Motor drive device having ground fault detection function

Abstract

This motor drive device comprises: a converter that has a three-phase full-bridge circuit having diodes provided on an upper arm on a high-potential side and a lower arm on a low-potential side of each of the three phases, and that converts AC power inputted from an AC power source into DC power and outputs the DC power to a DC link; a smoothing capacitor provided to the DC link; an inverter that has a three-phase full-bridge circuit in which switching elements are provided on an upper arm on a high-potential side and a lower arm on a low-potential side of each of the three phases, and that, as a result of a switching operations performed by the switching elements, converts DC power of the DC link into AC power and supplies the AC power to a motor; and a ground fault detection unit that detects a ground fault in either a three-phase power line between the inverter and the motor or a three-phase winding of the motor on the basis of information related to current that flows when any one of the switching elements of the inverter is turned on.

Description

Motor drive device with ground fault detection function

[0001] This disclosure relates to a motor drive device having a ground fault detection function.

[0002] In motor drive systems that drive motors installed in machine tools and robots, AC power supplied from an AC power source is converted to DC power by a converter (rectifier) ​​and output to a DC link. Furthermore, an inverter converts the DC power in the DC link back to AC power for motor drive and supplies it to the motor.

[0003] International Publication No. 2012 / 008022, Japanese Patent Publication No. 2009-033938, Japanese Patent Publication No. 2016-131426

[0004] In motor drive systems, there is a need for technology that can easily detect ground faults in either the power lines connecting the inverter and the motor, or in the motor windings.

[0005] According to one aspect of the present disclosure, the motor drive device comprises: a converter having a three-phase full-bridge circuit in which diodes are provided on the upper arm on the high-potential side and the lower arm on the low-potential side of each of the three phases, which converts AC power input from an AC power source into DC power and outputs it to a DC link; a smoothing capacitor provided on the DC link; an inverter having a three-phase full-bridge circuit in which switching elements are provided on the upper arm on the high-potential side and the lower arm on the low-potential side of each of the three phases, which converts the DC power of the DC link into AC power and supplies it to the motor by the switching operation of the switching elements; and a ground fault detection unit that detects a ground fault in either the three-phase power line between the inverter and the motor or the three-phase winding of the motor based on information related to the current that flows when any one of the switching elements of the inverter is turned on.

[0006] According to a further aspect of the present disclosure, the motor drive device comprises: a converter having a three-phase full-bridge circuit in which diodes are provided on each of the upper arm on the high-potential side and the lower arm on the low-potential side of each of the three phases, which converts AC power input from an AC power source into DC power and outputs it to a DC link; a smoothing capacitor provided in the DC link; an inverter having a three-phase full-bridge circuit in which switching elements and diodes are provided on each of the upper arm on the high-potential side and the lower arm on the low-potential side of each of the three phases, which converts the DC power of the DC link into AC power and supplies it to the motor by the switching operation of the switching elements; a switching unit that opens and closes the circuit on the three-phase power line between the AC power source and the converter; a resistor provided in the DC link between the converter and the smoothing capacitor; and a ground fault detection unit that detects a ground fault in either the power line between the inverter and the motor or the winding of the motor based on information related to the current that flows when the switching unit closes the circuit.

[0007] This is a circuit diagram showing a motor drive device according to the first embodiment of this disclosure. This is a flowchart showing the operation flow of the ground fault detection process in the motor drive devices according to the first and third embodiments of this disclosure. This is a circuit diagram showing a motor drive device according to the second embodiment of this disclosure. This is a flowchart showing the operation flow of the ground fault detection process in the motor drive devices according to the second and fourth embodiments of this disclosure. This is a circuit diagram showing a motor drive device according to the third embodiment of this disclosure. This is a circuit diagram showing a motor drive device according to the fourth embodiment of this disclosure. This is a circuit diagram showing a motor drive device according to the fifth embodiment of this disclosure. This is a flowchart showing the operation flow of the ground fault detection process in the motor drive device according to the fifth embodiment of this disclosure. This is a circuit diagram showing a motor drive device according to the sixth embodiment of this disclosure. This is a flowchart showing the operation flow of the ground fault detection process in the motor drive device according to the sixth embodiment of this disclosure. This is a circuit diagram showing the equivalent circuit when the ground fault detection process is executed in the motor drive devices according to the first, third and fifth embodiments of this disclosure. This is a circuit diagram showing the equivalent circuit when the ground fault detection process is executed in the motor drive devices according to the second, fourth and sixth embodiments of this disclosure. This is a circuit diagram showing a motor drive device according to the seventh embodiment of this disclosure. This is a circuit diagram showing a motor drive device according to the eighth embodiment of this disclosure. This is a circuit diagram showing a motor drive device according to the ninth embodiment of this disclosure. This is a circuit diagram showing a motor drive device according to the tenth embodiment of this disclosure. This is a flowchart showing the operation flow of ground fault detection processing in motor drive devices according to the seventh to tenth and eleventh embodiments of this disclosure. This is a circuit diagram showing a motor drive device according to the eleventh embodiment of this disclosure. This is a circuit diagram showing a motor drive device according to the twelfth embodiment of this disclosure. This is a flowchart showing the operation flow of ground fault detection processing in a motor drive device according to the twelfth embodiment of this disclosure. This is a circuit diagram showing the equivalent circuit when ground fault detection processing is executed in motor drive devices according to the seventh, eighth, eleventh and twelfth embodiments of this disclosure. This is a circuit diagram showing the equivalent circuit when ground fault detection processing is executed in motor drive devices according to the ninth and tenth embodiments of this disclosure.

[0008] The following describes an embodiment of a motor drive device with a ground fault detection function, with reference to the drawings. In the following description, components having the same or similar functions are denoted by the same reference numerals. Duplication of these components may be omitted. The drawings have been scaled appropriately for ease of understanding.

[0009] Furthermore, in the following description, terms are defined in consideration of the function in the embodiments of this disclosure, and therefore terms may differ depending on the intent or convention of the user or operator. For example, "connected" means "electrically connected." A converter that converts AC power supplied from an AC power source into DC power and outputs it may also be called a "rectifier," "rectifier device," "rectifier circuit," or "forward converter." An inverter that converts DC power into AC power and outputs it may also be called an "inverse converter." "DC link" refers to the circuit portion that electrically connects the DC output side of the converter and the DC input side of the inverter. "DC link" may also be called a "DC link section," "DC link," "DC bus," or "DC intermediate circuit." "DC link current" refers to the current flowing through the positive or negative power line of the DC link. "DC link voltage" refers to the potential difference between the positive potential on the positive power line of the DC link and the negative potential on the negative power line, and is equal to the terminal voltage of the smoothing capacitor provided in the DC link. "Power supply current" refers to the current flowing through the power line between the AC power supply and the converter. "Power supply voltage" refers to the line voltage in the power line between the AC power supply and the converter. "Inverter current" refers to the current flowing through the power line between the inverter and the motor (windings). "Inverter current" is sometimes also called "motor current". The pre-charging circuit is sometimes also called the "initial charging circuit" or "inrush current suppression circuit". "The state in which the smoothing capacitor is fully charged" refers to the state in which the terminal voltage of the smoothing capacitor has become sufficiently high and the DC link current flowing into the capacitor has decreased. However, the terminal voltage of the smoothing capacitor when it is "fully charged" does not necessarily coincide with the maximum value of the peak value of the power supply voltage, and can take on a value with a certain range depending on the pulsation of the power supply voltage. "The state in which the smoothing capacitor is not fully charged" refers to the state in which the applied voltage to the smoothing capacitor is rising and a DC link current is being generated flowing into the smoothing capacitor. When the smoothing capacitor is not fully charged, the voltage across its terminals can range from 0 to the maximum value of the peak of the power supply voltage."On" for a switching element means that the switching element closes, forming an electrical circuit through that switching element. "Off" for a switching element means that the switching element opens, interrupting the electrical circuit through that switching element. "Closed" for an opening / closing part means that the opening / closing part closes, forming an electrical circuit through that opening / closing part. "Open" for an opening / closing part means that the opening / closing part opens, interrupting the electrical circuit through that opening / closing part. "Closed" for a backup charge switch means that the backup charge switch closes, forming an electrical circuit through that backup charge switch. "Open" for a backup charge switch means that the backup charge switch opens, interrupting the electrical circuit through that backup charge switch. Furthermore, the numerical examples given below are just examples, and other numerical values ​​may be used. Also, the units of each parameter may be omitted.

[0010] Furthermore, in the motor drive device according to the embodiments of this disclosure, switching elements in the converter and inverter are switched on and off. Examples of switching elements include semiconductor elements such as IGBTs, FETs, thyristors, GTOs, and transistors, but other semiconductor elements may also be used. An IGBT has a gate terminal, a collector terminal, and an emitter terminal as its terminals. A transistor has a base terminal, a collector terminal, and an emitter terminal as its terminals. An FET has a gate terminal, a drain terminal, and a source terminal as its terminals. A thyristor and a GTO have a gate terminal, an anode terminal, and a cathode terminal as its terminals. The "current inflow terminals" of the switching elements correspond to the "collector" of IGBTs and transistors, the "drain" of FETs, and the "anode" of thyristors and GTOs, respectively. The "current outflow terminals" of the switching elements correspond to the "emitter" of IGBTs and transistors, the "source" of FETs, and the "cathode" of thyristors and GTOs, respectively. The "control terminals" of switching elements correspond to the "gate" of IGBTs, FETs, thyristors, and GTOs, and the "base" of transistors, respectively.

[0011] The following description will explain the case where the switching element is composed of an IGBT as an example, but the embodiments of this disclosure are also applicable to FETs, thyristors, GTOs, or transistors. Furthermore, when the switching element is composed of an FET, the current inflow terminal "collector" is read as "drain," and the current outflow terminal "emitter" is read as "source," and the embodiments of this disclosure apply accordingly. Furthermore, when the switching element is composed of a transistor, the control terminal "gate" is read as "base," and the embodiments of this disclosure apply accordingly. Furthermore, when the switching element is composed of a thyristor or GTO, the current inflow terminal "collector" is read as "anode," and the current outflow terminal "emitter" is read as "cathode," and the embodiments of this disclosure apply accordingly. The switching element performs an on / off operation when a voltage corresponding to a command is applied to the gate of the switching element.

[0012] <First Embodiment of the Present Disclosure> Figure 1 is a circuit diagram showing a motor drive device according to the first embodiment of the present disclosure.

[0013] In the first embodiment of this disclosure described below and the second to twelfth embodiments described later, as an example, a case in which a motor 3 is driven by a motor drive device 1 connected to an AC power supply 2 is shown. Examples of the AC power supply 2 include a three-phase AC 400V power supply, a three-phase AC 200V power supply, and a three-phase AC 600V power supply. The motor 3 may be either an induction motor or a synchronous motor. Machines in which the motor 3 is installed include, for example, machine tools and robots. The motor 3 is used as a drive source for, for example, the feed axis or spindle of a machine tool, or the arm of a robot.

[0014] As shown in FIG. 1, a motor drive device 1 according to a first embodiment of the present disclosure includes a converter 11, an inverter 12, a smoothing capacitor 13, a ground fault detection unit 14, a DC link current detection unit 15, an inverter control unit 10, and a pre-charge circuit 22. Note that the power supplies for driving each unit such as the ground fault detection unit 14, the DC link current detection unit 15, and the inverter control unit 10 are not shown in the figure. Also, even before the power is turned on to the motor drive device 1, power is supplied to drive each control unit in preparation for the operation when the power is turned on to the motor drive device 1.

[0015] The converter 11 is connected to an AC power supply 2 via an R-phase power line 32R, an S-phase power line 32S, and a T-phase power line 32T. An AC reactor and a switching unit (electromagnetic contactor) may be provided on the R-phase power line 32R, the S-phase power line 32S, and the T-phase power line 32T, but are not shown here.

[0016] The converter 11 converts the AC power input from the AC power supply 2 into DC power and outputs it to the DC link 19. The converter 11 has a three-phase full-bridge circuit in which at least a diode is provided in each of the upper arm on the high potential side and the lower arm on the low potential side of each of the three phases. Examples of the converter 11 include a diode rectifier, a PWM switching control type rectifier, and a 120-degree conduction type rectifier. In the example shown in FIG. 1, the converter 11 is composed of a PWM switching control type rectifier. The converter 11 composed of a PWM switching control type rectifier includes a switching element S in the upper arm of the R phase RU and a diode D connected in anti-parallel thereto RU and a switching element S in the lower arm of the R phase RL and a diode D connected in anti-parallel thereto RL and a switching element S in the upper arm of the S phase SU and a diode D connected in anti-parallel thereto SU and a switching element S in the lower arm of the S phase SL and a diode D connected in anti-parallel thereto SL and a switching element S in the upper arm of the T phase TU and a diode D connected in anti-parallel thereto TUAnd the switching element S of the lower T-phase arm TL and diode D connected in antiparallel to it TL It has a three-phase full-bridge circuit consisting of the above. Although not shown here, if the converter 11 is composed of a diode rectifier, a diode is provided on each of the upper arm on the high-potential side and the lower arm on the low-potential side of each of the three phases in the three-phase full-bridge circuit that constitutes the converter 11. If the converter 11 is composed of a 120-degree energized rectifier, switching elements connected in antiparallel to each of the upper arm on the high-potential side and the lower arm on the low-potential side of each of the three phases are provided on each of the upper arm on the high-potential side and the lower arm on the low-potential side of each of the three phases in the three-phase full-bridge circuit that constitutes the converter 11. If the converter 11 is composed of a PWM switching control rectifier or a 120-degree energized rectifier, a converter control unit (not shown) for controlling the switching elements is provided.

[0017] The inverter 12 is connected to the converter 11 via the DC link 19. In response to a motor drive command from the inverter control unit 10, the inverter 12 selectively performs a power operation, which converts the DC power in the DC link 19 into AC power and supplies it to the motor 3, and a regenerative operation, which converts the AC power regenerated by the motor 3 back into DC power and returns it to the DC link 19. The inverter 12 has a switching element S in the U-phase upper arm. UU and diode D connected in antiparallel to it UU And the switching element S of the U-phase lower arm UL and diode D connected in antiparallel to it UL And the switching element S of the V-phase upper arm VU and diode D connected in antiparallel to it VU And the switching element S of the V-phase lower arm VL and diode D connected in antiparallel to it VL And the switching element S of the W-phase upper arm WU and diode D connected in antiparallel to it WU And the switching element S of the W-phase lower arm WL and diode D connected in antiparallel to it WL It has a three-phase full-bridge circuit consisting of the following.

[0018] The inverter control unit 10 controls the operation of the inverter 12. The inverter control unit 10 generates motor drive commands and transmits them to the inverter 12. Upon receiving the motor drive commands, the inverter 12 selectively executes powering and regenerative braking operations. Note that the configuration of the inverter control unit 10 defined here is merely an example, and the configuration of the inverter control unit 10 may be defined to include terms such as a position command generation unit, a torque command generation unit, and a switching command generation unit.

[0019] The inverter 12 is connected to the motor 3 via a U-phase power line 33U, a V-phase power line 33V, and a W-phase power line 33W. The motor 3 operates in an accelerating or constant-speed mode based on the AC power output from the inverter 12. When the motor 3 decelerates, the AC power regenerated by the motor 3 is converted into DC power by the inverter 12, and this DC power is returned to the DC link 19.

[0020] A smoothing capacitor 13 is connected to the DC link 19 between the converter 11 and the inverter 12. The smoothing capacitor 13 is sometimes referred to as a "DC link capacitor" or "DC link capacitor." The smoothing capacitor 13 has the function of suppressing the oscillation of the DC output of the converter 11 and the function of storing the DC power used by the inverter 12 to generate AC power. Examples of smoothing capacitors 13 include electrolytic capacitors and film capacitors.

[0021] The auxiliary charging circuit 22 is provided on the DC link 19. In the first embodiment of this disclosure, the auxiliary charging circuit 22 is provided on the positive power line 31P of the DC link 19. As will be described later, the auxiliary charging circuit 22 may also be provided on the negative power line 31N of the DC link.

[0022] The auxiliary charging circuit 22 includes an auxiliary charging resistor 221 and an auxiliary charging switch 222.

[0023] The pre-charging resistor 221 is provided to suppress inrush current during the pre-charging period for the smoothing capacitor 13.

[0024] The auxiliary charge switch 222 is connected in parallel to the auxiliary charge resistor 221. The auxiliary charge switch 222 opens and closes the circuit between the converter 11 and the smoothing capacitor 13 under the control of an auxiliary charge control unit (not shown). The auxiliary charge control unit commands the auxiliary charge switch 222 to open during the auxiliary charge period and commands the auxiliary charge switch 222 to close during the motor drive period, which is a period other than the auxiliary charge period. Examples of the auxiliary charge switch 222 include relays and semiconductor switching elements, but other switch components may also be used. Examples of semiconductor switching elements include IGBTs, FETs, thyristors, GTOs, and transistors, but other semiconductor elements may also be used.

[0025] When power is supplied to the motor drive unit 1, power is supplied from the AC power supply 2 to the motor drive unit 1, and pre-charging of the smoothing capacitor 13 begins. During the pre-charging period from when the motor drive unit 1 is powered on until the motor 3 starts to run, the pre-charging switch 222 is open. As a result, during the pre-charging period, the current output from the converter 11 flows into the smoothing capacitor 13 through the pre-charging resistor 221, and the smoothing capacitor 13 is charged (pre-charged). In this way, during the pre-charging period, the current output from the converter 11 flows through the pre-charging resistor 221, which prevents the occurrence of inrush current. After the start of pre-charging, when the smoothing capacitor 13 is fully charged, the pre-charging switch 222 is closed. This completes the pre-charging of the smoothing capacitor 13. After the completion of pre-charging, the inverter control unit 10 starts driving the motor 3. During the motor driving period, the current output from the converter 11 flows through the closed pre-charging switch 222 towards the smoothing capacitor 13 and the inverter 12. When performing the ground fault detection process, the auxiliary charging switch 222 should be closed.

[0026] The DC link current detection unit 15 detects the DC link current flowing through the positive power line 31P of the DC link 19. The value of the current flowing from the converter 11 side to the inverter 12 side through the positive power line 31P is taken as positive. Examples of current detection methods by the DC link current detection unit 15 include detecting the current from the voltage drop across a shunt resistor, detecting the current from the magnetic field detected by a core placed around the power line, and detecting the current by converting the magnetic field generated around the power line into a voltage using the Hall effect.

[0027] In the first embodiment of this disclosure, the ground fault detection unit 14 detects the switching elements S on the upper arms of each phase of the inverter 12 when the smoothing capacitor 13 is fully charged. UU S VU , and S WU Based on information related to the current that flows when any one of the following is turned on, a ground fault is detected in either the three-phase power line between the inverter 12 and the motor 3 or in the three-phase winding of the motor 3.

