U.S. patent application number 14/492981 was filed with the patent office on 2015-01-08 for ground scheme identification method.
The applicant listed for this patent is ROCKWELL AUTOMATION TECHNOLOGIES, INC.. Invention is credited to David W. Kirschnik, Richard A. Lukaszewski, Gary L. Skibinski, Lixiang Wei.
Application Number | 20150009726 14/492981 |
Document ID | / |
Family ID | 46044357 |
Filed Date | 2015-01-08 |
United States Patent
Application |
20150009726 |
Kind Code |
A1 |
Wei; Lixiang ; et
al. |
January 8, 2015 |
GROUND SCHEME IDENTIFICATION METHOD
Abstract
The present techniques include methods and systems for detecting
the grounding condition of an electrical system to automatically
determine a suitable electrical drive configuration. The drive
includes a test resistor which may be connected or disconnected
from the drive to measure different drive voltages. The measured
drive voltages are analyzed to determine a type of grounding
configuration of the electrical system in which the drive is to be
installed. Embodiments also include determining ground resistance
condition such as a high resistance ground (HRG) fault or a ground
resistance fault when the drive is in operation.
Inventors: |
Wei; Lixiang; (Whitefish
Bay, WI) ; Kirschnik; David W.; (Germantown, WI)
; Lukaszewski; Richard A.; (New Berlin, WI) ;
Skibinski; Gary L.; (Milwaukee, WI) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
ROCKWELL AUTOMATION TECHNOLOGIES, INC. |
Mayfield Heights |
OH |
US |
|
|
Family ID: |
46044357 |
Appl. No.: |
14/492981 |
Filed: |
September 22, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
13077212 |
Mar 31, 2011 |
8841917 |
|
|
14492981 |
|
|
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|
Current U.S.
Class: |
363/37 ;
324/509 |
Current CPC
Class: |
H02M 5/458 20130101;
G01R 31/50 20200101; G01R 31/52 20200101; G01R 31/42 20130101 |
Class at
Publication: |
363/37 ;
324/509 |
International
Class: |
G01R 31/02 20060101
G01R031/02; H02M 5/458 20060101 H02M005/458 |
Claims
1. A method, comprising: connecting or disconnecting a test
resistor in a drive, wherein the drive comprises a power converter
configured to convert AC power to DC power applied to the DC bus
and an inverter configured to convert DC power from the DC bus to
output AC power, and wherein the test resistor is connected either
between the DC bus and a ground potential or between a load of the
drive and the ground potential; measuring a voltage at a node while
the test resistor is connected or disconnected and while the drive
is coupled to an electrical system, wherein the node is between a
low side of the DC bus and a ground potential in the drive; and
determining one or more of a ground condition of the electrical
system and a ground resistance condition of the drive based on the
voltage.
2. The method of claim 1, further comprising disconnecting the test
resistor from the drive and determining the ground condition of the
electrical drive to be a solid grounded .DELTA. when the voltage is
substantially similar to a phase voltage of the drive.
3. The method of claim 1, further comprising connecting the test
resistor to the drive and determining the ground condition of the
electrical drive to be a solid grounded Y configuration when the
voltage is substantially smaller than a DC voltage on the DC
bus.
4. The method of claim 1, further comprising connecting the test
resistor to the drive and determining the ground condition of the
electrical drive to be ungrounded when the voltage is greater than
or equal to approximately one half of a DC voltage on the DC
bus.
5. The method of claim 1, further comprising connecting the test
resistor to the drive and determining the ground condition of the
electrical drive to be a high resistance ground (HRG) configuration
when the voltage is smaller than approximately one half of a DC
voltage on the DC bus.
6. The method of claim 1, further comprising: connecting the test
resistor to the drive during a test duration, wherein the test
duration occurs in regular time intervals while the drive is
operating; measuring the voltage at the node during the test
duration; and determining the ground resistance condition based on
the voltage measured during the test duration.
7. The method of claim 6, wherein determining the ground resistance
condition comprises determining one or more of a shorted HRG
resistor, an open HRG resistor, a normally operating HRG resistor,
a shorted ground resistor, an open ground resistor, and a normally
operating ground resistor.
