Motor drive device

Abstract

The present invention provides a motor drive device. The motor drive device comprises: a converter, which converts AC power from an AC power source into DC power and outputs it to a DC link; a capacitor, which is arranged in the DC link; an inverter, which converts the DC power of the DC link into AC power for motor driving and outputs it; a discharge circuit, which is arranged in parallel with the capacitor in the DC link, and the discharge circuit selectively switches between a discharge action and a non-discharge action, wherein the discharge action is an action of electrically connecting the discharge circuit to the capacitor to discharge the DC power of the DC link, and the non-discharge action is an action of disconnecting the electrical connection between the discharge circuit and the capacitor; and a discharge circuit driving unit, which performs switching driving of the discharge circuit between the discharge action and the non-discharge action, and uses the DC power of the DC link as driving power for switching driving.

Description

Technical Field

[0001] The present invention relates to a motor driving device having a discharge circuit of a capacitor of a DC link. Background Art

[0002] In the motor drive device that drives the motor in the machine tool, forging machine, injection molding machine, industrial machinery or various robots, the AC power supplied from the AC power source is converted into DC power via a converter (rectifier) ​​and then output to the DC link, and then the DC power in the DC link is converted into AC power via an inverter and then the AC power is supplied as driving power to the motor provided for each drive axis. "DC link" refers to the circuit part that electrically connects the DC output side of the converter with the DC input side of the inverter, and is sometimes also called "DC link part", "DC link", "DC link part" or "DC intermediate circuit".

[0003] A capacitor having the function of storing energy and suppressing the pulse component of the output on the DC side of the converter is provided in the DC link. The capacitor provided in the DC link is also called a smoothing capacitor or a DC link capacitor, but is simply referred to as a "capacitor" in this specification.

[0004] In the case where the power consumption of the motor driven by the motor drive device is large, or multiple inverters are connected to the DC link in the motor drive device, the capacitance of the capacitor set in the DC link is large, sometimes reaching, for example, several thousand μF to hundreds of thousands of μF or more. After the power supply of the motor drive device is disconnected or a power outage occurs, in order to reduce the risk of electric shock caused by the charge remaining in the capacitor, it is required to discharge the charge as soon as possible. Therefore, in order to discharge the charge accumulated in the capacitor in a short time, a discharge circuit is sometimes set in the DC link.

[0005] For example, as described in Japanese Patent Application Laid-Open No. 2003-88144, there is known an inverter control device, characterized in that it comprises: a converter that converts an AC power source input via a contactor into a DC power source; an inverter that converts the DC power source output by the converter to the DC bus of a main circuit into an AC power source of an arbitrary frequency; a smoothing capacitor that is connected to the DC bus of the main circuit to smooth the DC power source; a control device that controls the converter and the inverter based on the voltage between the terminals of the smoothing capacitor, the input state of the converter, the output state of the inverter, etc.; a discharge circuit that is connected in parallel with the smoothing capacitor and includes a discharge transistor and a discharge resistor connected to the current input side of the discharge transistor; a first contact relay and a second contact relay, the first contact relay The electrical appliance and the second contact relay are two contact relays whose secondary sides are commonly connected to the control end of the discharge transistor and which perform opening and closing actions in conjunction with the connection and disconnection actions of the contactor, wherein the first contact relay is closed when the contactor is connected, and the second contact relay is closed when the contactor is disconnected; a transistor driving unit, which applies a power supply for cutting off the discharge transistor to the primary side of the first contact relay, and applies a power supply for turning on the discharge transistor to the primary side of the second contact relay; and a power supply backup circuit, which is composed of a backup capacitor and a diode, wherein the backup capacitor is charged by a power supply connected to the primary side of the second contact relay and turning on the discharge transistor, and the diode prevents discharge from the backup capacitor to the power supply side during a power outage. Summary of the invention

[0006] Regarding the capacitor of the DC link set between the converter and the inverter in the motor drive device, the larger the capacitance, the more time it takes to discharge. After the power supply of the motor drive device is disconnected or a power outage occurs, the charge remains in the capacitor for a period of time, so there is a risk of electric shock during this period, and maintenance, replacement and recovery operations cannot be performed, and the operating efficiency is reduced. In order to start the operation as soon as possible after the power supply of the motor drive device is disconnected or a power outage occurs, it is preferred to discharge the charge accumulated in the capacitor as quickly and reliably as possible to eliminate the risk of electric shock and ensure the safety of the operator. If a discharge circuit is set in the DC link between the converter and the inverter in the motor drive device, the discharge time of the capacitor can be shortened, so the risk of electric shock will be reduced and the operating efficiency will be improved. However, when the motor drive device is normally operated, unnecessary power consumption will be generated when the discharge circuit is discharged. Therefore, the discharge circuit should be disconnected from the DC link when the motor drive device is normally operated so as not to discharge (non-discharge action), and the discharge circuit should be connected to the DC link to discharge (discharge action) after the power supply of the motor drive device is disconnected or a power outage occurs. It is conceivable to control the switching between the non-discharge action and the discharge action of such a discharge circuit by the control unit in the motor drive device. However, when a power outage occurs, power is no longer supplied to the control unit in the motor drive device, so the discharge circuit cannot be connected to the DC link. As a result, the discharge achieved by the discharge circuit cannot function, the discharge time is long, and the risk of electric shock is also increased. In addition, in order to cope with the disappearance of power when a power outage occurs, it is conceivable to set a power backup circuit for the discharge circuit. However, setting a power backup circuit for the discharge circuit will lead to an increase in the circuit installation area, an increase in the number of components, and an increase in cost, which is not preferred. In addition, the more the number of components, the higher the risk of failure and the lower the reliability. Therefore, it is desired to have a technology that can discharge the capacitor of the DC link set between the converter and the inverter in the motor drive device as soon as possible and reliably when the power disappears, and it is desired that the technology has low cost and high reliability.

[0007] According to one embodiment of the present disclosure, a motor drive device includes: a converter, which converts AC power from an AC power source into DC power and outputs it to a DC link; a capacitor, which is arranged in the DC link; an inverter, which converts the DC power in the DC link into AC power for motor driving and outputs it; a discharge circuit, which is arranged in parallel with the capacitor in the DC link, and the discharge circuit selectively switches between a discharge action and a non-discharge action, wherein the discharge action is an action of electrically connecting the discharge circuit to the capacitor to discharge the DC power in the DC link, and the non-discharge action is an action of cutting off the electrical connection between the discharge circuit and the capacitor; and a discharge circuit driving unit, which performs switching drive between the discharge action and the non-discharge action of the discharge circuit, and uses the DC power in the DC link as a driving power for the switching drive. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] The present invention can be more clearly understood by referring to the following drawings.

[0009] Figure 1 It is a diagram showing a motor drive device according to a first embodiment of the present disclosure.

[0010] Figure 2 It is a diagram showing another aspect of the discharge circuit driving unit in the motor driving device according to the first embodiment of the present disclosure.

