WO2003023990A1

WO2003023990A1 - Line interface circuit for power line communication

Info

Publication number: WO2003023990A1
Application number: PCT/KR2002/001690
Authority: WO
Inventors: Il-Soo Lee
Original assignee: Mat Co., Ltd.
Priority date: 2001-09-07
Filing date: 2002-09-06
Publication date: 2003-03-20
Also published as: KR100401734B1; KR20030021676A

Abstract

Disclosed is a line interface circuit for power line communication for connecting a power line modem to a power line. The line interface circuit uses a loop via a neutral line (LP1), wherein the neutral line is grounded, together with a loop via ground (LP2) based on existing groundings in a household. The line interface circuit includes a hot line connection terminal (1), a neutral line connection terminal (2), and a ground line connection terminal (4). In a case where a ground-line wire (L3) is not installed in a household, or the installed ground-line wire (L3) is not installed to meet standard requirements, the loop via the neutral line (LP1) can be used for communication in the same manner as in the prior art. In a case where the ground-line wire (L3) is installed to meet standard requirements, the loop via ground (LP2) can be used for communication. The loop via ground LP2 has a signal gain higher than that of the loop via the neutral line LP1 by 15dB.

Description

LINE INTERFACE CIRCUIT FOR POWER LINE COMMUNICATION

Technical Field

The present invention relates to a line interface circuit for power line communication for connecting a power line modem to a power line using an existing power line as a communication line, and more particularly, to a line interface circuit for power line communication using either a loop via the neutral line or a loop via ground, based on existing grounding in a household. Here, the neutral line serves as a ground line to power lines.

Background Art

Power line communication is considered as a technology capable of being used for superhigh speed Internet connections, home networking, home automation and remote automatic control, and the like, at low costs, using power lines which are already installed in many households. The principle of the power line communication consists in adding a signal of 1-30MHz to a normal alternating current (AC) of 50-60Hz flowing through a power line, sending the added signal to a receiving unit, and then separating in the receiving unit the signal using a frequency filter. Functions such as communication and control can be performed based on the above principle.

The line interface circuit for power line communication is referred to as a circuit which converts and separates a signal by connecting a power line modem to a power line.

A conventional line interface circuit for power line communication, as shown in FIG. 1 , includes two connecting terminals 1 and 2 respectively connected to two power lines L1 and L2, a fuse F between the connecting terminals 1 and 2 and a power line modem 3, a surge discharger RV, a resistor R1 , a transformer T, and capacitors C1 and C2.

Here, the fuse F and the surge discharger RV protect the line interface circuit from an abnormal current and voltage generated in the power lines L1 and L2 due to an accidental surge, lightning, or the like. The resistor R1 is installed to discharge the surge discharger RV. The transformer T is an insulating transformer for high frequency composed of a primary coil and a secondary coil which are connected with each other to be insulated. The transformer T converts a transmitting frequency and a receiving frequency of data by a mutual induction action and transmits the converted frequencies to the power line modem 3. One end of the primary coil of the transformer T is connected to the connecting terminal 1 through the capacitor C1 and the fuse F, and the other end is directly connected to the connecting terminal 2. One end of the secondary coil of the transformer T is connected to a transmitting terminal Tx of the power line modem 3 through the capacitor C2, and simultaneously is directly connected to a receiving terminal Rx. The other of end of the secondary coil is grounded. The capacitor C1 of the primary coil of the insulating transformer T acts as a frequency bandpass filter to separate a frequency received through the power lines L1 and L2 from a normal frequency of the power lines L1 and L2, and simultaneously adjusts the frequency according to an impedance of the circuit. The capacitor C2 of the secondary coil of the insulating transformer T is used as a direct current (DC) filter for removing a DC bias of a signal output to the transmitting terminal Tx of the power line modem 3.

In the conventional line interface circuit for power line communication, the two connecting terminals 1 and 2 are connected to plug pins of a power supply plug (not shown), and then the plug pins are inserted in a power supply plug socket. By this, the connecting terminals 1 and 2 are respectively connected to the two power lines L1 and L2, which are wired to the plug socket.