8. The method of claim 6, wherein the test interval is
approximately 2-5 hours.
9. A drive, comprising: a power converter configured to convert AC
power to DC power; a DC bus configured to receive the DC power from
the power converter; an inverter configured to receive the DC power
from the DC bus and output AC power; a node between a low side of
the DC bus and a ground potential in the drive, wherein the node is
configured to be measured for a voltage indicative of one or more
of a grounding condition of an electrical system coupled to the
drive and a ground resistance condition of the drive; and a test
resistor coupled between the DC bus and a ground potential or
coupled between a load of the drive and the ground potential.
10. The drive of claim 9, further comprising a switch configured to
open to disconnect the test resistor from the drive and close to
connect the test resistor to the drive.
11. The drive of claim 9, further comprising a contactor configured
to open to disconnect the test resistor from the drive and close to
connect the test resistor to the drive.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional of U.S. patent application
Ser. No. 13/077,212, entitled "Ground Scheme Identification
Method," filed Mar. 31, 2011, which is herein incorporated by
reference.
BACKGROUND
[0002] The invention relates generally to the field of electrical
drives. More particularly, the invention relates to techniques for
detecting utility AC input grounding conditions for the drive.
[0003] Various power systems include power conversion systems such
as electric drives and motors which are employed to convert
electrical energy into mechanical energy. An electric drive
includes a device or group of devices which controls the torque,
speed, position, and/or performance of an electric motor. The drive
is typically connected to a power source such as a battery, a power
supply, or an AC generator, and controls the transmission of power
from the power source to the motor, which converts the electrical
power into mechanical power.
[0004] Electrical drives may be used for a wide range of industrial
applications. For example, different types of electrical systems
use electrical drives to drive power to various types of motors,
such as AC induction motors, servomotors, DC motors, etc., which
each perform different motions, such as rotary or linear motion
under torque, velocity or position control, etc. The system
configurations for such different applications and different
mechanical functions may also vary greatly. For instance, different
electrical systems may use different grounding configurations, such
as solid grounded Y, solid grounded .DELTA. (also referred to as
corner grounded), high resist ground (HRG) grounded Y, or
ungrounded, etc. The installation or configuration of an electrical
drive is generally different depending on the grounding
configuration of the system. An HRG system involves inserting a
resistance between a neutral node and the ground of the input AC
source of the system such that the system can operate under single
ground faulted condition with a small non-destructive ground fault
current.
[0005] Typically, improperly configuring an electrical drive
according to the grounding configuration of the electrical system
results in unexpected drive failure, as discussed in the Mar. 19-23
2006 IEEE APEC article, Failure Mode for AC Drives on High
Resistance Grounded Systems, by Rangarajan M. Tallam, et al. For
example, HRG faults may result in high voltage levels in bus lines
associated with the electrical drive and high voltage stresses in
electrical drive components, which may eventually result in
failures of the electrical drive or other system components.
Moreover, HRG faults are typically difficult to detect once a drive
is in operation, as the small amount of fundamental frequency
ground current is difficult to measure in the presence of high
frequency electronic noise created by the drive, especially in
larger electrical drives. It is now recognized that techniques for
reducing electrical drive configuration errors based on the
grounding configuration of the electrical system may reduce such
HRG fault conditions. The present techniques involve identifying a
HRG system and other properties of the HRG system to determine the
drive configuration.
BRIEF DESCRIPTION
[0006] The present invention relates generally to techniques for
detecting the grounding condition of an electrical system to
automatically determine a suitable electrical drive configuration.
Embodiments include systems and methods of measuring drive
voltages, and based on the measured drive voltages, determining the
grounding configuration of the electrical system in which the drive
is to be installed. Different embodiments include determining
grounding configurations using a test resistor, a switch, and/or a
contactor in the drive. Embodiments further include identifying a
ground resistance fault condition during operation of the
drive.
