JP2011091886A - Motor driver - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent the discharge in a boot capacitor. <P>SOLUTION: An inverter part 3 has transistor pairs SW1-SW3 comprising upper transistors Q1a-Q3a and lower transistors Q1b-Q3b for each phase of a motor 51. Upper element control units 41a-43a are provided to correspond to upper transistor Q1a-Q3a to control the action of each of the upper transistors Q1a-Q3a. Boot capacitors C1-C3 supply each of the upper element control units 41a-43a with operation power. A charger 6 charges each of the boot capacitors C1-C3. Lower element control units 41b-43b perform charge control for charging each of boot capacitors C1-C3 and discharge prevention control for keeping currents flowing to the first boot capacitor, while at least one of the second boot capacitors excluding the first boot capacitor thus charged performs charge among the boot capacitors C1-C3, as current application control units. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a motor drive device, and more particularly to a motor drive device that drives a motor having a plurality of phases.

  The air conditioner includes various devices such as a compressor and a fan, and a motor is often used as the power source. The air conditioner further includes a motor driving device that drives these motors.

  As disclosed in, for example, Patent Document 1 (Japanese Patent Laid-Open No. 2003-61363), the motor driving device includes an inverter unit that generates a driving voltage for driving the motor and outputs the driving voltage to the motor. In general, the inverter unit has a pair of switching elements including an upper switching element and a lower switching element connected in series with each other, corresponding to the number of phases of the motor. When each switching element is turned on and off, a drive voltage is generated and the motor is driven to rotate.

  The motor drive device according to Patent Document 1 further includes a plurality of boot capacitors provided so as to correspond to the upper switching elements. Each boot capacitor has one end connected between the upper switching element and the lower switching element, and the other end connected to the control power supply circuit. Each boot capacitor is charged one by one before starting the motor. The electric charge stored in each boot capacitor functions as an operation power source at the time of starting the motor of the upper element control unit that controls each upper switching element.

  However, while other boot capacitors are being charged in the state where there are already charged boot capacitors, the already charged boot capacitors are gradually increased by the time constant between the impedance of the upper element control unit and the capacitance value of the boot capacitor. It will discharge and a voltage drop will occur. Then, when the motor is started, the upper element control unit may not be able to normally turn on and off the upper switching element due to insufficient operating power.

  Therefore, an object of the present invention is to provide a motor drive device that can prevent discharge in a boot capacitor.

  The motor driving apparatus according to the first aspect drives a multi-phase motor. The motor drive device includes an inverter unit, a plurality of upper element control units, a plurality of boot capacitors, a charging unit, and an energization control unit. The inverter unit has a plurality of switching element pairs corresponding to each phase of the motor, and is connected to the motor. The switching element pair includes an upper switching element and a lower switching element connected in series with each other. The plurality of upper element control units are provided corresponding to the upper switching elements, and control operations of the upper switching elements. The plurality of boot capacitors can supply operating power to each upper element control unit. The charging unit can charge each boot capacitor. The energization control unit performs charge control and discharge prevention control. The charge control is a control for charging each boot capacitor by causing a current to flow sequentially from the charging unit to each boot capacitor. The discharge prevention control is a control in which a current is continuously supplied to the first boot capacitor while at least one of the remaining second boot capacitors other than the first boot capacitor that has been charged among the plurality of boot capacitors is being charged. .

  According to this motor drive device, in the discharge prevention control, while the charged boot capacitor (first boot capacitor) is present, the uncharged boot capacitor (second boot capacitor) is being charged. The current continues to flow through the first boot capacitor. As a result, it is possible to prevent the first boot capacitor from being gradually discharged and a voltage drop during charging of the second boot capacitor, so that the motor can be driven without any problem.

  A motor drive device according to a second aspect is the motor drive device according to the first aspect, wherein one end of each boot capacitor is connected to a charging unit. The other end of each boot capacitor is connected between the corresponding upper switching element and lower switching element. The energization control unit includes a plurality of lower element control units. The lower element control unit is provided corresponding to each lower switching element, and controls the operation of each lower switching element.

  In this motor drive device, the energization control unit is composed of a lower element control unit. Therefore, if the lower switching element is turned on by the energization control unit which is the lower element control unit, the current from the charging unit is supplied to the lower side via the boot capacitor connected to the turned on lower switching element. A current path that flows to the switching element is formed. As described above, since the lower element control unit provided corresponding to each lower switching element functions as an energization control unit, it is not necessary to provide an energization control unit separately from the lower element control unit.

  A motor drive device according to a third aspect of the present invention is the motor drive device according to the second aspect of the present invention, wherein the energization control unit includes a lower switching element connected to the upper switching element corresponding to the first boot capacitor in the discharge prevention control. By continuing to turn on, the current continues to flow from the charging unit to the first boot capacitor.

  In this motor drive device, during the discharge prevention control, the lower switching element connected to the upper switching element corresponding to the first boot capacitor is kept on. Thereby, since the current from the charging unit flows to the lower switching element via the first boot capacitor, the discharge of the first boot capacitor can be prevented.

  A motor drive device according to a fourth aspect of the present invention is the motor drive device according to the second or third aspect of the present invention, wherein the energization control unit turns on and off each lower switching element at a predetermined frequency a plurality of times in charge control, A current is passed from the live part to each boot capacitor.

  Thus, the boot capacitor is gradually charged when the boot capacitor is charged. Therefore, since a sudden large current (that is, inrush current) does not flow through the boot capacitor, it is possible to prevent the so-called inrush current from affecting other functional units.

  A motor drive device according to a fifth aspect of the present invention is the motor drive device according to any one of the second to fourth aspects, wherein the motor has a plurality of drive coils. Each drive coil has one end connected between the upper switching element and the lower switching element. The motor drive device further includes a current detection unit. The current detection unit is connected to the downstream side of each lower switching element and can detect the current flowing through the motor.

  In this motor drive device, while the second boot capacitor is charging, a current continues to flow through the charged first boot capacitor as the lower switching element is kept on. This current flows to the current detection unit via the first boot capacitor and the lower switching element, and is detected by the current detection unit.

  A motor drive device according to a sixth aspect of the present invention is the motor drive device according to the fifth aspect, wherein the energization control unit performs the discharge prevention control before starting the motor. The motor drive device further includes a first determination unit. The first determination unit determines that the motor is grounded when the detection result by the current detection unit is equal to or greater than the first predetermined value during the discharge prevention control.

