JP2008199094A - Power supply line communication system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a power supply line communication system that provides the communication of high quality by suppressing the attenuation of signals of power supply line communication and the unstableness of characteristics. <P>SOLUTION: An impedance upper 18 which increases the impedance of a circuit is provided between a pair of power supply lines 12 for supplying electric power and communicating signals and a PLC modem 14. The pair of power supply lines 12 are provided with a termination unit 17 comprising a series circuit of a resistance R1 and a capacitor C provided at the impedance upper 18. An impedance value of the termination unit 17 is made close to the characteristic impedance of the power supply lines 12 used for communication and the reflection of signals on the power supply lines caused by impedance mismatching is suppressed by the termination processing of the power supply lines 12 by the termination unit 17. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a power line communication system that performs communication between electronic devices using a power line connected to a DC power source.

  2. Description of the Related Art Conventionally, power line communication systems that use DC power lines in various devices or facilities as transmission media are known. In the case of power line communication, since an existing power line is used, there is no need to provide a dedicated line for communication. Therefore, it is not necessary to add or change wiring even when newly introducing a network device or the like or moving the arrangement of communication devices. In a system for performing DC power line communication as disclosed in Patent Document 1 and the like, a dedicated PLC (Power Line Communication) modem 4 is connected to a power line 2 connected to a power source as shown in FIG. Each device 6 exchanged communication signals via the PLC modem 4. Here, each device 6 has a built-in noise reduction capacitor. Since this capacitor has a low impedance, it is attenuated even if a communication signal is placed on the power supply line 2. Conventionally, as shown in FIGS. 3 and 4, the PLC modem 4 connected to the power supply line 2 has an impedance so that the signal on the power supply line 2 is prevented from being attenuated and each device 6 does not malfunction due to the signal. An impedance upper 8 is provided for increasing the frequency.

  As shown in FIG. 4, the impedance upper 8 includes a capacitor C connected between a pair of power supply lines 2 and an inductance element L provided on the power supply line 2 not on the ground side. The inductance element L increases the impedance of the power supply line 2 to prevent signal attenuation. The capacitor C decreases the impedance of the power supply unit of the PLC modem 4 to reduce the communication signal, thereby causing the malfunction of the PLC modem 4. Is to prevent.

Further, as disclosed in Patent Document 2, in power line communication using an AC indoor power line, a power line termination circuit is provided with a capacitor and inductor resonance circuit and a resistor corresponding to the characteristic impedance of the power line, and the termination circuit In order to maintain the quality of power line communication, the input impedance is matched, the signal reflection due to the impedance mismatch is suppressed, and so on.
JP 2006-108933 A JP 2004-304365 A

  Although the above conventional technique can prevent the attenuation of the transmission signal, the input / output impedance at the time of signal transmission / reception does not match the characteristic impedance of the power supply line, so the communication quality in power line communication is a problem. It was.

  The present invention has been made in view of the above problems of the prior art, and provides a power line communication system that suppresses signal attenuation and unstable characteristics of power line communication and enables high-quality communication. With the goal.

  The present invention is a power line communication system that communicates signals via a DC power line, and an impedance upper that increases the impedance of a circuit is provided between the pair of power lines and the PLC modem. A termination unit comprising a series circuit of a resistor and a capacitor provided in the impedance upper is provided, and the impedance value of this termination unit is set to a value close to the characteristic impedance of the power supply line used for communication, and the termination process of the power supply line by the termination unit Thus, the power line communication system is configured to suppress reflection of signals to the power line due to impedance mismatch.

  The impedance upper includes a first resistor connected in series with the capacitor and a second resistor connected to a driver side terminal of the PLC modem, and the resistors are substantially equal to each other.

  The resistor is set to a value about twice the characteristic impedance of the power line. Alternatively, the resistance is approximately equal to the characteristic impedance of the power line.

  According to the power line communication system of the present invention, signal attenuation in power line communication using a DC power line and change in attenuation due to frequency are eliminated, communication reliability is improved, and high quality power line communication is possible. To do.

  Hereinafter, an embodiment of a power line communication system of the present invention will be described with reference to FIGS. The power line communication system 10 of this embodiment is also connected as shown in FIG. 3, and a PLC modem 14 is connected to the power line 12 as shown in FIG. Further, an impedance upper 18 according to the present invention is connected to the power line 12.

