JP2015216746A - Overvoltage protection circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a motor driving apparatus including compact and low-cost overvoltage protection means for protecting an apparatus from momentary overvoltage.SOLUTION: In an overvoltage protection circuit 50, a control unit 40 turns off transistors Q3a to Q5b of both upper and lower arms at occurrence of overvoltage and executes overvoltage control for protecting switching elements from breakage. If standby control is executed during execution of the overvoltage control, voltage supply from a drive circuit power supply Vc is stopped, so that the switching elements cannot be surely held on an off state and the switching elements cannot be protected from overvoltage. Thereby, standby control is not performed during execution of the overvoltage control. Namely, the switching elements can be protected from overvoltage by inhibiting off of a first switch 11.

Description

  The present invention relates to an overvoltage protection circuit.

  In a device that obtains a DC voltage by rectifying an AC voltage, the DC voltage varies according to the AC voltage. In particular, a device used in an area where the power supply voltage is likely to fluctuate may cause a failure of the device depending on a countermeasure against a voltage increase. Therefore, overvoltage protection means as disclosed in Patent Document 1 (Japanese Patent Laid-Open No. 2007-166815) is provided. In this overvoltage protection means, the input transformer is a transformer with a load tap changer, and when the voltage exceeding the threshold is input to the inverter over a predetermined time, the tap of the transformer with the load tap changer is lowered. Switched to the side.

  However, although the transformer with a load tap changer as described above is suitable for a large-scale electric facility, it is not easy to apply to an inverter-controlled motor drive device such as a home appliance.

  In addition, the time required for the power supply voltage to become excessive is extremely short, and tap switching as described above takes too much time, so that it is difficult to reliably protect the device. Furthermore, a semiconductor element such as a semiconductor element that has a short time to withstand overvoltage cannot be protected by being interrupted by a relay. However, increasing the withstand voltage of a semiconductor element or the like only for an instantaneous excessive voltage leads to an increase in cost and size.

  Furthermore, since an excessive voltage may occur not only during operation of the inverter but also during standby, even when power supply to the inverter drive circuit is stopped to reduce power consumption during standby, It is necessary to assume an excessive voltage.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a small-sized and low-cost overvoltage protection circuit capable of protecting a device from a momentary excessive voltage and reducing power consumption during standby.

  The overvoltage protection circuit according to the first aspect of the present invention is configured by each of a plurality of upper and lower arms connecting two switching elements in series, and outputs a voltage from each of the connection points formed thereby to a corresponding load. An overvoltage protection circuit for a power conversion device includes a voltage detection unit, a drive circuit unit, a drive circuit power supply, a first switch, and a control unit. The voltage detector detects the voltage of the power supply. The drive circuit generates a voltage for turning on and off the switching element. The drive circuit power supply supplies a power supply voltage to the drive circuit. The first switch opens and closes a drive power supply line connecting the drive circuit power supply and the drive circuit. The control unit controls the switching element via the drive circuit. Further, the control unit includes over-voltage control and standby control as control modes. The overvoltage control is control that turns off both switching elements of the upper and lower arms when the detection value of the voltage detection unit exceeds a predetermined threshold value. The standby control is a control for electrically disconnecting the drive power supply line via the first switch when both the switching elements of the upper and lower arms are off. Further, the control unit does not perform the standby control while executing the overvoltage control.

  In this overvoltage protection circuit, in the overvoltage control, when the overvoltage occurs, both switching elements of the upper and lower arms are turned off so that the overvoltage is divided across the two switching elements connected in series. Since the overvoltage applied to the element is reduced to half that when either one is operating, the switching element can be protected from destruction until the DC voltage is about twice the breakdown voltage of one switching element.

  On the other hand, if the power supply of the drive circuit is turned off during standby control during the overvoltage control, the switching element cannot be reliably turned off, and the switching element cannot be protected from overvoltage. While the control is being executed, the switching element is protected from overvoltage by not performing the standby control.

  An overvoltage protection circuit according to a second aspect of the present invention is the overvoltage protection circuit according to the first aspect, and further includes a second switch. The second switch opens and closes a main power line connecting the power source and a circuit including the upper and lower arms. The control unit electrically disconnects the main power supply line via the second switch when the time during which the detection value of the voltage detection unit exceeds the predetermined threshold becomes longer than the predetermined time.

  In this overvoltage protection circuit, when the overvoltage is prolonged, the main power supply line is electrically disconnected so that the main power supply voltage is not applied to the switching element, and the switching element is reliably protected from the overvoltage.

  An overvoltage protection circuit according to a third aspect of the present invention is the overvoltage protection circuit according to the first aspect, and further includes a second switch. The second switch opens and closes a main power line connecting the power source and a circuit including the upper and lower arms. The control unit electrically disconnects the main power supply line via the second switch when the detection value of the voltage detection unit exceeds a predetermined second threshold value.

  In this overvoltage protection circuit, when the overvoltage value increases, the main power supply line is electrically disconnected so that the main power supply voltage is not applied to the switching element, and the switching element is reliably protected from the overvoltage.

  An overvoltage protection circuit according to a fourth aspect of the present invention is configured by each of a plurality of upper and lower arms connecting two switching elements in series, and outputs a voltage from each of the connection points formed thereby to a corresponding load. An overvoltage protection circuit for a power conversion device includes a voltage detection unit, a drive circuit, a drive circuit power supply, a first switch, a second switch, and a control unit. The voltage detector detects the voltage of the power supply. The drive circuit generates a voltage for turning on and off the switching element. The drive circuit power supply supplies a power supply voltage to the drive circuit. The first switch opens and closes a drive power supply line connecting the drive circuit power supply and the drive circuit. The second switch opens and closes a main power line connecting the power source and a circuit including the upper and lower arms. The control unit controls the switching element via the drive circuit. Further, the control unit includes over-voltage control and standby control as control modes. The overvoltage control is control that turns off both switching elements of the upper and lower arms when the detection value of the voltage detection unit exceeds a predetermined threshold value. The standby control is a control for electrically disconnecting the drive power supply line via the first switch when both the switching elements of the upper and lower arms are off. Further, the control unit electrically disconnects the main power supply line via the second switch when performing the standby control while executing the overvoltage control.

  In this overvoltage protection circuit, in the overvoltage control, when the overvoltage occurs, both switching elements of the upper and lower arms are turned off so that the overvoltage is divided across the two switching elements connected in series. Since the overvoltage applied to the element is reduced to half that when either one is operating, the switching element can be protected from destruction until the DC voltage is about twice the breakdown voltage of one switching element.

