JP2020092371A - Power line communication device and power line communication system - Google Patents

Abstract

To provide a power line communication device and a power line communication system, advantageous to reduce a size of a device configuration, for preventing signal degradation by preventing power supply and a signal to be superimposed thereon from affecting with each other with a higher degree of accuracy.SOLUTION: The power line communication device includes: a power supply 2 for supplying power to a slave device 6, which is a load; a transmitter and receiver 4 for generating a signal to be transmitted to the slave device 6; power lines 31a, 31b, which are a pair of signal common power lines for supplying the power supplied from the power supply 2 and the signal generated from the transmitter and receiver 4 to the slave device 6; a primary coil 41 in which the signal flows; a secondary coil 43 in which electromagnetic induction is generated by a change in magnetic flux generated by the primary coil 41; and a secondary coil 44 electromagnetically identical to the secondary coil 43. The same polarity ends of the primary coil 41 and the secondary coils 43, 44 are connected to the power lines 31a, 31b, respectively. The opposite ends of the secondary coil 43 and the secondary coil 44 are connected to a reference potential terminal t3.SELECTED DRAWING: Figure 1

Description

The present invention relates to a power line communication device and a power line communication system.

A technique for superimposing a signal for communication on a power line (cable) used for supplying power is called power line communication (PLC). A known example of power line communication is described in Patent Document 1, for example. In the power line communication system described in Patent Document 1, an electric vehicle and a power feeding device are connected by a charging cable including a power line, and a device included in the electric vehicle and a device included in the power feeding device communicate with each other via the power line. Is to do. According to FIG. 1 of Patent Document 1, the electric vehicle is connected to the AC line of the charging cable, and the electric power from the charging stand and the charging cable is guided to the charger in the electric vehicle by the AC line. Further, a capacitor is connected between the two ACs, and one AC line has a primary coil of a coupling transformer interposed between the connection point of the charging cable and the connection point of the capacitor. The capacitor between the AC lines constitutes a filter circuit.

JP 2012-175562 A

The power line communication system described in Patent Document 1 is performed over a relatively short distance between an electric vehicle and a power supply device. However, power line communication is also used in long-distance communication such as a system for managing operation outdoors such as a railway. In a long-distance power line communication system, high-frequency signal voltage is greatly attenuated, and signal quality may be deteriorated. Therefore, in long-distance power line communication, it is not enough to use a capacitor as a filter as in Patent Document 1, and it is required to perform communication with higher accuracy while preventing deterioration of signal quality.

What deteriorates the signal quality and makes communication difficult is a decrease in the S/N ratio, that is, the signal-to-noise ratio. This can occur due to problems on the power supply side as well as signal attenuation.
In recent years, the number of cases where an inverter AC power supply device is used instead of a power transformer is increasing. Since this is an object that generates an output of 50 Hz or 60 Hz by PWM modulation of high frequency switching, the output voltage contains the switching frequency and its harmonic components as ripple noise. Also, this ripple voltage is larger than the communication signal voltage.
The ripple noise becomes normal mode noise that is difficult to remove because its frequency band overlaps with the frequency band of PLC communication of 10 kHz to 500 kHz. The filter circuit of the power line communication system described in Patent Document 1 cannot remove such noise. Further, when the frequency of noise overlaps with the communication frequency, it is not possible to remove only noise.
The above-mentioned power source noise problem includes the same ripple noise as above even if the power source is a switching power source even if it is a DC power source, and the ripple voltage is equal to or lower than the communication signal voltage, but there is a degree difference. Also causes the same problem of decreasing the S/N ratio as described above.

Further, in the power line communication system described in Patent Document 1, since the primary coil of the coupling transformer is provided in the middle of the AC line as described in paragraph [0002], the charging current of several tens of amperes is applied to the primary coil. Flows. To prevent the magnetic circuit of the coupling transformer from being magnetically saturated by the magnetizing force generated by this current, an air gap is provided in the magnetic circuit or the volume of the iron core is increased. A large winding space is required to wind a thick wire. Such measures are disadvantageous in reducing the size of the device.
The present invention has been made in view of the above, and more accurately prevents the supply power and the signals superimposed thereon from affecting each other to prevent the deterioration of the signals, and further reduces the size of the device configuration. The present invention relates to an advantageous power line communication device and power line communication system.

