JP4204534B2 - Power converter - Google Patents

Description

  The present invention relates to a power conversion device having a configuration in which a freewheeling diode is connected in reverse parallel to a main circuit switching element.

  For example, as shown in FIG. 15, an inverter device includes a configuration in which freewheeling diodes Du to Dw and Dx to Dz are connected in reverse parallel to MOSFETs Su to Sw and Sx to Sz. In the case of this configuration, when the MOSFETs Su to Sw and Sx to Sz are turned off, the current energy stored in the load M is circulated through the freewheeling diodes Du to Dw and Dx to Dz.

  In this case, for example, when the MOSFET Su is turned on when the forward current Ia flows through the freewheeling diode Dx, a voltage between PNs (so-called DC link voltage) is applied as a reverse bias to both ends of the freewheeling diode Dx, as shown in FIG. After the reverse current flows through the freewheeling diode Dx due to the residual charge, the freewheeling diode Dx is cut off. For this reason, since a large loss occurs in the freewheeling diode Dx due to the voltage between the PN and the reverse current, it is necessary to increase the size of the radiator.

  Therefore, when a reverse voltage application circuit is provided and the freewheeling diode is cut off, a small reverse voltage is applied from the reverse voltage application circuit to the freewheeling diode, and reverse recovery of the freewheeling diode is caused by the low voltage DC voltage power supply of the reverse voltage application circuit. In some cases, the loss generated in the freewheeling diode is reduced (for example, see Patent Document 1).

  FIG. 17 is a circuit diagram of a conventional power converter provided with a reverse voltage application circuit. In FIG. 17, a DC voltage source 1 is obtained by rectifying a three-phase AC power source, and between a positive DC bus 1a and a negative DC bus 1b of the DC voltage source 1, a smoothing capacitor 2, The inverter main circuit 3 is connected. The inverter main circuit 3 is formed by three-phase bridge connection of MOSFETs 4u to 4w and 4x to 4z corresponding to main circuit switching elements, and a free-wheeling diode between the collectors and emitters of the MOSFETs 4u to 4w and 4x to 4z. 5 u to 5 w and 5 x to 5 z are connected in antiparallel, and a load 6 (for example, a motor) is connected to the output side of the inverter main circuit 3.

  A reverse voltage application circuit 7 is connected to each of the freewheeling diodes 5u to 5w and 5x to 5z. Each of these reverse voltage application circuits 7 has a low voltage DC voltage power supply 8 having a voltage value lower than that of the DC voltage source 1, and a low voltage DC voltage is provided between the collectors and emitters of the MOSFETs 4u to 4w and 4x to 4z. The power supply lines 8a and 8b of the power supply 8 are connected to each other.

  Each reverse voltage application circuit 7 has a base drive circuit 9, and power supply lines 9 a and 9 b of the base drive circuit 9 are connected to power supply lines 8 a and 8 b of the low voltage DC voltage power supply 8. When drive signals SGu to SGw and SGx to SGz are output from the circuit to the base drive circuit 9, the base drive circuit 9 is driven by the power supply from the low voltage DC voltage power supply 8, and the MOSFETs 4u to 4w and 4x to 4z are turned on. To do.

  Each reverse voltage application circuit 7 includes a MOSFET 17 corresponding to a reverse voltage application switching element. The MOSFET 17 is interposed in the power supply line 8a of the low voltage DC voltage power supply 8, and has a withstand voltage higher than those of the MOSFETs 4u to 4w and 4x to 4z. Low one is selected. The MOSFET 17 is turned on at the time of reverse recovery of the freewheeling diode.

  Each reverse voltage application circuit 7 includes a diode 13 and a capacitor 14, and each of the diode 13 and the capacitor 14 is connected in parallel to the power supply line 8a of the low-voltage DC voltage power supply 8, and the MOSFETs 4u to 4w and 4x to 4z are turned on. When the power is on, the capacitor 14 is charged from each low voltage DC voltage power source 8 through the diode 13. As a result, the capacitor 14 is charged with a driving power source for the base drive circuit 18. A capacitor 15 is connected between the power supply lines 8a and 8b, and a diode 19 is connected in series with the power supply line 8a. A diode 16 is connected between the power supply lines 8a and 8b.

