(19) United States
`(12) Patent Application Publication (10) Pub. No.: US 2011/0241590 A1
`HORKOSH et al.
`(43) Pub. Date:
`Oct. 6, 2011
`
`US 20110241590A1
`
`(54) MOTOR DRIVINGAPPARATUS HAVING
`FAULT DAGNOSTIC FUNCTION
`
`(75)
`
`Inventors:
`
`Shinichi HORIKOSHI,
`Minamitsuru-gun (JP): Takashi
`HARADA, Minamitsuru-gun (JP);
`Masatomo SHROUZU,
`Minamitsuru-gun (JP); Yasusuke
`IWASHITA, Minamitsuru-gun (JP)
`
`(73)
`
`Assignee:
`
`FANUC CORPORATION,
`Minamitsuru-gun (JP)
`
`(21)
`
`Appl. No.:
`
`13/025,210
`
`(22)
`
`Filed:
`
`Feb. 11, 2011
`
`Foreign Application Priority Data
`(30)
`Mar. 31, 2010 (JP) ................................. 2010-083257
`Publication Classification
`
`(51) Int. Cl.
`(2006.01)
`HO2H 7/08
`(52) U.S. Cl. ........................................................ 318/.490
`(57)
`ABSTRACT
`A motor driving apparatus capable of detecting during opera
`tion a ground fault and a phase-to-phase short circuit by
`distinguishing one from the other is provided while minimiz
`ing an increase in cost. The Sum of three-phase AC currents
`supplied from a three-phase AC power supply to an AC/DC
`converter is detected by a current sensor. When overcurrent is
`detected by an overcurrent detector, if the sum of the currents
`detected by the current sensor is zero, it is determined that the
`fault is a phase-to-phase short circuit, but if the Sum is not
`Zero, it is determined that the fault is a ground fault.
`
`
`
`r s - r
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`Patent Application Publication
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`Patent Application Publication
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`Oct. 6, 2011 Sheet 2 of 7
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`Patent Application Publication
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`Patent Application Publication
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`Patent Application Publication
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`Patent Application Publication
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`Oct. 6, 2011 Sheet 7 of 7
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`US 2011/0241590 A1
`
`Oct. 6, 2011
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`MOTOR DRIVINGAPPARATUS HAVING
`FAULT DAGNOSTIC FUNCTION
`
`BACKGROUND OF THE INVENTION
`1. Field of the Invention
`0001
`0002 The present invention relates to a motor driving
`apparatus having a fault diagnostic function.
`0003 2. Description of the Related Art
`0004 Providing a motor driving apparatus, which is con
`nected to a three-phase AC power Supply and which com
`prises an AC/DC converter for converting three-phase AC
`power Supplied from the three-phase AC power Supply into
`DC power and a DC/AC converter for converting the DC
`power output from the AC/DC converter into three-phase AC
`powerfor Supply to a motor, is known. In Sucha motor driving
`apparatus, if three current sensors are provided that detect the
`three-phase output currents independently of each other, the
`apparatus can reliably detect any overcurrent occurring in the
`DC/AC converter and can also identify whether the cause is a
`ground fault or a phase-to-phase short circuit. That is, if
`overcurrent occurs in the DC/AC converter because of a
`ground fault or a phase-to-phase short circuit, the overcurrent
`can be detected by one of the three sensors, and if the sum of
`the currents detected by the three current sensors is not zero,
`it is determined that the cause is a ground fault, but if the sum
`is Zero, it is determined that the cause is a phase-to-phase
`short circuit.
`0005. However, generally only two sensors are provided in
`order to reduce the cost, and the remaining one of the three
`phase currents is obtained through calculation by assuming
`that the sum of the three phase currents is Zero. As a result, in
`the case of a conventional DC/AC converter having two out
`put current sensors, there are cases where overcurrent caused
`by a ground fault cannot be detected, as will be described in
`detail later, and if the overcurrent can be detected, it is not
`possible to identify whether the cause is a ground fault or a
`phase-to-phase short circuit.
`0006. Accordingly, in the case of such a DC/AC converter
`having two output current sensors, the operation of the appa
`ratus has to be stopped in the event of the occurrence of an
`overcurrent alarm, and the insulation resistance of the motor
`and power lines has to be checked in order to determine
`whether the cause is a ground fault or a phase-to-phase short
`circuit. Further, if the ground fault is intermittent, it is difficult
`to identify the cause.
`0007. On the other hand, in the case of a motor driving
`apparatus provided with three output sensors by adding an
`extra current sensor as earlier described, if the apparatus is
`one constructed to drive a plurality of motors by Supplying the
`DC power output from the AC/DC converter to a plurality of
`DC/AC converters, the extra current sensor has to be added to
`each of the plurality of DC/AC converters, which greatly
`increases the cost.