The power line communication device of the present invention includes a voltage source that supplies power to a device that is a load, a signal source that generates a signal to be transmitted to the device, power supplied from the voltage source, and the signal source generated from the signal source. A pair of electric power for supplying the signal to the device and a signal-shared power supply line, a first coil through which the signal generated by the signal source flows, and a magnetic flux generated by the first coil that causes electromagnetic induction. A second coil, a third coil electromagnetically identical to the second coil, and a transformer device including one magnetic core around which the first coil, the second coil, and the third coil are wound, The same polarity ends of the second coil and the third coil are respectively connected to the pair of common power supply lines, and the opposite ends of the second coil and the third coil are connected to the signal reference potential point.

A power line communication system of the present invention includes the power line communication device and the device.

The present invention provides a power line communication device and a power line communication system, which can prevent the supply power and the signals superimposed thereon from affecting each other with higher accuracy to prevent signal deterioration and are advantageous for downsizing the device configuration. Can be provided.

It is a figure for explaining a power line communication system and a power line communication device of one embodiment of the present invention. It is a figure for demonstrating the modification of the power line communication system and power line communication apparatus shown in FIG.

An embodiment of the present invention will be described below with reference to the drawings. In all the drawings, the same constituents will be referred to with the same signs, while omitting their overlapping descriptions. In the present embodiment, an example of a power line communication system including a device having a power supply (referred to as a master device) and another device receiving power supplied from the power supply (referred to as a slave device) will be described.

[Constitution]
First, the configuration of the power line communication device according to the present embodiment will be described.
FIG. 1 is a schematic circuit diagram for explaining a power line communication system 1 including a power line communication device 10 that is a master device and a power line communication device 11 that is a slave device according to the present embodiment. The power line communication device 10 and the power line communication device 11 can bidirectionally transmit and receive signals to communicate. In order to smoothly perform bidirectional communication, the power line communication devices 10 and 11 have the same specifications.

The power line communication device 10 includes a power supply 2 that is a voltage source that supplies power to a power line communication device 11 that is a device that is a load. In addition, the power line communication device 10 includes a transceiver 4 that is a signal source that generates a signal to be transmitted to the power line communication device 11, power supplied from the power supply 2, and a signal that is generated from the transceiver 4 in the power line communication device 11. Power supply lines 31a and 31b for both power supply and signal sharing, a primary coil 41 through which a signal generated by the transceiver 4 flows, and a secondary coil 43 that causes electromagnetic induction by a change in magnetic flux generated by the primary coil 41. , A secondary coil 43 that is electromagnetically identical to the secondary coil 43, and a three-winding transformer Tr1 including a primary coil 41, a secondary coil 43, and a single magnetic core 42 around which the secondary coil 44 is wound, The same polarity ends of the secondary coil 43 and the secondary coil 44 are separately connected to the power supply line 31a and the power supply line 31b, respectively, and the opposite ends of the secondary coil 43 and the secondary coil 44 are connected to the reference potential terminal t3. There is.

The power supply 2 may be a power transformer having a rated power of 50 Hz or 60 Hz and an output voltage of 100 V or 200 V supplied from commercial power, or an inverter AC power supply device having a rated power of 50 Hz to 400 Hz and an output voltage of 100 V to 240 V. Good. Further, the power supply 2 may be a DC power supply device that outputs 12V to 48V.
The power source 2 must be capable of transmitting power in a non-floating manner in which any of the output terminals is separated and insulated from the ground. Similarly, the slave device 6 connected to the current loop of the power source 2 and serving as a load must also be electrically isolated from the ground.

In FIG. 1, the external wiring connection terminals of the power line communication device 10 connect the pair of cable terminals t1 and t2 to the external cables 33a and 33b. The output of the power supply 2 is connected to the power supply terminals t21 and t22. The reference potential terminal t3 is connected to the signal ground serving as the reference potential of the communication signal.
As the internal circuit of the power line communication device 10, a pair of power supply lines 31a and 31b connecting the cable terminals t1 and t2 and the power supply terminals t21 and t22, a transceiver 4 for transmitting and receiving by a bidirectional communication circuit, and a transceiver 4 and power supply lines 31a, 31b are insulated and a signal is injected and separated. A three-winding transformer Tr1 having individually insulated primary coils 41 and secondary coils 43, 44, and transformer terminals of the secondary coils 43, 44. Capacitors 45 and 46 that connect the t45 and t46 to the power supply lines 31a and 31b to form a high-pass filter, and winding-polarity terminal shared terminals of the transformer terminals t45 and 46 that are connected to the power supply lines 31a and 31b (hereinafter, simply A capacitor 47 that connects the t47 (referred to as "common terminal") and the reference potential terminal t3 and that also serves as an unbalanced current suppressor and a high-pass filter is provided.