The power supply lines 18a and 18b of the base drive circuit 18 are connected to both terminals of the capacitor 14 and output a drive signal based on the potentials at points A, B, and C of the inverter main circuit 3 (not shown). When the drive signals SGru to SGrw and SGrx to SGrz are output to the base drive circuit 18, the base drive circuit 18 is driven by the charging power of the capacitor 14 to turn on the MOSFET 17. Thereby, a reverse voltage smaller than that of the DC voltage source 1 is applied from the low voltage DC voltage power supply 8 through the MOSFET 17 to the freewheeling diodes 5u to 5w and 5x to 5z.
Japanese Patent Laid-Open No. 10-327585

  However, in such a conventional device, in order to operate the reverse voltage application circuit 7 at the time of reverse recovery of the freewheeling diode, the potentials at points A, B, and C of the inverter main circuit 3 are detected, and the direction of the main circuit current is determined. Since it is necessary to make a determination, a voltage detector is required. At the time of reverse recovery of the freewheeling diode, the current of the main circuit temporarily flows to the low voltage DC voltage power supply 8 of the reverse voltage application circuit, so that the voltage fluctuation of the auxiliary power supply becomes large. That is, at the time of reverse recovery of the freewheeling diode, the current flowing through the freewheeling diode is prevented from flowing by the reverse voltage applying circuit 7, so that the current flowing through the freewheeling diode temporarily flows into the reverse voltage applying circuit, A circuit is formed that bypasses the freewheeling diode through the low voltage DC voltage power supply 8 of the application circuit. For this reason, the voltage fluctuation of the low voltage DC voltage power supply 8 of the reverse voltage application circuit becomes large. As a result, it is necessary to increase the current capacity of the low voltage DC voltage power supply 8 of the reverse voltage application circuit.

  An object of the present invention is to properly perform reverse recovery of the freewheeling diode without providing a detector for detecting the direction of the current flowing through the freewheeling diode, and to assist the reverse voltage application circuit during reverse recovery of the freewheeling diode. An object of the present invention is to provide a power converter that can suppress a main circuit current flowing in a power source.

  The power conversion device of the present invention includes a pair of main circuit switching elements connected in series to a DC voltage source and supplying power to a load, freewheeling diodes connected in reverse parallel to the main circuit switching elements, A reverse voltage application circuit for applying a reverse voltage smaller than the direct current voltage source to each freewheel diode when the freewheeling diode cuts off, the reverse voltage application circuit having an auxiliary power supply whose voltage value is lower than that of the direct current voltage source; A reverse voltage application switching element that is turned on at the time of reverse recovery of the freewheeling diode and has a lower withstand voltage than the main circuit switching element, and a high speed auxiliary diode having a reverse recovery time shorter than that of the freewheeling diode and connected in series. A short of turning off both main circuit switching elements when switching the main circuit switching elements of the set between the on state and the off state. A main circuit switching control circuit for switching the main circuit switching element with a pause period in between, and turning on the reverse voltage application switching element during the pause period starting from the time when the main circuit switching element is turned off. And a reverse voltage application switching control circuit which is turned off after elapse of time.

  According to the present invention, the reverse voltage application circuit can be appropriately operated at a uniform timing regardless of the direction of the main circuit current, and a detector for detecting the direction of the current is not required, thereby simplifying the control mechanism. can do.

(First embodiment)
FIG. 1 is a circuit diagram of a power converter according to the first embodiment of the present invention. This first embodiment is different from the conventional example shown in FIG. 17 in that both main circuit switching elements 4u to 4w and 4x to 4z are switched between an on state and an off state with respect to each other. The main circuit switching control circuit 30 is switched by providing a short pause period in which both the switching elements 4u to 4w and 4x to 4z are turned off, and the pause period starting from when the main circuit switching elements 4u to 4w and 4x to 4z are turned off. And a reverse voltage application switching control circuit 31 that turns on the reverse voltage application switching element 17 and turns it off after the rest period. The same elements as those in FIG. 17 are denoted by the same reference numerals, and redundant description is omitted.

  In FIG. 1, the main circuit switching control circuit 30 outputs on / off commands for the main circuit switching elements 4u to 4w and 4x to 4z, and is complementary to the main circuit switching elements 4u to 4w and 4x to 4z forming a set. Outputs an on / off command. Although FIG. 1 shows the main circuit switching control circuit 30 connected only to the main circuit switching element 4u, it is also connected to other main circuit switching elements 4v to 4z.

  For example, when the main circuit switching element 4x is turned off, the main circuit switching control circuit 30 outputs an on command to the main circuit switching element 4u with respect to the main circuit switching element 4u and the main circuit switching element 4x. When the main circuit switching element 4x is turned on, an off command is output to the main circuit switching element 4u.

  At this time, the main circuit switching element 4u, 4x has a short pause period in which both are turned off, and the main circuit switching control circuit 30 switches the main circuit switching element 4u to the on state during the pause period. .

