Method and structure for coupling power-line carrier current signals using common-mode coupling

• US 5,406,249 A
• Filed: 03/09/1993
• Issued: 04/11/1995
• Est. Priority Date: 03/09/1993
• Status: Expired due to Term

• Current Assignee: Google Inc. (Alphabet Inc.)
• Original Assignee: Metricom, Inc.
• Inventors: Pettus, Michael G.
• Primary Examiner(s): Peng, John K.
• Assistant Examiner(s): TONG, NINA C
• Application Number:
  US08/028,487
• Time in Patent Office: 763 Days
• Field of Search: 340/310 R, 340/310 A, 340/310 CP, 370/36, 370/37
• US Class Current: 370/389
• CPC Class Codes: H04B 2203/5408 using protocols
• CPC Class Codes: H04B 2203/5466 using three phases conductors
• CPC Class Codes: H04B 2203/5483 using coupling circuits
• CPC Class Codes: H04B 2203/5491 using filtering and bypassing
• CPC Class Codes: H04B 3/56 Circuits for coupling, blocking, or by-passing of signals

Abstract

An apparatus and a method for communicating data among transceivers in an electrical utility distribution system where a signal path between the transceivers includes multiple power distribution transformers is described. A first transceiver, common-mode coupled to a secondary of a first power distribution transformer transmits a carrier signal modulated by a data stream to the secondary. The modulated signal is transferred to the primary of the first power distribution transformer which is coupled to the primary of a second power distribution transformer. A second transceiver, common-mode coupled to a secondary of the second power distribution transformer, receives the modulated signal from the secondary. Both transceivers are protected from the high power delivered at the line frequency by filtering capacitors which attenuate signals at the line frequency and pass signals at the carrier signal frequency.

Claims

1. A power line carrier communication system for communicating between a first subscriber site and a second subscriber site of a power distribution system which conveys power at an alternating current power line frequency, where the first subscriber site is coupled to a common primary distribution line through a first distribution transformer and the second subscriber is coupled to the common primary distribution line through a second distribution transformer, comprising:

a transmitter at the first subscriber site which outputs a signal at a transmitter output, said signal being referenced to an earth ground and being a modulated carrier signal characterized by a carrier frequency, said carrier frequency being different from the power line frequency;

first secondary distribution means coupled to a secondary side of the first distribution transformer and to a first power feeder at the first subscriber site for distributing power to said first power feeder;

second secondary distribution means coupled to a secondary side of the second distribution transformer and to a second power feeder at the second subscriber site for distributing power to said second power feeder;

a first plurality of coupling capacitors, wherein each of said coupling capacitors is coupled at a first terminal to said transmitter output and is coupled at a second terminal to a line of said first secondary distribution means; and

a second plurality of coupling capacitors, wherein each of said coupling capacitors is coupled at a first lead to a line of said second secondary distribution means; and

a receiver at the second subscriber site, commonly coupled at an input to a second lead of each one of said second plurality of coupling capacitors, said input receiving said signal from said transmitter as a voltage relative to said earth ground, said signal received after propagating through said first plurality of coupling capacitors, said first distribution transformer, the common primary distribution line, said second distribution transformer, and said second plurality of coupling capacitors.

2. The apparatus of claim 1, wherein said receiver and said transmitter are an element of separate transceivers, respectively, whereby communication between the first subscriber site and the second subscriber site is bi-directional communication.

3. The apparatus of claim 1, further comprising a plurality of receivers at a plurality of subscriber sites wherein each of said plurality of subscriber sites comprising a second secondary distribution means, wherein each of said plurality of subscriber sites receives electrical power from one of said second secondary distribution means of said plurality of subscriber sites and a plurality of similar distribution means.

4. The apparatus of claim 1, wherein said first secondary distribution means and said second secondary distribution means are three-phase distribution lines, respectively.

5. The apparatus of claim 1, wherein said first secondary distribution means and said second secondary distribution means are single phase distribution lines, respectively, and a center tap of a secondary winding of each of said first and second distribution transformers is connected to said earth ground.

6. A circuit for coupling a transmitter and a receiver through an electrical power distribution system, where power in the electrical power distribution system originates at a power station and is transmitted through high-voltage lines at a power line frequency to at least a first and a second distribution transformer, where at least one primary winding of the first distribution transformer is electrically coupled to the high-voltage lines and magnetically coupled to at least one secondary winding of the first distribution transformer which is electrically coupled to at least a first secondary distribution line, the first secondary distribution line for providing electrical power to at least a first electrical utility subscriber site, where at least one primary winding of the second distribution transformer is electrically coupled to the high-voltage lines and magnetically coupled to at least one secondary winding of the second distribution transformer which is electrically coupled to at least a second secondary distribution line, the second secondary distribution line for providing electrical power to at least a second electrical utility subscriber site, and where the first and second distribution transformers are optimized to transfer power at the power line frequency, comprising:

an output of the transmitter which imposes a common-mode signal relative to an earth ground onto a transmitter output wire, where said signal is a modulated carrier with a carrier frequency other than the power line frequency;

a first coupling capacitor coupled at a first terminal to said transmitter output wire and coupled at a second terminal to an end tap of one of the at least one secondary winding of the first distribution transformer; and

a second coupling capacitor coupled at a first lead to a signal node and coupled at a second lead to an end tap of one of the at least one secondary winding of the second distribution transformer, wherein said signal node is coupled to an input of the receiver.

7. A method for communicating between a first subscriber site and a second subscriber site of a power distribution system, where a communication path crosses at least a first distribution transformer and a second distribution transformer which are both coupled to a common primary distribution line, comprising the steps of:

common-mode coupling a transmitter to at least two lines of a first secondary distribution line, said first secondary distribution line also coupling electrical power from the first distribution transformer to the first subscriber site;

common-mode coupling a receiver to at least two lines of a second secondary distribution line, said second secondary distribution line also coupling electrical power from the second distribution transformer to the second subscriber site;

generating a packet comprising data to be communicated and an address corresponding to said second subscriber site;

outputting a signal representative of said packet from said transmitter, said signal conveyed as a varying voltage relative to earth ground on both of said at least two lines of said first secondary distribution line, said signal being of equal phase and amplitude on each of said at least two lines of said first secondary distribution line;

receiving said signal at least at said receiver, said signal conveyed as a varying voltage relative to earth ground on both of said at least two lines of said second secondary distribution line, said signal being of equal phase and amplitude on each of said at least two lines of said second secondary distribution line;

converting said signal into a received packet, said address being readable in said received packet;

comparing said address to a receiver address; and

accepting said received packet when said address and said receiver address match, and discarding said received packet when said address and said receiver address do not match.

8. The method of claim 7, further comprising the steps of:

designating at least one transceiver as a store-and-forward transceiver;

accepting said packet at said store-and-forward transceiver from said transmitter; and

retransmitting said packet from said store-and-forward transceiver to said receiver.