U.S. patent application number 10/649061 was filed with the patent office on 2004-03-11 for low frequency bilateral communication over distributed power lines.
This patent application is currently assigned to Hunt Technologies, Inc.. Invention is credited to Hunt, Paul C..
Application Number | 20040047406 10/649061 |
Document ID | / |
Family ID | 25464437 |
Filed Date | 2004-03-11 |
United States Patent
Application |
20040047406 |
Kind Code |
A1 |
Hunt, Paul C. |
March 11, 2004 |
Low frequency bilateral communication over distributed power
lines
Abstract
A system and method for providing full-duplex data
communications between an electric power distribution station and a
power consumer via the power distribution line providing electric
power is provided. A first information transmitter, coupled to the
power distribution circuit, provides first information signals
concurrently with the power signal to the power consumer via the
power distribution line. A first information receiver, coupled to a
power consumer device powered by the electrical power signal,
receives the first information signals via the electric power
distribution line. A second information transmitter coupled to the
power consumer device provides second information signals
concurrently with the electrical power signal. A second information
receiver, coupled to the power distribution circuit, receives the
second information signals via the electric power distribution
line. The information signals transmitted on the power distribution
line can be transmitted at a frequency lower than the frequency of
the transmitted power signal.
Inventors: |
Hunt, Paul C.; (Pequot
Lakes, MN) |
Correspondence
Address: |
Attention: John C. Reich
MERCHANT & GOULD P.C.
P.O. Box 2903
Minneapolis
MN
55402-0903
US
|
Assignee: |
Hunt Technologies, Inc.
Pequot Lakes
MN
|
Family ID: |
25464437 |
Appl. No.: |
10/649061 |
Filed: |
August 27, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10649061 |
Aug 27, 2003 |
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10208431 |
Jul 29, 2002 |
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10208431 |
Jul 29, 2002 |
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09723090 |
Nov 27, 2000 |
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09723090 |
Nov 27, 2000 |
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08933745 |
Sep 23, 1997 |
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6154488 |
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Current U.S.
Class: |
375/219 ;
340/310.12; 340/310.14 |
Current CPC
Class: |
Y04S 10/52 20130101;
H04B 2203/542 20130101; H04B 3/54 20130101; H02J 13/00009 20200101;
H02J 13/0001 20200101; H02J 13/00034 20200101 |
Class at
Publication: |
375/219 ;
340/310.01 |
International
Class: |
H04B 001/38; H04L
005/16; H04M 011/04 |
Claims
What is claimed is:
1. A full-duplex communications system for transmitting
information, comprising: an electric power distribution line to
transmit an electrical power signal; a power distribution circuit
coupled to the electric power distribution line to provide the
electrical power signal to a power consumer via the electric power
distribution line; a first information transmitter coupled to the
power distribution circuit to provide first information signals
concurrently with the electrical power signal to the power consumer
via the electric power distribution line; a first information
receiver, coupled to a power consumer device powered by the
electrical power signal, to receive the first information signals
via the electric power distribution line; a second information
transmitter coupled to the power consumer device to provide second
information signals concurrently with the electrical power signal
via the electric power distribution line; and a second information
receiver coupled to the power distribution circuit to receive the
second information signals via the electric power distribution
line, whereby full duplex communication between the power
distribution circuit and the power consumer is accomplished via the
electric power distribution line.
2. The full-duplex communications system as in claim 1, wherein the
first and second information transmitters each comprise a
sub-carrier signal generator circuit to respectively modulate the
first and second information signals onto the electrical power
signal.
3. The full-duplex communications system as in claim 2, wherein
each of the sub-carrier signal generator circuits comprise a low
frequency signal modulator to modulate the corresponding first and
second information signals onto the electrical power signal at a
frequency lower than a frequency of the electrical power
signal.
4. The full-duplex communications system as in claim 1, further
comprising a carrier signal generator to generate a carrier
signal.
5. The fill-duplex communications system as in claim 4, wherein the
first and second information transmitters each comprise a
sub-carrier signal generator circuit to respectively modulate the
first and second information signals onto the carrier signal.
6. The fill-duplex communications system as in claim 1, wherein the
power distribution circuit comprises a transformer circuit at a
utility power station.
7. The full-duplex communications system as in claim 1, wherein the
first information transmitter is coupled in series with a neutral
connection of the power distribution circuit.
8. The full-duplex communications system as in claim 7, further
comprising at least one protection module coupled between the
neutral connection and ground to provide a short-circuit connection
between the neutral connection and ground upon recognition of an
open-circuit condition at the first information transmitter.
9. The full-duplex communications system as in claim 8, wherein the
at least one overvoltage protection module comprises: a first
conductor, coupled to the neutral connection, having electrical
characteristics sufficient to conduct a current carried on the
neutral connection; a second conductor, coupled to the ground,
having electrical characteristics sufficient to conduct the current
carried on the neutral connection, the second conductor being
forcedly directed towards the first conductor; a voltage threshold
device coupled between the first and second conductors, having
resistance properties such that its resistance drops as voltage
increases; and a conductive restraining device coupled between the
first and second conductors and in series with the voltage
threshold device; and wherein the conductive restraining device
separates the first and second conductors until the voltage at the
neutral connection is sufficiently high to pass a current through
the voltage threshold device capable of diminishing rigidity of the
conductive separator, thereby causing the first and second
conductors to become juxtaposed.
10. The full-duplex communications system as in claim 1, wherein
the information signals comprise control signals to manipulate the
operation of the power consumer device.
11. A full-duplex communications system for disseminating
information from a power distribution station to a plurality of
power consumer sites via the electric power distribution line which
provides power to the plurality of power consumer sites,
comprising: a power distribution line coupled to each of the
plurality of power consumer sites; a power distribution circuit
coupled to the power distribution line at the power distribution
station to provide a power signal to the plurality of power
consumer sites via the power distribution line; an information
transmitter coupled to the power distribution circuit to provide
information signals concurrently with the power signal to the
plurality of power consumers via the power distribution line; at
least one information receiver at each of the plurality of power
consumer sites, each of the information receivers being coupled to
a power consumer device powered by the power signal, wherein each
of the information receivers receives the information signals via
the power distribution line; a consumer information transmitter at
each of the power consumer devices to provide consumer information
signals concurrently with the power signal to the power
distribution station via the power distribution line; and a
consumer information receiver coupled to the power distribution
circuit to receive the consumer information signals via the power
distribution line, whereby full duplex communication between the
power distribution circuit and the plurality of power consumer
sites is accomplished via the power distribution line.