  The reverse voltage application switching control circuit 31 of the reverse voltage application circuit 7 turns on the reverse voltage application switching element 17 to operate the reverse voltage application circuit 7 during the idle period starting from the time when the main circuit switching element 4u is turned off. Then, after the rest period, the reverse voltage application switching element 17 is turned off, and the operation of the reverse voltage application circuit 7 is stopped. Accordingly, the reverse voltage application circuit 7 can be appropriately operated regardless of the direction of the main circuit current flowing in the main circuit, and a detector for detecting the direction of the current is not necessary.

  FIG. 2 is a circuit diagram of a main part of the reverse voltage application circuit 7 in the power conversion device according to the first embodiment. The DC voltage source 1 is obtained, for example, by rectifying a three-phase AC power source and smoothing it with a smoothing capacitor 2. From the DC voltage source 1, a positive side DC bus 1a and a negative side DC bus 1b extend, and between the positive side DC bus 1a and the negative side DC bus 1b, two pieces corresponding to the main circuit switching elements 4u, 4x. MOSFETs are connected in series. Both the positive-side main circuit switching element 4u and the negative-side main circuit switching element 4x have freewheeling diodes 5u and 5x, respectively. A load terminal 11 connected to a load is taken out between the positive main circuit switching element 4u and the negative main circuit switching element 4x.

  The reverse voltage application circuits 7a and 7b are connected between the drain terminal and the source terminal of the main circuit switching elements 4u and 4x. That is, the reverse voltage application circuits 7a and 7b are connected between the cathode terminals of the freewheeling diodes 5u and 5x and the anode terminals of the freewheeling diodes 5u and 5x.

  The reverse voltage application circuits 7a and 7b include auxiliary power supplies 12a and 12b having constant voltage DC power supplies 8a and 8b whose voltage value is lower than that of the DC voltage source 1, and reverse voltage application switching whose breakdown voltage is lower than that of the main circuit switching elements 4u and 4x. It is constituted by a series connection of elements 17a and 17b and auxiliary diodes 29a and 29b that have a fast reverse recovery time and higher speed than the free-wheeling diodes 5u and 5x. The gate drive signals g1a and g1b of the main circuit switching elements 4u and 4x are input from the main circuit switching control circuit 30 through the base drive circuits 9a and 9b to the gate terminals of the main circuit switching elements 4u and 4x. The gate driving signals g2a and g2b of the reverse voltage application switching element 17 are input to the gate terminals of the reverse voltage application switching elements 17a and 17b from the reverse voltage application switching control circuit 31 via the base drive circuits 18a and 18b. .

  FIG. 3 is an explanatory diagram of the gate drive signal g1 from the main circuit switching control circuit 30 and the gate drive signal g2 from the reverse voltage application switching control circuit 31. The gate drive signal g1a is a gate drive signal input to the gate terminal of the positive side main circuit switching element 4u, and the gate drive signal g1b is a gate drive signal input to the gate terminal of the negative side main circuit switching element 4x, and the gate drive signal g2b. Is a gate drive signal inputted to the gate terminal of the reverse voltage application switching element 17.

  In FIG. 3, after the gate drive signal g1b of the negative main circuit switching element 4x is turned off at time t1, the gate drive signal g1a of the positive main circuit switching element 4u is turned on at time t3. During the rest period T, the gate drive signal g2b of the negative-side reverse voltage application switching element 17b is turned on at time t2, and is turned off at time t4 after the rest period T elapses. Although illustration is omitted, the gate drive signal g2a of the positive / reverse voltage application switching element 4u is similarly given on / off timing.

  Next, the operation will be described. The case where the load terminal 11 is switched from the state connected to the negative side DC bus 1b to the state connected to the positive side DC bus 1a will be described. In this case, first, when the load current flows into the load terminal 11 from the load side, when the gate drive signal g1b of the negative main circuit switching element 4x switches to the off command state, the negative main circuit switching element 4x is turned off immediately thereafter. Immediately after that, the load current flows into the positive DC bus 1a through the positive free-wheeling diode 5u.

  At this time, the potential state of the load terminal 11 is connected to the positive DC bus 1a. In this state, the potential of the drain terminal of the negative main circuit switching element 4x, that is, the cathode terminal of the negative auxiliary diode 29 is also connected to the positive DC bus 1a. On the other hand, since the negative side constant voltage DC voltage source 8b has a voltage value lower than that of the DC voltage source 1, a reverse voltage is applied to the negative side auxiliary diode 29b, and the negative side reverse voltage application switching element 17b is turned on. However, no current flows through the reverse voltage application circuit 7b.

