power distribution system - Google Patents

Description

  The present invention relates to a DC power distribution system.

2. Description of the Related Art Conventionally, there has been provided a DC power distribution system including a plurality of distributed power sources each capable of supplying DC power and a distribution path connecting each distributed power source and a plurality of loads. In such a DC power distribution system, similarly to the DC power supply device described in Patent Document 1, each distributed power supply shares and supplies power consumed by a load. In addition, as a distributed power source used in such a DC power distribution system, one having an AC / DC converter (AC / DC converter) that converts AC power supplied from a power system into DC power, a solar cell, and a fuel cell There are those having a power generation function such as those having a secondary battery.
JP 2002-171692 A

  By the way, a general AC / DC converter is configured so that the conversion efficiency when converting AC power to DC power is maximized when the rated output power is reached. Therefore, when the amount of power used in the entire system is small (in the case of a light load), the AC / DC converter cannot be operated at the maximum efficiency.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a DC distribution system capable of suppressing a decrease in conversion efficiency of an AC / DC converter included in a distributed power source even in the case of a light load or a heavy load. Is to provide.

In order to achieve the above object, the invention of claim 1 includes a plurality of distributed power sources for supplying DC power and a distribution path for distributing DC power from each distributed power source to one to a plurality of loads, One distributed power supply has the characteristic that the conversion efficiency when converting AC power supplied from the power system to DC power and converting AC power to DC power becomes maximum at a predetermined value lower than the rated output power. A DC / DC converter, and at least one other distributed power source includes a secondary battery, a charging device that charges the secondary battery with DC power distributed through a distribution path, and a DC that is discharged from the secondary battery. A discharge device for sending electric power to the distribution path; and a control device for controlling the charging operation of the secondary battery by the charging device; the direct current power output from the alternating current / direct current converter is monitored, and the direct current power is the predetermined value Than Causes powered DC power from other distributed power when it is higher predetermined upper limit value or more, the control when the direct current power outputted from the AC / DC converter is below a lower predetermined limit value than the predetermined value A monitoring device that causes the device to charge the secondary battery by the charging device is provided.

  According to the first aspect of the present invention, since the conversion efficiency of the AC / DC converter has the maximum characteristic at a predetermined value lower than the rated output power, the AC / DC converter has a characteristic that the conversion efficiency is close to the maximum value even in the case of a light load. The DC converter can be operated, and even in the case of heavy loads, the AC / DC converter can be operated where the conversion efficiency is close to the maximum value by sharing power with other distributed power sources. As a result, it is possible to suppress a decrease in conversion efficiency of the AC / DC converter included in the distributed power source in both cases of light load and heavy load.

  According to a second aspect of the present invention, in the first aspect of the invention, the monitoring device causes the DC power to be fed from another distributed power source according to the difference between the DC power output from the AC / DC converter and the predetermined value or the upper limit value. It is characterized by increasing or decreasing.

  According to the invention of claim 2, the AC / DC converter is configured to increase or decrease the amount of DC power fed from the distributed power source according to the difference between the DC power output from the AC / DC converter and the predetermined value or the upper limit value. The conversion efficiency of can be brought closer to the maximum value more reliably.

According to a third aspect of the present invention, in the first or second aspect of the present invention, the monitoring device is a secondary battery by a charging device according to a difference between the DC power output from the AC / DC converter and the predetermined value or the lower limit value. It is characterized by increasing or decreasing the amount of charge.

According to the invention of claim 3, the amount of charge to the secondary battery by the charging device is increased / decreased in accordance with the difference between the DC power output by the AC / DC converter and the predetermined value or the lower limit value. The conversion efficiency of the direct current converter can be more reliably brought close to the maximum value.

The invention of claim 4 is the invention of any one of claims 1 to 3 , comprising a plurality of switches inserted between each load and the power distribution path, and the monitoring device is an AC / DC converter. A load connected to the switch by controlling at least one switch when the output DC power is equal to or greater than the upper limit and the DC power output from another distributed power source is less than a predetermined threshold. Is characterized in that it is disconnected from the distribution line.

According to invention of Claim 4 , the fall of the conversion efficiency of an alternating current / direct current converter can be suppressed by separating a load from a power distribution path at the time of heavy load.