The power supply line 31a and the power supply line 31b are conductor portions in the power line communication device 10 and connected to external cables 33a and 33b of the power line communication device 10, respectively. The power supply line 31a and the power supply line 31b are not limited to wiring by what is called an insulated wire, and for example, the power supply line 31a can be an integral terminal shape including the cable terminal t1, the connection point j1, and the power supply terminal t21. .. The power supply lines 31b, 32a, 32b are configured similarly to the power supply line 31a. The power supply line 31a and the power supply line 31b form a closed circuit that passes through the power line communication device 11 connected by the external cables 33a and 33b.
Arrows P1, P2, and P3 indicate the directions of current flowing from the power supply terminal t21 to the power supply terminal t22 in the closed circuit. Among such currents, the power supply current indicated by the arrow P1 (hereinafter, referred to as “power supply current of arrow P1”) is consumed as power for moving the slave device 6. The power supply current of the arrow line P2 and the power supply current of the arrow line P3 are also currents supplied from the power supply 2, but the power supply current of the arrow line P2 and the power supply current of the arrow line P3 are sufficiently larger than the power supply current of the arrow line P1. Since it is small, the power supply current of the arrow line P2 and the power supply current of the arrow line P3 are ignored as the power of the system and are not added to P1.

The external cables 33a and 33b have high ground impedance when laid, and it is desirable that the ground impedance be equal. Therefore, it is preferable that the external cables 33a and 33b are two-core parallel oval cables that are capty power cables and do not include a ground wire, or round cables in which two core wires are twisted together.

The transceiver 4 has a transmitting circuit (not shown), a receiving circuit (not shown), and a bidirectional communication circuit (not shown) inside, and supports simultaneous communication on one communication path. The bidirectional communication method may be any of known methods such as a time division method, a band division method, and a directional coupling (hybrid transformer), but in the present embodiment, the band division method and the time division method are used together.

Further, unlike the present embodiment, when the communication is fixed in one direction, one of the transceivers 4 and 5 is a transmission-only communication device and the other is a reception-only communication device. In this way, if the master device and the slave device are selectively used for transmission and reception, the bidirectional communication circuit can be omitted. The configuration of such a power line communication system is the same as that of the power line communication system 1 except for the functional elements for transmitting and receiving from the transceivers 4 and 5 which are the constituent elements of this embodiment and the bidirectional communication circuit. .. A communication system in which one of the transceivers 4 and 5 is a transmission-only communication device and the other is a reception-only communication device is a backward compatible device of the power line communication system 1, and therefore its description is omitted.

The three-winding transformer Tr1 included in the power line communication device 10 includes a primary coil 41 through which an output signal of the transceiver 4 flows and a pair of secondary coils 43 and 44. In the present embodiment, the winding start of the secondary coil 43 is connected to the transformer terminal t45, and is connected to the connection point j1 of the power supply line 31a via the capacitor 45. The winding start of the secondary coil 44 is connected to the transformer terminal t46, and is connected to the connection point j2 of the power supply line 31b via the capacitor 46. The winding ends of the secondary coils 43 and 44 are connected to the common terminal t47, and the common terminal t47 is connected to the signal reference point via the capacitor 47. In this embodiment, the reference potential terminal t3 is used as a signal reference point, and the reference potential terminal t3 is grounded.

In the three-winding transformer Tr1, it is preferable that the electromagnetic characteristics of the secondary coils 43 and 44 are the same, and mutual induction is performed in order to reduce the transmission loss from the primary coil 41 to the secondary coils 43 and 44. It is necessary to increase the coupling coefficient. Therefore, in the present embodiment, the same wire is used for the primary coil 41 and the secondary coils 43 and 44, and a total of three wire rods are arranged in parallel and wound the same number of times. As a winding method for increasing the coupling coefficient, it is also effective for a transformer having a relatively small number of turns to wind three wire rods as a twisted wire in addition to the above parallel winding.
The three windings referred to here are not limited to the presence of three windings, and if a plurality of windings are connected in series or in parallel to form one coil electrically, it is regarded as one winding. deal with.

Further, in the present embodiment, it is preferable that the capacitors 45 and 46 have the same capacitance. Here, “having the same capacitance” includes that the difference in capacitance is as small as several percent. In order to realize such an example, for example, two capacitors may be selected and used from a plurality of capacitors so that the difference in capacitance between the capacitors 45 and 46 is minimized.
The capacitance of the capacitor is selected under the following conditions.
The impedance Zc of the capacitor is represented by the following equation.
Zc=1/(2πf C)
In the above formula, f is a frequency (Hz) and C is a capacitance (F).
In this embodiment, the impedance Zc is selected to be sufficiently small with respect to the communication frequency and sufficiently large with respect to the power supply frequency.
In the case of a DC power supply, since f=0, the direct current impedance Zc becomes infinite and the direct current cannot pass through the capacitor, so only the impedance at the communication frequency need be considered. The capacitance of the capacitor 47 does not need to be highly accurate, but it is preferable to have a capacitance equivalent to the total value of the capacitances of the capacitors 45 and 46.