  In this case, if the negative side reverse voltage application switching element 17b is turned on too early, the negative main circuit switching element 4x may not be completely turned off, and the auxiliary power supply 12b is short-circuited. . Then, although the voltage value is lower than that of the DC voltage source 1, an extra loss occurs, which is not preferable. Therefore, the timing at which the negative-side reverse voltage application switching element 17 is turned on (time point t2 in FIG. 3) is the timing after the negative-side main circuit switching element 4x is completely turned off.

  Next, when the load current flows out from the load terminal 11 to the load side, even if the gate drive signal g1b of the negative main circuit switching element 4x switches to the off command state, the negative side freewheeling diode 5x causes the current to flow in the forward direction. to continue. For this reason, the potential state of the load terminal 11 is still connected to the negative DC bus 1b. In this state, no reverse voltage is applied to the negative side auxiliary diode 29b, and a current flows from the low voltage DC voltage source 8b of the auxiliary power source 12b by turning on the negative side reverse voltage application switching element 17b.

  Thereby, the negative side freewheeling diode 5x can be turned off by flowing a reverse recovery current from the reverse voltage application circuit 7b into the negative side freewheeling diode 5x. Thereafter, after the elapse of the pause period T, the positive main circuit switching element 4u is turned on, and for the first time, the potential state of the load terminal 11 is connected to the positive DC bus 1a.

  In this case, if the negative side reverse voltage application switching element 17b is turned on too late, there is not enough time for the reverse recovery current to flow into the negative side freewheeling diode 5x, and the negative side freewheeling diode 5x is sufficiently reversed. I can't recover. Therefore, the timing at which the negative side reverse voltage application switching element 17b is turned on is a timing at which the negative side free-wheeling diode 5x can secure a time necessary for reverse recovery by the reverse recovery current from the reverse voltage application circuit 7b.

  Thus, there is a problem whether the reverse voltage application switching element 17 is turned on too early or too late, and is determined in consideration of these tradeoffs. In addition, the suspension period T may be set slightly longer depending on the balance between these.

  According to the first embodiment, the reverse voltage application circuit 7 can be appropriately operated at a uniform timing regardless of the direction of the main circuit current (load current), so that the detection for detecting the direction of the main circuit current is performed. A controller is not required, and the control mechanism can be simplified.

(Second Embodiment)
FIG. 4 is a circuit diagram of a main part of the reverse voltage application circuit 7 in the power conversion device according to the second embodiment. This second embodiment is different from the first embodiment shown in FIG. 2 in that the auxiliary power supplies 12a and 12b are low voltage DC voltage power supplies 8a and 8b lower than the voltage of the DC voltage source 1, and low voltage Current suppression circuits 10a and 10b that are connected in series with the DC voltage power supplies 8a and 8b and suppress the main circuit current flowing through the low voltage DC voltage power supplies 8a and 8b during reverse recovery of the freewheeling diode, and the low voltage DC voltage power supplies 8a and 8b and the current High frequency capacitors 32a and 32b that are connected in parallel to a series circuit with the suppression circuits 10a and 10b and have low internal impedance even in a high frequency range are provided.

  In FIG. 4, auxiliary power supplies 12a and 12b include low voltage DC voltage power supplies 8a and 8b that are lower than about 1/4 of the voltage of the DC voltage source 1, resistors as current suppression circuits 10a and 10b, and internal impedance even in a high frequency range. The high frequency capacitors 32a and 32b having a low frequency are connected in series.

  Here, the high frequency capacitors 32a and 32b are not a smooth electrolytic capacitor but a high frequency capacitor such as a ceramic capacitor or a film capacitor. Moreover, the resistors as the current suppression circuits 10a and 10b may substitute, for example, a wiring resistance of a copper foil pattern of a printed wiring board or a wiring resistance such as a copper wire or a copper plate. Further, it may be replaced with a constant current circuit as shown in FIG. In the configuration of FIG. 4, the discharge path connecting the high frequency capacitors 32a and 32b, the reverse voltage application switching elements 17a and 17b, the auxiliary diodes 29a and 29b, and the freewheeling diodes 5u and 5x is wired as short as possible so that the inductance is reduced. Constitute.

  In the second embodiment configured as described above, since the high frequency capacitors 32a and 32b having a low internal impedance even in the high frequency region are used, the charge discharge from the high frequency capacitors 32a and 32b is executed at a high speed. The rise time of the current that flows when the diodes 5u and 5x are reversely recovered can be shortened, and the maximum current can be increased. Further, in synergy with the operation of the current suppression circuits 10a and 10b, such an impulse-like current does not flow directly to the low-voltage DC voltage power supplies 8a and 8b, but a current with a more average waveform is generated. It flows to 8b.