[0011] Figure 3 This is a diagram showing another form of the discharge circuit in the motor drive device according to the first embodiment of the present disclosure.

[0012] Figure 4 This is a diagram showing still another embodiment of the discharge circuit and the discharge circuit driving unit in the motor drive device according to the first embodiment of the present disclosure.

[0013] Figure 5 It is a diagram showing a motor drive device according to a second embodiment of the present disclosure.

[0014] Figure 6 This is a diagram showing another form of the discharge circuit in the motor drive device according to the second embodiment of the present disclosure. DETAILED DESCRIPTION

[0015] Hereinafter, a motor drive device having a capacitor discharge circuit of a DC link will be described with reference to the accompanying drawings. For ease of understanding, the scales of these drawings are appropriately changed. The embodiments shown in the drawings are examples for implementation and are not limited to the illustrated embodiments.

[0016] First, a circuit configuration of a motor drive device according to a first embodiment of the present disclosure will be described. Figure 1It is a diagram showing a motor drive device according to a first embodiment of the present disclosure.

[0017] As an example, a case where an AC motor (hereinafter referred to as "motor") 3 is controlled by a motor drive device 1 connected to an AC power supply 2 is shown. The number of motors 3 is not particularly limited in this embodiment, and it can also be a number other than that. For example, when a plurality of motors 3 are driven by a motor drive device 1, an inverter 13 is provided for each motor 3, so that a plurality of inverters 13 are connected to a DC link. In addition, the number of phases of the AC power supply 2 and the motor 3 is not particularly limited in this embodiment, and it can be, for example, three-phase or single-phase. When an example of the AC power supply 2 is listed, there are three-phase 400V AC power supply, three-phase 200V AC power supply, three-phase 600V AC power supply, single-phase 100V AC power supply, etc. In addition, the type of motor 3 is not particularly limited in this embodiment, and it can be, for example, an induction motor or a synchronous motor. Here, the equipment provided with the motor 3 includes, for example, machine tools, robots, forging machines, injection molding machines, industrial machinery, various electrical products, trams, automobiles, aircraft, etc.

[0018] like Figure 1 As shown, the motor drive device 1 of the present embodiment includes a converter 11 , a capacitor 12 , an inverter 13 , a discharge circuit 14 , a discharge circuit drive unit 15 , a control unit 16 , and a control power supply 17 .

[0019] The control unit 16 in the motor drive device 1 controls the inverter 13, which is used to perform power conversion between the DC power in the DC link and the driving power or regenerative power of the motor 3, that is, the AC power. That is, the control unit 16 generates a switch command for controlling the speed, torque or rotor position of the motor 3 based on the speed of the motor 3 (speed feedback), the current flowing through the winding of the motor 3 (current feedback), the specified torque command, the operation program of the motor 3, etc. The power conversion operation performed by the inverter 13 is controlled based on the power conversion command generated by the control unit 16.

[0020] In addition, the control unit 16 controls the opening and closing action of the electromagnetic contactor 19. That is, the control unit 16 outputs a closing command to the electromagnetic contactor 19 when the power of the motor drive device 1 is turned on, and outputs an opening command to the electromagnetic contactor 19 when the power of the motor drive device 1 is turned off. The closing action of electrically connecting the AC power supply 2 and the converter 11 is realized by closing the contacts of the electromagnetic contactor 19 by receiving the closing command from the control unit 16, and the opening action of electrically disconnecting the AC power supply 2 and the converter 11 is realized by separating the contacts of the electromagnetic contactor 19. In addition, as long as the inflow of AC power to the converter 11 can be cut off when receiving the closing command from the control unit 16, the electromagnetic contactor 19 can be replaced by a relay, a power semiconductor switching element, etc.

[0021] In addition, the control unit 16 can be constructed, for example, in the form of a software program, or can also be constructed by a combination of various electronic circuits and software programs. For example, when the control unit is constructed in the form of a software program, the functions of the above-mentioned various parts can be realized by causing the arithmetic processing device in the motor drive device 1 to operate according to the software program. In addition, the control unit 16 can also be realized as a semiconductor integrated circuit in which a software program for realizing the functions of each part is written. In addition, the control unit 16 can also be, for example, a numerical control device for a machine tool.

[0022] The control power supply 17 is provided in another system separate from the converter 11 and the inverter 13 for supplying driving power to the motor 3, and generates DC power for driving the control unit 16 based on the AC power from the AC power supply 2. The control power supply 17 is omitted from the figure, but for example, it has a converter (rectifier) ​​that converts the AC power supplied from the AC power supply 2 side into DC power and outputs it, and a DC converter that converts the DC power output by the converter into DC power for the control power supply 17 and outputs it. In addition, the DC power generated by the control power supply 17 can also be supplied to other peripheral devices (not shown) of the motor drive device 1. The control power supply 17 outputs a DC voltage of 3.3 [V], 5 [V], 24 [V], etc. For example, 3.3 [V] and 5 [V] are used for driving the control unit 16, and 24 [V] is used for the operation of the electromagnetic brake (not shown) and other control systems of the motor 3.

[0023] A circuit breaker 18 is provided between the converter 11 and the control power supply 17 and the AC power supply 2. The circuit breaker 18 is also called a wiring disconnector (Molded Case Circuit Breaker). The circuit breaker 18 closes the circuit (closes the circuit) under normal circumstances, and disconnects the circuit (opens the circuit) when an abnormal overcurrent flows through the motor drive device 1 (secondary side) due to overload, short circuit, etc., to cut off the power supply from the AC power supply 2 (primary side). When the circuit of the circuit breaker 18 is disconnected, the power supply from the AC power supply 2 to each converter 11 and the control power supply 17 is cut off, so that the converter 11 no longer outputs DC power to the DC link, and the control power supply 17 no longer outputs DC power to the control unit 16.

[0024] The converter 11 converts the AC power supplied from the AC power source 2 into DC power and outputs it to the DC link. In addition, when the AC power source 2 and the converter 11 are electrically connected when both the circuit breaker 18 and the electromagnetic contactor 19 are in a closed state, AC power is supplied from the AC power source 2 to the converter 11. When at least one of the circuit breaker 18 and the electromagnetic contactor 19 is in an open state, AC power is not supplied to the converter 11.

[0025] The converter 11 can convert the supplied AC power into DC power and output it. For example, it can be a diode rectifier circuit or a PWM switch control type rectifier circuit with a switch element inside. When the converter 11 is a diode rectifier, it can perform power conversion in only one direction from AC power to DC power. When the converter 11 is a PWM switch control type rectifier circuit, it can perform power conversion in two directions, from AC power to DC power and from DC power to AC power. When the AC power source 2 is a three-phase power source, the converter 11 is configured as a three-phase bridge circuit, and when the AC power source 2 is a single-phase power source, it is configured as a single-phase bridge circuit. When the converter 11 is a PWM switch control type rectifier circuit, it includes a semiconductor switch element and a bridge circuit of a diode connected in anti-parallel to the semiconductor switch element. In this case, as examples of semiconductor switching elements, there are FET, IGBT, thyristor, GTO (Gate Turn-OFF thyristor: gate turn-off thyristor), SiC (silicon carbide), transistors, etc., but the type of semiconductor switching element itself is not limited to this embodiment, and other semiconductor switching elements may also be used. In addition, an AC reactor is connected to the AC input side of the converter 11, but the illustration is omitted here.

