JP2000023365A - Power generation system - Google Patents

Abstract

(57) [Problem] To provide a power generation system capable of individually and safely and easily diagnosing a failure of each power conversion device. SOLUTION: When a diagnostic device 100 is connected by disconnecting an inverter 6, the diagnostic device 100 and each DC / DC are connected.
Each solar cell module 1 is communicated with the converter 3
Is diagnosed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power generation system including a plurality of power generation means and a power conversion device to which outputs of the power generation means are supplied.

[0002]

2. Description of the Related Art In the case of a power generation system, for example, a standard household photovoltaic power generation system, a maximum of 3 kW of generated power can be obtained by using about 30 solar cell modules (panels) each having a capacity of about 100 W. An example of using such a plurality of solar cell modules is disclosed in
There is a solar cell power generation system disclosed in Japanese Patent No. 46231.
This is shown in FIGS.

[0003] Reference numeral 1 denotes a solar cell module which connects a large number of solar cells, that is, solar cells 2 in series, and generates DC power by receiving sunlight. This DC power is supplied to a DC / DC converter 3 which is a power converter, where it is converted into DC power having a predetermined level of voltage and output.

The solar cell module 1 and DC / D
A plurality of sets of C converters 3 are prepared, and these sets are connected in parallel via the backflow preventing diodes 4.
If the DC / DC converter 3 has a backflow prevention function,
The diode 4 can be omitted. This parallel circuit is connected to the input terminal of the inverter 6 via the switches 5 and 5. The inverter 6 converts DC power input from the parallel circuit into AC power of a predetermined frequency and outputs the AC power.

[0005]

In the above-described photovoltaic power generation system, as a method of detecting a failure of each DC / DC converter 3, detection by an output current can be considered. That is, if there are 30 DC / DC converters 3 and one of them fails, the total output current is reduced to 29 units (decrease rate 3.3%).

However, in the case of a photovoltaic power generation system that tracks and controls the maximum power point in response to a change in generated power due to weather conditions, a failure such as a current decrease of about 3% always occurs, and failure detection is impossible. .

In addition, even if a decrease in the output current can be detected,
It is completely unknown which DC / DC converter 3 has failed. On the other hand, as another method of failure detection, only one of the solar cell modules 1 is exposed to light and the other solar cell modules 1 are not exposed to light, and a failure is determined from the overall output voltage at that time. There is an example to detect. In this case, in order to perform the work of irradiating or shielding each solar cell module 1, it is necessary to climb the roof, which is dangerous. The performance of the work will also depend on the weather.

[0008] The present invention has been made in view of the above circumstances,
It is an object of the present invention to provide a power generation system capable of individually and safely and easily diagnosing a failure of each power converter.

[0009]

According to a first aspect of the present invention, there is provided a power generation system including a plurality of power generation units and a plurality of power conversion devices to which outputs of the power generation units are supplied. Communication means for communicating with the power conversion device is provided in each of the power conversion devices.

According to a second aspect of the present invention, in the power generation system according to the first aspect, at least one of the power generating means is a solar cell. According to a third aspect of the present invention, in the power generation system according to the first or second aspect, each communication unit also uses an output line of each power converter as a communication line.

A power generation system according to a fourth aspect of the present invention is the power generation system according to any one of the first to third aspects,
The output line of each power converter is a power line that carries power. According to a fifth aspect of the present invention, in the power generation system according to the fourth aspect, each communication unit conveys the communication data by superimposing the communication data on the electric power carried by the power line.

According to a sixth aspect of the present invention, in the power generation system according to the fourth aspect, each communication means carries communication data in a time-sharing manner with respect to the power carrying by the power line. In the power generation system according to claim 7, in the invention according to claim 6, each communication means conveys communication data when each power conversion device is not operating.

According to an eighth aspect of the present invention, in the power generation system according to the fifth or seventh aspect, each communication means receives data sent from an external device when each power conversion device is not operating. Wait state.

According to a ninth aspect of the present invention, in the power generation system according to the eighth aspect, even when each of the power conversion devices is in an operable state, the power conversion device does not immediately start operating, and each of the communication means has It has means for starting operation after receiving output permission data from an external device.