Generally, the power line for the purpose of power transmission protects electric instruments from an abnormal voltage by one-line ground fault of a power transmission and distribution line of the power line. Further, a neutral point of a secondary coil of a transformer installed in the power transmission and distribution line or one end of the power line is grounded for reducing an electric shock caused, for example, to a human body, or preventing the power line communication from being cut off. Thus, two power lines wired to a household may be regarded as a hot line, to which power is supplied, that is, which is not grounded, and as a neutral line having the same potential as the ground.

In such power transmission and distribution line, the power line communication can use two circuit loops configured by the hot line and the neutral line, that is, a loop via the neutral line connected from the hot line to the neutral line, or a loop via ground connected from the hot line to ground, as a communication circuit. Since the power line used as a main power supply circuit of various power loads is exposed to various noises generated when using electric instruments, the noises have a negative influence on the communication. It is well-known that it is more preferable to employ the loop via ground for good performance of the power line communication than the loop via the neutral line.

However, while the loop via ground is effective in some areas in which grounding meets standard requirements, the loop via ground cannot be applied in other areas. Further, in a case where the grounding is poor in a household, the communication using the loop via ground cannot be performed.

Accordingly, the above-described conventional line interface circuit for power line communication shown in FIG. 1 has been widely used irrespective of households' grounding. However, since even the households, in which grounding is well, employ the loop via the neutral line, wherein the neutral line is used as the power supply line of many power loads, there is a problem in that communication performance becomes low. Particularly, a capacitor having a relative large capacity is used in the power supply line of the power line for reducing an electromagnetic wave generated when using electric instruments. While the capacitor is effective in reducing the electromagnetic wave, the capacitor serves as a capacitive load in the communication circuit, so that the line impedance of the communication circuit becomes low and the communication signal is damped, thereby resulting in a large loss.

In order to communicate using the loop via ground, the line interface circuit must be designed such that the hot line and the neutral line are distinguished from each other to be correctly connected to corresponding terminals. However, the plug socket installed in a general household is not designed such that the hot line and the neutral line are distinguished from each other to be correctly connected to the corresponding terminals. Therefore, if a communication state is poor after inserting the plug of the line interface circuit in the plug socket, the plug must be reinserted after pulling the plug out of the plug socket.

Disclosure of the Invention

The present invention recognizes and solves the problems occurring in the related art. A first object of the present invention is to provide a line interface circuit for power line communication using either a loop via ground, the loop via ground being employed in some households in which grounding well meets standard requirements to obtain an excellent communication performance, or a loop via the neutral line, the loop via the neutral line being employed in other households capable of not employing the loop via ground as in the prior art. A second object of the present invention is to provide a line interface circuit for power line communication capable of being automatically connected to an optimum loop for an correct connection and for preventing a troublesome situation in which a power supply plug must be reinserted in a power supply plug socket after pulling the plug out of the plug socket.

In order to achieve the above first object, according to one aspect of the present invention, there is provided a line interface circuit for power line communication comprising two bandpass filters which separate a frequency of a signal received through a power line, a direct current (DC) filter which removes a DC component of a signal modified by and output from a power line modem, a transformer having a primary coil connected to the power line and a secondary coil connected to the power line modem, the transformer converting a signal between the primary coil and the secondary coil by a mutual induction action, and transmitting the signal, a hot line connection terminal which connects one end of a primary coil of the transformer to a hot line side of the power line, a neutral line connection terminal which connects the other end of the primary coil of the transformer to a neutral line side of the power line via one bandpass filter of the two bandpass filters, and a ground line connection terminal which connects the other end of the primary coil of the transformer to a separate ground line side of the power line via the other bandpass filter of the two bandpass filters.

In order to achieve the above second object, the line interface circuit further comprises a connection sensing means which senses connection positions of the hot line connection terminal and the neutral line connection terminal with respect to the power line in order to detect signals informing of the respective connection positions, and a switching means which operates according to the signals detected in the connection sensing means to reverse the connection positions of the hot line connection terminal and the neutral line connection terminal with respect to the power line.

Preferably, the connection sensing means includes bridge circuits which detect a current flowing according to a potential difference between the hot line connection terminal and the ground line connection terminal, and a current flowing according to a potential difference between the neutral line connection terminal and the ground line connection terminal, respectively, and rectify the detected currents. The switching means is operated according to a differential signal between the currents output from the bridge circuits. The switching means includes a driving switch switching on/off according to the differential signal detected by the connection sensing means, and a relay element which has switches electrically connected to the driving switch and reversing the connection positions of the hot line connection terminal and the neutral line connection terminal according to a connection state. The switching means may include a plurality of contactless switching elements which are triggered by a contactless signal to reverse the connection positions of the hot line connection terminal and the neutral line connection terminal, respectively.