According to a fifth aspect of the present invention, in the fourth aspect of the invention, the monitoring device increases or decreases the number of loads to be disconnected from the distribution line according to the difference between the DC power output from the AC / DC converter and the predetermined value or the upper limit value. It is characterized by doing.

According to the invention of claim 5 , the number of loads to be disconnected from the distribution path is increased or decreased according to the difference between the DC power output from the AC / DC converter and the predetermined value or the upper limit value. The conversion efficiency of can be brought closer to the maximum value more reliably.

A sixth aspect of the invention is characterized in that, in the fifth aspect of the invention, the monitoring device is separated from the power distribution path in order from a load having a predetermined low priority.

According to the invention of claim 6, high priority load by stopping the power supply in order from the lower priority load it can be prevented from being stopped.

According to a seventh aspect of the present invention, in the invention according to any one of the fourth to sixth aspects, the monitoring device remotely controls each switch by a transmission signal transmitted through a power distribution path.

According to the invention of claim 7, the switch can be remotely controlled without providing a separate transmission line for transmitting the transmission signal.

  ADVANTAGE OF THE INVENTION According to this invention, the fall of the conversion efficiency of the alternating current / direct current converter which a distributed power supply has in the case of a light load and a heavy load can be suppressed.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  The DC power distribution system according to the present embodiment distributes DC power from a plurality of distributed power sources 1, 2, and 3 that feed DC power to a plurality of loads L as shown in FIG. 1. And a power distribution path Lp. The distributed power source 1 includes an AC / DC converter (AC / DC converter) that converts AC power supplied from a power system (commercial power system) AC into DC power. This AC / DC converter 1 is a so-called switching power supply device, and as shown in FIG. 2 (a), the conversion efficiency when converting AC power into DC power is a predetermined value Wa lower than the rated output power Ws. It is configured to have the maximum characteristics. Note that a general AC / DC converter is configured such that the conversion efficiency is maximized at the rated output power Ws as shown in FIG. However, the characteristic shown in FIG. 2 (a) is an example. For example, after the conversion efficiency reaches the maximum value, the conversion efficiency remains almost constant even if the current value increases. There is also.

  The distributed power source 2 is discharged from the secondary battery 20, the charging device 22 that charges the secondary battery 20 with DC power distributed from the other distributed power sources 1 and 3 via the distribution path Lp, and the secondary battery 20. A discharge device 23 for sending the direct-current power to the distribution path Lp, and a control device 21 for controlling the charging operation of the secondary battery 20 by the charging device 22 and the discharging operation from the secondary battery 20 to the distribution path Lp by the discharging device 23; have. The secondary battery 20 is a nickel metal hydride battery or a lithium ion battery. The discharge device 23 is provided with a DC / DC converter that boosts or lowers the discharge voltage of the secondary battery 20.

  The distributed power source 3 has a power generation function such as a solar cell or a fuel cell, and includes a DC / DC converter (not shown) that increases or decreases the output voltage of the solar cell or the fuel cell.

  Moreover, the monitoring apparatus 4 is connected to the power distribution path Lp. The monitoring device 4 monitors the DC power output from the AC / DC converter 1, and when the DC power is equal to or higher than a predetermined upper limit value Wu higher than the predetermined value Wa, the DC power is supplied from the other distributed power sources 2 and 3. When the DC power output from the AC / DC converter 1 is equal to or lower than a predetermined lower limit value Wd lower than the predetermined value Wa, the control unit 21 of the distributed power source 2 is charged by the charging device 22 while supplying electric power. The charging operation of the secondary battery 20 is performed. For this purpose, the monitoring device 4 and the distributed power supply 2 (control device 20), 3 are equipped with a communication function for transmitting data via the distribution line Lp. However, the AC / DC converter 1 may be equipped with a communication function so that information on its own DC output power is transmitted to the monitoring device 4 via the distribution line Lp. This type of communication function is well known in the art and will not be described in detail.

  Further, a switch 5 is connected between the load L and the distribution path Lp. The switch 5 has a communication function for communicating between the switch 50 for turning on and off the connection between the distribution path Lp and the load L and the monitoring device 4 via the distribution path Lp. And a drive unit 51 for turning on and off the switch 50 in accordance with a control signal transmitted via the terminal. Therefore, when the drive unit 51 turns off the switch 50 in accordance with the control signal received from the monitoring device 4, the load L connected to the switch 5 is disconnected from the distribution path Lp.