[0015] The power generation system of the invention according to claim 10 is as follows.
In the invention according to claim 8 or claim 9, each power converter has means for starting operation when each communication means does not receive data for a predetermined time or more.

[0016] The power generation system of the invention according to claim 11 is:
In the invention according to claim 9, each power conversion device sets a communication ID unique to the power conversion device based on a time from when the power conversion device becomes operable to when each communication unit receives output permission data. It has a means for automatic setting.

According to a twelfth aspect of the present invention, there is provided a power generation system.
In the invention according to claim 1, each power conversion device has means for transmitting an instruction for installation as data for setting an ID unique to the power conversion device to an external device by each communication means.

The power generation system according to the invention according to claim 13 is:
In any one of the first to twelfth aspects of the invention, each power converter has a protection unit that stops output when an abnormality occurs.

According to a fourteenth aspect of the present invention, there is provided a power generation system.
A plurality of power generating means, a power converter to which outputs of the power generating means are supplied, and the same power when the output voltage of the power converter is abnormally increased and exceeds a limit value. And protection means for stopping the output of the conversion device.

According to a fifteenth aspect of the present invention,
In the invention according to claim 13, each communication means enters a communication standby state for performing communication with an external device when the output of the protection means is stopped.

The power generation system according to claim 16 is
In the invention according to claim 15, each communication means first sets a reception mode for receiving data sent from an external device as a communication standby state.

A power generation system according to a seventeenth aspect of the present invention
In the invention according to claim 15, after the protection means stops the output of the power conversion device, the stop state is determined by a period from when each communication means receives a communication start instruction to when a communication end instruction is received. Hold about.

The power generation system according to claim 18 is
In any one of the first to seventeenth aspects of the present invention, each of the power converters is a DC / DC converter that performs power conversion from DC to DC.

A power generation system according to a nineteenth aspect of the present invention
In the invention according to claim 18, each communication means does not perform communication during the operation of the corresponding DC / DC converter,
When the / DC converter is not operating, communication is performed through the output terminal of the DC / DC converter and using the reverse voltage of the output voltage of the DC / DC converter.

[0025] The power generation system of the invention according to claim 20 is:
In the invention according to claim 19, when there is a reverse voltage input from an external device to the output terminal of each DC / DC converter during non-operation, the reverse voltage input is prevented from entering the circuit of the DC / DC converter. Blocking means.

The power generation system according to the twenty-first aspect is
In the invention according to claim 20, the blocking means is DC / D
A normally open contact inserted into the output line of the C converter, and a relay having the normally open contact as a component and energized when the DC / DC converter is operating and deactivated when not operating.

[0027] The power generation system of the invention according to claim 22 is:
In the invention according to claim 20, the blocking means is DC / D
A synchronous rectifier circuit mounted as a rectifier circuit of the C converter and linked to the operation / non-operation of the DC / DC converter.

The power generation system according to claim 23 is
In any one of the inventions according to claims 18 to 22, each communication unit transmits and receives data via a light emitting element and a light receiving element.

[0029]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. In the drawings, the same parts as those in FIGS. 5 and 6 are denoted by the same reference numerals, and detailed description thereof will be omitted.

In the DC / DC converter 3 as a power converter, as shown in FIG. 1, a switching circuit 10 is connected to input terminals 3a and 3b.
The rectifier circuit 20 is connected to the output terminal of the zero. Output terminals 3c and 3d are connected to the output terminal of the rectifier circuit 20 via a switch, for example, a relay contact (normally open contact) 30a.
A communication circuit 40 is connected between the relay contact 30a and the output terminals 3c and 3d.

The switching circuit 10 includes the capacitor 1
1, an inductor 12, and a switching element 13. When the switching element 13 is turned on and off by a control unit 60 described later, the input voltage to the input terminals 3a and 3b (the DC output from the solar cell module 1). ) Is converted into an AC voltage having a predetermined frequency.

