Title: Method and apparatus for detecting conditions in paralleled DC power cables
Abstract: To provide protection for power supplies in which a plurality of paralleled identical DC power cables are provided between a source and a load, one aspect of the present invention provides a method for detecting conditions in parallel DC power cables. The method includes supplying current from a power supply to each of a plurality of DC power cables, determining an average current per cable flowing in the plurality of parallel DC power cables, comparing currents in each of the DC power cables with the determined average current, and signaling the existence of a condition in response to the comparison.
Patent Number: 6,995,570 Issued on 02/07/2006 to Halstead, et al.
| Inventors:
|
Halstead; David C. (Rochester, NY);
Gilbert; Michael R. (Rochester, NY)
|
| Assignee:
|
ENI Technology, Inc. (Rochester, NY)
|
| Appl. No.:
|
180273 |
| Filed:
|
June 26, 2002 |
| Current U.S. Class: |
324/539; 324/542 |
| Current Intern'l Class: |
G01R 31/02 (20060101) |
| Field of Search: |
324/542,539
|
References Cited [Referenced By]
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| 4820991 | Apr., 1989 | Clark.
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| 4887041 | Dec., 1989 | Mashikian et al.
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| 4896114 | Jan., 1990 | Donner.
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| 5414343 | May., 1995 | Flaherty et al.
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| 5530365 | Jun., 1996 | Lefeldt.
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| 5570028 | Oct., 1996 | Sperlazzo et al.
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| 5600248 | Feb., 1997 | Westrom et al.
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| 5608328 | Mar., 1997 | Sanderson.
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| 5714885 | Feb., 1998 | Lulham.
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| 5754040 | May., 1998 | Shannon.
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| 5894223 | Apr., 1999 | Medelius et al.
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| 5922996 | Jul., 1999 | Ryeczek.
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| 5946172 | Aug., 1999 | Hansson et al.
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| 5977773 | Nov., 1999 | Medelius et al.
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| 5986860 | Nov., 1999 | Scott.
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| 6163084 | Dec., 2000 | Yamaguchi.
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| 6512378 | Jan., 2003 | Fernandez.
| |
| Foreign Patent Documents |
| 10332771 | Dec., 1998 | JP.
| |
Primary Examiner: Chau; Minh
Attorney, Agent or Firm: Harness, Dickey & Pierce, P.L.C.
Claims
What is claimed is:
1. A method for detecting conditions in parallel DC power cables comprising:
supplying current from a power supply simultaneously to each of a plurality of
DC power cables;
determining an average current per cable flowing in the plurality of parallel
DC power cables;
comparing currents in each of the DC power cables with the determined average
current; and signaling the existence of a condition in response to the comparison,
said signaling including shutting down the power supply that is providing current
to the plurality of DC power cables.
2. A method in accordance with claim 1 wherein said determining an average current
comprises utilizing a first set of sensors to measure currents in hot leads of
each of the DC power cables, and a second set of sensors to measure currents in
return leads of each of the DC power cables.
3. A method in accordance with claim 1 wherein said comparing currents in each
of the DC power cables further comprises utilizing separate comparators to monitor
a difference between currents in each of the DC power cables and the determined
average current.
4. A method in accordance with claim 3 wherein said signaling the existence of
a condition comprises activating a cable condition signal corresponding to one
of said DC power cables when current in said corresponding DC power cable drops
below the determined average current by a predetermined percentage of the average current.
5. A method in accordance with claim 4 wherein said signaling the existence of
a condition further comprises analyzing the cable condition signals corresponding
to each of the plurality of DC power cables.
6. A method in accordance with claim 1 wherein current for the plurality of DC
power cables is supplied by a DC plasma generator.
7. A method in accordance with claim 1 wherein a maximum power supply current
is limited by an overcurrent protection circuit, and wherein said signaling a condition
comprises signaling a condition when the total current in all of the DC supply
cables is less than the maximum total current.
