Motor driving apparatus having discharging function

A motor driving apparatus includes an AC-DC conversion unit that converts AC power into DC power, a power storage unit provided in a DC link between the AC-DC conversion unit and a DC-AC conversion unit, an initial charging unit that is provided in the DC link, includes a switch unit and a charging resistor connected to the switch unit in parallel, and initially charges the power storage unit, an electromagnetic contactor that opens and closes an electrical path between the AC power source and the AC-DC conversion unit, and a control unit, and after completion of driving of a motor, the control unit performs an opening operation on the electromagnetic contactor and the switch unit and performs a turn-on operation on each of the switching devices provided on the upper and lower arms in the same phase to discharge charge stored in the power storage unit by the charging resistor.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a motor driving apparatus for controlling a motor that converts alternating-current (AC) power of an AC power source side into direct-current (DC) power and then further converts the DC power into the AC power to use the AC power as driving power, in particular, to a motor driving apparatus including an initial charging unit that initially charges a power storage unit provided in a DC link.

2. Description of the Related Art

Motor driving apparatuses that drive and control servomotors in machine tools, industrial machines, forging machines, injection molding machines, or various robots after converting AC power on AC power source sides into DC power, further convert DC power into AC power, and use t AC power as driving power of the motors. The motor driving apparatus includes: an AC-DC conversion unit (also referred to as a “forward converter” or a “converter”) that converts AC power supplied from an AC power source side of a commercial three-phase AC power source into DC power and output the DC power; and a DC-AC conversion unit (also referred to as a “reverse converter” or an “inverter”) that is connected to a DC link at a DC output side of the AC-DC conversion unit and converts the DC power in the DC link into the AC power for driving a motor and outputs the AC power, and controls a speed, torque, or a position of a rotor of the motor connected to an AC output side of the DC-AC conversion unit.

The DC link connecting the DC output side of the AC-DC conversion unit and a DC input side of the DC-AC conversion unit is provided with a power storage unit that can store the DC power. A DC capacitor is an example of the power storage unit.

The power storage unit needs to be initially charged in a period from immediately after start-up of the motor driving apparatus to before start of driving of the motor (i.e., before the DC-AC conversion unit starts a power conversion operation for supplying the AC power to the motor). Charge is stored in the power storage unit after completion of driving of the motor, and the charge stored in the power storage unit may be discharged to prevent an electric shock. For example, there are a method for reducing the charge in the power storage unit using self-discharge of the power storage unit and a method for consuming the charge by a resistor separately prepared.

FIG. 7illustrates a configuration of a general motor driving apparatus including an initial charging unit. A motor driving apparatus100includes an AC-DC conversion unit111that converts AC power supplied from a commercial three-phases (an R-phase, an S-phase, and a T-phase) AC power source3into DC power and outputs the DC power and a DC-AC conversion unit117that is connected to a DC link at a DC output side of the AC-DC conversion unit111and converts the DC power in the DC link into the AC power for driving a motor and outputs the AC power, and controls a speed, torque, or a position a rotor of a motor2connected to an AC output side of the DC-AC conversion unit117.

The AC-DC conversion unit111is configured as a full-bridge circuit in which a switching device and a feedback diode connected in reverse parallel to the switching device are provided in an upper arm and a lower arm in each phase. The switching devices provided in the upper arm and the lower arm are on-off controlled or all of the switching devices are turned off in response to a switching command received from a control unit115, so that the AC power supplied from the AC power source3side is rectified by the diodes and converted and output as the DC power. An AC reactor118is connected to an AC input side of the AC-DC conversion unit111.

An electromagnetic contactor114is provided on the AC input side of the AC-DC conversion unit111so as to open and close an electrical path between the AC power source3and the AC-DC conversion unit111. In the electromagnetic contactor114, contacts124are normally in a disconnected state by spring force, however, when power is supplied to a control coil123, attraction force greater than the spring force is generated by an electromagnet, the contacts124connect the circuit, and the power is supplied from the AC power source3to the AC-DC conversion unit111. When the power to the control coil123is turned off, the circuit is disconnected by the spring force, and the power supply from the AC power source3to the AC-DC conversion unit111is cut off. An opening/closing operation of an electrical path of the electromagnetic contactor114is controlled by an electromagnetic contactor opening/closing command output from the control unit115.