[0028] For example, as shown by the dotted line in Figure 1, if the W-phase power line 33W is ground faulted, the switching element S on the W-phase upper arm WU Turn on the other switching elements S UU S UL S VU S VL , and S WL When turned off, the AC power supply 2 is connected to the converter 11, the positive power line 31P of the DC link 19, and the switching element S of the W-phase upper arm. WU A ground fault current flows to the ground (earth) via the W-phase power line 33W. A similar ground fault current also flows through the same path if the W-phase winding of motor 3, which is connected to the W-phase power line 33W, is ground faulted. In the example shown in Figure 1, diode D of the R-phase upper arm of converter 11 is also shown. RU Although it is shown that a ground fault current is flowing, since the converter 11 is connected to the three-phase AC power supply 2, depending on the phase of the AC power supply 2, the diode D of the S-phase upper arm of the converter 11 SU Or the diode D of the upper arm of the T phase TU There is a timing when ground fault current flows.

[0029] Also, although not shown in Figure 1, if the U-phase power line 33U is ground faulted, the switching element S of the U-phase upper arm UU Turn on the other switching elements S UL S VU S VL S WU , and S WL When turned off, the AC power supply 2 is connected to the converter 11, the positive power line 31P of the DC link 19, and the switching element S of the U-phase upper arm. UU A ground fault current flows to the ground via the U-phase power line 33U. A similar ground fault current also flows through the same path if the U-phase winding of the motor 3 connected to the U-phase power line 33U is experiencing a ground fault.

[0030] Similarly, although not shown in Figure 1, if the V-phase power line 33V is ground faulted, the switching element S on the V-phase upper arm VU Turn on the other switching elements S UU S UL S VL S WU , and S WL When turned off, the AC power supply 2 is connected to the converter 11, the positive power line 31P of the DC link 19, and the switching element S of the V-phase upper arm. VU A ground fault current flows to the ground via the V-phase power line 33V. A similar ground fault current also flows through the same path if the V-phase winding of motor 3, which is connected to the V-phase power line 33V, is experiencing a ground fault.

[0031] Thus, if a ground fault occurs in either the three-phase power line between the inverter 12 and the motor 3 or in the three-phase winding of the motor 3, the switching element S of the upper arm of each phase of the inverter 12 will be activated. UU S VU , and S WU Among these, when the switching element in the same phase as the phase in which a ground fault occurs is turned on, a ground fault current flows in the positive power line 31P of the DC link 19. Therefore, in the first embodiment of this disclosure, the switching elements S on the upper arm of each phase of the inverter 12 UU S VU , and S WUBased on whether a ground fault current occurs in the positive power line 31P of the DC link 19 when only one of the following is turned on, it is determined whether there is a ground fault in either the three-phase power line between the inverter 12 and the motor 3 or the three-phase winding of the motor 3.

[0032] If a ground fault occurs in either the three-phase power line between the inverter 12 and the motor 3 or in the three-phase winding of the motor 3, a ground fault current larger than the DC link current that flows under normal conditions will flow through the positive power line 31P of the DC link 19. A threshold is set to distinguish between the DC link current that flows under normal conditions and the ground fault current. If the DC link current detected by the DC link current detection unit 15 is greater than a predetermined threshold, it is determined that a ground fault current has occurred. If the DC link current detected by the DC link current detection unit 15 is less than a predetermined threshold, it is determined that no ground fault current has occurred. The threshold can be set appropriately, for example, by operating the motor drive unit 1 during a trial run or actual operation, or by performing a computer simulation. The threshold may be stored in a rewritable memory device (not shown) and rewritable by an external device, and even after the threshold has been set, it can be changed to an appropriate value as needed.

[0033] The ground fault detection unit 14 is the switching element S of the U-phase upper arm of the inverter 12. UU When only is turned on, if the DC link current detected by the DC link current detection unit 15 is greater than a predetermined threshold, it is determined that a ground fault has occurred in either the U-phase power line 33U or the U-phase winding. The ground fault detection unit 14 detects the switching element S of the V-phase upper arm of the inverter 12. VU When only is turned on, if the DC link current detected by the DC link current detection unit 15 is greater than a predetermined threshold, it is determined that a ground fault has occurred in either the V-phase power line 33V or the V-phase winding. The ground fault detection unit 14 detects the switching element S of the W-phase upper arm of the inverter 12. WU When only the DC link current detection unit 15 is turned on, if the detected DC link current is greater than a predetermined threshold, it is determined that a ground fault has occurred in either the W-phase power line 33W or the W-phase winding.

[0034] Figure 2 is a flowchart showing the operation flow of the ground fault detection process in a motor drive device according to the first and third embodiments of this disclosure. The flowchart shown in Figure 2 is also applicable to the third embodiment described later.

[0035] When the auxiliary charge switch 222 is closed and the smoothing capacitor 13 is fully charged, in step S101, the inverter control unit 10 controls the switching element S of the U-phase upper arm of the inverter 12. UU Only the other switching elements S are turned on. UL S VU S VL S WU , and S WL Turn it off.

[0036] In step S102, the ground fault detection unit 14 determines whether the DC link current detected by the DC link current detection unit 15 is greater than a threshold value.

[0037] If the DC link current detected by the DC link current detection unit 15 in step S102 is determined to be greater than the threshold value, then in step S103, the ground fault detection unit 14 determines that a ground fault has occurred in either the U-phase power line 33U or the U-phase winding.

[0038] If the DC link current detected by the DC link current detection unit 15 in step S102 is not determined to be greater than the threshold, then in step S104, the inverter control unit 10 controls the switching element S of the V-phase upper arm of the inverter 12. VU Only the other switching elements S are turned on. UU S UL S VL S WU , and S WL Turn it off.

[0039] In step S105, the ground fault detection unit 14 determines whether the DC link current detected by the DC link current detection unit 15 is greater than a threshold value.

[0040] If the DC link current detected by the DC link current detection unit 15 in step S105 is determined to be greater than the threshold value, then in step S106, the ground fault detection unit 14 determines that a ground fault has occurred in either the V-phase power line 33V or the V-phase winding.

[0041] If the DC link current detected by the DC link current detection unit 15 in step S105 is not determined to be greater than the threshold, then in step S107, the inverter control unit 10 controls the switching element S of the W-phase upper arm of the inverter 12. WU Only the other switching elements S are turned on. UU S UL S VU S VL , and S WL Turn it off.

[0042] In step S108, the ground fault detection unit 14 determines whether the DC link current detected by the DC link current detection unit 15 is greater than a threshold value.

[0043] If the DC link current detected by the DC link current detection unit 15 in step S108 is determined to be greater than the threshold value, then in step S109, the ground fault detection unit 14 determines that a ground fault has occurred in either the W-phase power line 33W or the W-phase winding.

[0044] If the DC link current detected by the DC link current detection unit 15 in step S108 is not determined to be greater than the threshold, then in step S110, the ground fault detection unit 14 determines that all of the U-phase power line 33U, U-phase winding, V-phase power line 33V, V-phase winding, W-phase power line 33W, and W-phase winding are normal.

[0045] In the flowchart described above, the switching elements were turned on in the order of U-phase, V-phase, and W-phase. However, as a variation of this, the switching elements may be turned on in the order of V-phase, W-phase, and U-phase, or in the order of W-phase, U-phase, and V-phase, or in the order of V-phase, U-phase, and W-phase, or in the order of W-phase, V-phase, and U-phase.

[0046] <Second Embodiment of the Present Disclosure> Figure 3 is a circuit diagram showing a motor drive device according to the second embodiment of the present disclosure.

[0047] A second embodiment of the present disclosure is a modification of the first embodiment. In the second embodiment of the present disclosure, the switching elements S of the lower arms of each phase of the inverter 12 UL S VL , and S WL Based on whether a ground fault current occurs in the negative power line 31N of the DC link 19 when only one of the following is turned on, it is determined whether there is a ground fault in either the three-phase power line between the inverter 12 and the motor 3 or the three-phase winding of the motor 3.

[0048] As shown in Figure 3, the motor drive device 1 according to the second embodiment of the present disclosure comprises a converter 11, an inverter 12, a smoothing capacitor 13, a ground fault detection unit 14, a DC link current detection unit 15, an inverter control unit 10, and a pre-charging circuit 22. The power supply for driving each of these units, such as the ground fault detection unit 14, the DC link current detection unit 15, and the inverter control unit 10, is not shown in the figure. Furthermore, even before power is supplied to the motor drive device 1, power is supplied to drive each control unit in preparation for operation when power is supplied to the motor drive device 1.

[0049] The AC power supply 2, motor 3, converter 11, inverter 12, smoothing capacitor 13, inverter control unit 10, and auxiliary charging circuit 22 are as described in the first embodiment. The positive power line 31P, negative power line 31N, R-phase power line 32R, S-phase power line 32S, T-phase power line 32T, U-phase power line 33U, V-phase power line 33V, and W-phase power line 33W are also as described in the first embodiment. When performing ground fault detection processing, the auxiliary charging switch 222 is closed.

[0050] The DC link current detection unit 15 detects the DC link current flowing through the negative-side power line 31N of the DC link 19. Note that the value of the current flowing from the inverter 12 side to the converter 11 side through the positive-side power line 31P is taken as positive. An example of the current detection method by the DC link current detection unit 15 is as described in the first embodiment.

[0051] For example, as shown by the dotted line in FIG. 3, when the V-phase power line 33V is grounded, the switching element S of the V-phase lower arm VL is turned on, and the other switching elements S UU , S UL , S VU , S WU , and S WL are turned off, then a ground fault current flows from the ground through the V-phase power line 33V, the switching element S of the V-phase lower arm VL , the negative-side power line 31N of the DC link 19, and the converter 11 to the AC power supply 2. When the V-phase winding of the motor 3 connected to the V-phase power line 33V is grounded, the ground fault current also flows through the same path. In the example shown in FIG. 3, although it is shown that the ground fault current flows through the diode D SL of the S-phase lower arm of the converter 11, since the converter 11 is connected to the three-phase AC power supply 2, depending on the phase of the AC power supply 2, there is a timing when the ground fault current flows through the diode D RL of the R-phase lower arm or the diode D TL of the T-phase lower arm of the converter 11.

[0052] Also, although not shown in FIG. 3, when the U-phase power line 33U is grounded, the switching element S of the U-phase lower arm UL is turned on, and the other switching elements S UU , S VU , S VL , S WU , and S WL are turned off, then a ground fault current flows from the ground through the U-phase power line 33U, the switching element S of the U-phase lower arm UL , the negative-side power line 31N of the DC link 19, and the converter 11 to the AC power supply 2. When the U-phase winding of the motor 3 connected to the U-phase power line 33U is grounded, the ground fault current also flows through the same path.

[0053] Similarly, although not shown in Figure 3, if the W-phase power line 33W is ground faulted, the switching element S of the W-phase lower arm WL Turn on the other switching elements S UU S UL S VU S VL , and S WU When turned off, the W-phase power line 33W from the ground and the switching element S of the W-phase lower arm are connected. WL A ground fault current flows to the AC power supply 2 via the negative power line 31N of the DC link 19 and the converter 11. A similar ground fault current flows if the W-phase winding of the motor 3, which is connected to the W-phase power line 33W, is ground faulted.

[0054] Thus, if a ground fault occurs in either the three-phase power line between the inverter 12 and the motor 3 or in the three-phase winding of the motor 3, the switching element S of the lower arm of each phase of the inverter 12 will be activated. UL S VL , and S WL Among these, when the switching element in the same phase as the phase in which the ground fault occurs is turned on, a ground fault current flows in the negative power line 31N of the DC link 19. Therefore, in the second embodiment of this disclosure, the switching elements S of the lower arms of each phase of the inverter 12 UL S VL , and S WL The presence or absence of a ground fault in either the three-phase power line between the inverter 12 and the motor 3 or the three-phase winding of the motor 3 is determined based on whether or not a ground fault current occurs in the negative power line 31N of the DC link 19 when only one of the following is turned on. The presence or absence of a ground fault current is determined by whether or not the DC link current detected by the DC link current detection unit 15 provided on the negative power line 31N of the DC link 19 is greater than a predetermined threshold. The threshold is as described in the first embodiment.

[0055] The ground fault detection unit 14 is the switching element S of the lower U-phase arm of the inverter 12. ULWhen only is turned on, if the DC link current detected by the DC link current detection unit 15 is greater than a predetermined threshold, it is determined that a ground fault has occurred in either the U-phase power line 33U or the U-phase winding. The ground fault detection unit 14 detects the switching element S of the V-phase lower arm of the inverter 12. VL When only is turned on, if the DC link current detected by the DC link current detection unit 15 is greater than a predetermined threshold, it is determined that a ground fault has occurred in either the V-phase power line 33V or the V-phase winding. The ground fault detection unit 14 detects the switching element S of the W-phase lower arm of the inverter 12. WL When only the DC link current detection unit 15 is turned on, if the detected DC link current is greater than a predetermined threshold, it is determined that a ground fault has occurred in either the W-phase power line 33W or the W-phase winding.

[0056] Figure 4 is a flowchart showing the operation flow of the ground fault detection process in the motor drive device according to the second and fourth embodiments of this disclosure. The flowchart shown in Figure 4 is also applicable to the fourth embodiment described later.

[0057] When the auxiliary charge switch 222 is closed and the smoothing capacitor 13 is fully charged, in step S201, the inverter control unit 10 controls the switching element S of the lower U-phase arm of the inverter 12. UL Only the other switching elements S are turned on. UU S VU S VL S WU , and S WL Turn it off.

[0058] In step S202, the ground fault detection unit 14 determines whether the DC link current detected by the DC link current detection unit 15 is greater than a threshold value.

[0059] If the DC link current detected by the DC link current detection unit 15 in step S202 is determined to be greater than the threshold value, then in step S203, the ground fault detection unit 14 determines that a ground fault has occurred in either the U-phase power line 33U or the U-phase winding.

[0060] If the DC link current detected by the DC link current detection unit 15 in step S202 is not determined to be greater than the threshold, then in step S204, the inverter control unit 10 controls the switching element S of the V-phase lower arm of the inverter 12. VL Only the other switching elements S are turned on. UU S UL S VU S WU , and S WL Turn it off.

[0061] In step S205, the ground fault detection unit 14 determines whether the DC link current detected by the DC link current detection unit 15 is greater than a threshold value.

[0062] If the DC link current detected by the DC link current detection unit 15 in step S205 is determined to be greater than the threshold value, then in step S206, the ground fault detection unit 14 determines that a ground fault has occurred in either the V-phase power line 33V or the V-phase winding.

[0063] If the DC link current detected by the DC link current detection unit 15 in step S205 is not determined to be greater than the threshold, then in step S207, the inverter control unit 10 controls the switching element S of the W-phase lower arm of the inverter 12. WL Only the other switching elements S are turned on. UU S UL S VU S VL , and S WU Turn it off.

[0064] In step S208, the ground fault detection unit 14 determines whether the DC link current detected by the DC link current detection unit 15 is greater than a threshold value.

[0065] If the DC link current detected by the DC link current detection unit 15 in step S208 is determined to be greater than the threshold value, then in step S209, the ground fault detection unit 14 determines that a ground fault has occurred in either the W-phase power line 33W or the W-phase winding.

[0066] If the DC link current detected by the DC link current detection unit 15 in step S208 is not determined to be greater than the threshold, then in step S210, the ground fault detection unit 14 determines that all of the U-phase power line 33U, U-phase winding, V-phase power line 33V, V-phase winding, W-phase power line 33W, and W-phase winding are normal.

[0067] In the flowchart described above, the switching elements were turned on in the order of U-phase, V-phase, and W-phase. However, as a variation of this, the switching elements may be turned on in the order of V-phase, W-phase, and U-phase, or in the order of W-phase, U-phase, and V-phase, or in the order of V-phase, U-phase, and W-phase, or in the order of W-phase, V-phase, and U-phase.

[0068] <Third Embodiment of the Present Disclosure> Figure 5 is a circuit diagram showing a motor drive device according to the third embodiment of the present disclosure.

[0069] In a third embodiment of this disclosure, the switching element S of the upper arm of each phase of the inverter 12 UU S VU , and S WU When only one of the following is turned on, the presence or absence of a ground fault in either the three-phase power lines between the inverter 12 and the motor 3 or the three-phase windings of the motor 3 is determined based on whether or not a ground fault current occurs in at least one of the power lines among the R-phase power line 32R, S-phase power line 32S, and T-phase power line 32T.

[0070] As shown in Figure 5, the motor drive device 1 according to the third embodiment of the present disclosure comprises a converter 11, an inverter 12, a smoothing capacitor 13, a ground fault detection unit 14, a power supply current detection unit 16, an inverter control unit 10, and a pre-charging circuit 22. The power supply for driving each of the parts, such as the ground fault detection unit 14, the power supply current detection unit 16, and the inverter control unit 10, is not shown in the figure. Furthermore, even before power is supplied to the motor drive device 1, power is supplied to drive each control unit in preparation for operation when power is supplied to the motor drive device 1.

[0071] The AC power supply 2, motor 3, converter 11, inverter 12, smoothing capacitor 13, inverter control unit 10, and auxiliary charging circuit 22 are as described in the first embodiment. The positive power line 31P, negative power line 31N, R-phase power line 32R, S-phase power line 32S, T-phase power line 32T, U-phase power line 33U, V-phase power line 33V, and W-phase power line 33W are also as described in the first embodiment. When performing ground fault detection processing, the auxiliary charging switch 222 is closed.

[0072] The power supply current detection unit 16 detects the power supply current flowing through at least one of the R-phase power line 32R, S-phase power line 32S, and T-phase power line 32T. In the illustrated example, the power supply current detection unit 16 detects the power supply current flowing through each of the R-phase power line 32R, S-phase power line 32S, and T-phase power line 32T. As a variation, the power supply current detection unit 16 may detect the power supply current flowing through two of the R-phase power line 32R, S-phase power line 32S, and T-phase power line 32T, or it may detect the power supply current flowing through one of the R-phase power line 32R, S-phase power line 32S, and T-phase power line 32T. Examples of current detection methods by the power supply current detection unit 16 include detecting the current from the voltage drop across a shunt resistor, detecting the current from a magnetic field detected by a core provided around the power line, and detecting the current by converting the magnetic field generated around the power line into a voltage using the Hall effect.