12. The full-duplex communications system as in claim 11, wherein
each of the information receivers at the plurality of power
consumer sites accepts ones of the information signals having an
address identifying itself as an intended recipient.
13. The full-duplex communications system as in claim 11, wherein
the information signals comprise control signals to manipulate the
operation of the power consumer devices.
14. The full-duplex communications system as in claim 11, wherein
the information signals comprise non-control signals corresponding
to general information comprehensible by the power consumer
devices.
15. A communications system for transmitting information from a
utility power distribution node to a power consumer via an electric
power distribution line used to provide power to the power
consumer, the communications system comprising: a transmitting
circuit at the power distribution node to transmit an information
signal via the electric power distribution line at a frequency no
greater than a power transmission frequency at which the power is
transmitted; and a receiving circuit at a customer site coupled to
the transmitting circuit via the electric power distribution line
to receive the information signal for use at the customer site.
16. The communications system as in claim 15, wherein the
transmitting circuit comprises a low frequency modulating circuit
to modulate the information signal on a power signal providing the
power to the power consumer.
17. The communications system as in claim 16, wherein the low
frequency modulating circuit comprises: a zero-crossover sense
circuit to determine approximate zero-crossover points of the power
signal; a signal inversion circuit coupled to the zero-crossover
sense circuit to modulate the information signal at predetermined
ones of the approximate zero-crossover points to create a carrier
power signal which embodies the power signal and the information
signal modulated thereon; and signal driving circuitry coupled to
the signal inversion circuit and to the electric power distribution
line to drive the carrier power signal onto the electric power
distribution line.
18. The communications system as in claim 17, wherein the signal
inversion circuit comprises an inverter to invert every nth
half-period of the power signal of the power signal between
successive ones of the zero-crossover points.
19. The communications system as in claim 17, wherein the signal
inversion circuit comprises a phase-shifting circuit to shift the
phase of every nth half-period of the power signal by approximately
180 degrees between successive ones of the zero-crossover
points.
20. The communications system as in claim 17, wherein the signal
inversion circuit comprises phase-inverting circuitry to invert the
phase of every nth half-period of the power signal between
successive ones of the zero-crossover points, and wherein
consecutive positive phases of the power signal correspond to a
first logic state of the information signal and consecutive
negative phases of the power signal correspond to a second logic
state of the information signal, whereby the information signal has
a frequency which is necessarily no greater than the frequency of
the power signal.
21. The communications system as in claim 15, further comprising a
transformer coupled in parallel with the electric power
distribution line, and further coupled to the transmitting circuit,
to induce the information signal from the transmitting circuit onto
the electric power distribution line concurrently with a power
signal provided to the power consumer.
22. The communications system as in claim 15, further comprising at
least one customer device coupled to the receiving circuit, and
wherein the information signal comprises control signals to
manipulate the operation of the at least one customer device.
23. The communications system as in claim 15, wherein: the customer
site further comprises a customer site transmitting circuit to
transmit a customer information signal to the distribution node via
the electric power distribution line at a frequency no greater than
the power transmission frequency; and the distribution node further
comprises a distribution node receiving circuit coupled to the
customer site transmitting circuit via the electric power
distribution line to receive the customer information signal for
use at the distribution node.
24. The communications system as in claim 15, further comprising a
plurality of customer sites, each comprising at least one receiving
circuit coupled to the electric power distribution line to receive
the information signal and accept information having a matching
address.
25. The communication system as in claim 15, wherein the
transmitting circuit comprises: (a) an information signal
modulating circuit to superimpose an information signal on a power
signal transmitting the power, wherein the information signal has a
frequency less than a frequency of the power signal, comprising:
(i) a zero-crossover sense circuit to determine approximate
zero-crossover points of the power signal; (ii) a signal inversion
circuit coupled to the zero-crossover sense circuit to invert the
phase of every nth half-period of the power signal between
successive ones of the zero-crossover points to create a carrier
power signal, wherein consecutive positive phases of the carrier
power signal correspond to a first logic state of the information
signal and consecutive negative phases of the carrier power signal
correspond to a second logic state of the information signal; and
(b) signal driving circuitry coupled to the signal inversion
circuit and to the electric power distribution line to drive the
carrier power signal to the power consumer via the electric power
distribution line.
26. A communication method for communicating between an electric
power provider and an electric power consumer via an electric power
distribution line, the communication method comprising: providing a
power signal to the power consumer via the electric power
distribution line at a predetermined power signal frequency; and
concurrently transmitting a control signal, corresponding to the
control information, to the power consumer via the electric power
distribution line at a control frequency less than the power signal
frequency, wherein the control information manipulates the
operation of at least one consumer device at a power consumer
site.
27. The method of claim 26, wherein concurrently transmitting a
control signal comprises superimposing the control signal onto the
power signal.
28. The method of claim 27, wherein superimposing the control
signal onto the power signal comprises utilizing the power signal
frequency as a carrier signal and modulating the carrier signal to
correspond to the control signal.
29. The method of claim 26, wherein the control frequency is
derived from the power signal frequency.
30. The method of claim 26, wherein concurrently transmitting a
control signal comprises modifying waveforms of the power signal to
create patterns of half-period waveforms corresponding to a digital
representation of the control information.
31. The method of claim 30, wherein modifying waveforms of the
power signal comprises detecting zero-crossover points of the power
signal, and inverting selected ones of the half-period waveforms to
create the patterns of half-period waveforms corresponding to a
digital representation of the control information.
32. The method of claim 26, wherein providing a power signal to the
power consumer comprises providing the power signal at a frequency
set by the electric power provider.
33. The method of claim 26, wherein providing a power signal to the
power consumer comprises providing the power signal at a frequency
of approximately 50 Hz.
34. The method of claim 26, wherein providing a power signal to the
power consumer comprises providing the power signal at a frequency
of approximately 60 Hz.
35. The method of claim 26, further comprising controlling active
and inactive intervals of the at least one consumer device.
36. The method of claim 35, wherein controlling active and inactive
intervals of the at least one consumer device comprises managing
maximum power loads by inactivating selected ones of the at least
one consumer device when power loads exceed a predetermined
threshold.
37. The method of claim 26, further comprising providing general
information to the power consumer via the control signal, the
general information including information selected from the group
comprising: current time, price of power, and temperature.
38. The method of claim 26, wherein transmitting the control signal
comprises implementing a control signal protocol having a packet
type indicator to designate an information category, an address
field to designate an address of one or more of the consumer
devices at one or more of the power consumer sites, and a data
field to provide the control information to the one or more power
consumer sites.