`0008 JP7-239359A discloses an apparatus that uses one
`or two current sensors and that provides protection against
`ground faults by detecting the presence or absences of a
`ground fault before starting the operation by applying a
`ground-fault detecting control signal to the AC/DC converter.
`However, no description is given of how a distinction is made
`between a ground fault and a phase-to-phase short circuit.
`0009. On the other hand, JP4-10536A discloses an appa
`ratus in which a Zero phase current detector is provided
`between the three-phase AC power Supply and the apparatus,
`with provisions made to stop the operation of the inverter
`
`apparatus upon detection of a ground fault. However, no
`description is given of the detection of a phase-to-phase short
`circuit.
`O010 JP63-85380A cited in JP7-239359A discloses a
`method that provides a detector for detecting the DC current
`input to the inverter apparatus, wherein the current detection
`pattern generated when a test control signal was applied to the
`inverter apparatus before starting the operation is compared
`with a known pattern to detect the presence or absence of a
`ground fault or a short circuit fault. However, this method not
`only has the drawback that the detected current contains a
`reactive current that flows through free wheel diodes in the
`inverter apparatus, as described in JP7-239359A (paragraph
`0004), but also has the problem that a ground fault or a
`phase-to-phase short circuit that occurs after starting the
`operation or a ground fault that occurs intermittently during
`the operation cannot be detected.
`
`SUMMARY OF THE INVENTION
`0011. Accordingly, it is an object of the present invention
`to achieve, while minimizing an increase in cost, a motor
`driving apparatus having a fault diagnostic function capable
`of detecting during operation a ground fault and a phase-to
`phase short circuit by distinguishing one from the other.
`0012. According to the present invention, there is provided
`a motor driving apparatus comprising an AC/DC converter
`for converting three-phase AC power Supplied from a three
`phase AC power supply into DC power and a DC/AC con
`verter for converting the DC power output from the AC/DC
`converter into three-phase AC power for Supply to a motor,
`wherein the motor driving apparatus further comprises: a Sum
`current detector which detects the sum of currents flowing
`from the three-phase AC power supply through the AC/DC
`converter to the DC/AC converter; an overcurrent detector
`which detects overcurrent on an output current of the DC/AC
`converter, and a determining unit which, when overcurrent is
`detected by the overcurrent detector, determines that a ground
`fault has occurred if the sum of currents detected by the sum
`current detector can be judged to be not Zero, but determines
`that a phase-to-phase short circuit has occurred if the Sum of
`currents detected by the Sum current detector can be judged to
`be zero.
`0013 By thus detecting the sum of currents, it can be
`determined whether the cause is a ground fault or a phase-to
`phase short circuit, when overcurrent occurs during opera
`tion.
`0014 Further, in a configuration in which the DC/AC con
`verter includes a plurality of inverters in order to drive a
`plurality of motors, since the Sum current detector and the
`determining unit added in order to make the determination are
`provided on the AC/DC converter side, the increase in cost is
`less than would beifan extracurrent sensor was added to each
`inverter in order to make the ground-fault/phase-to-phase
`short circuit determination.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`0015 FIG. 1 is a diagram explaining a phase-to-phase
`short circuit;
`0016 FIG. 2 is a waveform diagram explaining overcur
`rent occurring due to the phase-to-phase short circuit;
`0017 FIG. 3 is a diagram explaining a ground fault;
`0018 FIG. 4 is a diagram explaining overcurrent occur
`ring due to the ground fault;
`
`HALLIBURTON EXHIBIT 1008
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`US 2011/0241590 A1
`
`Oct. 6, 2011
`
`0019 FIG. 5 is a diagram showing the configuration of a
`motor driving apparatus according to one embodiment of the
`present invention;
`0020 FIG. 6 is a diagram showing the configuration of a
`motor driving apparatus according to an alternative embodi
`ment of the present invention;
`0021
`FIG. 7 is a diagram showing the configuration of a
`motor driving apparatus according to another alternative
`embodiment of the present invention;
`0022 FIG. 8 is a diagram showing the configuration of a
`motor driving apparatus according to still another alternative
`embodiment of the present invention; and
`0023 FIG. 9 is a diagram showing the configuration of a
`motor driving apparatus according to yet another alternative
`embodiment of the present invention.
`
`DESCRIPTION OF THE PREFERRED
`EMBODIMENTS
`0024. When a short circuit (a phase-to-phase short circuit)
`momentarily occurs, for example, between the S phase and T
`phase, at the output side of a DC/AC converter 10, as shown
`in FIG. 1, overcurrent 12 and overcurrent 14 appear on the
`S-phase current Is and T-phase current I, respectively, as
`shown in FIG. 2. In the case of a phase-to-phase short circuit,
`since there is no current return via ground, the following
`relationship holds between the phase currents I, Is, and I.