[0073] For example, as shown by the dotted line in Figure 5, if the U-phase power line 33U is ground faulted, the switching element S of the U-phase upper arm UU Turn on the other switching elements S UL S VU S VL S WU , and S WL When turned off, the AC power supply 2 is connected to the converter 11, the positive power line 31P of the DC link 19, and the switching element S of the U-phase upper arm. UUA ground fault current flows to the ground via the U-phase power line 33U. A similar ground fault current also flows through the same path if the U-phase winding of the motor 3 connected to the U-phase power line 33U is experiencing a ground fault. In the example shown in Figure 5, the T-phase power line 32T and the diode D on the T-phase upper arm of the converter 11 are also involved. TU Although it is shown that a ground fault current is flowing, since the converter 11 is connected to a three-phase AC power supply 2, depending on the phase of the AC power supply 2, the R-phase power line 32R and the diode D on the R-phase upper arm of the converter 11 may be affected. RU , or the S-phase power line 32S and the diode D of the S-phase upper arm of the converter 11 SU There is a timing when ground fault current flows.

[0074] Also, although not shown in Figure 5, if the V-phase power line 33V is ground faulted, the switching element S on the V-phase upper arm VU Turn on the other switching elements S UU S UL S VL S WU , and S WL When turned off, the AC power supply 2 is connected to the converter 11, the positive power line 31P of the DC link 19, and the switching element S of the V-phase upper arm. VU A ground fault current flows to the ground via the V-phase power line 33V. A similar ground fault current also flows through the same path if the V-phase winding of motor 3, which is connected to the V-phase power line 33V, is experiencing a ground fault.

[0075] Similarly, although not shown in Figure 5, if the W-phase power line 33W is ground faulted, the switching element S on the W-phase upper arm WU Turn on the other switching elements S UU S UL S VU S VL , and S WL When turned off, the AC power supply 2 is connected to the converter 11, the positive power line 31P of the DC link 19, and the switching element S of the W-phase upper arm. WU A ground fault current flows to the ground via the W-phase power line 33W. If the W-phase winding of motor 3, which is connected to the W-phase power line 33W, is ground faulted, a ground fault current will flow through the same path.

[0076] Thus, if a ground fault occurs in either the three-phase power line between the inverter 12 and the motor 3 or in the three-phase winding of the motor 3, the switching element S of the upper arm of each phase of the inverter 12 will be activated. UU S VU , and S WU When a switching element in the same phase as the phase in which a ground fault occurs is turned on, a ground fault current flows through the power line of one of the phases: R-phase power line 32R, S-phase power line 32S, or T-phase power line 32T. Therefore, in the third embodiment of this disclosure, the switching element S on the upper arm of each phase of the inverter 12 UU S VU , and S WU Based on whether a ground fault current occurs in at least one of the power lines among the R-phase power line 32R, S-phase power line 32S, and T-phase power line 32T when only one of the above is turned on, it is determined whether there is a ground fault in either the three-phase power lines between the inverter 12 and the motor 3 or the three-phase windings of the motor 3.

[0077] Since a three-phase balanced AC current is supplied to the converter 11 from the AC power supply 2, the phase of the power line through which the ground fault current flows and the phase of the switching element on the upper arm switch sequentially in the order of R phase, S phase, and T phase during one cycle of the AC power supply 2. In the example shown in Figure 5, the power supply current detection unit 16 detects the power supply current flowing through each of the R phase power line 32R, S phase power line 32S, and T phase power line 32T, so that the power supply current detection unit 16 can detect the ground fault current with little delay regardless of which of the R phase, S phase, and T phase occurs. Modified versions in which the power supply current detection unit 16 detects the power supply current flowing through two of the R phase power line 32R, S phase power line 32S, and T phase power line 32T, or in which it detects the power supply current flowing through one of the R phase power line 32R, S phase power line 32S, and T phase power line 32T, may have a larger detection delay for the power supply current detection unit 16, but have the advantage of being low cost.

[0078] If a ground fault occurs in either the three-phase power line between the inverter 12 and the motor 3 or in the three-phase winding of the motor 3, a ground fault current larger than the normal power supply current will flow through the R-phase power line 32R, the S-phase power line 32S, and the T-phase power line 32T. A threshold is set to distinguish between the normal power supply current and the ground fault current. If the current detected by the power supply current detection unit 16 is greater than a predetermined threshold, it is determined that a ground fault current has occurred. If the current detected by the power supply current detection unit 16 is less than a predetermined threshold, it is determined that no ground fault current has occurred. The threshold can be set appropriately, for example, by operating the motor drive device 1 during a trial run or actual operation, or by performing a computer simulation. The threshold may be stored in a rewritable memory device (not shown) and rewritable by an external device, and even after the threshold has been set, it can be changed to an appropriate value as needed.

[0079] The ground fault detection unit 14 is the switching element S of the U-phase upper arm of the inverter 12. UU When only is turned on, if the power supply current detected by the power supply current detection unit 16 is greater than a predetermined threshold, it is determined that a ground fault has occurred in either the U-phase power line 33U or the U-phase winding. The ground fault detection unit 14 detects the switching element S of the V-phase upper arm of the inverter 12. VU When only is turned on, if the power supply current detected by the power supply current detection unit 16 is greater than a predetermined threshold, it is determined that a ground fault has occurred in either the V-phase power line 33V or the V-phase winding. The ground fault detection unit 14 detects the switching element S of the W-phase upper arm of the inverter 12. WU When only the power supply current detection unit 16 is turned on, if the power supply current detected by the power supply current detection unit 16 is greater than a predetermined threshold, it is determined that a ground fault has occurred in either the W-phase power line 33W or the W-phase winding.

[0080] Next, the operation flow of the ground fault detection process in the motor drive device according to the third embodiment of this disclosure will be explained using the flowchart shown in Figure 2.

[0081] When the auxiliary charge switch 222 is closed and the smoothing capacitor 13 is fully charged, in step S101, the inverter control unit 10 controls the switching element S of the U-phase upper arm of the inverter 12. UU Only the other switching elements S are turned on. UL S VU S VL S WU , and S WL Turn it off.

[0082] In step S102, the ground fault detection unit 14 determines whether the power supply current detected by the power supply current detection unit 16 is greater than a threshold value.

[0083] If the power supply current detected by the power supply current detection unit 16 in step S102 is determined to be greater than the threshold value, then in step S103, the ground fault detection unit 14 determines that a ground fault has occurred in either the U-phase power line 33U or the U-phase winding.

[0084] If, in step S102, the power supply current detected by the power supply current detection unit 16 is not determined to be greater than the threshold, then in step S104, the inverter control unit 10 controls the switching element S of the V-phase upper arm of the inverter 12. VU Only the other switching elements S are turned on. UU S UL S VL S WU , and S WL Turn it off.

[0085] In step S105, the ground fault detection unit 14 determines whether the power supply current detected by the power supply current detection unit 16 is greater than a threshold value.

[0086] If the power supply current detected by the power supply current detection unit 16 in step S105 is determined to be greater than the threshold, then in step S106, the ground fault detection unit 14 determines that a ground fault has occurred in either the V-phase power line 33V or the V-phase winding.

[0087] If the power supply current detected by the power supply current detection unit 16 in step S105 is not determined to be greater than the threshold, then in step S107, the inverter control unit 10 controls the switching element S of the W-phase upper arm of the inverter 12. WU Only the other switching elements S are turned on. UU S UL S VU S VL , and S WL Turn it off.

[0088] In step S108, the ground fault detection unit 14 determines whether the power supply current detected by the power supply current detection unit 16 is greater than a threshold value.

[0089] If the power supply current detected by the power supply current detection unit 16 in step S108 is determined to be greater than the threshold value, then in step S109, the ground fault detection unit 14 determines that a ground fault has occurred in either the W-phase power line 33W or the W-phase winding.

[0090] If the power supply current detected by the power supply current detection unit 16 in step S108 is not determined to be greater than the threshold, then in step S110, the ground fault detection unit 14 determines that all of the U-phase power line 33U, U-phase winding, V-phase power line 33V, V-phase winding, W-phase power line 33W, and W-phase winding are normal.

[0091] In the flowchart described above, the switching elements were turned on in the order of U-phase, V-phase, and W-phase. However, as a variation of this, the switching elements may be turned on in the order of V-phase, W-phase, and U-phase, or in the order of W-phase, U-phase, and V-phase, or in the order of V-phase, U-phase, and W-phase, or in the order of W-phase, V-phase, and U-phase.

[0092] <Fourth Embodiment of the Present Disclosure> Figure 6 is a circuit diagram showing a motor drive device according to the fourth embodiment of the present disclosure.

[0093] A fourth embodiment of the present disclosure is a modification of the third embodiment. In the fourth embodiment of the present disclosure, the switching elements S of the lower arms of each phase of the inverter 12 UL S VL , and SWL Based on whether a ground fault current occurs in at least one of the power lines among the R-phase power line 32R, S-phase power line 32S, and T-phase power line 32T when only one of the above is turned on, it is determined whether there is a ground fault in either the three-phase power lines between the inverter 12 and the motor 3 or the three-phase windings of the motor 3.

[0094] As shown in Figure 6, the motor drive device 1 according to the fourth embodiment of this disclosure comprises a converter 11, an inverter 12, a smoothing capacitor 13, a ground fault detection unit 14, a power supply current detection unit 16, an inverter control unit 10, and a pre-charging circuit 22. The power supply for driving each of the parts, such as the ground fault detection unit 14, the DC link current detection unit 15, and the inverter control unit 10, is not shown in the figure. Furthermore, even before power is supplied to the motor drive device 1, power is supplied to drive each control unit in preparation for operation when power is supplied to the motor drive device 1.

[0095] The AC power supply 2, motor 3, converter 11, inverter 12, smoothing capacitor 13, inverter control unit 10, and auxiliary charging circuit 22 are as described in the first embodiment. The positive power line 31P, negative power line 31N, R-phase power line 32R, S-phase power line 32S, T-phase power line 32T, U-phase power line 33U, V-phase power line 33V, and W-phase power line 33W are also as described in the first embodiment. The power supply current detection unit 16 is as described in the third embodiment. When performing ground fault detection processing, the auxiliary charging switch 222 is closed.

[0096] For example, as shown by the dotted line in Figure 6, if the W-phase power line 33W is ground faulted, the switching element S of the W-phase lower arm WL Turn on the other switching elements S UU S UL S VU S VL , and S WU When turned off, the W-phase power line 33W from the ground and the switching element S of the W-phase lower arm are connected. WLA ground fault current flows to the AC power supply 2 via the negative power line 31N of the DC link 19 and the converter 11. A similar ground fault current flows if the W-phase winding of the motor 3 connected to the W-phase power line 33W is ground faulted. In the example shown in Figure 6, the S-phase power line 32S and the diode D of the S-phase lower arm of the converter 11 are connected. SL Although it is shown that a ground fault current is flowing, a three-phase AC power supply 2 is connected to the converter 11, so depending on the phase of the AC power supply 2, the R-phase power line 32R and the diode D of the lower R-phase arm of the converter 11 may be affected. RL , or the T-phase power line 32T and the diode D of the T-phase lower arm of the converter 11 ST There is a timing when ground fault current flows.

[0097] Also, although not shown in Figure 6, if the U-phase power line 33U is ground faulted, the switching element S of the lower U-phase arm UL Turn on the other switching elements S UU S VU S VL S WU , and S WL When turned off, the U-phase power line 33U and the switching element S of the U-phase lower arm are connected to the ground. UL A ground fault current flows to the AC power supply 2 via the negative power line 31N of the DC link 19 and the converter 11. A similar ground fault current flows if the U-phase winding of the motor 3, which is connected to the U-phase power line 33U, is ground faulted.

[0098] Similarly, although not shown in Figure 6, if the V-phase power line 33V is ground faulted, the switching element S of the V-phase lower arm VL Turn on the other switching elements S UU S UL S VU S WU , and S WL When turned off, the V-phase power line 33V from the ground and the switching element S on the V-phase lower arm are connected. UV A ground fault current flows to the AC power supply 2 via the negative power line 31N of the DC link 19 and the converter 11. A similar ground fault current flows if the V-phase winding of the motor 3, which is connected to the V-phase power line 33V, is ground faulted.

[0099] Thus, if a ground fault occurs in either the three-phase power line between the inverter 12 and the motor 3 or in the three-phase winding of the motor 3, the switching element S of the lower arm of each phase of the inverter 12 will be activated. UL S VL , and S WL When a switching element in the same phase as the phase in which a ground fault occurs is turned on, a ground fault current flows through the power line of one of the phases: R-phase power line 32R, S-phase power line 32S, or T-phase power line 32T. Therefore, in the fourth embodiment of this disclosure, the switching element S of the lower arm of each phase of the inverter 12 UL S VL , and S WL Based on whether a ground fault current occurs in at least one of the power lines among the R-phase power line 32R, S-phase power line 32S, and T-phase power line 32T when only one of the above is turned on, the presence or absence of a ground fault in either the three-phase power lines between the inverter 12 and the motor 3 or the three-phase windings of the motor 3 is determined. The threshold is as described in the third embodiment.

[0100] Since a three-phase balanced AC current is supplied to the converter 11 from the AC power supply 2, the phase of the power line through which the ground fault current flows and the switching element of the upper arm switch sequentially in the order of R phase, S phase, and T phase during one cycle of the AC power supply 2. In the example shown in Figure 6, the power supply current detection unit 16 detects the power supply current flowing through each of the R phase power line 32R, S phase power line 32S, and T phase power line 32T, so that the power supply current detection unit 16 can detect the ground fault current with little delay regardless of which of the R phase, S phase, and T phase occurs. Modified versions in which the power supply current detection unit 16 detects the power supply current flowing through two of the R phase power line 32R, S phase power line 32S, and T phase power line 32T, or in which it detects the power supply current flowing through one of the R phase power line 32R, S phase power line 32S, and T phase power line 32T, may have a larger detection delay for the power supply current detection unit 16, but have the advantage of being low cost.

[0101] The ground fault detection unit 14 is the switching element S of the lower U-phase arm of the inverter 12. ULWhen only is turned on, if the power supply current detected by the power supply current detection unit 16 is greater than a predetermined threshold, it is determined that a ground fault has occurred in either the U-phase power line 33U or the U-phase winding. The ground fault detection unit 14 detects the switching element S of the V-phase lower arm of the inverter 12. VL When only is turned on, if the power supply current detected by the power supply current detection unit 16 is greater than a predetermined threshold, it is determined that a ground fault has occurred in either the V-phase power line 33V or the V-phase winding. The ground fault detection unit 14 detects the switching element S of the W-phase lower arm of the inverter 12. WL When only the power supply current detection unit 16 is turned on, if the power supply current detected by the power supply current detection unit 16 is greater than a predetermined threshold, it is determined that a ground fault has occurred in either the W-phase power line 33W or the W-phase winding.

[0102] Next, the operation flow of the ground fault detection process in the motor drive device according to the fourth embodiment of this disclosure will be explained using the flowchart shown in Figure 4.

[0103] When the auxiliary charge switch 222 is closed and the smoothing capacitor 13 is fully charged, in step S201, the inverter control unit 10 controls the switching element S of the lower U-phase arm of the inverter 12. UL Only the other switching elements S are turned on. UU S VU S VL S WU , and S WL Turn it off.

[0104] In step S202, the ground fault detection unit 14 determines whether the power supply current detected by the power supply current detection unit 16 is greater than a threshold value.

[0105] If the power supply current detected by the power supply current detection unit 16 in step S202 is determined to be greater than the threshold value, then in step S203, the ground fault detection unit 14 determines that a ground fault has occurred in either the U-phase power line 33U or the U-phase winding.

[0106] If the power supply current detected by the power supply current detection unit 16 in step S202 is not determined to be greater than the threshold, then in step S204, the inverter control unit 10 controls the switching element S of the V-phase lower arm of the inverter 12.VL Only the other switching elements S are turned on. UU S UL S VU S WU , and S WL Turn it off.

[0107] In step S205, the ground fault detection unit 14 determines whether the power supply current detected by the power supply current detection unit 16 is greater than a threshold value.

[0108] If the power supply current detected by the power supply current detection unit 16 in step S205 is determined to be greater than the threshold value, then in step S206, the ground fault detection unit 14 determines that a ground fault has occurred in either the V-phase power line 33V or the V-phase winding.

[0109] If the power supply current detected by the power supply current detection unit 16 in step S205 is not determined to be greater than the threshold, then in step S207, the inverter control unit 10 controls the switching element S of the W-phase lower arm of the inverter 12. WL Only the other switching elements S are turned on. UU S UL S VU S VL , and S WU Turn it off.

[0110] In step S208, the ground fault detection unit 14 determines whether the power supply current detected by the power supply current detection unit 16 is greater than a threshold value.

[0111] If the power supply current detected by the power supply current detection unit 16 in step S208 is determined to be greater than the threshold value, then in step S209, the ground fault detection unit 14 determines that a ground fault has occurred in either the W-phase power line 33W or the W-phase winding.

[0112] If the power supply current detected by the power supply current detection unit 16 in step S208 is not determined to be greater than the threshold, then in step S210, the ground fault detection unit 14 determines that all of the U-phase power line 33U, U-phase winding, V-phase power line 33V, V-phase winding, W-phase power line 33W, and W-phase winding are normal.

[0113] In the flowchart described above, the switching elements were turned on in the order of U-phase, V-phase, and W-phase. However, as a variation of this, the switching elements may be turned on in the order of V-phase, W-phase, and U-phase, or in the order of W-phase, U-phase, and V-phase, or in the order of V-phase, U-phase, and W-phase, or in the order of W-phase, V-phase, and U-phase.

[0114] <Fifth Embodiment of the Present Disclosure> Figure 7 is a circuit diagram showing a motor drive device according to the fifth embodiment of the present disclosure.

[0115] When an overcurrent, which is a ground fault current generated by a ground fault, flows through an ON switching element in the inverter 12, the voltage between the emitter and collector of the switching element becomes higher than normal. In the fifth embodiment of this disclosure, the switching element S of the upper arm of each phase of the inverter 12 UU S VU , and S WU When only one of the switching elements is turned on, the voltage between the emitter and collector of that switched element is detected, and based on this voltage, it is determined whether or not a ground fault current, which is an overcurrent, has occurred, thereby determining whether or not there is a ground fault in either the three-phase power line between the inverter 12 and the motor 3 or the three-phase winding of the motor 3.

[0116] As shown in Figure 7, the motor drive device 1 according to the fifth embodiment of the present disclosure comprises a converter 11, an inverter 12, a smoothing capacitor 13, a ground fault detection unit 14, a voltage detection unit 17, an overcurrent detection unit 18, an inverter control unit 10, and a pre-charging circuit 22. The power supply for driving each of the parts, such as the ground fault detection unit 14, the voltage detection unit 17, the overcurrent detection unit 18, and the inverter control unit 10, is not shown in the figure. Furthermore, even before power is supplied to the motor drive device 1, power is supplied to drive each control unit in preparation for operation when power is supplied to the motor drive device 1.

