JP2015050862A - Power converter - Google Patents

Abstract

Provided is a power converter capable of suppressing a switching element from being turned on due to a malfunction in a charging operation of a boot capacitor. A boot capacitor Cx1 has a high potential end and a low potential end connected to an electrode of a first switching element Sx1, and applies an operating voltage to a drive circuit DRx1. The boot diode Dx10 has a cathode connected to the high potential end of the boot capacitor Cx1, and serves as a charging path for the boot capacitor Cx1 together with the second switching element Sx2 that is turned on. The adjustment unit 40 has the second switching element in the initial charging operation more than the maximum value of the decrease rate of the voltage V2 across the second switching element Sx2 during the period in which the second switching element Sx2 shifts from the off state to the on state in the normal operation. The maximum value of the decrease rate during the period in which Sx2 shifts from the off state to the on state is reduced. [Selection] Figure 2

Description

  The present invention relates to a power conversion device.

  For example, a three-phase inverter has an upper switching element and a lower switching element for three phases. In each phase, the upper switching element and the lower switching element are connected in series between the positive electrode end and the negative electrode end. A DC voltage is applied between the positive electrode end and the negative electrode end. A connection point between the upper switching element and the lower switching element functions as an output terminal of each phase.

  Then, by appropriately controlling the upper switching element and the lower switching element, the three-phase inverter converts the DC voltage into a three-phase AC voltage, and outputs the three-phase AC voltage via the output terminal. To do.

  Each of the upper switching element and the lower switching element is provided with a drive circuit. The drive circuit receives a switching signal from the outside and outputs it to each of the upper switching element and the lower switching element. A DC power supply is connected to the drive circuit for the lower switching element. A boot capacitor may be connected to the drive circuit for the upper switching element in order to reduce the number of DC power supplies. A diode is provided between the high potential end of the boot capacitor and the high potential end of the DC power supply. The forward direction of the diode is the direction from the DC power source to the boot capacitor. The diode prevents the boot capacitor from discharging to the DC power supply side.

  In such an inverter, when the lower switching element is turned on, the boot capacitor can be charged using a DC power supply. More specifically, a current flows through a path having a DC power supply, a diode, a boot capacitor, and a lower switching element, and the boot capacitor is charged.

  As a result, the number of DC power supplies can be reduced and the manufacturing cost can be reduced as compared with a structure in which DC power supplies are provided in all the drive circuits.

  Moreover, patent document 1 is disclosed as a technique relevant to this invention.

JP 2009-159697 A

  However, in the related art, when the lower switching element is turned on to charge the boot capacitor, the upper switching element is likely to malfunction and turn on, as will be described in detail later. If both the upper switching element and the lower switching element are simultaneously turned on, a large current flows through the upper switching element and the lower switching element, and this situation is not preferable.

  Therefore, an object of the present invention is to provide a power converter that can suppress a switching element from being turned on due to a malfunction in a charging operation of a boot capacitor.

  A first aspect of the power conversion device according to the present invention includes a positive electrode (P1) and a negative electrode (P2) to which a DC voltage is applied, a first electrode connected to the positive electrode, a second electrode, and the second electrode. A first switching element (Su1, Sv1, Sw1, Sx1) having a control electrode for short-circuiting the electrode to turn off the first electrode and the second electrode; and a first end connected to the control electrode A first drive circuit (DRx1) having a second end connected to the second electrode, and a drive switch element (DS2) provided between the first end and the second end; A boot capacitor (Cx1) having a potential end and a low potential end connected to the second electrode and supplying an operating voltage to the first drive circuit; and between the positive electrode and the negative electrode on the negative electrode side Connected in series with the first switching element, and is turned on exclusively with the first switching element in normal operation The second switching element (Su2, Sv2, Sw2, Sx2) that is turned on in the initial charging operation of the boot capacitor prior to the normal operation and the cathode connected to the high potential end, A boot diode (Dx10) that serves as a charging path for the boot capacitor together with the switching element, and a rate of decrease in voltage across the second switching element during a period in which the second switching element shifts from an off state to an on state in the normal operation. And an adjustment unit (40) that reduces the maximum value of the decrease rate during the period in which the second switching element shifts from the off state to the on state in the initial charging operation.