Brief Description of the Drawings

The above and other objects and advantages of the present invention will become more apparent by describing in detail preferred embodiments thereof with reference to the attached drawings in which: FIG. 1 is a circuit diagram of a conventional line interface circuit for power line communication;

FIG. 2 is a circuit diagram of a line interface circuit for power line communication according to a first embodiment of the present invention; FIG. 3 is a circuit diagram of a line interface circuit for power line communication according to a second embodiment of the present invention; and FIG. 4 is a circuit diagram of a switching unit having a different structure from that in the line interface circuit shown in FIG. 3.

Best mode for carrying out the Invention The present invention will now be described more fully with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. Same reference numerals in different drawings represent the same elements.

, FIG. 2 is a schematic circuit diagram of a line interface circuit for power line communication according to a first embodiment of the present invention. The line interface circuit for power line communication of the present embodiment has the same basic configuration as the conventional line interface circuit, except for a ground line connecting terminal 4 which divides one end of a primary coil of a transformer T connected to an existing neutral line connecting terminal 2 to then be connected to a separate ground line side through a separate capacitor C3 for a bandpass filter, so as to use a loop via ground as well as a loop via the neutral line.

The ground line connecting terminal 4 used in the present embodiment is connected to a ground-line wire L3 through, for example, a grounding device (not shown) which is installed to a power supply plug for a normal AC 220V network generally used in Korea. The ground-line wire L3 is wired to a power supply plug socket of a household as the power lines. According to the present embodiment, in a case where the ground-line wire L3 is not installed in the plug socket, or the installed ground-line wire L3 does not meet standard requirements, a loop via the neutral line LP1 , which is connected from a hot line connection terminal 1 of power lines L1 and L2 to a neutral line connection terminal 2 of the power lines L1 and L2 via the primary coil of the Transformer T and a capacitor C1 for a bandpass filter, can be used for communication in the same manner as in the prior art. In a case where the ground-line wire L3 is installed in the plug socket to meet standard requirements, a loop via ground LP2, which is connected from the hot line connection terminal 1 of the power lines L1 and L2 to the separate ground line connecting terminal 4 via the primary coil of the Transformer T and the capacitor C3 for the bandpass filter, can be used for communication. It can be seen that the loop via ground LP2 has a signal gain higher than that of the loop via the neutral line LP1 by 15dB. If a communication performance is not improved or is poor although the ground-line wire L3 is installed to meet standard requirements, the hot line connection terminal 1 is connected to the power line to which the neutral line connection terminal 2 must be connected. A problem as the above can be simply solved by correctly reinserting the plug.