In the power line communication device 10, since the capacitors 45, 46 and 47 are connected in series to both ends of the secondary coils 43 and 44, it looks like a series LC resonance filter, but in the present embodiment, the LC resonance filter is used for the following reason. Not used as
The winding of the three-winding transformer Tr1 is not a pure self-inductance but has a parallel impedance due to mutual induction with another coil electromagnetically coupled, which is different from a general LC filter. Further, in the three-winding transformer Tr1 of the present embodiment, when a current flows through the secondary coils 43 and 44, the magnetizing force is reversed in the magnetic circuit, and the magnetic flux is canceled by the mutual induction of the secondary coils 43 and 44. Since they match, the self-inductance apparently becomes zero. Therefore, it cannot be an LC filter for an AC voltage source such as the power supply 2 between the power supply lines 31a and 31b.
On the other hand, when a voltage exists between the power supply lines 31a and 31b and the reference potential terminal t3, the three-winding transformer Tr1 can be an LC filter. However, it is difficult to manage the variation of the self-inductance and the parallel impedance due to the mutual induction described above, which makes practical use difficult. An example of such a frequency resonance pass filter is not described here.
In the present embodiment, the transmission characteristics of the three-winding transformer are designed so that resonance does not occur in the signal frequency band (10 kHz to 500 kHz). That is, the present embodiment is designed so that equal output and reception sensitivity are obtained for all frequencies within the band, and noise removal for frequencies other than the communication frequency is performed for band division communication provided in the receiving circuit. Secure with a narrow band filter.

Next, the filtering of the power supply 2 by the capacitors 45 and 46 and the three-winding transformer Tr1 will be described. A series circuit including a connection point j1-capacitor 45-secondary coil 43-(shared terminal t47)-secondary coil 44-capacitor 46-connection point j2 is formed between the power supply lines 31a and 31b. For convenience, the power source 2 has a positive electrode on the connection point j1 side, a negative electrode on the connection point j2 side, and an output voltage of V1. Regarding the impedances of the secondary coils 43 and 44, the impedance of the self-inductance and the internal impedance of the transceiver 4 (referred to as equivalent resistance R) are seen in parallel due to mutual induction, and in addition to these parallel components, the resistance of the winding is It exists in series.

When the power supply 2 is connected to the series circuit, the voltage V1 is applied between the connection points j1 and j2, and the power supply current of the arrow P2 flows. The coil current i3 flowing through the secondary coil 43 and the coil current i5 flowing through the secondary coil 44 have the same value as the power supply current of the arrow P2 and are equal to each other (i3=i5), but the coil current i5 is the common terminal t47. Since the three-winding transformer Tr1 is folded back, the direction of the current is reversed in the magnetic circuit of the three-winding transformer Tr1 and the value becomes equal to the coil current i3.
Since the secondary coils 43 and 44 have the same number of turns, the product of the current and the number of turns, which is the source of the magnetizing force, is also equal, and the generated magnetizing forces have opposite directions and the same value. Therefore, twin magnetic fluxes in opposite directions are generated in the magnetic core 42, but these magnetic fluxes apparently cancel each other and disappear. In other words, since the magnetizing forces of the secondary coils 43 and 44 cancel each other out by mutual induction, self-inductance disappears, and mutual induction between the secondary coils 43 and 44 and the primary coil 41 also disappears, so that the equivalent resistance R exists. Disappear. Therefore, the impedance of the secondary coils 43 and 44 is only the DC resistance component of the winding.

Further, as a result of the magnetic flux being canceled, no voltage is induced in the primary coil 41, and the coil current i35 does not flow. Due to such an electromagnetic phenomenon, voltage transfer from the secondary coils 43 and 44 connected to the power supply lines 31a and 31b to the primary coil 41 connected to the transceiver 4 is blocked, and the power supply 2 interferes with the transceiver 4. Disability is prevented.
The disappearance of the magnetic flux and the inductance occurs not only with respect to the AC power source but also with respect to all AC voltages existing as a voltage between the connection point j1 and the connection point j2. Therefore, the ripple noise included in the AC power supply or the DC power supply also disappears in the three-winding transformer Tr1. Further, in addition to the noise generated from the power source 2, noise existing as a voltage between the connection point j1 and the connection point j2 disappears in the three-winding transformer Tr1 due to a similar electromagnetic phenomenon. ..
For example, when a lightning surge enters the power supply lines 31a and 31b, a surge voltage exceeding the power supply voltage may remain between the lines even if the ground lightning voltage is protected by an arrester or the like. When a surge current due to such a surge voltage is generated, a voltage is generated between the connection point j1 and the connection point j2, but the voltage disappears in the three-winding transformer Tr1 due to the electromagnetic phenomenon described above, and the failure of the transceiver 4 is prevented. You can