[0117] The AC power supply 2, motor 3, converter 11, inverter 12, smoothing capacitor 13, inverter control unit 10, and auxiliary charging circuit 22 are as described in the first embodiment. The positive power line 31P, negative power line 31N, R-phase power line 32R, S-phase power line 32S, T-phase power line 32T, U-phase power line 33U, V-phase power line 33V, and W-phase power line 33W are also as described in the first embodiment. When performing ground fault detection processing, the auxiliary charging switch 222 is closed.

[0118] The voltage detection unit 17 is the switching element S of the U-phase upper arm of the inverter. UU V-phase upper arm switching element S VU , and the switching element S of the W-phase upper arm WU The voltage between the collector, which is the current inflow terminal, and the emitter, which is the current outflow terminal, is detected.

[0119] The overcurrent detection unit 18 determines that an overcurrent has occurred in the upper arm switching element of the phase in which the voltage detected by the voltage detection unit 17 is greater than a predetermined threshold. A threshold is set to distinguish between the current flowing normally through the switched-on switching element and the ground fault current. If the current detected by the overcurrent detection unit 18 is greater than a predetermined threshold, it is determined that an overcurrent has occurred, and if the current detected by the overcurrent detection unit 18 is less than a predetermined threshold, it is determined that no overcurrent has occurred. The threshold can be set appropriately, for example, by operating the motor drive device 1 during a trial run or actual operation, or by performing a computer simulation. The threshold may be stored in a rewritable memory device (not shown) and rewritable by an external device, and even after the threshold has been set, it can be changed to an appropriate value as needed.

[0120] The voltage detection unit 17 and the overcurrent detection unit 18 may be implemented as separate detection circuits, but they may also be implemented as an integrated detection circuit (for example, a DESAT detection circuit). The DESAT detection circuit has the function of turning off a switching element and outputting a FAULT-N signal when the voltage between the emitter and collector of the switching element exceeds a threshold. The FAULT-N signal output from the DESAT detection circuit may be used as the signal output by the overcurrent detection unit 18 when an overcurrent is detected.

[0121] For example, as shown by the dotted line in Figure 7, if the W-phase power line 33W is ground faulted, the switching element S on the W-phase upper arm WU Turn on the other switching elements S UU S UL S VU S VL , and S WL When turned off, the AC power supply 2 is connected to the converter 11, the positive power line 31P of the DC link 19, and the switching element S of the W-phase upper arm. WU A ground fault current, which is an overcurrent, flows to the ground via the W-phase power line 33W. A similar ground fault current also flows through the same path if the W-phase winding of motor 3, which is connected to the W-phase power line 33W, is experiencing a ground fault. The switching element S of the W-phase upper arm... WU When an overcurrent, which is a ground fault current, flows through the W-phase upper arm, the switching element S WU The emitter-collector voltage becomes higher than normal. The overcurrent detection unit 18 detects the switching element S of the W-phase upper arm detected by the voltage detection unit 17. WU If the emitter-collector voltage is greater than a predetermined threshold, the switching element S of the W-phase upper arm WU It is determined that an overcurrent has occurred. In the example shown in Figure 7, diode D of the S-phase upper arm of converter 11 SU Although it is shown that a ground fault current is flowing, a three-phase AC power supply 2 is connected to the converter 11, so depending on the phase of the AC power supply 2, the diode D of the upper R-phase arm of the converter 11 RU Or the diode D of the upper arm of the T phase TU There is a timing when ground fault current flows.

[0122] Also, although not shown in Figure 7, if the U-phase power line 33U is ground faulted, the switching element S of the U-phase upper arm UU Turn on the other switching elements S UL S VU S VL S WU , and S WL When turned off, the AC power supply 2 is connected to the converter 11, the positive power line 31P of the DC link 19, and the switching element S of the U-phase upper arm. UU A ground fault current flows to the ground via the U-phase power line 33U. A similar ground fault current also flows through the same path if the U-phase winding of the motor 3 connected to the U-phase power line 33U is ground faulted. The switching element S of the U-phase upper arm... UU When an overcurrent, which is a ground fault current, flows through the U-phase upper arm, the switching element S UU The emitter-collector voltage becomes higher than normal. The overcurrent detection unit 18 detects the switching element S of the U-phase upper arm detected by the voltage detection unit 17. UU If the emitter-collector voltage is greater than a predetermined threshold, the switching element S of the U-phase upper arm UU It is determined that an overcurrent has occurred.

[0123] Similarly, although not shown in Figure 7, if the V-phase power line 33V is ground faulted, the switching element S on the V-phase upper arm VU Turn on the other switching elements S UU S UL S VL S WU , and S WL When turned off, the AC power supply 2 is connected to the converter 11, the positive power line 31P of the DC link 19, and the switching element S of the V-phase upper arm. VU A ground fault current flows to the ground via the V-phase power line 33V. A similar ground fault current also flows through the same path if the V-phase winding of motor 3, which is connected to the V-phase power line 33V, is ground faulted. The switching element S of the V-phase upper arm... VU When an overcurrent, or ground fault current, flows through it, the switching element S of the V-phase upper arm... VUThe emitter-collector voltage becomes higher than normal. The overcurrent detection unit 18 detects the switching element S of the V-phase upper arm detected by the voltage detection unit 17. VU If the emitter-collector voltage is greater than a predetermined threshold, the switching element S of the V-phase upper arm VU It is determined that an overcurrent has occurred.

[0124] Thus, when the smoothing capacitor 13 is fully charged, if a ground fault occurs in either the three-phase power line between the inverter 12 and the motor 3 or in the three-phase winding of the motor 3, the switching element S of the upper arm of each phase of the inverter 12 will be activated. UU S VU , and S WU In this case, when a switching element in the same phase as the phase in which a ground fault occurs is turned on, an overcurrent is generated in that switching element. Therefore, in the fifth embodiment of this disclosure, when the smoothing capacitor 13 is fully charged, the switching elements S on the upper arms of each phase of the inverter 12 UU S VU , and S WU When only one of the switching elements is turned on, the voltage between the emitter and collector of that switched element is detected, and based on this voltage, it is determined whether or not a ground fault current, which is an overcurrent, has occurred, thereby determining whether or not there is a ground fault in either the three-phase power line between the inverter 12 and the motor 3 or the three-phase winding of the motor 3.

[0125] The ground fault detection unit 14 is the switching element S of the U-phase upper arm of the inverter 12. UU When only is turned on, if the overcurrent detection unit 18 detects an overcurrent, it is determined that a ground fault has occurred in either the U-phase power line 33U or the U-phase winding. The ground fault detection unit 14 detects the switching element S of the V-phase upper arm of the inverter 12. VU When only is turned on, if the overcurrent detection unit 18 detects an overcurrent, it is determined that a ground fault has occurred in either the V-phase power line 33V or the V-phase winding. The ground fault detection unit 14 detects the switching element S of the W-phase upper arm of the inverter 12. WU If the overcurrent detection unit 18 detects an overcurrent when only the power line is turned on, it is determined that a ground fault has occurred in either the W-phase power line 33W or the W-phase winding.

[0126] Figure 8 is a flowchart showing the operation flow of the ground fault detection process in a motor drive device according to the fifth embodiment of the present disclosure.

[0127] When the auxiliary charge switch 222 is closed and the smoothing capacitor 13 is fully charged, in step S301, the inverter control unit 10 controls the switching element S of the U-phase upper arm of the inverter 12. UU Only the other switching elements S are turned on. UL S VU S VL S WU , and S WL Turn it off.

[0128] In step S302, the voltage detection unit 17 detects the switching element S of the U-phase upper arm of the inverter 12. UU The voltage between the collector, which is the current inflow terminal, and the emitter, which is the current outflow terminal, is detected by the voltage detection unit 17. The overcurrent detection unit 18 detects the switching element S of the U-phase upper arm. UU Based on the emitter-collector voltage, the switching element S of the U-phase upper arm UU Determine whether or not an overcurrent has occurred.

[0129] In step S302, the switching element S of the U-phase upper arm UU If it is determined that an overcurrent has occurred, in step S303 the ground fault detection unit 14 determines that a ground fault has occurred in either the U-phase power line 33U or the U-phase winding.

[0130] In step S302, the switching element S of the U-phase upper arm UU If it is not determined that an overcurrent has occurred, in step S304, the inverter control unit 10 controls the switching element S of the V-phase upper arm of the inverter 12. VU Only the other switching elements S are turned on. UU S UL S VL S WU , and S WL Turn it off.

[0131] In step S305, the voltage detection unit 17 detects the switching element S of the V-phase upper arm of the inverter 12. VU The voltage between the collector, which is the current inflow terminal, and the emitter, which is the current outflow terminal, is detected by the voltage detection unit 17. The overcurrent detection unit 18 detects the switching element S of the V-phase upper arm. VU Based on the emitter-collector voltage, the switching element S of the V-phase upper arm VU Determine whether or not an overcurrent has occurred.

[0132] In step S305, the switching element S of the V-phase upper arm VU If it is determined that an overcurrent has occurred, in step S306 the ground fault detection unit 14 determines that a ground fault has occurred in either the V-phase power line 33V or the V-phase winding.

[0133] In step S305, the switching element S of the V-phase upper arm VU If it is not determined that an overcurrent has occurred, in step S307, the inverter control unit 10 controls the switching element S of the W-phase upper arm of the inverter 12. WU Only the other switching elements S are turned on. UU S UL S VU S VL , and S WL Turn it off.

[0134] In step S308, the voltage detection unit 17 detects the switching element S of the W-phase upper arm of the inverter 12. WU The voltage between the collector, which is the current inflow terminal, and the emitter, which is the current outflow terminal, is detected by the voltage detection unit 17. The overcurrent detection unit 18 detects the switching element S of the W-phase upper arm. WU Based on the emitter-collector voltage, the switching element S of the W-phase upper arm WU Determine whether or not an overcurrent has occurred.

[0135] In step S308, the switching element S of the W-phase upper arm WUIf it is determined that an overcurrent has occurred, in step S309 the ground fault detection unit 14 determines that a ground fault has occurred in either the W-phase power line 33W or the W-phase winding.

[0136] In step S308, the switching element S of the W-phase upper arm WU If it is not determined that an overcurrent has occurred, in step S310, the ground fault detection unit 14 determines that all of the U-phase power line 33U, U-phase winding, V-phase power line 33V, V-phase winding, W-phase power line 33W, and W-phase winding are normal.

[0137] In the flowchart described above, the switching elements were turned on in the order of U-phase, V-phase, and W-phase. However, as a variation of this, the switching elements may be turned on in the order of V-phase, W-phase, and U-phase, or in the order of W-phase, U-phase, and V-phase, or in the order of V-phase, U-phase, and W-phase, or in the order of W-phase, V-phase, and U-phase.

[0138] <Sixth Embodiment of the Disclosure> Figure 9 is a circuit diagram showing a motor drive device according to the sixth embodiment of the Disclosure.

[0139] A sixth embodiment of the present disclosure is a modification of the fifth embodiment. In the sixth embodiment of the present disclosure, the switching elements S of the lower arms of each phase of the inverter 12 are UL S VL , and S WL When only one of the switching elements is turned on, the voltage between the emitter and collector of that switched element is detected, and based on this voltage, it is determined whether or not a ground fault current, which is an overcurrent, has occurred, thereby determining whether or not there is a ground fault in either the three-phase power line between the inverter 12 and the motor 3 or the three-phase winding of the motor 3.

[0140] As shown in Figure 9, the motor drive device 1 according to the ninth embodiment of the present disclosure comprises a converter 11, an inverter 12, a smoothing capacitor 13, a ground fault detection unit 14, a voltage detection unit 17, an overcurrent detection unit 18, an inverter control unit 10, and a pre-charging circuit 22. Power supplies for driving each of these units, such as the ground fault detection unit 14, the voltage detection unit 17, the overcurrent detection unit 18, and the inverter control unit 10, are not shown in the figure. Furthermore, even before power is supplied to the motor drive device 1, power is supplied to drive each control unit in preparation for operation when power is supplied to the motor drive device 1.

[0141] The AC power supply 2, motor 3, converter 11, inverter 12, smoothing capacitor 13, inverter control unit 10, and auxiliary charging circuit 22 are as described in the first embodiment. The positive power line 31P, negative power line 31N, R-phase power line 32R, S-phase power line 32S, T-phase power line 32T, U-phase power line 33U, V-phase power line 33V, and W-phase power line 33W are also as described in the first embodiment. When performing ground fault detection processing, the auxiliary charging switch 222 is closed.

[0142] The voltage detection unit 17 is the switching element S of the lower U-phase arm of the inverter. UL V-phase upper arm switching element S VL , and the switching element S of the W-phase upper arm WL The voltage between the collector, which is the current inflow terminal, and the emitter, which is the current outflow terminal, is detected.

[0143] The overcurrent detection unit 18 determines that an overcurrent has occurred in the switching element of the lower arm of the phase in which the voltage detected by the voltage detection unit 17 is greater than a predetermined threshold. A threshold is set to distinguish between the current flowing normally through the switched element when it is turned on and the ground fault current. If the current detected by the overcurrent detection unit 18 is greater than the predetermined threshold, it is determined that an overcurrent has occurred, and if the current detected by the overcurrent detection unit 18 is less than the predetermined threshold, it is determined that no overcurrent has occurred. The threshold is as described in the fifth embodiment.

[0144] For example, as shown by the dotted line in Figure 9, if the U-phase power line 33U is ground faulted, the switching element S of the lower U-phase arm UL Turn on the other switching elements S UU S VU S VL S WU , and S WL When turned off, the U-phase power line 33U and the switching element S of the U-phase lower arm are connected to the ground. UL A ground fault current flows to the AC power supply 2 via the negative power line 31N of the DC link 19 and the converter 11. A similar ground fault current also flows if the U-phase winding of the motor 3, which is connected to the U-phase power line 33U, is ground faulted. The switching element S of the U-phase lower arm... UL When an overcurrent, or ground fault current, flows through it, the switching element S of the lower U-phase arm... UL The emitter-collector voltage becomes higher than normal. The overcurrent detection unit 18 detects the switching element S of the U-phase lower arm detected by the voltage detection unit 17. UL If the emitter-collector voltage is greater than a predetermined threshold, the switching element S of the lower U-phase arm UL It is determined that an overcurrent has occurred. In the example shown in Figure 9, diode D of the lower R-phase arm of converter 11 is determined to be RL Although it is shown that a ground fault current is flowing, a three-phase AC power supply 2 is connected to the converter 11, so depending on the phase of the AC power supply 2, the diode D of the S-phase lower arm of the converter 11 SL Or the diode D of the lower arm of the T phase TL There is a timing when ground fault current flows.

[0145] Also, although not shown in Figure 9, if the V-phase power line 33V is ground faulted, the switching element S of the V-phase lower arm VL Turn on the other switching elements S UU S UL S VU S WU , and S WL When turned off, the V-phase power line 33V from the ground and the switching element S on the V-phase lower arm are connected. VLA ground fault current flows to the AC power supply 2 via the negative power line 31N of the DC link 19 and the converter 11. A similar ground fault current also flows if the V-phase winding of the motor 3, which is connected to the V-phase power line 33V, is ground faulted. The switching element S of the V-phase lower arm... VL When an overcurrent, or ground fault current, flows through the V-phase lower arm, the switching element S VL The emitter-collector voltage becomes higher than normal. The overcurrent detection unit 18 detects the switching element S of the V-phase lower arm detected by the voltage detection unit 17. VL If the emitter-collector voltage is greater than a predetermined threshold, the switching element S of the V-phase lower arm VL It is determined that an overcurrent has occurred.

[0146] Similarly, although not shown in Figure 9, if the W-phase power line 33W is ground faulted, the switching element S of the W-phase lower arm WL Turn on the other switching elements S UU S UL S VU S VL , and S WU When turned off, the W-phase power line 33W from the ground and the switching element S of the W-phase lower arm are connected. WL A ground fault current flows to the AC power supply 2 via the negative power line 31N of the DC link 19 and the converter 11. A similar ground fault current also flows if the W-phase winding of the motor 3, which is connected to the W-phase power line 33W, is ground faulted. The switching element S of the W-phase lower arm... WL When an overcurrent, which is a ground fault current, flows through the W-phase lower arm, the switching element S WL The emitter-collector voltage becomes higher than normal. The overcurrent detection unit 18 detects the switching element S of the W-phase lower arm detected by the voltage detection unit 17. WL If the emitter-collector voltage is greater than a predetermined threshold, the switching element S of the W-phase lower arm WL It is determined that an overcurrent has occurred.

[0147] Thus, when the smoothing capacitor 13 is fully charged, if a ground fault occurs in either the three-phase power line between the inverter 12 and the motor 3 or in the three-phase winding of the motor 3, the switching element S of the lower arm of each phase of the inverter 12 will be activated. UL S VL , and S WL Among these, when a switching element in the same phase as the phase in which a ground fault occurs is turned on, an overcurrent is generated in that switching element. Therefore, in the sixth embodiment of this disclosure, when the smoothing capacitor 13 is fully charged, the switching elements S of the lower arms of each phase of the inverter 12 UL S VL , and S WL When only one of the switching elements is turned on, the voltage between the emitter and collector of that switched element is detected, and based on this voltage, it is determined whether or not a ground fault current, which is an overcurrent, has occurred, thereby determining whether or not there is a ground fault in either the three-phase power line between the inverter 12 and the motor 3 or the three-phase winding of the motor 3.

[0148] The ground fault detection unit 14 is the switching element S of the lower U-phase arm of the inverter 12. UL When only is turned on, if the overcurrent detection unit 18 detects an overcurrent, it is determined that a ground fault has occurred in either the U-phase power line 33U or the U-phase winding. The ground fault detection unit 14 detects the switching element S of the V-phase lower arm of the inverter 12. VL When only is turned on, if the overcurrent detection unit 18 detects an overcurrent, it is determined that a ground fault has occurred in either the V-phase power line 33V or the V-phase winding. The ground fault detection unit 14 detects the switching element S of the W-phase lower arm of the inverter 12. WL If the overcurrent detection unit 18 detects an overcurrent when only the power line is turned on, it is determined that a ground fault has occurred in either the W-phase power line 33W or the W-phase winding.

[0149] Figure 10 is a flowchart showing the operation flow of the ground fault detection process in a motor drive device according to the sixth embodiment of the present disclosure.

[0150] When the auxiliary charge switch 222 is closed and the smoothing capacitor 13 is fully charged, in step S401, the inverter control unit 10 controls the switching element S of the lower U-phase arm of the inverter 12. UL Only the other switching elements S are turned on. UU S VU S VL S WU , and S WL Turn it off.