  Next, the operation of the monitoring device 4 will be described. The monitoring device 4 stores the upper limit value Wu and the lower limit value Wd in a memory and stores them. If the DC power output from the AC / DC converter 1 is equal to or higher than the upper limit value Wu, the monitoring device 4 controls the distributed power supply 2. A control signal for instructing the device 21 to operate the discharge device 23 is generated, and the control signal is transmitted to the control device 21 via the distribution line Lp. And the control apparatus 21 which received the said control signal operates the discharge device 23, and feeds DC power from the secondary battery 20 to the power distribution path Lp, and the DC power which the AC / DC converter 1 outputs decreases. Therefore, the AC / DC converter 1 can be operated with a conversion efficiency close to the maximum value Wa. Accordingly, since the conversion efficiency of the AC / DC converter 1 has the maximum characteristic at the predetermined value Wa lower than the rated output power Ws, the AC / DC converter 1 is located near the maximum value even in the case of a light load. In addition, even in the case of heavy loads, the AC / DC converter 1 can be operated where the conversion efficiency is close to the maximum value Wa by sharing power with the other distributed power sources 2 and 3. . As a result, a reduction in conversion efficiency of the AC / DC converter 1 can be suppressed in both cases of light load and heavy load.

  Further, when the DC power output from the AC / DC converter 1 is equal to or lower than the lower limit value Wd, the monitoring device 4 controls the control device 21 to perform the charging operation of the secondary battery 20 by the charging device 22. A signal is generated, and the control signal is transmitted to the control device 21 via the power distribution path Lp. And the control apparatus 21 which received the said control signal operates the charging device 22, and charges the secondary battery 20 with the direct-current power distributed via the distribution path Lp, and the alternating current / direct current converter 1 outputs. Since the DC power increases, the AC / DC converter 1 can be operated with a conversion efficiency close to the maximum value Wa.

  Here, the monitoring device 4 indicates the amount of DC power supplied from the secondary battery 20 to the distribution path Lp and the amount of charge when charging the secondary battery 20 in the control signal sent to the control device 21. The DC power amount and the charge amount at this time may be the upper limit value Wu or the difference (fixed value) between the lower limit value Wd and the maximum value Wa, or may be the actual output from the AC / DC converter 1. It may be a difference between the DC power and the maximum value Wa, the upper limit value Wu, or the lower limit value Wd. In the latter case, the direct current power supplied from the secondary battery 20 is increased or decreased according to the difference between the direct current power output from the alternating current / direct current converter 1 and the maximum value Wa or the upper limit value Wu or the lower limit value Wd. The conversion efficiency of the DC converter 1 can be more reliably brought close to the maximum value Wa. It is also possible to perform control so that the conversion efficiency of the AC / DC converter 1 is always close to the maximum value Wa by setting the difference between the upper limit value Wu and the lower limit value Wd and the maximum value Wa of the conversion efficiency small. it can.

  By the way, when the weather is not good or at night, sufficient DC power cannot be supplied from the distributed power source 3 that generates power with a solar cell. Further, when the remaining capacity of the secondary battery 20 is small, sufficient DC power cannot be supplied from the distributed power supply 2. Under such circumstances, when the DC power output from the AC / DC converter 1 exceeds the upper limit value Wu, the monitoring device 4 switches the switch 50 to any switch 5 in order to reduce the power consumption of the entire system. A control signal instructing to turn off is transmitted. And in the switch 5 which received the said control signal, since the drive part 51 cuts off the switch 50 according to a control signal and isolate | separates the load L from the power distribution path Lp, since the power consumption of the whole system reduces, it is maximum value Wa. The AC / DC converter 1 can be operated with a conversion efficiency close to. However, depending on the type of load L, it is not desirable to stop it easily. Therefore, a predetermined priority order of the load L is stored and stored in the memory of the monitoring device 4, and the situation as described above. When it becomes, it is made to isolate | separate in order from the load L with the low priority memorize | stored in memory. In this way, it is possible to prevent the load L having a high priority from stopping.

