SYSTEM FOR MEASURING SOFT STARTER CURRENT AND METHOD OF
MAKING SAME
BACKGROUND OF THE INVENTION
[OOOl] Embodiments of the invention rclate gencrally to alternating current (AC)
motors and, more particularly, to a system and method for measuring current flowing
through a motor soft starter.
[0002] Motor soft starters are devices that control transmission of voltage and
current from an AC power source to an induction motor. Soft starters are configured to
limit the transient voltages and current to the induction motor during start-up, resulting
in a "soft" motor starting. In operation, power from the AC source is passed through
switching devices in the soft starter, such as a pair of anti-parallel solid-state switches in
the form of thyristors or silicon controlled rectifiers (SCRs), to control the current flow
and, in turn, the terminal voltages of the induction motor.
[0003] In general, the soft starter temporarily reduces load and torque in a powertrain
of the motor during startup. This reduction allows for reduced stresses on the motor and
electrical network, which increases the life of the system. The soft starter or motor
drive allows for reducing the voltage or current input to the motor via selective control
of the thyristors. A failure of one or more thyristors in the soft starter may lead to
system inoperability or to elimination of the soft starting technique for extending the life
of the motor.
[0004] Detection devices have been designed that generate feedback regarding the
amount of current flowing through the soft starter. The feedback may be monitored to
determine the power dissipation through the soft starter and may be used to calculate the
temperature of the soft starter for heat regulation. A common industrial practice is to
measure current using the same principles as a transformer. A magnetic field is induced
around a conductor as current is passed through the conductor. This magnetic field may
be induced into a magnetic coil looped around the conductor. This method is similar to
an air core transformer and is commonly referred to as a current transformer. The
amount of magnetically induced current into the coil is dependent on the number of coil
loops and the amount of signal current desired. The current signal, therefore, should be
proportional to the actual current in the conductor of interest. A scale is developed to
read the coupled current signal value in the conductor as an actual current signal.
[0005] The output of the current transformer may be used to sense an on-state
condition in the soft starter by sensing a high current passing through the conductor, for
example. Sensing a high current through the soft starter includes sensing a wide range
of currcnt that may pass through the conductor. Often, the sensed current is converted
from an analog signal to a digital signal. Sensing and converting such a wide range of
current to a digital signal results in a large step size between each digital value. Such a
coarse digital step size scale is often adequate to estimate the power flowing through the
soft starter. However, it may be desirable to sense the currents flowing through
thyristors of the soft starter both in the on state as well as in the off state to more
accurately measure the operational status of the soft starter. In this case, the coarse
digital step size of the scale set up for wide-range current detection is often too large to
provide reliable accurate information for currents flowing through off-state thyristors.
[0006] It would therefore be desirable to have a system for more accurately sensing
the current flowing through a soft starter.
BRIEF DESCRIPTION OF THE INVENTION
[0007] According to one aspect of the invention, a current monitoring system
comprises a controller and a current transfer device that includes a first thyristor and a
first conductor coupled to the first thyristor and configured to convey a first current
flowing through the first thyristor, wherein the first current comprises current flowing
through the first thyristor when the first thyristor is in an off state. The system also
comprises a first current sensor configured to sense the first current and a first current
measurement circuit coupled to the first current sensor and coupleable to the controller
and configured to output a first output value to the controller representative of the first
current flowing through the first thyristor. The controller is configured to determine an
impending inoperability of the first thyristor based on the first current and alert a user if
the first current indicates the impending inoperability.