The DC link for connecting the DC output side of the AC-DC conversion unit111and a DC input side of the DC-AC conversion unit117is provided with a power storage unit112that can store the DC power. In the illustrated example, the power storage unit112is a DC capacitor. The power storage unit112is initially charged in a period from immediately after start-up of the motor driving apparatus100(i.e., immediately after the electromagnetic contactor114is closed (turned on)) to before start of driving of the motor2(i.e., before start of a power conversion operation by the DC-AC conversion unit117). Immediately after the start of the initial charging of the power storage unit112from a state in which no charge is stored therein, a large inrush current flows through the AC-DC conversion unit111. In particular, as the power storage unit112has a larger capacitance, a larger inrush current is generated. As a countermeasure against the inrush current, the motor driving apparatus100is provided with an initial charging unit113between the AC-DC conversion unit111and the power storage unit112. The initial charging unit113includes a switch unit121for shorting a charging resistor and a charging resistor122connected to the switch unit121in parallel. The switch unit121is opened (turned off) only during a period of the initial charging of the power storage unit112executed immediately after the start-up of the motor driving apparatus100and maintains a closed (turned on) state during a normal operation period in which the motor driving apparatus100drives the motor2. During the initial charging period of the power storage unit112, the switch unit121is opened (turned off), and the DC power output from the AC-DC conversion unit111flows through the charging resistor122and is consumed by the charging resistor122as heat, so that generation of an excessive inrush current is suppressed during the initial charging period. An opening/closing operation of an electrical path of the switch unit121in the initial charging unit113is controlled by a shorting command output from the control unit115.

In order to discharge the charge in the power storage unit112after completion of driving of the motor, for example, a discharging unit116is provided. The discharging unit116includes a switch unit125for a discharging resistor and a discharging resistor126connected to the switch unit125in series. After completion of driving of the motor, the electromagnetic contactor114is opened (turned off), and the switch unit125is closed (turned on), so that the charge stored in the power storage unit112is consumed by the discharging resistor126. An opening/closing operation of an electrical path of the switch unit125in the discharging unit116is controlled by a discharging command output from the control unit115.

Other than a method of discharging using the discharging resistor as described above, there is a method of discharging using a resistance component included in a motor as described in Japanese Patent No. 5444304 and Japanese Unexamined Patent Publication (Kokai) No. 2004-357412.FIG. 8illustrates discharging of a power storage unit in a motor driving apparatus described in Japanese Patent No. 5444304. Operations and configurations of an AC-DC conversion unit111, a power storage unit112, an initial charging unit113, an electromagnetic contactor114, a DC-AC conversion unit117, and an AC reactor118in a motor driving apparatus200are as described above with reference toFIG. 7. In the motor driving apparatus200described in Japanese Patent No. 5444304, the electromagnetic contactor114is closed (turned on) by an electromagnetic contactor opening/closing command generated by the control unit115, and the switch unit121for shorting the charging resistor is closed (turned on) by a shorting command generated by the control unit115so as to discharge the charge in the power storage unit112stored at the time of deceleration control of the motor. The DC power stored in the power storage unit112is converted into a reactive current by the DC-AC conversion unit117based on a reactive current command from the control unit115and supplied to the motor2. Accordingly, the motor2consumes the DC power stored in the power storage unit112in a form of the reactive current.

Other than the above-described method, there is a method of discharging using a resistance component included in an element other than a resistor in a circuit.

For example, as described in Japanese Patent No. 5721787, there is a method for discharging a capacitor by appropriately controlling a switching operation of a switching device in a boost converter provided at a preceding stage of an inverter.

As described above, the charge is stored in the power storage unit after completion of driving of the motor, and thus the charge stored in the power storage unit may be discharged to prevent an electric shock.

However, the method using self-discharge of the power storage unit has a problem that it takes time to reduce the charge in the power storage unit.

The method for separately providing the discharging unit for discharging the power storage unit has a problem that the apparatus is enlarged and costs increase because the switch unit and the discharging resistor are needed.

The methods described in Japanese Patent No. 5444304 and Japanese Unexamined Patent Publication (Kokai) No. 2004-357412 have a problem that the motor and the DC-AC conversion unit may have cooling capacities sufficient for dealing with discharging of the charge stored in the power storage unit that enlarge the apparatus and increase costs.