[0026] The DC output side of the converter 11 and the DC input side of the inverter 13 are connected via a DC link. A capacitor 12 is provided in the DC link. The capacitor 12 has the function of storing energy (DC power) in the DC link and the function of suppressing the pulse component of the output on the DC side of the converter 11. DC power is stored in the DC link by charging the capacitor 12. Examples of the capacitor 12 provided in the DC link include electrolytic capacitors and film capacitors. In addition, the voltage (DC link voltage) applied between the positive and negative terminals of the capacitor 12 provided in the DC link is used for controlling the inverter 13 using the control unit 16, but in Figure 1 The detection unit for detecting the DC link voltage is omitted in the figure.

[0027] The inverter 13 converts the DC power in the DC link into AC power for driving the motor and outputs it to the motor 3. The inverter 13 may have a structure capable of converting DC power into AC power, for example, a PWM inverter circuit having a switching element inside. The inverter 13 is configured as a three-phase bridge circuit when the motor 3 is a three-phase AC motor, and is configured as a single-phase bridge circuit when the motor 3 is a single-phase motor. The inverter 13 receives a power conversion instruction from the control unit 16 to convert the DC power in the DC link into AC power for driving the motor and output it to the motor 3, and converts the AC power regenerated by the motor 3 during motor regeneration into DC power and returns it to the DC link side. When the inverter 13 is configured as a PWM inverter circuit, it includes a bridge circuit of a semiconductor switching element and a diode connected in anti-parallel to the semiconductor switching element. In this case, examples of semiconductor switching elements include FET, IGBT, thyristor, GTO (Gate Turn-OFF thyristor), SiC (silicon carbide), transistor, etc., but the type of semiconductor switching element itself is not limited to this embodiment, and other semiconductor switching elements can also be used.

[0028] The discharge circuit 14 is provided in parallel with the capacitor 12 in the DC link. The discharge circuit 14 is selectively switched between a discharge operation and a non-discharge operation by switching drive of a discharge circuit driving unit 15 described later. The discharge operation is an operation of electrically connecting the discharge circuit 14 to the capacitor 12 to discharge the DC power in the DC link, and the non-discharge operation is an operation of disconnecting the electrical connection between the discharge circuit 14 and the capacitor 12. Therefore, the discharge circuit 14 has a discharge unit 21 and a discharge switching switch. Figure 1 In the example shown, the discharge section 21 is provided on the high potential side in the discharge circuit 14, and the discharge switching switch is provided on the low potential side, but these may be provided in reverse.

[0029] exist Figure 1 In the example shown, the discharge switching switch in the discharge circuit 14 is configured as a semiconductor switch circuit 22-1 that electrically connects the discharge section 21 and the capacitor 12 and disconnects the electrical connection between the discharge section 21 and the capacitor 12 according to the switching drive performed by the discharge circuit driving section 15. The semiconductor switch circuit 22-1 as the discharge switching switch includes, for example, a semiconductor switch element and a diode connected in anti-parallel to the semiconductor switch element. Examples of semiconductor switch elements include FET, IGBT, thyristor, GTO (Gate Turn-OFF thyristor), SiC (silicon carbide), transistor, etc., but the type of semiconductor switch element itself is not limited to this embodiment, and other semiconductor switch elements may also be used. The semiconductor switch circuit 22-1 has a signal input terminal connected to the high potential side terminal of the constant voltage output section 32 in the discharge circuit driving section 15 described later. The detailed connection relationship between the discharge circuit 14 and the discharge circuit driving section 15 will be described later. In addition, other forms of the discharge switching switch will be described later.

[0030] The discharge section 21 in the discharge circuit 14 is configured to discharge the DC power accumulated in the capacitor 12 provided in the DC link when the discharge section 21 and the capacitor 12 are electrically connected via a semiconductor switch circuit 22-1 as a discharge switching switch and the output of DC power from the converter 11 is stopped. That is, when the semiconductor switch circuit 22-1 electrically connects the discharge section 21 and the capacitor 12 when the output of DC power from the converter 11 is stopped, a closed loop is formed between the capacitor 12 and the discharge section 21, and the DC power in the DC link is consumed by the discharge section 21. The discharge section 21 is composed of a device that consumes electric energy (current) by converting the electric energy (current) flowing through the discharge section 21 into other energy. Specific examples of the discharge section 21 include light-emitting devices such as LEDs and electric lamps, audio devices such as buzzers and speakers, resistor elements, motors, etc., but it may also be other devices other than these. Figure 1 In the embodiment, the discharge unit 21 is formed of a resistor element as an example.

[0031] For example, when the discharge unit 21 is composed of a resistor, the electric energy flowing through the discharge unit 21 is consumed in the form of heat energy converted by the resistor. In this case, the operator can recognize that the discharge unit 21 is discharging based on the heat generated by the resistor of the discharge unit 21, and thus can take measures such as not touching the capacitor 12 and its surroundings, thereby avoiding the risk of electric shock and ensuring the safety of the operator.

[0032] For example, when the discharge unit 21 is composed of a light emitting device, the electric energy flowing through the discharge unit 21 is consumed in the form of light energy converted by the light emitting device. In this case, the operator can recognize that the discharge unit 21 is discharging based on the light emitted by the light emitting device as the discharge unit 21, and thus can take measures such as not touching the capacitor 12 and its surroundings, thereby avoiding the risk of electric shock and ensuring the safety of the operator.

[0033] For example, when the discharge unit 21 is composed of an audio device, the electric energy flowing through the discharge unit 21 is consumed in the form of sound energy converted by the audio device. In this case, the operator can recognize that the discharge unit 21 is discharging based on the sound emitted by the audio device as the discharge unit 21, and thus can take measures such as not touching the capacitor 12 and its surroundings, thereby avoiding the risk of electric shock and ensuring the safety of the operator.

[0034] For example, when the discharge section 21 is composed of an electric motor, the electric energy flowing through the discharge section 21 is consumed in the form of kinetic energy converted by the electric motor. For example, if a vibration plate is added to the electric motor as the discharge section 21, the electric energy flowing through the discharge section 21 can be converted into vibration energy. In this case, the operator can recognize that the discharge section 21 is discharging based on the vibration of the vibration plate installed on the electric motor as the discharge section 21, and thus can take measures such as not touching the capacitor 12 and its surroundings, thereby avoiding the risk of electric shock and ensuring the safety of the operator.

[0035] Furthermore, the discharge unit 21 may convert the electrical energy into other energy than the energy exemplified here.