[0008] According to another aspect of the invention, a current monitoring system
comprises an analog-to-digital conversion device, a current transfer device comprising a
pair of thyristors coupled together in an anti-parallel arrangement, and a first conductor
coupled to a first thyristor of the pair of thyristors and configured to convey a first
current flowing through the first thyristor. The system also comprises a second
conductor coupled to a second thyristor of the pair of thyristors and configured to
convey a second current flowing through the second thyristor and a third conductor
coupled to the first and second conductors and configured to convey the first and second
currents. A first current sensor is configured to sense the first current, a first current
measurement circuit coupled to the first current sensor is configured to output a first
output voltage based on the first current, and a first turn-off circuit is coupled to the
analog-to-digital conversion device and to the first current measurement circuit. The
first turn-off circuit is configured to couple the first output voltage to the analog-todigital
conversion device if a voltage across the first thyristor is above a threshold and
decouple the first output voltage from the analog-to-digital conversion device if the
voltage across the first thyristor is below the threshold. The analog-to-digital
conversion device is configured to obtain the first output voltage from the first current
measurement circuit, determine an operability of the first thyristor based on the first
output voltage, and alert a user if the first thyristor is operating outside of a
predetermined status.
[0009] According to yet another aspect of the invention, a method of manufacturing
a current-to-voltage conversion system comprises coupling a current transfer device to a
first current measurement circuit via a first current sensor, wherein the current transfer
device comprises a first thyristor and a first conductor coupled to the first thyristor and
configured to convey a first current flowing through the first thyristor. The first current
comprises current flowing through the first thyristor when the first thyristor is in an off
state. The method also comprises coupling a controller to the first current measurement
circuit configuring the first current measurement circuit to output a first output value to
the controller representative of the first current flowing through the first thyristor, and
configuring the controller to determine an impending inoperability of the first thyristor
based on the first current and alert a user if the first current indicates the impending
inoperability.
[0010] Various other features and advantages of the present invention will be made
apparent from the following detailed description and the drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] The drawings illustrate preferred embodiments presently contemplated for
carrying out the invention.
[0012] In the drawings:
[0013] FIG. 1 is a block diagram of a soft starter current monitoring system
according to an embodiment of the invention.
[0014] FIG. 2 is a schematic illustration of a current measurement circuit according
to an embodiment of the invention.
[0015] FIG. 3 is a schematic illustration of an inverterlgain circuit according to an
embodiment of the invention.
[0016] FIG. 4 is a schematic illustration of a voltage drop out circuit according to an
embodiment of the invention.
DETAILED DESCEUPTION
[0017] FIG. 1 illustrates a block diagram of a soft starter current monitoring system
100 according to an embodiment of the invention. Monitoring system 100 includes a
soft starter 102 including a pair of thyristors 104, 106 arranged in an anti- or reverseparallel
arrangement. That is, the anode 108 and cathode 110 of thyristor 104 are
respectively coupled to the cathode 112 and anode 114 of thyristor 106. A pair of
conductors 116, 11 8 of soft starter 102 are coupled to a pair of pin conductors 120, 122
to allow current to be supplied to and to flow through pins 124, 126 of soft starter 102.
[0018] A current sensing device 128 positioned to sense the current flowing through
soft starter 102 in a full SCR soft starter conduction mode is coupled to a current
measurement circuit 130 designed to measure current flowing through soft starter 102
when either thyristor 104 or thyristor 106 is in an on state and conducting current
therethrough. In one embodiment, current sensing device 128 is a current transformer
inductively coupled to pin conductor 122 leading to or from pin 126. Embodiments of
the invention, however, contemplate the coupling of current sensing device 128 to pin
conductor 120 or to any conductor carrying the current flowing through soft starter 102.
Current sensing device 128 is configured to measure a high current flowing through soft
starter 102 and thus includes the ability to sense a wide range of current. The measured
or sensed current is converted from an analog signal to a digital signal via an AID
converter 132. Sensing and converting such a wide range of current to a digital signal
results in a large or coarse step size between each digital value that is not sensitive
enough to detect current flowing through an off-state thyristor of soft starter 102.
[0019] Accordingly, embodiments of the invention include a current sensing device
134 coupled to an off-state current measurement circuit 136 configured to measure offstate
current flowing through thyristor 104 and a current sensing device 138 coupled to
an off-state current measurement circuit 140 configured to measure off-state current
flowing through thyristor 106. Off-state current measurement circuits 136, 140 are
scaled and configured to generate an output voltage representative of the current
flowing through thyristors 104, 106 in their off states. Such off-state currents are very
small relative to the amount of current able to flow through thyristors 104, 106 in their
on states.
