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BACKGROUND OF THE INVENTION
The present invention relates to the art of power transmission and
electronic communication. Particular application is found in the
concurrent transmission of electrical power and control signals to
undersea and other remote installations and the invention will be
described with particular reference thereto. It is to be appreciated,
however, that the invention is also applicable for supplying power and
communication signals to remote, relatively inaccessible, under fluid,
downhole, or like locations.
Heretofore, various techniques have been used for concurrently providing
power and communications to undersea and other remote locations. Commonly,
separate electrical lines in a cable were used to convey electrical power
and control signals.
To ensure safe interconnection and disconnection under water, inductive
couplers were provided for transferring electrical power and control
signals between the undersea apparatus and the cable. Conventionally, low
frequency AC power voltages were transmitted from the surface along the
electrical cable to the undersea inductive coupling. Higher frequency
control and communication signals were transmitted concurrently along
communication lines and across high frequency inductive couplers. However,
inductive couplers for lower frequency AC power voltages required a
relatively large transformer core for efficient power transfer. The
commonly used laminated steel coupler cores were subject to corrosion,
particularly by salt water. Although coatings or non-magnetic
corrosion-resistant barriers could be applied to inhibit corrosion, they
also increased the gap between coupler halves and diminished energy
transfer efficiency.
One method for overcoming this shortcoming was to transmit high frequency
AC power voltages along the power transmission cables and across the
inductive coupler. Inductive coupler for high frequency signals oftentimes
used ferrite pot cores which were relatively small and relatively immune
to salt water corrosion. The higher the signal frequency, the smaller the
core required to transmit a given power level. However, high frequency
power transmission causes crosstalk on the high frequency communication
lines. Further, high frequency power transmissions attenuated more quickly
than lower frequency transmissions, rendering them disadvantageous for
long distance power transfer and communication.
The present invention provides an improved electrical power and data signal
transmission system which overcomes the above-reference disadvantages and
others.
SUMMARY OF THE INVENTION
In accordance with the present invention, electrical power and
communication signals are transmitted concurrently along a common
electrical conductor. Preferably, the electrical communication signal is
superimposed on or modulates the electrical power signal transmitted along
the electrical conductor. At a remote location, the communication signal
is separated from the power signal. The electrical power signal is
converted to a high frequency electrical power signal which is modulated
as a function of the separated electrical communication signal. After the
high frequency signal is transmitted across an inductive coupler, the high
frequency signal is converted to an appropriate DC or other electrical
power signal and to a communication signal. In the preferred embodiment,
the power signal comprises a DC power signal, and the communication signal
comprises a low frequency modulated signal, a digital signal, or the like.
In accordance with another aspect of the invention, a combined electrical
power and communication signal transmission apparatus is provided. A
source of electrical power is operatively connected with an electrical
conductor. A communication signal superimposing means is operatively
connected with the electrical conductor for superimposing an electrical
communication signal on the electrical power signal transmitted along the
electrical conductor. At a remote location, a communication separating
means is provided for separating the communication signal from the
electrical power signal. A variably modulated DC to AC converter is
operatively connected with the power cable and the communication signal
separating means for converting the electrical power signal to a high
frequency signal which is modulated as a function of the communication
signal. An inductive coupler is connected with the DC to AC converter for
transferring the high frequency signal thereacross.
A first advantage of the present invention is the provision of a method and
arrangement which enable power and communications to be transmitted on a
common carrier.
Another advantage of the invention is the elimination of interference and
crosstalk between the power and communication channels.
Further advantages reside in relatively low power loses and efficient power
transfer across relatively small inductive couplers.
Yet other advantages of the present invention are attributable to redundant
operation, greater immunity to salt water corrosion, simplified power
transmission cables, and the like.
Still further advantages of the invention will become apparent to those
skilled in the art upon a reading and understanding of the following
detailed description of the preferred embodiments.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention may take physical form in various parts and arrangements of
parts, preferred embodiments of which will be described in detail in this
specification and illustrated in the accompanying drawings which form a
part hereof and wherein:
FIG. 1 is a schematic diagram of a circuit for concurrent transmission of
electrical power and downlink control signals to undersea modules or the
like;
FIGS. 2A and 2B together illustrate a circuit diagram in accordance with
the present invention in which electrical power is transmitted
concurrently along the same power conducting cable as downlink command
communications and uplink data communications in a half duplex mode; and,
FIGS. 3A, 3B, and 3C illustrate electrical wave forms in conjunction with
the power and communication signal transmissions.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring now to the drawings wherein the showings are for purposes of
illustrating preferred embodiments of the invention only and not for
purposes of limiting same, FIG. 1 shows a first station A, which is
commonly disposed on land, which provides appropriate electrical power and
command signals to a transmission cable or conductor B. The cable extends
from the first station to a second, controlled station C, which is
commonly disposed in a remote, underwater location.
The first station A includes a source 10 of electrical power, particularly
DC electrical power. A command encoder 12 selectively generates command
signals which are superimposed by a signal combiner 14. In the preferred
embodiment, the command encoder generates low frequency AC command
communication signals. The signal combiner 14 may comprise a transformer
or other components which combine the DC electrical power signal and the
low frequency command communication signal.