  The impedance upper 18 includes a terminal end 17 that is connected between the pair of power supply lines 12 and includes a series circuit of a capacitor C and a resistor R1. In the termination portion 17, the capacitor C is connected to the + side of the power supply line 12, and one end of the resistor R <b> 1 is connected to the ground side. Further, an inductance element L is provided in series on the + side of the power supply line 12 and is connected to the power supply side terminal 20 of the PLC modem 14. The middle point of the capacitor C and the inductance element L is connected to the receiver side terminal 22 of the PLC modem 14. One end of a resistor R2 is further provided at the midpoint between the capacitor C and the inductance element L, and the other end of the resistor R2 is connected to the driver side terminal 24 of the PLC modem 14.

  The inductance element L has a sufficiently large impedance in the frequency band used for communication with respect to the characteristic impedance Z0 of the communication cable of the power supply line 12. The capacitor C prevents the power of the DC power source from being consumed by the resistor R1. The resistors R1 and R2 determine the input impedance and the output impedance of the communication cable by the power supply line 12 used for communication, thereby terminating the communication path with its characteristic impedance. In this embodiment, since the resistors R1 and R2 are connected in parallel, by setting R1 = R2 = 2Z0, both the output impedance and the input impedance of the PLC modem 14 can be set to Z0.

  In the case of the circuit of FIG. 1, the driver is always connected, and the impedance of the impedance upper 18 with respect to the communication cable is Z0 at the time of transmission and reception.

  Further, the impedance padper 18 connected to the power supply line 12 may be configured to have the same transmission / reception signal line as shown in FIG. In this case, the driver becomes active only at the time of transmission and becomes high impedance at the time of reception. In FIG. 2, it is a transceiver. Also in this case, a series circuit of the capacitor C and the resistor R1 is provided between the pair of power supply lines 12, the capacitor C is connected to the + side of the power supply line 12, and one end of the resistor R1 is connected to the ground side. Further, an inductance element L is provided in series on the + side of the power supply line 12 and is connected to the power supply side terminal 20 of the PLC modem 14. Further, one end of a resistor R2 is further provided at the midpoint between the capacitor C and the inductance element L, and the other end of the resistor R2 is connected to the transceiver side terminal 26 of the PLC modem 14.

  In this embodiment, the input impedance of the impedance upper 18 with respect to the cable during reception is the resistor R1, and the output impedance of the impedance upper 18 with respect to the cable during transmission is such that the resistors R1 and R2 are connected in parallel. Therefore, when R1 = R2, the value of the output impedance is 1/2 with respect to the input impedance.

  Table 1 shows values of output impedance and input impedance of the PLC modem 14 by the circuits of FIGS.

  In the case of the circuit shown in FIG. 1 of the power line communication system of this embodiment, since the input impedance and the output impedance are equal to the characteristic impedance Z0 of the communication cable, reflection of the signal that has entered from the communication cable occurs during reception and transmission. do not do. As a result, transmission characteristics of power line communication can be improved and communication quality can be improved. In the case of the circuit shown in FIG. 2, the impedance to the cable at the time of transmission or reception does not match the characteristic impedance Z0 of the power line, but the transmission characteristic by the power line is improved compared to the case where this matching is not performed. Is.

  The power line communication system of the present invention is not limited to the above-described embodiment. As a configuration of an impedance upper for power line communication, the power line is terminated with its characteristic impedance or a value close thereto, and the communication signal is reflected. Anything that suppresses this is sufficient.

It is a circuit diagram of the impedance upper used for the power line communication system of one Embodiment of this invention. It is a circuit diagram of the impedance upper used for the power line communication system of other embodiment of this invention. It is a block diagram which shows the example of a connection field of a power line communication system. It is a circuit diagram which shows the conventional impedance upper.

Explanation of symbols

10 power line communication system 12 power line 14 PLC modem 18 impedance upper 20 power source side terminal 22 receiver side terminal 24 driver side terminal

Claims (4)

  In a power line communication system that communicates signals via a DC power line, an impedance upper that increases a circuit impedance is provided between the pair of power lines and the PLC modem, and the impedance upper is provided on the pair of power lines. A terminal unit comprising a series circuit of a resistor and a capacitor is provided, and the impedance value of the terminal unit is set to a value close to the characteristic impedance of the power supply line used for communication. A power line communication system characterized in that reflection of a signal to a power line is suppressed.   The impedance upper includes a first resistor connected in series with the capacitor and a second resistor connected to a driver side terminal of the PLC modem, and the resistors are substantially equal to each other. Item 4. The power line communication system according to Item 1.   3. The power line communication system according to claim 2, wherein the resistance is set to a value about twice the characteristic impedance of the power line. The power line communication system according to claim 2, wherein the resistance is substantially equal to a characteristic impedance of the power line.

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