[0036] The discharge circuit driving unit 15 performs switching driving between the discharge operation and the non-discharge operation of the discharge circuit 14. As the driving power for the switching driving performed by the discharge circuit driving unit 15, the DC power stored in the capacitor 12 provided in the DC link is used. The discharge circuit driving unit 15 has a structure for switching driving the discharge circuit 14 from the non-discharge operation to the discharge operation when the power from the control power supply 17 disappears. This will be described in more detail below.

[0037] like Figure 1 As shown, the discharge circuit driving unit 15 includes a current limiting resistor 31, a constant voltage output unit 32, and a power failure detection switch.

[0038] The current limiting resistor 31 has a first terminal connected to the positive terminal of the capacitor 12 and a second terminal for outputting the current input from the first terminal. The resistance value of the current limiting resistor 31 in the discharge circuit driving unit 15 is set to a value greater than the resistance value of the discharge unit 21 in the discharge circuit 14. For example, the current limiting resistor 31 in the discharge circuit driving unit 15 is several tens of kΩ to several hundred kΩ, and the discharge unit 21 in the discharge circuit 14 is several Ω to several tens of Ω. The numerical values ​​listed here are just examples, and other numerical values ​​may also be used.

[0039] The constant voltage output unit 32 has a high potential side terminal connected to the second terminal of the current limiting resistor 31 and a low potential side terminal connected to the negative side terminal of the capacitor 12. The constant voltage output unit 32 outputs a predetermined constant voltage between the high potential side terminal and the low potential side terminal. The constant voltage output unit 32 includes, for example, a Zener diode connected in a manner such that the high potential side terminal is a cathode and the low potential side terminal is an anode. The Zener diode is also called a constant voltage diode (Reference Diode). The Zener diode exhibits substantially the same characteristics as a normal diode when a voltage is applied in the forward bias direction, but exhibits a characteristic of rapidly flowing current due to avalanche breakdown when a voltage applied in the reverse bias direction exceeds the breakdown voltage (Zener voltage). Regarding the Zener diode as the constant voltage output unit 32, the cathode is connected to the second terminal of the current limiting resistor 31 and the signal input terminal of the semiconductor switch circuit 22-1, which is a discharge switching switch in the discharge circuit 14, and the anode is connected to the negative side terminal of the capacitor 12. Therefore, the direction from the second terminal of the current limiting resistor 31 and the signal input terminal of the semiconductor switch circuit 22-1 to the negative terminal of the capacitor 12 is the reverse bias direction of the Zener diode. When the voltage applied to the Zener diode as the constant voltage output unit 32 exceeds the breakdown voltage of the Zener diode, a current will flow rapidly due to avalanche breakdown, and a constant voltage equivalent to the breakdown voltage will appear at the high potential side terminal of the constant voltage output unit 32, that is, the cathode of the Zener diode. The high potential side terminal of the constant voltage output unit 32, that is, the cathode of the Zener diode, is connected to the signal input terminal of the semiconductor switch circuit 22-1, which is the discharge switching switch in the discharge circuit 14, so a constant voltage equivalent to the breakdown voltage is applied to the signal input terminal of the semiconductor switch element in the semiconductor switch circuit 22-1. In this embodiment, the Zener diode and the current limiting resistor 31 are pre-selected in such a way that the constant voltage output unit 32 can output a voltage that turns on the semiconductor switch element in the semiconductor switch circuit 22-1. Furthermore, the constant voltage output unit 32 may be formed by a variable resistor (Varistor), a series regulator, a three-terminal regulator, or the like, instead of forming the constant voltage output unit 32 by a Zener diode.

[0040] exist Figure 1In the example shown, the power failure detection switch in the discharge circuit driving section 15 is composed of a photocoupler 33-1, which has a light-emitting element that emits light by the current output from the control power supply 17 and a light-receiving element that energizes the input terminal and the output terminal when receiving light from the light-emitting element. The photocoupler 33-1 as a power failure detection switch has an input terminal connected to the second terminal of the current limiting resistor 31 and an output terminal connected to the negative terminal of the capacitor 12. The light-emitting element of the photocoupler 33-1 is connected to a lead wire drawn from a power line through a resistor 34, and the power line is a power line for the control power supply 17 to supply power for operating the control section 16. The input terminal of the light-receiving element of the photocoupler 33-1 is connected to the second terminal of the current limiting resistor 31, the high potential side terminal of the constant voltage output section 32, and the signal input terminal of the semiconductor switch circuit 22-1, which is the discharge switching switch. In addition, the output terminal of the light receiving element of the photocoupler 33-1 is connected to the negative terminal of the capacitor 12 and the low potential terminal of the constant voltage output unit 32. When the control power supply 17 outputs current, the light emitting element of the photocoupler 33-1 emits light, and the light receiving element receives the light and the input terminal and the output terminal are energized. When the control power supply 17 does not output current, the light emitting element of the photocoupler 33-1 does not emit light, and the light receiving element does not receive light and the input terminal and the output terminal are not energized.

[0041] The connection relationship between the above-mentioned capacitor 12, discharge circuit 14 and discharge circuit driving unit 15 is summarized as follows. The positive terminal of the capacitor 12 is connected to the first terminal of the current limiting resistor 31 in the discharge circuit driving unit 15. The second terminal of the current limiting resistor 31 in the discharge circuit driving unit 15, the high potential side terminal of the constant voltage output unit 32, that is, the cathode of the Zener diode, the input terminal of the light receiving element of the photocoupler 33-1, and the signal input terminal of the semiconductor switch circuit 22-1 are connected. The low potential side terminal of the capacitor 12 is connected to the low potential side terminal of the constant voltage output unit 32, that is, the anode of the Zener diode.

[0042] Next, the operation of the motor drive device 1 according to the first embodiment of the present disclosure will be described.

[0043] When the motor 3 is driven by the motor drive device 1, the circuit breaker 18 and the electromagnetic contactor 19 are both in a closed circuit state, the AC power source 2 is electrically connected to the converter 11, and the converter 11 converts the AC power supplied from the AC power source 2 into DC power and outputs it to the DC link. The inverter 13 receives the power conversion instruction from the control unit 16, and performs a power conversion action (power operation action) of converting the DC power in the DC link into AC power for motor driving and outputting it to the motor 3, or a power conversion action (regeneration action) of converting the AC power regenerated by the motor 3 into DC power and returning it to the DC link side. The control unit 16 operates with the power supplied from the control power source 17. Therefore, power is supplied from the control power source 17 to the control unit 16, so that current flows through the light-emitting element of the photocoupler 33-1 as a switch for power failure detection, and light is emitted. At this time, the light-receiving element of the photocoupler 33-1 receives the light from the light-emitting element, so that power is passed between the input terminal and the output terminal. Therefore, a closed loop is formed by the second terminal of the current limiting resistor 31, the input terminal of the light receiving element of the photocoupler 33-1, the output terminal of the light receiving element, the low potential side terminal of the constant voltage output section 32, i.e., the anode of the Zener diode, and the high potential side terminal of the constant voltage output section 32, i.e., the cathode of the Zener diode. That is, the second terminal of the current limiting resistor 31 and the high potential side terminal of the constant voltage output section 32, i.e., the cathode of the Zener diode, are short-circuited. Therefore, no voltage is applied to the second terminals of these current limiting resistors 31 and the signal input terminal of the semiconductor switch circuit 22-1 connected to the high potential side terminal of the constant voltage output section 32. Therefore, the semiconductor switch element in the semiconductor switch circuit 22-1 remains disconnected, and a closed loop is not formed between the discharge section 21 and the capacitor 12, so the capacitor 12 is not electrically connected to the discharge section 21, and the power stored in the capacitor 12 is not discharged in the discharge section 21 (non-discharge operation).