39. The method of claim 38, wherein implementing a control signal
protocol further comprises providing synchronization designators to
delineate the control signals.
40. A signal transmission device for transmitting information
signals from a utility power distribution node to a power consumer
via a power distribution line used to provide a power signal to the
power consumer, the signal transmission device comprising: (a) an
information signal modulating circuit to superimpose an information
signal on the power signal, wherein the information signal has a
frequency less than a frequency of the power signal, comprising:
(i) a zero-crossover sense circuit to determine approximate
zero-crossover points of the power signal; (ii) a signal inversion
circuit coupled to the zero-crossover sense circuit to invert the
phase of every nth half-period of the power signal between
successive ones of the zero-crossover points to create a carrier
power signal, wherein consecutive positive phases of the carrier
power signal correspond to a first logic state of the information
signal and consecutive negative phases of the carrier power signal
correspond to a second logic state of the information signal; and
(b) signal driving circuitry coupled to the signal inversion
circuit and to the power distribution line to drive the carrier
power signal to the power consumer via the power distribution line.
Description
FIELD OF THE INVENTION
[0001] This invention relates generally to data communications, and
more particularly to a system and method for providing full-duplex
data communications between an electric power distribution station
and a power consumer, via the same power distribution line that
provides electric power to the power consumer, at frequencies at or
below the frequency of the electric power signal.
BACKGROUND OF THE INVENTION
[0002] As is true with most companies, utility companies are
striving to reduce overhead costs, while providing more convenience
to customers. For example, electric companies are migrating from
costly and time-consuming manual methods of determining the amount
of power consumed by customers of the power company. Traditionally,
a person periodically came to the customer's home, and requested
entry to read the consumer power usage from a power meter. This
type of process was costly, slow, and intrusive to their customers.
In order to alleviate some of the problems associated with the
traditional approach, other approaches have been employed,
including wireless and modem transmission of power usage
amount.
[0003] However, it is often the case that there is information that
the power company may want to provide to their customers. While
general information, such as the current price of power, price
increases, etc. may be made available to customers via mail or
telephone, it is again costly, time consuming, and intrusive.
[0004] Furthermore, many power companies provide customers with
cost discounts if the customer agrees to allow the power company to
temporarily adjust or terminate their power consumption for certain
"non-essential" power-consuming devices (e.g., air conditioners,
water heaters, swimming pool heaters, etc.) during peak operation.
This is commonly referred to as "load control" or "load limiting".
This allows the power company to limit the peak power consumption
when necessary. Otherwise, the power company may have to purchase
more expensive power from alternative sources to meet its peak load
demand. A one-way wireless pager technology could be used to
service the peak load in this manner. For example, a power company
could send a digital message via one-way pager technology to a
particular geographic area including a number of customers who have
agreed to allow the power company to alter their power during peak
power periods. The pager at the destination would receive a digital
word indicating that the power should be temporarily terminated.
Because the communication would be unilateral, no signal
acknowledge would be provided, and there would be no manner, short
of a trial-and-error method, to determine whether the customer's
power to these appliances was ever suspended. Furthermore,
customers could also tamper with the pager systems to avoid having
their power temporarily terminated, while continuing to obtain the
cost discount.
[0005] Therefore, it would be desirable to allow information to be
provided from the power company to any one or more of their power
consumers, while allowing for receipt acknowledgment and other
signals. It would also be desirable to utilize power distribution
line to provide such information, in order to avoid new wiring and
its associated costs and installation time requirements. Utilizing
the existing power distribution line would also minimize customer
tampering during load control periods, as tampering with or
severing the control line would be tantamount to eliminating their
own source of power because the power is transmitted on the same
conductor. The use of frequencies having a very long wavelength
would also be desirable, to minimize the need for signal repeaters,
and to minimize harmonic effects and reduce the overall noise on
the power line which can adversely affect electronic devices such
as computers.
[0006] While the prior art does not provide the aforementioned
functionality, the present invention provides a solution to these
and other shortcomings of the prior art, and further provides
additional advantages over the prior art.
SUMMARY OF THE INVENTION
[0007] Generally, the present invention relates to a system and
method for providing full-duplex data communications between an
electric power distribution station and a power consumer via the
same power distribution line that provides electric power to the
power consumer.
[0008] In accordance with one embodiment of the invention, a
full-duplex communications system for transmitting information is
provided. A power distribution circuit is coupled to an electric
power distribution line to transmit an electrical power signal to a
power consumer. A first information transmitter, which is coupled
to the power distribution circuit, provides first information
signals concurrently with the electrical power signal to the power
consumer via the electric power distribution line. A first
information receiver, coupled to a power consumer device powered by
the electrical power signal, receives the first information signals
via the electric power distribution line. A second information
transmitter coupled to the power consumer device provides second
information signals concurrently with the electrical power signal
via the electric power distribution line. A second information
receiver, coupled to the power distribution circuit, receives the
second information signals via the electric power distribution
line. This configuration allows for full-duplex communication
between the power distribution circuit and the power consumer via
the electric power distribution line.
[0009] In accordance with another embodiment of the invention, a
full-duplex communications system for disseminating information
from a power distribution station to a plurality of power consumer
sites via the electric power distribution line providing power to
the plurality of power consumer sites is provided. An information
transmitter at the power distribution circuit provides information
signals via the power distribution line to the plurality of power
consumer sites while also providing the power consumer sites with
electric power. Each of the power consumer sites includes at least
one information receiver which is coupled to a power consuming
device which also receives the information signals. Each consumer
site also includes a consumer information transmitter to provide
consumer information to the power distribution station via the
power distribution line, which is received at the power
distribution circuit by a consumer information receiver. This
configuration provides for full-duplex communication between a
utility power source and each of the power consumer sites, without
the need for additional wiring.
[0010] In accordance with yet another embodiment of the invention,
a communications system for transmitting information from a utility
power distribution node to a power consumer via an electric power
distribution line is provided. A transmitting circuit at the power
distribution node transmits an information signal via the power
distribution line at a frequency less than the frequency at which
the power is transmitted on the power distribution line. This low
frequency signal is received by a receiving circuit at a customer
site via the power distribution line. In one embodiment of the
invention, a low frequency modulating circuit superimposes the
information signal onto the electric power signal which provides
power to the consumer.