  A second aspect of the power conversion device according to the present invention is the power conversion device according to the first aspect, wherein the second drive circuit (DRx2) for driving the second switching element (Sx2), and the second A DC power source (E1) for supplying an operating voltage to the drive circuit, wherein the second switching element includes a third electrode connected to the second electrode, a fourth electrode connected to the negative electrode, A second control electrode that controls ON / OFF of the third electrode and the fourth electrode, and the adjustment unit (40) connects the DC power supply and the second control electrode via the second drive circuit. A resistor (R40) provided in a path to be connected; and a switch element (S40) connected in parallel with the resistor and turned off in the initial charging operation and turned on in the normal operation.

  A third aspect of the power conversion device according to the present invention is the power conversion device according to the second aspect, wherein the resistor (R40) and the switch element (S40) are connected to the DC power supply (E1) and the first power supply. Two drive circuits (DRx2) are provided.

  A fourth aspect of the power conversion device according to the present invention is the power conversion device according to the second aspect, wherein the resistor (R40) and the switch element (S40) are connected to the second drive circuit (DRx2). Provided between the second control electrode.

  According to the first aspect of the power conversion device of the present invention, since the operating voltage is not applied to the first drive circuit before the boot capacitor charging operation, the impedance of the drive switch is high. When the second switching element is turned on during the charging operation, the voltage across the second switching element decreases at a relatively gradual change rate. Thereby, due to this turn-on, the peak of the current flowing from the positive electrode to the drive circuit (drive switch element) via the parasitic capacitance between the first electrode and the control electrode of the first switching element is reduced. be able to. When this current flows through the high-impedance driving switch element, the control voltage of the control electrode of the first switching element is increased. As a result, the current peak can be reduced, so that the increase of the control voltage can be suppressed. As a result, ON of the first switching element can be suppressed by malfunction.

  According to the second aspect of the power conversion device of the present invention, the first aspect can be realized with a simple configuration.

  According to the 3rd aspect of the power converter device concerning this invention, when one set of the 1st switching element and the 2nd switching element is provided with two or more, one DC power supply is provided with respect to several 2nd switching element. In addition, one adjustment unit can be used in common.

  According to the fourth aspect of the power conversion device of the present invention, there is no need to provide a resistor and a switch element between the DC power supply and the second drive circuit, so the operating voltage of the second drive circuit ( A drop in the DC voltage from the DC power supply can be avoided.

It is a figure which shows an example of a notional structure of a power converter. It is a figure which shows an example of a notional structure of a drive device. It is a figure which shows an example of the internal structure of a drive circuit. It is a figure which shows typically an example of the voltage and electric current when a lower side switching element turns on. It is a figure for demonstrating the electric current which flows into the structure by the side of an upper switching element when a lower switching element turns on. It is a figure which shows typically an example of the both-ends voltage of a switching element. It is a figure which shows typically an example of the electric current which flows into the structure of the upper side switching element when a lower side switching element turns on, and the both-ends voltage of an upper side switching element. It is a figure which shows an example of a notional structure of a drive device. It is a figure which shows an example of a notional structure of a power converter device. It is a figure which shows typically an example of the relationship between the electrostatic capacitance of the parasitic capacitance of an upper switching element, and the both-ends voltage of an upper switching element.

Embodiment.
<Power conversion device>
As illustrated in FIG. 1, the power conversion unit 1 includes switching elements Su1, Su2, Sv1, Sv2, Sw1, and Sw2. In FIG. 1, the power line LH is connected to the positive terminal P1, and the power line LL is connected to the negative terminal P2. A DC voltage is applied between the positive terminal P1 and the negative terminal P2 so that the potential of the positive terminal P1 is high. Switching elements Su1, Su2 are connected in series between power supply lines LH, LL. A point between the switching elements Su1 and Su2 is connected to the AC line Pu. The same applies to the switching elements Sv1, Sv2 and the switching elements Sw1, Sw2, the point between the switching elements Sv1, Sv2 is connected to the AC line Pv, and the point between the switching elements Sw1, Sw2 is connected to the AC line Pw. Is done.

  Hereinafter, the switching elements Su1, Sv1, and Sw1 are collectively referred to as the switching element Sx1, the switching elements Su2, Sv2, and Sw2 are collectively referred to as the switching element Sx2, and the AC lines Pu, Pv, and Pw are collectively referred to as the AC line Px. Also called. Further, here, since the switching element Sx1 is disposed on the power supply line LH side with respect to the switching element Sx2, hereinafter, the switching element Sx1 is also referred to as an upper switching element Sx1, and the switching element Sx2 is also referred to as a lower switching element Sx2. .