A second embodiment shown in FIGS. 3 and 4 prevents the reduction of the communication performance caused by the misconnection of the plug, and prevents a troublesome situation in which the power supply plug is reinserted. A line interface circuit for power line communication according to the second embodiment is based on the structure presented in the first embodiment. The line interface circuit includes a connection sensing unit 10 which automatically senses connection positions of the hot line connection terminal 1 and the neutral line connection terminal 2 with respect to the power lines L1 and L2 in order to detect position signals informing of the respective connection positions, and a switching unit 20 which operates according to the signals detected in the connection sensing unit 10 to reverse the connection positions of the hot line connection terminal 1 and the neutral line connection terminal 2 with respect to the power lines L1 and L2. The connection sensing unit 10 includes bridge circuits D1 and D2 for full-wave rectification, which respectively have four diodes, and detect a current flowing according to a potential difference between the hot line connection terminal 1 and the ground line connecting terminal 4, and a current flowing according to a potential difference between the neutral line connection terminal 2 and the ground line connecting terminal 4 so that the currents are full-wave rectified, capacitors C4 and C5 for current limitation respectively connected to input sides of the bridge circuits D1 and D2, zener diodes ZD1 and ZD2 to provide a constant current respectively connected to output sides of the bridge circuits D1 and D2, smoothing capacitors C6 and C7, and resistor R2. The bridge circuits D1 and D2 together with the capacitors C4 and C5 and the zener diodes ZD1 and ZD2 detect a constant and stable direct current. The switching unit 20 has a driving switch element 21 which is switched on/off according to a differential signal between the currents output from the bridge circuits D1 and D2 of the connection sensing unit 10, and a relay element Ry having switches S1 and S2, which are connected by the driving switch element 21 , and which reverse the connection positions of the connecting terminals 1 and 2 according to a connection state. The driving switch element 21 has a photocoupler including a light-emitting diode 22, which lights up when the differential signal flows in only one direction, and a light-receiving unit 23 which is responsive to light so that the relay element Ry is activated. That is, noise of the power lines is blocked from being transmitted by space-insulation of the light-emitting diode 22 and the light-receiving unit 23. The relay element Ry is connected to a separate driving power supply Vcc through a resistor R3. The switches S1 and S2 of the relay element Ry are interposed between the hot line connection terminal 1 and one end of the primary coil, and between the capacitor C1 of the neutral line connection terminal 2 and the other end of the primary coil, respectively. The switches S1 and S2 have one fixed switch corresponding to the connecting terminals 1 and 2, and two movable switches corresponding to both ends of the primary coil, respectively. Generally, a potential difference between the hot line and ground of the power lines L1 and L2 is larger than that between the neutral line and ground. Thus, if the hot line connection terminal 1 and the neutral line connection terminal 2 are correctly connected to the power lines L1 and L2, a current output from the bridge circuits between the hot line connection terminal 1 and ground is larger than a current output from the bridge circuits between the neutral line connection terminal 2 and ground, and the differential signal between the currents output from the bridge circuits makes the light-emitting diode 22 of the driving switch element 21 to be activated in the forward direction. At this time, the light-receiving unit 23 is turned on and the relay element Ry is activated. When the relay element Ry is activated, as described above, one end of the primary coil is connected to the hot line connection terminal 1 , and the other end of the primary coil is connected to the neutral line connection terminal 2 by the switches S1 and S2. If the hot line connection terminal 1 and the neutral line connection terminal 2 are reversely connected to the power lines L1 and L2, a current output from the bridge circuits between the hot line connection terminal 1 and ground is smaller than a current output from the bridge circuits between the neutral line connection terminal 2 and ground, and the differential signal between the currents output from the bridge circuits makes the light-emitting diode 22 of the driving switch element 21 not to be activated in the reverse direction. At this time, the light-receiving unit 23 is turned off and the relay element Ry is not activated. Thus, the switches S1 and S2 of the relay element Ry are reversely connected so that the one end of the primary coil is connected to the neutral line connection terminal 2, and the other end of the primary coil is connected to the hot line connection terminal 1.

FIG. 4 shows a different switching unit 20 having a different structure from that shown in FIG. 3. The switching unit 20 includes four trigger elements 24, an inverter 25 making two trigger elements among the four trigger elements 24 to be reversely connected, and four triacs 26 used as a contactless switching element, which are respectively triggered by the trigger elements to be activated.

The trigger elements 24 are connected in parallel between the output ends c and d of the above-described connection sensing unit 10, and have a photocoupler including a light-emitting diode 24a and a light-receiving unit 24b. The light-emitting diodes 24a of the two trigger elements among the four trigger elements 24 are connected so as to allow a differential signal between currents output from the output ends c and d to flow in the forward direction. Further, the light-emitting diodes 24a of the remaining two trigger elements are connected to the inverter 25 so as to allow the differential signal to flow in the reverse direction. The light-receiving units 24b of the trigger elements 24 for triggering gate terminals of the triacs 26 may be, for example, diacs. The triacs 26 respectively have a gate terminal, which is triggered by a signal from the light-receiving units 24b, and a power supply terminal and a load terminal which are electrically connected with each other by a trigger signal from the gate terminal. The two power supply terminals of the two triacs among the four triacs 26 are connected in parallel to a hot line terminal a, and the two load terminals are connected to two terminals a' and b' respectively corresponding to both ends of the primary coil of the above-described transformer. Resistors R4 to R6 and capacitors C8 and C9 are used as a snubber for absorbing a surge voltage or a ringing voltage of the triacs 26. The two triacs among the four triacs 26, which are connected in the forward direction, or the two triacs among the four triacs 26, which are connected in the reverse direction, are operated by the differential signal between the currents output from the terminals c and d, according to the connection state of the hot line connection terminal 1 and the neutral line connection terminal 2 with respect to the power lines L1 and L2, whereby the two triacs among the four triacs 26 are triggered to be activated. Thus, one triac among the two triacs which are connected to the hot line side terminal a and the neutral line side terminal b, respectively is activated so that the hot line side terminal a is connected to either the terminal a' or the terminal b' corresponding to both ends of the primary coil of the transformer.