DRAWINGS
[0007] These and other features, aspects, and advantages of the
present invention will become better understood when the following
detailed description is read with reference to the accompanying
drawings in which like characters represent like parts throughout
the drawings, wherein:
[0008] FIG. 1 is a circuit diagram of an application of an
electrical drive system, in accordance with an embodiment of the
present techniques;
[0009] FIG. 2 is a circuit diagram of an electrical drive having a
test resistor for determining a grounding configuration of an
electrical system, in accordance with an embodiment of the present
techniques;
[0010] FIG. 3 is a flow chart summarizing a method for determining
a grounding condition of the electrical system, in accordance with
an embodiment of the present techniques;
[0011] FIG. 4 is a plot representing a voltage characteristic when
the electrical system is in a delta grounding condition, in
accordance with an embodiment of the present techniques;
[0012] FIG. 5 is a plot representing a voltage characteristic when
the electrical system is in a Y grounding condition, in accordance
with an embodiment of the present techniques;
[0013] FIG. 6 is a plot representing a voltage condition when the
electrical system is in an ungrounded condition, in accordance with
an embodiment of the present techniques;
[0014] FIG. 7 is a plot representing a voltage condition when the
electrical system is in a high resistance ground (HRG) condition,
in accordance with an embodiment of the present techniques;
[0015] FIG. 8 is a circuit diagram of an electrical drive having a
switch for determining a grounding configuration of an electrical
system, in accordance with an embodiment of the present
techniques;
[0016] FIG. 9 is a circuit diagram of an electrical drive having a
contactor for determining a grounding configuration of an
electrical system, in accordance with an embodiment of the present
techniques;
[0017] FIG. 10 is a timing diagram for identifying a ground
resistance fault of the electrical drive in an HRG system, in
accordance with an embodiment of the present techniques;
[0018] FIG. 11 is a flow chart of a method for identifying a ground
resistance fault of an electrical drive in an HRG configuration, in
accordance with an embodiment of the present techniques; and
[0019] FIG. 12 is a flow chart of a method for identifying a ground
resistance fault of an electrical drive that is not in an HRG
configuration, in accordance with an embodiment of the present
techniques.
DETAILED DESCRIPTION
[0020] The present invention relates generally to techniques for
detecting the grounding condition of an electrical system to
automatically determine a suitable electrical drive configuration.
Embodiments include systems and methods of measuring drive voltages
to determine a type of grounding configuration. Embodiments also
include identifying faults based on the high resistant grounding
condition.
[0021] Turning to the figures, FIG. 1 depicts an exemplary
application of a drive system 10 which may be used in various
electrical systems. The drive system 10, also referred to as the
drive 10, includes a converter 12 configured to receive an AC
voltage from one or more power sources 14 and to convert the AC
voltage to DC voltage applied to a DC bus 16. The drive 10 also
includes an inverter 18, which receives the DC voltage through the
DC bus 16 and converts DC voltage from the DC bus 16 to output AC
voltage at any desired frequency. A motor 20 connected to the
inverter 18 is driven by the AC voltage which is supplied to the
motor by the inverter 18. Depending on the electrical system in
which the drive 10 is operating, different types of voltage may be
needed to drive the motor 20. In one embodiment, the electrical
drive system 10 also includes bus capacitors 22 configured to
filter harmonics associated with the DC bus 16 and/or common mode
capacitors (22a, 22b) used to filter the electrical switching noise
generated by the drive system 10 through parasitic capacitances to
ground.
[0022] In some embodiments, the converter 12 includes a 3.times.2
arrangement of thyristors 24 arranged in an integrated diode bridge
configuration. The converter 12 may also be replaced with an
arrangement of diodes, a rectifier bridge, or active control pulse
width modulating (PWM) rectifiers which may be consistent with the
3.times.2 array of thyristors 24. The converter 12, also referred
to as an rectifier 12, rectifies the incoming AC voltage to DC
voltage in one direction to output a discretized output voltage
waveform through the DC bus 16. The inverter 18 includes a
3.times.2 array of transistors 26 and power diodes 28, wherein each
diode 28 is configured antiparallel to the respective transistor
26. The discretized output voltage from the DC bus 16 is switched
by the transistors 26 which are configured to switch at a certain
switching frequency to output voltages to the motor 20. While the
illustrated embodiment depicts three-phase voltages (e.g., v.sub.a,
v.sub.b, v.sub.c), it should be noted that in different
embodiments, the drive 10 may be suitable for inputting and
outputting voltages of different phases (e.g., single phase
voltage, two-phase voltages). The configurations of the converter
12 and inverter 18 may also be different, depending on the
operating voltage(s) of the drive 10.