[0044] When an abnormal overcurrent flows through the motor drive device 1 due to overload, short circuit, etc., the circuit breaker 18 disconnects the circuit and no longer supplies the AC power of the AC power supply 2 to the control power supply 17 and the converter 11. In addition, in the event of a power outage in the AC power supply 2, the AC power of the AC power supply 2 is no longer supplied to the control power supply 17 and the converter 11. The control power supply 17 is not supplied with the AC power of the AC power supply 2, and therefore no power is output for operating the control unit 16. Therefore, no current flows through the light-emitting element of the photocoupler 33-1, and the light-emitting element does not emit light. The light-receiving element of the photocoupler 33-1 does not receive the light from the light-emitting element, so no power is supplied between the input terminal and the output terminal. Therefore, the voltage applied to the capacitor 12 is applied to the series circuit of the current-limiting resistor 31 and the Zener diode serving as the constant voltage output unit 32. When the voltage applied to the Zener diode as the constant voltage output section 32 exceeds the breakdown voltage of the Zener diode, a current flows rapidly due to avalanche breakdown, and a constant voltage equivalent to the breakdown voltage appears at the high potential side terminal of the constant voltage output section 32, that is, the cathode of the Zener diode. The high potential side terminal of the constant voltage output section 32, that is, the cathode of the Zener diode, is connected to the signal input terminal of the semiconductor switch circuit 22-1, which is the switch for switching discharge. Therefore, a constant voltage equivalent to the breakdown voltage of the Zener diode as the constant voltage output section 32 is applied to the signal input terminal of the semiconductor switch circuit 22-1, so that the semiconductor switch element in the semiconductor switch circuit 22-1 is turned on. In addition, the AC power of the AC power source 2 is no longer supplied to the converter 11, so the DC power output from the converter 11 is stopped. Therefore, a closed loop is formed between the discharge section 21 and the capacitor 12. As a result, the capacitor 12 is electrically connected to the discharge section 21, and the power stored in the capacitor 12 is discharged through the discharge section 21 (discharge operation).

[0045] As described above, when an abnormal overcurrent flows through the motor drive device 1 due to an overload, a short circuit, etc., and the circuit breaker 18 disconnects the circuit, or when a power failure occurs in the AC power source 2, the AC power of the AC power source 2 is no longer supplied to the control power source 17 and the converter 11, and the power from the control power source 17 to the control unit 16 is lost. In the present embodiment, the photocoupler 33-1 as a power failure detection switch is used to detect the loss of the driving power from the control power source 17 to the control unit 16, and the detection result is electrically transmitted to the signal input terminal of the semiconductor switch circuit 22-1, which is a discharge switching switch in the discharge circuit 14, and the capacitor 12 is electrically connected to the discharge unit 21 in the discharge circuit 14. In the present embodiment, based on the DC power accumulated in the capacitor 12, a voltage is generated at the cathode of the Zener diode, which is the high potential side terminal of the constant voltage output unit 32, and the semiconductor switch element of the semiconductor switch circuit 22-1 is turned on by the voltage, thereby switching the discharge circuit 14 from the non-discharge operation to the discharge operation. That is, the driving power for the switching drive performed by the discharge circuit driving unit 15 uses the DC power stored in the capacitor 12 provided in the DC link. Therefore, according to the present embodiment, there is no need to provide a dedicated power backup circuit for supplying power for switching the discharge circuit from the non-discharge operation to the discharge operation, and the circuit installation area and the number of components will not increase, and the cost is low. In addition, the structure of the discharge circuit driving unit 15 is simpler than that of the power backup circuit, and the number of components is small, so the risk of failure is low and the reliability is high. In addition, by using the discharge unit 21 in the discharge circuit 14 to discharge the DC power stored in the capacitor 12 to shorten the discharge time, it is possible to start maintenance replacement operations and recovery operations as soon as possible after the power supply of the motor drive device 1 is disconnected or a power outage occurs, thereby reducing the risk of electric shock and improving the operating efficiency. For example, if the discharge unit 21 in the discharge circuit 14 is composed of light-emitting devices such as LEDs and electric lights, sound devices such as buzzers and speakers, and motors, it will work in a form that the operator can see that these devices are discharging during the discharge period, so the operator can be reminded of the risk of electric shock to ensure safety. In addition, when the motor drive device 1 is normally operated, no discharge is performed in the discharge circuit 14, so no unnecessary power consumption is generated, which is efficient. As described above, according to the present embodiment, a low-cost and highly reliable motor drive device 1 can be realized, which can discharge the capacitor 12 of the DC link provided between the converter 11 and the inverter 13 as soon as possible and reliably when the power supply is lost.

[0046] In addition, in addition to the above-mentioned discharge when an abnormal overcurrent flows through the motor drive device 1 due to overload, short circuit, etc. and the circuit breaker 18 disconnects the circuit, or when the AC power source 2 fails, the above-mentioned discharge can also be performed when the operation of the motor drive device 1 is normally stopped. For example, if the AC power input to the control power source 17 is obtained from the electromagnetic contactor 19 and the converter 11, when the electromagnetic contactor 19 is set to the disconnected state in order to stop the operation of the motor drive device 1 normally, the AC power of the AC power source 2 is not supplied to the control power source 17 and the converter 11, so that the discharge circuit 14 and the discharge circuit driver 15 can also perform the above-mentioned operation. In addition, when a stop command is output from the control unit 16 to the inverter 13, the stop command is amplified to a current having a predetermined size and the current is caused to flow through the light-emitting element of the photocoupler 33-1, so that the discharge circuit 14 and the discharge circuit driver 15 can also perform the above-mentioned operation.

[0047] exist Figure 1 In the first embodiment shown, the photocoupler 33-1 is used as a power failure detection switch in the discharge circuit driving unit 15, but an A-contact relay may be used as a power failure detection switch instead of using the photocoupler 33-1 as a power failure detection switch. Figure 2 FIG. 2 is a diagram showing another embodiment of the discharge circuit driving unit in the motor driving device according to the first embodiment of the present disclosure. Figure 2 As shown, the power loss detection switch in the discharge circuit driving unit 15 includes an A-contact relay 33-2. The A-contact relay 33-2 is a "normally open (normally-off)" type relay in which the contacts are connected when current flows and the contacts are disconnected when current does not flow. Regarding the A-contact relay 33-2 as a power loss detection switch, when current is output from the control power supply 17, the contacts are connected, and power is passed between the input terminal and the output terminal. When current is not output from the control power supply 17, the contacts are disconnected, and no power is passed between the input terminal and the output terminal. Therefore, the power loss detection switch in the discharge circuit driving unit 15 can be constituted by the A-contact relay 33-2, which can achieve the same as the reference. Figure 1 The same operation as the photocoupler 33-1 described above. In addition, the circuit components other than the A contact relay 33-2 are the same as Figure 1 The circuit components shown are the same, and therefore the same circuit components are denoted by the same reference numerals and detailed descriptions of the circuit components are omitted.