Next, the filter effect of the capacitors 45 and 46 connecting the three-winding transformer Tr1 and the power supply lines 31a and 31b will be described. A series circuit including a connection point j1-capacitor 45-secondary coil 43-(shared terminal t47)-secondary coil 44-capacitor 46-connection point j2 is formed between the power supply lines 31a and 31b. In the description here, for convenience, the power supply 2 has a positive electrode on the connection point j1 side and a negative electrode on the connection point j2 side, and the output voltage of the power supply 2 is the voltage V1.
As the impedance of the secondary coils 43 and 44, the impedance of the self-inductance (denoted by Ze) and the internal impedance of the transceiver 4 (here, the output resistance of the transmitter) are seen in parallel due to mutual induction. Let R be the resistance. The winding resistance of the secondary coils 43 and 44 is Rw. The impedance of the capacitors 45 and 46 is Zc.
Here, in the three-winding transformer Tr1, the impedance Ze is usually sufficiently larger than the equivalent parallel resistance R, but in the operating state of the present embodiment, the self-inductance of the secondary coils 43 and 44 disappears, and Ze≈0Ω. .. From this, the equivalent parallel resistance R also disappears, and the impedance of the secondary coils 43 and 44 becomes only the DC resistance Rw of the winding.

In this embodiment, the impedance Zc is sufficiently larger than the DC resistance Rw (Rw<<Zc), and the DC resistance Rw can be ignored. Impedance _{Z 12} for the power supply of the series circuit between the connection point j1- connection point j2 becomes a series circuit of a capacitor 45 and 46 is expressed as follows.
Z ₁₂ ≈ 2Zc
The impedance Zc needs to be sufficiently small with respect to the communication signal frequency. If the maximum value of the allowable impedance Zc is the same as the input/output impedance of the transceiver, and is 150Ω at 10 kHz, the impedance for the power supply 2 rated at 50 Hz is (10000/50) times 30 kΩ, and the impedance Z ₁₂ is the impedance. It is 60 kΩ, which is twice Zc.

The power supply current of the arrow P2 flowing from the connection point j1 to the connection point j2 is calculated by the formula of V1/60 kΩ. If V1=200V in this formula, the power supply current of the arrow P2 (marked as P2 for convenience in the formula) is P2=3.3 mA. Such a value is within the range of the minute current value used for simultaneous communication on one communication path.
According to the method described above, in the present embodiment, it is possible to set a capacitor having an electrostatic capacity having an impedance sufficiently small with respect to a signal frequency and sufficiently large with respect to a power supply frequency.

The capacitor 47 connects the common terminal t47 and the reference potential terminal t3 of the series circuit between the connection point j1 and the connection point j2, and suppresses the unbalanced current. The unbalanced current mainly occurs when the ground impedances of the power supply lines 31a and 31b do not match. The ground impedance of the power supply lines 31a and 31b mainly depends on the capacitance with the ground of the power supply lines 31a and 31b, but it is difficult to completely match them. If the ground impedance does not match, the voltage V1 is divided into the ratio of the ground impedance, and a potential difference occurs between the ground, which is the voltage dividing point, and the arithmetic intermediate voltage. The common terminal t47 is designed according to the arithmetic intermediate voltage, and if t47 is directly connected to the ground of t3, the current due to the potential difference flows to the ground.

The unbalanced current appears as a difference between the current values of the coil current i3 and the coil current i5, and the magnetic flux to be canceled cannot be canceled completely and a voltage is generated in the primary coil 41. Such unbalanced voltages are negligible in carefully designed systems, but can be temporarily high due to temporary disturbances in the electromagnetic environment around the cable, such as passing trains. In order to suppress the unbalanced current generated in such a case, the present embodiment proactively includes the capacitor 47, but it is not an essential component for the operation of the communication system.