`I+Is+1-0
`(1)
`0025. On the other hand, when a short circuit to ground (a
`ground fault) momentarily occurs, for example, in the Tphase
`at the output side of the DC/AC converter 10, as shown in
`FIG. 3, overcurrent 16 appears on the T-phase current I, as
`shown in FIG. 4. In this case, the relation defined by equation
`(1) does not hold because of the presence of a current return
`via ground; hence,
`(2)
`I+Is+1720
`0026. If the DC/AC converter 10 is provided at the output
`side with three current sensors for detecting the three phase
`currents independently of each other, whether the short cir
`cuit is a ground fault or a phase-to-phase short circuit can be
`determined by taking the sum of the currents and checking
`whether the relation defined by equation (1) holds or not.
`However, generally only two sensors are provided in order to
`reduce the cost, and the remaining one of the three phase
`currents is obtained through calculation by assuming that the
`Sum of the three phase currents is Zero. As a result, using only
`two current sensors, it is not possible to distinguish between
`the ground fault and the phase-to-phase short circuit. In the
`example shown in FIG. 1 (a phase-to-phase short circuit
`occurs between the S phase and T phase), even when the R
`phase is not provided with a current sensor, if the S phase and
`T phase are each provided with a current sensor, the occur
`rence of the phase-to-phase short circuit can be detected by
`detecting the overcurrent with the two current sensors. How
`ever, in the case where the R phase is provided with a current
`sensor but one of the S phase and T phase is not provided with
`a current sensor, it is possible to detect the overcurrent caused
`by a phase-to-phase short circuit or a ground fault, but it is not
`possible to determine whether the cause is a phase-to-phase
`short circuit or a ground fault. Further, in the example shown
`in FIG. 3 (a short circuit occurs in the T phase), if the T phase
`is not provided with a current sensor, even the occurrence of
`the overcurrent due to the ground fault cannot be detected.
`
`0027 FIG. 5 shows the configuration of a motor driving
`apparatus, according to a first embodiment of the present
`invention, that has a function to detect the occurrence of
`overcurrent and to determine whether the cause is a phase-to
`phase short circuit or a ground fault. An AC/DC converter 18
`converts three-phase AC power Supplied from a three-phase
`AC power supply 20 into DC power for output. A DC/AC
`converter 10 converts the DC power output from the AC/DC
`converter 18 into frequency variable three-phase AC power
`for output. Portions for controlling the transistors in the
`DC/AC converter 10 and AC/DC converter 18 are not shown
`here.
`0028. A Zero phase current detector 22 detects the sum of
`the three-phase AC currents supplied from the three-phase AC
`power supply to the AC/DC converter 18. Current sensors 24
`and 26 detect two of the three-phase AC currents output from
`the DC/AC converter 10. An overcurrent detector 28 detects
`overcurrent based on the currents detected by the current
`sensors 24 and 26. When overcurrent is detected by the over
`current detector 28, a ground-fault/short-circuit determining
`unit 30 determines, based on the current detected by the Zero
`phase current detector 22, whether the cause of the overcur
`rent is a ground fault or a phase-to-phase short circuit.
`0029 When the overcurrent is caused by a phase-to-phase
`short circuit, since there is no current return via ground for the
`three phases at the input side of the AC/DC converter 18 as
`well as at the outputside of the DC/AC converter 10 described
`earlier, the relationship similar to that defined by equation (1)
`holds and no current is detected by the Zero phase current
`detector 22. On the other hand, when the overcurrent is
`caused by a ground fault, a ground fault current flows and this
`ground fault current is detected by the Zero phase current
`detector 22. Accordingly, when the overcurrent is detected by
`the overcurrent detector 28, if the sum of the currents detected
`by the Zero phase current detector 22 is so small as to be
`judged to be equal to Zero, the ground-fault/phase-to-phase
`short-circuit determining unit 30 determines that the cause of
`the overcurrent is a phase-to-phase short circuit; on the other
`hand, if the Sum of the currents is not so Small as to be judged
`to be equal to Zero, it is determined that the cause of the
`overcurrent is a ground fault.
`0030. In the example of FIG. 5, since overcurrent is
`detected on two of the three output phases of the DC/AC
`converter 10, if a ground fault occurs on the phase not pro
`vided with a current sensor, the overcurrent cannot be
`detected by the overcurrent detector 28. However, since the
`ground fault current is detected by the Zero phase current
`detector 22, the ground-fault/phase-to-phase short-circuit
`determining unit 30 can detect the occurrence of the ground
`fault.