The method described in Japanese Patent No. 5721787 also has a problem that the charge stored in the power storage unit is to be consumed by an element other than the discharging resistor, so that a thermal capacity and a cooling capacity of the element other than the discharging resistor are to be improved that enlarge the apparatus and increase costs.

SUMMARY OF INVENTION

In view of the problems as described above, it is an object of the invention to provide a space saving and low cost motor driving apparatus converting AC power supplied from an AC power source side to DC power by an AC-DC conversion unit, outputting the DC power to a DC link provided with a power storage unit, and further converting the DC power into the AC power for driving a motor and supplying the AC power to the motor, that can discharge charge stored in the power storage unit in a short time.

In order to achieve the above-described object, a motor driving apparatus includes an AC-DC conversion unit configured to convert AC power supplied from an AC power source side into DC power by the motor driving apparatus performing on-off control on switching devices respectively provided on an upper arm and a lower arm or turning off all of the switching devices and rectifying the AC power by diodes, a power storage unit provided in a DC link between a DC output side of the AC-DC conversion unit and a DC input side of a DC-AC conversion unit configured to convert DC power on the DC output side of the AC-DC conversion unit into AC power for driving a motor, an initial charging unit provided in the DC link and including a switch unit configured to open and close an electrical path between the AC-DC conversion unit and the power storage unit and a charging resistor connected to the switch unit in parallel, wherein the initial charging unit is configured to initially charge the power storage unit by a direct current from the AC-DC conversion unit flowing through the charging resistor when the switch unit is opened before start of driving of the motor, an electromagnetic contactor configured to open and close an electrical path between the AC power source and the AC-DC conversion unit, and a control unit configured to control each of the switching devices, the switch unit, and the electromagnetic contactor, wherein, after completion of driving of the motor, the control unit performs an opening operation on the electromagnetic contactor and the switch unit and performs a turn-on operation on each of the switching devices provided on the upper arm and the lower arm in the same phase, and thus forms a closed circuit constituted of the power storage unit and the charging resistor to discharge charge stored in the power storage unit by the charging resistor.

Before start of driving of the motor, the control unit may perform a closing operation on the electromagnetic contactor and perform an opening operation on the switch unit to open the switch unit, and initially charge the power storage unit by a direct current from the AC-DC conversion unit flowing through the charging resistor, and after a voltage of the power storage unit reaches a specified voltage by initial charging, the control unit may perform a closing operation on the switch unit to complete initial charging of the power storage unit.

The motor driving apparatus may further include a temperature detection unit configured to detect a temperature of the charging resistor, wherein after completion of driving of the motor, when a temperature detected by the temperature detection unit becomes a specified temperature or higher, the control unit may perform a turn-off operation on each of the switching devices provided on the upper arm or the lower arm in the same phase to pause discharging by the charging resistor.

The motor driving apparatus may further include a temperature detection unit configured to detect a temperature of the charging resistor, wherein, after completion of driving of the motor, when a temperature detected by the temperature detection unit is lower than a specified temperature, the control unit may perform an opening operation on the electromagnetic contactor and the switch unit, perform a turn-on operation on each of the switching devices provided on the upper arm and the lower arm in the same phase, and thus form a closed circuit constituted of the power storage unit and the charging resistor to discharge charge stored in the power storage unit by the charging resistor, and when a temperature detected by the temperature detection unit is the specified temperature or higher, the control unit may perform a turn-off operation on each of the switching devices provided on the upper arm or the lower arm in the same phase to stop discharging by the charging resistor.

DETAILED DESCRIPTION

A motor driving apparatus having a discharging function will be described below with reference to the drawings. It should be understood that the invention is not limited to the drawings or embodiments described below.

FIG. 1is a circuit diagram illustrating a motor driving apparatus in a first embodiment. Hereinbelow, components denoted by the same reference numerals in the different drawings have the same function. A type of a motor2driven by a motor driving apparatus1does not limit the present invention and may be, for example, an induction motor or a synchronous motor. Further, the number of phases does not limit the present invention and may be, for example, a single phase or multiple phases other than three phases.