[0048] In addition, Figure 1In the first embodiment shown, the semiconductor switch circuit 22-1 is used as the discharge switching switch in the discharge circuit 14, but an A-contact relay may be used as the discharge switching switch instead of using the semiconductor switch circuit 22-1 as the discharge switching switch. Figure 3 FIG. 2 is a diagram showing another embodiment of the discharge circuit in the motor drive device according to the first embodiment of the present disclosure. Figure 3 As shown, the discharge switching switch in the discharge circuit 14 includes an A-contact relay 22-2. The A-contact relay 22-2 is a "normally open" type relay whose contacts are connected when current flows and disconnected when current does not flow. When the constant voltage output by the constant voltage output unit 32 is applied to the A-contact relay 22-2 as the discharge switching switch, the contacts are connected to electrically connect the capacitor 12 and the discharge unit 21. When the constant voltage output by the constant voltage output unit 32 is not applied, the contacts are disconnected to cut off the electrical connection between the capacitor 12 and the discharge unit 21. Therefore, the discharge switching switch in the discharge circuit 14 is constituted by the A-contact relay 22-2, which can also be realized as in reference. Figure 1 The semiconductor switch circuit 22-1 described above operates in the same manner. In addition, the circuit components other than the A-contact relay 22-2 are the same as those Figure 1 The circuit components shown are the same, and therefore the same circuit components are denoted by the same reference numerals and detailed descriptions of the circuit components are omitted.

[0049] You can refer to Figure 2 The A contact relay 33-2 as a power failure detection switch described above is the same as that of the reference Figure 3 The discharge circuit driving unit 15 and the discharge circuit 14 in the first embodiment are realized by combining the A-contact relay 22 - 2 as the discharge switching switch described above. Figure 4 FIG. 2 is a diagram showing another embodiment of the discharge circuit and the discharge circuit driving unit in the motor drive device according to the first embodiment of the present disclosure. Figure 4As shown, the power failure detection switch in the discharge circuit driving unit 15 includes an A-contact relay 33-2, and the discharge switching switch in the discharge circuit 14 includes an A-contact relay 22-2. When current is output from the control power supply 17, the A-contact relay 33-2 as the power failure detection switch has its contacts closed, and power is passed between the input terminal and the output terminal; when current is not output from the control power supply 17, the contacts are disconnected, and no power is passed between the input terminal and the output terminal. When the constant voltage output by the constant voltage output unit 32 is applied, the A-contact relay 22-2 as the discharge switching switch has its contacts closed, and the capacitor 12 and the discharge unit 21 are electrically connected; when the constant voltage output by the constant voltage output unit 32 is not applied, the contacts are disconnected, and the electrical connection between the capacitor 12 and the discharge unit 21 is cut off. Therefore, by forming the power failure detection switch in the discharge circuit driving unit 15 with the A-contact relay 33-2 and forming the discharge switching switch in the discharge circuit 14 with the A-contact relay 22-2, the same as the reference can be achieved. Figure 1 The photocoupler 33-1 and the semiconductor switch circuit 22-1 described above operate in the same manner. In addition, the circuit components other than the A contact relay 22-2 and the A contact relay 33-2 are the same as those of the Figure 1 The circuit components shown are the same, and therefore the same circuit components are denoted by the same reference numerals and detailed descriptions of the circuit components are omitted.

[0050] Next, the circuit structure of the motor drive device 1 according to the second embodiment of the present disclosure will be described. Figure 1 or Figure 3 The photocoupler 33-1 shown or Figure 2 or Figure 4 The A contact relay 33-2 shown constitutes a power failure detection switch. In the second embodiment of the present disclosure, the power failure detection switch is constituted by a B contact relay instead of the photocoupler 33-1 or the A contact relay 33-2.

[0051] Figure 5 It is a diagram showing a motor drive device according to a second embodiment of the present disclosure.

[0052] exist Figure 5 In the example, the B contact relay 33-3 is used to form a power failure detection switch, instead of the reference Figure 1 and Figure 3 The photocoupler 33-1 described above constitutes a switch for detecting power failure. Figure 5 As shown, the discharge circuit driving unit 15 includes a current limiting resistor 31, a constant voltage output unit 32, and a B-contact relay 33-3 as a power failure detection switch.

[0053] The current limiting resistor 31 has a first terminal connected to the positive terminal of the capacitor 12 and a second terminal for outputting a current input from the first terminal.

[0054] The B contact relay 33-3, which is a switch for detecting power failure, is a "normally closed" type relay in which the contact is disconnected when current flows and the contact is connected when no current flows. The B contact relay 33-3 has an input terminal connected to the second terminal of the current limiting resistor 31 and an output terminal for outputting the current input to the input terminal when power is supplied. When current is output from the control power supply 17, the B contact relay 33-3 disconnects the contact and energizes the input terminal and the output terminal. When current is not output from the control power supply 17, the contact is connected and no power is supplied between the input terminal and the output terminal.

[0055] The constant voltage output unit 32 has a high potential side terminal connected to the output terminal of the B contact relay 33-3, which is a switch for power failure detection, and a low potential side terminal connected to the negative side terminal of the capacitor 12. The constant voltage output unit 32 outputs a predetermined constant voltage between the high potential side terminal and the low potential side terminal. The constant voltage output unit 32 includes, for example, a Zener diode connected in such a manner that the high potential side terminal is a cathode and the low potential side terminal is an anode. Regarding the Zener diode as the constant voltage output unit 32, the cathode is connected to the output terminal of the B contact relay 33-3 and the signal input terminal of the semiconductor switch circuit 22-1, which is a switch for discharge switching in the discharge circuit 14, and the anode is connected to the negative side terminal of the capacitor 12. Therefore, the direction from the output terminal of the B contact relay 33-3 and the signal input terminal of the semiconductor switch circuit 22-1 to the negative side terminal of the capacitor 12 is the reverse bias direction of the Zener diode. When the voltage applied to the Zener diode as the constant voltage output unit 32 exceeds the breakdown voltage of the Zener diode, a current flows rapidly due to avalanche breakdown, and a constant voltage corresponding to the breakdown voltage appears at the high potential side terminal of the constant voltage output unit 32, that is, the cathode of the Zener diode. The high potential side terminal of the constant voltage output unit 32, that is, the cathode of the Zener diode, is connected to the signal input terminal of the semiconductor switch circuit 22-1, which is the discharge switching switch in the discharge circuit 14, so a constant voltage corresponding to the breakdown voltage is applied to the signal input terminal of the semiconductor switch element in the semiconductor switch circuit 22-1. However, in this embodiment, the Zener diode and the current limiting resistor 31 are pre-selected so that the constant voltage output unit 32 can output a voltage that turns on the semiconductor switch element in the semiconductor switch circuit 22-1. In addition, the constant voltage output unit 32 may be formed by a variable resistor (Varistor), a series regulator, or a three-terminal regulator, etc., instead of forming the constant voltage output unit 32 by a Zener diode.