[0011] In accordance with another embodiment of the invention, a
signal transmission device transmits information signals from a
utility power distribution node to a power consumer via a power
distribution line. The signal transmission device includes an
information signal modulating circuit to superimpose an information
signal on the power signal. The frequency of the information signal
generated has a frequency less than the frequency of the power
signal. The modulating circuit includes a zero-crossover sense
circuit to determine the approximate zero-crossover points of the
power signal. A signal inversion circuit inverts the phase of every
nth half-period of the power signal between successive
zero-crossover points. By altering the phases of the power signal,
the control signal can be superimposed onto it, wherein consecutive
positive phases of the altered power signal correspond to a first
logic state (e.g., a "high" logic level) of the information signal,
and consecutive negative phases of the altered power signal
correspond to a second logic state (e.g., a "low" logic level) of
the information signal. Signal driving circuitry concurrently
drives the altered power signal, and the electric power, to the
power consumer via the power distribution line.
[0012] In accordance with another aspect of the invention, a
communication method for communicating between an electric power
provider and an electric power consumer via an electric power
distribution line is provided. A power signal is provided to the
power consumer via the electric power distribution line at a
predetermined power signal frequency. A control signal,
corresponding to the control information, is concurrently
transmitted to the power consumer via the electric power
distribution line. The control signal is transmitted at a frequency
less than the frequency of the power signal. The control
information can be used to manipulate the operation of the consumer
devices at the power consumer site.
[0013] The above summary of the present invention is not intended
to describe each illustrated embodiment or every implementation of
the present invention. The figures and the detailed description
which follow more particularly exemplify these embodiments.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIG. 1 is a block diagram of one link of an electric
distribution system distributing power between a utility substation
and a customer device at the power consumer's site;
[0015] FIG. 2 is a block diagram of a power distribution system
implementing an information transmitter in accordance with the
present invention;
[0016] FIG. 3 is block diagram illustrating one embodiment of the
connection of the power generation and control information
transmitter at the utility substation;
[0017] FIG. 4 is a block diagram of one embodiment of a control
information transmitter in accordance with the present
invention;
[0018] FIG. 5 is a block diagram of a zero-crossover sense circuit
in accordance with one embodiment of the present invention;
[0019] FIG. 6 is a waveform diagram illustrating the anticipation
of the zero-crossover point;
[0020] FIG. 7 is a diagram illustrating the function of the
zero-crossover synchronization in accordance with one embodiment of
the present invention;
[0021] FIG. 8 is a schematic diagram of a power transistor circuit
in accordance with one embodiment of the invention;
[0022] FIG. 9 is a waveform diagram illustrating one embodiment in
which a low frequency control signal is derived using the frequency
of the power signal as a carrier signal;
[0023] FIG. 10 is a functional illustration of one embodiment of a
high voltage protection unit in accordance with the present
invention; and
[0024] FIG. 11 is a diagram illustrating one embodiment of the
control signal protocol of the present invention.
DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS
[0025] FIG. 1 is a block diagram of one link of an electric
distribution system 100 distributing power between a utility
substation and a customer device at the power consumer's site. An
electric distribution system, or distribution plant as it is
sometimes referred to, is all of that part of an electric power
system between the bulk power source or sources and the consumer
service switches. The bulk power sources are located in or near the
load area to be served by the distribution system, and may be
either generating stations or power substations supplied over
transmission lines. Subtransmission circuits extend from the bulk
power source or sources to the various distribution substations
located in the load area. The subtransmission circuits typically
consist of underground cable, aerial cable, or overhead open-wire
conductors carried on poles, or some combination of them.
[0026] Each distribution substation normally serves its own load
area, which is a subdivision of the area served by the distribution
system. At the distribution substation the subtransmission voltage
is reduced for general distribution throughout the area. The
substations consists of one or more power-transformer banks
together with the necessary voltage regulating equipment, buses,
and switchgear. Distribution transformers are ordinarily connected
to the distribution transformer, which serve to step-down from the
distribution voltage to the utilization voltage. These step-down
transformers, often referred to as pole transformers, supply a
consumer or group of consumers over a secondary circuit. Each
consumer is connected to the secondary circuit through its service
leads and meter.
[0027] The utility substation 102 shown in FIG. 1 represents any
power distribution point in an electric distribution system.
Therefore, in a small distribution system, the utility substation
102 may represent the originating bulk power source, or may
represent a distribution substation further down the distribution
chain. The utility substation 102 provides power to a customer
device 104 at a power consumer site via a power distribution line
106. The power distribution line 106 may be coupled to one or more
step-down transformers prior to reaching the customer site. The
power distribution line provides the power necessary to operate
electrical devices, such as the customer device 104, at the
customer site.
[0028] For a variety of reasons, it may be desirable to communicate
information from the utility substation 102 to one or more customer
devices 104 at a particular customer site. For example, it may be
desirable to control or monitor a meter reading device, which is
installed at a customer site to determine the power consumption at
that customer site. Control information could provide the ability
to control or alter the operation of the meter reading device.
Furthermore, utility companies often provide a customer with a
power rate discount if the customer agrees to allow for a temporary
adjustment of their consumption. For example, a power company may
provide a customer with a rate discount where the customer agrees
to allow the power company to temporarily adjust or terminate their
power consumption for certain nonessential power consuming devices,
such as water heaters, swimming pool heaters, air conditioners,
etc. during peak operation. This allows the utility company to
limit the peak power consumption when necessary, hereinafter
referred to as "load control".
[0029] Other more general information, which is not necessarily to
"control" customer devices, can also be provided via the power
distribution lines. These general information signals are
transmitted in the same manner as signals intended to control a
customer device. Such general information signals include
information to display or store the price of power at the customer
site, the date and time, the temperature or other information
capable of being received and translated at the customer site. For
example, the time displayed on an electronic device at the customer
site could be periodically adjusted to display an accurate time as
transmitted by the utility station.
[0030] The present invention therefore allows control signals and
general information signals to be sent to the particular customer
device via the power distribution line 106 to control customer
devices and provide more general information to the customer.
Information from the customer device may also be sent via the power
distribution line to the utility substation 102, thereby creating a
two-way control information communication link via the power
distribution line 106. The aforementioned examples of control
signal applications where control signals (and/or general
information signals) are provided by the utility substation to a
customer site are merely representative of the various uses that
such control signals provide. Therefore, the examples provided
throughout the application are illustrative in nature, as the
invention is not limited to any particular control signal use.