The motor driving apparatus1in the first embodiment includes an AC-DC conversion unit11, a power storage unit12, an initial charging unit13, an electromagnetic contactor14, and a control unit15. An AC power source3is connected to an AC input side of the motor driving apparatus1, and a three-phase motor2is connected to an AC motor side of the motor driving apparatus1. The motor driving apparatus1that drives and controls a piece of the motor2is described here, however, the number of the motors2driven and controlled by the motor driving apparatus1does not limit the present invention, and a plurality of the motors2may be provided. The motor driving apparatus1includes a DC-AC conversion unit17that supplies AC power for driving the motor2, and when there is a plurality of the motors2, a plurality of the DC-AC conversion units17is also provided.

The AC-DC conversion unit (also referred to as “the forward converter” or “the converter”)11is configured as a full-bridge circuit in which a switching device and a feedback diode connected in reverse parallel to the switching device are provided in an upper arm and a lower arm in each phase. In the illustrated example, the AC-DC conversion unit11is configured as a three-phase full-bridge circuit that converts three-phase AC power into DC power. The AC-DC conversion unit11performs on-off control on the switching devices or turns off all of the switching devices provided in the upper arm and the lower arm in response to a switching command received from the control unit15, rectifies the AC power by the diodes, and thus converts the AC power supplied from the AC power source3side and outputs the DC power. Examples of the switching devices include IGBT, FET, GTO (a thyristor, a gate turn-off thyristor), transistors, and the like. However, a type itself of the switching device does not limit the present invention, and other switching devices may be used.

An AC reactor18is connected to an AC input side of the AC-DC conversion unit11.

The DC-AC conversion unit (also referred to as “the reverse converter” or “the inverter”)17is connected to the AC-DC conversion unit11via the DC link. The DC-AC conversion unit17converts the DC power in the DC link into the AC power for driving the motor and output the AC power. The DC-AC conversion unit17is configured as a three-phase full-bridge circuit including a switching device and a feedback diode connected in reverse parallel to the switching device, such as a pulse-width modulation (PWM) inverter. As examples of semiconductor switching devices, there are an IGBT, an FET, a thyristor, a GTO, a transistor, and the like, however, a type itself of the switching device does not limit the present invention, and other semiconductor switching devices may be used. The DC-AC conversion unit17performs a switching operation on the internal switching device based on a switching command received from a high-order controller (not illustrated) and converts the DC power supplied from the DC link side into the three-phase AC power having a desired voltage and a desired frequency for driving the motor2. The motor2is operated based on the supplied three-phase AC power of which voltage and frequency are variable. The control unit15described below may generate the switching command for controlling the switching operation of the DC-AC conversion unit17.

The power storage unit12is provided in the DC link between a DC output side of the AC-DC conversion unit11and a DC input side of the DC-AC conversion unit17and can store the DC power. A DC capacitor is an example of the power storage unit12. In the present embodiment, the power storage unit12is a separate entity from the AC-DC conversion unit11and the DC-AC conversion unit17, however, generally, a smoothing capacitor (not illustrated) having a function of suppressing a ripple of the DC output is built in the DC output side of the AC-DC conversion unit11, and a smoothing capacitor (not illustrated) having a function of suppressing a ripple of the DC input is built in the DC input side of the DC-AC conversion unit17, so that the smoothing capacitors built in the AC-DC conversion unit11and the DC-AC conversion unit17may be used as the power storage unit12as a modification of the present embodiment.FIG. 1illustrates an example provided with one piece of the DC-AC conversion unit17, however, for example, when a plurality of the DC-AC conversion units17is connected in parallel, the individual power storage unit12may be provided on the DC input side of each of the DC-AC conversion units17, and in this case, the power storage units12are in a parallelly connected relationship with each other. The power storage unit12is initially charged by the DC power output from the AC-DC conversion unit11by the initial charging unit13described next in a period from immediately after start-up of the motor driving apparatus1(i.e., immediately after the electromagnetic contactor14is closed (turned on)) to before start of driving of the motor2(i.e., before start of a power conversion operation by the DC-AC conversion unit17). A voltage of the power storage unit12is detected by a voltage detection unit19.