[0151] In step S402, the voltage detection unit 17 detects the switching element S of the lower U-phase arm of the inverter 12. UL The voltage between the collector, which is the current inflow terminal, and the emitter, which is the current outflow terminal, is detected by the voltage detection unit 17. The overcurrent detection unit 18 detects the switching element S of the U-phase lower arm. UL Based on the emitter-collector voltage, the switching element S of the U-phase lower arm UL Determine whether or not an overcurrent has occurred.

[0152] In step S402, the switching element S of the U-phase lower arm UL If it is determined that an overcurrent has occurred, in step S403 the ground fault detection unit 14 determines that a ground fault has occurred in either the U-phase power line 33U or the U-phase winding.

[0153] In step S402, the switching element S of the U-phase lower arm UL If it is not determined that an overcurrent has occurred, in step S404, the inverter control unit 10 controls the switching element S of the V-phase lower arm of the inverter 12. VL Only the other switching elements S are turned on. UU S UL S VU S WU , and S WL Turn it off.

[0154] In step S405, the voltage detection unit 17 detects the switching element S of the V-phase lower arm of the inverter 12. VLThe voltage between the collector, which is the current inflow terminal, and the emitter, which is the current outflow terminal, is detected by the voltage detection unit 17. The overcurrent detection unit 18 detects the switching element S of the V-phase lower arm. VL The switching element S of the V-phase lower arm is based on the emitter-collector voltage. VL Determine whether or not an overcurrent has occurred.

[0155] In step S405, the switching element S of the V-phase lower arm VL If it is determined that an overcurrent has occurred, in step S406 the ground fault detection unit 14 determines that a ground fault has occurred in either the V-phase power line 33V or the V-phase winding.

[0156] In step S405, the switching element S of the V-phase lower arm VL If it is not determined that an overcurrent has occurred, in step S407, the inverter control unit 10 controls the switching element S of the W-phase lower arm of the inverter 12. WL Only the other switching elements S are turned on. UU S UL S VU S VL , and S WU Turn it off.

[0157] In step S408, the voltage detection unit 17 detects the switching element S of the W-phase lower arm of the inverter 12. WL The voltage between the collector, which is the current inflow terminal, and the emitter, which is the current outflow terminal, is detected by the voltage detection unit 17. The overcurrent detection unit 18 detects the switching element S of the W-phase lower arm. WL Based on the emitter-collector voltage, the switching element S of the W-phase lower arm WL Determine whether or not an overcurrent has occurred.

[0158] In step S408, the switching element S of the W-phase lower arm WL If it is determined that an overcurrent has occurred, in step S409 the ground fault detection unit 14 determines that a ground fault has occurred in either the W-phase power line 33W or the W-phase winding.

[0159] In step S408, the switching element S of the W-phase lower armWL If it is not determined that an overcurrent has occurred, in step S410 the ground fault detection unit 14 determines that all of the U-phase power line 33U, U-phase winding, V-phase power line 33V, V-phase winding, W-phase power line 33W, and W-phase winding are normal.

[0160] In the flowchart described above, the switching elements were turned on in the order of U-phase, V-phase, and W-phase. However, as a variation of this, the switching elements may be turned on in the order of V-phase, W-phase, and U-phase, or in the order of W-phase, U-phase, and V-phase, or in the order of V-phase, U-phase, and W-phase, or in the order of W-phase, V-phase, and U-phase.

[0161] <Execution timing of ground fault detection processing in the first to sixth embodiments of this disclosure> Figure 11A is a circuit diagram showing the equivalent circuit during execution of ground fault detection processing in the motor drive device of the first, third, and fifth embodiments of this disclosure. Figure 11B is a circuit diagram showing the equivalent circuit during execution of ground fault detection processing in the motor drive device of the second, fourth, and sixth embodiments of this disclosure.

[0162] When power is supplied to the motor drive unit 1, power is supplied from the AC power supply 2 to the motor drive unit 1, and pre-charging of the smoothing capacitor 13 begins. When the smoothing capacitor 13 is charged to a predetermined voltage, the smoothing capacitor 13 is fully charged. In the motor drive units of the first to sixth embodiments of this disclosure, the ground fault detection process is performed when the pre-charging switch 222 is closed and the smoothing capacitor 13 is fully charged. For example, the ground fault detection process may be performed immediately after the pre-charging of the smoothing capacitor 13 is completed and it is fully charged, or it may be performed at any timing while the motor drive unit 1 is operating normally with the smoothing capacitor 13 fully charged.

[0163] Figure 11A shows an equivalent circuit when the ground fault detection process of the motor drive device 1 shown in FIGS. 1, 5, and 7 is executed. Further, FIG. 11B shows an equivalent circuit when the ground fault detection process of the motor drive device 1 shown in FIGS. 3, 6, and 9 is executed. In FIGS. 11A and 11B, one switching element turned on for the ground fault detection process among the six switching elements of the inverter 12 is indicated by reference numeral S, and the diode connected in antiparallel to the switching element S is indicated by reference numeral D. Further, in FIGS. 11A and 11B, the ground fault location in either the three-phase power line between the inverter 12 and the motor 3 or the three-phase winding of the motor 3 is indicated by a resistor 200. Also, the AC power supply 2 that becomes the source of the ground fault current when the switching element S is on is represented by an AC power supply 100 in FIGS. 11A and 11B.

[0164] In the motor drive devices of the first, third, and fifth embodiments of the present disclosure, as shown in FIGS. 1, 5, and 7, when the smoothing capacitor 13 is in a fully charged state, with the ground potential 0V of the ground interposed therebetween, the positive potential of the smoothing capacitor 13 becomes positive and the negative potential of the smoothing capacitor 13 becomes negative. At this time, a ground fault current flows through the resistor 200 at the ground fault location from the positive potential of the smoothing capacitor 13 toward the ground through the turned-on switching element S in the inverter 12. Also, in the motor drive devices of the second, fourth, and sixth embodiments of the present disclosure, as shown in FIGS. 3, 6, and 9, when the smoothing capacitor 13 is in a fully charged state, with the ground potential 0V of the ground interposed therebetween, the positive potential of the smoothing capacitor 13 becomes positive and the negative potential of the smoothing capacitor 13 becomes negative. At this time, a ground fault current flows through the resistor 200 at the ground fault location from the ground toward the negative potential of the smoothing capacitor 13 through the turned-on switching element S in the inverter 12. In the motor drive devices of the first to sixth embodiments of the present disclosure, when this ground fault current is detected, it is determined that a ground fault has occurred in either the three-phase power line between the inverter 12 and the motor 3 or the three-phase winding of the motor 3.

[0165] <Seventh Embodiment of the Present Disclosure> FIG. 12 is a circuit diagram showing a motor drive device according to the seventh embodiment of the present disclosure.

[0166] As shown in FIG. 12, a motor drive device 1 according to the seventh embodiment of the present disclosure includes a converter 11, an inverter 12, a smoothing capacitor 13, a ground fault detection unit 23, a DC link current detection unit 15, an inverter control unit 10, a switching unit 21, and a pre-charge circuit 22. Note that the power supplies for driving each unit such as the ground fault detection unit 23, the DC link current detection unit 15, and the inverter control unit 10 are not shown in the figure. Also, even before the power is applied to the motor drive device 1, power for driving each control unit is supplied in preparation for the operation when the power is applied to the motor drive device 1.

[0167] The AC power supply 2, the motor 3, the converter 11, the inverter 12, the smoothing capacitor 13, the DC link current detection unit 15, and the inverter control unit 10 are as described in the first embodiment. Also, the positive power line 31P, the negative power line 31N, the R-phase power line 32R, the S-phase power line 32S, the T-phase power line 32T, the U-phase power line 33U, the V-phase power line 33V, and the W-phase power line 33W are also as described in the first embodiment. An AC reactor may be provided on the R-phase power line 32R, the S-phase power line 32S, and the T-phase power line 32T, but is not shown here.

[0168] The switching unit 21 opens and closes the circuits on the R-phase power line 32R, the S-phase power line 32S, and the T-phase power line 32T between the AC power supply 2 and the converter 11 under the control of a switching control unit (not shown). The switching unit 21 is composed of, for example, an electromagnetic contactor (MCC), a semiconductor switching element, or the like. For example, when the switching unit 21 is composed of an electromagnetic contactor, the closing operation for forming the circuit between the AC power supply and the converter 11 is realized by the contacts of the electromagnetic contactor closing, and the opening operation for cutting off the circuit between the AC power supply and the converter 11 is realized by the contacts of the electromagnetic contactor opening.

[0169] The pre-charge circuit 22 is provided between the converter 11 and the smoothing capacitor 13 on the positive power line 31P of the DC link 19. The configuration and operation of the pre-charge circuit 22 are as described in the first embodiment. When performing the ground fault detection process, the switching element S of the converter 11 RU , SRL S SU S SL S TU , and S TL , and the switching element S of the inverter 12 UU S UL S VU S VL S WU , and S WL Keep it in the OFF position. Also, when performing ground fault detection processing, open the auxiliary charge switch 222.

[0170] The DC link current detection unit 15 detects the DC link current flowing through the positive power line 31P of the DC link 19, specifically the power line 31P between the inverter 12 and the smoothing capacitor 13. The value of the current flowing through the positive power line 31P from the inverter 12 to the smoothing capacitor 13 is taken as positive. An example of the current detection method by the DC link current detection unit 15 is as described in the first embodiment.

[0171] In a seventh embodiment of the present disclosure, the ground fault detection unit 23 detects a ground fault in either the three-phase power lines between the inverter 12 and the motor 3 or in the windings of the motor 3, based on information related to the current that flows when the switching unit 21 closes the circuits on the R-phase power line 32R, S-phase power line 32S, and T-phase power line 32T, while the auxiliary charging switch 222 is open and the smoothing capacitor 13 is not fully charged.

[0172] For example, as shown by the dotted line in Figure 12, if the W-phase power line 33W is ground faulted, and the auxiliary charging switch 222 is open and the smoothing capacitor 13 is not fully charged, when the switching unit 21 switches the circuits on the R-phase power line 32R, S-phase power line 32S, and T-phase power line 32T from open to closed, immediately after the switching, the ground fault current flows from the ground to the W-phase power line 33W and the diode D on the W-phase upper arm of the inverter 12. WUThe current flows through to the positive power line 31P of the DC link 19. Since the auxiliary charging switch 222 of the auxiliary charging circuit 22, which is provided on the positive power line 31P between the converter 11 and the smoothing capacitor 13, is open, the ground fault current flows into the smoothing capacitor 13, which has a lower impedance than the auxiliary charging resistor 221, and then flows to the AC power supply 2 via the negative power line 31N of the DC link 19 between the smoothing capacitor 13 and the converter 11, and the converter 11. If the W-phase winding of the motor 3 connected to the W-phase power line 33W is ground faulted, the ground fault current will flow through a similar path. Note that in the example shown in Figure 12, diode D of the R-phase lower arm of the converter 11 is open. RL Although it is shown that a ground fault current is flowing, since the converter 11 is connected to the three-phase AC power supply 2, depending on the phase of the AC power supply 2, the diode D of the S-phase lower arm of the converter 11 SL Or the diode D of the lower arm of the T phase TL There is a timing when ground fault current flows.

[0173] Furthermore, although not shown in Figure 12, if the U-phase power line 33U is ground faulted, and the auxiliary charging switch 222 is open and the smoothing capacitor 13 is not fully charged, when the switching unit 21 switches the circuits on the R-phase power line 32R, S-phase power line 32S, and T-phase power line 32T from open to closed, immediately after the switching, the ground fault current flows from the ground to the U-phase power line 33U and the diode D on the U-phase upper arm of the inverter 12. UU The current flows through to the positive power line 31P of the DC link 19. Since the auxiliary charging switch 222 of the auxiliary charging circuit 22, which is provided on the positive power line 31P between the converter 11 and the smoothing capacitor 13, is open, the ground fault current flows into the smoothing capacitor 13, which has a lower impedance than the auxiliary charging resistor 221, and then flows to the AC power supply 2 via the negative power line 31N of the DC link 19 between the smoothing capacitor 13 and the converter 11, and the converter 11. The ground fault current flows through a similar path if the U-phase winding of the motor 3, which is connected to the U-phase power line 33U, is ground faulted.

[0174] Similarly, although not shown in Figure 12, if the V-phase power line 33V is ground faulted, and the auxiliary charging switch 222 is open and the smoothing capacitor 13 is not fully charged, when the switching unit 21 switches the circuits on the R-phase power line 32R, S-phase power line 32S, and T-phase power line 32T from open to closed, immediately after the switching, the ground fault current flows from the ground to the V-phase power line 33V and the diode D on the V-phase upper arm of the inverter 12. VU The current flows through to the positive power line 31P of the DC link 19. Since the auxiliary charging switch 222 of the auxiliary charging circuit 22, which is provided on the positive power line 31P between the converter 11 and the smoothing capacitor 13, is open, the ground fault current flows into the smoothing capacitor 13, which has a lower impedance than the auxiliary charging resistor 221, and then flows to the AC power supply 2 via the negative power line 31N of the DC link 19 between the smoothing capacitor 13 and the converter 11, and the converter 11. The ground fault current flows through a similar path if the V-phase winding of the motor 3, which is connected to the V-phase power line 33V, is ground faulted.

[0175] Thus, if a ground fault occurs in either the three-phase power line between the inverter 12 and the motor 3 or the three-phase winding of the motor 3, when the switch 21 switches the circuit on the R-phase power line 32R, S-phase power line 32S, and T-phase power line 32T from open to closed while the auxiliary charging switch 222 is open and the smoothing capacitor 13 is not fully charged, a ground fault current flows in the positive power line 31P between the inverter 12 and the smoothing capacitor 13 immediately after the switch 21 switches the circuit on the R-phase power line 32R, S-phase power line 32S, and T-phase power line 32T from open to closed while the auxiliary charging switch 222 is open and the smoothing capacitor 13 is not fully charged, the presence or absence of a ground fault in either the three-phase power line between the inverter 12 and the motor 3 or the three-phase winding of the motor 3 is determined based on whether or not a ground fault current flows in the positive power line 31P between the inverter 12 and the smoothing capacitor 13 immediately after the switch 21 switches the circuit on the R-phase power line 32R, S-phase power line 32S, and T-phase power line 32T from open to closed.

[0176] A threshold is set to detect ground fault current. If the DC link current detected by the DC link current detection unit 15 is greater than a predetermined threshold, it is determined that a ground fault current has occurred. If the DC link current detected by the DC link current detection unit 15 is less than a predetermined threshold, it is determined that no ground fault current has occurred. The threshold can be set as appropriate, for example, by operating the motor drive unit 1 during a trial run or actual operation, or by performing a computer simulation. The threshold may be stored in a rewritable memory device (not shown) and rewritable by an external device, and even after the threshold has been set, it can be changed to an appropriate value as needed.

[0177] The ground fault detection unit 23 determines that a ground fault has occurred in the U-phase power line 33U, V-phase power line 33V, and W-phase power line 33W between the inverter 12 and the motor 3, or in one of the U-phase winding, V-phase winding, or W-phase winding of the motor 3, if the DC link current detected by the DC link current detection unit 15 is greater than a predetermined threshold when the auxiliary charge switch 222 is in the open position and the smoothing capacitor 13 is not fully charged, and the switching unit 21 switches the circuit on the R-phase power line 32R, S-phase power line 32S, and T-phase power line 32T from open to closed.

[0178] <Eighth Embodiment of the Present Disclosure> Figure 13 is a circuit diagram showing a motor drive device according to the eighth embodiment of the present disclosure.

[0179] The eighth embodiment of this disclosure is a modification of the seventh embodiment. In the seventh embodiment, the presence or absence of a ground fault was determined based on whether or not a ground fault current flowed in the positive power line 31P between the inverter 12 and the smoothing capacitor 13. In the eighth embodiment, the presence or absence of a ground fault is determined based on whether or not a ground fault current flowed in the positive power line 31P between the smoothing capacitor 13 and the converter 11.

[0180] As shown in Figure 13, the motor drive device 1 according to the eighth embodiment of the present disclosure comprises a converter 11, an inverter 12, a smoothing capacitor 13, a ground fault detection unit 23, a DC link current detection unit 15, an inverter control unit 10, a switching unit 21, and a pre-charging circuit 22. Power supplies for driving each of these units, such as the ground fault detection unit 23, the DC link current detection unit 15, and the inverter control unit 10, are not shown in the figure. Furthermore, even before power is supplied to the motor drive device 1, power is supplied to drive each control unit in preparation for operation when power is supplied to the motor drive device 1.

[0181] The AC power supply 2, motor 3, converter 11, inverter 12, smoothing capacitor 13, DC link current detection unit 15, and inverter control unit 10 are as described in the first embodiment. The positive power line 31P, negative power line 31N, R-phase power line 32R, S-phase power line 32S, T-phase power line 32T, U-phase power line 33U, V-phase power line 33V, and W-phase power line 33W are also as described in the first embodiment. The switching unit 21 is as described in the seventh embodiment. The auxiliary charging circuit 22 is as described in the first and seventh embodiments. When ground fault detection processing is performed, the switching element S of the converter 11 RU S RL S SU S SL S TU , and S TL , and the switching element S of the inverter 12 UU S UL S VU S VL S WU , and S WL Keep it in the OFF position. Also, when performing ground fault detection processing, open the auxiliary charge switch 222.

[0182] In the eighth embodiment of this disclosure, as in the seventh embodiment, the pre-charging circuit 22 is provided between the converter 11 and the smoothing capacitor 13 on the positive power line 31P of the DC link 19. Therefore, when a ground fault occurs in the U-phase power line 33U, V-phase power line 33V, and W-phase power line 33W between the inverter 12 and the motor 3, or in any of the U-phase winding, V-phase winding, or W-phase winding of the motor 3, the ground fault current that flows follows the same path as in the seventh embodiment. That is, in the DC link 19, the ground fault current flows from the positive power line 31P between the inverter 12 and the smoothing capacitor 13, through the smoothing capacitor 13, and to the negative power line 31N between the smoothing capacitor 13 and the converter 11. In the eighth embodiment of this disclosure, the DC link current detection unit 15 detects the DC link current flowing through the positive power line 31P between the smoothing capacitor 13 and the converter 11, which is one of the negative power lines 31N of the DC link 19. Note that the value of the current flowing from the smoothing capacitor 13 to the converter 11 in the negative power line 31N is taken as positive. An example of the current detection method by the DC link current detection unit 15 is as described in the first embodiment.

[0183] The ground fault detection unit 23 determines that a ground fault has occurred in the U-phase power line 33U, V-phase power line 33V, and W-phase power line 33W between the inverter 12 and the motor 3, or in one of the U-phase winding, V-phase winding, or W-phase winding of the motor 3, if the DC link current detected by the DC link current detection unit 15 is greater than a predetermined threshold when the auxiliary charge switch 222 is in the open position and the smoothing capacitor 13 is not fully charged, and the switching unit 21 switches the circuit on the R-phase power line 32R, S-phase power line 32S, and T-phase power line 32T from open to closed.