The rectifier circuit 20 includes a diode 21 as a rectifier and a capacitor 22, and rectifies an output voltage (AC voltage) of the switching circuit 10. Communication circuit 4
0 is a receiving photocoupler 41 comprising a light emitting element such as a photodiode 41a and a light receiving element such as a phototransistor 41b, a light emitting element such as a photodiode 42a and a light receiving element such as a phototransistor 42b.
And a transmission photocoupler 42 composed of

The cathode of the photodiode 41a is connected to the output terminal 3d, and the anode of the photodiode 41a is connected to the output terminal 3c via the resistor 43 and the forward diode 44. The collector of the phototransistor 41b is connected to a control circuit DC power supply terminal (Vdd) via a resistor 45, and the emitter of the phototransistor 41b is connected to a control unit 60 described later.

The cathode of the photodiode 42 a is connected to a control circuit DC power supply terminal (Vdd) via a resistor 46, and the anode of the photodiode 42 a is connected to the control unit 60. The collector of the phototransistor 42b is connected to the output terminal 3d, and the emitter of the phototransistor 42b is connected to the output terminal 3c via the resistor 47 and the diode 44 in the forward direction.

The communication circuit 40 employs a simple configuration using only a photocoupler and its peripheral circuits, so that an increase in cost can be suppressed. Further, in the DC / DC converter 3, a voltage detector 51 is connected between the input terminals 3a and 3b, and the detection result of the voltage detector 51 is supplied to the maximum power tracking control circuit 50. A current detector 52 is provided between the connection between the input terminal 3 a and the switching circuit 10, and the detection result of the current detector 52 is supplied to the maximum power tracking control circuit 50. Maximum power tracking control circuit 50
Is the switching circuit 1 by the control unit 60 so that the maximum output power is always obtained regardless of the fluctuation of the input power.
0 is controlled.

A transistor 31 is connected to the output terminal of the rectifier circuit 20.
The relay 30 is connected via the collector and the emitter. The relay 30 has the relay contact 30a as a component, and is energized when the DC / DC converter 3 is operated and deenergized when it is not operated.

When a reverse voltage is input from an external device to the output terminals 3c and 3d when the DC / DC converter 3 is not operating, the relay 30 applies the reverse voltage to the DC / DC converter 3.
It also functions as blocking means for preventing the DC / DC converter 3 from entering the circuit (on the rectifier circuit 20 side).

The reverse voltage input is transmission data from an external device to the communication circuit 40. By preventing the reverse voltage input from entering the rectifier circuit 20, the communication by the communication circuit 40 is ensured. I have. The relay 30
Is inexpensive, and its adoption has the advantage of suppressing an increase in cost.

Between the connection between the rectifier circuit 20 and the communication circuit 40, a voltage generated downstream of the relay contact 30a is detected by the voltage detector 53, and the detection result is supplied to the control unit 60 for abnormality detection.

The communication circuit 40, together with the control unit 60, passes through the output terminals 3c and 3d, and
A communication unit for communicating with an external device is constructed while also using the output line of the C converter 3, that is, the power line for power transfer as a communication line.

The communication means is means for conveying the communication data in a manner superimposed on the power transfer by the power line, and the communication means is to transfer the communication data in a time sharing manner with the power transfer by the power line (the DC / DC based on the opening of the relay contact 30a). Converter 3
Transporting when the device is not operating).

Specifically, the means for conveying in a time-division manner does not perform communication during the operation of the DC / DC converter 3 based on the closing of the relay contact 30a, but performs the DC / DC based on the opening of the relay contact 30a. When the converter 3 is not operating, communication is performed through the output terminals 3 c and 3 d and using the reverse voltage of the output voltage of the DC / DC converter 3. During the operation (at the time of power conversion), the communication is not performed.
Power consumption is almost eliminated, and power loss can be minimized.

Further, the communication means has a means for entering a communication standby state for performing communication with a later-described diagnostic device 100 which is an external device when the output of the DC / DC converter 3 is stopped by the later-described protection means. Specifically, the diagnostic device 1
First, a reception mode for receiving data transmitted from 00 is set. By setting the reception mode, it is possible to remotely execute the failure diagnosis by the diagnostic device 100.

On the other hand, the control unit 60 has a communication function and A /
It is composed of a one-chip microcomputer with a D converter, and the following [1] to [5] as main functional means
Is provided.

[1] Even if power is generated from the solar cell module 1 and it becomes operable, the operation is not started immediately (the relay contact 30a is not closed immediately), and the communication means diagnoses. Means for starting operation (closing the relay contact 30a) after receiving data of output permission (operation command) from the device 100; This is to prevent accidents such as electric shock even when construction is performed on the output power line.