The initial charging unit13is provided in the DC link and includes a switch unit21for opening and closing an electrical path between the AC-DC conversion unit11and the power storage unit12and a charging resistor22connected to the switch unit21in parallel. The charging resistor22may be a fixed resistor or a variable resistor as long as the charging resistor22is a high breakdown voltage resistor. Alternatively, the charging resistor22may be an element (i.e., a coil) including a resistance component other than these resistors. Although the details are described below, in the present invention, discharging is performed using the charging resistor22. In order to realize discharging using the charging resistor22, the switch unit21for shorting the charging resistor may be realized by a mechanical component, such as a mechanical relay and a mechanical switch, that does not allow a current to flow when opened (turned off) or an electronic component, such as a triac (registered trademark) (a bidirectional thyristor) that does not easily allow a current to flow when opened (turned off) and a switching device (i.e., a gallium nitride (GaN) FET) that does not include a parasitic diode.

The switch unit21for shorting the charging resistor is opened (turned off) only during a period of the initial charging of the power storage unit12executed immediately after the start-up of the motor driving apparatus1and maintains a closed (turned on) state during a normal operation period in which the motor driving apparatus1drives the motor2. More specifically, the switch unit21is opened (turned off) during the initial charging period from immediately after the start-up of the motor driving apparatus1(i.e., immediately after the electromagnetic contactor14is closed (turned on)) to before the start of driving of the motor2(i.e., before the start of a power conversion operation by the DC-AC conversion unit17), so that a DC current output from the AC-DC conversion unit11flows into the power storage unit12through the charging resistor22, and the power storage unit12is charged. When the power storage unit12is charged to a specified voltage, the switch unit21is closed (turned on) to short-circuit both ends of the charging resistor22, and the initial charging operation is completed. Subsequently, the DC-AC conversion unit17starts the power conversion operation and supplies driving power to the motor2, and the motor2is driven based on the driving power. As described above, during the initial charging period of the power storage unit12, the switch unit21is opened (turned off), and the DC power output from the AC-DC conversion unit11flows through the charging resistor22and is consumed by the charging resistor22as heat, so that generation of an excessive inrush current is suppressed during the initial charging period. An opening/closing operation of an electrical path of the switch unit21in the initial charging unit13is controlled by a shorting command output from the control unit15. A shorting command may be generated by a higher-order controller (not illustrated) than the control unit15.

The electromagnetic contactor14is provided on the AC input side of the AC-DC conversion unit11so as to open and close an electrical path between the AC power source3and the AC-DC conversion unit11. In the present embodiment, the electromagnetic contactor14is provided further nearer to the AC power source3side than the AC reactor18provided on the AC input side of the AC-DC conversion unit11. In the electromagnetic contactor14, contacts24are normally in a disconnected state by spring force. However, when power is supplied to a control coil23, attraction force greater than the spring force is generated by an electromagnet, the contacts24connect the circuit, and the power is supplied from the AC power source3to the AC-DC conversion unit11. When the power to the control coil23is turned off, the circuit is disconnected by the spring force, and the power supply from the AC power source3to the AC-DC conversion unit11is cut off. An opening/closing operation of an electrical path of the electromagnetic contactor14is controlled by an electromagnetic contactor opening/closing command output from the control unit15. The opening/closing command to the electromagnetic contactor14may be generated by the higher-order controller (not illustrated) than the control unit15.

The control unit15generates the switching command for controlling the switching operation of each switching device in the AC-DC conversion unit11, the shorting command for controlling the opening/closing operation of the electrical path of the switch unit21for shorting the charging resistor in the initial charging unit13, and the electromagnetic contactor opening/closing command for controlling the opening/closing operation of the electrical path of the electromagnetic contactor14. Operations of the control unit15are described in details with reference to flowcharts inFIG. 2andFIG. 3.

FIG. 2is a flowchart illustrating an operation flow regarding the initial charging of the motor driving apparatus in the first embodiment.

Before the start of driving of the motor, the electromagnetic contactor14and the switch unit21are both opened (turned off) (step S101).

In step S102, the control unit15determines whether to start initial charging of the power storage unit12. The determination is made based on, for example, whether an initial charging start command is received from the high-order controller (not illustrated) of the control unit15. The initial charging start command is transmitted to the control unit15by, for example, an operator performing a start operation (i.e., pressing of a start-up button) on the motor driving apparatus1. In step S102, when determining to start the initial charging of the power storage unit12, the control unit15outputs a closing command to the electromagnetic contactor14.