  The switching elements Sx1 and Sx2 are, for example, MOS (Metal-Oxide-Semiconductor) field effect transistors, insulated gate bipolar transistors, junction transistors, and the like.

  Further, for example, diodes Dx1 and Dx2 are connected in parallel to the switching elements Sx1 and Sx2, respectively. The diodes Dx1 and Dx2 are provided such that their forward directions are directed from the power supply line LL to the power supply line LH. Note that the diodes Dx1 and Dx2 need not be provided as long as the switching elements Sx1 and Sx2 can conduct from the power supply line LL to the power supply line LH.

  A switching signal is input to the switching elements Sx1 and Sx2 by the control unit 3. In other words, the switching elements Sx1 and Sx2 are controlled by the control unit 3. With this control, the power conversion unit 1 operates appropriately to convert a DC voltage into an AC voltage. Here, although the three-phase power conversion unit 1 that converts a DC voltage into a three-phase AC voltage is illustrated, it may be a single phase or may be three or more phases.

  In the illustration of FIG. 1, a load 2 is connected to the AC lines Pu, Pv, Pw. The load 2 is, for example, a motor, and rotates according to the AC voltage applied by the power conversion unit 1.

<Drive device>
Next, a driving device for driving the switching elements Sx1 and Sx2 will be described. FIG. 2 shows an example of a conceptual configuration of a pair of switching elements Sx1 and Sx2 and a driving device that drives the switching elements Sx1 and Sx2. In the example of FIG. 2, the DC voltage Vdc between the power supply lines LH and LL is shown using the capacitor C1. This capacitor C1 may actually be provided. Such a capacitor C1 can function as a smoothing capacitor or a snubber capacitor.

  Hereinafter, the electrode on the power supply line LH side of the switching elements Sx1 and Sx2 is referred to as a first electrode, and the electrode on the power supply line LL side is referred to as a second electrode.

  As shown in FIG. 2, a drive circuit DRx1 is provided between the control electrode and the second electrode of the switching element Sx1. The drive circuit DRx1 has terminals P11 and P12. The terminal P11 is connected to the control electrode of the switching element Sx1 via the resistor Rx1, and the terminal P12 is connected to the second electrode of the switching element Sx1. The drive circuit DRx1 receives a switching signal from the control unit 3 and outputs it to the control electrode of the switching element Sx1. The control electrode controls on / off of the switching element Sx1. More specifically, when the control voltage Vg1 applied to the control electrode of the switching element Sx1 exceeds the on voltage, the switching element Sx1 is turned on. When the control voltage Vg1 falls below the on voltage, the switching element Sx1 is turned off.

  The resistor Rx1 can function as a so-called gate resistor, and can suppress, for example, oscillation of the control voltage Vg1. The resistor Rx1 may not be provided.

  A drive circuit DRx2 is provided between the control electrode and the second electrode of the switching element Sx2. The drive circuit DRx2, the terminals P21 and P22, and the resistor Rx2 are the same as the drive circuit DRx1, the terminals P11 and P12, and the resistor Rx1, and thus repeated description is avoided.

  A DC power supply E1 is connected to the drive circuit DRx2. The low potential end of the DC power supply E1 is commonly connected to the second electrode of the switching element Sx2 and the drive circuit DRx2 via the adjusting unit 40 described later, and the high potential end is connected to the drive circuit DRx2. . This DC power supply E1 applies an operating voltage to the drive circuit DRx2.

  As shown in FIG. 3, the drive circuit DRx2 includes drive switch elements DS1 and DS2. Note that since an example of the internal configuration of the drive circuit DRx1 is the same as that of the drive circuit DRx2, the reference numeral as the drive circuit DRx1 is also appended in FIG.

  The drive circuit DRx2 will be described. The drive switch elements DS1 and DS2 are connected in series between the high potential end and the low potential end of the DC power supply E1. Here, the drive switch element DS1 is disposed on the higher potential end side of the DC power supply E1 than the drive switch element DS2. The connection point connecting the drive switch elements DS1 and DS2 functions as the terminal P21, and the electrode of the drive switch element DS2 on the opposite side of the drive switch element DS1 functions as the terminal P22.