  At the time of discharge prevention control, if the motor has a ground fault, in addition to the current flowing through the first boot capacitor and the current flowing through the second boot capacitor, the current due to the motor ground fault passes through the lower switching element that is turned on. It flows to the current detector. Therefore, the first determination unit determines that the motor is grounded when the detection result by the current detection unit is equal to or greater than the first predetermined value during the discharge prevention control. That is, according to this motor drive device, in addition to turning on and off the predetermined lower switching element by the charge control, the predetermined lower switching element continues to be turned on by the discharge prevention control, so that it is possible to determine the motor ground fault. Therefore, before starting the motor, it is possible to perform control corresponding to a motor ground fault such as not starting the motor.

  A motor drive device according to a seventh aspect of the present invention is the motor drive device according to the fifth or sixth aspect of the present invention, further comprising a second determination unit. The second determination unit determines that the current detection unit is short-circuited when the detection result by the current detection unit is equal to or less than the second predetermined value during the discharge prevention control.

  If the current detection unit is short-circuited, for example, during discharge prevention control performed before starting the motor, the current detection unit should detect the total value of the current flowing through the first boot capacitor and the current flowing through the second boot capacitor. It can no longer be detected. Therefore, the second determination unit can determine that the current detection unit is short-circuited, for example, when the detection result by the current detection unit is equal to or less than the second predetermined value during the discharge prevention control. Thereby, it is possible to know the state abnormality of the current detection unit before starting the motor.

  A motor drive device according to an eighth aspect of the present invention is the motor drive device according to any of the fifth to seventh aspects, wherein the energization control unit performs the discharge prevention control before starting the motor. The motor drive device further includes a third determination unit. The third determination unit determines that the motor is driven when the detection result by the current detection unit is equal to or less than a third predetermined value during the discharge prevention control.

  Here, it is assumed that the motor is, for example, a fan motor. Since the motor is not started during the discharge prevention control, the current detection unit should detect the total value of the current flowing through the first boot capacitor and the current flowing through the second boot capacitor. However, when the motor is driven by a normal wind, a reverse wind, or the like, the current flows back between the lower switching element that is turned on and the motor, and thus the current detection unit cannot detect the current. Therefore, the third determination unit may determine that the motor that should not have been started is erroneously driven when the detection result by the current detection unit is equal to or less than the third predetermined value during the discharge prevention control. it can. Thereby, it is possible to know the malfunction of the motor.

  A motor driving device according to a ninth aspect is the motor driving device according to any one of the first to eighth aspects, wherein the motor is a three-phase motor. The inverter unit has three switching element pairs.

  In this motor drive device, since the inverter unit has three switching element pairs, three boot capacitors are also provided. Even in this case, since the discharge of each of the three boot capacitors can be prevented, the motor can be driven without any problem.

  According to the motor driving device of the first aspect of the present invention, it is possible to prevent the first boot capacitor from being gradually discharged and a voltage drop during charging of the second boot capacitor, so that the motor can be driven without any problem.

  According to the motor drive device of the second aspect, since the lower element control unit provided corresponding to each lower switching element functions as the energization control unit, the energization control unit is provided separately from the lower element control unit. You do n’t have to.

  According to the motor drive device of the third aspect of the invention, the current from the charging unit flows to the lower switching element via the first boot capacitor, so that the first boot capacitor can be prevented from discharging.

  According to the motor drive device of the fourth aspect of the present invention, since a sudden large current (that is, inrush current) does not flow through the boot capacitor, it is possible to prevent the inrush current from affecting other functional units.

  According to the motor drive device of the fifth aspect of the present invention, while the second boot capacitor is being charged, a current continues to flow through the charged first boot capacitor as the lower switching element is kept on. This current flows to the current detection unit via the first boot capacitor and the lower switching element, and is detected by the current detection unit.

  According to the motor drive device of the sixth aspect of the present invention, the predetermined lower switching element is kept on by the discharge prevention control in addition to the predetermined lower switching element being turned on / off by the charge control, so that it is possible to determine the motor ground fault. . Therefore, before starting the motor, it is possible to perform control corresponding to a motor ground fault such as not starting the motor.

  The motor drive device according to the seventh aspect of the invention can determine that the current detection unit is short-circuited, for example, when the detection result by the current detection unit is equal to or less than the second predetermined value during discharge prevention control. Therefore, it is possible to know the state abnormality of the current detection unit before the motor is started.

  The motor drive device according to the eighth aspect of the present invention determines that the motor that should not have been started is erroneously driven when the detection result by the current detection unit is equal to or less than the third predetermined value during the discharge prevention control. Can do. Therefore, it is possible to know the malfunction of the motor.

  According to the motor drive device of the ninth aspect of the present invention, since the discharge of each of the three boot capacitors can be prevented, the motor can be driven without any problem.

1 is an overall configuration diagram of a motor drive system including a motor drive device according to the present embodiment. The structure schematic of a motor. The timing chart for demonstrating the process of ON / OFF of the transistor of each phase which concerns on a motor drive device, and the change of the both-ends voltage of a boot capacitor after a motor starting command is made until a motor starts normal rotation. FIG. 2 is an enlarged view of the vicinity of an inverter unit of the motor driving device according to FIG. FIG. 2 is an enlarged view of the vicinity of an inverter unit of the motor drive device according to FIG. 1, showing a current path flowing in the motor drive device when the boot capacitor C <b> 2 is continuously charged after the boot capacitor C <b> 1 is charged. Figure. FIG. 2 is an enlarged view of the vicinity of an inverter unit of the motor drive device according to FIG. 1, illustrating an example of a current path that flows in the motor drive device when a motor before starting is erroneously driven. The figure which shows notionally the relationship between a 1st predetermined value, a 2nd predetermined value, and a 3rd predetermined value. The flowchart for demonstrating operation | movement of the motor drive device which concerns on this embodiment. The flowchart for demonstrating operation | movement of the motor drive device which concerns on this embodiment.

  Hereinafter, a motor drive device according to the present invention will be specifically described with reference to the drawings.

(1) Overall and Motor Configuration FIG. 1 is an overall configuration diagram of a motor drive system 100 including a motor 51 and a motor drive device 1 that drives the motor 51. Here, as a kind of motor, although a direct current motor, an alternating current motor, a stepping motor, a brushless motor etc. are mentioned generally, as a motor 51 concerning this embodiment, a three-phase brushless motor is used.

  The motor 51 is a fan motor used for the outdoor fan 61 in the outdoor unit of the air conditioner. As shown in FIG. 2, the motor 51 includes a stator 52, a rotor 53, and three Hall elements 54u, 54v, 54w.