[0031] In order to provide control information at the utility
substation 102, a transmitter 108 is used to drive the control
signals along the power distribution line 106 in the direction
represented by the arrow 110. A receiver 112 at the customer device
is configured to recognize the control signals transmitted by the
control information transmitter 108. Similarly, the utility
substation 102 may be equipped with an information receiver 114 to
receive information, such as a power consumption reading, from a
transmitter 116 at the customer device 104 in the direction
represented by arrow 118.
[0032] The control information communications link 100 shown in
FIG. 1 therefore provides a full-duplex communications link between
the utility substation 102 and the customer site. Full-duplex in
this sense refers to simultaneous communications in both
directions, although the information sent in one direction may
travel at a speed different than that of the information provided
in the opposite direction. This full-duplex communication link via
the power distribution line 106 provides for reliable transmission
of control information, without the need for additional wiring,
thereby minimizing cost and increasing data integrity.
[0033] The full-duplex communication link 100 is designed for the
transfer of control information at a frequency at or below the
frequency at which the power is being distributed on the power
distribution line 106. Such low frequency control signals provides
for longer transmission links, and there is little chance that the
data will interfere with the electrical power transmission.
Furthermore, a low frequency signal can pass through downstream
transformers and capacitors with minimal signal degradation, and
without the aid of additional equipment such as repeaters.
[0034] Data analyzation using low frequency control signals over a
period of time can provide a great deal of valuable information.
For example, in load control situations where a power consumer has
agreed to have nonessential power consuming devices regulated by
the power company, each request by the power company to adjust or
temporarily terminate the power to the consumer can be stored and
compared to an acknowledgment received at a later time. If it is
determined that power consumption at the customer site decreased
over a period of time and/or over a number of occurrences of
request/acknowledgment events, the power adjusting or terminating
request was likely successful. On the other hand, if the peak power
consumption did not decrease during these times, an equipment
failure may have occurred, or the customer may have tampered with
the control signal receiver at the customer device 104. Statistical
information gathered over time can protect the utility companies
from providing a discount to a power consumer where it is
unwarranted.
[0035] Referring now to FIG. 2, a block diagram of a power
distribution system. 200 implementing an information transmitter in
accordance with the present invention is provided. A utility
central office 202 provides the bulk power, and a transmit control
signal, to the utility substation 204 including the control
information transmitter 206. As can be seen by the example of FIG.
2, the control information transmitter can simultaneously transmit
control information via the power distribution lines 208 to
multiple customer devices residing in multiple customer sites. The
control information can pass through transformers 210, and
ultimately to a particular customer site 212. A plurality of
customer sites may be serviced by a particular transformer 210, as
illustrated by customer site n 214. Furthermore, a customer site
such as site 216 may include a plurality of different customer
devices 218. The transfer of control information from a utility
substation information transmitter 206 to a great number of
customer sites is very useful, yet cost effective.
[0036] FIG. 3 is block diagram illustrating one embodiment of the
connection of the power generation and control information
transmitter at the utility substation 300. The substation 300
typically includes a main transformer 302 which provides 3-phase
power to the customer site 304. Phases A, B and C on lines 306, 308
and 310 respectfully are transmitted to the receiver 312 at the
customer site 304. In order to induce the control information onto
the three phases 306, 308 and 310 of the power distribution line
314, the control information transmitter 316 generates a voltage on
the secondary windings 318 of the transformer 320 onto the primary
windings 322 according to the transformer 320 turns ratio. The
customer site 304 is equipped with receivers 312 at the customer
devices so that the control information can be extracted from the
power signal. In one embodiment of the present invention, the
receiver is a digital signal processing (DSP) device requiring no
analog components. DSP technology used to extract such a control
signal is readily available to those skilled in the art. The
customer site 304 also includes transmit circuitry 313, which
allows information, such as power consumption usage measured by a
meter, to be sent back to the utility substation 300 via the power
distribution line 314.
[0037] Transmit control circuitry at the utility central office is
used to provide a bitstream of binary data, shown as the transmit
control signal on line 315, to assist in modulating the control
signal at the control information transmitter 316. The transmit
control circuitry at the utility central office may include a modem
connection to a remote site in order to receive the actual
information which is to be converted into the control signal. The
transmit control signal is a bitstream which corresponds to the
actual information to be converted into the control signal. For
example, the bitstream can include binary indications of the
modulation points in a frequency modulated system, so that a binary
"1" corresponds to a first frequency, and a binary "0" corresponds
to a second frequency in the frequency modulated system. The
transmit control signal is described in further detail in
connection with FIG. 9.
[0038] The control information transmitter 316 is coupled in series
with the neutral line 324 of the main transformer 302. Therefore,
the control signal voltage generated by the control information
transmitter 316 causes the voltage on the neutral line to
correspond to the control signal generated. The control signal is
also applied to the three phases of the power distribution line
314. Therefore, while the voltage on each of the phases of the
power distribution line 314 may go to a higher voltage than where
only the power signal were present on the line, the voltage on the
neutral line 324 is similarly modulated such that the voltage at
each of the phases does not change with respect to the voltage on
the neutral line 324.
[0039] Because the control information transmitter 316 is coupled
in series with the neutral line 324, an open-circuited condition in
the control information transmitter 316 could result in an
excessively large voltage being present at the customer site 304.
In order to address this situation, at least one high voltage
protection unit 326 is coupled between the neutral line 324 and
earth ground. Other voltage protection also resides in the control
information transmitter 316. These protection modules, as well as
the high voltage protection circuit 326, will be described in
greater detail in connection with the descriptions corresponding to
FIGS. 4 and 10.
[0040] Referring now to FIG. 4, a block diagram is provided of one
embodiment of a control information transmitter 400 in accordance
with the present invention. The control information transmitter 400
is coupled in series with the power line at the neutral line 402,
rather than in parallel. This causes the reference value to be
changed from reference ground to a reference that changes as the
control signal changes. While a transmitter could transmit
information in parallel across the secondary windings 404, the very
low impedance of the secondary windings 404 results in a large
power dissipation. By coupling the control information transmitter
400 in series with the neutral line 402, only the unbalanced
current in the neutral line 402 is dissipated. In a perfectly
balanced circuit, no current would exist at all. However, typical
circuits are not perfectly balanced, and the unbalanced current is
often in the range of 120 amps.
[0041] The control signal is consequently injected in the neutral
line 402 of the power distribution line due to its in-series
connection. This signal can have various peak or RMS voltage
values, and in one embodiment of the invention is set to a value in
the range of 20 volts to 120 volts utilizing phase modulation to
generate the control signal. The signal is generated by the
electronics module 406, and is passed through the protection module
408 onto the secondary windings 404 via the secondary winding power
1 line 410 and a secondary winding power 2 line 412.