[0020] Referring to FIG. 2, a schematic illustration of a current measurement circuit
200 is shown according to an embodiment of the invention. Current measurement
circuit 200 includes an embodiment suitable for circuits 130, 136, or 140 of FIG. 1.
Circuit 200 includes a coil 202 looped around a conductor 204 (e.g., conductor 116,
118, or 122 of FIG. 1). In one ernbodimcnt, coil 202 has multiple turns looped around
conductor 204. Accordingly, a current from soft starter 102 or one of the thyristors 104,
106 in its off state passing through coil 202 along conductor 204 inductively generates a
current in coil 202 that is converted to a voltage via current-to-voltage device 206,
which is a resistor as shown. The current induced in coil 202 and, hence, the voltage
generated across resistor 206 is proportional to the current passing through soft starter
102 or one of the thyristors 104, 106 in its off state along conductor 204. The
proportional voltage is available at a node 208 coupled to a scaling circuit 210 and to
any other additional scaling circuits (not shown) coupled thereto.
[0021] Scaling circuit 210 includes an amplifier 212 having a pair of power
terminals 214,2 16 electrically coupled to a positive DC voltage bus 2 18 and to a ground
bus 220, respectively. A single, positive DC power supply 222 is coupled between
positive DC voltage bus 218 and ground bus 220 and provides single-source power to
energize amplifier 212. A positive voltage input 224 of amplifier 212 is configured to
receive a first DC offset voltage 226 designed, in one embodiment, based on a
combination (e.g., multiplication) of the median of a desired output voltage range of
scaling circuit 210 with an inverse of the scaling factor of scaling circuit 210. The
scaling factor of scaling circuit 210 may be determined by a pair of resistors 228, 230
coupled to node 208 and between a negative voltage input 232 of amplifier 212 and a
scaled voltage output 234 of amplifier 212. Thus, the scaling factor may be tailored to
measure the wide range of currents configured to flow through soft starter 102 in its
operating state by current measurement circuit 130 or to measure the narrower range of
leakage currents flowing through off-state thyristors 104, 106 as needed by current
measurement circuits 136, 140. A capacitor 236 is also coupled to negative voltage
input 232 and helps provide EMC filtering of the voltage at negative voltage input 232.
Off-state current measurement circuit 136 or 140 is coupled to an analog-to-digital
converter channel 238 of A/D converter 132 according to an embodiment of the
invention.
[0022] Referring again to FIG. 1, the scaling factor of current measurement circuits
136, 140 will cause their output voltage to quickly rise to the rail voltage when the
respective thyristor 104, 106 is conducting current in an on state. That is, because any
off-state currents flowing through thyristors 104, 106 is much less than currents flowing
through thyristors 104, 106 during their on states, off-state current measurement circuits
136, 140 generally become quickly saturated when their respective thyristors 104, 106
begin conducting in their on states. Since the rail voltage is not indicative of a leakage
current of the thyristor 104, 106 in an off state, a first current measurement turn off
circuit 142 is coupled to receive both the output voltage from off-state current
measurement circuit 136 and a current measurement from a current sensing device 144
coupled to conductor 116. A second current measurement turn off circuit 146 is
coupled to receive both the output voltage from off-state current measurement circuit
140 and a current measurement from a current sensing device 148 coupled to conductor
118. Current sensing devices 144, 148 may be, for example, current transformers. First
and second current measurement turn off circuits 142, 146 are configured to cause the
output voltage from off-state current measurement circuits 136, 140 to be delivered to
A/D converter 132 when the respective thyristor 104 or 106 is in an off state. That is,
when either thyristor 104, 106 is in a reverse blocking mode where a higher voltage is
applied to its cathode 110, 112 than to its anode 108, 114, a small amount of reversebias
leakage current flows through the device. An anode-cathode current and a gate
leakage current contribute to the current flowing through the device in its off state. This
reverse-bias leakage current is measured by off-state current measurement circuits 136,
140 and delivered to A/D converter 132.