  The stator 52 includes U-phase, V-phase, and W-phase drive coils 52u, 52v, and 52w that are star-connected. One end of each of the U-phase, V-phase, and W-phase drive coils 52u to 52w is connected to the connection points PU, PV, and PW of the upper transistors Q1a to Q3a and the lower transistors Q1b to Q3b in the inverter unit 3, respectively. The other end is all connected to the terminal PN. These three-phase drive coils 52u to 52w generate an induced voltage corresponding to the rotational speed and the position of the rotor 53 as the rotor 53 rotates.

  The rotor 53 has a permanent magnet composed of a plurality of magnetic poles, and rotates around the rotation axis with respect to the stator 52 in a fixed state. The rotor 53 has, for example, four N-pole permanent magnets and four S-pole permanent magnets, and has a configuration in which N-pole permanent magnets and S-pole permanent magnets are alternately combined. The rotation of the rotor 53 is transmitted to the outdoor fan 61 via an output shaft (not shown) that is on the same axis as the rotation shaft.

  The three Hall elements 54u to 54w are provided at positions 120 degrees apart from each other in electrical angle. Specifically, the hall elements 54u to 54w are provided so as to correspond to the drive coils 52u to 52w, respectively. Each Hall element 54u to 54w detects the position of the rotor 53 with respect to the stator 52 based on the induced voltage generated in each corresponding drive coil 52u to 52w, and outputs a position detection signal indicating the position of the rotor 53. This position detection signal is output to a microcomputer (not shown) included in the motor drive device 1.

  A microcomputer (not shown) performs overall control of the motor drive device 1.

(2) Configuration of Motor Drive Device As shown in FIG. 1, the motor drive device 1 mainly includes a power supply unit 2, an inverter unit 3, an inverter control circuit 4, a charging unit 6, and a shunt resistor 7 (corresponding to a current detection unit). And a state determination unit 9. Each of these functional units constituting the motor drive device 1 is configured on one printed circuit board P1, and is connected to the motor 51 via the interfaces IF1, IF2, and IF3.

〔Power supply part〕
The power supply unit 2 supplies power for the motor drive device 1 to the inverter unit 3. Specifically, the power supply unit 2 has a rectification unit 22 connected to a three-phase commercial power supply 21 outside the motor drive device 1. Although not shown, the rectification unit 22 is configured by a diode or the like, and rectifies the AC voltage output from the commercial power supply 21. That is, the AC voltage output from the commercial power supply 21 is converted into a DC voltage in the power supply unit 2 and then supplied to the inverter unit 3.

[Inverter part]
The inverter unit 3 includes a plurality of insulated gate bipolar transistors Q1a, Q2a, Q3a, Q1b, Q2b, Q3b (corresponding to switching elements, hereinafter simply referred to as transistors), and a plurality of reflux diodes D1a, D2a, D3a, D1b, D2b and D3b. The transistors Q1a and Q1b, Q2a and Q2b, Q3a and Q3b are connected in series between the power supply line L1 and the GND line L2. Here, since the transistors Q1a, Q2a, and Q3a are located closer to the power supply wiring L1 than the transistors Q1b, Q2b, and Q3b, they are hereinafter referred to as upper transistors (corresponding to upper switching elements), and the transistors Q1b, Q2b, and Q3b are Since the transistors are located closer to the GND line L2 than the transistors Q1a, Q2a, and Q3a, they are hereinafter referred to as lower transistors (corresponding to lower switching elements). That is, the inverter unit 3 includes three transistor pairs (corresponding to switching element pairs) SW1, SW2, and SW3 including upper transistors Q1a to Q3a and lower transistors Q1b to Q3b corresponding to the number of phases of the motor 51. Have.

  The connection point PU of the upper transistor Q1a and the lower transistor Q1b in the transistor pair SW1 is connected to the motor 51 via the interface IF1 on the printed circuit board P1. Similarly, the connection points PV and PW of the upper transistors Q2a and Q3a and the lower transistors Q2b and Q3b in each transistor pair SW2 and SW3 are connected to the motor 51 via the interfaces IF2 and IF3 on the printed circuit board P1. . As shown in FIGS. 1 and 2, a transistor pair SW1 composed of transistors Q1a and Q1b, a transistor pair SW2 composed of transistors Q2a and Q2b, and a transistor pair SW3 composed of transistors Q3a and Q3b are composed of a U-phase drive coil 52u and a V-phase in this order. Drive coil 52v and W-phase drive coil 52w.

  The free-wheeling diodes D1a to D3a and D1b to D3b have characteristics such that they are turned on when a reverse voltage is applied to the transistors Q1a to Q3a and Q1b to Q3b. Connected in parallel.

  The inverter unit 3 having such a configuration is configured to drive the motor 51 by turning on and off the transistors Q1a to Q3a and Q1b to Q3b based on the gate control voltage sent from the inverter control circuit 4. A drive voltage is generated. With this drive voltage, the motor 51 can be driven to rotate.

[Inverter control circuit]
The inverter control circuit 4 is a circuit that applies a gate control voltage to each of the transistors Q1a to Q3a and Q1b to Q3b of the inverter unit 3 to control on and off of each of the transistors Q1a to Q3a and Q1b to Q3b. The inverter control circuit 4 mainly corresponds to the upper element control units 41a, 42a, 43a and the boot capacitors C1, C2, C3 provided corresponding to the upper transistors Q1a to Q3a, and the lower transistors Q1b to Q3b, respectively. The lower element control units 41b, 42b, and 43b are provided.

  Three upper element control units 41a to 43a are provided in the same manner as the upper transistors Q1a to Q3a. Input terminals of the upper element control units 41a to 43a are connected to a microcomputer (not shown), and output terminals are connected to base terminals of the upper transistors Q1a to Q3a. The upper element control units 41a to 43a generate gate control voltages for turning on or off the connected upper transistors Q1a to Q3a based on a command sent from a microcomputer (not shown). In other words, the upper element control units 41a to 43a control operations of the corresponding upper transistors Q1a to Q3a.

  Similarly to the upper transistors Q1a to Q3a, three boot capacitors C1 to C3 are provided corresponding to the upper transistors Q1a to Q3a. The terminals on the high voltage side of the boot capacitors C1 to C3 are connected so as to be the power supply terminals of the upper element control units 41a to 43a, and the diodes D1, D2, D3, and the resistors R1, R2, R3 are connected. To the charging unit 6 (see FIG. 4). The terminals on the low voltage side of the boot capacitors C1 to C3 are connected so as to be the GND side terminals of the upper element control units 41a to 43a, and between the upper transistors Q1a to Q3a and the lower transistors Q1b to Q3b. (Ie, downstream of the upper transistors Q1a to Q3a and upstream of the lower transistors Q1b to Q3b). Such boot capacitors C1 to C3 can store electric charges when current is supplied from the charging unit 6, and can supply the electric charges as operation power to the corresponding upper element control units 41a to 43a.