  The drive switch elements DS1 and DS2 receive the switching signal from the control unit 3 and are exclusively turned on. For example, when the drive switch element DS1 is turned on and the drive switch element DS2 is turned off, the operating voltage input to the drive circuit DRx2 can be applied to the control electrode of the switching element Sx2 via the resistor Rx2. As a result, the control voltage Vg2 of the switching element Sx2 exceeds the ON voltage, and the switching element Sx2 is turned ON. On the other hand, when the drive switch element DS1 is turned off and the drive switch element DS2 is turned on, the control electrode of the switching element Sx2 is short-circuited to the second electrode of the switching element Sx2 via the resistor Rx2. As a result, the control voltage Vg2 falls below the on voltage, and the switching element Sx2 is turned off.

  In the illustration of FIG. 2, a capacitor Cx2 connected in parallel to the DC power supply E1 is provided between the DC power supply E1 and the drive circuit DRx2. The capacitor Cx2 can smooth the operating voltage. Note that the capacitor Cx2 may not be provided.

  A boot capacitor Cx1 is connected to the drive circuit DRx1. The low potential end of the boot capacitor Cx1 is commonly connected to the second electrode of the switching element Sx1 and the drive circuit DRx1, and the high potential end is connected to the drive circuit DRx1. The voltage across the boot capacitor Cx1 is applied to the drive circuit DRx1 as an operating voltage.

  An example of the internal configuration of the drive circuit DRx1 is the same as that of the drive circuit DRx2, and thus repeated description is avoided here.

  A boot diode Dx10 is provided between the high potential end of the boot capacitor Cx1 and the high potential end of the DC power supply E1. Boot diode Dx10 is provided such that its forward direction is directed from DC power supply E1 to boot capacitor Cx1. The boot diode Dx10 can prevent the boot capacitor Cx1 from being discharged to the DC power supply E1 side.

  According to such a circuit, the boot capacitor Cx1 can be charged using the DC power supply E1 by turning on the switching element Sx2. More specifically, when the switching element Sx2 is turned on, a current (hereinafter also referred to as a charging current) flows through a charging path including the DC power supply E1, the boot diode Dx10, the boot capacitor Cx1, and the switching element Sx2, and the boot capacitor Cx1 Charged.

  Such charging of the boot capacitor Cx1 is performed prior to normal operation of the power conversion unit 1 (operation for converting a DC voltage into a three-phase AC voltage). This is because if the boot capacitor Cx1 is not charged, the operating voltage cannot be applied to the drive circuit DRx1, and the switching element Sx1 cannot be controlled. Hereinafter, this charging is also referred to as an initial charging operation.

  In the example of FIG. 2, a resistor Rx10 is provided between the high potential end of the boot capacitor Cx1 and the high potential end of the DC power supply E1. The resistor Rx10 is connected in series with the boot diode Dx10. The resistor Rx10 can suppress an inrush current flowing from the DC power supply E1 to the boot capacitor Cx1 when the boot capacitor Cx1 is charged. For example, if the inrush current is not a problem even if the resistor Rx10 is not present because the capacitance of the boot capacitor Cx1 is small, the resistor Rx10 may not be provided.

  Here, a malfunction of the switching element Sx1 that may occur in the initial charging operation of the boot capacitor Cx1 when the adjustment unit 40 is not provided will be described. First, the control unit 3 turns on the switching element Sx2 to charge the boot capacitor Cx1. FIG. 4 schematically shows an example of each voltage when the switching element Sx2 is turned on.

  As shown in FIG. 4, at time t1, the control voltage Vg2 rises and exceeds the on-voltage Von. As a result, the switching element Sx2 is turned on. With this turn-on, the voltage V2 at both ends of the switching element Sx2 decreases and reaches almost zero, whereas the voltage V1 at both ends of the switching element Sx1 increases to take substantially the same value as the DC voltage Vdc. This is because the switching element Sx1 alone supports the DC voltage Vdc by turning on the switching element Sx2. FIG. 4 is a schematic diagram, and the control voltage Vg1 and the both-ends voltage V1 actually rise with an inclination.

  When the voltage V1 across the switching element Sx1 increases in this way, a current i11 flows through the parasitic capacitance C11 between the first electrode and the control electrode of the switching element Sx1, as shown in FIG. The current i11 can flow from the power supply line LH to the second electrode of the switching element Sx1 via the following two paths via the parasitic capacitance C11. The first path is a path including the resistor Rx1 and the portion of the drive circuit Dx1 between the terminals P11 and P12 (such as the parasitic capacitance or resistance of the drive switch element DS2 and the parasitic capacitance of the pattern wiring). The second path is a path including a parasitic capacitance C12 between the control electrode and the second electrode of the switching element Sx1.