[0042] The protection module 408 provides overvoltage protection
for different voltage levels (i.e., different voltage thresholds)
and at different speeds than the overvoltage protection provided by
the high voltage protection unit 326 shown in FIG. 3. The
protection module 408 provides higher speed solid-state protection
to detect excessive voltages, but does so for voltages lower than
the potentially very high voltages detected by the high voltage
protection unit 326 of FIG. 3. For example, in one embodiment of
the invention, the protection module 408 includes capacitance banks
(not shown) coupled between the power 1 410 and power 2 412 lines,
which can respond on the order of nanoseconds, which impedes
voltage rise times by shunting voltage transients to ground. Large
silicon-controlled rectifiers (SCRS) coupled between the power 1
410 and power 2 412 lines, which can respond on the order of
microseconds, are used to switch voltages to ground which exceed a
predetermined voltage quantity. SCRs typically refer to a
three-lead device which substantially becomes a short-circuit when
its gate lead is triggered by a special voltage level, and returns
to an open circuit when its gate lead is returned to a low voltage.
Large solid-state relays can also be used across the power 1 and
power 2 lines 410, 412. High voltage protection, such as the high
voltage protection unit 326 of FIG. 3, is described in greater
detail in connection with FIG. 10.
[0043] The electronics module 406 generates the low-frequency
control signal corresponding to the desired control function to be
performed. In one embodiment of the invention, the electronics
module 406 includes crossover sense circuitry 414, crossover
synchronization circuit 416, signal drivers 418, 420, 422, 424, and
power switching transistors 426, 428, 430, 432. The crossover sense
circuit 414 detects approximately when a carrier signal, such as
the power signal transmitted on the power distribution line,
crosses the zero-voltage point. This circuit is used when the
control signal is to be modulated onto the power signal itself, and
modulating the control signal during near-zero crossover points
minimizes harmonics and other noise on the line. The crossover
sense circuitry 414 is described in greater detail in connection
with the description corresponding to FIG. 5.
[0044] The electronics module 406 also includes crossover
synchronization circuitry 416 which receives a bitstream of
information from the transmit control circuit at the utility
central office which corresponds to the actual information to be
converted into the control signal. From this transmit control
signal on line 417, the crossover synchronize block 416 manipulates
the on/off operation of the power switching transistors 426, 428,
430, 432, and does so at a time dictated by the crossover sense 414
output.
[0045] FIG. 5 is a block diagram of a zero-crossover sense circuit
500 in accordance with one embodiment of the present invention.
Because the control signals are transmitted on a physical
transmission medium common to the transmission of the power being
provided to a power consumer, it may be advantageous to use the
power signal itself as a carrier wave for the control signal. In
one embodiment of the invention, a low frequency control signal is
modulated onto the 60 Hz power signal transmitted to the power
consumer. Furthermore, the control signal is transmitted at a
frequency lower than that of the power signal, because of the
desirable transmission qualities of low frequency transmission. In
order to effectively modulate a low frequency signal on the power
signal, the present invention provides a zero-crossover sense
circuit 500, which anticipates the zero-crossover point of the 60
Hz power signal, therefore providing for state transitions of the
low frequency control signal at the approximate zero-crossing
point. This "near zero-cross switching" minimizes harmonics and
other noise on the line, so as to avoid affecting a customer's
electrical devices, such as computers, phone lines, and the
like.
[0046] The voltage applied to the primary windings 322 of the
transformer 320 are induced onto the center-tapped secondary
windings 318, as was shown in FIG. 3. This causes a secondary
winding power 1 line 502 and a secondary winding power 2 line 504
of FIG. 5 to each provide a signal of equal frequency to the
voltage on the primary windings. Each has a peak voltage equal to
one-half of the peak primary voltage, and is 180 degrees
phase-shifted from the other, due to the characteristics of the
center-tapped transformer. Although the invention is capable of
operation at various RMS voltages and frequencies, a 120 volt RMS
voltage at 60 Hz in the primary windings will be assumed for
purposes of the ensuing description. Therefore, the secondary
winding power 1 line 502 and the secondary winding power 2 line 504
are 60 volt RMS signals transmitted at 60 Hz.
[0047] The secondary winding power signals on lines 502 and 504 are
applied across a voltage dividing circuit, which in FIG. 5 is
represented by a series of resistances R1-A 506, R2-A 508, R2-B
510, and R1-B 512. In one embodiment of the invention, R1-A 506 and
R1-B 512 are approximately equal to each other in resistance, and
R2-A 508 and R2-B 510 are also approximately equal to each other. A
reference voltage, 2.5 volts in one embodiment of the invention, is
applied to node 514. The voltage dividing circuit provides a
reduced voltage at the inputs of the comparing circuit, illustrated
as a 2-input operational amplifier 516. For example, where R1-A 506
and R1-B 512 are each approximately 100 kilo-ohms, and R2-A 508 and
R2-B 510 are each approximately 1 kilo-ohm, a voltage signal is
generated at the + and - inputs of the op amp 516 which is at a
voltage level capable of recognition by the op amp 516. Op amp 516
compares the input values, and provides a high logic level when the
voltage at node 518 exceeds the voltage at node 520. Alternatively,
op amp 516 provides a low logic level when the voltage at node 518
is lower than the voltage at node 520. Because the signals at the
secondary winding power 1 and 2 lines 502 and 504 are 180 degrees
out of phase, the op amp 516 will provide a high logic level for a
time corresponding to 180 degrees of the 60 Hz signal, and will
provide a low logic level for the time corresponding to the
remaining 180 degrees of the 60 Hz signal. Therefore, a square wave
on line 522 is generated having the same frequency as the primary
and secondary power signals.
[0048] The generated square wave is then fed back into a
schmidt-trigger inverting device 524, which has built-in
hysteresis. This inverting device sources or sinks current,
depending on the state of the square wave signal on line 522,
through the resistance R3 526, which affects the voltage at node
518 and at the non-inverting input of the op amp 516. This results
in triggering the state of the square wave signal on line 522
slightly before the zero-crossing of the 60 Hz sine wave signal.
This square wave signal is then used to trigger transitions of the
low frequency control signal.
[0049] It should be noted that the control signal need not be
modulated onto the existing power signal. While it may be
beneficial to use the power signal as a carrier because it is
already available on the power distribution line, the present
invention is not limited to use of the power signal as a carrier.