In step S103, the electromagnetic contactor14performs a closing (turn-on) operation in response to the received closing command. Accordingly, the AC power flows from the AC power source3to the AC-DC conversion unit11. Although it is not illustrated here, the AC-DC conversion unit11performs the on-off control on the switching devices or turns off all of the switching devices by receiving the switching command from the control unit15, rectifies the AC power by the diodes, and converts the AC power supplied from the AC power source3side and outputs the DC power. Accordingly, the DC current output from the AC-DC conversion unit11flows into the power storage unit12through the charging resistor22, and the power storage unit12is charged. The voltage of the power storage unit12is gradually increased by the charging.

In step S104, the control unit15determines whether the voltage of the power storage unit12reaches a specified voltage. A voltage value of the power storage unit12is detected by the voltage detection unit19and transmitted to the control unit15. When it is determined that the voltage of the power storage unit12reaches the specified voltage, the processing proceeds to step S105.

In step S105, the control unit15outputs the closing command to the initial charging unit13, and the switch unit21in the initial charging unit13is closed (turned on). Accordingly, the initial charging of the power storage unit12is completed. After completion of the initial charging, the motor driving apparatus1starts to drive the motor2.

FIG. 3is a flowchart illustrating an operation flow regarding discharging of the power storage unit of the motor driving apparatus in the first embodiment.

During a motor driving period by the motor driving apparatus1, the electromagnetic contactor14and the switch unit21are both closed (turned on) (step S201).

In step S202, the control unit15determines whether to start discharging of the power storage unit12. The determination is made based on, for example, whether a discharging start command is received from the high-order controller (not illustrated) of the control unit15. The discharging start command is transmitted to the control unit15by, for example, the operator performing a pause operation (i.e., pressing of a pause button) on the motor driving apparatus1. In step S202, when determining to start the discharging of the power storage unit12, the control unit15outputs an opening command to the electromagnetic contactor14.

In step S203, the electromagnetic contactor14performs an opening (turn-off) operation in response to the received opening command. Accordingly, the AC power supply from the AC power source3to the AC-DC conversion unit11is cut off.

In step S204, the control unit15outputs the opening command to the initial charging unit13. Accordingly, the switch unit21in the initial charging unit13is opened (turned off).

Next, in step S205, the control unit15outputs, to the AC-DC conversion unit11, the switching command for causing the switching devices respectively provided on the upper arm and the lower arm in the same phase to perform the turn-on operation. Accordingly, the switching devices respectively provided on the upper arm and the lower arm in the same phase are electrically connected in the AC-DC conversion unit11, and a point A and a point B in the drawing are brought into a short-circuited state. The phase (the R-phase, the S-phase, and the T-phase) of the upper and lower arms of the switching devices to be electrically connected may be only one phase, two phases, or all of the three phases. When the switching devices respectively provided on the upper arm and the lower arm are electrically connected, the point A and the point B are brought into the short-circuited state, and the electrical path of the switch unit21in the initial charging unit13is opened (turned off), so that a closed circuit constituted of the power storage unit12and the charging resistor22is formed, and the charge stored in the power storage unit12flows into the charging resistor22through the electrically connected respective switching devices in the same phase. Accordingly, the energy stored in the power storage unit12is discharged by the charging resistor22, and the voltage of the power storage unit12is gradually decreased.

In step S206, the control unit15determines whether the discharging of the power storage unit12is completed. The determination is made based on, for example, whether the voltage of the power storage unit12detected by the voltage detection unit19becomes a predetermined voltage or less (i.e., a value close to zero volt). In step S206, when it is determined that the discharging of the power storage unit12is completed, the processing proceeds to step S207.

In step S207, the control unit15outputs the switching command for turning off all of the switching devices to the AC-DC conversion unit11. Accordingly, the power conversion operation by the AC-DC conversion unit11is paused, and the operation of the motor driving apparatus1is completely paused. Through each processing in the above-described step S201to step S207, the power storage unit12is discharged, and thus, for example, when an operator touches the power storage unit12for maintenance, he/she will not get an electric shock.

As described above, in the present invention, the switch unit21for shorting the charging resistor is opened (turned off) to flow the charge stored in the power storage unit12to the charging resistor22, so that it is preferable that the switch unit21for shorting the charging resistor is realized by a mechanical component, such as a mechanical relay and a mechanical switch, that does not allow a current to flow when opened (turned off) or an electronic component, such as a triac (registered trademark) (a bidirectional thyristor) that does not easily allow a current to flow when opened (turned off) and a switching device (i.e., a GaN FET) that does not include a parasitic diode.