  Now, in the initial charging operation of the boot capacitor Cx1 prior to the normal operation, the operating voltage is not yet supplied to the drive circuit DRx1, and it is not operating. Therefore, the driving switch element DS2 has a high impedance. Although the drive switch element DS2 has a high impedance, in reality, a slight current can flow through the drive switch element DS2 via a resistance or a parasitic capacitance. In addition, since the driving switch element DS2 is high impedance, a large current flows through the parasitic capacitor C12. The impedance between the control electrode and the second electrode is higher than that in the normal operation OFF state. Therefore, when the current i11 flows through the parasitic capacitance C11, the voltage between the control electrode and the second electrode has a high impedance, so that the voltage due to the current i11 and the high impedance is applied to the control electrode of the switching element Sx1. Therefore, this voltage becomes the control voltage Vg1. When the control voltage Vg1 exceeds the ON voltage of the switching element Sx1, the switching element Sx1 is turned on. In the example of FIG. 4, since the control voltage Vg1 exceeds the on-voltage, the switching element Sx1 is turned on.

  As a result, both the switching elements Sx1 and Sx2 are turned on. Therefore, a short-circuit current flows from the power supply line LH to the power supply line LL via the switching elements Sx1 and Sx2. The DC voltage Vdc is sufficiently larger than the operating voltages of the drive circuits DRx1 and DRx2, and there is no large resistance in the path (switching elements Sx1 and Sx2) through which the short circuit current flows. large.

  In the illustration of FIG. 4, the current I2 flowing through the switching element Sx2 increases as the switching element Sx1 is turned on. Note that since a charging current for charging the boot capacitor Cx1 and a short-circuit current flow through the switching element Sx2, the current I2 is the sum of the short-circuit current and the charging current. Then, when the control voltage Vg1 starts to decrease and falls below the on-voltage Von at the time t2, the switching element Sx1 is turned off. As a result, the short circuit current becomes zero, and only the charging current flows through the switching element Sx2. Therefore, after time t2, the current I2 coincides with the charging current.

  As described above, in the initial charging operation of the boot capacitor Cx1, when the switching element Sx1 malfunctions and turns on, a relatively large short-circuit current flows. Such a short circuit current is undesirable.

  In normal operation, the driving switch element DS2 of the switching element Sx1 when the switching element Sx2 is turned on has a low impedance. This is because, in normal operation, the switching elements Sx1 and Sx2 are controlled so as to be exclusively turned on, so that when the switching element Sx2 is turned on, the switching element Sx1 is off. That is, when the switching element Sx2 is turned on, the driving switch element DS2 is turned on. Therefore, even if the current i11 flows when the switching element Sx2 is turned on (see FIG. 5), from the viewpoint of impedance, the increase amount of the control voltage Vg1 in the normal operation is the increase amount of the control voltage Vg1 in the initial charging operation. Smaller than that.

  Therefore, in the present embodiment, it is intended to reduce the maximum value of the current that flows as the switching element Sx2 is turned on in the initial charging operation of the boot capacitor Cx1.

  In the drive device according to the present embodiment, an adjustment unit 40 is provided as shown in FIG. The adjustment unit 40 adjusts the rate of decrease of the voltage V2 across the switching element Sx2 with respect to time during the period in which the switching element Sx2 transitions from the off state to the on state. That is, the slope of the fall of the both-end voltage V2 when the switching element Sx2 is turned on is adjusted. Since the sum of both-end voltages V1 and V2 is equal to the DC voltage Vdc, the adjustment unit 40 also adjusts the rising slope of the both-end voltage V1.

  FIG. 6 schematically shows an example of the voltage V2 across the switching element Sx2 and the voltage Vx1 across the switching element Sx1 when the switching element Sx2 is turned on in order to charge the boot capacitor Cx1. Here, in a state before the boot capacitor Cx1 is charged, the DC voltage Vdc is applied to one set of the switching elements Sx1 and Sx2, and each of the switching elements Sx1 and Sx2 corresponds to the DC voltage Vdc. A voltage is applied.

  Then, when the switching element Sx2 is turned on, the voltage V2 across the switching element Sx2 decreases with time and reaches almost zero. Since the sum of the both-end voltages V1 and V2 becomes the DC voltage Vdc, the both-end voltage V1 increases with a decrease in the both-end voltage V2, and takes a value almost equal to the DC voltage Vdc.