  On the other hand, if the power supply of the drive circuit is turned off during standby control during the overvoltage control, the switching element cannot be reliably turned off, and the switching element cannot be protected from overvoltage. When performing standby control during execution of control, the main power supply line is electrically disconnected to prevent the main power supply voltage from being applied to the switching element, thereby protecting the switching element from overvoltage.

  An overvoltage protection circuit according to a fifth aspect of the present invention is the overvoltage protection circuit according to the fourth aspect, wherein the control unit disconnects the drive power supply line after disconnecting the main power supply line.

  In this overvoltage protection circuit, for example, when the main power supply voltage becomes overvoltage immediately after the drive power supply line is cut first and the OFF state of the switching element becomes unstable, both the upper and lower arm switching elements are turned off. By doing so, there is a possibility that the action of “dividing the excessive voltage across each of the two switching elements connected in series” may not be exhibited. Therefore, the switching element is reliably protected from overvoltage by cutting the main power supply line first.

  An overvoltage protection circuit according to a sixth aspect of the present invention is the overvoltage protection circuit according to any one of the first to fifth aspects, wherein the power supply is a DC power supply.

  In this overvoltage protection circuit, for example, when a semiconductor switch is used for circuit interruption, the switch for turning on and off the alternating current needs bidirectionality, but the switch arranged on the downstream side of the DC power source is a one-way switch. Therefore, the cost of the switch can be reduced.

  An overvoltage protection circuit according to a seventh aspect of the present invention is the overvoltage protection circuit according to any one of the first to fifth aspects, and the power source is an AC power source.

  In this overvoltage protection circuit, even if the supply voltage from the AC power supply is an excessive voltage, the inverter switching element can be protected in a short time by the overvoltage control. Therefore, it is not necessary to design the equipment with a high voltage rating only for protection from excessive voltage for a short time, and it is reasonable

  In the overvoltage protection circuit according to the first aspect of the present invention, in the overvoltage control, the overvoltage is applied to both ends of each of the two switching elements connected in series by turning off both switching elements of the upper and lower arms when an overvoltage occurs. The overvoltage applied to one switching element is reduced to half that when either one was operating, so the switching element is destroyed until the DC voltage is about twice the breakdown voltage of one switching element. Can be protected from.

  On the other hand, if the power supply of the drive circuit is turned off during standby control during the overvoltage control, the switching element cannot be reliably turned off, and the switching element cannot be protected from overvoltage. While the control is being executed, the switching element is protected from overvoltage by not performing the standby control.

  In the overvoltage protection circuit according to the second aspect of the present invention, when the overvoltage is prolonged, the main power supply line is electrically disconnected so that the main power supply voltage is not applied to the switching element, and the switching element is protected from the overvoltage. Secure protection.

  In the overvoltage protection circuit according to the third aspect of the present invention, when the overvoltage value increases, the main power supply line is electrically disconnected so that the main power supply voltage is not applied to the switching element, and the switching element is protected from the overvoltage. Secure protection.

  In the overvoltage protection circuit according to the fourth aspect of the present invention, in the overvoltage control, the overvoltage is applied to both ends of each of the two switching elements connected in series by turning off both the switching elements of the upper and lower arms when the overvoltage occurs. The overvoltage applied to one switching element is reduced to half that when either one was operating, so the switching element is destroyed until the DC voltage is about twice the breakdown voltage of one switching element. Can be protected from.

  On the other hand, if the power supply of the drive circuit is turned off during standby control during the overvoltage control, the switching element cannot be reliably turned off, and the switching element cannot be protected from overvoltage. When performing standby control during execution of control, the main power supply line is electrically disconnected to prevent the main power supply voltage from being applied to the switching element, thereby protecting the switching element from overvoltage.

  In the overvoltage protection circuit according to the fifth aspect of the present invention, for example, when the drive power supply line is cut first, and the main power supply becomes overvoltage immediately after the switching element becomes unstable, By turning off both switching elements, there is a possibility that the action of “dividing an excessive voltage across each of the two switching elements connected in series” may not be exhibited. Therefore, the switching element is reliably protected from overvoltage by cutting the main power supply line first.

  In the overvoltage protection circuit according to the sixth aspect of the present invention, for example, when a semiconductor switch is used for circuit interruption, the switch for turning on and off the alternating current requires bidirectionality, but is disposed downstream of the DC power supply. The switch can be a one-way switch, so that the cost of the switch can be reduced.

  In the overvoltage protection circuit according to the seventh aspect of the present invention, even when the supply voltage from the AC power supply is an excessive voltage, the switching element of the inverter can be protected in a short time by the overvoltage control. Therefore, it is not necessary to design the equipment with a high voltage rating only for protection from excessive voltage for a short time, and it is reasonable

1 is a block diagram showing an overall configuration of a system in which an overvoltage protection circuit according to a first embodiment of the present invention is employed, and a circuit configuration of a motor drive device that uses the system. The figure which shows how to apply the voltage to an up-and-down arm at the time of operation | movement of a motor drive device. The figure which shows how to apply the voltage to an up-and-down arm at the time of a motor drive device stopping. Control flow of overvoltage control in the first embodiment Control flow of standby control in the first embodiment The block diagram which shows the whole structure of the system by which the overvoltage protection circuit which concerns on the modification of 1st Embodiment is employ | adopted, and the circuit structure of the motor drive device using the system. The circuit diagram of the voltage detection part in the modification of 1st Embodiment. The block diagram which shows the whole structure of the system by which the overvoltage protection circuit which concerns on 2nd Embodiment of this invention is employ | adopted, and the internal structure of the motor drive device using the system. The control flow of standby control in 2nd Embodiment. The control flow of standby control in the 1st modification of 2nd Embodiment. The control flow of standby control in the 2nd modification of 2nd Embodiment. The block diagram which shows the whole structure of the system by which the overvoltage protection circuit which concerns on the 3rd modification of 2nd Embodiment is employ | adopted, and the internal structure of the motor drive unit using the system.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. The following embodiments are specific examples of the present invention and do not limit the technical scope of the present invention.

<First Embodiment>
(1) Overview FIG. 1 is a block diagram showing an overall configuration of a system 100 in which an overvoltage protection circuit 50 according to a first embodiment of the present invention is employed, and an internal configuration of a motor driving apparatus 10 that uses the system 100. FIG. In FIG. 1, a system 100 includes a motor driving device 10 and a motor 51. The overvoltage protection circuit 50 includes a voltage detection unit 23, the first switch 11, and a control unit 40.