The various preselected commands are distinguished by frequency modulating
the command communication signal. In the one embodiment, preselected
frequency shifts of the AC command communication signal designate ones and
zeros of a digitally encoded transmission. In another embodiment, a
plurality of discrete frequencies each designate a different one of the
preselected commands. In yet another embodiment, the command encoder
provides a digital command communication signal by superimposing square
wave pulses on the DC electrical power signal. The binary ones and zeros
may be designated by the presence and absence of such a pulse, by pulses
of differing polarity, or the like.
The cable B includes a pair of wires 20, 22 having good conductivity and
with good insulation therearound. When transmitting DC electrical power,
capacitance between the wires is of relatively small importance.
At the remote station C, the cable is connected with a coupler circuit 30
for converting the command signal encoded DC electrical power signal into
a high frequency signal encoded in accordance with the command. A power
and command signal separator 32 reads the encoded command signal and
produces an output signal in accordance therewith. For a frequency
modulated AC command signal, the signal separator circuit 32 preferably
includes a voltage level detector which detects variations in voltage
during each cycle of the AC command signal. The voltage level detector
will also detect a digital command communication signal which includes a
plurality of pulses or pulses of opposite polarity. The separator circuit
may include filter circuits for passing AC components but not DC
components, transformers, and other circuits which produce an output which
varies in proportion to the selected control communication signal. The
output of the signal separator circuit 32 is connected with a DC to AC
converter 34 to control the frequency modulation of the converter in
accordance with the control communication signal. A filter and rectifier
(not shown) may advantageously be provided to assure that only DC power is
received by the DC to AC converter.
Optionally, a signal processor 36 may be interconnected between the signal
separator 32 and the DC to AC converter 34. The signal processor is
preferred when the command communication signal is digitally encoded. The
signal processor reads the appropriate ones and zeros, ascertains the
transmitted control signal, and causes the converter to modulate the high
frequency signal correspondingly.
In the preferred embodiment, the DC to AC converter produces an output with
a constant frequency and variable pulse width. The control signal
modulates the output high frequency signal by varying the pulse width in
accordance with the control signal. The exact frequency of the high
frequency signal is selected in accordance with the construction of an
inductive coupler 40. Specifically, the high frequency is selected to
coincide with the optimal transfer frequency of a primary ferromagnetic
core 42, preferably a ferrite composition. Alternately, the control signal
may vary the frequency of the high frequency signal about the optimal
transfer frequency.
The modulated high frequency signal is applied to a primary winding 42
which is magnetically coupled to a primary ferromagnetic core 44,
preferably of a ferrite composition. The primary core is magnetically
coupled to a secondary ferromagnetic core 46. Secondary windings 48 which
are wrapped around the secondary magnetic core convert the transferred
magnetic signals back into a modulated high frequency electrical signal.
The inductivity coupled remote equipment includes a command unit 50 and a
power supply 52 connected with the secondary coupler winding 48. The
command unit reads the frequency encoded command signal and causes a
preselected response. Specifically, the control unit causes one or more of
switches 54 to be closed for supplying power to one or more components 56,
or to be opened for terminating the supply of power thereto. In this
manner, signals from the first station A control various remote
components, such as test circuits for testing various physical conditions
adjacent the equipment, motive power means for moving the equipment,
lights, heaters, pumps, or the like.
The exact command unit construction varies with the selected frequency
modulation encoding scheme. In the preferred embodiment in which the width
of square wave pulses is varied, the command unit rectifies the high
frequency signal. The voltage of the rectified high frequency signal
varies in proportion to the width of the square wave. By comparing the
magnitude of the rectified high frequency signal with preselected
magnitudes, the appropriate switch(es) can be closed. For example, the
rectified high frequency signal magnitude can be digitized and used to
address a pre-programmed memory, such as a PROM chip. Alternatively, if
the frequency is varied to encode the command signal, a series of
descending frequency filters may compare the high frequency signal with
preselected frequencies and address the memory.
FIGS. 2A and 2B illustrates a combined electrical power, downlink control
communication, and uplink data communication system in which like
components of FIG. 1 are identified by like reference numerals with a
primed (') suffix and new components are identified by new numerals. The
first station A includes a DC power source 10', and command signal encoder
12', and a signal combiner 14' for combining the DC power and command
communication signals. A wire pair 20', 22' of the cable B conveys the
encoded power signal to the remote station C.
A power and command communication signal separator 32' separates the
command communication signal from the power signal. A signal processor 36'
converts the command signal into an appropriate modulation control for a
DC to AC converter 34'. The DC to AC converter produces a high frequency
signal which is modulated in accordance with the command communication
signal to convey the command contained therein to and across an inductive
coupler 40'. Again, the signal processor may modulate the frequency, pulse
width, or other frequency related functions of the DC to AC converter 34'.