[0023] To detect thyristor off states, first and second current measurement turn off
circuits 142, 146 include an inverter and gain circuit 150 coupled to current sensing
devices 144, 148 and to a voltage drop out circuit 152, which is also coupled to
respective off-state current measurement circuits 136, 140 and to AID converter 132.
[0024] FIGS. 3 and 4 respectively illustrate exemplary embodiments for inverter and
gain circuit 150 and voltage drop out circuit 152 of FIG. 1 according to an embodiment
of the invention. Inverter and gain circuit 150 receives a voltage from the line voltage
and inverts the voltage in an inverter stage 300. In this manner, negative voltages from
current sensing device 144 or 148 are inverted to positive voltages and boosted in a gain
stage 302 of inverter and gain circuit 150. An output voltage, volt-amp, from gain stage
302 is input into a comparator stage 400 of voltage drop out circuit 152 as illustrated in
FIG. 4. A relay 402 driven by the result of comparator stage 400 toggles a connection
of A/D converter 132 to off-state current measurement circuit 136 or 140 depending on
the result. As illustrated in this embodiment, if the value of volt - amp is below a
predetermined threshold, relay 402 decouples A/D converter 132 from off-state current
measurement circuit 136 or 140 as illustrated. The value of volt-amp will typically be
below the predetermined threshold when the respective thyristor 104, 106 is in an onstate.
Alternatively, when the respective thyristor 104, 106 is in an off-state, the value
of volt-amp will typically be above the predetermined threshold, and relay 402 will
couple AID converter 132 to off-state current measurement circuit 136 or 140.
[0025] Referring back to FIG. 1, a controller 154 is shown coupled to A/D converter
132. It is contemplated, however, that controller 154 may incorporate an A/D converter
and that a separate A/D converter as shown may not be incorporated in some
embodiments. Controller 154 is configured to receive the digitally-converted current
measurements of current measurementfturn off circuits 142, 146 from A/D converter
132. The off-state reverse bias leakage currents measured by circuits 142, 146 allow
controller 154 to compare the measured values with expected or rated values spccified
for the thyristors 104, 106 to determine an operational status thereof. Controller 154
may compare the measured values with values obtained from a lookup table stored in
the controller or in a separate database 156. If the leakage current or average leakage
current flowing through thyristors 104, 106 falls within the values or range of values
allowed for, controller 154 may indicate that the measured thyristor 104, 106 is in an
expected working order. However, if the leakage current or average leakage current
flowing through thyristors 104, 106 falls outside of the values or range of values
allowed for, controller 154 may indicate that the measured thyristor 104, 106 is in an
abnormal working state and may indicate a possible impending failure of the affected
thyristor. In this case, preventative maintenance of soft starter 102 may be
accomplished to ensure that it remains in working order. For example, the affected
thyristor may be replaced with a replacement thyristor known to be good. In an
embodiment of the invention, an average DC current during the off state or the voltage
notch during firing of soft starter 102 taken over a number of cycles can be determined.
For example, the average DC current taken over ten cycles may be used.