(1-1) Motor 51
The motor 51 is a three-phase brushless DC motor, and includes a stator 52 and a rotor 53. The stator 52 includes U-phase, V-phase, and W-phase drive coils Lu, Lv, and Lw that are star-connected. One ends of the drive coils Lu, Lv, and Lw are connected to drive coil terminals TU, TV, and TW of U-phase, V-phase, and W-phase wirings extending from the inverter 25, respectively. The other ends of the drive coils Lu, Lv, and Lw are connected to each other as a terminal TN. These three-phase drive coils Lu, Lv, and Lw generate an induced voltage according to the rotational speed and the position of the rotor 53 as the rotor 53 rotates.

  The rotor 53 includes a plurality of permanent magnets including N poles and S poles, and rotates about the rotation axis with respect to the stator 52.

  The motor 51 is, for example, a compressor motor or a fan motor of a heat pump type air conditioner.

(1-2) Motor drive device 10
As shown in FIG. 1, the motor driving device 10 includes a rectifying unit 21, a smoothing capacitor 22, a voltage detecting unit 23, a current detecting unit 24, an inverter 25 (power converter), a gate driving circuit 26, And a control unit 40. These may be mounted on, for example, one printed board.

(2) Detailed configuration of motor drive device (2-1) Rectifier 21
The rectifying unit 21 is configured in a bridge shape by four diodes D1a, D1b, D2a, and D2b. Specifically, the diodes D1a and D1b and D2a and D2b are respectively connected in series. The cathode terminals of the diodes D1a and D2a are both connected to the plus side terminal of the smoothing capacitor 22 and function as the positive side output terminal of the rectifying unit 21. The anode terminals of the diodes D1b and D2b are both connected to the negative side terminal of the smoothing capacitor 22 and function as the negative side output terminal of the rectifying unit 21.

  A connection point between the diode D1a and the diode D1b is connected to one pole of the commercial power supply 91. A connection point between the diode D2a and the diode D2b is connected to the other pole of the commercial power supply 91. The rectifying unit 21 rectifies the AC voltage output from the commercial power supply 91 to generate a DC power supply, and supplies this to the smoothing capacitor 22.

(2-2) Smoothing capacitor 22
The smoothing capacitor 22 has one end connected to the positive output terminal of the rectifying unit 21 and the other end connected to the negative output terminal of the rectifying unit 21. The smoothing capacitor 22 smoothes the voltage rectified by the rectifying unit 21. Hereinafter, for the convenience of explanation, the voltage after smoothing by the smoothing capacitor 22 is referred to as a DC voltage Vdc.

  The DC voltage Vdc is applied to the inverter 25 connected to the output side of the smoothing capacitor 22. That is, the rectifying unit 21 and the smoothing capacitor 22 constitute a power supply unit 20 for the inverter 25.

  In addition, as a kind of capacitor | condenser, although an electrolytic capacitor, a film capacitor, a tantalum capacitor etc. are mentioned, a film capacitor is employ | adopted as the smoothing capacitor 22 in this embodiment.

(2-3) Voltage detection unit 23
The voltage detector 23 is connected to the output side of the smoothing capacitor 22 and detects the voltage across the smoothing capacitor 22, that is, the value of the DC voltage Vdc. For example, the voltage detection unit 23 is configured such that two resistors connected in series with each other are connected in parallel to the smoothing capacitor 22 and the DC voltage Vdc is divided. The voltage value at the connection point between the two resistors is input to the control unit 40.

(2-4) Current detection unit 24
The current detection unit 24 is connected between the smoothing capacitor 22 and the inverter 25 and connected to the negative output terminal side of the smoothing capacitor 22. The current detection unit 24 detects the motor current Im flowing through the motor 51 after the motor 51 is started as a total value of currents for three phases.

  The current detection unit 24 may be configured by, for example, an amplifier circuit using a shunt resistor and an operational amplifier that amplifies the voltage across the resistor. The motor current detected by the current detection unit 24 is input to the control unit 40.

(2-5) Inverter 25
In the inverter 25, three upper and lower arms corresponding to the U-phase, V-phase, and W-phase drive coils Lu, Lv, and Lw of the motor 51 are connected in parallel to each other and to the output side of the smoothing capacitor 22.

  In FIG. 1, an inverter 25 includes a plurality of IGBTs (insulated gate bipolar transistors, hereinafter simply referred to as transistors) Q3a, Q3b, Q4a, Q4b, Q5a, Q5b and a plurality of free-wheeling diodes D3a, D3b, D4a, D4b, D5a and D5b are included.

  Transistors Q3a and Q3b, Q4a and Q4b, Q5a and Q5b are connected to each other in series to form each upper and lower arm, and the corresponding phase from each of connection points NU, NV, and NW formed thereby. Output lines extend toward the drive coils Lu, Lv, and Lw.

  The diodes D3a to D5b are connected in parallel to the transistors Q3a to Q5b so that the collector terminal of the transistor and the cathode terminal of the diode are connected, and the emitter terminal of the transistor and the anode terminal of the diode are connected. Each of these transistors and diodes connected in parallel constitutes a switching element.

  The inverter 25 is applied with the DC voltage Vdc from the smoothing capacitor 22 and the transistors Q3a to Q5b are turned on and off at the timing instructed by the gate drive circuit 26, whereby the drive voltages SU, SV and SW are generated. The drive voltages SU, SV, SW are output to the drive coils Lu, Lv, Lw of the motor 51 from the connection points NU, NV, NW of the transistors Q3a and Q3b, Q4a and Q4b, and Q5a and Q5b.

  In addition, although the inverter 25 of this embodiment is a voltage source inverter, it is not limited to it, A current source inverter may be sufficient.

(2-6) Gate drive circuit 26
The gate drive circuit 26 changes the on / off states of the transistors Q3a to Q5b of the inverter 25 based on the command voltage Vpwm from the control unit 40. Specifically, the gate drive circuit 26 includes the transistors Q3a to Q5b so that pulsed drive voltages SU, SV, and SW having a duty determined by the control unit 40 are output from the inverter 25 to the motor 51. Gate control voltages Gu, Gx, Gv, Gy, Gw, and Gz to be applied to the gate are generated. The generated gate control voltages Gu, Gx, Gv, Gy, Gw, Gz are applied to the gate terminals of the respective transistors Q3a to Q5b.

(2-7) Control unit 40
The control unit 40 is connected to the voltage detection unit 23, the current detection unit 24, and the gate drive circuit 26. In the present embodiment, the control unit 40 drives the motor 51 by a rotor position sensorless method. In addition, since it is not limited to a rotor position sensorless system, you may carry out by a sensor system.