The high frequency signal is electromagnetically conveyed to a first
detachable portion of an inductive coupler 40'. A command decode unit 50'
and a rectifier 52' are connected with a second magnetically coupled
portion of the inductive coupler. The command decode unit monitors the
encoded frequency modulation and derives the corresponding commands
therefrom to control switches 54' and components 56'. The rectifier 52'
converts the high frequency signal to a DC power signal. In the embodiment
in which the signal processor 36' modulates the pulse width of the DC to
AC converter 34' while holding its frequency constant, the rectified
voltage at the output of rectifier 52' varies with the command signal.
Accordingly, in that embodiment, the command decode unit may be connected
with the downstream end of the rectifier.
A DC regulator 60 converts the variable DC component from the rectifier 52'
into a regulated DC power source, eg., 7.5 VDC. One of the controlled
components 56' is a condition monitor such as a full bridge pressure
transducer 62. The condition monitor is powered by the regulated DC power
signal to produce an output which varies in coordination with a monitored
condition, such as pressure. An amplifier 64 adjusts the amplitude of the
output of the transducer to the appropriate level for a voltage to
frequency converter 66. The voltage to frequency converter produces an
output signal whose frequency varies in proportion to changes in the
monitored condition. The voltage to frequency converter cyclically
connects a load 68 across the rectifier with a frequency or periodicity
which again varies with the sensed condition. Because the magnitude of the
load 68 is large relative to the remainder of the circuit, connecting the
load across the rectifier causes a significant increase in the amount of
current drawn, and which increase is detectable across the inductive
coupler 40'.
Specifically, with reference to FIGS. 3A, 3B, and 3C, the output of the DC
to AC converter 34' is a square wave 70 of fixed amplitude and frequency,
and whose pulse width is modulated in proportion to the control signal. As
illustrated in FIG. 3B, each time the established magnetic field within
the inductive coupler collapses, an inductive flyback voltage spike 72
occurs. The amplitude or energy content of each flyback voltage spike is
dependent upon the load which is connected with the inductive coupler. The
flyback voltage spikes have a greater amplitude or energy content when a
smaller load is applied and a smaller amplitude or energy content when a
larger load is applied. That is, the magnitude of the flyback voltage
spikes varies or is modulated with the periodic application of the load
68. As illustrated in FIG. 3C, when the square wave from the DC to AC
converter 34' is filtered out, a flyback voltage spike train 74 is
produced. The amplitude and energy content of the flyback voltage spike
train 74 varies with an envelope 76 which analogously varies with the
frequency of the applied load 68.
Referring again to FIGS. 2A and 2B, a decoder circuit 80 detects the
variations in the electrical load applied by the variable load or load
modulator means 68 and transfers the information around the DC to AC
converter to the cable B. A load modulation detector 82 separates the
flyback voltage spikes 72 from the square wave 70 and converts the flyback
spikes to the envelope or oscillating signal 76 which oscillates at the
same frequency as the frequency at which the voltage to frequency
converter 66 applies the load 68. A low pass filter 84 and a shaper 86
convert the envelope into a square wave whose frequency is the same as the
voltage to frequency converter 66. A signal combining means 90
superimposes the data communication information from the shaper 86 onto
the cable B.
Various techniques known in the art may be utilized in superimposing the
data communication signal. As a first alternative, the downlink control
communication signals and the uplink data communication signals may be
duplexed or alternated. The signal processor 36', under appropriate
controls from the command encoder 12', may alternately enable the signal
combiner 90 and disable the signal separator 32', and disable the signal
combiner 90 and enable the signal separater 32'. Alternately, the encoding
techniques for applying the downlink control communication signals and the
uplink data communication signals may be such that both may be conducted
simultaneously along the cable B without interference.
As a second specific alternative, the downlink communications may be
encdoded with a frequency modulated low frequency voltage signal and the
uplink communications may take the form of a current modulation. For
example, as shown in phantom in FIG. 2B, a resistive load may be connected
between the hot wire of the cable B and ground by a switch controlled with
the shaper 86 such that the load is applied with the same periodicity as
load 68 which, in turn, is applied in proportion to the monitored
condition.
As yet another alternative, the uplink and downlink communications may both
be frequency modulations in significantly different frequency ranges such
that the superimposed signals may be readily filtered or separated. As a
fourth alternative, the downlink communications may be digitally encoded
with square wave pulses of a first polarity and the uplink communications
may be digitally encoded with square wave pulses of the opposite polarity.
With appropriate filters in the signal separator 32', the uplink
communications could be separated and discarded such that they do not
affect the modulation of the DC to AC converter 34'.
With continuing reference to FIGS. 2A and 2B, the first station A further
includes an uplink communication signal separator 92 which separates the
uplink data communication signal from the DC power signal and downlink
command signals on the cable B. An appropriate decoder 94 for the selected
uplink encoding technique converts the uplink communication to an
appropriate format for display. For example, the decoder 94 may convert
the uplink data communication to a voltage which varies in proportion to
the frequency of the voltage to frequency converter 66, hence, with
changes in the sensed condition. The analog voltage is applied to a meter
or other man-readable display 96 which provides an indication of the
sensed condition.
The invention has been described with reference to the preferred
embodiments. Obviously, modifications and alterations will occur to others
upon a reading and understanding of this specification, it is intended to
include all such modifications and alterations insofar as they come within
the scope of the appended claims or the equivalents thereof.
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