  Here, if the number of loads L separated from the distribution path Lp is increased or decreased according to the difference between the actual DC power output from the AC / DC converter 1 and the maximum value Wa or the upper limit value Wu, the AC / DC The conversion efficiency of the conversion device 1 can be brought closer to the maximum value Wa more reliably. Note that the monitoring device 4 has a priority order and the number of loads L to be disconnected from the distribution line Lp with respect to the difference between the actual DC power output from the AC / DC converter 1 and the maximum value Wa or the upper limit value Wu. Stored in a non-volatile memory in the form of a data table.

  Now, another embodiment of the present invention will be described with reference to FIG. Although the embodiment described below assumes a detached house as a building to which the present invention is applied, it does not prevent the technical idea of the present invention from being applied to an apartment house. In the house H, as shown in FIG. 3, in addition to the distributed power source 2 including the secondary battery 20, the control device 21, the charging device 22, and the discharging device 23, the distributed power source 3 including solar cells, and the distributed power source including fuel cells. 3 is connected to the output side of the AC / DC converter 1 via the cooperative control unit 113. Then, DC power is supplied to the DC device 102 through the distribution path Wdc branched from the output end of the cooperative control unit 113. Between the cooperative control unit 113 and the DC device 102, the current flowing through the distribution path Wdc is monitored, and when an abnormality is detected, the power supply from the cooperative control unit 113 to the DC device 102 is restricted or cut off on the distribution path Wdc. A DC breaker 114 is provided.

  The distribution path Wdc is a DC power supply path and is also used as a communication path, and is a device connected to the distribution path Wdc by superimposing a communication signal for transmitting data on a DC voltage using a high-frequency carrier wave. Communication between them. This technique is similar to a power line carrier technique in which a communication signal is superimposed on an AC voltage in a power line that supplies AC power.

  The distribution path Wdc is connected to the home server 116 via the AC / DC converter 1. The in-home server 116 is a main device for constructing a home communication network (hereinafter referred to as “home network”), and communicates with a subsystem constructed by the DC device 102 in the home network.

  In the example shown in the drawing, as an subsystem, an illumination system comprising an information equipment system K101 comprising an information-system DC device 102 such as a personal computer, a wireless access point, a router, and an IP telephone, and an illumination system DC equipment 102 such as a lighting fixture. K102, K105, entrance system K103 composed of DC device 102 for dealing with visitors, monitoring intruders, etc., and residential alarm system K104 composed of alarm DC device 102 such as a fire detector. Each subsystem constitutes a self-supporting distributed system, and can operate even with the subsystem alone.

  The above-described DC breaker 114 is provided in association with the subsystem. In the illustrated example, four DC breakers are associated with the information equipment system K101, the lighting system K102 and the entrance system K103, the house alarm system K104, and the lighting system K105. 114 is provided. When a plurality of subsystems are associated with one DC breaker 114, a connection box 121 that divides the system of the DC supply line Wdc is provided for each subsystem. In the illustrated example, a connection box 121 is provided between the illumination system K102 and the entrance system K103.

  As the information equipment system K101, there is provided an information equipment system K101 composed of a DC equipment 102 connected to a DC outlet 131 arranged in advance in the house H (constructed when the house H is constructed) in the form of a wall outlet or a floor outlet.

  The lighting systems K102 and K105 include a lighting system K102 including a lighting fixture (DC device 102) arranged in advance in the house H, and a lighting fixture (DC device 102) connected to a hook ceiling 132 arranged in advance on the ceiling. An illumination system K105 is provided. At the time of interior construction of the house H, the contractor attaches the lighting fixture to the hook ceiling 132, or the resident himself attaches the lighting fixture.

  In addition to using an infrared remote control device, a control instruction for the lighting apparatus that is the DC device 102 constituting the lighting system K102 can be given using a communication signal from the switch 141 connected to the power distribution path Wdc. That is, the switch 141 has a communication function together with the DC device 102. In addition, a control instruction may be given by a communication signal from another DC device 102 in the home network or the home server 116 regardless of the operation of the switch 141. The instructions to the lighting fixture include lighting, extinguishing, dimming, and blinking lighting.

  Since any DC device 102 can be connected to the DC outlet 131 and the hooking ceiling 132 described above and DC power is output to the connected DC device 102, the DC outlet 131 and the hooking ceiling 132 are distinguished below. When it is not necessary, it is called “DC outlet”.