  The rotor position sensorless method uses various parameters indicating the characteristics of the motor 51, the detection result of the voltage detection unit 23 after the motor 51 is started, the detection result of the current detection unit 24, a predetermined mathematical model related to the control of the motor 51, and the like. Thus, the rotor position and the rotational speed are estimated, the PI control for the rotational speed, the PI control for the motor current, and the like are driven. Examples of various parameters indicating the characteristics of the motor 51 include the winding resistance, inductance component, induced voltage, and number of poles of the motor 51 used. Since there are many patent documents regarding the rotor position sensorless control, refer to them for details (for example, JP 2013-17289 A).

  The control unit 40 also monitors the detection value of the voltage detection unit 23, and performs protection control to turn off the transistors Q3a to Q5b when the detection value of the voltage detection unit 23 exceeds a predetermined threshold value.

(2-8) First switch 11
The first switch 11 opens and closes a drive power supply line 803 that connects the drive circuit power supply Vc and the gate drive circuit 26. Here, opening and closing the drive power supply line 803 means making the drive power supply line 803 conductive or interrupted to make it nonconductive.

  The first switch 11 closes the drive power supply line 803 when the standby control is not performed in the normal state, that is, keeps the conductive state. On the other hand, during standby control, the first switch 11 is turned off and the drive power supply line 803 is shut off.

  The first switch 11 cuts off the drive power supply line 803 and stops the voltage supply to the gate drive circuit 26, thereby eliminating unnecessary power consumption. Since the first switch 11 does not require high speed, a relay circuit is employed.

  As shown in FIG. 1, the first switch 11 includes a relay contact 11a for opening and closing the drive power line 803, a relay coil 11b for operating the relay contact 11a, and a transistor 11c for energizing and de-energizing the relay coil 11b. Including. One end of the relay coil 11b is connected to the positive electrode of the power supply Vb, and the other end is connected to the collector side of the transistor 11c. The controller 40 switches between the presence and absence of the base current of the transistor 11c, turns on and off the collector and the emitter, and energizes and de-energizes the relay coil 11b.

(3) Operation of Motor Drive Device 10 Hereinafter, the operation of the motor drive device 10 will be described. In FIG. 1, the control unit 40 outputs a waveform to the gate drive circuit 26 and controls the waveform output state to drive the motor 51 at a predetermined rotational speed.

  FIG. 2A is a diagram illustrating how voltage is applied to the upper and lower arms during operation of the motor drive device 10, and FIG. 2B is a diagram illustrating how voltage is applied to the upper and lower arms when the motor drive device 10 is stopped.

  As shown in FIG. 2A, during operation, the upper arm transistor Q3a corresponding to the drive coil Lu, the lower arm transistor Q4b corresponding to the drive coil Lv, and the lower arm transistor Q5b corresponding to the drive coil Lw are turned on. The DC voltage Vdc is applied to the switching elements (transistors Q3b, Q4a, Q5a, diodes D3b, D4a, D5a) in which the upper and lower arms are off.

  At this time, when the DC voltage Vdc becomes an excessive voltage, the excessive voltage is applied to the transistor and the diode of the switching element that is turned off. When the element breakdown voltage of one switching element (transistors Q3a to Q5b and diodes D3a to D5b) is Vr, the transistors Q3a to Q5b or the diodes D3a to D5b of the switching element are destroyed when the DC voltage Vdc> the element breakdown voltage Vr. There is a high possibility of being.

  Therefore, when the control unit 40 determines that the detection value of the voltage detection unit 23 has exceeded a predetermined threshold value, the control unit 40 performs over-voltage control to turn off both the transistors Q3a, Q3b, Q4a, Q4b, Q5a, and Q5b of the upper and lower arms. Do.

(3-1) Overvoltage Control FIG. 3 is a control flow of overvoltage control in the first embodiment. In FIG. 3, the control unit 40 confirms that power is applied in step S1, and proceeds to step S2. Next, the control unit 40 detects the DC voltage Vdc via the voltage detection unit 23 in step S2.

  Next, in step S3, the control unit 40 determines whether or not the DC voltage Vdc has reached Vdcmax, which is an upper limit voltage that can be applied to the inverter 25. When Vdc ≧ Vdcmax, the control unit 40 proceeds to step S4, and Vdc ≧ Vdcmax. If not, the process returns to step S2.

  Next, in step S4, the controller 40 turns off both the transistors Q3a, Q3b, Q4a, Q4b, Q5a, and Q5b of all the upper and lower arms. Thereby, as shown in FIG. 2B, the excessive voltage is applied to each of the two switching elements (transistors Q3a, Q3b, Q4a, Q4b, Q5a, Q5b, diodes D3a, D3b, D4a, D4b, D5a, D5b) connected in series. Divided at both ends.

  For example, the divided voltage value V1 is applied to both ends of the upper arm switching elements (transistors Q3a, Q4a, Q5a, diodes D3a, D4a, D5a), and the lower arm switching elements (transistors Q3b, Q4b, Q5b, diodes D3b, D4b). , D5b) is applied with a partial pressure value V2. Ideally, V1 = V2 if the impedance of each switching element is equal, so that the overvoltage applied to one switching element is reduced to half that when either one is operating, and each switching element is destroyed. Can be protected.

  Next, in step S5, the control unit 40 determines whether or not the DC voltage Vdc is lower than the voltage Vdcret that may be released from over-voltage control. If Vdc <Vdcret, the control unit 40 proceeds to step S6, and Vdc <Vdcret. If not, continue the determination.

  Then, the control unit 40 receives Vdc <Vdcret, and cancels the overvoltage control in step S6.

(3-2) Standby Control FIG. 4 is a control flow of standby control in the first embodiment. In FIG. 4, the control unit 40 determines whether or not there is a standby control command in step S11. If there is a standby control command, the control unit 40 proceeds to step S12.

  Next, in step S12, the control unit 40 determines whether or not the overvoltage control is being executed. When the overvoltage control is being executed, the control unit 40 proceeds to step S13. When the overvoltage control is not being executed, the control unit 40 performs the step. Fly to S15.

  Next, the control part 40 refuses execution of standby control in step S13. Specifically, the first switch 11 is kept on. If the first switch 11 is turned off during overvoltage control, the minimum voltage required to turn off the transistors Q3a, Q3b, Q4a, Q4b, Q5a, and Q5b is 0. One transistor may turn on due to unstable operation, and an overvoltage may be applied to the other transistor that is turned off.

  Then, two switching elements (transistors Q3a, Q3b, Q4a, Q4b, Q5a, Q5b, diodes D3a, D3b, D4a, D4b, D5a and D5b) cannot achieve the purpose of overvoltage control, which divides the voltage at both ends and halves the overvoltage applied to one switching element. Therefore, the first switch 11 is kept on.

  Next, in step S14, the control unit 40 determines whether or not the overvoltage control is released. When the overvoltage control is released, the control unit 40 proceeds to step S15, and when the overvoltage control is not released, Continue judgment.