As described above, the filter effect with respect to the power supply 2 does not cause electromagnetic interference because only a small current flows due to the provision of the capacitors 45 and 46 and the magnetomotive force due to the flowing current is canceled out to generate no magnetic flux. Further, in the present embodiment, the current from the power source 2 is very small, and since no magnetic flux is generated, magnetic saturation does not occur. The power line communication system 1 of the present embodiment as described above is advantageous in miniaturization because it does not require an excessive core volume or wire diameter that exceeds the amount required for the signal power used by the three-winding transformer Tr1.

Next, a transmission loop of transmission/reception signals transmitted/received in the power line communication system 1 will be described. For the sake of convenience, it is assumed that it is transmitted from the master side and is received by the slave side.
In the power line communication system 1, an exciting current flows in the primary coil 41 of the three-winding transformer Tr1 by the signal voltage sent from the transceiver 4 in the power line communication device 10, and a magnetic flux is generated in the magnetic core 42 to generate the secondary coil 43, A voltage is induced at 44. Since the primary coil 41 and the secondary coils 43 and 44 have the same number of turns, the coil terminal voltage values are all the same. In this embodiment, the voltage of the coil terminal becomes the transmission signal voltage.
The coil current i2 generated by the voltage of the secondary coil 43 flows from the transformer terminal t45 through the capacitor 45 into the power supply line 31a from the connection point j1. At the connection point j1, there is a signal current S1 toward the slave device 6 and a current NG1 toward the power supply 2 side.

The coil current i4 generated by the voltage of the secondary coil 44 flows from the transformer terminal t46, the capacitor 46, and the connection point j2 into the power supply line 31b. At the connection point j2, there is a signal current S2 directed to the slave device 6 and a current NG1 directed to the power supply 2 side. Here, the impedance of the transformer terminal t45-connection point j1-power supply terminal t21 which is the path of the current NG1 of the power supply line 31a and the impedance of the passage transformer terminal t46-connection point j2-power supply terminal t22 of the current NG1 of the power supply line 31b are the same. Since the transformer terminals t45 and t46 have the same voltage, the signal voltages at the power supply terminal t21 and the power supply terminal t22 are the same, and there is no potential difference across the internal impedance of the power supply 2, so that no current flows.

Further, since the power supply 2 is insulated from the ground and has a high impedance to ground, the leakage current from the power supply terminals t21 and t22 to the ground can be ignored. Therefore, it can be considered that the current NG1 does not exist in the present embodiment.
From the above, in the power line communication system 1, the relationship of signal current S1=coil current i2 and signal current S2=coil current i4 is established.
Due to mutual induction with respect to the magnetomotive forces of the two outflow currents, a current of i1=(i2+i4) flows from the transmitter into the primary coil 41 according to the law of equal ampere-turn. From the viewpoint of the transceiver 4, this process is equivalent to the fact that the transmission current is shunted from the primary of the three-winding transformer Tr1 to the two secondary coils 43 and 44.

Here, the circuit through which the signal current S1 passes is referred to as S1 loop, and the circuit through which the signal current S2 passes is referred to as S2 loop. The S1 loop includes a transformer terminal t45-capacitor 45-connection point j1-cable terminal t1-external cable 33a-cable terminal t4-connection point j4-capacitor 55-transformer terminal t55-secondary coil 53-shared terminal t57-capacitor 57-. It becomes a loop of reference potential terminal t6-ground-reference potential terminal t3-capacitor 47-secondary coil 43-transformer terminal t45. In addition, the S2 loop includes a transformer terminal t46-capacitor 46-connection point j2-cable terminal t2-cable 33b-cable terminal t5-connection point j5-capacitor 56-transformer terminal t56-secondary coil 54-shared terminal t57-capacitor 57. -Reference potential terminal t6-ground-reference potential terminal t3-capacitor 47-secondary coil 44-transformer terminal t45 forms a loop.
Since the S1 loop and the S2 loop are set such that the corresponding circuit elements of the same type have the same characteristics, the difference in impedance between the S1 loop and the S2 loop is so small that they can be regarded as the same. Therefore, the signal currents S1 and S2 of the same voltage at the transformer terminals t45 and t46 are both ½ of the coil current i1 (S1=S2=(i1/2)).