8. A condition detecting apparatus for cables connecting a DC power supply to
a load, said apparatus configured to:
determine an average current per cable flowing in a plurality of parallel DC
power cables simultaneously connected to the DC power supply;
compare currents in each of the DC power cables with the determined average current;
and
signal the existence of a condition in response to the comparison; and shut down
a power supply that is providing current to the plurality of DC power cables in
response to said condition signal.
9. An apparatus in accordance with claim 8 comprising a first set of current
sensors and a second set of current sensors, and wherein to determine an average
current, said apparatus is configured to utilize the first set of current sensors
to measure currents in hot leads of each of the DC power cables and a second set
of sensors to measure currents in return leads of each of the DC power cables.
10. An apparatus in accordance with claim 9 further comprising separate comparators
configured to monitor a difference between currents in each of the DC power cables
and the determined average current.
11. An apparatus in accordance with claim 10 configured to activate a cable condition
signal corresponding to one of said DC power cables when current in said corresponding
DC power cable drops below the determined average current by a predetermined percentage
of the average current.
12. An apparatus in accordance with claim 11 further configured to analyze cable
condition signals corresponding to each of the DC power cables to signal the existence
of a condition.
13. A DC power supply configured to supply power to a load through a plurality
of parallel DC cables, said power supply comprising:
a DC current source;
connectors coupled to the DC current source and configured to provide current
from the DC current source to a plurality of parallel DC cables;
current sensors configured to measure DC current flowing through each of the
connectors;
an averaging circuit responsive to the current sensors and configured to determine
an average of the measured DC currents;
a comparison circuit responsive to the averaging circuit and to the current sensors
and configured to compare measured DC current flowing through each of the connectors
with the average of the measured DC currents; and
a control circuit responsive to the comparison circuit and configured to shut
down the DC current source when the comparison circuit detects that at least one
of the measured DC currents has dropped below the average of the measured DC currents
by a predetermined percentage of the average current.
14. A power supply in accordance with claim 13 wherein the DC current source
comprises a DC plasma generator.
15. A power supply in accordance with claim 14 having current sensors configured
to measure current in both the hot lead of DC cables connected to the connectors
and the return leads of DC cables connected to the connectors.
16. A power supply in accordance with claim 14 further comprising an overcurrent
protection circuit, and further wherein the control circuit is configured to shut
down the power supply in response to the comparison circuit even though the power
supply is operating within a current limit of the overcurrent protection circuit.
17. A power supply in accordance with claim 13 further comprising an overcurrent
protection circuit, and further wherein the control circuit is configured to shut
down the power supply in response to the comparator even though the power supply
is operating within a limit of the overcurrent protection circuit.
Description
FIELD OF THE INVENTION
The present invention relates to methods and apparatus for condition detection
in power supplies, and more particularly to methods and apparatus for detection
of and protection from certain conditions in paralleled DC power cables between
a source and a load.
BACKGROUND OF THE INVENTION
In some applications in which power is provided to high current loads, DC power
cables are run in parallel between a power supply and the high current load. For
example, parallel DC power cables may be used to supply power to plasma chambers
that are used for manufacturing of semiconductor wafers, flat panel displays, compact
disks, hard coatings, and other objects. To provide sufficient current to operate
the plasma chamber, one known DC power supply comprising a DC plasma generator
supplies current to two or three identical DC cables. These cables each carry up
to 40 to 60 amperes at voltages up to 500 to 800 volts DC. The cables are typically
coaxial power cables that connect to terminations at the DC plasma generator.
Overcurrent devices or circuits are known that are useful for protecting
DC plasma generators, cables, and the plasma chamber in the event of an overload.
However, overcurrent devices do not provide protection from some conditions. For
example, overcurrent devices do not indicate or provide protection in the event
of a poor cable connection or a break within a cable.