Any time base that has long-term and short-term stability similar
to the power grid may be used to generate the sub-carrier control
signal. For example, the time base from global positioning system
(GPS) signals could be used to generate any sub-carrier frequency
desired, including a 60 Hz signal.
[0050] Referring now to FIG. 6, a waveform diagram illustrating the
anticipation of the zero-crossover point is provided. As was
described in connection with FIG. 5, the primary winding power has
a peak voltage of V(max), which in one embodiment of the invention
is 169.7 volts for a 120 volt RMS power signal. Due to the
center-tapped transformer 320, the peak voltage on the secondary
winding power 1 line is V(max)/2, as is the peak voltage on the
secondary winding power 2 line. However, as can be seen, the power
1 and power 2 lines are phase-shifted by 180 degrees.
[0051] The circuit of FIG. 5 provides for a square wave which is
slightly shifted in time with respect to the zero-crossing point of
the transformer power signal. The circuit of FIG. 5 therefore
provides a square wave having a frequency substantially equal to
the frequency of the transformer power signal, yet shifted by an
anticipation lead time illustrated by time duration t.sub.ANT 600
in FIG. 6. This time duration, set to approximately 40 microseconds
in one embodiment of the invention, allows time for the low
frequency signal to be modulated at or very near to the
zero-crossing points of the transformer power signal.
[0052] FIG. 7 is a diagram illustrating zero-crossover
synchronization in accordance with one embodiment of the present
invention. The zero-crossover synchronization 700 receives the
transmit control signal on line 702 and the crossover sense output
on line 704. The crossover sense output is a square wave having a
frequency substantially equal to the frequency of the transformer
power signal, yet shifted by an anticipation lead time illustrated
by time duration t.sub.ANT. This signal indicates when the
crossover synchronize should output a value indicative of which of
the power switching transistors 426, 428, 430, 432 are to be turned
on and off through drivers 418, 420, 422 and 424 respectively. For
example, at a logic high (1) level of the transmit control signal
on line 702, a logic high (1) level of the crossover sense output
on line 704 will cause the switch 426 to turn on. The anticipation
lead time of the crossover sense output allows the switch to be
turned on slightly before another switch is turned off by the power
signal.
[0053] Referring now to FIG. 8, a schematic diagram of a power
transistor circuit 800 in accordance with one embodiment of the
invention is provided. The output power switching circuit includes
four power switching transistors, shown in FIG. 7 as transistors
426, 428, 430 and 432. FIG. 8 illustrates the relationship between
two of the transistors, such as transistors 430 and 432, each of
which contain a diode 802, 804 that is reverse biased. When a
voltage is applied to V.sub.CNTL with the polarity indicated, and
the AC SOURCE on line 806 is on the positive half of its cycle,
then transistor 430 and diode 804 will conduct in a forward-biased
condition. If a voltage is applied to V.sub.CNTL with the polarity
indicated, and the AC SOURCE is negative with respect to the AC
OUTPUT on line 808, then transistor 432 and diode 802 will conduct
in a forward-biased condition. Where V.sub.CNTL is at 0 volts or at
a slightly reverse polarity, no current will flow in this circuit.
This allows half-periods of the power signal to be inverted
depending on the state of the crossover synchronize circuit
416.
[0054] FIG. 9 is a waveform diagram illustrating one embodiment in
which a low frequency control signal is derived using the frequency
of the power signal as a carrier signal. The 60 Hz line represents
a power transmission signal 900 on a power distribution line which
can be used as a carrier for the control signal. The 60 Hz signal
is a sinusoidal signal having a period of approximately 16.7
milliseconds. Because the zero-crossover point can be estimated
using the crossover sense circuitry of the present invention,
selected half-period waveforms can be inverted (or phase-shifted
180 degrees at the near-zero crossing). For example, the
half-period waveforms 902, 904 and 906 can be inverted or
phase-shifted to produce corresponding inverted half-period
waveforms 908, 910 and 912 respectively. Digital signal processing
can be used to provide low-pass filtering to allow only the low
frequency to pass. As can be seen, an approximate square wave
signal 914 having a frequency of approximately 20 Hz can be
generated for the first period of the control signal by inverting
the selected portions of the 60 Hz signal 900. Any frequency having
a period which is an integer value of one-half of the carrier
period can be generated in a similar manner. This allows the
low-frequency control signal to be modulated onto a carrier having
a higher frequency than the control signal.
[0055] In order to determine which half-period waveforms are to be
inverted, the crossover sense output and the transmit control
signal are used. As was indicated in FIG. 7, the state of these
signals determines which of the power switching transistors 426,
428, 430, 432 will turn on and off, which is dictated by the
crossover sense output and the transmit control signal. Referring
now to FIGS. 7 and 9, it can be seen that a high logic level from
the crossover sense and a high logic level from the transmit
control signal cause switch 426 and 428 to turn on, which results
in no inversion of the power signal. However, where a low logic
level from the crossover sense and a high logic level from the
transmit control occur, switches 430 and 432 turn on, thereby
causing an inversion of the power signal as shown at inverted
waveform 908.
[0056] In the example of FIG. 9, frequency modulation is providing
the control signal, as can be seen by the variance between 20 Hz
and 15 Hz. Subcarrier signals lasting for 1.5 periods of the 60 Hz
signal are 20 Hz signals, and subcarrier signals lasting for 2 full
periods of the 60 Hz signal are 15 Hz signals. This frequency
modulation allows the control signal to be superimposed on the
power signal at a lower frequency than the power signal. As will be
recognized by those skilled in the art, phase-modulation, or a
combination of phase modulation and frequency modulation, could
also be implemented in a similar manner without departing from the
scope and spirit of the invention. Therefore, the exemplary
embodiment described is merely illustrative, and should not be
limited to a frequency modulated system.
[0057] FIG. 10 is a functional illustration of one embodiment of a
high voltage protection unit 1000 in accordance with the present
invention. Because the control information transmitter 1002 is
connected in series with the neutral line 1004 of the power
distribution line, an electrical failure of the control information
transmitter 1002 may affect the power transmission itself. While a
short-circuit failure of the control information transmitter 1002
to ground will not affect the power distribution (because a circuit
loop for power transmission is still available), an open-circuit
condition would cause the transformer reference to ground to
vanish, which would result in an unacceptably high voltage to be
present at the local transformer. This is a result of the in-series
operation which causes both the ground reference and the secondary
windings (e.g., windings 318 of FIG. 3) to be modulated. Because it
is the voltage differential that is used, both the transformer
windings and the ground reference may be modulated together.
