Power distribution grid communication system

#The present invention relates to transmission of communication signals over a power transmission grid from at least a power distribution station to individual households and to a system which uses the received communication for control of electrical appliances and user viewing of other information. The system optionally includes an outbound communication channel from the household to a predetermined computer over a different channel such as a telephone channel, cable channel or RF link. This outbound channel allows a report signal to be sent and the report is carried out by a device in the household using this different channel.

#Electrical power systems have long been recognized as having the potential to be used as an effective communication channel but in practice, this potential is severely restricted due to the strong power signal being transmitted and the harmonics of the power signal, as well as the frequency characteristics of local power distribution equipment. To overcome this problem, some powerline carrier line systems have used a high frequency communication signal which is not affected by the power signal. Unfortunately, such high frequency signals encounter problems where the power distribution system includes power factor correction capacitor banks. In order for the high frequency signal to be transmitted, these capacitor banks have to be trapped. Unfortunately, it is difficult and expensive to carry this out and it is even more difficult to ensure that this always occurs. Failure to take this corrective step results in the loss of the communication signal. The high cost and the difficulty of controlling this arrangement renders a high frequency transmitter system ineffective. The potential of powerline transmission systems being used as a communication channel continues to be attractive, however, the effective use of this potential communication path has proven difficult to realize.

#Powerline carrier systems (PLC) can be divided into two segments, a powerline transmission segment and a downstream powerline distribution network segment.

#Preferred embodiments of the invention are shown in the drawings, wherein:

#FIG. 1 is an overview of the system involving the power distribution grid and the eventual termination thereof in various households;

#FIG. 2 is a schematic showing further details of the communication arrangement for transmitting of signals from a distribution station to the household;

#FIG. 1 shows a power distribution system 2 including a power generation source 4, which supplies power to a transformer station 6, and the distribution station 8. As can be appreciated, there will be many distribution stations and each distribution station 8 in turn, distributes power to a series of distribution transformers 10. These distribution transformers are sometimes referred to as feeder transformers. Typically, in North America, each distribution transformer 10 feeds anywhere from four to ten households. The segment between transformer station 6 and the distribution station 8 is normally referred to as a power transmission network and the signal between distribution station 8 and the distribution transformers is the distribution network.

#The schematic of FIG. 2 shows further details of the power distribution network between the distribution station 8 and individual households shown as 12. The power distribution network has been modified by including at the distribution station 8, a device 14 for injecting a coded communication signal on to the powerline signal. The injected signal is a broadcast signal, which is received and decoded on the low voltage side of the distribution transformer 10. The injected signal is a coded signal and is not affected by the corrective capacitor banks 16 which often are present between the originating station and the distribution transformers 10. The frequencies of the communication broadcast signal are relatively low and are unaffected by the corrective capacitor banks 16. This is in contrast to high frequency communication signals which could be introduced at the distribution station 8, however, with such high frequency signals, the corrective capacitor bank 16 would have to be trapped to allow the signal to pass therethrough. Unfortunately, this is a relatively expensive process and it also requires constant monitoring and quality control to ensure that all capacitor banks that are added, are properly trapped. By using a lower frequency signal, the signal passes through the capacitor banks, however, as will be further discussed, it has the disadvantage that the lower frequency signal is adversely affected by harmonics of the power signal.

#Outbound communication receiver and transmitter 18 are located on the low voltage side of the distribution transformers 10. The precise location is not important as the households are interconnected by the transformer 10. It may be desirable to locate this receiver at the meter interface unit of a household for more convenient access while all households on the low voltage side of the transformer, continue to receive the retransmitted signal, as will be explained. The receiver, as generally shown by arrow 11, receives the incoming signal from the distribution transformer station. This signal is a combination of the power signal and the communication signal. The receiver/transmitter 18 processes the signal to strip out the communication signal and decode the signal. It then encodes the signal according to a different protocol and injects it on the secondary side of the distribution transformer 10 as indicated by line 13. This signal is preferrably injected, using CEBus transmission protocols and will be received by any of the plurality of households located downstream of the distribution transformer 10 as a broadcast signal.