  Similar to the lower transistors Q1b to Q3b, three lower element control units 41b to 43b are provided corresponding to the lower transistors Q1b to Q3b. The input terminals of the lower element control units 41b to 43b are connected to a microcomputer (not shown), and the output terminals are connected to the base terminals of the lower transistors Q1b to Q3b. The lower element control units 41b to 43b generate gate control voltages for turning on or off the connected lower transistors Q1b to Q3b based on a command sent from a microcomputer (not shown). In other words, the lower element control units 41b to 43b control the operations of the corresponding lower transistors Q1b to Q3b.

  In particular, the lower element control units 41b to 43b according to the present embodiment function as an energization control unit that performs charge control and discharge prevention control of the boot capacitors C1 to C3. The charge control is control for ensuring that sufficient electric charges used as the operation power supply for the upper element control units 41a to 43a are accumulated in the boot capacitors C1 to C3. The discharge prevention control is control for preventing the electric charge accumulated in the boot capacitors C1 to C3 from gradually discharging before being used as the operation power source of the upper element control units 41a to 43a. The charge control and the discharge prevention control are performed before the motor 51 is started.

-Charge control-
In the charge control, when the lower transistors Q1b to Q3b are turned on and off in order several times while all the upper transistors Q1a to Q3a are turned off, a current flows in order from the charging unit 6 to the boot capacitors C1 to C3. Capacitors C1 to C3 are charged. In particular, in the present embodiment, as shown in FIG. 3, when a start command for the motor 51 is sent from a microcomputer (not shown), the lower element control unit 41b first performs the charging operation of the boot capacitor C1. The corresponding lower U-phase transistor Q1b is turned on and off a plurality of times at a predetermined frequency. At this time, the other lower element control units 42b and 43b do not turn on the corresponding V-phase and W-phase lower transistors Q2b and Q3b, respectively, and maintain the off state. That is, when the boot capacitor C1 is charged, the other boot capacitors C2 and C3 are not charged. This is because the charging operation to the plurality of boot capacitors C1 to C3 is performed all at once, and the total value of the inrush current flowing through each of the boot capacitors C1 to C3 increases, so that other functional units and motors other than the inverter unit 3 This is to reduce adverse effects on other devices other than the driving device 1.

  Here, the predetermined frequency and the period during which the boot capacitor C1 is charged are controlled according to, for example, the capacitance value of the boot capacitor C1, the magnitude of the inrush current expected to flow through the capacitor C1, the amount of stored charge, and the like. Therefore, it is determined as appropriate by simulation, desktop calculation, experiment, or the like. The reason why the lower transistor Q1b is repeatedly turned on and off a plurality of times when the boot capacitor C1 is charged is to suppress the inrush current to the boot capacitor C1.

  As described above, when the lower transistor Q1b is repeatedly turned on and off, a current path from the charging unit 6 to the resistor R1, the diode D1, the boot capacitor C1, and the lower transistor Q1b is formed as shown by the arrows in FIG. Is done. Thereby, the current from the charging unit 6 flows through the boot capacitor C1 and is charged.

  The charging control is performed for the other boot capacitors C2 and C3 one by one in the same manner as the boot capacitor C1. That is, when the boot capacitor C2 is charged, the V-phase lower transistor Q2b is turned on and off a plurality of times at a predetermined frequency, and when the boot capacitor C3 is charged, the W-phase lower transistor Q3b is turned on. And turning off a plurality of times at a predetermined frequency.

  In the gate control voltage according to FIG. 3, “H” indicates that the transistors Q1a to Q3a and Q1b to Q3b are turned on, and “L” indicates that the transistors are turned off. Further, in FIG. 3, the change with time of the voltage across the boot capacitors C1 to C3 is shown together with the gate control voltage.

−Discharge prevention control−
In the discharge prevention control, at least one of the remaining boot capacitors (hereinafter referred to as the second boot capacitor) excluding the boot capacitor (hereinafter referred to as the first boot capacitor) that has been fully charged among the plurality of boot capacitors C1 to C3. While charging, current continues to flow through the first boot capacitor. Specifically, while at least one of the second boot capacitors is charging, a current flows through the second boot capacitor, but the lower element control units 41b to 43b correspond to the first boot capacitor. By continuing to turn on the lower transistors Q1b to Q3b connected to the upper transistors Q1a to Q3a, a current is continuously supplied to the charged first boot capacitor. During the discharge prevention control, all the upper transistors Q1a to Q3a are kept off as in the charge control.

  For example, it is assumed that only the boot capacitor C1 has been charged (in this case, the boot capacitor C1 is the “first boot capacitor”). In this case, as described above, the V-phase lower transistor Q2b is turned on and off a plurality of times, and the uncharged boot capacitor C2 is charged. While this charging is being performed, the U-phase upper transistor Q1a is kept turned off while the lower transistor Q1b is kept turned on (see the period of “C2 charging” in FIG. 3). The current continues to flow through the already charged boot capacitor C1. As a result, as shown in FIG. 5, current flows from the charging unit 6 to the resistor R2, the diode D2, the boot capacitor C2, and the lower transistor Q2b that is repeatedly turned on and off, and the resistor R1, the diode D1, Current flows to the boot capacitor C1 and the lower transistor Q1b that is kept on. That is, the current flowing from the resistor R1 to the boot capacitor C1 and the lower transistor Q1b (I1 in FIG. 5) is a current for preventing the voltage drop of the boot capacitor C1 and maintaining the charge (that is, preventing discharge), It can be said that the current flowing from the resistor R2 to the boot capacitor C2 and the lower transistor Q2b (I2 in FIG. 5) is a current for storing charge (that is, charging) in the boot capacitor C2.

  Further, after the charging of the boot capacitor C2 is completed, the uncharged boot capacitor C3 is subsequently charged (see the “C3 charging” period in FIG. 3). During the charging period of the boot capacitor C3, the above-described discharge prevention control is performed on the already charged boot capacitors C1 and C2. Specifically, the U-phase and V-phase upper transistors Q1a and Q2a are turned off, and the lower transistors Q1b and Q2b are kept on. As a result, a charging current flows through the boot capacitor C3 being charged, and a discharge preventing current flows through the boot capacitors C1 and C2 that have been charged.