According to the present embodiment, by switching on/off the switches of the above-described relay element in the contactless manner, abrasion of the mechanical switches, and noise caused by the on/off switching of the switches can be prevented.

Industrial Applicability

As described so far, the present invention provides a line interface circuit for power line communication using a loop via the neutral line connected from a hot line to a neutral line of power lines together with a loop via ground connected from the hot line to ground, thereby improving the performance of the power line communication in some households in which the grounding meets standard requirements.

Further, since the power supply plug of the line interface circuit for power line communication is automatically switched after sensing the connection state of the hot line connection terminal 1 and the neutral line connection terminal 2 with respect to the power lines L1 and L2, a troublesome situation, in which a power supply plug must be reinserted, can be eliminated. Thus, the convenience is served to the user and simultaneously the optimum communication environment is provided.

Claims

What is claimed is:

1. A line interface circuit for power line communication comprising: two bandpass filters which separate a frequency of a signal received through a power line; a direct current (DC) filter which removes a DC component of a signal modified by and output from a power line modem; a transformer having a primary coil connected to the power line and a secondary coil connected to the power line modem, the transformer converting a signal between the primary coil and the secondary coil by a mutual induction action, and transmitting the signal; a hot line connection terminal which connects one end of a primary coil of the transformer to a hot line side of the power line; a neutral line connection terminal which connects the other end of the primary coil of the transformer to a neutral line side of the power line via one bandpass filter of the two bandpass filters; and a ground line connection terminal which connects the other end of the primary coil of the transformer to a separate ground line side of the power line via the other bandpass filter of the two bandpass filters.

2. The line interface circuit for power line communication of claim 1 , further comprising: a connection sensing means which senses connection positions of the hot line connection terminal and the neutral line connection terminal with respect to the power line in order to detect signals informing of the respective connection positions; and a switching means which operates according to the signals detected in the connection sensing means to reverse the connection positions of the hot line connection terminal and the neutral line connection terminal with respect to the power line.

3. The line interface circuit for power line communication of claim 2, wherein the connection sensing means includes bridge circuits which detect a current flowing according to a potential difference between the hot line connection terminal and the ground line connection terminal, and a current flowing according to a potential difference between the neutral line connection terminal and the ground line connection terminal, respectively, and rectify the detected currents, wherein the switching means is operated according to a differential signal between the currents output from the bridge circuits.

4. The line interface circuit for power line communication of claim 3, wherein capacitors for current drop, in which an alternating current is input to limit in a smaller value than a constant value, are connected to input sides of the bridge circuits, respectively.

5. The line interface circuit for power line communication of claim 4, wherein zener diodes, which bypass a direct current larger than a constant value so as to maintain in the constant value, are connected to output sides of the bridge circuits, respectively.

6. The line interface circuit for power line communication of claim 2, wherein the switching means includes a driving switch switching on/off according to the differential signal detected by the connection sensing means, and a relay element which has switches electrically connected to the driving switch and reversing the connection positions of the hot line connection terminal and the neutral line connection terminal according to a connection state.

7. The line interface circuit for power line communication of claim 6, wherein the driving switch includes a photocoupler having a light-emitting diode in which lights up when the differential signal flows in the forward direction, and a light-receiving unit activated according to the light light-emitting diode.

8. The line interface circuit for power line communication of claim 2, wherein the switching means includes a plurality of trigger elements, which are respectively operated according to the signal of the connection sensing means, an inverter inverting the signal directions of two trigger elements among the plurality of trigger elements, and a plurality of contactless switching elements which are triggered by the plurality of trigger elements to reverse the connection positions of the hot line connection terminal and the neutral line connection terminal, respectively.

9. The line interface circuit for power line communication of claim 7, wherein the trigger element includes a photocoupler having a light-emitting diode in which lights up when the differential signal flows in the forward direction, and a light-receiving unit activated according to the light light-emitting diode.