[0184] <Ninth Embodiment of the Present Disclosure> Figure 14 is a circuit diagram showing a motor drive device according to the ninth embodiment of the present disclosure.

[0185] The ninth embodiment of this disclosure is a modification of the seventh embodiment. In the seventh embodiment, the auxiliary charging circuit 22 was provided on the positive power line 31P of the DC link 19, but in the ninth embodiment, the auxiliary charging circuit 22 is provided on the negative power line 31N of the DC link 19.

[0186] As shown in Figure 14, the motor drive device 1 according to the eighth embodiment of the present disclosure comprises a converter 11, an inverter 12, a smoothing capacitor 13, a ground fault detection unit 23, a DC link current detection unit 15, an inverter control unit 10, a switching unit 21, and a pre-charging circuit 22. Power supplies for driving each of these units, such as the ground fault detection unit 23, the DC link current detection unit 15, and the inverter control unit 10, are not shown in the figure. Furthermore, even before power is supplied to the motor drive device 1, power is supplied to drive each control unit in preparation for operation when power is supplied to the motor drive device 1.

[0187] The AC power supply 2, motor 3, converter 11, inverter 12, smoothing capacitor 13, DC link current detection unit 15, and inverter control unit 10 are as described in the first embodiment. The positive power line 31P, negative power line 31N, R-phase power line 32R, S-phase power line 32S, T-phase power line 32T, U-phase power line 33U, V-phase power line 33V, and W-phase power line 33W are also as described in the first embodiment. The switching unit 21 is as described in the seventh embodiment.

[0188] The auxiliary charging circuit 22 is provided between the converter 11 and the smoothing capacitor 13 in the negative power line 31N of the DC link 19. The configuration and operation of the auxiliary charging circuit 22 are as described in the first embodiment. When ground fault detection processing is performed, the switching element S of the converter 11 RU S RL S SU S SL S TU , and S TL , and the switching element S of the inverter 12 UU S UL S VU S VL S WU , and S WL Keep it in the OFF position. Also, when performing ground fault detection processing, open the auxiliary charge switch 222.

[0189] The DC link current detection unit 15 detects the DC link current flowing through the negative power line 31N of the DC link 19, specifically the negative power line 31N between the smoothing capacitor 13 and the inverter 12. The value of the current flowing through the negative power line 31N from the smoothing capacitor 13 to the inverter 12 is taken as positive. An example of the current detection method by the DC link current detection unit 15 is as described in the first embodiment.

[0190] For example, as shown by the dotted line in Figure 14, if the W-phase power line 33W is ground faulted, and the auxiliary charging switch 222 is open and the smoothing capacitor 13 is not fully charged, when the switching unit 21 switches the circuits on the R-phase power line 32R, S-phase power line 32S, and T-phase power line 32T from open to closed, immediately after the switching, the ground fault current flows from the AC power supply 2 through the converter 11 to the positive power line 31P of the DC link 19. Switching element S of the inverter 12 UU S UL S VU S VL S WU , and S WL Since it is in the off position, the ground fault current flows from the smoothing capacitor 13 to the diode D of the W-phase lower arm of the inverter 12, which has a lower impedance than the auxiliary charging resistor 221. WL The current flows into the power line 33W and then to the ground. If the W-phase winding of motor 3 connected to the W-phase power line 33W is ground faulted, the ground fault current will flow through a similar path. In the example shown in Figure 14, diode D of the R-phase upper arm of converter 11 is also present. RU Although it is shown that a ground fault current is flowing, since the converter 11 is connected to the three-phase AC power supply 2, depending on the phase of the AC power supply 2, the diode D of the S-phase upper arm of the converter 11 SU Or the diode D of the upper arm of the T phase TU There is a timing when ground fault current flows.

[0191] Furthermore, although not shown in Figure 14, if the U-phase power line 33U is ground faulted, and the auxiliary charging switch 222 is open and the smoothing capacitor 13 is not fully charged, when the switching unit 21 switches the circuits on the R-phase power line 32R, S-phase power line 32S, and T-phase power line 32T from open to closed, immediately after the switching, the ground fault current flows from the AC power supply 2 through the converter 11 to the positive power line 31P of the DC link 19. Switching element S of the inverter 12 UU S UL S VU S VL S WU , and S WL Since it is in the off position, the ground fault current flows from the smoothing capacitor 13 to the diode D of the lower U-phase arm of the inverter 12, which has a lower impedance than the auxiliary charging resistor 221. UL The current flows into the ground and then through the U-phase power line 33U to the earth. If the U-phase winding of the motor 3 connected to the U-phase power line 33U is ground faulted, the ground fault current will flow through the same path.

[0192] Similarly, although not shown in Figure 14, if the V-phase power line 33V is ground faulted, and the auxiliary charging switch 222 is open and the smoothing capacitor 13 is not fully charged, when the switching unit 21 switches the circuits on the R-phase power line 32R, S-phase power line 32S, and T-phase power line 32T from open to closed, immediately after the switching, the ground fault current flows from the AC power supply 2 through the converter 11 to the positive power line 31P of the DC link 19. Switching element S of the inverter 12 UU S UL S VU S VL S WU , and S WL Since it is in the off position, the ground fault current flows from the smoothing capacitor 13 to the diode D of the lower V-phase arm of the inverter 12, which has a lower impedance than the auxiliary charging resistor 221. VL The current flows into the ground and then through the V-phase power line 33V to the earth. If the V-phase winding of motor 3, which is connected to the V-phase power line 33V, is ground faulted, the ground fault current will flow through the same path.

[0193] Thus, if a ground fault occurs in either the three-phase power line between the inverter 12 and the motor 3 or the three-phase winding of the motor 3, when the switch 21 switches the circuits on the R-phase power line 32R, S-phase power line 32S, and T-phase power line 32T from open to closed while the auxiliary charging switch 222 is open and the smoothing capacitor 13 is not fully charged, a ground fault current flows in the negative power line 31N between the smoothing capacitor 13 and the inverter 12 immediately after the switch 21 switches the circuits on the R-phase power line 32R, S-phase power line 32S, and T-phase power line 32T from open to closed while the auxiliary charging switch 222 is open and the smoothing capacitor 13 is not fully charged, the presence or absence of a ground fault in either the three-phase power line between the inverter 12 and the motor 3 or the three-phase winding of the motor 3 is determined based on whether or not a ground fault current flows in the negative power line 31N between the smoothing capacitor 13 and the inverter 12 immediately after the switch 21 switches the circuits on the R-phase power line 32R, S-phase power line 32S, and T-phase power line 32T from open to closed.

[0194] The ground fault detection unit 23 determines that a ground fault has occurred in the U-phase power line 33U, V-phase power line 33V, and W-phase power line 33W between the inverter 12 and the motor 3, or in one of the U-phase winding, V-phase winding, or W-phase winding of the motor 3, if the DC link current detected by the DC link current detection unit 15 is greater than a predetermined threshold when the auxiliary charge switch 222 is in the open position and the smoothing capacitor 13 is not fully charged, and the switching unit 21 switches the circuits on the R-phase power line 32R, S-phase power line 32S, and T-phase power line 32T from open to closed. The threshold is as described in the seventh embodiment.

[0195] <Tenth Embodiment of the Present Disclosure> Figure 15 is a circuit diagram showing a motor drive device according to the tenth embodiment of the present disclosure.

[0196] The tenth embodiment of this disclosure is a modification of the ninth embodiment. In the ninth embodiment, the presence or absence of a ground fault was determined based on whether or not a ground fault current flowed in the negative power line 31N between the smoothing capacitor 13 and the inverter 12. In the tenth embodiment, the presence or absence of a ground fault is determined based on whether or not a ground fault current flowed in the positive power line 31P between the converter 11 and the smoothing capacitor 13.

[0197] As shown in Figure 15, the motor drive device 1 according to the tenth embodiment of the present disclosure comprises a converter 11, an inverter 12, a smoothing capacitor 13, a ground fault detection unit 23, a DC link current detection unit 15, an inverter control unit 10, a switching unit 21, and a pre-charging circuit 22. Power supplies for driving each of these units, such as the ground fault detection unit 23, the DC link current detection unit 15, and the inverter control unit 10, are not shown in the figure. Furthermore, even before power is supplied to the motor drive device 1, power is supplied to drive each control unit in preparation for operation when power is supplied to the motor drive device 1.

[0198] The AC power supply 2, motor 3, converter 11, inverter 12, smoothing capacitor 13, DC link current detection unit 15, and inverter control unit 10 are as described in the first embodiment. The positive power line 31P, negative power line 31N, R-phase power line 32R, S-phase power line 32S, T-phase power line 32T, U-phase power line 33U, V-phase power line 33V, and W-phase power line 33W are also as described in the first embodiment. The switching unit 21 is as described in the seventh embodiment. The auxiliary charging circuit 22 is as described in the first and ninth embodiments. When ground fault detection processing is performed, the switching element S of the converter 11 RU S RL S SU S SL S TU , and S TL , and the switching element S of the inverter 12 UU S UL S VU S VL S WU , and S WL Keep it in the OFF position. Also, when performing ground fault detection processing, open the auxiliary charge switch 222.

[0199] In the tenth embodiment of the present disclosure as well, similar to the ninth embodiment, the pre-charge circuit 22 is provided between the converter 11 and the smoothing capacitor 13 on the negative power line 31N of the DC link 19. Therefore, when a ground fault occurs in any of the U-phase power line 33U, V-phase power line 33V, and W-phase power line 33W between the inverter 12 and the motor 3 and the U-phase winding, V-phase winding, and W-phase winding of the motor 3, the ground fault current that flows follows the same path as in the ninth embodiment. That is, in the DC link 19, the ground fault current flows from the positive power line 31P between the converter 11 and the smoothing capacitor 13, through the smoothing capacitor 13, and then through the negative power line 31N between the smoothing capacitor 13 and the inverter 12. In the tenth embodiment of the present disclosure, the DC link current detection unit 15 detects the DC link current flowing through the positive power line 31P between the converter 11 and the smoothing capacitor 13 among the positive power lines 31P of the DC link 19. Note that the value of the current flowing from the converter 11 to the smoothing capacitor 13 through the positive power line 31P is taken as positive. An example of the current detection method by the DC link current detection unit 15 is as described in the first embodiment.

[0200] When the ground fault detection unit 23 determines that the pre-charge switch 222 is in the open state and the smoothing capacitor 13 is not fully charged, and when the switching unit 21 switches the circuits on the R-phase power line 32R, S-phase power line 32S, and T-phase power line 32T from open to closed, if the DC link current detected by the DC link current detection unit 15 is greater than a predetermined threshold value, it is determined that a ground fault has occurred in any of the U-phase power line 33U, V-phase power line 33V, and W-phase power line 33W between the inverter 12 and the motor 3 and the U-phase winding, V-phase winding, and W-phase winding of the motor 3.

[0201] <Operation Flow of Ground Fault Detection Processing in the Seventh to Tenth Embodiments of the Present Disclosure> FIG. 16 is a flowchart showing the operation flow of ground fault detection processing in a motor drive device according to the seventh to tenth and eleventh embodiments of the present disclosure. The flowchart shown in FIG. 16 is also applicable to the eleventh embodiment described later, but here, the operation flow of ground fault detection processing in the seventh to tenth and eleventh embodiments will be described.

[0202] Initially, the switching element S of the converter 11 RU S RL S SU S SL S TU , and S TL , and the switching element S of the inverter 12 UU S UL S VU S VL S WU , and S WL Keep it in the OFF position. Also, keep the auxiliary charging switch 222 in the open position.

[0203] When the smoothing capacitor 13 is not fully charged, in step S501, the switching unit 21 switches the circuits on the R-phase power line 32R, S-phase power line 32S, and T-phase power line 32T from open to closed.

[0204] In step S502, the DC link current detection unit 15 detects the DC link current, and the ground fault detection unit 23 determines whether the DC link current detected by the DC link current detection unit 15 is greater than a threshold value.

[0205] If the DC link current detected by the DC link current detection unit 15 in step S502 is determined to be greater than the threshold, then in step S503, the ground fault detection unit 23 determines that a ground fault has occurred in the U-phase power line 33U, V-phase power line 33V, and W-phase power line 33W between the inverter 12 and the motor 3, as well as in any of the U-phase winding, V-phase winding, and W-phase winding of the motor 3.

[0206] If the DC link current detected by the DC link current detection unit 15 in step S502 is not determined to be greater than the threshold, then in step S504, the ground fault detection unit 23 determines that all of the U-phase power line 33U, U-phase winding, V-phase power line 33V, V-phase winding, W-phase power line 33W, and W-phase winding are normal.

[0207] <Eleventh Embodiment of the Present Disclosure> Figure 17 is a circuit diagram showing a motor drive device according to the eleventh embodiment of the present disclosure.

[0208] The eleventh embodiment of this disclosure is a modification of the seventh embodiment. In the seventh embodiment, the presence or absence of a ground fault was determined based on whether or not a ground fault current flowed through the positive power line 31P between the inverter 12 and the smoothing capacitor 13. In the eleventh embodiment, the presence or absence of a ground fault is determined based on whether or not a ground fault current flowed through at least one of the R-phase power line 32R, S-phase power line 32S, and T-phase power line 32T.

[0209] As shown in Figure 15, the motor drive device 1 according to the eleventh embodiment of the present disclosure comprises a converter 11, an inverter 12, a smoothing capacitor 13, a ground fault detection unit 23, a power supply current detection unit 16, an inverter control unit 10, a switching unit 21, and a pre-charging circuit 22. The power supply for driving each of the parts, such as the ground fault detection unit 23, the power supply current detection unit 16, and the inverter control unit 10, is not shown in the figure. Furthermore, even before power is supplied to the motor drive device 1, power is supplied to drive each control unit in preparation for operation when power is supplied to the motor drive device 1.

[0210] The AC power supply 2, motor 3, converter 11, inverter 12, smoothing capacitor 13, and inverter control unit 10 are as described in the first embodiment. The positive power line 31P, negative power line 31N, R-phase power line 32R, S-phase power line 32S, T-phase power line 32T, U-phase power line 33U, V-phase power line 33V, and W-phase power line 33W are also as described in the first embodiment. The switching unit 21 is as described in the seventh embodiment. The auxiliary charging circuit 22 is as described in the first and seventh embodiments. The auxiliary charging circuit 22 is provided on either the positive power line 31P or the negative power line 31N in the DC link 19 between the converter 11 and the smoothing capacitor 13. In the example shown in Figure 15, the auxiliary charging circuit 22 is provided on the positive power line 31P between the converter 11 and the smoothing capacitor 13. Note that when ground fault detection processing is performed, the switching element S of the converter 11 is... RU S RL S SU S SL S TU , and S TL, and the switching element S of the inverter 12 UU S UL S VU S VL S WU , and S WL Keep it in the OFF position. Also, when performing ground fault detection processing, open the auxiliary charge switch 222.

[0211] The power supply current detection unit 16 detects the power supply current flowing through at least one of the power lines among the R-phase power line 32R, the S-phase power line 32S, and the T-phase power line 32T. In the illustrated example, the power supply current detection unit 16 detects the power supply current flowing through each of the R-phase power line 32R, the S-phase power line 32S, and the T-phase power line 32T. As a variation of this, the power supply current detection unit 16 may detect the power supply current flowing through two of the power lines among the R-phase power line 32R, the S-phase power line 32S, and the T-phase power line 32T, or it may detect the power supply current flowing through one of the power lines among the R-phase power line 32R, the S-phase power line 32S, and the T-phase power line 32T. An example of the current detection method by the power supply current detection unit 16 is as described in the third embodiment.

[0212] In the eleventh embodiment of this disclosure, as in the seventh embodiment, the pre-charging circuit 22 is provided between the converter 11 and the smoothing capacitor 13 on the positive power line 31P of the DC link 19. Therefore, when a ground fault occurs in the U-phase power line 33U, V-phase power line 33V, and W-phase power line 33W between the inverter 12 and the motor 3, or in any of the U-phase winding, V-phase winding, and W-phase winding of the motor 3, the ground fault current flows along the same path as in the seventh embodiment. That is, the ground fault current flows from the location of the ground fault that occurred in any of the U-phase power line 33U, V-phase power line 33V, and W-phase power line 33W, or in any of the U-phase winding, V-phase winding, and W-phase winding of the motor 3, through the positive power line 31P between the inverter 12 and the smoothing capacitor 13, the smoothing capacitor 13, the negative power line 31N between the smoothing capacitor 13 and the converter 11, and then through any of the R-phase power line 32R, S-phase power line 32S, and T-phase power line 32T. In the eleventh embodiment of the present disclosure, the ground fault detection unit 23 determines whether or not a ground fault exists based on whether or not a ground fault current flows through at least one of the power lines among the R-phase power line 32R, the S-phase power line 32S, and the T-phase power line 32T.

[0213] Since a three-phase balanced AC current is supplied to the converter 11 from the AC power supply 2, the phase of the power line through which the ground fault current flows and the phase of the switching element on the upper arm switch sequentially in the order of R phase, S phase, and T phase during one cycle of the AC power supply 2. In the example shown in Figure 5, the power supply current detection unit 16 detects the power supply current flowing through each of the R phase power line 32R, S phase power line 32S, and T phase power line 32T, so that the power supply current detection unit 16 can detect the ground fault current with little delay regardless of which of the R phase, S phase, and T phase occurs. Modified versions in which the power supply current detection unit 16 detects the power supply current flowing through two of the R phase power line 32R, S phase power line 32S, and T phase power line 32T, or in which it detects the power supply current flowing through one of the R phase power line 32R, S phase power line 32S, and T phase power line 32T, may have a larger detection delay for the power supply current detection unit 16, but have the advantage of being low cost.

[0214] The ground fault detection unit 23 determines that a ground fault has occurred in the U-phase power line 33U, V-phase power line 33V, and W-phase power line 33W between the inverter 12 and the motor 3, or in one of the U-phase winding, V-phase winding, or W-phase winding of the motor 3, if the power supply current detected by the power supply current detection unit 16 is greater than a predetermined threshold when the auxiliary charge switch 222 is in the open position and the smoothing capacitor 13 is not fully charged, and the switching unit 21 switches the circuits on the R-phase power line 32R, S-phase power line 32S, and T-phase power line 32T from open to closed.

[0215] Although not shown in the diagram, even when a pre-charging circuit 22 is provided between the converter 11 and the smoothing capacitor 13 in the negative power line 31N of the DC link 19, the ground fault detection unit 23 can determine whether or not a ground fault is present based on whether or not a ground fault current flows through at least one of the power lines among the R-phase power line 32R, the S-phase power line 32S, and the T-phase power line 32T.