[0023] Traditionally, drive systems are used in a wide range of
industrial applications, and the electrical systems for such
different applications often use different grounding
configurations, such as solid grounded Y, solid corner grounded,
HRG grounded Y, or ungrounded, etc. Moreover, drive systems are
used globally, and different countries may have different
electrical requirements and standards. Due to the various
electrical requirements and standards of different countries, the
electrical systems used in these countries may have different
grounding configurations. Accordingly, drive systems are typically
configured to be suitable for a wide range of industrial
applications and suitable for global use. However, the installation
or configuration of a particular drive system is generally
dependent on the grounding configuration used by the electrical
systems in which the drive system is utilized. In the embodiment
illustrated in FIG. 1, the drive system 10 includes multiple
components such as jumpers 30, 32 and capacitors 34 which may be
used in the drive 10 or removed from the drive 10, depending on the
grounding configuration of the electrical system. The capacitors 34
may be configured to minimize drive electromagnetic interference to
the grid generated by the drive. The jumpers 30, 32 represent any
type of switching device or connecting device that may be switched
closed or attached to a location in the drive 10, thereby grounding
the drive 10 at the location, or switched open or detached from the
drive 10, thereby not grounding the drive 10 at the location. For
example, the jumper 30 may be removed from the drive 10 to ground
the drive via the jumper 32. Alternatively, the jumper 32 may be
removed from the drive 10 to ground the drive 10 via jumper 30.
Both jumpers 30 and 32 are typically required to be removed under
HRG systems to prevent drive components failures under grounded
fault condition.
[0024] An improperly grounded drive may result in undesirable
effects such as high resistance ground (HRG) faults. Such HRG
faults are generally difficult to detect. HRG faults typically
generate a relatively small amount of ground current which may be
difficult to measure, especially in larger drives. However, the
generated grounded current may result in high voltage levels in bus
lines (e.g., DC bus 16) and high voltage stresses in the electrical
drive components (e.g., the transistors 26) due to interaction of
inverter [18] making and breaking the current into ground, which
may eventually result in failures of the drive or failures in other
components of the electrical system in which the drive is
configured.
[0025] Embodiments of the present invention include systems and
methods for determining a grounding condition (e.g., solid grounded
Y, solid grounded .DELTA., HRG grounded Y, ungrounded) of an
electrical system. In some embodiments, the identification of the
system grounding configuration is indicated to a user. Further,
based on the indicated grounding configuration, the user may remove
various components (e.g., capacitors, jumpers) and/or configure an
associated drive (e.g., drive 10) to be suitably grounded in the
associated electrical system, thereby avoiding or decreasing the
likelihood of HRG faults. It should be noted that, while the
present techniques for detecting a grounding condition are
described in connection with a motor drive (e.g., drive 10), the
techniques are not limited to such applications. Rather, the same
methodology may be utilized for determining grounding conditions in
a wide range of circuit applications, particularly those in which a
DC bus is used in conjunction with AC/DC rectification, DC/AC
conversion, or conversion circuitry in general.
[0026] Different embodiments for determining a grounding condition
of an electrical system are described below. The different
embodiments include measuring drive voltages at different locations
of the base drive 10 in accordance with present embodiments. It
should be noted that the references to various embodiments of
drives 10a, 10b, and 10c (as will be discussed in FIGS. 2, 8, and
9) generally include components of the base drive 10 (e.g., the
converter 12, the voltage source 14, the DC bus 16, and the
inverter 18). As will be discussed, different embodiments (e.g.,
drives 10a, 10b, and 10c) involve incorporating a test resistor at
different locations of the base drive 10, using different elements
(e.g., switch, contactor) to incorporate the test resistor, and/or
measuring drive voltages from different locations of the base drive
10. Furthermore, as used herein, a drive 10 generally refers to any
or all of the embodiments (e.g., drives 10a, 10b, and 10c) of the
present techniques.