  Since the charged boot capacitor (first boot capacitor) is already in a state where electric charge has been accumulated, the electric charge is not accumulated, and the current is smaller than that of the boot capacitor being charged (second boot capacitor). Will flow. Therefore, even if the boot capacitors C1 and C2 are subjected to discharge prevention control and the boot capacitor C3 is subjected to charge control, a relatively large current such as a so-called inrush current is applied to all the boot capacitors C1 to C3. Therefore, other functions of the motor drive device 1 and other devices other than the motor drive device 1 are not affected.

  When charging of all the boot capacitors C1 to C3 is completed in this way, all the lower transistors Q1b to Q3b are kept on for a predetermined time, so that discharge prevention control is performed for all phases (FIG. 3). . After the predetermined time has elapsed, a pause period (so-called zero vector) is given, and then the inverter control circuit 4 turns on and off each of the transistors Q1a to Q3a and Q1b to Q3b so that the motor 51 is started. When the motor 51 is started, the electric charge stored in each of the boot capacitors C1 to C3 is used as an operating power source for each of the upper element control units 41a to 43a connected to the corresponding upper transistors Q1a to Q3a. Thereby, the drive voltage for driving the motor 51 is output from the inverter unit 3, and the motor 51 starts normal rotation.

[Charging section]
The charging unit 6 can charge the boot capacitors C1 to C3. The charging unit 6 is provided separately from the power supply unit 2, and is configured by, for example, a switching power supply. The output side terminal of the charging unit 6 is connected to the boot capacitors C1 to C3 via the respective phase resistors R1 to R3, and the GND side terminal is connected to the GND terminal L2. The charging unit 6 is disposed between the inverter unit 3 and the rectifying unit 22 of the power supply unit 2.

[Shunt resistance]
The shunt resistor 7 is connected in series on the downstream side of each of the lower transistors Q1b to Q3b, more specifically, between the inverter unit 3 and the charging unit 6 and on the GND wiring L2. The shunt resistor 7 detects a current flowing on the GND wiring L2. For example, when the motor 51 is driven and normally rotating, a current flowing through the motor 51 (that is, a motor current) flows on the GND wiring L2, and the shunt resistor 7 detects this. be able to. When a current flows through the shunt resistor 7, a potential difference based on the amount of the flowing current is generated at both ends of the shunt resistor 7. This potential difference is amplified by a predetermined gain by the amplifier circuit 8 and then input to the state determination unit 9.

  In particular, in the present embodiment, when the discharge prevention control is performed, the motor 51 is not started as described above, but at least one of the lower transistors Q1b to Q3b is kept on. Therefore, the first boot capacitor that has been charged from the charging unit 6 and the current for preventing discharge that has flowed through the lower transistor that is kept on, and the second boot capacitor that is being charged and the lower side that is repeatedly turned on and off. The charging current that has flowed through the transistor also flows on the shunt resistor 7. Therefore, when the ground fault or malfunction of the motor 51 does not occur and the shunt resistor 7 is not short-circuited, the shunt resistor 7 can detect the total value of the currents.

[Status Judgment Unit]
The state determination unit 9 is composed of a microcomputer including a memory and a CPU separately from a microcomputer (not shown). When the voltage amplified by the amplifier circuit 8 is input, the state determination unit 9 calculates a current flowing on the GND wiring L2, that is, a detection result by the shunt resistor 7, based on the voltage value. The current value calculated by the state determination unit 9 when the motor 51 is rotating normally is sent to a microcomputer (not shown) and used for feedback control of the motor 51.

  In particular, the state determination unit 9 according to the present embodiment determines the state of the motor 51 and the state of the shunt resistor 7 based on the calculated current value while the lower element control units 41b to 43b are performing discharge prevention control. To do. In order to perform such an operation, the state determination unit 9 functions as a first determination unit 91, a second determination unit 92, and a third determination unit 93. Here, the state of the motor 51 means a state of whether or not the motor 51 is grounded and a state of whether or not the motor 51 is malfunctioning. The state of the shunt resistor 7 refers to a state of whether or not the shunt resistor 7 is short-circuited.

  The first determination unit 91 determines that the motor 51 is grounded when the detection result by the shunt resistor 7 is equal to or greater than the first predetermined value during the discharge prevention control. Conversely, when the detection result by the shunt resistor 7 is equal to or less than the first predetermined value, the first determination unit 91 determines that the motor 51 is not grounded. As described above, since the discharge prevention control is performed before the motor 51 is started, if the motor 51 is not grounded during the discharge prevention control, the shunt resistor 7 flows to the charged first boot capacitor. The sum of the current for preventing discharge and the current for charging flowing through the second boot capacitor being charged should be detected. Therefore, the first determination unit 91 can determine that the motor 51 is not grounded if the detection result of the shunt resistor 7 is equal to or less than the first predetermined value. However, if the motor 51 has a ground fault, during the discharge prevention control, not only the charging current flowing through the second boot capacitor and the discharge preventing current flowing through the first boot capacitor, but also the current due to the ground fault of the motor 51 Further flows to the shunt resistor 7. Therefore, the first determination unit 9 can determine that the motor 51 is grounded if the detection result is equal to or greater than the first predetermined value.

  The second determination unit 92 determines that the shunt resistor 7 is short-circuited and in an abnormal state when the detection result by the shunt resistor 7 is equal to or less than the second predetermined value during the discharge prevention control. Conversely, when the detection result by the shunt resistor 7 is equal to or greater than the second predetermined value, the second determination unit 92 determines that the shunt resistor 7 is not short-circuited and is in a normal state. As already described, since there are the lower transistors Q1b to Q3b that are kept on during the discharge prevention control, the shunt resistor 7 is used for preventing the discharge that flows through the first boot capacitor if it is in a normal state. And the total value of the charging current flowing through the second boot capacitor should be detected. Therefore, the second determination unit 92 can determine that the shunt resistor 7 is not short-circuited if the detection result is equal to or greater than the second predetermined value. However, if the shunt resistor 7 is short-circuited, current detection cannot be performed. Therefore, the second determination unit 92 can determine that the shunt resistor 7 is short-circuited if the detection result is equal to or less than the second predetermined value.