  The adjusting unit 40 adjusts the decrease rate of the both-end voltage V2. More specifically, the maximum value of the change rate of the both-end voltage V2 in the initial charging operation of the boot capacitor Cx1 is made smaller than the maximum value of the decrease rate of the both-end voltage V2 of the switching element Sx2 in the normal operation. In FIG. 6, both-end voltages V1 and V2 in the normal operation are indicated by broken lines, and both-end voltages V1 and V2 in the initial charging operation are indicated by solid lines.

  The operation of the adjustment unit 40 can be paraphrased as follows. That is, the time required for turning on the switching element Sx2 in the initial charging operation is made longer than that in the normal operation. Alternatively, it can be explained that the turn-on speed of the switching element Sx2 in the initial charging operation is reduced as compared with the normal operation.

  As a result, the both-end voltage V2 in the initial charging operation decreases relatively slowly, and similarly, the both-end voltage V1 increases relatively gradually.

  In order to realize this, the adjustment unit 40 includes, for example, a resistor R40 and a switch element S40. The resistor R40 is provided between the control electrode of the switching element Sx2 and the DC power source E1. More specifically, it is provided in a path for turning on the switching element Sx2 (a path including the DC power supply E1, the driving switch element DS1, the resistor Rx2, and the switching element Sx2). In the illustration of FIG. 2, the resistor R40 is provided between the low potential end of the DC power supply E1 and the drive circuit DRx2.

  The switch element S40 is, for example, a MOS field effect transistor or the like, and is connected in parallel with the resistor R40, and is controlled by the control unit 3, for example. In the initial charging operation of the boot capacitor Cx1, the control unit 3 turns on the switching element Sx2 with the switch element S40 turned off.

  Therefore, in the initial charging operation of the boot capacitor Cx1, the resistance value of the path for turning on the switching element Sx2 is relatively large by the resistance value of the resistor R40. When this resistance value is large, the control voltage Vg2 of the switching element Sx2 increases gently. As a result, the voltage V2 across the switching element Sx2 is also gently reduced. As a result, the voltage V1 across the switching element Sx1 also gradually increases.

  And if the both-ends voltage V1 increases gently, the maximum value of the electric current i11 which flows according to this can be reduced. FIG. 7 schematically shows an example of the both-end voltage V1 and the current i11 when the switching element Sx2 is turned on.

  Unlike the present embodiment, when the both-end voltage V1 increases relatively steeply, the both-end voltage of the parasitic capacitance C11 also increases relatively quickly according to this. That is, the maximum value of the current i11 is relatively large (see the current i11 shown by the broken line in FIG. 7).

  The reason why the current i11 increases as described above can also be explained as follows. That is, when the DC voltage Vdc is very large compared to the control voltage, it can be considered that the voltage of the parasitic capacitance C11 is substantially the same as the voltage V1 across the switching element Sx1. Therefore, if the change in the voltage V1 across the switching element Sx1 is steep, the change in the voltage of the parasitic capacitance C11 is also steep, and the current i11 is also steep in order to bring about a steep voltage change. Therefore, the peak of the current i11 increases as the increase rate of the both-end voltage V1 increases.

  On the other hand, when the voltage V1 at both ends increases relatively slowly, the maximum value of the current i11 becomes relatively small correspondingly (see the solid line current i11 in FIG. 7). As a result, an increase in the control voltage Vg1 of the switching element Sx1 due to the current i11 can be suppressed. Therefore, it can suppress that switching element Sx1 malfunctions and turns on. Thereby, a short circuit current can be suppressed and the boot capacitor Cx1 can be charged.

  Next, the control unit 3 turns on the switch element S40 before starting normal operation. Thereby, in normal operation, when the switching element Sx2 is turned on, the rate of decrease of the both-ends voltage V2 can be increased. In other words, the switching element Sx2 can be quickly turned on. This is desirable from the viewpoint of reducing the switching loss.

  Note that when the switching element Sx2 is turned on in normal operation, the drive switch element DS2 has a low impedance as described above, so that an increase in the control voltage Vg1 due to the current i11 is unlikely to be a problem.