[0027] One embodiment for determining a grounding configuration of
an electrical system using a test resistor with a drive is
illustrated in the circuit diagram of FIG. 2. As illustrated in
FIG. 2, a drive 10a includes similar components to the base drive
10 discussed in FIG. 1, including the converter 12, the voltage
source 14, the DC bus 16, and the inverter 18. Additionally, as
illustrated in FIG. 2, the drive 10a is configured to supply AC
power to a load 44. In other embodiments, the drive 10a may supply
power to any type of load 44 or motor 20 (as in FIG. 1), or some
combination of the motor 20 and the load 44, depending on the
application for which the drive 10a is used.
[0028] In some embodiments, the grounding configuration of the
electrical system may be tested by including a test resistor
(R.sub.test) 46 on the DC bus 16, between the converter 12 and the
inverter 18. The test resistor 46 is coupled to a test switch 48
which may be switched closed to enable current flow through the
test resistor 46 from the other circuitry of the drive 10a or
switched open to prevent current flow through the test resistor 46.
To determine the grounding configuration of the system, the
neutral-to-ground voltage V.sub.ng is measured at node 42 while the
test resistor 46 is switched open and switched closed. The node 42
is between a low side of the DC bus 16 and a ground potential 49.
The measured V.sub.ng for the system with the test resistor 46 in
opened and closed configurations is analyzed to determine the
grounding configuration of the electrical system. For example, in
one or more embodiments, the measured V.sub.ng may be analyzed by a
processor 50 which determines various grounding conditions based on
the measured V.sub.ng. The resistance of the test resistor 46 is
typically larger than the resistance of the effective resistance of
the ground (R.sub.gnd) 52 of the drive 10a and small enough to
enable a path to ground such that the voltage at node 42 is
measurable. For example, for HRG systems, R.sub.gnd 52 may be the
effective neutral to ground resistor and may have a resistance of
approximately 27.OMEGA. to approximately 277.OMEGA. for a system
operating at 480V. For non-HRG systems, R.sub.gnd 52 may be an
effective resistance representing the resistance of wires in the
grounding system, and may generally be relatively low. For an
ungrounded system, R.sub.gnd 52 may generally be relatively high.
For example, in some embodiments, the resistance of the test
resistor 46 may be greater than 277.OMEGA. (e.g., approximately
600.OMEGA. to approximately 1000.OMEGA.) for a 480V input voltage
system. Such high resistances may reduce the likelihood of
generating a HRG ground fault condition when the test resistor 46
is switched into the system. The different embodiments and
different systems, the test resistance R.sub.test may be different
and may depend on the voltages of different systems.
[0029] One embodiment of a process 60 for determining the system
grounding condition using the drive 10a of FIG. 2 is illustrated in
the flow chart of FIG. 3. Certain steps or procedures of the
process 60 are represented by blocks in the flow chart of FIG. 3.
Additionally, corresponding voltage responses measured at the node
42 using the process 60 of FIG. 3 are provided in FIGS. 4-7. As
such, FIGS. 3-7 will be explained together below.
[0030] To test the grounding configuration of the electrical
system, the drive 10a is powered (e.g., at the voltage source 14)
in a manner such that the inverter 18 is not switching. As
illustrated in FIG. 3, the process 60 begins with opening the test
switch 48, as represented by block 62. When the test switch 48 is
open, the neutral-to-ground voltage V.sub.ng is measured at node
42, as represented by block 64. The measured V.sub.ng represents
the fundamental voltage (V.sub.fund) of the drive 10a. As
represented by block 66, the process 60 determines whether the
fundamental frequency of the fundamental voltage V.sub.fund is
approximately equal to the frequency of the phase voltage
(V.sub.phase) of the power supply 14. For example, in several
countries (e.g., in North America), the frequency component of the
phase voltage will be approximately 60 Hz. In some other countries
(e.g., in Europe), the frequency of the phase voltage will be
approximately 50 Hz. In some embodiments, a processor 50 performs a
comparison, as represented by block 66. When the fundamental
voltage V.sub.fund is substantially similar to the phase voltage
V.sub.phase (e.g., greater than approximately 0.9*V.sub.phase), the
electrical system of the drive 10a is determined to be in a solid
grounded .DELTA. (also referred to as corner grounded)
configuration, as represented by block 68. The processor 50
includes software suitable for comparing the fundamental voltage
V.sub.fund to an appropriate V.sub.phase (e.g., depending on the
country in which the drive 10a is being installed and/or depending
on an input or measured phase voltage). The measured V.sub.ng for a
solid grounded .DELTA. configuration is illustrated in the plot 84
of FIG. 4. The plot 84 includes the V.sub.ng plotted with respect
to time 86 and voltage 88. As illustrated in FIG. 4, V.sub.ng is
relatively high (e.g., between approximately -331V to 331V) and
similar to the voltage on the DC bus 16 (e.g., approximately 662 V
is the DC bus voltage used in this simulation) for 480V input
system voltage, indicating a significantly high frequency component
that is the same as that of the phase voltage (e.g., 60 Hz).