Energy WCstored in the power storage unit12is expressed by Equation 1 when capacitance of the power storage unit12is C, and a voltage of the power storage unit12(i.e., a potential difference between the point A and the point B) is V.

Energy WRconsumed in the charging resistor22when the power storage unit12is charged from zero volt to V volt is expressed by Equation 2 when a resistance value of the charging resistor22is R, and a current flowing through the power storage unit12is i.

Equation 3 is established from Equation 1 and Equation 2.
WC=WR(3)

Equation 3 represents that it is not particularly necessary to increase a cooling performance when the charging resistor22is used in the discharging of the power storage unit12. In other words, according to the present invention, a discharging function can be imparted to the power storage unit12with the present configuration of the initial charging unit13without additional costs and an additional mounting area.

Subsequently, second and third embodiments are described which include a temperature detection unit for detecting a temperature of the charging resistor22.

FIG. 4is a circuit diagram illustrating a motor driving apparatus in the second and third embodiments. The second and third embodiments have a configuration in which a temperature detection unit16for detecting a temperature of the charging resistor22is added to the motor driving apparatus1in the first embodiment described with references toFIG. 1toFIG. 3. The temperature detection unit16may be realized by a method for directly measuring a temperature of the charging resistor22using a temperature detecting element or a method for calculating a temperature based on information pieces such as the capacitance of the power storage unit12, the voltage of the power storage unit12detected by the voltage detection unit19, and a time. Circuit components other than the temperature detection unit16are similar to circuit components illustrated inFIG. 1, so that the same circuit components are denoted by the same reference numerals and detail descriptions of the circuit components are omitted.

First, operations of the motor driving apparatus in the second embodiment are described with references toFIG. 4andFIG. 5.FIG. 5is a flowchart illustrating an operation flow regarding discharging of the power storage unit of the motor driving apparatus in the second embodiment. In the second embodiment, when a temperature detected by the temperature detection unit16becomes a specified temperature or more during a discharging operation period after completion of driving of the motor, the control unit15performs a turn-off operation on the switching devices respectively provided on the upper arm and the lower arm in the same phase and pauses the discharging by the charging resistor22to realize protection of the charging resistor22from overheat. Needless to say, the switching device to be turned off to prevent the overheat of the charging resistor22may be either one of the upper arm or the lower arm.

In the second embodiment, the initial charging operation of the power storage unit12by the initial charging unit13is similar to that in the first embodiment described with reference toFIG. 2, so that the description thereof is omitted, and the discharging operation of the power storage unit12is described here.

InFIG. 5, each processing in step S201to step S205is similar to that in the first embodiment described with reference toFIG. 3.

In step S208inFIG. 5, the control unit15determines whether the temperature detected by the temperature detection unit16becomes the specified temperature or higher. The specified temperature may be set to, for example, a temperature at which the charging resistor22is not fused when the charging resistor22is overheated by an excessive current flowing through the charging resistor22.

When it is determined in step S208that the temperature detected by the temperature detection unit16becomes the specified temperature or higher, the processing proceeds to step S207, and the control unit15outputs the switching command for turning off all of the switching devices to the AC-DC conversion unit11. Accordingly, the power conversion operation by the AC-DC conversion unit11is paused, and the operation of the motor driving apparatus1is completely paused. Accordingly, overheat of the charging resistor22can be prevent from occurring.

When it is determined in step S208that the temperature detected by the temperature detection unit16is lower than the specified temperature, the processing proceeds to step S206. In step S206, the control unit15determines whether the discharging of the power storage unit12is completed. The determination is made based on, for example, whether the voltage of the power storage unit12detected by the voltage detection unit19becomes the predetermined voltage or less (i.e., a value close to zero volt). When it is not determined in step S206that the discharging of the power storage unit12is completed, the processing returns to step S205, and the discharging of the power storage unit12is continued. When it is determined in step S206that the discharging of the power storage unit12is completed, the processing proceeds to step S207.