  These DC outlets have a plug-in connection port into which a contact (not shown) provided directly on the DC device 102 or a contact (not shown) provided via a connection line is inserted into the body. The contact receiver that directly contacts the contact inserted into the connection port is held by the container. That is, the direct current outlet supplies power in a contact manner. When the DC device 102 connected to the DC outlet has a communication function, a communication signal can be transmitted through the power distribution path Wdc. A communication function is provided not only in the DC device 102 but also in the DC outlet.

  The home server 116 not only is connected to the home network, but also has a connection port connected to the wide area network NT that constructs the Internet. When the in-home server 116 is connected to the wide area network NT, it is possible to receive services from the center server 200 that is a computer server connected to the wide area network NT.

  The service provided by the center server 200 includes a service that enables monitoring and control of equipment (including mainly the DC equipment 102 but also other equipment having a communication function) connected to the home network through the wide area network NT. is there. This service makes it possible to monitor and control devices connected to the home network using a communication terminal (not shown) having a browser function such as a personal computer, Internet TV, or mobile phone.

  The in-home server 116 has both functions of communication with the center server 200 connected to the wide area network NT and communication with equipment connected to the home network, and identification information about equipment in the home network ( Here, it is assumed that an IP address is used).

  The home server 116 enables monitoring and control of home devices through the center server 200 from a communication terminal connected to the wide area network NT by using a communication function with the center server 200. The center server 200 mediates between home devices and communication terminals on the wide area network NT.

  When monitoring and controlling home devices from a communication terminal, monitoring and control requests are stored in the center server 200, and the home device periodically performs one-way polling communication to monitor from the communication terminal. And receive control requests. With this operation, it is possible to monitor and control devices in the house from the communication terminal.

  Further, when an event that should be notified to the communication terminal, such as a fire detection, occurs in the home device, the home device notifies the center server 200, and the center server 200 notifies the communication terminal by e-mail.

  An important function among the communication functions with the home network in the home server 116 is the detection and management of the devices constituting the home network. The home server 116 automatically detects devices connected to the home network by applying UPnP (Universal Plug and Play). The home server 116 includes a display device 117 having a browser function, and displays a list of detected devices on the display device 117. The display device 117 has a configuration with a touch panel type or an operation unit, and can perform an operation of selecting desired contents from options displayed on the screen of the display device 117. Therefore, the user (contractor or householder) of the home server 116 can monitor or control the device on the screen of the display device 117. The display device 117 may be provided separately from the home server 116.

  The in-home server 116 manages information related to device connection, and grasps the type, function, and address of the device connected to the home network. Accordingly, the devices in the home network can be operated in conjunction with each other. Information on the connection of the device is automatically detected as described above. In order to operate the device in an interlocking manner, the device itself is automatically associated with the attribute held by the device itself, and the home server 116 is configured as a personal computer. It is also possible to connect various information terminals and use the browser function of the information terminals to associate devices.

  Each device holds the relationship of the interlocking operation of the devices. Therefore, the device can operate in an interlocked manner without passing through the home server 116. By associating the linked operations for each device, for example, by operating a switch that is a device, it is possible to turn on or off the lighting fixture that is the device. In many cases, the association of the interlocking operations is performed within the subsystem, but the association beyond the subsystem is also possible.

  By the way, the AC / DC converter 1 is housed in the distribution board 110 and is connected to the power system AC through the main breaker 111 housed in the distribution board 110. The cooperative control unit 113 connected to the output side of the AC / DC converter 1 controls the distribution of power from the DC power system including the AC / DC converter 1 and the distributed power sources 2, 3, 3 to the DC device 102. It has a function to do.

  Since the driving voltage of the DC device 102 is selected from a plurality of types of voltages depending on the device, a DC / DC converter is provided in the cooperative control unit 113, and the DC voltage obtained from the DC power system and the distributed power sources 2, 3, and 3 is used. It is desirable to convert it to the required voltage. Normally, one type of voltage is supplied to one subsystem (or DC device 102 connected to one DC breaker 114), but three or more wires are used for one subsystem. A plurality of types of voltages may be supplied. Alternatively, it is possible to adopt a configuration in which the DC supply line Wdc is of a two-wire type and the voltage applied between the lines is changed with time. The DC / DC converter may be provided in a plurality of dispersed manners like the DC breaker.