[0026] In addition to checking the measured leakage current against expected values,
controller 154 may use the measured leakage current together with the measured current
on pin conductor 122 to calculate a more-accurate power dissipation through soft starter
102 than using the measured current on pin conductor 122 alone. That is, given the
difference in the magnitude of the currents on conductors 116, 118 when one thyristor
(e.g., thyristor 104) is in an on state and when the other thyristor (e.g., thyristor 106) is
in an off state, the scale of the measured current on pin conductor 122 may mask the
leakage current through the off-state thyristor (e.g., thyristor 106) and may thus
inaccurately represent the total power dissipated by soft starter 102. However, using the
measured currents from both pin conductor 122 and the off-state thyristor (e.g., thyristor
106) allows the power dissipation through soft starter 102 to be more accurately
represented such that a temperature of soft starter 102 may be determined or calculated
by controller 154 to determine whether the temperature is outside of expected or rated
temperature values of soft starter 102 in an operating mode. If the calculated
temperature or an average temperature is outside of the values or range of values
allowed for, controller 154 may indicate that soft starter 102 is in an abnormal working
state and may indicate a failure mode of soft starter 102 or may indicate that a possible
failure of soft starter 102 is impending. In addition, controller 154 may provide the
power dissipation andlor calculated temperature of soft starter 102 in its working state to
assist in the determination of an appropriate heat sink to handle the heat transfer
therefrom. In an embodiment of the invention, an average soft starter power dissipation
may be calculated based on a sum of the averages of soft starter off state power and soft
starter on state power.
[0027] Therefore, according to one embodiment of the invention, a current
monitoring system comprises a controller and a current transfer device that includes a
first thyristor and a first conductor coupled to the first thyristor and configured to
convey a first current flowing through the first thyristor, wherein the first current
comprises current flowing through the first thyristor when the first thyristor is in an off
state. The system also comprises a first current sensor configured to sense the first
current and a first current measurement circuit coupled to the first current sensor and
coupleable to the controller and configured to output a first output value to the
controller representative of the first current flowing through the first thyristor. The
controller is configured to determine an impending inoperability of the first thyristor
based on the first current and alert a user if the first current indicates the impending
inoperability.
[0028] According to another embodiment of the invention, a current monitoring
system comprises an analog-to-digital conversion device, a current transfer device
comprising a pair of thyristors coupled together in an anti-parallel arrangement, and a
first conductor coupled to a first thyristor of the pair of thyristors and configured to
convey a first current flowing through the first thyristor. The system also comprises a
second conductor coupled to a second thyristor of the pair of thyristors and configured
to convey a second current flowing through the second thyristor and a third conductor
coupled to the first and second conductors and configured to convey the first and second
currents. A first current sensor is configured to sense the first current, a first current
measurement circuit coupled to the first current sensor is configured to output a first
output voltage based on the first current, and a first turn-off circuit is coupled to the
analog-to-digital conversion device and to the first current measurement circuit. The
first turn-off circuit is configured to couple the first output voltage to the analog-todigital
conversion device if a voltage across the first thyristor is above a threshold and
decouple the first output voltage from the analog-to-digital conversion device if the
voltage across the first thyristor is below the threshold. The analog-to-digital
conversion device is configured to obtain the first output voltage from the first current
measurement circuit, determine an operability of the first thyristor based on the first
output voltage, and alert a user if the first thyristor is operating outside of a
predetermined status.
[0029] According to yet another embodiment of the invention, a method of
manufacturing a current-to-voltage conversion system comprises coupling a current
transfer device to a first current measurement circuit via a first current sensor, wherein
the current transfer device comprises a first thyristor and a first conductor coupled to the
first thyristor and configured to convey a first current flowing through the first thyristor.
The first current comprises current flowing through the first thyristor when the first
thyristor is in an off state. The method also comprises coupling a controller to the first
current measurement circuit configuring the first current measurement circuit to output a
first output value to the controller representative of the first current flowing through the
first thyristor, and configuring the controller to determine an impending inoperability of
the first thyristor based on the first current and alert a user if the first current indicates
the impending inoperability.
[0030] Embodiments of the present invention have been described in terms of the
preferred embodiment, and it is recognized that equivalents, alternatives, and
modifications, aside from those expressly stated, are possible and within the scope of
the appending claims.
WO 20141004158
We Claim:
1. A current monitoring system comprising:
a controller;
a current transfer device comprising:
a first thyristor; and
a first conductor coupled to the first thyristor and configured to
convey a first current flowing through the first thyristor, wherein the first current
comprises current flowing through the first thyristor when the first thyristor is in an off
state;
a first current sensor configured to sense the first current;
a first current measurement circuit coupled to the first current sensor and
coupleable to the controller and configured to output a first output value to the
controller representative of the first current flowing through the first thyristor; and
wherein the controller is configured to:
determine an impending inoperability of the first thyristor based
on the first current; and
alert a user if the first current indicates the impending
inoperability.