  As described above, in the present embodiment, in the initial charging operation in which the malfunction of the switching element Sx1 is more likely to occur, the rate of decrease in the voltage V2 across the switching element Sx2 at the time of turn-on is reduced to suppress the malfunction of the switching element Sx1. In the normal operation in which the malfunction of the switching element Sx1 is unlikely to occur, the rate of decrease of the voltage V2 across the switching element Sx2 at the time of turn-on is increased to realize high-speed switching of the switching element Sx2.

  As shown in FIG. 2, if the adjustment unit 40 is formed by the switch element S40 and the resistor R40, the function of the adjustment unit 40 can be realized with a simple configuration.

  In the above example, the drive circuit DRx1 includes the drive switch elements DS1 and DS2, but a pull-up resistor may be provided instead of the drive switch element DS1. Also by this, the switching element Sx1 can be driven.

  In the above example, the boot capacitor Cx1 is charged by turning on the switching element Sx2 once. However, the present invention is not limited to this, and the boot capacitor Cx1 may be intermittently charged by repeatedly switching the switching element Sx2 on and off.

  In the above example, the low potential end of the DC power source E1 is connected to the second electrode of the switching element Sx2 via the adjustment unit 40, but bypasses the adjustment unit 40 and directly switches to the switching element Sx2. The second electrode may be connected.

<Position A of Adjustment Unit 40>
The second electrodes of the switching elements Su2, Sv2, and Sw2 are commonly connected to the power supply line LL (see also FIG. 1). Therefore, the potential applied to the power supply line LL functions as a reference for the control voltage Vg2 of the switching elements Su2, Sv2, Sv2. Therefore, the DC power supply E1 whose low potential end is connected to the power supply line LL can be commonly used as the operation power supply for the drive circuit DRx2 of each switching element Su2, Sv2, Sw2.

  Further, the adjustment unit 40 may be provided between each of the three drive circuits DRu2, DRv2, DRw2 and the DC power supply E1. In other words, the adjustment unit 40 may be provided in common for the drive circuits DRu2, DRv2, and DRw2.

  In this case, even if any of the switching elements Sx2 is turned on, the adjustment unit 40 is interposed in the charging path of the corresponding boot capacitor Cx1, so the maximum value of the decrease rate of the voltage V2 across the switching element Sx2 is reduced. be able to. Therefore, the maximum value of the increase rate of the corresponding both-ends voltage V1 can be reduced, and thus malfunction of the switching element Sx1 can be reduced.

  In addition, since the adjustment unit 40 is used in common, the manufacturing cost can be reduced as compared with the case where the adjustment unit 40 is provided corresponding to each of the drive circuits DRx2.

<Position B of Adjustment Unit 40>
In the example of FIG. 8, the adjustment unit 40 is provided between the drive circuit DRx2 and the switching element Sx2. According to this structure, the voltage across the DC power supply E1 functions as the operating voltage of the drive circuit DRx2. That is, it is not necessary to provide the resistor R40 and the switch element S40 between the DC power supply E1 and the drive circuit DRx2. Therefore, it is possible to avoid a decrease in the operating voltage of the drive circuit DRx2 due to these.

  Hereinafter, another drive device will be described as a reference example.

Reference example.
FIG. 9 is a diagram illustrating a conceptual example of the power conversion device according to the reference example. In this reference example, resistors Ru3, Rv3, and Rw3 connected in parallel to the switching elements Su2, Sv2, and Sw2, respectively, are provided. Hereinafter, the resistors Ru3, Rv3, and Rw3 are collectively referred to as a resistor Rx3. On the other hand, no resistance is provided for the switching element Sx1.

  The resistors Ru3, Rv3, and Rw3 have sufficiently large resistance values, and the current flowing through the resistor Rx3 is sufficiently small when the switching element Sx2 is turned off during normal operation. Thereby, the resistor Rx3 does not substantially hinder the on / off switching function of the switching element Sx2.

  Further, since the resistor Rx3 is provided, the voltage V2 across the switching element Sx2 when both the switching elements Sx1 and Sx2 are turned off before the normal operation can be further reduced. The reason for this will be briefly explained at the expense of accuracy. By providing the resistor Rx3, a combined resistance value of the switching element Sx2 and the resistor Rx3 can be reduced, so that the voltage V2 at both ends can be reduced. It is.

  Here, the resistance value of the resistor Rx3 is set as follows. That is, the voltage V2 across the switching element Sx2 before the initial charging operation of the boot capacitor Cx1 is set to be k (0 <k <0.5) times the DC voltage Vdc. As an example, when the DC voltage Vdc is 300V, the resistance value of the resistor Rx3 is set so that the both-ends voltage V2 is 50V.