  The third determination unit 93 determines that the motor 51 is erroneously driven when the detection result by the shunt resistor 7 is equal to or less than the third predetermined value during the discharge prevention control. Conversely, if the detection result by the shunt resistor 7 is equal to or greater than the third predetermined value, the third determination unit 93 determines that the motor 51 is not driven. As described above, since the discharge prevention control is performed before the motor 51 is started, that is, when the motor 51 is not driven, the shunt resistor 7 has the discharge prevention current and the first current flowing through the first boot capacitor. 2 The total value of the charging current flowing through the boot capacitor should be detected. However, when the outdoor fan 61 is affected by a normal wind, a reverse wind, or the like, an external force is applied to the outdoor fan 61 in the forward direction or the reverse direction, and the motor 51 that is not started rotates. Then, the current that should be detected by the shunt resistor 7 (that is, the total value of the currents flowing through the boot capacitors C1 to C3) is the lower transistors Q1b to Q3b and the drive coils 52u to 52w of the motor 51 as shown in FIG. Therefore, the shunt resistor 7 cannot detect the current. Therefore, if the detection result of the shunt resistor 7 is equal to or less than the third predetermined value, the third determination unit 93 can determine that the motor 51 that should not have started is driving, that is, a so-called malfunction.

  In FIG. 6, as an example, when the motor 51 malfunctions in a state where the discharge prevention control is performed on the boot capacitor C1 and the charge control is performed on the boot capacitor C2, the W-phase This shows a case where current is flowing back through the freewheeling diode D3b, the drive coils 52u to 52w, the U-phase and V-phase lower transistors Q1b and Q2b of the lower transistor Q3b.

  Here, the relationship between the first predetermined value, the second predetermined value, and the third predetermined value is shown in FIG. FIG. 7 is a diagram conceptually showing the relationship between the first predetermined value, the second predetermined value, and the third predetermined value. As shown in FIG. 7, the first predetermined value used when determining the ground fault of the motor 51 is based on the second predetermined value used when determining the short circuit of the shunt resistor 7 and the third predetermined value used when determining malfunction of the motor 51. Is also big. When the detection result (current value) of the shunt resistor 7 is smaller than the first predetermined value and larger than the second predetermined value and the third predetermined value, both the state of the motor 51 and the shunt resistor 7 are normal. Since it can be determined that there is, a portion between the first predetermined value and the second predetermined value is indicated as a “normal region” in FIG. In FIG. 7, a region where the detection result of the shunt resistor 7 is larger than the first predetermined value is “motor ground fault region”, and a region where the detection result of the shunt resistor 7 is smaller than the second predetermined value is “short circuit of the shunt resistor”. An area ”and an area where the detection result of the shunt resistor 7 is smaller than the third predetermined value are indicated as“ motor malfunction area ”.

  The first predetermined value is a value obtained by adding a predetermined value to the maximum value of the total value of the discharge preventing current flowing through the first boot capacitor and the charging current flowing through the second boot capacitor by, for example, desktop calculation or simulation. It is determined. As a specific example, it is assumed that discharge prevention control is performed for the two boot capacitors C1 and C2, and charge control is performed for the remaining boot capacitors C3. It is determined to be a numerical value obtained by adding a margin of the total value to the total value of the charging current flowing through the boot capacitor C3. Further, the first predetermined value may be determined to be the minimum value of the current value predicted to flow through the shunt resistor 7 if the motor 51 is grounded.

  The second predetermined value and the third predetermined value are determined from a minimum value of a total value of a discharge preventing current flowing through the first boot capacitor and a charging current flowing through the second boot capacitor by, for example, a desktop calculation or a simulation. Is determined by subtracting. As a specific example, it is assumed that discharge control is performed for one boot capacitor C1, charge control is performed for the boot capacitor C2, and no control is performed for the remaining boot capacitor C3. The value is determined by subtracting the margin from the total value of the discharge preventing current flowing through and the charging current flowing through the boot capacitor C2. In addition, the second predetermined value and the third predetermined value may be detected by the shunt resistor 7 when the shunt resistor 7 is short-circuited during the discharge prevention control and when the motor 51 is erroneously driven. The minimum value of each predicted current value may be determined.

  In FIG. 7, the third predetermined value is expressed as being smaller than the second predetermined value. However, both the second predetermined value and the third predetermined value may be values smaller than the first predetermined value. The magnitudes of the second predetermined value and the third predetermined value are not limited to those shown in FIG. The second predetermined value may be the same value as the third predetermined value (for example, 10 mA for both), or the second predetermined value may be larger than the third predetermined value.

  The state determination of the motor 51 and the shunt resistor 7 described above is performed every predetermined time while the discharge prevention control is being performed. That is, the state determination unit 9 captures the detection result of the shunt resistor 7 every predetermined time, and determines the state of the motor 51 and the shunt resistor 7 using the detection result. As the predetermined time is shorter, the number of times that the state determination unit 9 determines the state of the motor 51 and the shunt resistor 7 increases. Therefore, the state determination unit 9 can perform the state determination of the motor 51 and the shunt resistor 7 in real time. .

(3) Operation Next, the operation of the motor drive device 1 will be described with reference to FIGS.

  Steps S1 and 2: When the motor drive device 1 obtains a start command for the motor 51 from a microcomputer (not shown) (Yes in S1), the charging control of the boot capacitors C1 to C3 of each phase is sequentially performed from the U-phase boot capacitor C1. Start (S2). That is, the inverter control circuit 4 starts charging the boot capacitor C1 by first turning on and off only the lower transistor Q1b a plurality of times.

  Step S3: When the charging of the boot capacitor C1 is completed, the inverter control circuit 4 then charges the V-phase boot capacitor C2, so that the lower switching element Q2b is turned on a plurality of times while the V-phase upper transistor Q2a remains off. Turn off. Further, the inverter control circuit 4 starts discharge prevention control for the already charged boot capacitor C1 (S3). That is, the inverter control circuit 4 keeps the U-phase upper transistor Q1a off and the lower transistor Q1b on. When charging of the boot capacitor C2 is completed, the inverter control circuit 4 then performs charge control for the W-phase boot capacitor C3 and performs discharge prevention control for the U-phase and V-phase charged boot capacitors C1 and C2. .

  Steps S4 to 5: While the discharge prevention control of Step S3 is being performed, the state determination unit 9 takes in the detection result of the shunt resistor 7 every predetermined time, and the detection result is a first predetermined value and a second predetermined value. The third predetermined value is compared (S4, S6, S8). When the detection result is equal to or greater than the first predetermined value (Yes in S4), the state determination unit 9 functioning as the first determination unit 91 determines that the motor 51 is grounded (S5).

  Steps S6-7: When the detection result of the shunt resistor 7 is equal to or less than the second predetermined value (Yes in S6), the state determination unit 9 functioning as the second determination unit 92 determines that the shunt resistor 7 is short-circuited. (S7).