SUMMARY OF THE INVENTION
To provide protection for certain conditions in which a plurality of paralleled
DC power cables are provided between a DC power source and a load, one aspect of
the present invention provides a method for detecting conditions in parallel DC
power cables. The method includes supplying current from a power supply to each
of a plurality of DC power cables, determining an average current per cable flowing
in the plurality of parallel DC power cables, comparing currents in each of the
DC power cables with the determined average current, and signaling the existence
of a condition in response to the comparison.
In another aspect, the present invention provides a condition detecting apparatus
for cables connecting a power supply to a load. The condition detecting apparatus
is configured to determine an average current per cable flowing in a plurality
of parallel DC power cables connected to the DC power supply, compare currents
in each of the DC power cables with the determined average current, and signal
the existence of a condition in response to the comparison.
In yet another aspect, the present invention provides a DC power supply configured
to supply power to a load through a plurality of parallel DC cables. The power
supply includes a DC current source, connectors coupled to the DC current source
and configured to provide current from the DC current source to a plurality of
parallel DC cables, current sensors configured to measure DC current flowing through
each of the connectors, an averaging circuit responsive to the current sensors
and configured to determine an average of the measured DC currents, a comparison
circuit responsive to the averaging circuit and to the current sensors and configured
to compare measured DC current flowing through each of the connectors with the
average of the measured DC currents, and a control circuit responsive to the comparator
and configured to shut down the DC current source when the comparator detects that
at least one of the measured DC currents drops below the average of the measured
DC currents by a predetermined percentage of the average current.
Embodiments of the present invention provide condition detection for
partially loaded power supplies (and each paralleled cable) when only partially
loaded, in contrast to overcurrent devices that only protect during an overload.
Further areas of applicability of the present invention will become apparent
from the detailed description provided hereinafter. It should be understood that
the detailed description and specific examples, while indicating the preferred
embodiment of the invention, are intended for purposes of illustration only and
are not intended to limit the scope of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention will become more fully understood from the detailed description
and the accompanying drawings, wherein:
FIG. 1 is a block diagram representative of one configuration of the present invention;
FIG. 2 is a schematic diagram of an analyzer circuit useful for the configuration
represented in FIG. 1;
FIG. 3 is a flow chart of a program suitable for controlling a digital signal
processor utilized as an analyzer circuit in the configuration represented in FIG.
1; and
FIG. 4 is a flow chart providing further details of the condition signaling
function represented in the flow chart of FIG. 3.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)
The following description of the preferred embodiment(s) is merely exemplary
in nature and is in no way intended to limit the invention, its application, or uses.
As used herein, "current magnitude" refers to an amount of current flowing, irrespective
the direction in which it is flowing. Also as used herein, an "average current"
refers to an average current magnitude, and a measured current is less than an
average current when the measured current magnitude is less than the average current magnitude.
In one configuration of the present invention and referring to FIG. 1, a power
supply
10 provides a source of DC current to a load
12 via two or
more parallel DC power cables, for example three DC power cables
14,
16
and
18. Hall effect sensors
20,
22 and
24 in connectors
utilized to connect DC power cables
14,
16 and
18, respectively,
to power supply
10 are utilized to sense the magnitude of current flowing
through the connectors to each cable. Alternately, resistors are used to sense
current flowing in cables
14,
16 and
18, and current is sensed
as a voltage drop across each resistor. In yet another alternative, cables
14,
16 and
18 are passed through current sensors such as a LEM LA 100-P
closed loop sensor, available from LEM Holding SA, Geneva, Switzerland.
Separate signals provided by current sensors
20,
21,
22,
23,
24 and
25 are indicative of current flow in corresponding
monitored cables
14,
16, and
18. Analyzer
26 analyzes
these separate signals by determining an average current flow per cable and comparing
currents in individual cables
14,
16 and
18 to the determined
average current. In one configuration, a remote current sensor/analyzer
26A
with remote current sensors is utilized instead of or in addition to internal analyzer
26 and current sensors
20,
21,
22,
23,
24
and
25.