  In this state, when the switching element Sx2 is turned on to charge the boot capacitor Cx1, the voltage V1 across the switching element Sx1 changes from 250V to 300V.

  Thus, the voltage V1 across the switching element Sx1 can be changed in a relatively high region.

  FIG. 10 is a schematic diagram showing the relationship between the electrostatic capacitance of the parasitic capacitance C11 and the voltage V1 across the switching element Sx1. As can be understood from FIG. 10, the capacitance of the parasitic capacitance C11 is smaller as the both-end voltage V1 is larger.

  In this reference example, by providing the resistor Rx3, the voltage V1 at both ends can be changed in a relatively high region, so that the capacitance of the parasitic capacitance C11 can be reduced. The smaller the electrostatic capacitance of the parasitic capacitance C11, the smaller the current flowing through the parasitic capacitance C11 due to the turn-on of the switching element Sx2. This is because the smaller the capacitance of the parasitic capacitance C11, the smaller the current required to increase the voltage of the parasitic capacitance C11 in accordance with the increase of the both-end voltage V1.

  In this reference example, the boot capacitor Cx1 is charged by turning on the switching element Sx2 once. However, it is not limited to this. In the initial charging operation of the boot capacitor Cx1, the switching element Sx2 may be repeatedly switched. At this time, the voltage V2 across the switching element Sx2 can be changed within a small range by adjusting the period during which the switching element Sx2 is turned off. For example, when the control voltage is 10V, the voltage V2 across the switching element Sx2 can be changed within a range of 0V to (10V + 1V). At this time, the voltage V1 across the switching element Sx1 changes within the range of (300V− (10V + 1V)) to 300V, and the electrostatic capacitance of the parasitic capacitance C11 can be further reduced. Therefore, the malfunction of the switching element Sx1 due to the turn-on of the switching element Sx2 can be further suppressed.

40 adjustment unit Cx1 boot capacitor Dx10 boot diode DRx2 drive circuit DS2 drive switch element P1 positive electrode P2 negative electrode R40 resistance S40 switch element Su1, Sv1, Sw1, Sx1, Su2, Sv2, Sw2, Swx2 switching element

Claims (4)

A positive electrode (P1) and a negative electrode (P2) to which a DC voltage is applied;
A first switching element (Su1) having a first electrode connected to the positive electrode, a second electrode, and a control electrode that is short-circuited with the second electrode to turn off the first electrode and the second electrode. , Sv1, Sw1, Sx1) and
A first end connected to the control electrode; a second end connected to the second electrode; and a drive switch element (DS2) provided between the first end and the second end. A first drive circuit (DRx1);
A boot capacitor (Cx1) having a high potential end and a low potential end connected to the second electrode, and applying an operating voltage to the first drive circuit;
Connected in series with the first switching element on the negative electrode side between the positive electrode and the negative electrode, and is turned on exclusively with the first switching element in normal operation, and the boot capacitor prior to the normal operation A second switching element (Su2, Sv2, Sw2, Sx2) that is turned on in the initial charging operation;
A boot diode (Dx10) having a cathode connected to the high potential end and serving as a charging path for the boot capacitor together with the second switching element turned on;
In the initial charging operation, the second switching element is in the off state, rather than the maximum value of the decrease rate of the voltage across the second switching element in the period during which the second switching element shifts from the off state to the on state in the normal operation. A power converter comprising: an adjustment unit (40) that reduces a maximum value of the decrease rate during a period of transition from an ON state to an ON state. A second driving circuit (DRx2) for driving the second switching element (Sx2);
A DC power supply (E1) for supplying an operating voltage to the second drive circuit;
The second switching element includes a third electrode connected to the second electrode, a fourth electrode connected to the negative electrode, and a second control for controlling on / off of the third electrode and the fourth electrode. An electrode,
The adjustment section (40)
A resistor (R40) provided in a path connecting the DC power supply and the second control electrode via the second drive circuit;
The power conversion device according to claim 1, further comprising: a switch element connected in parallel with the resistor, turned off in the initial charging operation, and turned on in the normal operation.   The power converter according to claim 2, wherein the resistor (R40) and the switch element (S40) are provided between the DC power supply (E1) and the second drive circuit (DRx2).   The power converter according to claim 2, wherein the resistor (R40) and the switch element (S40) are provided between the second drive circuit (DRx2) and the second control electrode.

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