[0056] The connection relationship between the above-mentioned capacitor 12, discharge circuit 14 and discharge circuit driver 15 is summarized as follows. The positive terminal of the capacitor 12 is connected to the first terminal of the current limiting resistor 31 in the discharge circuit driver 15. The second terminal of the current limiting resistor 31 in the discharge circuit driver 15 is connected to the input terminal of the B contact relay 33-3 as a switch for power failure detection. The output terminal of the B contact relay 33-3 as a switch for power failure detection, the high potential side terminal of the constant voltage output unit 32, that is, the cathode of the Zener diode, and the signal input terminal of the semiconductor switch circuit 22-1 are connected. The low potential side terminal of the capacitor 12 is connected to the low potential side terminal of the constant voltage output unit 32, that is, the anode of the Zener diode.

[0057] Next, the operation of the motor drive device 1 according to the second embodiment of the present disclosure will be described.

[0058] When the motor 3 is driven by the motor drive device 1, the circuit breaker 18 and the electromagnetic contactor 19 are both in a closed circuit state, the AC power source 2 is electrically connected to the converter 11, and the converter 11 converts the AC power supplied from the AC power source 2 into DC power and outputs it to the DC link. The inverter 13 receives the power conversion instruction from the control unit 16, and performs a power conversion action (power running action) of converting the DC power in the DC link into AC power for motor driving and outputting it to the motor 3, or a power conversion action (regeneration action) of converting the AC power regenerated by the motor 3 into DC power and returning it to the DC link side. The control unit 16 operates with the power supplied from the control power source 17. Therefore, power is supplied from the control power source 17 to the control unit 16, so the contact of the B contact relay 33-3 as a switch for power failure detection is disconnected, and no power is supplied between the input terminal and the output terminal. Therefore, no voltage is applied to the signal input terminal of the semiconductor switch circuit 22-1 connected to the high potential side terminal of the constant voltage output unit 32. Therefore, the semiconductor switch element in the semiconductor switch circuit 22-1 remains disconnected, and a closed loop is not formed between the discharge part 21 and the capacitor 12, so the capacitor 12 is not electrically connected to the discharge part 21, and the power stored in the capacitor 12 is not discharged in the discharge part 21 (non-discharge operation).

[0059] When an abnormal overcurrent flows through the motor drive device 1 due to an overload, a short circuit, or the like, the circuit breaker 18 disconnects the circuit and stops supplying the AC power of the AC power source 2 to the control power source 17 and the converter 11. In addition, when a power outage occurs in the AC power source 2, the AC power of the AC power source 2 is also stopped from being supplied to the control power source 17 and the converter 11. When the AC power of the AC power source 2 is stopped from being supplied to the control power source 17, the control power source 17 stops outputting power for operating the control unit 16. Therefore, the contact of the B contact relay 33-3, which is a switch for detecting power failure, is turned on, and power is supplied between the input terminal and the output terminal. Therefore, the voltage applied to the capacitor 12 is applied to the series circuit of the current limiting resistor 31 and the Zener diode, which is the constant voltage output unit 32. When the voltage applied to the Zener diode, which is the constant voltage output unit 32, exceeds the breakdown voltage of the Zener diode, a current flows rapidly due to avalanche breakdown, and a constant voltage equivalent to the breakdown voltage appears at the high potential side terminal of the constant voltage output unit 32, that is, the cathode of the Zener diode. The cathode of the Zener diode, which is the high potential side terminal of the constant voltage output section 32, is connected to the signal input terminal of the semiconductor switch circuit 22-1, which is the switch for switching the discharge. Therefore, a constant voltage equivalent to the breakdown voltage of the Zener diode, which is the constant voltage output section 32, is applied to the signal input terminal of the semiconductor switch circuit 22-1, so that the semiconductor switch element in the semiconductor switch circuit 22-1 is turned on. In addition, the AC power of the AC power source 2 is no longer supplied to the converter 11, so the DC power output from the converter 11 is stopped. Therefore, a closed loop is formed between the discharge section 21 and the capacitor 12. As a result, the capacitor 12 is electrically connected to the discharge section 21, and the power stored in the capacitor 12 is discharged through the discharge section 21 (discharge action). In addition, the circuit components other than the discharge circuit 14 and the discharge circuit driving section 15 are the same as Figure 5 The circuit components shown are the same, and therefore the same circuit components are denoted by the same reference numerals and detailed descriptions of the circuit components are omitted.

[0060] By referring to it like this Figure 5 The second embodiment described above can also realize the discharge operation and non-discharge operation of the discharge circuit 14 similar to the first embodiment.

[0061] exist Figure 2 In the second embodiment shown, the semiconductor switch circuit 22-1 is used as the discharge switching switch in the discharge circuit 14, but an A-contact relay may be used as the discharge switching switch instead of using the semiconductor switch circuit 22-1 as the discharge switching switch. Figure 6 FIG. 2 is a diagram showing another embodiment of the discharge circuit in the motor drive device according to the second embodiment of the present disclosure. Figure 6As shown in FIG. 1 , the discharge switching switch in the discharge circuit 14 includes an A-contact relay 22-2. When the constant voltage output by the constant voltage output unit 32 is applied, the A-contact relay 22-2 as the discharge switching switch closes the contact to electrically connect the capacitor 12 and the discharge unit 21. When the constant voltage output by the constant voltage output unit 32 is not applied, the contact opens to cut off the electrical connection between the capacitor 12 and the discharge unit 21. Therefore, even if the discharge switching switch in the discharge circuit 14 is set to the A-contact relay 22-2, the same as the reference can be achieved. Figure 5 The semiconductor switch circuit 22-1 described above operates in the same manner. Figure 5 The circuit components shown are the same, and therefore the same circuit components are denoted by the same reference numerals and detailed descriptions of the circuit components are omitted.

[0062] According to one aspect of the present disclosure, a low-cost and highly reliable motor drive device can be realized that can discharge a capacitor of a DC link provided between a converter and an inverter as quickly and reliably as possible when power is lost.