  Next, the control part 40 receives the determination of control release at the time of overvoltage, and turns off the 1st switch 11 in step S15. This is because the control at the time of overvoltage is released, so that it is possible to turn off the first switch 11 and suppress standby power consumption in the gate drive circuit 26. Even when it is determined in step S12 that the overvoltage control is not being executed, the first switch 11 is turned off in step S15 to suppress standby power consumption.

  Then, in step S16, the control unit 40 determines whether or not there is a standby control release command. If there is a standby control release command, the control unit 40 ends the standby control.

  As described above, in the present embodiment, the voltage detection unit 23, the first switch 11, and the control unit 40 constitute the overvoltage protection circuit 50.

(4) Features of the first embodiment (4-1)
In the overvoltage protection circuit 50, when the control unit 40 turns off the transistors Q3a to Q5b of the upper and lower arms when an overvoltage is generated, the overvoltage is divided into both ends of each of the two switching elements connected in series. Since the excessive voltage applied to the two switching elements (transistors Q3a to Q5b, diodes D3a to D5b) is reduced to half that when either one is operating, the switching elements can be protected from destruction.

(4-2)
Further, if standby control is executed during overvoltage control, voltage supply from the drive circuit power supply Vc is stopped, the switching element cannot be reliably turned off, and the switching element cannot be protected from overvoltage. Therefore, the switching element is protected from overvoltage by not performing standby control during execution of the overvoltage control, that is, by not turning off the first switch 11.

(5) Modified Example FIG. 5 shows an overall configuration of a system 100 in which an overvoltage protection circuit 50 according to a modified example of the first embodiment is adopted, and an internal configuration of a motor driving apparatus 10 that uses the system 100. It is a block diagram. In FIG. 5, the inverter 25 is supplied with power from the power supply unit 20 via a pair of power supply lines 801 and 802. A part of the overvoltage protection circuit 50 is connected between the commercial power supply 91 and the power supply unit 20, and the other part is connected between the power supply unit 20 and the inverter 25.

  The overvoltage protection circuit 50 includes a voltage detection unit 33, the first switch 11, and a control unit 40.

  The difference between the overvoltage protection circuit 50 in the modification and the overvoltage protection circuit in the first embodiment already described is that the voltage detection unit, which is a component of the overvoltage protection circuit 50, is between the commercial power supply 91 and the power supply unit 20. Is provided.

  In view of the fact that the voltage detection unit is replaced from the direct current specification to the alternating current specification, a voltage detection unit 33 is employed instead of the voltage detection unit 23 of the first embodiment. Therefore, only the voltage detection unit 33 will be described here.

(5-1) Voltage detection unit 33
The voltage detection unit 33 is configured by an AC voltage detection circuit. There are various AC voltage detection circuits, and they are appropriately adopted depending on use conditions. For example, FIG. 6 is a circuit diagram of a general voltage detection unit 33. In FIG. 6, the voltage detection unit 33 includes a transformer circuit 331 and a converter circuit 332.

  The transformer circuit 331 is located on the input side and includes a primary winding 331a and a secondary winding 331b.

  The converter circuit 332 is a circuit in which a rectifying unit 332a formed of a rectifying diode and a smoothing capacitor 332b are connected in parallel.

  In the voltage detection unit 33, when an AC voltage is applied to the transformer circuit 331, the AC voltage is transformed by the transformer circuit 331. Then, the voltage across the secondary winding 331 b is input to the converter circuit 332.

  The transformed AC voltage input to the converter circuit 332 is converted into a DC voltage by the rectifying unit 332a and smoothed by the smoothing capacitor 332b. This smoothed DC voltage is input to the control unit 40. That is, a DC voltage corresponding to the voltage applied to the primary winding 331a is input to the control unit 40.

(5-2) Operation of Motor Drive Device 10 In a modified example, the control flow at the time of overvoltage control is performed by replacing the DC voltage Vdc of the control flow of overvoltage control described in FIG. 3 with the AC voltage Vac of the commercial power supply 91. In place of Vdcmax in S2, Vacmax, which is the upper limit voltage that AC voltage Vac can be applied to the device including inverter 25, is set. Further, in place of Vdcret in step S5, AC voltage Vacret that may cancel overvoltage control is set. As a result, overvoltage control and standby control equivalent to those of the first embodiment can be realized.

Second Embodiment
(1) Overview FIG. 7 is a block diagram showing an overall configuration of a system 100 in which an overvoltage protection circuit 50 according to a second embodiment of the present invention is employed, and an internal configuration of a motor drive device 10 that uses the system 100. FIG.

  In FIG. 7, the overvoltage protection circuit 50 according to the second embodiment has a configuration in which a second switch 12 is added to the overvoltage protection circuit 50 in the first embodiment shown in FIG. Therefore, the second switch 12 will be described here, and the other elements are the same as those in the first embodiment.

(2) Detailed configuration of motor drive device (2-1) Second switch 12
The second switch 12 opens and closes the power line 801. Here, opening and closing the power supply line 801 is to turn the power supply line 801 on or off to make it non-conductive.

  The second switch 12 normally closes the power supply line 801, that is, keeps it conductive. On the other hand, when the power supply to the gate drive circuit 26 is stopped to suppress power consumption during standby, the transistors Q3a to Q5b cannot be reliably turned off. If an overvoltage occurs at such time, the switching element cannot be protected from the overvoltage.

  The role of the second switch 12 is to cut off the power supply line 801 so that the main power supply voltage (DC voltage Vdc) is not applied to the switching elements of the upper and lower arms. Thereby, the switching element can be protected from overvoltage.

  Since the second switch 12 is required to have high speed, a semiconductor switch is employed in this embodiment.

  As shown in FIG. 7, the first switch 12 includes a photocoupler 12a, a drive circuit 12b, and a transistor 12c with a freewheeling diode. The photocoupler 12a includes a light emitting diode 121 and a phototransistor 122.

  The light emitting diode 121 of the photocoupler 12a is connected to the input side (between A1 and A2) of the first switch 12. The anode A1 of the light emitting diode 121 is connected to the power source Vb via the resistor R1. The cathode A2 of the light emitting diode 121 is connected to the control unit 40 via a signal line. The phototransistor 122 is connected between the drive circuit 11b and the drive circuit GND.

  A transistor 12c is provided on the output side of the first switch 12 (between B1 and B2). The emitter B1 of the transistor 12c is connected to the high potential side of the inverter 25. The collector B2 of the transistor 12c is connected to the high potential side of the smoothing capacitor 22.