  Steps S8 to 9: When the detection result of the shunt resistor 7 is equal to or smaller than the third predetermined value (Yes in S8), the state determination unit 9 functioning as the third determination unit 93 determines that the motor 51 is driven by mistake. Judgment is made (S9).

  In steps S4, S6, and S8, if the detection result of the shunt resistor 7 is not more than the first predetermined value and not less than the second predetermined value and the third predetermined value, the state determination unit 9 It is determined that the ground fault and malfunction of 51 and the short circuit of the shunt resistor 7 have not occurred, and the motor 51 and the shunt resistor 7 are in a normal state.

  Steps S10 to 12: Steps S4 to S9 are performed until charging of all the boot capacitors C1 to C3 is completed (No in S10). When charging of all the boot capacitors C1 to C3 is completed (Yes in S10), the inverter control circuit 4 performs the discharge prevention control for all the boot capacitors C1 to C3 for a predetermined period, and then all the lower transistors Q1a to Q3a. , Q1b to Q3b are turned off (S11), and then the motor 51 is started (S12).

  When the state determination unit 9 determines that the motor 51 is grounded (S5), when the state determination unit 9 determines that the shunt resistor 7 is short-circuited (S7), the motor 51 is erroneously driven. If it is determined (S9), the motor drive device 1 ends the series of operations without starting the motor 51.

(4) Effect (A)
The motor drive device 1 according to the present embodiment is in a state where there is a charged boot capacitor (first boot capacitor), while the uncharged boot capacitor (second boot capacitor) is being charged. Discharge prevention control is performed to keep current flowing through one boot capacitor. Accordingly, since it is possible to prevent the first boot capacitor from being gradually discharged and a voltage drop during charging of the second boot capacitor, the upper element control units 41a to 43a are configured so that the boot capacitor C1 is activated when the motor 51 is started. A sufficient electric charge stored in .about.C3 can be used as an operation power source. Therefore, the motor 51 can be driven without any problem.

(B)
In particular, in the present embodiment, the lower element control units 41b to 43b function as an energization control unit that performs the discharge prevention control and the charge control. Therefore, during the discharge prevention control, if the lower transistors Q1b to Q3b are turned on by the energization control unit, which is the lower element control units 41b to 43b, the current from the charging unit 6 is turned on by the lower transistors Q1b to Q3b that are turned on. A current path is formed to flow to the lower transistors Q1b to Q3b via the boot capacitors C1 to C3 connected to. As described above, the lower element control units 41b to 43b provided corresponding to the lower transistors Q1b to Q3b function as an energization control unit, so that the energization control is performed separately from the lower element control units 41b to 43b. There is no need to provide a part.

(C)
In the present embodiment, during the discharge prevention control, the lower transistors Q1b to Q3b connected to the upper transistors Q1a to Q3a corresponding to the first boot capacitor are kept on. Thereby, since the current from the charging unit 6 flows to the lower transistors Q1b to Q3b via the first boot capacitor, the first boot capacitor can be prevented from discharging.

(D)
Further, in the present embodiment, when charging control is performed, the lower transistors Q1b to Q3b corresponding to the boot capacitors C1 to C3 to be charged are turned on and off at a predetermined frequency a plurality of times, so that the charging unit 6 supplies the boot capacitors. A current is passed through C1 to C3. As a result, when the boot capacitors C1 to C3 are charged, the boot capacitors C1 to C3 are gradually charged. Therefore, since a sudden large current (that is, inrush current) does not flow through the boot capacitors C1 to C3, it is possible to prevent the inrush current from affecting other functional units.

(E)
Further, in the present embodiment, during the discharge prevention control, a current continues to flow through the charged first boot capacitor by continuing to turn on the lower transistors Q1b to Q3b of the phase corresponding to the first boot capacitor. This current flows to the shunt resistor 7 via the first boot capacitor and the lower transistors Q1b to Q3b.

(F)
If the motor 51 has a ground fault during the discharge prevention control, the current due to the motor 51 ground fault is turned on in addition to the discharge prevention current flowing through the first boot capacitor and the charging current flowing through the second boot capacitor. Current flows to the shunt resistor 7 via the lower transistors Q1b to Q3b. Therefore, the first determination unit 91 determines that the motor 51 is grounded when the detection result by the shunt resistor 7 is equal to or greater than the first predetermined value during the discharge prevention control. That is, according to the motor drive device 1 according to the present embodiment, the predetermined lower transistors Q1b to Q3b are continuously turned on by the discharge prevention control in addition to the predetermined lower transistors Q1b to Q3b being turned on and off by the charge control. The motor 51 ground fault can be determined. Therefore, before starting the motor, it is possible to perform control corresponding to the ground fault of the motor 51, such as not starting the motor 51.

(G)
If the shunt resistor 7 is short-circuited, during the discharge prevention control performed before the motor 51 is started, the sum of the discharge preventing current flowing through the first boot capacitor and the charging current flowing through the second boot capacitor by the shunt resistor 7. A value should be detected, but it cannot be detected. Therefore, the second determination unit 92 can determine that the shunt resistor 7 is short-circuited when the detection result by the shunt resistor 7 is equal to or less than the second predetermined value during the discharge prevention control. Thereby, it is possible to know the state abnormality of the shunt resistor 7 before the motor 51 is started.

(H)
The motor 51 according to the present embodiment is a fan motor. Since the motor 51 is not activated during the discharge prevention control, the shunt resistor 7 should detect the total value of the discharge prevention current flowing through the first boot capacitor and the charging current flowing through the second boot capacitor. However, when the motor 51 is driven by a normal wind or a reverse wind, the current flows back between the lower transistors Q1b to Q3b that are turned on and the motor 51, so the shunt resistor 7 detects the current. become unable. Therefore, the third determination unit 93 determines that the motor 51 that should not have been started is erroneously driven when the detection result by the shunt resistor 7 is equal to or smaller than the third predetermined value during the discharge prevention control. be able to. Thereby, malfunction of the motor 51 can be known.

(I)
In the present embodiment, since the motor 51 is a three-phase motor and the inverter unit 3 has three transistor pairs SW1 to SW3, three boot capacitors C1 to C3 are also provided. Also in this case, since the discharge of each of the three boot capacitors C1 to C3 can be prevented, the motor 51 can be driven without any problem.

<Other embodiments>
(A)
In the above embodiment, the case where the motor 51 is a three-phase motor has been described. However, the motor is not limited to three phases, and may have any number of phases as long as it has a plurality of phases. Further, the drive coils 52u to 52w of the motor 51 may be delta-connected instead of star-connected.