Normally, current supplied to load
12 is distributed equally in
parallel DC power cables
14,
16 and
18. A broken cable or
a loose connection may result in an unequal distribution of current. Thus, one
configuration of the present invention activates a condition signal when the current
in any monitored cable
14,
16 or
18 is less than the determined
average current by a predetermined amount. For example, if the current in one of
cables
14,
16 or
18 is 5% less than the average current of
all three cables, this condition is signaled. An audible or visual alarm
28
is provided to signal the condition. An electrical signal is also provided to controller
30 of power supply
10 to shut down current
32 supplied to
cables
14,
16 and
18 from current source
34 in an orderly
manner. Analyzer
26 is configured to inhibit generation of the condition
signal and shutdown of power supply
10 when power supply
10 is lightly
loaded, to prevent false alarms and nuisance shutdowns.
One configuration of power supply
10 not shown in FIG. 1 includes a battery
back-up source, which is also electrically disconnected from cables
14,
16 and
18. In this configuration, a plurality of DC power cables
connects a battery to power supply
10, and sensors are provided so that
cable faults in the DC cables connecting the battery to power supply
10
are detected.
An overcurrent protection circuit such as a fuse, circuit breaker or electronic
shutdown circuit, is provided to limit current flowing in the two or more parallel
DC cables
14,
16 and
18. In the configuration illustrated
in FIG. 1, an electronic shutdown circuit is not separately illustrated, but is
included in main controller
30. A loose connection or a broken cable condition
that results in a reduced flow of current in one or more cables
14,
16
or
18 will not activate the overcurrent protection circuit. However, analyzer
26 does not depend upon the current limit set by the overcurrent protection
circuit. Instead, analyzer
26 signals a condition when the current flowing
in at least one of DC cables
14,
16 and
18 is a predetermined
percentage less than an average of the current flow in each cable. This condition
is signaled even when the total current drawn by load
12 or the current
flowing in any individual cable
14,
16 or
18 is less than
a maximum current permitted by the overcurrent protection circuit, so that the
overcurrent protection circuit is not activated.
For example, in one configuration, power supply
10 is a DC plasma generator
configured to provide current to a load
12 comprising a plasma chamber.
Three output cables
14,
16 and
18 provide a total current
of
120 amperes from power supply
10, with each cable providing 40
amperes. The overcurrent protection circuit is set to limit when the total current
drawn by load
12 is greater than 120 amperes, for example, 126 amperes.
However, analyzer
26 will cause power supply
10 to shut down if the
current in output cables
14 and
16 remain constant and the current
in output cable
18 drops below a specified threshold, or if cables
14,
16, and
18 all exceed threshold.
In one configuration, parallel DC supply cables
14,
16 and
18
are coaxial cables connected to power supply
10 via standard PL-259 and
SO-259 coaxial connectors. Coaxial cables
14,
16 and
18 comprise
hot leads
40,
42 and
44, respectively, and return leads
46,
48 and
50, respectively. A condition may occur in either the hot
lead of a coaxial cable or the return lead. Therefore, a first set of current sensors
20,
22 and
24 is configured to sense current flowing in hot
leads
40,
42 and
44. A separate, second set of sensors
21,
23, and
25 is also provided and is configured to sense current in
return leads
46,
48 and
50. Such sensors may be embedded in
specially fabricated cables, for example, or may be incorporated into specially
designed connectors or adapters. An average current magnitude is determined utilizing
all of the sensors from either the first set of sensors
20,
22 and
24, the second set of sensors
21,
23, and
25, or both
sets of sensors. A condition is signaled if the current magnitude in any of leads
40,
42,
44,
46,
48 or
50 drops below
a predetermined percentage of the determined average current magnitude.