Next, the transmission loop to the slave device 6 side will be described. Here, it is assumed that the impedances of the S1 loop and the S2 loop are equal. The signal currents S1 and S2 output from the power line communication device 10 travel from the cable terminals t1 and t2 through the two-core external cables 33a and 33b and reach the cable terminals t4 and t5 of the power line communication device 11. The impedances of the S1 loop and the S2 loop during this period increase in proportion to the distance of the transmission line and attenuate the signal voltage, but there is a limit to the minimum reception voltage that can be sensed by the receiver. In this embodiment, the effective sensitivity voltage is limited to 1/100 of the transmission output voltage, which limits the communication distance.
The current flowing from the connection points j4 and j5 forward is divided into the signal currents S1 and S2 flowing toward the three-winding transformer Tr2 and the current NG2 flowing toward the slave device 6, but the power supply terminal on the slave device 6 side. Since t61 and t62 are at the same potential and a current does not flow in the internal impedance of the child device 6, and the child device 6 is insulated from the ground, the ground impedance is high. Therefore, the leakage current to the ground can be ignored, and thus the current NG2 exists. Consider not to.
Therefore, in the power line communication system 1, the signal current S1 and the coil current i7 have the same value, and the signal current S2 and the coil current i9 have the same value. The magnetomotive forces generated by the inflows of the signal currents S1 and S2 are added in the same direction, so that the magnetic flux is generated twice in the magnetic core 52. At this time, the coil current i6 (i6=i7+i9), which is a combined current of the coil current i7 and the coil current i9, flows toward the transceiver 5 in the primary coil 51 according to the law of equal ampere-turn. From the viewpoint of the transmitter/receiver 5, this process is equivalent to carrying the signal power used for reception by the transmitter/receiver 5 by the two loops, sharing half each. The power line communication system 1 of the present embodiment is advantageous for long-distance communication because the signal voltage attenuation is also halved by dividing the signal current into two cores of the power cable.

The signal current S1 that has passed through the S1 loop and the signal current S2 that has passed through the S2 loop merge at the shared terminal t57 to become the feedback current S3. The feedback current S3 reaches the reference potential terminal t6 via the capacitor 57. The reference potential terminals t3 and t6 are grounded at the reference potential points on the power line communication device 10 and the power line communication device 11, respectively. At the reference potential terminals t3 and t6, the same feedback current S3 flows in the opposite direction to the ground, and it can be seen that they are offset each other, and thus they become virtual equipotential points. The apparent feedback current S3 passes from the reference potential terminal t6 to the ground, and reaches the common terminal t47 from the reference potential terminal t3 via the capacitor 47. Further, the feedback current S3 flows back to the secondary coil 43 of the three-winding transformer Tr1 as a coil current i2 and to the secondary coil 44 as a coil current i4. The feedback current S3 completes the S1 loop and the S2 loop, and the signal transmission between the power line communication devices 10 and 11 is completed.

The power supply current of the arrow line P3 on the side of the slave device 6 flows in the same manner as the power supply current of the arrow line P2 on the side of the power line communication device 10 functioning as the master device. The power line communication devices 10 and 11 have the same structure, and the power supply current of the arrow line P2 and the power supply current of the arrow line P3 are substantially equal (P2≈P3), so description thereof will be omitted here. In the three-winding transformer Tr2, the magnetizing force due to the power source current of the arrow line P3 is canceled and the magnetic flux disappears, similarly to the power source current of the arrow line P2 in the three-winding transformer Tr1. Due to such an action, in the power line communication system 1 of the present embodiment, the power line communication device 11 on the slave side does not cause interference or trouble with the transceiver 5 due to the power supply.

The capacitors 47 and 57 of the power line communication devices 10 and 11 are high-pass filters for the feedback current S3, and the AC voltage due to the difference voltage between the ground potentials of the parent device and the child device of the power line communication devices 10 and 11 and its irregular fluctuations. It functions as a filter that prevents intrusion into the communication signal loop and becomes an obstacle. However, it is not an essential component for the operation of the communication system.

The signal quality in the communication signal loop will be summarized.
(1) As a result of dividing the transmission signal current into two cores of the power cable and adding them on the receiving side, the signal voltage attenuation is smaller than that of the prior art.
(2) The noise originating from the power source and the external noise existing between the two cores of the power source cable do not move to the receiver side because they cancel and disappear in the three-winding transformer. Due to this effect, noise having the same frequency as the communication signal frequency is also removed.
(3) Due to the effects of (1) and (2), the S/N ratio does not decrease much even in long-distance communication.
As described above, the power line communication system 1 and the power line communication devices 10 and 11 of the present embodiment can perform power communication with high signal quality regardless of whether the power supply 2 is AC or DC.