[0031] If the process 60 determines that V.sub.fund is not greater
than approximately 0.9*V.sub.phase, the system is determined not to
be .DELTA. grounded, and the process 60 then proceeds to block 70,
which represents closing the test switch 48 for approximately 50 ms
to approximately 1 s, thereby including the test resistor 46 in the
drive system 10a during that time. The inclusion of the test
resistor 46 results in a DC bias of V.sub.ng. The DC bias of
V.sub.ng, represented as V.sub.ngdc, is then measured, as
represented by block 72. Further, the process 60 determines whether
the DC bias V.sub.ngdc is significantly smaller than the voltage on
the DC bus 16 (V.sub.dc) of the drive 10a, as represented by block
74. For example, in one embodiment, the procedure represented by
block 74 includes the processor 50 comparing V.sub.ngdc to
approximately 0.03*V.sub.dc. If V.sub.ngdc is smaller than
0.03*V.sub.dc, the processor 50 determines, as represented by block
76, that the electrical system of the drive 10a is in a solid
grounded Y configuration. One example of a measured V.sub.ng for a
solid grounded Y configuration is illustrated in the plot 90 of
FIG. 5. The plot 90 includes the V.sub.ng plotted with respect to
time 86 and voltage 88. As illustrated in FIG. 5, V.sub.ng is
relatively low (e.g., at approximately -50V to 50V), indicating a
significantly low frequency component of the V.sub.fund that is the
same as that of the phase voltage V.sub.phase.
[0032] If V.sub.ngdc is determined to be larger than 0.03*V.sub.dc
in block 74, the processor 50 determines, as represented by block
78, whether the DC bias V.sub.ngdc is larger than approximately
half of the DC bus voltage V.sub.dc (e.g., 1/2 V.sub.dc is 331V).
Such a large DC bias generally indicates that the system is
floating and not connected to ground. In some embodiments, the
processor 50 determines, as represented by block 78, whether
V.sub.ngdc is greater than 0.47*V.sub.dc (e.g., approximately half
the DC bus voltage V.sub.dc). If this condition is met, the
processor 50 determines, as indicated by block 80, that the system
of the drive 10a is in an ungrounded configuration. For example,
the measured V.sub.ng for an ungrounded configuration is
illustrated in the plot 92 of FIG. 6. Because the system is not
grounded, the V.sub.ng of the drive 10a has no frequency component
and appears in the plot 92 as a flat voltage line at approximately
340V, which is higher than 1/2 V.sub.dc at 331V.
[0033] In some embodiments, if the V.sub.ngdc is determined to be
smaller than 0.47*V.sub.dc in block 78, the processor 50
determines, as represented by block 82, that the system of the
drive 10a is in a HRG grounded configuration. The typical V.sub.ng
voltage range for an HRG grounded system falls approximately
between the limits below:
1 2 V dc 27 R test + 27 < V ngdc < 1 2 V dc 277 R test + 277
equation ( 1 ) ##EQU00001##
where R.sub.test is approximately between 277.OMEGA. to 600.OMEGA.,
as previously discussed. Selecting an R.sub.test of 600.OMEGA., and
using a V.sub.dc of 662V, the voltage range in a HRG grounded
configuration would be approximately 28.5V to 180V. A plot 94
illustrating the V.sub.ngdc of the drive 10a when the system is HRG
grounded is provided in FIG. 7, where the voltage is between
approximately 30V to 180V and the grounding current is lower than 1
ampere, which is within the typical limits for an HRG system. In
some embodiments, a typical grounding resistance for a 480V HRG
system may be approximately 27.OMEGA. to approximately 277.OMEGA.
and a typical grounding fault current range may be approximately 10
mA to 1 A.