Referring to FIG. 2, analyzer
26 comprises an averaging circuit
52 and a comparison circuit
54. Averaging circuit
52 determines
an average current magnitude flowing in each of DC power supply cables
14,
16 and
18 utilizing signals from sensors
20,
22 and
24. Averaging circuit
52 produces a signal
53 representative
of the average current magnitude to comparison circuit
54. Comparison circuit
54 compares the average current magnitude to the actual current measured
in each hot and return conductor of each DC power supply cable by sensor
20,
21,
22,
23,
24 and
25 utilizing comparators
such as comparator
58 to generate separate signals
60,
62
and
64 indicative of cable conditions in cables
14,
16 and
18, respectively. A reference voltage at an input of comparator
58
(and other comparators not shown in FIG. 3) is scaled to a desired error limit.
In normal operation, small deviations from the average current flow may occur in
each cable
14,
16, and
18. The error limit is set to prevent
activation of signals
60,
62 and
64 unless the current magnitude
measured by at least one of sensor
20,
22 or
24 falls below
average by at least a predetermined amount. In one configuration, even when the
current magnitude measured by at least one sensor
20,
21,
22,
23,
24 or
25 falls below average by the predetermined percentage
set for signaling a condition, a condition is not signaled as long as the magnitude
of the difference is less than a predetermined amount.
Signals
60,
62 and
64 are analyzed to determine and
signal the existence of a condition. A condition signal
68 is generated
when any of signals
60,
62 and
64 are active.
In one configuration, analyzer
26 is a digital signal processor (DSP)
controlled
by a program in software or firmware. A flow chart of one such program is represented
in FIG.
3. Current is supplied to a load
12 through a plurality of
DC power cables
14,
16 and
18. Analyzer
26 utilizes
signals from sensors
20,
22 and
24 to determine
100
an average current magnitude flowing in each of the hot leads of DC power cables
14,
16 and
18. The average currents in each DC power cable
14,
16 and
18 are compared to the average current. In another
configuration, additional sensors are provided to measure currents in return leads
of DC power cables
14,
16 and
18, and signals from these sensors
are also utilized to determine the average current magnitude and in the comparison
to the average current. If none of the compared currents are a predetermined percentage
less than the determined average current, another average is computed
100
and comparison
102 is performed again. Otherwise, a condition is signaled
106. Depending upon the circumstances of the condition, execution of the
DSP program may resume at step
100 and power may continue to be provided
to load
12.
FIG. 4 is a simplified flow chart showing a portion of condition signaling function
step
106 in greater detail. When a decision
104 is made that a compared
current is too low, a nuisance timer
108 is set to prevent shutting off
power due to spurious noise transients. A check
110 is then made to determine
whether the nuisance timer has expired. If the nuisance timer has expired, a signal
is sent to control circuit
30 to perform an orderly shutdown of power from
power supply
10. Otherwise, another average current is determined and another
comparison
114 is performed between the average current and each individual
current. If no compared current is too low, a decision
116 is made to resume
execution at step
100 in FIG.
3. Otherwise, another nuisance timer
is checked again
110, and if the nuisance timer has expired, power is shut
off
112.
It will thus be recognized that configurations of the present invention provide
enhanced protection against various conditions in all types of power supplies in
which current is supplied to a load via a plurality of parallel DC power supply
cables. Conditions occurring in the DC supply cables are detected, and power shut
down in appropriate instances, even in the absence of an overload condition drawing
excess current from the power supply. Although configurations of the present invention
are applicable to DC power supplies generally, they are particularly useful in
conjunction with DC plasma generators. Protection apparatus and methods incorporating
configurations of the present invention may be provided as external accessories
to DC power supplies. However, other configurations of the present invention include
DC power supplies comprising such protection apparatus and methods.
The description of the invention is merely exemplary in nature and, thus, variations
that do not depart from the gist of the invention are intended to be within the
scope of the invention. Such variations are not to be regarded as a departure from
the spirit and scope of the invention.
*