[2] After the power is generated from the solar cell module 1 to be in an operable state, or after abnormal stop by the protection means described later, data of output permission (operation command) is received for a certain time or more. Means to start operation when not. This is a so-called automatic return function.

[3] Each solar cell module 1 and each D
When the C / DC converter 3 is installed, the DC / DC converter 3 is based on the time from when power is generated from the corresponding solar cell module 1 to an operable state until the communication means receives output permission data. Means for automatically setting a communication ID unique to the server. The communication ID is used for address designation during communication from the diagnostic device 100 to each DC / DC converter 3.

[4] In the event of an abnormality, for example, when the output voltage of the DC / DC converter 3 (detection result of the voltage detector 53) abnormally rises and exceeds the limit value, the switching circuit 10
And the output of the DC / DC converter 3 is stopped to stop the output of the DC / DC converter 3. After the output is stopped, the stopped state is determined by the period from when the communication means receives the communication start command to when the communication means receives the communication end command. Protective measures to hold over. DC /
The cause of the abnormal rise in the output voltage of the DC converter 3 is disconnection of the inverter 6, which is for preventing an electric shock accident in that case. When the inverter 6 is disconnected and the diagnostic device 100 is connected, the diagnosis is performed. Apparatus 100
Even if the communication with the device becomes impossible for some reason, the security in that case is ensured.

[5] The presence / absence and type of abnormality relating to the solar cell module 1 to be connected are monitored, and the monitoring result is transmitted to the diagnostic device 100 when the failure diagnostic mode is set according to the diagnostic command sent from the diagnostic device 100. Means to do. Specific examples of the abnormality include an abnormality relating to the detection result of the voltage detector 51, an abnormality relating to the detection result of the current detector 52, and an abnormality in which the detection result of the voltage detector 53 does not reach a required level (<limit value at abnormal rise). and so on.

In place of the means of [3], the following [6]
Means may be provided. [6] An instruction for installation is assigned to an ID unique to the power converter.
Means for transmitting to the diagnostic apparatus 100 by communication means as data for setting

On the other hand, when diagnosing whether or not each solar cell module 1 has a failure, as shown in FIG.
Is connected.

The diagnostic apparatus 100 has the following [0], [1] and [2] as main functional means. [0] Means for simultaneously transmitting the start and end of communication.

[1] A means for sequentially sending a diagnostic command to each DC / DC converter 3 based on the communication ID (address data) of each DC / DC converter 3. [2] Means for receiving data sent from each DC / DC converter 3 in the failure diagnosis mode and diagnosing which of the solar cell modules 1 has a failure based on the data and the communication ID.

Next, the operation of the above configuration will be described. When diagnosing a failure of each solar cell module 1, the connection of the inverter 6 is disconnected, and the diagnostic device 100 is connected instead. When the inverter 6 is disconnected, each DC /
Since the DC converter 3 cannot supply electric power, the output voltage rises abnormally. At this time, the protection means of each DC / DC converter 3 functions, the operation of each DC / DC converter 3 stops, the relay 30 is deenergized and the contact 30a opens, and the operation of each DC / DC converter 3 is stopped. It will be stopped.

In this stopped state, the control unit 60 enters a communication standby state waiting for a diagnostic command from the diagnostic device 100. The diagnostic device 100 is connected and the diagnostic device 100
, Diagnostic commands modulated with a DC voltage having a polarity opposite to the normal polarity are sequentially sent to each DC / DC converter 3. Thereby, each DC / DC converter 3 is sequentially switched to the failure diagnosis mode.

Control unit 60 of each DC / DC converter 3
Monitors the presence / absence and type of abnormality of the solar cell module 1 to be connected. Then, when a diagnostic command is received from the diagnostic device 100 following the communication start command, the failure diagnostic mode is set and the monitoring result is transmitted to the diagnostic device 100. That is, if there is an abnormality, data indicating the presence / absence and type of the abnormality is transmitted, and if there is no abnormality, data indicating that there is no abnormality is transmitted.