In step S207, the control unit15outputs the switching command for turning off all of the switching devices to the AC-DC conversion unit11. Accordingly, the power conversion operation by the AC-DC conversion unit11is paused, and the operation of the motor driving apparatus1is completely paused. Through each processing in the above-described step S201to step S207, the power storage unit12is discharged, and thus, for example, when an operator touches the power storage unit12for maintenance, he/she will not get an electric shock.

Subsequently, operations of the motor driving apparatus in the third embodiment are described with references toFIG. 4andFIG. 6.FIG. 6is a flowchart illustrating an operation flow regarding discharging of the power storage unit of the motor driving apparatus in the third embodiment. In the third embodiment, the control unit15continues or stops the discharging of the power storage unit12depending on whether the temperature detected by the temperature detection unit16is the specified temperature or more and thus realizes secure discharging of the power storage unit12and overheat protection for the charging resistor22during the discharging operation period after completion of driving of the motor.

In the third embodiment, the initial charging operation of the power storage unit12by the initial charging unit13is similar to that in the first embodiment described with reference toFIG. 2, so that the description thereof is omitted, and the discharging operation of the power storage unit12is described here.

InFIG. 6, each processing in step S201to step S205is similar to that in the first embodiment described with reference toFIG. 3.

In step S208inFIG. 6, the control unit15determines whether the temperature detected by the temperature detection unit16becomes the specified temperature or higher. The specified temperature may be set to, for example, a temperature at which the charging resistor22is not fused when the charging resistor22is overheated by an excessive current flowing through the charging resistor22.

When it is determined in step S208that the temperature detected by the temperature detection unit16becomes the specified temperature or higher, the processing proceeds to step S209, and the control unit15outputs the switching command for turning off all of the switching devices to the AC-DC conversion unit11. Accordingly, the power conversion operation by the AC-DC conversion unit11is once stopped. Accordingly, overheat of the charging resistor22can be prevent from occurring. After the processing in step S209, the processing returns to step S208. Needless to say, the switching device to be turned off to prevent the overheat of the charging resistor22may be either one of the upper arm or the lower arm.

When it is determined in step S208that the temperature detected by the temperature detection unit16is lower than the specified temperature, the processing proceeds to step S206.

When it is determined in step S208that the temperature detected by the temperature detection unit16is lower than the specified temperature, the processing proceeds to step S206. In step S206, the control unit15determines whether the discharging of the power storage unit12is completed. The determination is made based on, for example, whether the voltage of the power storage unit12detected by the voltage detection unit19becomes the predetermined voltage or less (i.e., a value close to zero volt). When it is not determined in step S206that the discharging of the power storage unit12is completed, the processing returns to step S205, and the discharging of the power storage unit12is continued. In step S206, when it is determined that the discharging of the power storage unit12is completed, the processing proceeds to step S207.

In step S207, the control unit15outputs the switching command for turning off all of the switching devices to the AC-DC conversion unit11. Accordingly, the power conversion operation by the AC-DC conversion unit11is paused, and the operation of the motor driving apparatus1is completely paused. Through each processing in the above-described step S201to step S207, the power storage unit12is discharged, and thus, for example, when an operator touches the power storage unit12for maintenance, he/she will not get an electric shock.

As described above, in the third embodiment, when the temperature detected by the temperature detection unit16is lower than the specified temperature, the discharging of the power storage unit12is continued, whereas when the temperature becomes the specified temperature or higher, the discharging of the power storage unit12is once stopped during the discharging operation period after completion of driving of the motor. Accordingly, secure discharging of the power storage unit12and overheat protection for the charging resistor22can be realized.

According to the present invention, the motor driving apparatus which converts the AC power supplied from the AC power source side into the DC power by the AC-DC conversion unit, outputs the DC power to the DC link provided with the power storage unit, and further converts the DC power into the AC power for driving the motor and supplying the AC power to the motor can be realized as a space saving and low cost motor driving apparatus which can discharge the charge stored in the power storage unit in a short time.

According to the present invention, the charge stored in the power storage unit is discharged using the charging resistor in the initial charging unit which initially charges the power storage unit provided in the DC link, so that addition of a mounting area for discharging and additional costs are not generated.

Further, according to the present invention, when the temperature of the charging resistor becomes the specified temperature or higher, the discharging of the charging resistor is stopped or paused, so that the overheat of the charging resistor can be prevent from occurring, and there is no risk of fusing of the charging resistor.