[0216] Next, the operation flow of the ground fault detection process in the motor drive device according to the eleventh embodiment of this disclosure will be explained using the flowchart shown in Figure 16.

[0217] Initially, the switching element S of the converter 11 RU S RL S SU S SL S TU , and S TL , and the switching element S of the inverter 12 UU S UL S VU S VL S WU , and S WL Keep it in the OFF position. Also, keep the auxiliary charging switch 222 in the open position.

[0218] When the smoothing capacitor 13 is not fully charged, in step S501, the switching unit 21 switches the circuits on the R-phase power line 32R, S-phase power line 32S, and T-phase power line 32T from open to closed.

[0219] In step S502, the power supply current detection unit 16 detects the power supply current, and the ground fault detection unit 23 determines whether the power supply current detected by the power supply current detection unit 16 is greater than a threshold value.

[0220] If the power supply current detected by the power supply current detection unit 16 in step S502 is determined to be greater than the threshold, then in step S503, the ground fault detection unit 23 determines that a ground fault has occurred in the U-phase power line 33U, V-phase power line 33V, and W-phase power line 33W between the inverter 12 and the motor 3, as well as in any of the U-phase winding, V-phase winding, and W-phase winding of the motor 3.

[0221] If the power supply current detected by the power supply current detection unit 16 in step S502 is not determined to be greater than the threshold, then in step S504, the ground fault detection unit 23 determines that all of the U-phase power line 33U, U-phase winding, V-phase power line 33V, V-phase winding, W-phase power line 33W, and W-phase winding are normal.

[0222] <Twelfth Embodiment of the Present Disclosure> Figure 18 is a circuit diagram showing a motor drive device according to the twelfth embodiment of the present disclosure.

[0223] The twelfth embodiment of this disclosure is a modification of the seventh embodiment. In the seventh embodiment, the presence or absence of a ground fault was determined based on whether or not a ground fault current flowed in the positive power line 31P between the inverter 12 and the smoothing capacitor 13. In the twelfth embodiment, the presence or absence of a ground fault is determined based on whether or not a ground fault current flowed in the U-phase power line 33U, the V-phase power line 33V, and the W-phase power line 33W.

[0224] As shown in Figure 18, the motor drive device 1 according to the twelfth embodiment of the present disclosure comprises a converter 11, an inverter 12, a smoothing capacitor 13, a ground fault detection unit 23, an inverter current detection unit 24, an inverter control unit 10, a switching unit 21, and a pre-charging circuit 22. Power supplies for driving each of these units, such as the ground fault detection unit 23, the inverter current detection unit 24, and the inverter control unit 10, are not shown in the figure. Furthermore, even before power is supplied to the motor drive device 1, power is supplied to drive each control unit in preparation for operation when power is supplied to the motor drive device 1.

[0225] The AC power supply 2, motor 3, converter 11, inverter 12, smoothing capacitor 13, and inverter control unit 10 are as described in the first embodiment. The positive power line 31P, negative power line 31N, R-phase power line 32R, S-phase power line 32S, T-phase power line 32T, U-phase power line 33U, V-phase power line 33V, and W-phase power line 33W are also as described in the first embodiment. The switching unit 21 is as described in the seventh embodiment. The auxiliary charging circuit 22 is as described in the first and seventh embodiments. The auxiliary charging circuit 22 is provided on either the positive power line 31P or the negative power line 31N in the DC link 19 between the converter 11 and the smoothing capacitor 13. In the example shown in Figure 15, the auxiliary charging circuit 22 is provided on the positive power line 31P between the converter 11 and the smoothing capacitor 13. Note that when ground fault detection processing is performed, the switching element S of the converter 11 is... RU S RL S SU S SL S TU , and S TL , and the switching element S of the inverter 12 UU S UL S VU S VL S WU , and S WL Keep it in the OFF position. Also, when performing ground fault detection processing, open the auxiliary charge switch 222.

[0226] The inverter current detection unit 24 detects the inverter current flowing through the U-phase power line 33U, V-phase power line 33V, and W-phase power line 33W between the inverter 12 and the motor 3. Examples of current detection methods by the inverter current detection unit 24 include detecting the current from the voltage drop across a shunt resistor, detecting the current from a magnetic field detected by a core provided around the power line, and detecting the current by converting the magnetic field generated around the power line into a voltage using the Hall effect.

[0227] In the eleventh embodiment of this disclosure, as in the seventh embodiment, the pre-charging circuit 22 is provided between the converter 11 and the smoothing capacitor 13 on the positive power line 31P of the DC link 19. Therefore, when a ground fault occurs in the U-phase power line 33U, V-phase power line 33V, and W-phase power line 33W between the inverter 12 and the motor 3, or in any of the U-phase winding, V-phase winding, and W-phase winding of the motor 3, the ground fault current flows along the same path as in the seventh embodiment. That is, the ground fault current flows from the location of the ground fault that occurred in any of the U-phase power line 33U, V-phase power line 33V, and W-phase power line 33W, or in any of the U-phase winding, V-phase winding, and W-phase winding of the motor 3, through the positive power line 31P between the inverter 12 and the smoothing capacitor 13, the smoothing capacitor 13, the negative power line 31N between the smoothing capacitor 13 and the converter 11, and then through any of the R-phase power line 32R, S-phase power line 32S, and T-phase power line 32T. In the twelfth embodiment of this disclosure, the ground fault detection unit 23 determines which phase of the power line among the U-phase power line 33U, V-phase power line 33V, and W-phase power line 33W has a ground fault current flowing through it.

[0228] A threshold is set to detect ground fault current. If the inverter current detected by the inverter current detection unit 24 is greater than a predetermined threshold, it is determined that a ground fault current has occurred. If the inverter current detected by the inverter current detection unit 24 is less than a predetermined threshold, it is determined that no ground fault current has occurred. The threshold can be set as appropriate, for example, by operating the motor drive unit 1 during a trial run or actual operation, or by performing a computer simulation. The threshold may be stored in a rewritable memory device (not shown) and rewritable by an external device, and even after the threshold has been set, it can be changed to an appropriate value as needed.

[0229] The ground fault detection process by the ground fault detection unit 23 is performed when the auxiliary charge switch 222 is in the open position and the smoothing capacitor 13 is not fully charged. The ground fault detection unit 23 determines that a ground fault has occurred in either the U-phase power line 33U or the U-phase winding if the inverter current flowing through the U-phase power line detected by the inverter current detection unit 24 is greater than a threshold when the switching unit 21 switches the circuits on the R-phase power line 32R, S-phase power line 32S, and T-phase power line 32T from open to closed. The ground fault detection unit 23 determines that a ground fault has occurred in either the V-phase power line 33V or the V-phase winding if the inverter current flowing through the V-phase power line detected by the inverter current detection unit 24 is greater than a threshold when the switching unit 21 switches the circuits on the R-phase power line 32R, S-phase power line 32S, and T-phase power line 32T from open to closed. The ground fault detection unit 23 determines that a ground fault has occurred in either the W-phase power line 33W or the W-phase winding if the inverter current flowing through the W-phase power line detected by the inverter current detection unit 24 is greater than a threshold value when the switching unit 21 switches the circuits on the R-phase power line 32R, S-phase power line 32S, and T-phase power line 32T from open to closed.

[0230] Figure 19 is a flowchart showing the operation flow of the ground fault detection process in a motor drive device according to the twelfth embodiment of the present disclosure.

[0231] Initially, the switching element S of the converter 11 RU S RL S SU S SL S TU , and S TL , and the switching element S of the inverter 12 UU S UL S VU S VL S WU , and S WL Keep it in the OFF position. Keep the auxiliary charging switch 222 in the open position.

[0232] When the smoothing capacitor 13 is not fully charged, in step S601, the switching unit 21 switches the circuits on the R-phase power line 32R, S-phase power line 32S, and T-phase power line 32T from open to closed.

[0233] In step S602, the inverter current detection unit 24 detects the inverter current flowing through the U-phase power line 33U, and the ground fault detection unit 23 determines whether the U-phase inverter current detected by the inverter current detection unit 24 is greater than a threshold value.

[0234] If, in step S602, it is determined that the inverter current of the U phase is greater than the threshold, then in step S603, the ground fault detection unit 23 determines that a ground fault has occurred in either the U phase power line 33U or the U phase winding.

[0235] If, in step S602, the inverter current of the U phase is not determined to be greater than the threshold, then in step S604, the inverter current detection unit 24 detects the inverter current flowing through the V phase power line 33V, and the ground fault detection unit 23 determines whether the V phase inverter current detected by the inverter current detection unit 24 is greater than the threshold.

[0236] If, in step S604, it is determined that the inverter current of the V phase is greater than the threshold, then in step S605, the ground fault detection unit 23 determines that a ground fault has occurred in either the V phase power line 33V or the V phase winding.

[0237] If, in step S604, the inverter current of the V phase is not determined to be greater than the threshold, then in step S606, the inverter current detection unit 24 detects the inverter current flowing through the W phase power line 33W, and the ground fault detection unit 23 determines whether the inverter current of the W phase detected by the inverter current detection unit 24 is greater than the threshold.

[0238] If, in step S606, it is determined that the inverter current of the W phase is greater than the threshold, then in step S607, the ground fault detection unit 23 determines that a ground fault has occurred in either the W phase power line 33W or the W phase winding.

[0239] If the inverter current of the W phase is not determined to be greater than the threshold in step S606, then in step S608, the ground fault detection unit 23 determines that all of the U phase power line 33U, U phase winding, V phase power line 33V, V phase winding, W phase power line 33W, and W phase winding are normal.

[0240] <Execution timing of ground fault detection processing in the seventh to twelfth embodiments of this disclosure> Figure 20A is a circuit diagram showing the equivalent circuit during execution of ground fault detection processing in the motor drive device of the seventh, eighth, eleventh, and twelfth embodiments of this disclosure. Figure 20B is a circuit diagram showing the equivalent circuit during execution of ground fault detection processing in the motor drive device of the ninth and tenth embodiments of this disclosure.

[0241] In the motor drive devices of the seventh to twelfth embodiments of this disclosure, the ground fault detection process is performed when the pre-charge switch 222 is open and the smoothing capacitor 13 is not fully charged. When the switch 21 is closed on the motor drive device 1 and power is turned on, power is supplied from the AC power supply 2 to the motor drive device 1, and pre-charging of the smoothing capacitor 13 begins. From the time the power is turned on until the pre-charging is completed, the terminal voltage of the smoothing capacitor 13 can range from 0 (zero) to the maximum value of the peak value of the power supply voltage. In the motor drive devices of the seventh to twelfth embodiments of this disclosure, the ground fault detection process is performed when the smoothing capacitor 13 is not fully charged. For example, the ground fault detection process is performed at any timing when the smoothing capacitor 13 is not fully charged, after power has been turned on to the motor drive device 1 and before the pre-charging is completed.

[0242] Figure 20A shows the equivalent circuit during the execution of the ground fault detection process of the motor drive device 1 shown in Figures 12, 13, 17, and 18. Figure 20B also shows the equivalent circuit during the execution of the ground fault detection process of the motor drive device 1 shown in Figures 14 and 15. In Figures 20A and 20B, one of the six switching elements of the inverter 12 is denoted by reference numeral S, and the diode connected in antiparallel to the switching element S is denoted by reference numeral D. In Figures 20A and 20B, the ground fault location in either the three-phase power line between the inverter 12 and the motor 3, or in the three-phase winding of the motor 3, is indicated by resistor 200. In Figures 20A and 20B, the AC power supply 2, which is the source of the ground fault current when the switching element S is ON, is represented by AC power supply 100.

[0243] In the motor drive devices of the seventh, eighth, eleventh, and twelfth embodiments of this disclosure, as shown in Figures 12, 13, 17, and 18, immediately after the switching unit 21 of the motor drive device 1 is switched from open to closed, the smoothing capacitor 13 is not fully charged, and both the positive and negative potentials of the smoothing capacitor 13 are negative. At this time, a ground fault current flows through the resistor 200 at the ground fault location from the ground (0V) through the diode D in the inverter 12 toward the negative positive potential of the smoothing capacitor 13. Furthermore, in the motor drive devices of the ninth and tenth embodiments of this disclosure, as shown in Figures 14 and 15, immediately after the switching unit 21 of the motor drive device 1 is switched from open to closed, the smoothing capacitor 13 is not fully charged, and both the positive and negative potentials of the smoothing capacitor 13 are positive. At this time, a ground fault current flows through the resistor 200 at the ground fault location from the positive positive potential of the smoothing capacitor 13 through the diode D in the inverter 12 toward the ground (0V). In the motor drive devices of the seventh to twelfth embodiments of this disclosure, when this ground fault current is detected, it is determined that a ground fault has occurred in either the three-phase power line between the inverter 12 and the motor 3 or in the three-phase winding of the motor 3. Since the electrical energy stored in the smoothing capacitor 13 is weak, the ground fault current disappears in a short time.

[0244] <Notification to Workers> The determination results from the ground fault detection units 14 and 23 may be notified to the workers by a notification unit (not shown), such as a display device, audio device, or printer. Based on the determination results from the ground fault detection units 14 and 23 that are notified, the workers can quickly and reliably determine whether or not there is a ground fault in the U-phase power line 33U, U-phase winding, V-phase power line 33V, V-phase winding, W-phase power line 33W, and W-phase winding.

[0245] Examples of display devices include standalone display monitors, display monitors attached to the motor drive unit 1, display monitors attached to a higher-level control device (not shown) that controls the motor drive unit 1, and display monitors attached to personal computers and mobile terminals. Alternatively, the display device may be composed of light-emitting elements such as LEDs or lamps. For example, the light-emitting element may not emit light when there is no ground fault, and may emit light when a ground fault occurs.

[0246] Audio equipment may be designed to not emit sound when there is no ground fault, but to emit sound when a ground fault occurs. Examples of audio equipment include speakers, buzzers, and chimes.

[0247] The printer may be configured to print out the date and time of a ground fault on paper or elsewhere if one occurs.

[0248] Furthermore, the ground fault detection units 14 and 23 can store and accumulate the determination results in memory each time they are obtained, creating a database that can be used for maintenance work, parts ordering, and other purposes.

[0249] <Processor and Memory> The motor drive device 1 is provided with at least one processor, which is an arithmetic processing unit. Examples of arithmetic processing units include ICs, LSIs, CPUs, MPUs, DSPs, etc. The arithmetic processing unit has ground fault detection units 14 and 23, a DC link current detection unit 15, a power supply current detection unit 16, an inverter current detection unit 24, an inverter control unit 10, a converter control unit, a pre-charge control unit, a switching control unit, and other processing units. Each of these units of the arithmetic processing unit is a functional module realized by, for example, a program executed on the processor. For example, if the ground fault detection units 14 and 23, the DC link current detection unit 15, the power supply current detection unit 16, the inverter current detection unit 24, the inverter control unit 10, the converter control unit, the pre-charge control unit, the switching control unit, and other processing units are constructed in program format, the functions of each unit can be realized by operating the arithmetic processing unit according to this program. The programs for executing each process in the ground fault detection units 14 and 23, the DC link current detection unit 15, the power supply current detection unit 16, the inverter current detection unit 24, the inverter control unit 10, the converter control unit, the pre-charge control unit, the switchgear control unit, and other processing units may be provided in the form of a program product stored (recorded) on a computer-readable storage medium (recording medium), such as a semiconductor memory, a magnetic storage medium (magnetic recording medium), or an optical storage medium (optical recording medium). Alternatively, the ground fault detection units 14 and 23, the DC link current detection unit 15, the power supply current detection unit 16, the inverter current detection unit 24, the inverter control unit 10, the converter control unit, the pre-charge control unit, the switchgear control unit, and other processing units may be implemented as semiconductor integrated circuits on which programs that realize the functions of each unit are written.

[0250] Furthermore, the motor drive unit 1 is provided with at least one memory, which is a storage device (recording device). The memory also includes various storage units (recording units) within the ground fault detection units 14 and 23, DC link current detection unit 15, power supply current detection unit 16, inverter current detection unit 24, inverter control unit 10, converter control unit, pre-charge control unit, switching control unit, and other processing units. The memory may be an electrically erasable and recordable non-volatile memory such as EEPROM (registered trademark), or a high-speed read / write random access memory such as DRAM or SRAM. The storage device may also have a configuration such as an HDD (hard disk drive) or SSD (solid state drive). The memory stores programs for operating the ground fault detection units 14 and 23, DC link current detection unit 15, power supply current detection unit 16, inverter current detection unit 24, inverter control unit 10, converter control unit, pre-charge control unit, switching control unit, and other processing units. Furthermore, the memory stores the current detection results from the DC link current detection unit 15, the current detection results from the power supply current detection unit 16, and the current detection results from the inverter current detection unit 24. The memory also stores the determination results from the ground fault detection units 14 and 23. The memory stores threshold values. The memory stores various programs and data related to the converter control unit (not shown). The memory stores various programs and data related to the converter 11. The memory stores various programs and data related to the inverter control unit 10. The memory stores various programs and data related to the inverter 12. The memory stores various programs and data related to the motor drive unit 1.

[0251] <Advantages of Embodiments and Modifications of the Disclosure> According to embodiments and modifications of the disclosure, in a motor drive device, a ground fault in either the power line connecting the inverter and the motor or the motor winding can be easily detected.

[0252] Conventionally, ground fault circuit breakers have sometimes been used to detect ground faults in motor drive systems. However, because high-frequency switching noise from the inverter easily flows as ground fault current through the capacitance to ground, ground fault circuit breakers were sometimes not used to avoid malfunctions. Furthermore, in the TN system, which is particularly common in Europe and the United States, it is assumed that a large current will flow during a ground fault, so there are few opportunities to use ground fault circuit breakers in the first place. The embodiments and modifications thereof of this disclosure can detect ground faults without using ground fault circuit breakers, making them suitable for use in all situations and regions and highly versatile.

[0253] Although the present disclosure has been described in detail above, it is not limited to the individual embodiments and modifications described above. These embodiments and modifications can be added, replaced, modified, partially deleted, etc., in any way that does not depart from the gist of the present disclosure or from the spirit of the present disclosure derived from the claims and their equivalents. Furthermore, these embodiments and modifications can be implemented in combination. For example, the order of operations and processes in the embodiments and modifications described above are shown as examples only and are not limited thereto. The same applies when numerical values ​​or mathematical formulas are used in the description of the embodiments and modifications described above.

[0254] <Note> The following additional information is disclosed regarding the above embodiments and modifications.