The diagnostic device 100 that has received the reply determines which DC / DC converter 3 the reply came from based on the communication ID, and determines the solar cell module 1 corresponding to the DC / DC converter 3, that is, the roof. A diagnosis is made as to which position of the solar cell module 1 is out of order.

When the diagnosis for all DC / DC converters 3 has been completed, the diagnosis device 100
A command to end the diagnosis is sent to converter 3. And / or a simultaneous communication end command is transmitted. With this, the failure diagnosis ends, the diagnosis device 100 is disconnected, and the inverter 6 is connected. After a certain period of time, each DC / DC converter 3 returns its output while confirming safety.

For a failure in which the control unit 60 does not operate, the diagnostic device 100 waits for a reaction for a certain period of time, determines that the time has expired, and obtains a diagnostic result indicating that communication is impossible. The cause of the communication failure state is that the output power line is disconnected,
The operating voltage is not supplied to the control unit 69, or the control unit 60 itself fails.

Normally, the communication circuit 40 and the control unit 60 of the DC / DC converter 3 start operating near the sunrise time, and temporarily enter a communication standby state, but do not communicate with the diagnostic device 100. After a certain time, the communication standby state is released, and the DC / DC converter 3 outputs power. After sunset, the operating power of the communication circuit 40 and the control unit 60 is lost, so that the system is automatically stopped.

The maximum power follow-up control circuit 50 obtains an output voltage capable of operating at the maximum power in accordance with the detection results of the voltage detector 51 and the current detector 52, and outputs the voltage value to the control unit 60.
Command. The control unit 60 calculates the ratio between the output voltage for obtaining the maximum power and the voltage VI preset as the input voltage to the inverter 6, the detection result of the voltage detector 51 and the detection of the voltage detector 53. The driving of the switching circuit 10 is controlled so that the ratio with the result matches.

By this operation, each solar cell module 1
, The outputs of the DC / DC converter 3 connected to the output terminal are all set to the set voltage VI on the input side of the inverter 6,
It is input to the inverter 6 via the backflow prevention diode 4 and the switch 5.

As described above, by connecting the diagnostic device 100 instead of the inverter 6, even if each solar cell module 1 is installed on the roof of a house, the failure of each solar cell module 1 can be individually and safely performed. And it can be easily diagnosed.

In the above embodiment, the rectifier circuit 20
As shown in FIG. 3, a configuration including a transformer 23, diodes 24, 24, and capacitors 25, 25 may be adopted.

As shown in FIG. 4, a synchronous rectifier circuit including a transformer 23, capacitors 25 and 25, switching elements 26 and 26, and a drive circuit 27 may be employed as the rectifier circuit 20. The synchronous rectifier circuit is linked to the operation / non-operation of the DC / DC converter 3, and also has a function of a blocking unit which is a role of the relay 30 in the above embodiment. In other words, the adoption of this synchronous rectification circuit allows the relay 3
0 is not required, and the circuit configuration can be simplified. Others
The present invention is not limited to the above embodiment, and various modifications can be made without departing from the scope of the invention.

[0066]

As described above, according to the present invention, since the communication means for communicating with the external device is provided in each power conversion device, the failure of each power conversion device can be individually, safely and easily diagnosed. And a power generation system capable of performing the operation.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a DC / DC converter according to one embodiment.

FIG. 2 is a block diagram showing the overall configuration of the embodiment.

FIG. 3 is a block diagram showing a configuration of a modified example of the DC / DC converter in the embodiment.

FIG. 4 is a block diagram showing a configuration of another modification of the DC / DC converter in the embodiment.

FIG. 5 is a block diagram showing the overall configuration of a conventional device.

FIG. 6 is a diagram showing a configuration of a solar cell module in an embodiment and a conventional apparatus.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Solar cell module 2 ... Solar cell 3 ... DC / DC converter 6 ... Inverter 10 ... Switching circuit 20 ... Rectifier circuit 30 ... Relay (blocking means) 40 ... Communication circuit 41, 42 ... Photocoupler 50 ... Maximum power tracking control Circuit 51: Voltage detector 52: Current detector 53: Voltage detector 60: Control unit 100: Diagnostic device (external device)