  The control signal of the control unit 40 is input to the drive circuit 12b via the photocoupler 12a. A driving power supply (not shown) is connected to the driving circuit 12b. When the control unit 40 turns on the signal line of the light emitting diode 121, the light emitting diode 121 emits light and the phototransistor 122 is turned on. While the phototransistor 122 is conducting, a driving signal is output from the driving circuit 12b to the base of the transistor 12c, and the collector B2 and the emitter B1 of the transistor 12c are conducted.

  Conversely, when the control unit 40 turns off the signal line of the light emitting diode 121, the light emitting diode 121 does not emit light, and thus the phototransistor 122 does not conduct. While the phototransistor 122 is not conductive, the collector B2 and the emitter B1 of the transistor 12c are not conductive.

(3) Operation of Motor Drive Device (3-1) Overvoltage Control Since the overvoltage control in the second embodiment employs the overvoltage control in the first embodiment, description thereof is omitted here.

(3-2) Standby Control FIG. 8 is a control flow of standby control in the second embodiment. In FIG. 8, the control unit 40 determines whether or not there is a standby control command in step S21. If there is a standby control command, the control unit 40 proceeds to step S22.

  Next, in step S22, the control unit 40 determines whether or not the overvoltage control is being executed. When the overvoltage control is being executed, the control unit 40 proceeds to step S23. When the overvoltage control is not being executed, the control unit 40 performs the step. Fly to S24.

  Next, in step S <b> 23, the control unit 40 turns off the second switch 12 to cut off the power supply line 801 so that the main power supply voltage (DC voltage Vdc) is not applied to the inverter 25. If the first switch 11 is first turned off during the overvoltage control, the minimum voltage required to turn off the transistors Q3a, Q3b, Q4a, Q4b, Q5a, and Q5b cannot be secured. This is because one transistor of the arm is turned on due to unstable operation, and an overvoltage is applied to the other transistor that is turned off.

  Next, the control unit 40 turns off the first switch 11 in step S24. This is because the DC voltage Vdc is no longer applied to the inverter 25, so that it is possible to turn off the first switch 11 and suppress standby power consumption in the gate drive circuit 26. Even when it is determined in step S22 that the overvoltage control is not being executed, the first switch 11 is turned off in step S24 to suppress standby power consumption.

  Then, in step S25, the control unit 40 determines whether or not there is a standby control release command. If there is a standby control release command, the control unit 40 ends the standby control.

  As described above, in this embodiment, the voltage detection unit 23, the first switch 11, the second switch 12, and the control unit 40 constitute the overvoltage protection circuit 50.

(4) Features of the second embodiment (4-1)
In the overvoltage protection circuit 50, when the control unit 40 turns off the transistors Q3a to Q5b of the upper and lower arms when an overvoltage is generated, the overvoltage is divided into both ends of each of the two switching elements connected in series. Since the excessive voltage applied to the two switching elements (transistors Q3a to Q5b, diodes D3a to D5b) is reduced to half that when either one is operating, the switching elements can be protected from destruction.

(4-2)
In addition, during overvoltage control, the control unit 40 electrically disconnects the power supply line 801 via the first switch 11 so that the DC voltage Vdc is not applied to each switching element of the upper and lower arms, and the switching element is overvoltaged. Protect from.

(4-3)
Further, the control unit 40 can eliminate the waste of power consumption in the gate drive circuit 26 by cutting off the drive power supply line 803 via the second switch 12.

(4-4)
Further, the control unit 40 disconnects the power supply line 801 first and then shuts off the drive power supply line 803, thereby reliably protecting the switching element from overvoltage. If the drive power supply line 803 is disconnected first, an overvoltage of the main power supply voltage (DC voltage Vdc) is passed through both ends of the switching element in which the OFF state becomes unstable. By turning off the power supply line 801, the power line 801 is cut first in order to prevent the effect of dividing the excessive voltage across the two switching elements connected in series.

(5) Modified Example In the second embodiment, the control unit 40 immediately turns off the second switch 12 and applies the voltage to the inverter 25 when the standby voltage control command is received during overvoltage control. The first switch 11 is turned off. However, the timing for turning off the second switch 12 may be determined by the magnitude of the overvoltage or the time during which the overvoltage is active.
(5-1) First Modification FIG. 9 is a control flow of standby control in a first modification of the second embodiment. In FIG. 9, the control unit 40 determines whether or not there is a standby control command in step S31. If there is a standby control command, the control unit 40 proceeds to step S32.

  Next, in step S32, the control unit 40 determines whether or not the overvoltage control is being executed. When the overvoltage control is being executed, the control unit 40 proceeds to step S33, and when the overvoltage control is not being executed, the control unit 40 performs the step. Fly to S35.

  Next, in step S33, the control unit 40 determines whether or not the elapsed time t from the start of overvoltage control has reached a predetermined time ts. When t ≧ ts, the control unit 40 proceeds to step S34 and does not satisfy t ≧ ts. If so, the determination is continued.

  Since the overvoltage control starts when the DC voltage Vdc reaches Vdcmax, which is the upper limit voltage that can be applied to the inverter 25, the state where Vdc ≧ Vdcmax continues beyond the predetermined time ts from that point in time. Since the inverter 25 and other devices are adversely affected, it is necessary to continuously monitor the time (ts) when Vdc ≧ Vdcmax.

  Next, in step S <b> 34, the control unit 40 turns off the second switch 12 to cut off the power supply line 801 so that the main power supply voltage (DC voltage Vdc) is not applied to the inverter 25. If the first switch 11 is first turned off during the overvoltage control, the minimum voltage required to turn off the transistors Q3a, Q3b, Q4a, Q4b, Q5a, and Q5b cannot be secured. This is because one transistor of the arm is turned on due to unstable operation, and an overvoltage is applied to the other transistor that is turned off.

  Next, the control unit 40 turns off the first switch 11 in step S35. This is because the DC voltage Vdc is no longer applied to the inverter 25, so that it is possible to turn off the first switch 11 and suppress standby power consumption in the gate drive circuit 26. Even when it is determined in step S32 that the overvoltage control is not being executed, the first switch 11 is turned off in step S35 to suppress standby power consumption.

  Then, in step S36, the control unit 40 determines whether or not there is a standby control release command. If there is a standby control release command, the control unit 40 ends the standby control.

As described above, when the overvoltage state is prolonged, the power supply line 801 is electrically disconnected so that the DC voltage Vdc that has become the overvoltage is not applied to the switching element, so that the switching element is reliably protected from the overvoltage. In addition to protection, the first switch 11 can be turned off to suppress standby power consumption.
(5-2) Second Modification FIG. 10 is a control flow of standby control in a second modification of the second embodiment. In FIG. 10, the control unit 40 determines whether or not there is a standby control command in step S41. If there is a standby control command, the control unit 40 proceeds to step S42.