2. The current monitoring system of claim 1 wherein the first current
comprises a reverse-bias leakage current.
3. The current monitoring system of claim 1 wherein the current transfer
device further comprises:
a second thyristor coupled in an anti-parallel arrangement with
the first thyristor; and
a second conductor coupled to the second thyristor and
configured to convey a second current flowing through the second thyristor, wherein the
second current comprises current flowing through the second thyristor when the second
thyristor is in an off state;
wherein the current monitoring system further comprises:
a second current sensor configured to sense the second current;
and
a second current measurement circuit coupled to the second
current sensor and to the controller and configured to output a second output value to
the controller representative of the second current flowing through the second thyristor;
and
wherein the controller is mher configured to:
detcrrnine an impending inoperability of the second thyristor
based on the first current; and
alert the user if the second current indicates the impending
inoperability of the second thyristor.
4. The current monitoring system of claim 3 wherein the current transfer
device hrther comprises a third conductor coupled to the first and second conductors
and configured to convey a third current comprising a total amount of current flowing
through the current transfer device in a hll SCR soft starter conduction mode;
wherein the current monitoring system hrther comprises:
a third current sensor configured to sense the third current; and
a third current measurement circuit coupled to the third current
sensor and to the controller and configured to output a third output value to the
controller representative of the third current; and
wherein the controller is firther configured to calculate an average power
flowing through the current transfer device based on the first, second, and third currents.
5. The current monitoring system of claim 4 wherein the controller is
further configured to calculate an average power flowing through the current transfer
device based on an average of a plurality of current measurements based on the first and
second currents and based on the third current.
6. The current monitoring system of claim 1 further comprising:
a second current sensor configured to sense the first current;
a first turn-off circuit coupled to the controller and to the first current
measurement circuit, wherein the turn-off circuit is configured to:
couple the first output value to the controller if a voltage across
the first thyristor is above a threshold; and
decouple the first output value from the controller if the voltage
across the first thyristor is below the threshold.
7. The current monitoring system of claim 6 wherein the first turn-off
circuit comprises:
an inverter and gain circuit configured to invert and boost a voltage from
the second current sensor;
a voltage drop out circuit configured to:
compare the inverted and boosted voltage from the inverter and
gain circuit with a voltage threshold;
couple the first output value to the controller if the inverted and
boosted voltage is greater than the voltage threshold; and
decouple the first output value from the controller if the inverted
and boosted voltage is lesser than the voltage threshold.
8. The current monitoring system of claim 1 wherein the controller, in
being configured to determine an impending inoperability of the first thyristor, is
configured to:
compare the first output value with a reference value stored in a lookup
table; and
alert the user if the first output value is greater than the reference value.
9. A current monitoring system comprising:
an analog-to-digital conversion device;
a current transfer device comprising a pair of thyristors coupled together
in an anti-parallel arrangement;
a first conductor coupled to a first thyristor of the pair of thyristors and
configured to convey a first current flowing through the first thyristor;
a second conductor coupled to a second thyristor of the pair of thyristors
and configured to convey a second current flowing through the second thyristor;
a third conductor coupled to the f ~ s tan d second conductors and
configured to convey the first and second currents;
a first current sensor configured to sense the first current;
a first current measurement circuit coupled to the first current sensor and
configured to output a first output voltagc based on the first current;
a first turn-off circuit coupled to the analog-to-digital conversion device
and to the first current measurement circuit, wherein the first turn-off circuit is
configured to:
couple the first output voltage to the analog-to-digital conversion
device if a voltage across the first thyristor is above a threshold; and
decouple the first output voltage from the analog-to-digital
conversion device if the voltage across the first thyristor is below the threshold; and
wherein the analog-to-digital conversion device is configured to:
obtain the first output voltage from the first current measurement
circuit;
determine an operability of the first thyristor based on the first
output voltage; and
alert a user if the first thyristor is operating outside of a
predetermined status.