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H04B 3/56 H01L 31/04 K (72) Inventor Tatsuaki Security 1 Toshiba-cho, Fuchu-shi, Tokyo Toshiba Corporation F-term in the Fuchu plant (reference) XX33 XX35 XX42 5K046 AA03 AA07 BB05 BB06 CC11 CC16 CC18 PP02 PP03 PS44 PS45 PS47 ZZ05 ZZ15

Claims (23)

[Claims] In a power generation system including a plurality of power generation means and a plurality of power conversion devices to which outputs of the power generation means are supplied, communication means for performing communication with an external device is provided in each of the power conversion devices. A power generation system, characterized in that: 2. The power generation system according to claim 1, wherein at least one of the power generation units is a solar cell. 3. The power generation system according to claim 1, wherein each of the communication means also uses an output line of each of the power conversion devices as a communication line. 4. The power generation system according to claim 1, wherein an output line of each of the power conversion devices is a power line that carries power. 5. The power generation system according to claim 4, wherein each of the communication units conveys the communication data by superimposing the communication data on the electric power carried by the power line. 6. The power generation system according to claim 4, wherein each of the communication units carries communication data in a time-sharing manner with respect to power transmission by the power line. 7. The power generation system according to claim 6, wherein each of the communication means conveys communication data when each of the power conversion devices is not operating. 8. The power generation system according to claim 5, wherein each communication unit is in a standby state for receiving data sent from the external device when each of the power conversion devices is not operating. A power generation system, characterized in that: 9. The power generation system according to claim 8, wherein each of the power conversion devices does not immediately start operating even when the power conversion device is in an operable state, and each of the communication units permits output from the external device. A means for starting operation after receiving the data of the power generation. 10. The power generation system according to claim 8, wherein each of the power conversion devices has a unit that starts an operation when each of the communication units does not receive data for a predetermined time or more. And power generation system. 11. The power conversion system according to claim 9, wherein each of the power conversion devices is based on a time from when the power conversion device becomes operable to when each of the communication means receives output permission data. A power generation system comprising means for automatically setting a communication ID unique to a device. 12. The power generation system according to claim 1, wherein each of the power conversion devices is provided with a command for installation as data for setting a unique ID to the power conversion device by the communication device. A power generation system, comprising: 13. The power generation system according to claim 1, wherein each of the power conversion devices includes a protection unit that stops output when an abnormality occurs. 14. A plurality of power generating means, a power converter to which the output of the power generating means is supplied, and an output voltage of the power converter provided in these power converters abnormally rises and exceeds a limit value. And a protection means for stopping the output of the power converter in the event that the power generation device is in use. 15. The power generation system according to claim 13, wherein each of the communication units is in a communication standby state for performing communication with the external device when the output of the protection unit is stopped. . 16. The power generation system according to claim 15, wherein said communication means first sets a reception mode for receiving data sent from said external device as said communication standby state. system. 17. The power generation system according to claim 15, wherein the protection unit stops the output of the power conversion device, and changes the stop state after the communication units receive a communication start command. A power generation system, wherein the power generation system retains the information until a command is received. 18. The power generation system according to claim 1, wherein each of the power conversion devices is a DC / DC converter that performs power conversion from DC to DC. system. 19. The power generation system according to claim 18, wherein each communication unit does not perform communication during operation of the corresponding DC / DC converter, and outputs an output terminal of the DC / DC converter when the DC / DC converter is not operating. Through and DC /
A power generation system for performing communication using a reverse voltage of an output voltage of a DC converter. 20. The power generation system according to claim 19, wherein when each of the DC / DC converters receives a reverse voltage input from an external device at an output terminal during non-operation, the reverse voltage input is applied to the DC / DC converter. A power generation system, comprising: a blocking unit that blocks entry into a circuit. 21. The power generation system according to claim 20, wherein the blocking means is a normally open contact inserted into an output line of the DC / DC converter, and operates the DC / DC converter using the normally open contact as a constituent element. A power generation system characterized in that the power generation system is a relay that is energized at times and deenergized when not operating. 22. The power generation system according to claim 20, wherein the blocking means is a synchronous rectification circuit mounted as a rectification circuit of a DC / DC converter and linked to the operation / non-operation of the DC / DC converter. And power generation system. 23. The power generation system according to claim 18, wherein each of the communication units transmits and receives data via a light emitting element and a light receiving element.