`0031. To detect the sum of the currents at the input side,
`use may be made, instead of the Zero phase current detector
`22, of a clamp-on sensor or the like that detects current by
`detecting the magnetic field around the current using a Hall
`element. That is, by passing all of the three power lines
`through the detection ring of the clamp-on sensor, the Sum of
`the currents can be detected, as in the case of the Zero phase
`current detector.
`0032 FIG. 6 shows an example in which, instead of
`detecting the Sum of the three-phase AC currents at the input
`side by the Zero phase current detector 22, the three-phase AC
`currents at the input side are detected independently of each
`other by current sensors 32,34, and 36 and are added together
`by an adder 38 to obtain the sum of the currents.
`
`HALLIBURTON EXHIBIT 1008
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`US 2011/0241590 A1
`
`Oct. 6, 2011
`
`0033 FIG. 7 shows an example in which, as a means for
`detecting the sum of the currents at the inputside, a clamp-on
`sensor 40 similar to the one described above is provided to
`detect the sum of the currents flowing on the two lines through
`which the DC power from the AC/DC converter 18 is supplied
`to the DC/AC converter 10.
`0034 FIG. 8 shows an example in which the current sen
`sors 24 and 26 shown in the example of FIG. 5 are omitted
`and, instead, a current sensor 44 is provided which detects
`overcurrent by detecting the current flowing on one of the two
`lines through which the DC power from the AC/DC converter
`18 is supplied to the DC/AC converter 10 via a smoothing
`capacitor 42. As the means for detecting the sum of the
`currents, the means described with reference to FIG. 6 or 7
`may be used instead of the current sensor 22 described with
`reference to FIG. 5.
`0035 FIG.9 shows an example in which the DC/AC con
`verter 10 is constructed from a plurality of inverters 10-1,
`10-2, ... in order to drive a plurality of motors. In this case,
`since the current sensor 22 and the ground-fault/phase-to
`phase short-circuit determining unit 30 for making the
`ground-fault/phase-to-phase short circuit determination are
`provided on the AC/DC converter 18 side, the increase in cost
`is less than would be if an extra current sensor was added to
`each inverter.
`1. A motor driving apparatus comprising an AC/DC con
`verter for converting three-phase AC power supplied from a
`three-phase AC power supply into DC power and a DC/AC
`converter for converting the DC power output from said
`AC/DC converter into three-phase AC power for supply to a
`motor, said motor driving apparatus further comprising:
`a Sum current detector detecting a sum of currents flowing
`from said three-phase AC power Supply through said
`AC/DC converter to said DC/AC converter;
`an overcurrent detector detecting overcurrent on an output
`current of said DC/AC converter; and
`a determining unit which, when overcurrent is detected by
`said overcurrent detector, determines that a ground fault
`has occurred if the sum of currents detected by said sum
`current detector can be judged to be not zero, but deter
`
`mines that a phase-to-phase short circuit has occurred if
`the sum of currents detected by said sum current detector
`can be judged to be Zero.
`2. A motor driving apparatus according to claim 1, wherein
`said Sum current detector includes a current sensor which
`detects the sum of the currents flowing on three lines through
`which said three-phase AC power from said three-phase AC
`power supply is supplied to said AC/DC converter.
`3. A motor driving apparatus according to claim 1, wherein
`said Sum current detector includes:
`three current sensors which detect the respective currents
`flowing on three lines through which said three-phase
`AC power from said three-phase AC power supply is
`supplied to said AC/DC converter; and
`Summing means for calculating the Sum of the currents
`detected by said three current sensors.
`4. A motor driving apparatus according to claim 1, wherein
`said Sum current detector includes a current sensor which
`detects the Sum of the currents flowing on two lines through
`which said DC power from said AC/DC converter is supplied
`to said DC/AC converter.
`5. A motor driving apparatus according to claim 1, wherein
`said overcurrent detector includes two current sensors which
`detect said overcurrent by detecting the respective currents
`flowing on two of three lines through which said three-phase
`AC power from said DC/AC converter is supplied to said
`motor.
`6. A motor driving apparatus according to claim 1, wherein
`said overcurrent detector includes a current sensor which
`detects said overcurrent by detecting the current flowing on
`one of the two lines through which said DC power from said
`AC/DC converter is supplied to said DC/AC converter.
`7. A motor driving apparatus according to claim 1, wherein
`said DC/AC converter includes a plurality of inverters which
`convert DC power into three-phase AC power for supply to a
`plurality of motors, respectively, and wherein
`said AC/DC converter supplies said DC power, converted
`from three-phase AC power, in parallel to said plurality
`of inverters.
`
`HALLIBURTON EXHIBIT 1008
`Halliburton Energy Services, Inc. v. U.S. Well Services, LLC, IPR2023-00558, Page 11
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