[0058] In order to account for this condition, the present
invention provides for substation protection modules, such as
protection unit 1000. These protection modules are referred to as
"anti-fuses", because where there is an open-circuit condition,
they cause a short-circuit to ground, which is the opposite of what
the operation of a standard "fuse" is. When the protection unit
1000 is activated upon recognition of an open-circuit condition in
the control information transmitter 1002, it provides a
short-circuit path from the neutral line 1004 to ground 1006,
thereby maintaining a ground connection.
[0059] In one embodiment of the invention, the protection module
1000 includes two bypass conductors 1008, 1010, which are
ultimately short-circuited together if the control information
transmitter 1002 fails to provide a continuous connection to ground
1012. Where the control information transmitter 1002 open-circuits,
the voltage on the neutral line 1004 causes a current to flow
through bypass conductor 1008, through a device which has
properties such that its resistance to current drops as voltage
increases. In one embodiment of the invention, a metal oxide
varistor (MOV) 1014 is used which utilizes the nonlinear resistance
property of zinc oxide to form a variable resistor whose resistance
to current drops as voltage increases. Therefore, at relatively low
voltages, the MOV has non-conductive insulating characteristics,
while at high voltages the MOV conducts current.
[0060] The current from the neutral line 1004 passes through the
MOV 1014, through a conducting device 1016 which is used to
separate the bypass conductors 1008, 1010 under normal
circumstances, and back through the bypass conductor 1010. In one
embodiment of the invention, the conducting device 1016 is a solder
joint which holds the bypass conductors 1008, 1010 apart until the
current through the MOV 1014 is high enough to melt the solder
joint, thereby causing the tensioned bypass conductors 1008, 1010
to snap together and provide a high current path for the current to
flow to ground 1006.
[0061] In summary, the protection unit 1000 provides a high-current
path to ground when the control information transmitter 1002 fails
in an open-circuit mode. As will be readily apparent to those
skilled in the art from the description of the protection unit
1000, various other components other than MOVs, solder joints, and
the like can be similarly used to generate the "anti-fuse"
function, as the protection unit 1000 of the present invention is
not limited to such. It will also be readily apparent to those
skilled in the art that the device 1014 and the conducting device
1016 can be calibrated such that the bypass conductors 1008, 1010
are coupled together at a desired voltage on the neutral line 1004
through the selection of appropriate resistance values. Further,
the precise mechanical configuration utilized is irrelevant,
however the physical and electrical properties of the bypass
conductors 1008, 1010 must be selected such that they can
adequately carry the large currents that they will conduct.
[0062] FIG. 11 is a diagram illustrating one embodiment of the
control signal protocol 1100 of the present invention. The sync
fields 1102, 1103 are frame synchronization fields. In one
embodiment of the invention, sync field 1102 is a predetermined
number of continuous binary "1" values. Each byte is sent least
significant bit first, with one start bit and no stop bits. The
packet type field 1104 indicates the length of the address is if
there is an address associated with the information, and what the
contents of the information are. Although the exact binary value
corresponding to particular information may vary, one embodiment of
the invention utilizes binary codes to indicate the address and
information content as shown in Table 1 below:
1TABLE 1 Types 0-3 0000 Time Broadcast 0001 Close (no address) 0010
Data 0011 Options Types 4-7 0100 Time Group Address 0101 Open
(8-bit address) 0110 Data 0111 Options Types 8-B 1000 Time Serial
Number Address 1001 Open (32-bit address) 1010 Data 1011 Options
Types C-F 1100 Time F Serial Number Range 1101 Open (2 32-bit
addresses) 1110 Data 1111 Options 0x10 File Name and Header
0x11-0xEF File Data 0xF0-0xFF Reserved
[0063] The packet type corresponding to "time" provides the time
and temperature, and may be transmitted such that the end of the
stop bit is exactly at the top of the minute. In one embodiment of
the invention, the temperature is a signed byte with 0.5 C degree
steps, and the time is defined in two bytes. In a first byte, bits
(0-5) correspond to 0-59 minutes, bit (6) corresponds to the state
of a DST (daylight savings time) flag to indicate whether the end
device is in daylight savings time, and bit (7) is for a special
schedule flag which is used for holidays or other special daily
schedules. A second byte uses bits (0-4) to represent hours 0-23, a
GMT (Greenwich Mean Time) flag to indicate whether the end device
corresponds to GMT, a timezone offset flag to indicate whether a
timezone offset has been applied to the end device time, and a
second DST flag to indicate whether the end device includes a
daylight savings time adjustment. These times and schedules allow
for control of particular customer devices at particular times, and
accounts for special circumstances due to holidays and other
special events.
[0064] The packet type corresponding to "time" also includes the
date, which, in one embodiment, includes 3 bytes of information. A
first byte uses bits (0-4) to indicate the day of the month, and
bits (5-7) to indicate the day of the week. A second byte uses bits
(0-3) to indicate the month, and bits (4-7) to indicate the
"season" (which can be defined), or a special schedule. A third
byte uses bits (0-6) to indicate the binary year from 0-99, and bit
(7) is reserved.
[0065] The packet type corresponding to "open" is a command to
select multiple end units, and "close" causes all units to be
deselected. The "data" packet type corresponds to general data to
be passed on to the unit. The "options" type can be used for
various options, including bit rates, bandwidth and frequency.
[0066] Referring again to FIG. 11, the address field 1106 can
include information ranging from no bits to 2 32-bit values. For a
broadcast message (i.e., sent to all end devices), no address needs
to be provided. For a Group Address, an 8-bit address denotes an
address of a particular group. Serial number addresses may be 1 or
2 32-bit addresses, which addresses end units by serial number. The
data field 1108 provides any data to be sent, and the checksum
fields 1110 up to two different checksum values calculated in two
different ways.
[0067] While the foregoing protocol is used in one embodiment of
the invention, it is provided for illustrative purposes only.
Various fields and binary value representations can be modified
without departing from the scope and spirit of the invention, as
will be readily recognized by those skilled in the art. Therefore,
the foregoing is merely illustrative, and the invention is not to
be limited to a protocol as provided in connection with FIG. 11
above.
[0068] The invention has been described in its presently
contemplated best mode, and it is clear that it is susceptible to
various modifications, modes of operation and embodiments, all
within the ability and skill of those skilled in the art and
without the exercise of further inventive activity. Accordingly,
what is intended to be protected by Letters Patents is set forth in
the appended claims.
* * * * *