10. The current monitoring system of claim 9 further comprising:
a second current sensor configured to sense the third current;
a second current measurement circuit coupled to the analog-to-digital
conversion device and to the second current sensor and configured to output a second
output voltage based on the third current;
wherein the analog-to-digital conversion device is further configured to
calculate an average power flowing through the current transfer device based on the first
and second output voltages.
11. The current monitoring system of claim 10 further comprising:
a third current sensor configured to sense the second current;
a third current measurement circuit coupled to the third current sensor
and configured to output a third output voltage based on the second current;
a second turn-off circuit coupled to the analog-to-digital conversion
device and to the third current measurement circuit, wherein the second turn-off circuit
is configured to:
couple the third output voltage to the analog-to-digital conversion
device if a voltage across the second thyristor is above a threshold; and
decouple the third output voltage from the analog-to-digital
conversion device if the voltage across the second thyristor is below the threshold.
12. The current monitoring system of claim 11 wherein the analog-to-digital
conversion device is further configured to calculate an average power flowing through
the current transfer device based on the first, second, and third output voltages.
13. The current monitoring system of claim 9 wherein the first current sensor
comprises a current transformer.
14. The current monitoring system of claim 9 wherein the first current sensor
is configured to inductively sense the first current.
15. The current monitoring system of claim 14 wherein the first current
sensor comprises a multi-turn coil configured to be positioned about the first conductor.
16. A method of manufacturing a current-to-voltage conversion system
comprising:
coupling a current transfer device to a first current measurement circuit
via a first current sensor, wherein the current transfer device comprises:
a first thyristor; and
a first conductor coupled to the first thyristor and configured to
convey a first current flowing through the first thyristor, wherein the first current
comprises current flowing through the first thyristor when the first thyristor is in an off
state;
coupling a controller to the first current measurement circuit;
configuring the first current measurement circuit to output a first output
value to the controller representative of the first current flowing through the first
thyristor; and
configuring the controller to:
determine an impending inoperability of the first thyristor based
on the first current; and
alert a user if the first current indicates the impending
inoperability.
17. The method of claim 16 further comprising:
coupling a second current sensor configured to sense the first current;
coupling a turn-off circuit to the controller and to the first current
measurement circuit and configuring the turn-off circuit to:
couple the first output value to the controller if the first thyristor
is in an off state; and
decouple the first output value from the controller if the first
thyristor is in an on state.
18. The method of claim 17 wherein coupling the turn-off circuit to the
controller and to the first current measurement circuit comprises:
coupling an inverter and gain circuit to the second current sensor;
configuring the inverter and gain circuit to invert and boost a voltage
from the second current sensor;
coupling a voltage drop out circuit to the controller and to the first
current measurement circuit; and
configuring the voltage drop out circuit to:
compare the inverted and boosted voltage from the inverter and
gain circuit with a voltage threshold;
couple the first output value to the controller if the inverted and
boosted voltage is greater than the voltage threshold; and
decouple the first output value from the controller if the inverted
and boosted voltage is lesser than the voltage threshold.
19. The method of claim 16 furthcr comprising:
coupling the current transfcr device to a second current measurement
circuit via a second current sensor, wherein the current transfer device comprises:
a second thyristor; and
a second conductor coupled to the second thyristor and
configured to convey a second current flowing through the second thyristor, wherein the
second current comprises current flowing through the second thyristor when the second
thyristor is in an off state;
coupling the controller to the second current measurement circuit; and
configuring the second current measurement circuit to output a second
output value to the controller representative of the second current flowing through the
second thyristor.
20. The method of claim 19 further comprising configuring the controller to
calculate an average power flowing through the current transfer device based on an
average of a plurality of current measurements based on the first and second currents.