[0255] (Note 1) A motor drive device comprising: a converter having a three-phase full-bridge circuit in which diodes are provided on the upper arm on the high-potential side and the lower arm on the low-potential side of each of the three phases, which converts AC power input from an AC power source into DC power and outputs it to a DC link; a smoothing capacitor provided on the DC link; an inverter having a three-phase full-bridge circuit in which switching elements are provided on the upper arm on the high-potential side and the lower arm on the low-potential side of each of the three phases, which converts the DC power of the DC link into AC power and supplies it to a motor by the switching operation of the switching elements; and a ground fault detection unit that detects a ground fault in either the three-phase power line between the inverter and the motor or the three-phase winding of the motor based on information related to the current that flows when any one of the switching elements of the inverter is turned on. (Note 2) The motor drive device as described in Note 1, further comprising a DC link current detection unit for detecting the current flowing through the positive power line of the DC link, wherein the ground fault detection unit determines that a ground fault has occurred in the U phase when the smoothing capacitor is fully charged and the current detected by the DC link current detection unit is greater than a predetermined threshold when only the switching element of the upper arm of the U phase of the inverter is turned on, determines that a ground fault has occurred in the V phase when the current detected by the DC link current detection unit is greater than a threshold when only the switching element of the upper arm of the V phase of the inverter is turned on, and determines that a ground fault has occurred in the W phase when the current detected by the DC link current detection unit is greater than a threshold. (Note 3) The motor drive device as described in Note 1, further comprising a DC link current detection unit for detecting the current flowing through the negative power line of the DC link, wherein the ground fault detection unit determines that a ground fault has occurred in the U phase when the smoothing capacitor is fully charged and the current detected by the DC link current detection unit is greater than a predetermined threshold when only the switching element of the lower arm of the U phase of the inverter is turned on, determines that a ground fault has occurred in the V phase when the current detected by the DC link current detection unit is greater than a predetermined threshold when only the switching element of the lower arm of the V phase of the inverter is turned on, and determines that a ground fault has occurred in the W phase when the current detected by the DC link current detection unit is greater than a threshold.(Note 4) The motor drive device as described in Note 1, further comprising a power supply current detection unit that detects the current flowing through at least one phase of the three-phase power lines between the AC power supply and the converter, wherein the ground fault detection unit determines that a ground fault has occurred in the U phase when the smoothing capacitor is fully charged and the current detected by the power supply current detection unit is greater than a predetermined threshold when only the switching element of the upper arm of the U phase of the inverter is turned on, determines that a ground fault has occurred in the V phase when the current detected by the power supply current detection unit is greater than a threshold when only the switching element of the upper arm of the V phase of the inverter is turned on, and determines that a ground fault has occurred in the W phase when the current detected by the power supply current detection unit is greater than a threshold when only the switching element of the upper arm of the W phase of the inverter is turned on. (Note 5) The motor drive device according to Note 1, further comprising a power supply current detection unit that detects the current flowing through at least one phase of the three-phase power lines between the AC power supply and the converter, wherein the ground fault detection unit determines that a ground fault has occurred in the U phase when the smoothing capacitor is fully charged and the current detected by the power supply current detection unit is greater than a predetermined threshold when only the switching element of the lower arm of the U phase of the inverter is turned on, determines that a ground fault has occurred in the V phase when the current detected by the power supply current detection unit is greater than a threshold when only the switching element of the lower arm of the V phase of the inverter is turned on, and determines that a ground fault has occurred in the W phase when the current detected by the power supply current detection unit is greater than a threshold when only the switching element of the lower arm of the W phase of the inverter is turned on.(Note 6) The motor drive device as described in Note 1, further comprising: a voltage detection unit that detects the voltage between the current inflow terminal and the current outflow terminal of the respective switching elements of the upper arms of the U-phase, V-phase, and W-phase of the inverter; and an overcurrent detection unit that determines that an overcurrent has occurred in the switching element of the upper arm of the phase in which the voltage detected by the voltage detection unit is greater than a predetermined threshold, wherein the ground fault detection unit determines that a ground fault has occurred in the U-phase when the overcurrent detection unit detects an overcurrent when only the switching element of the upper arm of the U-phase of the inverter is turned on when the smoothing capacitor is fully charged; determines that a ground fault has occurred in the V-phase when the overcurrent detection unit detects an overcurrent when only the switching element of the upper arm of the V-phase of the inverter is turned on; and determines that a ground fault has occurred in the W-phase when the overcurrent detection unit detects an overcurrent when only the switching element of the upper arm of the W-phase of the inverter is turned on. (Note 7) The motor drive device according to Note 1, further comprising: a voltage detection unit that detects the voltage between the current inflow terminal and the current outflow terminal of the respective switching elements of the lower arms of the U-phase, V-phase, and W-phase of the inverter; and an overcurrent detection unit that determines that an overcurrent has occurred in the switching element of the lower arm of the phase in which the voltage detected by the voltage detection unit is greater than a predetermined threshold, wherein the ground fault detection unit determines that a ground fault has occurred in the U-phase when the overcurrent detection unit detects an overcurrent when only the switching element of the lower arm of the U-phase of the inverter is turned on when the smoothing capacitor is fully charged; determines that a ground fault has occurred in the V-phase when the overcurrent detection unit detects an overcurrent when only the switching element of the lower arm of the V-phase of the inverter is turned on; and determines that a ground fault has occurred in the W-phase when the overcurrent detection unit detects an overcurrent when only the switching element of the lower arm of the W-phase of the inverter is turned on.(Note 8) A motor drive device comprising: a converter having a three-phase full-bridge circuit in which diodes are provided on the upper arm on the high-potential side and the lower arm on the low-potential side of each of the three phases, which converts AC power input from an AC power source into DC power and outputs it to a DC link; a smoothing capacitor provided in the DC link; an inverter having a three-phase full-bridge circuit in which switching elements and diodes are provided on the upper arm on the high-potential side and the lower arm on the low-potential side of each of the three phases, which converts the DC power of the DC link into AC power and supplies it to a motor by the switching operation of the switching elements; a switching unit that opens and closes the circuit on the three-phase power line between the AC power source and the converter; a resistor provided in the DC link between the converter and the smoothing capacitor; and a ground fault detection unit that detects a ground fault in either the three-phase power line between the inverter and the motor or in the windings of the motor based on information related to the current that flows when the switching unit closes the circuit. (Note 9) The motor drive device according to Note 8, further comprising a DC link current detection unit that detects the current flowing through the positive power line of the DC link between the inverter and the smoothing capacitor when a resistor is provided in the positive power line of the DC link between the converter and the smoothing capacitor, wherein the ground fault detection unit determines that a ground fault has occurred if the current detected by the DC link current detection unit is greater than a predetermined threshold when the switching unit closes the circuit while the smoothing capacitor is not fully charged. (Note 10) The motor drive device according to Note 8, further comprising a DC link current detection unit that detects the current flowing through the negative power line of the DC link between the smoothing capacitor and the converter when a resistor is provided in the positive power line of the DC link between the converter and the smoothing capacitor, wherein the ground fault detection unit determines that a ground fault has occurred if the current detected by the DC link current detection unit is greater than a predetermined threshold when the switching unit closes the circuit while the smoothing capacitor is not fully charged.(Note 11) The motor drive device according to Note 8, further comprising a DC link current detection unit that detects the current flowing through the negative power line of the DC link between the smoothing capacitor and the inverter when a resistor is provided in the negative power line of the DC link between the converter and the smoothing capacitor, wherein the ground fault detection unit determines that a ground fault has occurred if the current detected by the DC link current detection unit is greater than a predetermined threshold when the switching unit closes the circuit while the smoothing capacitor is not fully charged. (Note 12) The motor drive device according to Note 8, further comprising a DC link current detection unit that detects the current flowing through the positive power line of the DC link between the converter and the smoothing capacitor when a resistor is provided in the negative power line of the DC link between the converter and the smoothing capacitor, wherein the ground fault detection unit determines that a ground fault has occurred if the current detected by the DC link current detection unit is greater than a predetermined threshold when the switching unit closes the circuit while the smoothing capacitor is not fully charged. (Note 13) The motor drive device according to Note 8, further comprising a power supply current detection unit that detects the current flowing through at least one phase of the three-phase power lines between the AC power supply and the converter, wherein the ground fault detection unit determines that a ground fault has occurred if the current detected by the power supply current detection unit is greater than a predetermined threshold when the switching unit closes the circuit while the smoothing capacitor is not fully charged. (Note 14) The motor drive device according to Note 8, further comprising an inverter current detection unit that detects the current flowing through each phase of the three-phase power lines between the inverter and the motor, wherein the ground fault detection unit determines that a ground fault has occurred in the U phase if the current flowing through the U phase power line detected by the inverter current detection unit is greater than a predetermined threshold when the switching unit closes the circuit while the smoothing capacitor is not fully charged, determines that a ground fault has occurred in the V phase if the current flowing through the V phase power line detected by the inverter current detection unit is greater than a predetermined threshold, and determines that a ground fault has occurred in the W phase if the current flowing through the W phase power line detected by the inverter current detection unit is greater than a threshold. (Note 15) The motor drive device according to any one of Notes 8 to 14, wherein the resistor is a pre-charging resistor that suppresses the inrush current to the smoothing capacitor during the pre-charging period.

[0256] 1 Motor drive unit 2 AC power supply 3 Motor 10 Inverter control unit 11 Converter 12 Inverter 13 Smoothing capacitor 14 Ground fault detection unit 15 DC link current detection unit 16 Power supply current detection unit 17 Voltage detection unit 18 Overcurrent detection unit 19 DC link 21 Switching unit 22 Backup charging circuit 23 Ground fault detection unit 24 Inverter current detection unit 31P Positive power line 31N Negative power line 32R R-phase power line 32S S-phase power line 32T T-phase power line 33U U-phase power line 33V V-phase power line 33W W-phase power line 100 AC power supply 200 Resistor 221 Backup charging resistor 222 Backup charging switch D Diode D RL Diode D on the lower arm of the R phase RU Diode D on the upper arm of the R phase SL Diode D on the S-phase lower arm SU Diode D on the upper arm of the S phase TL Diode D of the lower arm of the T phase TU Diode D on the upper arm of the T phase UL Diode D of the lower arm of the U phase UU Diode D on the U-phase upper arm VL Diode D on the lower arm of the V phase VU Diode D on the upper arm of the V-phase WL Diode D of the W-phase lower arm WU W-phase upper arm diode S switching element S RL R-phase lower arm switching element S RU R-phase upper arm switching element S SL S-phase lower arm switching element S SU S-phase upper arm switching element S TL T-phase lower arm switching element S TU T-phase upper arm switching element S UL U-phase lower arm switching element S UU Switching element S of the U-phase upper armVL V-phase lower arm switching element S VU V-shaped upper arm switching element S WL W-phase lower arm switching element S WU W-phase upper arm switching element

Claims

A three-phase full-bridge circuit has diodes provided on the upper arm on the high-potential side and the lower arm on the low-potential side of each of the three phases, and a converter that converts AC power input from an AC power source into DC power and outputs it to a DC link, A smoothing capacitor provided in the DC link, An inverter has a three-phase full-bridge circuit in which switching elements are provided on the upper arm on the high-potential side and the lower arm on the low-potential side of each of the three phases, and the switching elements convert the DC power of the DC link into AC power and supply it to the motor. A ground fault detection unit detects a ground fault in either the three-phase power line between the inverter and the motor or the three-phase winding of the motor, based on information related to the current that flows when any one of the switching elements of the inverter is turned on. A motor drive device equipped with the following features. 　 The DC link current detection unit further includes a DC link current detection unit that detects the current flowing through the positive power line of the DC link, The motor drive device according to claim 1, wherein the ground fault detection unit determines that a ground fault has occurred in the U phase when the smoothing capacitor is fully charged and the current detected by the DC link current detection unit is greater than a predetermined threshold when only the switching element of the upper arm of the U phase of the inverter is turned on; determines that a ground fault has occurred in the V phase when the current detected by the DC link current detection unit is greater than the threshold when only the switching element of the upper arm of the V phase of the inverter is turned on; and determines that a ground fault has occurred in the W phase when the current detected by the DC link current detection unit is greater than the threshold when only the switching element of the upper arm of the W phase of the inverter is turned on. 　 The DC link current detection unit further includes a DC link current detection unit that detects the current flowing through the negative power line of the DC link, The motor drive device according to claim 1, wherein the ground fault detection unit determines that a ground fault has occurred in the U phase when the smoothing capacitor is fully charged and the current detected by the DC link current detection unit is greater than a predetermined threshold when only the switching element of the lower arm of the U phase of the inverter is turned on; determines that a ground fault has occurred in the V phase when the current detected by the DC link current detection unit is greater than the threshold when only the switching element of the lower arm of the V phase of the inverter is turned on; and determines that a ground fault has occurred in the W phase when the current detected by the DC link current detection unit is greater than the threshold when only the switching element of the lower arm of the W phase of the inverter is turned on. 　 The system further includes a power supply current detection unit that detects the current flowing through at least one phase of the three-phase power lines between the AC power supply and the converter. The motor drive device according to claim 1, wherein the ground fault detection unit determines that a ground fault has occurred in the U phase when the smoothing capacitor is fully charged and the current detected by the power supply current detection unit is greater than a predetermined threshold when only the switching element of the upper arm of the U phase of the inverter is turned on; determines that a ground fault has occurred in the V phase when the current detected by the power supply current detection unit is greater than the threshold when only the switching element of the upper arm of the V phase of the inverter is turned on; and determines that a ground fault has occurred in the W phase when the current detected by the power supply current detection unit is greater than the threshold when only the switching element of the upper arm of the W phase of the inverter is turned on. 　 The system further includes a power supply current detection unit that detects the current flowing through at least one phase of the three-phase power lines between the AC power supply and the converter. The motor drive device according to claim 1, wherein the ground fault detection unit determines that a ground fault has occurred in the U phase when the smoothing capacitor is fully charged and the current detected by the power supply current detection unit is greater than a predetermined threshold when only the switching element of the lower arm of the U phase of the inverter is turned on; determines that a ground fault has occurred in the V phase when the current detected by the power supply current detection unit is greater than the threshold when only the switching element of the lower arm of the V phase of the inverter is turned on; and determines that a ground fault has occurred in the W phase when the current detected by the power supply current detection unit is greater than the threshold when only the switching element of the lower arm of the W phase of the inverter is turned on. 　 A voltage detection unit for detecting the voltage between the current inflow terminal and current outflow terminal of the respective current inflow terminal and current outflow terminal of the switching element of the upper arm of the U-phase, V-phase, and W-phase of the inverter, An overcurrent detection unit determines that if the voltage detected by the voltage detection unit is greater than a predetermined threshold, an overcurrent has occurred in the switching element of the upper arm of the phase in which the voltage was detected. Furthermore, The motor drive device according to claim 1, wherein the ground fault detection unit determines that a ground fault has occurred in the U phase when the smoothing capacitor is fully charged and the overcurrent detection unit detects an overcurrent when only the switching element of the upper arm of the U phase of the inverter is turned on; determines that a ground fault has occurred in the V phase when the overcurrent detection unit detects an overcurrent when only the switching element of the upper arm of the V phase of the inverter is turned on; and determines that a ground fault has occurred in the W phase when the overcurrent detection unit detects an overcurrent when only the switching element of the upper arm of the W phase of the inverter is turned on. 　 A voltage detection unit for detecting the voltage between the current inflow terminal and current outflow terminal of the respective switching elements of the lower arms of the U-phase, V-phase, and W-phase of the inverter, An overcurrent detection unit determines that if the voltage detected by the voltage detection unit is greater than a predetermined threshold, an overcurrent has occurred in the switching element of the lower arm of the phase in which the voltage was detected. Furthermore, The motor drive device according to claim 1, wherein the ground fault detection unit determines that a ground fault has occurred in the U phase when the smoothing capacitor is fully charged and the overcurrent detection unit detects an overcurrent when only the switching element of the lower arm of the U phase of the inverter is turned on; determines that a ground fault has occurred in the V phase when the overcurrent detection unit detects an overcurrent when only the switching element of the lower arm of the V phase of the inverter is turned on; and determines that a ground fault has occurred in the W phase when the overcurrent detection unit detects an overcurrent when only the switching element of the lower arm of the W phase of the inverter is turned on. 　 A three-phase full-bridge circuit has diodes provided on the upper arm on the high-potential side and the lower arm on the low-potential side of each of the three phases, and a converter that converts AC power input from an AC power source into DC power and outputs it to a DC link, A smoothing capacitor provided in the DC link, An inverter has a three-phase full-bridge circuit in which switching elements and diodes are provided on the upper arm on the high-potential side and the lower arm on the low-potential side of each of the three phases, and the switching elements perform a switching operation to convert the DC power of the DC link into AC power and supply it to the motor, A switching unit for opening and closing the circuit on the three-phase power line between the AC power supply and the converter, A resistor is provided in the DC link between the converter and the smoothing capacitor, A ground fault detection unit detects a ground fault in either the three-phase power line between the inverter and the motor or in the motor windings, based on information related to the current that flows when the switching unit closes the circuit. A motor drive device equipped with the following features. 　 The system further includes a DC link current detection unit that detects the current flowing through the DC link between the inverter and the smoothing capacitor. The motor drive device according to claim 8, wherein the ground fault detection unit determines that a ground fault has occurred when the switching unit closes the circuit while the smoothing capacitor is not fully charged and the current detected by the DC link current detection unit is greater than a predetermined threshold. 　 The system further includes a DC link current detection unit that detects the current flowing through the DC link between the smoothing capacitor and the converter, The motor drive device according to claim 8, wherein the ground fault detection unit determines that a ground fault has occurred when the switching unit closes the circuit while the smoothing capacitor is not fully charged and the current detected by the DC link current detection unit is greater than a predetermined threshold. 　 The system further includes a power supply current detection unit that detects the current flowing through at least one phase of the three-phase power lines between the AC power supply and the converter. The motor drive device according to claim 8, wherein the ground fault detection unit determines that a ground fault has occurred when the switching unit closes the circuit while the smoothing capacitor is not fully charged and the current detected by the power supply current detection unit is greater than a predetermined threshold. 　 The inverter further comprises an inverter current detection unit that detects the current flowing through each phase of the three-phase power line between the inverter and the motor. The motor drive device according to claim 8, wherein the ground fault detection unit determines that a ground fault has occurred in the U phase when the switching unit closes the circuit while the smoothing capacitor is not fully charged, if the current flowing through the U phase power line detected by the inverter current detection unit is greater than a predetermined threshold, if the current flowing through the V phase power line detected by the inverter current detection unit is greater than the threshold, and if the current flowing through the W phase power line detected by the inverter current detection unit is greater than the threshold, a ground fault has occurred in the W phase. 　 The motor drive device according to any one of claims 8 to 12, wherein the resistor is a pre-charging resistor that suppresses inrush current to the smoothing capacitor during the pre-charging period.

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