  Next, in step S42, the control unit 40 determines whether or not the overvoltage control is being executed. When the overvoltage control is being executed, the control unit 40 proceeds to step S43, and when the overvoltage control is not being executed, the control unit 40 performs a step. Fly to S45.

  Next, in step S43, the control unit 40 determines whether or not the DC voltage Vdc has reached the second threshold value Vdclim. When Vdc ≧ Vdclim, the control unit 40 proceeds to step S44, and when Vdc ≧ Vdclim, the determination is made. Continue.

  The over-voltage control starts when the DC voltage Vdc reaches Vdcmax, which is the upper limit voltage that can be applied to the inverter 25. However, if the voltage rises suddenly, it will be seriously damaged, so that the limit can be avoided. It is necessary to monitor whether or not Vdc ≧ Vdclim after setting the voltage Vdclim.

  Next, in step S44, the control unit 40 turns off the second switch 12 to cut off the power supply line 801 so that the main power supply voltage (DC voltage Vdc) is not applied to the inverter 25. If the first switch 11 is first turned off during the overvoltage control, the minimum voltage required to turn off the transistors Q3a, Q3b, Q4a, Q4b, Q5a, and Q5b cannot be secured. This is because one transistor of the arm is turned on due to unstable operation, and an overvoltage is applied to the other transistor that is turned off.

  Next, the control unit 40 turns off the first switch 11 in step S45. This is because the DC voltage Vdc is no longer applied to the inverter 25, so that it is possible to turn off the first switch 11 and suppress standby power consumption in the gate drive circuit 26. Even when it is determined in step S42 that the overvoltage control is not being executed, the first switch 11 is turned off in step S45 to suppress standby power consumption.

  Then, the control unit 40 determines whether or not there is a standby control release command in step S46, and ends the standby control when there is a standby control release command.

  As described above, in this embodiment, the voltage detection unit 23, the first switch 11, the second switch 12, and the control unit 40 constitute the overvoltage protection circuit 50.

  As described above, when the DC voltage Vdc suddenly rises, the power supply line 801 is electrically disconnected, so that the DC voltage Vdc that has become an overvoltage is not applied to the switching element, and the switching element is removed from the overvoltage. While protecting reliably, the 1st switch 11 can be turned off and standby power consumption can be suppressed.

(5-3) Third Modified Example FIG. 11 shows an overall configuration of a system 100 in which an overvoltage protection circuit 50 according to a third modified example of the second embodiment is employed, and a motor drive device 10 using the system 100. It is a block diagram which shows the internal structure of. In FIG. 11, the inverter 25 is supplied with power from the power supply unit 20 via a pair of power supply lines 801 and 802. A part of the overvoltage protection circuit 50 is connected between the commercial power supply 91 and the power supply unit 20, and the other part is connected between the power supply unit 20 and the inverter 25.

  The overvoltage protection circuit 50 includes a voltage detection unit 33, a first switch 11, a second switch 13, and a control unit 40.

  The difference between the overvoltage protection circuit 50 in the third modification and the overvoltage protection circuit in the second embodiment, the first modification, and the second modification already described is the voltage detection that is a component of the overvoltage protection circuit 50. And the second switch are provided between the commercial power supply 91 and the power supply unit 20.

  In view of the replacement of the voltage detector and the second switch from the DC specification to the AC specification, the voltage detection unit 33 and the second switch 13 are employed instead of the voltage detection unit 23 and the second switch 12 of the second embodiment. ing. The voltage detection unit 33 is the same as that employed in the modification of the first embodiment, and therefore the description thereof is omitted. Only the second switch 13 will be described here.

(5-3-1) Second switch 13
The second switch 13 opens and closes the power line 901. Here, opening and closing the power supply line 901 means that the power supply line 901 is turned on or off to make it non-conductive.

  The second switch 13 normally closes the power supply line 901, that is, keeps it conductive. On the other hand, when the power supply to the gate drive circuit 26 is stopped to suppress power consumption during standby, the transistors Q3a to Q5b cannot be reliably turned off. If an overvoltage occurs at such time, the transistors Q3a to Q5b and the diodes D3a to D5b (hereinafter collectively referred to as switching elements) cannot be protected from the overvoltage.

  The role of the second switch 13 is to cut off the power supply line 901 so that the main power supply voltage (DC voltage Vdc) is not applied to the switching elements of the upper and lower arms. Thereby, the switching element can be protected from overvoltage.

  Since the second switch 13 requires high speed, a semiconductor switch is employed in the present embodiment. As specific switches, a triac, a MOSFET connected so as to conduct in both directions, an SSR (solid state relay), or the like is employed. In this embodiment, SSR is adopted.

  As shown in FIG. 11, an example in which the second switch 13 is an SSR is shown. The SSR includes a light emitting diode 13a, a phototriac 13b, a trigger circuit 13c, and a triac 13d. The second switch 13 includes a light emitting diode 13a on the input side (between E1 and E2) and a triac 13d on the output side (between F1 and F2). The equivalent circuit of the phototriac 13b has a configuration in which two photothyristors 131 and 132 are connected in parallel in opposite directions. Similarly, the equivalent circuit of the triac 13d has a configuration in which two photothyristors are connected in parallel in opposite directions.

  The anode E1 of the light emitting diode 13a is connected to the power source Vb via the resistor R1. The cathode E2 of the light emitting diode 13a is connected to the control unit 40 through a signal line.

  The first anode F1 of the phototriac 13b is connected to the rectifying unit 21 side of the power supply line 902. The second anode F2 of the phototriac 13b is connected to the power supply line 902 on the commercial power supply 90 side.

  The light emitting diode 13a emits light when a current flows. When the phototriac 13b receives light from the light emitting diode 13a in a state where the potential of the first anode F1 is higher than the potential of the second anode F2, the photothyristor 131 is turned on. On the other hand, when the light from the light emitting diode 13a is received in a state where the potential of the first anode F1 is smaller than the potential of the second anode F2, the photothyristor 132 is turned on. When the photo triac 13b is turned on, the trigger circuit 13c operates and the triac 13d is turned on.

  As described above, the SSR is a bidirectional element that operates with respect to a bidirectional applied voltage, and operates at a high speed, so that it is used as a bidirectional high-speed switch.

  Note that the bidirectional high-speed switch is not limited to the SSR alone, but when a high-speed switch of another form is used, a drive circuit corresponding to the form of the switch is appropriately used.

  The control unit 40 performs operation control of the second switch 13, that is, energization control to the light emitting diode 13a.