(B)
In the above embodiment, the case where there is one charging unit 6 has been described. However, similarly to the boot capacitors C1 to C3, the resistors R1 to R3, and the diodes D1 to D3, a plurality of charging units may be provided corresponding to each phase.

(C)
In the above embodiment, the case where the lower element control units 41b to 43b are used as the energization control unit has been described. However, a separate control circuit may be provided as the energization control unit separately from the lower element control units 41b to 43b.

(D)
In the above embodiment, it has been described that the second determination unit 92 determines whether or not the shunt resistor 7 is short-circuited during the discharge prevention control. However, the second determination unit 92 determines whether or not the shunt resistor 7 is short-circuited not only during the discharge prevention control but also when only the charging control is performed or when the motor 51 is driven. May be.

(E)
In the above embodiment, as illustrated in FIG. 3, the case where the charging control is performed so that any one of the boot capacitors C1 to C3 performs the charging operation has been described. However, the charge control may not be performed for all the boot capacitors C1 to C3 all at once, and may be performed simultaneously for two boot capacitors such as the boot capacitors C1 and C2. However, in this case, when the boot capacitor C3 is charged, discharge prevention control is performed on the boot capacitors C1 and C2.

(F)
In the above-described embodiment, as shown in FIG. 3, a case has been described in which a pause period is provided from the completion of charging of all the boot capacitors C <b> 1 to C <b> 3 until the motor 51 is started. However, the rest period may not be provided.

(G)
In the above embodiment, in “(3) operation”, any one of the ground fault (S5) of the motor 51, the short circuit of the shunt resistor 7 (S7), and the malfunction of the motor 51 (S9) occurs. It has been described that the motor 51 is not started when it is determined. However, even if it is a case where it is judged as mentioned above, the motor drive device 1 may start the motor 51 according to the degree of each state of the motor 51 and the shunt resistor 7, and corresponds to each state. The motor 51 may be started after the control to be performed is performed separately.

(H)
In the above embodiment, the case where the current detection unit is configured by the shunt resistor 7 has been described. However, as long as the current flowing on the GND wiring L2 can be detected, the current detection unit may be configured by other than a shunt resistor.

  The motor drive device according to the present invention can prevent the first boot capacitor from being gradually discharged and a voltage drop during charging of the second boot capacitor, and thus has an effect that the motor can be driven without any problem. The motor drive device according to the present invention can be applied as a motor drive device used as a rotational drive source such as a fan in an air conditioner.

DESCRIPTION OF SYMBOLS 1 Motor drive device 2 Power supply part 3 Inverter part Q1a-Q3a Upper side transistor Q1b-Q3b Lower side transistor 4 Inverter control circuit 41a-43a Upper side element control part 41b-43b Lower side element control part C1-C3 Boot capacitor 6 Charging part 7 Shunt Resistance 9 State determination unit 91 First determination unit 92 Second determination unit 93 Third determination unit 100 Motor drive system 51 Motors 52u to 52w Drive coil

JP 2003-61363 A

Claims (9)

A motor driving device for driving a motor (51) of a plurality of phases,
A plurality of switching element pairs (SW1 to SW3) each composed of an upper switching element (Q1a to Q3a) and a lower switching element (Q1b to Q3b) connected in series with each other of the motor, and the motor An inverter unit (3) connected to
A plurality of upper element control units (41a to 43a) that are provided corresponding to the upper switching elements (Q1a to Q3a) and control the operation of the upper switching elements;
A plurality of boot capacitors (C1 to C3) capable of supplying operating power to each of the upper element control units (41a to 43a);
A charging unit (6) capable of charging each of the boot capacitors (C1 to C3);
Charge control for charging each of the boot capacitors (C1 to C3) by flowing current from the charging unit (6) to each of the boot capacitors (C1 to C3) in order, and a plurality of the boot capacitors (C1 to C3) An energization control unit (41b to 41b) that performs discharge prevention control that keeps current flowing through the first boot capacitor while at least one of the remaining second boot capacitors other than the first boot capacitor that has been charged is charging. 43b)
A motor drive device (1) comprising: Each of the boot capacitors (C1 to C3) has one end connected to the charging unit (6) and the other end corresponding to the upper switching element (Q1a to Q3a) and the lower switching element (Q1b to Q3b). Connected between and
The energization control units (41b to 43b) are provided corresponding to the lower switching elements (Q1b to Q3b), and control a plurality of lower elements that control the operations of the lower switching elements (Q1b to Q3b). Consists of a control unit,
The motor drive device (1) according to claim 1. In the discharge prevention control, the energization control units (41b to 43b) connect the lower switching elements (Q1b to Q3b) connected to the upper switching elements (Q1a to Q3a) corresponding to the first boot capacitor. By continuing to turn on, the current continues to flow from the charging unit (6) to the first boot capacitor.
The motor drive device (1) according to claim 2. In the charging control, the energization control units (41b to 43b) turn on and off each of the lower switching elements (Q1b to Q3b) at a predetermined frequency a plurality of times from the charging unit (6). Current is passed through the boot capacitors (C1 to C3).
The motor drive device (1) according to claim 2 or 3. The motor (51) has a plurality of drive coils (52u to 52w) having one end connected between each of the upper switching elements (Q1a to Q3a) and the lower switching elements (Q1b to Q3b),
A current detector (7) connected to the downstream side of each of the lower switching elements (Q1b to Q3b) and capable of detecting a current flowing through the motor (51);
The motor drive device (1) according to any one of claims 2 to 4, further comprising: The energization control unit (41b to 43b) performs the discharge prevention control before starting the motor,
A first determination unit (91) that determines that the motor (51) is grounded when the detection result by the current detection unit (7) is equal to or greater than a first predetermined value during the discharge prevention control;
The motor drive device (1) according to claim 5, further comprising: A second determination unit (92) for determining that the current detection unit (7) is short-circuited when the detection result by the current detection unit (7) is less than or equal to a second predetermined value during the discharge prevention control;
The motor drive device (1) according to claim 5 or 6, further comprising: The energization control unit (41b to 43b) performs the discharge prevention control before starting the motor,
A third determination unit (93) for determining that the motor (51) is driven when the detection result by the current detection unit (7) is equal to or less than a third predetermined value during the discharge prevention control;
The motor drive device (1) according to any one of claims 5 to 7, further comprising: The motor (51) is a three-phase motor,
The inverter unit (3) includes three switching element pairs (SW1 to SW3).
The motor drive device (1) according to any one of claims 1 to 8.

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