  In the above configuration example, only one AC / DC converter 1 is illustrated, but a plurality of AC / DC converters 1 can be arranged in parallel, and a plurality of AC / DC converters 1 are provided. Sometimes, it is desirable to increase or decrease the number of AC / DC converters 1 that are operated according to the magnitude of the load.

  The AC / DC converter 1, the cooperative control unit 113, the DC breaker 114, and the distributed power sources 2, 3, 3 are provided with a communication function, and the AC / DC converter 1 and the distributed power sources 2, 3, 3, It is possible to perform a cooperative operation to cope with a load state including the DC device 102. The communication signal used for this communication is transmitted in the form of being superimposed on the DC voltage in the same manner as the communication signal used for the DC device 102.

  In the above example, the AC / DC converter 1 is arranged in the distribution board 110 in order to convert the AC power output from the main breaker 111 into DC power by the AC / DC converter 1. On the output side of 111, an AC supply line is branched into a plurality of systems by a branch breaker (not shown) provided in the distribution board 110, and an AC / DC converter 1 is provided on the AC supply line of each system. You may employ | adopt the structure converted into direct-current power.

  In this case, since a DC power system can be provided for each floor or room of the house H, the DC power system can be managed for each unit, and the DC device 102 that uses DC power can be managed. Since the distance of the power distribution path Wdc in between becomes short, the power loss by the voltage drop in the power distribution path Wdc can be reduced. In addition, the main breaker 111 and the branch breaker are housed in the distribution board 110, and the AC / DC converter 1, the cooperative control unit 113, the DC breaker 114, and the home server 116 are housed in a separate board from the distribution board 110. May be.

It is a system configuration figure showing an embodiment of the present invention. (A) is a figure which shows the conversion efficiency characteristic of the AC / DC converter in the same as the above, (b) is a figure which shows the conversion efficiency characteristic of the conventional AC / DC converter. It is a system block diagram which shows other embodiment.

Explanation of symbols

AC power system 1 AC / DC converter (distributed power supply)
2 Distributed power supply 3 Distributed power supply 4 Monitoring device 5 Switch L Load Lp Distribution line

Claims (7)

A plurality of distributed power sources for supplying DC power, and a distribution path for distributing DC power from each distributed power source to one to a plurality of loads,
At least one distributed power source has a characteristic that the conversion efficiency when converting AC power supplied from the power system into DC power and converting AC power into DC power becomes maximum at a predetermined value lower than the rated output power. It consists of an AC / DC converter,
At least one other distributed power source sends a secondary battery, a charging device that charges the secondary battery with DC power distributed via the distribution path, and DC power discharged from the secondary battery to the distribution path A discharge device and a control device for controlling the charging operation of the secondary battery by the charging device;
DC power output from the AC / DC converter is monitored, and when the DC power is equal to or higher than a predetermined upper limit value higher than the predetermined value, DC power is supplied from another distributed power source, and from the AC / DC converter A DC power distribution comprising: a monitoring device that causes the control device to charge the secondary battery by the charging device when the output DC power is equal to or lower than a predetermined lower limit value lower than the predetermined value. system.   The direct current power supplied from another distributed power source is increased or decreased according to a difference between the direct current power output from the alternating current / direct current converter and the predetermined value or the upper limit value. Power distribution system. The monitoring device increases or decreases the amount of charge to the secondary battery by the charging device according to the difference between the DC power output from the AC / DC converter and the predetermined value or the lower limit value. The described DC power distribution system. With multiple switches inserted between each load and distribution line,
The monitoring device controls at least one switch when the DC power output from the AC / DC converter is greater than or equal to the upper limit value and the DC power output from another distributed power source is less than a predetermined threshold. The DC power distribution system according to any one of claims 1 to 3, wherein a load connected to the switch is disconnected from the power distribution path . 5. The DC power distribution system according to claim 4 , wherein the monitoring device increases or decreases the number of loads to be disconnected from the power distribution path according to a difference between the DC power output from the AC / DC converter and the predetermined value or the upper limit value. . 6. The DC power distribution system according to claim 5, wherein the monitoring device is disconnected from the power distribution path in order from a load having a predetermined low priority . The DC power distribution system according to any one of claims 4 to 6, wherein the monitoring device remotely controls each switch by a transmission signal transmitted through the power distribution path .

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