(5-3-2) Operation of Motor Drive Device 10 In the third modification, the control flow for overvoltage control is obtained by using the DC voltage Vdc of the control flow for overvoltage control described in FIG. Will be replaced. Further, instead of Vdcmax in step S2, Vacmax, which is an upper limit voltage that AC voltage Vac can be applied to devices including inverter 25, is set. Further, in place of Vdcret in step S5, an AC voltage Vacret that may cancel the overvoltage control is set.

  With the above settings, overvoltage control equivalent to that of the first embodiment can be realized.

As the control flow of the standby control, the standby control flow described in FIGS. 4, 8, and 9 can be adopted. The standby control flow described in FIG. 10 is used by replacing the DC voltage Vdc in step S43 with the AC voltage Vac of the commercial power supply 91, and setting a limit AC voltage Vaclim that can avoid destruction in place of Vdclim. Can do.

<Other embodiments>
(A)
The third modification of the second embodiment is a modification of the second embodiment in that the voltage detection unit and the first switch are provided between the commercial power supply 91 and the power supply unit 20. Only the detection unit may be provided between the commercial power supply 91 and the power supply unit 20.

(B)
The first switch 11 in the first embodiment and the second embodiment, or the second switch 12 in the second embodiment and the second switch 13 in the third modification may employ semiconductor switches.

  However, since the 2nd switch 13 in the 3rd modification of 2nd Embodiment turns on and off alternating current, a semiconductor switch requires bidirectionality. On the other hand, since the first switch 11 in the first and second embodiments and the second switch 12 in the second embodiment are arranged downstream of the DC power supply, the semiconductor switch may be a one-way switch.

  From the viewpoint of cost, the first switch 11 in the first embodiment and the second embodiment and the second switch 12 in the second embodiment can employ a one-way switch, so that the cost of the switch can be reduced.

  Since the present invention can protect each transistor of the upper and lower arms from overvoltage, it is useful not only for motor drive devices but also for other drive devices using inverters.

11 First switch 12, 13 Second switch 23, 33 Voltage detector 26 Gate drive circuit (drive circuit)
40 control unit 50 overvoltage protection circuit Q3a transistor (switching element)
Q3b transistor (switching element)
Q4a transistor (switching element)
Q4b transistor (switching element)
Q5a transistor (switching element)
Q5b Transistor (switching element)
D3a Diode (switching element)
D3b Diode (switching element)
D4a Diode (switching element)
D4b Diode (switching element)
D5a Diode (switching element)
D5b Diode (switching element)
NU Connection point NV Connection point NW Connection point Vc Drive circuit power supply Vdc DC voltage

JP 2007-166815 A

Claims (7)

Each of the plurality of upper and lower arms is formed by connecting two switching elements (Q3a, Q3b, Q4a, Q4b, Q5a, Q5b, D3a, D3b, D4a, D4b, D5a, D5b) in series. An overvoltage protection circuit for a power converter that outputs a voltage from each connection point (NU, NV, NW) to a corresponding load,
A voltage detector (23) for detecting the voltage of the power source;
A drive circuit (26) for generating a voltage for turning on and off the switching elements (Q3a, Q3b, Q4a, Q4b, Q5a, Q5b);
A drive circuit power supply (Vc) for supplying a power supply voltage to the drive circuit (26);
A first switch (11) for opening and closing a drive power supply line connecting the drive circuit power supply (Vc) and the drive circuit (26);
A control unit (40) for controlling the switching elements (Q3a, Q3b, Q4a, Q4b, Q5a, Q5b) via the drive circuit (26);
With
The control unit (40) is configured as a control mode.
Overvoltage control for turning off the switching elements (Q3a, Q3b, Q4a, Q4b, Q5a, Q5b) of both the upper and lower arms when the detection value of the voltage detection unit (23) exceeds a predetermined threshold;
Standby control for electrically disconnecting the drive power line via the first switch (11) when the switching elements (Q3a, Q3b, Q4a, Q4b, Q5a, Q5b) of both the upper and lower arms are off When,
Including
Further, the control unit (40) does not perform the standby control during the overvoltage control.
Overvoltage protection circuit (50). A second switch (12) for opening and closing a main power line connecting the power source and a circuit including the upper and lower arms;
When the time when the detection value of the voltage detection unit (23) exceeds the predetermined threshold becomes longer than a predetermined time, the control unit (40) passes the main switch via the second switch (12). Electrically disconnect the power line,
The overvoltage protection circuit (50) according to claim 1. A second switch (12) for opening and closing a main power line connecting the power source and a circuit including the upper and lower arms;
The control unit (40) electrically disconnects the main power line via the second switch (12) when a detection value of the voltage detection unit (23) exceeds a predetermined second threshold value.
The overvoltage protection circuit (50) according to claim 1. Each of the plurality of upper and lower arms is formed by connecting two switching elements (Q3a, Q3b, Q4a, Q4b, Q5a, Q5b, D3a, D3b, D4a, D4b, D5a, D5b) in series. An overvoltage protection circuit for a power converter that outputs a voltage from each connection point (NU, NV, NW) to a corresponding load,
A voltage detector (23) for detecting the voltage of the power source;
A drive circuit (26) for generating a voltage for turning on and off the switching elements (Q3a, Q3b, Q4a, Q4b, Q5a, Q5b);
A drive circuit power supply (Vc) for supplying a power supply voltage to the drive circuit (26);
A first switch (11) for opening and closing a drive power supply line connecting the drive circuit power supply (Vc) and the drive circuit (26);
A second switch (12) for opening and closing a main power line connecting the power source and a circuit including the upper and lower arms;
A control unit (40) for controlling the switching elements (Q3a, Q3b, Q4a, Q4b, Q5a, Q5b) via the drive circuit (26);
With
The control unit (40) is configured as a control mode.
Overvoltage control for turning off the switching elements (Q3a, Q3b, Q4a, Q4b, Q5a, Q5b) of both the upper and lower arms when the detection value of the voltage detection unit (23) exceeds a predetermined threshold;
Standby control for electrically disconnecting the drive power line via the first switch (11) when the switching elements (Q3a, Q3b, Q4a, Q4b, Q5a, Q5b) of both the upper and lower arms are off When,
Including
Further, the control unit (40) electrically disconnects the main power supply line via the second switch (12) when performing the standby control during execution of the overvoltage control.
Overvoltage protection circuit (50). The controller (40) disconnects the drive power supply line after disconnecting the main power supply line.
The overvoltage protection circuit (50) according to claim 4. The power source is a DC power source;
The overvoltage protection circuit (50) according to any one of claims 1 to 5. The power source is an AC power source;
The overvoltage protection circuit (50) according to any one of claims 1 to 5.

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