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`Patent Application Publication
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`Oct. 6, 2011 Sheet 1 of 7
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`US 2011/0241590 Al
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`LIBERTY EXHIBIT 1025, Page 2
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`Patent Application Publication
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`Oct. 6, 2011 Sheet 5 of 7
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`US 2011/0241590 Al
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`LIBERTY EXHIBIT 1025, Page 6
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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 Al
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`LIBERTY EXHIBIT 1025, Page 8
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`US 2011/0241590 Al
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`Oct. 6, 2011
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`1
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`MOTOR DRIVING APPARATUS HAVING
`FAULT DIAGNOSTIC 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(cid:173)
`nected to a three-phase AC power supply and which com(cid:173)
`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
`power for supply to a motor, is known. In such a 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 ifthe 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(cid:173)
`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(cid:173)
`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, ifthe 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.
`JP7-239359A discloses an apparatus that uses one
`[0008]
`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(cid:173)
`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.
`JP63-85380A cited in JP7-239359A discloses a
`[0010]
`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(cid:173)
`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(cid:173)
`phase AC power supply into DC power and a DC/AC con(cid:173)
`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 ifthe 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(cid:173)
`phase short circuit, when overcurrent occurs during opera(cid:173)
`tion.
`[0014] Further, in a configuration in which the DC/ AC con(cid:173)
`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 be if an extra current 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(cid:173)
`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(cid:173)
`ring due to the ground fault;
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`LIBERTY EXHIBIT 1025, Page 9
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`US 2011/0241590 Al
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`Oct. 6, 2011
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`2
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`[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(cid:173)
`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 In 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 IR, Is, and Ir-
`
`(1)
`
`[0025] On the other hand, when a short circuit to ground (a
`ground fault) momentarily occurs, for example, in the T phase
`at the output side of the DC/AC converter 10, as shown in
`FIG. 3, overcurrent 16 appears on the T-phase current In 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)
`
`If the DC/AC converter 10 is provided at the output
`[0026]
`side with three current sensors for detecting the three phase
`currents independently of each other, whether the short cir(cid:173)
`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(cid:173)
`rence of the phase-to-phase short circuit can be detected by
`detecting the overcurrent with the two current sensors. How(cid:173)
`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), ifthe 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(cid:173)
`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(cid:173)
`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(cid:173)
`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 forthe
`three phases at the input side of the AC/DC converter 18 as
`well as at the output side 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, ifthe 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.
`In the example of FIG. 5, since overcurrent is
`[0030]
`detected on two of the three output phases of the DC/ AC
`converter 10, if a ground fault occurs on the phase not pro(cid:173)
`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.
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`LIBERTY EXHIBIT 1025, Page 10
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`US 2011/0241590 Al
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`Oct. 6, 2011
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`3
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`[0033] FIG. 7 shows an example in which, as a means for
`detecting the sum of the currents at the input side, 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(cid:173)
`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(cid:173)
`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(cid:173)
`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(cid:173)
`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.
`
`* * * * *
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`LIBERTY EXHIBIT 1025, Page 11
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