[0034] In other embodiments, the process 60 used to determine a
grounding condition of the electrical system of the drive system
10a may also be used with different configurations of drives 10.
For example, as illustrated in FIG. 8, the drive system 10b may be
configured with the test resistor 46 and test switch 48 between the
output phase at node 96 and a ground potential 49. Yet another
embodiment for determining a grounding condition is illustrated in
FIG. 9, where drive system 10c is configured with the test resistor
46 and a contactor 100. In some embodiments, the contactor 100 is
employed to substantially isolate the test resistor 46 and other
testing circuitry when the system 10a is not being tested and the
contactor 100 may not necessarily rely on a switching voltage to
isolate the circuit (e.g., from a traditional switch 48, as in FIG.
8). To prevent the inverter 18 from switching during the process 60
in either of the embodiments in FIGS. 8 and 9, either all the lower
transistors 26 or all of the upper transistors 26 may be shorted
(e.g., by including a bus line between the DC bus 16 and the node
96).
[0035] In addition to determining the grounding configuration of
the electrical system in which a drive 10 is installed, the present
techniques are also applicable for identifying ground resistance
faults. Ground resistance faults may refer to any fault associated
with the ground resistor (R.sub.gnd) 52. For example, if the
temperature of R.sub.gnd 52 becomes too hot during operation of the
drive 10, R.sub.gnd 52 may open, such that the drive is no longer
grounded at the source 14. Furthermore, R.sub.gnd 52 may be
shorted, or may otherwise not be properly connected to the neutral
of the power source 14. One or more embodiments involve determining
the status of the HRG grounding resistor R.sub.gnd 52, such as
whether R.sub.gnd 52 is open or shorted. In some embodiments,
determining the status of R.sub.gnd 52 may be performed before the
drive begins to operate or after the drive begins to operate.
[0036] In some embodiments, the test resistor 46 in the drive 10
(e.g., as illustrated in drives 10a-c in FIGS. 2, 8, and 9) is used
to periodically verify that R.sub.gnd 52 is properly connected
between ground and the neutral of the power source 14 of the drive
10. In some embodiments, the test resistor 46 is used to determine
if or when R.sub.gnd 52 is in fault. For example, in some
embodiments, during the operation of the drive 10, the test
resistor 46 is switched closed for a test duration (e.g., between
approximately 0.05 s to 1 s) in regular time intervals (e.g.,
approximately every 3-4 hours). By testing the drive voltage at
regular intervals during operation of the drive, faults which occur
during drive operation may be detected. FIG. 10 illustrates a
timing diagram 102 for identifying a ground resistance fault. At
every test interval (.DELTA.t.sub.interval) 104, the test switch 48
is closed for the test duration (.DELTA.t.sub.duration) 106, and
V.sub.ng is measured to analyze the ground resistance condition and
determine whether a ground resistance fault has occurred.
[0037] Different embodiments involve different processes for
analyzing V.sub.ng, depending on the grounding condition of the
system in which the drive is installed. A process for identifying
ground resistance faults for drives installed in an HRG grounded
system is provided in FIG. 11, and a process for identifying ground
resistance faults for drives installed in systems having different
grounding configurations (e.g., not HRG) is provided in FIG. 12.
Each of the processes described in FIGS. 11 and 12 may occur
substantially during and/or immediately after the closing of the
test switch 48. Furthermore, either of the processes described with
respect to FIGS. 11 and 12 may be performed by a processor 50, for
example, or by any other suitable processing unit capable of
analyzing V.sub.ng to determine ground resistance faults in various
types of grounding configurations of the electrical system in which
the drive 10 is operating.