[Modification]
Next, a modified example of the power line communication system 1 described above will be described.
The present embodiment described with reference to FIG. 1 shows a power line communication system in which the signal reference potential is the ground. However, the present embodiment can configure a power line communication system that achieves the same effect even when the ground cannot be grounded.
FIG. 2 is a modified example of this embodiment in which the signal ground line 33c is used instead of the ground. The power line communication system 1 described with reference to FIG. 1 is premised on that the power line communication device 10 (main device side) and the power line communication device 11 (slave device side) are sufficiently grounded, but the power line communication device 10, It is possible that either or both of the power line communication devices 11 cannot be grounded. In that case, the reference potential terminals t3 and t6 can be connected by an insulated wire as in the power line communication system 100 of FIG.
The power line communication system 100 shown in FIG. 2 is different from the power line communication system 1 of FIG. 1 only in the signal ground line 33c, and is otherwise configured similarly to the power line communication system 1. Therefore, in the modified example, description other than the part of the signal ground line 33c is omitted.

The signal ground line 33c is a signal line through which the feedback current S3 flows from the reference potential terminal t6 to the reference potential terminal t3. In order to reduce the signal voltage attenuation due to the impedance of the signal ground line 33c, it is preferable that the signal ground line 33c has a high ground impedance like the external cable 33a for the signal current S1 and the cable 33b for the signal current S2. Further, as the signal ground line 33c, it is preferable to use an electric wire having a sufficient conductor area according to the feedback current S3. However, the signal ground line 33c need not be thicker than the external cables 33a and 33b. For such a signal ground wire 33c, a three-core twisted round capty cable may be used, one core among the three cores may be used as the signal ground wire 33c, and the other two cores may be used as 33a and 33b. preferable.

The above embodiments and examples include the following technical ideas.
(1) A voltage source for supplying power to a device serving as a load, a signal source for generating a signal to be transmitted to the device, power supplied from the voltage source, and the signal generated from the signal source, A pair of power and signal sharing power supply lines to be supplied to the device, a first coil through which the signal generated by the signal source flows, a second coil that causes electromagnetic induction by a change in magnetic flux generated by the first coil, and A transformer device including a third coil electromagnetically identical to the second coil, and one magnetic core around which the first coil, the second coil, and the third coil are wound, and the second coil and the A power line communication device in which the same polarity end of a third coil is connected to each of the pair of common power supply lines, and the opposite ends of the second coil and the third coil are connected to a signal reference potential point.
(2) The power line communication device according to (1), wherein the reference potential point is connected to the ground.
(3) The power line communication device according to (1), wherein the reference potential point is connected to a potential different from the ground.
(4) The power line communication device according to any one of (1) to (3), including a capacitive element connected to a signal reference potential point of the second coil and the third coil.
(5) The power line communication device according to any one of (1) to (4), wherein the voltage source is an AC voltage source.
(6) The power line communication device according to any one of (1) to (4), wherein the voltage source is a DC voltage source.
(7) A power line communication system including the power line communication device according to any one of (1) to (6) and the device.

1, 100... Power line communication system 2... Power sources t1, t2, t4, t5... Cable terminals 4, 5... Transceiver 6... Handset device 10, 11... Power line communication device 31a, 31b, 32a, 32b... Power supply lines 33a, 33b... External cable 33c... Signal ground lines 41, 51... Primary coils 42, 52... Magnetic cores 43, 44, 53, 54... ..Secondary coils 45, 46, 47, 55, 56, 57... Capacitors j1, j2, j4, j5... Connection points t1, t2, t4, t5... Cable terminals t21, t22, t61, t62... Power supply terminals t3, t6... Reference potential terminals t45, t46, t55, t56... Transformer terminals Tr1, Tr2... Three-winding transformer

Claims (7)

A voltage source that supplies power to a device that is a load, a signal source that generates a signal to be transmitted to the device, and power supplied from the voltage source and the signal that is generated from the signal source to the device A pair of electric power and signal sharing power supply line, a first coil through which the signal generated by the signal source flows, a second coil that causes electromagnetic induction by a change in magnetic flux generated by the first coil, and the second coil And a third coil that is electromagnetically identical to the above, and a transformer device including one magnetic core around which the first coil, the second coil, and the third coil are wound, and the second coil and the third coil A power line communication device in which the ends of the same polarity are connected to each of the pair of common power supply lines, and the ends of the counter electrodes of the second coil and the third coil are connected to a signal reference potential point. The power line communication device according to claim 1, wherein the reference potential point is connected to the ground. The power line communication device according to claim 1, wherein the reference potential point is connected to a potential different from the ground. The power line communication device according to any one of claims 1 to 3, further comprising a capacitive element connected to a signal reference potential point of the second coil and the third coil. The power line communication device according to claim 1, wherein the voltage source is an AC voltage source. The power line communication device according to claim 1, wherein the voltage source is a DC voltage source. A power line communication system including the power line communication device according to claim 1, and the device.

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