Claims

1. A motor drive device, comprising: A converter, which converts AC power from an AC power source into DC power and outputs it to a DC link; A capacitor, which is arranged in the DC link; An inverter that converts the DC power in the DC link into AC power for driving the motor and then outputs the AC power; a discharge circuit provided in parallel with the capacitor in the DC link, the discharge circuit selectively switching between a discharge operation and a non-discharge operation via a discharge switching switch, the discharge operation being an operation of discharging the DC power in the DC link by electrically connecting the discharge circuit to the capacitor via the discharge switching switch, and the non-discharge operation being an operation of disconnecting the electrical connection between the discharge circuit and the capacitor via the discharge switching switch; as well as a discharge circuit driving unit that performs switching driving between the discharge operation and the non-discharge operation of the discharge circuit and includes a current limiting resistor, The current limiting resistor has a first terminal connected to the positive terminal of the capacitor and a second terminal for outputting the current input from the first terminal. The discharge circuit driving unit is configured to perform the switching drive of the discharge operation by applying a voltage generated by the DC power in the DC link flowing from the capacitor through the current limiting resistor to a control terminal of the discharge switching switch.

2. The motor drive device according to claim 1, characterized in that: The discharge circuit has: a discharge unit; and The discharge switching switch switches between electrical connection between the discharge unit and the capacitor and disconnection of the electrical connection between the discharge unit and the capacitor in accordance with switching drive of the discharge circuit driving unit.

3. The motor drive device according to claim 1 or 2, characterized in that: Also available: a control unit that controls the inverter; and a control power supply that generates power for operating the control unit based on the AC power from the AC power supply, Here, when the power from the control power supply disappears, the discharge circuit driving unit switches the discharge circuit from the non-discharge operation to the discharge operation.

4. The motor drive device according to claim 3, characterized in that: A circuit breaker is further provided, and the circuit breaker is provided between the converter and the control power supply and the AC power supply.

5. A motor drive device comprising: A converter, which converts AC power from an AC power source into DC power and outputs it to a DC link; A capacitor, which is arranged in the DC link; An inverter that converts the DC power in the DC link into AC power for driving the motor and then outputs the AC power; a discharge circuit provided in parallel with the capacitor in the DC link, the discharge circuit selectively switching between a discharge operation and a non-discharge operation, the discharge operation being an operation of electrically connecting the discharge circuit to the capacitor to discharge the DC power in the DC link, and the non-discharge operation being an operation of disconnecting the electrical connection between the discharge circuit and the capacitor; a discharge circuit driving unit that performs switching driving between the discharge operation and the non-discharge operation of the discharge circuit, and uses the DC power in the DC link as driving power for the switching driving; A control unit that controls the inverter; as well as a control power supply that generates power for operating the control unit based on the AC power from the AC power supply, Wherein, the discharge circuit has: a discharge unit; and a discharge switching switch that switches between electrical connection between the discharge unit and the capacitor and disconnection of the electrical connection between the discharge unit and the capacitor according to switching drive of the discharge circuit driving unit, The discharge circuit driving unit comprises: a current limiting resistor having a first terminal connected to the positive terminal of the capacitor and a second terminal for outputting a current input from the first terminal; a constant voltage output unit having a high potential side terminal connected to the second terminal of the current limiting resistor and a low potential side terminal connected to the negative side terminal of the capacitor, the constant voltage output unit outputting a predetermined constant voltage between the high potential side terminal and the low potential side terminal; and a power failure detection switch, comprising an input terminal connected to the second terminal of the current limiting resistor and an output terminal connected to the negative terminal of the capacitor, wherein when current is output from the control power supply, power is supplied between the input terminal and the output terminal, and when current is not output from the control power supply, power is not supplied between the input terminal and the output terminal. In which, the discharge switching switch of the discharge circuit has a signal input terminal connected to the high potential side terminal of the constant voltage output unit, and the discharge switching switch electrically connects the discharge unit and the capacitor when the constant voltage output by the constant voltage output unit is applied via the signal input terminal, and cuts off the electrical connection between the discharge unit and the capacitor when the constant voltage output by the constant voltage output unit is not applied.

6. The motor drive device according to claim 5, characterized in that: The power failure detection switch includes a photocoupler having a light emitting element that emits light by a current output from the control power supply and a light receiving element. When the light receiving element receives light from the light emitting element, current is passed between the input terminal and the output terminal.

7. The motor drive device according to claim 5, characterized in that: The power failure detection switch includes the following A-contact relay: when the control power supply outputs current, the input terminal and the output terminal are energized, and when the control power supply does not output current, the input terminal and the output terminal are not energized.

8. The motor drive device according to claim 5, characterized in that: The power failure detection switch includes a B-contact relay in which no current is supplied between the input terminal and the output terminal when current is output from the control power supply, and current is supplied between the input terminal and the output terminal when current is not output from the control power supply.

9. The motor drive device according to any one of claims 5 to 8, characterized in that: The constant voltage output unit includes a Zener diode connected such that the high potential side terminal serves as a cathode and the low potential side terminal serves as an anode.

10. A motor drive device comprising: A converter, which converts AC power from an AC power source into DC power and outputs it to a DC link; A capacitor, which is arranged in the DC link; An inverter that converts the DC power in the DC link into AC power for driving the motor and then outputs the AC power; a discharge circuit provided in parallel with the capacitor in the DC link, the discharge circuit selectively switching between a discharge operation and a non-discharge operation, the discharge operation being an operation of electrically connecting the discharge circuit to the capacitor to discharge the DC power in the DC link, and the non-discharge operation being an operation of disconnecting the electrical connection between the discharge circuit and the capacitor; a discharge circuit driving unit that performs switching driving between the discharge operation and the non-discharge operation of the discharge circuit, and uses the DC power in the DC link as driving power for the switching driving; A control unit that controls the inverter; as well as a control power supply that generates power for operating the control unit based on the AC power from the AC power supply, Wherein, the discharge circuit has: a discharge unit; and a discharge switching switch that switches between electrical connection between the discharge unit and the capacitor and disconnection of the electrical connection between the discharge unit and the capacitor according to switching drive of the discharge circuit driving unit, The discharge circuit driving unit comprises: a current limiting resistor having a first terminal connected to the positive terminal of the capacitor and a second terminal for outputting a current input from the first terminal; a power failure detection switch having an input terminal connected to the second terminal of the current limiting resistor and an output terminal for outputting a current input to the input terminal when power is supplied, wherein when the current is output from the control power supply, no power is supplied between the input terminal and the output terminal, and when the current is not output from the control power supply, power is supplied between the input terminal and the output terminal; and a constant voltage output unit having a high potential side terminal connected to the output terminal of the power failure detection switch and a low potential side terminal connected to the negative side terminal of the capacitor, wherein the constant voltage output unit outputs a predetermined constant voltage between the high potential side terminal and the low potential side terminal, In which, the discharge switching switch of the discharge circuit has a signal input terminal connected to the high potential side terminal of the constant voltage output unit, and the discharge switching switch electrically connects the discharge unit and the capacitor when the constant voltage output by the constant voltage output unit is applied via the signal input terminal, and cuts off the electrical connection between the discharge unit and the capacitor when the constant voltage output by the constant voltage output unit is not applied.

11. The motor drive device according to claim 10, characterized in that: The constant voltage output unit includes a Zener diode connected such that the high potential side terminal serves as a cathode and the low potential side terminal serves as an anode.

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