[0038] Beginning first with FIG. 11, the process 110 involves
measuring the neutral-to-ground voltage V.sub.ng (e.g., at node 42
in FIGS. 2, 8, and 9), as represented by block 112, and filtering
disturbances such as switching ripples from the V.sub.ng, as
represented by block 114. The V.sub.ng signal is also bandpass
filtered to remove the frequency of the inverter 18, resulting in
the V.sub.ngo, as represented by block 116. The process 110 then
involves calculating k=V.sub.ngo/V.sub.o, as represented by block
118, where V.sub.o represents the output voltage of the drive 10.
As represented by block 120, when k is calculated, the process 110
determines that if k is approximately equal to zero, approximately
equal to 1, or approximately equal to the relationship of equation
(2) below:
k .apprxeq. R HRG R test + R HRG equation ( 2 ) ##EQU00002##
[0039] If k is approximately equal to zero, the process 110
determines that the HRG resistor is shorted, as represented by
block 122. If k is approximately equal to 1, the process 110
determines that the HRG resistor is open, as represented by block
124. Furthermore, if the process 110 determines that the
relationship in equation (2) is met, the HRG resistor is determined
to be operating normally, and no HRG fault is found to have
occurred, as represented by block 126.
[0040] FIG. 12 illustrates a process 130 suitable for identifying
ground resistance faults for drives 10 installed in systems having
other (not HRG) grounding configurations. The process 130 involves
measuring the neutral-to-ground voltage V.sub.ng (e.g., at node 42
in FIGS. 2, 8, and 9), as represented by block 132, and filtering
disturbances such as switching ripples from the V.sub.ng, as
represented by block 134. The DC bias (V.sub.ngdc) of the
neutral-to-ground voltage V.sub.ng is then calculated, as
represented by block 136. The process 130 may determine whether the
V.sub.ngdc meets various conditions, as represented by block 138.
If V.sub.ngdc meets the condition in equation (3) below, the
process 130 proceeds to block 140, which represents a determination
that the R.sub.gnd 52 is shorted.
|V.sub.ngdc|<0.03V.sub.dc equation (3)
If V.sub.ngdc meets the condition in equation (4) below, the
process 130 determines that the R.sub.gnd 52 is open, as
represented by block 144.
|V.sub.ngdc|>0.47V.sub.dc equation (4)
Alternatively, if neither of the two conditions represented in
equations (3) or (4) are met, the process 130 determines that
R.sub.gnd 52 is operating normally, as represented by block 142,
and that no ground resistance fault has occurred.
[0041] Therefore, in one or more embodiments, configuring a drive
10 with a test resistor 46 and analyzing the V.sub.ng under various
conditions (e.g., opening or closing a switch 48 or contactor 100,
according to the process 60 of FIG. 3) provides indication of the
grounding configuration of the electrical system in which the drive
10 is to be installed. Furthermore, during operation of the drive
10, the same test resistor 46 may be used in the drive 10, and
V.sub.ng may be measured to provide indication of a ground
resistance condition (according to the processes 110 and 130 of
FIGS. 11 and 12).
[0042] In one or more embodiments, the determined grounding
configuration and/or ground resistance conditions are indicated or
communicated to a user of the drive 10. The grounding configuration
indication may also include instructions on how to properly
configure the drive 10 in the electrical system. For example, an
output of a ground identification test may instruct a user on how
to configure the drive 10 (e.g., jumpers 30, 32 and capacitors 34,
22a, 22b may typically be removed when installing a drive 10 in an
HRG system). In some embodiments, properly removing certain
components may prevent high voltage stresses and/or component
failures from occurring in HRG system.
[0043] It should be noted that though various reference values,
such as 0.9*V.sub.phase, 0.03*V.sub.dc, and 0.47*V.sub.dc are
provided for determining the grounding configuration of a system,
such reference values are only approximate and may be adjusted
based on different tolerances in different drives 10 and/or
systems. Moreover, as previously mentioned, the resistance values
give (e.g., for R.sub.gnd, R.sub.test, etc.) are also approximate
and may vary depending on the drive 10 and/or the system.
[0044] While only certain features of the invention have been
illustrated and described herein, many modifications and changes
will occur to those skilled in the art. It is, therefore, to be
understood that the appended claims are intended to cover all such
modifications and changes as fall within the true spirit of the
invention.
* * * * *