  According to the first embodiment, in addition to the effects of the first embodiment, the current necessary for reverse recovery of the freewheeling diodes 5u and 5x can be passed in a short time, and the rest period needs to be extended. Therefore, deterioration of the control quality (waveform deterioration) of the power conversion device caused by the suspension period can be suppressed. Further, during the time when the reverse recovery current is supplied to the freewheeling diodes 5u and 5x, the main circuit current (load current) also passes through the reverse voltage application circuit 7, and the loss due to the main circuit current also increases. Therefore, it is desirable to complete the reverse recovery of the freewheeling diodes 5u and 5x as soon as possible, but this requirement can also be achieved. Furthermore, since the burden on the low voltage DC voltage power supplies 8a and 8b is reduced, the low voltage DC voltage power supplies 8a and 8b only need to have a low current capacity, and the internal heat generation of the low voltage DC voltage power supplies 8a and 8b is also reduced. .

(Third embodiment)
FIG. 6 is a circuit diagram of a main part of the reverse voltage application circuit 7 in the power conversion device according to the third embodiment of the present invention. In the third embodiment, the low-voltage DC voltage power supply 8 is used as a driving power supply for the main circuit switching element 4 in contrast to the first embodiment.

  In FIG. 6, the base drive circuit 9 of the main circuit switching element 4 includes a gate drive amplifier 27 and a gate resistor 19. The gate drive amplifier 27 obtains electric power from the low-voltage DC voltage power supply 8 and passes through the gate resistor 19. The gate drive signal of the main circuit switching element 4 is input to the gate terminal of the main circuit switching element 4. FIG. 6 shows a case where a resistor is used as the current suppression circuit 10. The main circuit switching control circuit 30 outputs an on / off command to the gate drive amplifier 27 of the base drive circuit 9 to control the on / off of the main circuit switching element 4, and the reverse voltage application switching control circuit 31 is controlled by the base drive circuit 18. An on / off command is output to the reverse voltage application switching element 17 via the.

  In the configuration of FIG. 6, an impulse-like current accompanying reverse recovery flows through the free-wheeling diode 5 to the low-voltage DC voltage power supply 8 due to the current suppression action of the current suppression circuit 10 and the high-frequency impedance reduction action of the high-frequency capacitor 32. Therefore, even when the freewheeling diode 5 is reversely recovered, the voltage fluctuation of the low-voltage DC voltage power supply 8 becomes very small.

  According to the third embodiment, in addition to the effects of the first embodiment, voltage fluctuations of the low-voltage DC voltage power supplies 8a and 8b are reduced and stabilized, so that the base drive circuit 9 of the main circuit switching element 4 is Even when power is supplied, adverse effects such as fluctuations in the power supply voltage can be prevented even when the freewheeling diode 5 is reversely recovered. Further, by sharing the power source between the low voltage DC voltage power source 8 and the power source of the base drive circuit 9, the circuit can be simplified.

(Fourth embodiment)
FIG. 7 is a circuit diagram of the main part of the reverse voltage application circuit 7 in the power conversion apparatus according to the fourth embodiment of the present invention. The fourth embodiment is different from the first embodiment in that the drive power for the reverse voltage application switching element 17 is supplied from the drive power for the main circuit switching element 4 by the bootstrap circuit 33. is there.

  In FIG. 7, the base drive circuit 18 of the reverse voltage application switching element 17 includes a gate drive amplifier 34 and a gate resistor 35, and obtains power from the low-voltage DC voltage power supply 8 by the bootstrap circuit 33. The bootstrap circuit 33 includes a bootstrap diode 36 and a bootstrap capacitor 37.

Then, the base drive circuit 18 of the reverse voltage application switching element 17 obtains power from the bootstrap circuit 33 in response to a command from the reverse voltage application switching control circuit 31 and uses it as a gate drive signal for the reverse voltage application switching element 17. It outputs to the gate terminal of the reverse voltage application switching element 17.

  During the period in which the main circuit switching element 4 is on or the period in which the freewheeling diode 5 is energized, the positive electrode of the low-voltage DC voltage power supply 8 → the bootstrap diode 36 → the bootstrap capacitor 37 → the auxiliary diode 29 → the main circuit switching element 4 → A negative charge loop of the low-voltage DC voltage power supply 8 is formed, and the bootstrap capacitor 37 is charged from the low-voltage DC voltage power supply 8. The power charged in the bootstrap capacitor 37 is used as a driving power source for the reverse voltage application switching element 17.

  According to the fourth embodiment, in addition to the effects of the first embodiment, the power source of the base drive circuit 18 of the reverse voltage application switching element 17 can be obtained without preparing another insulated power source. Therefore, the circuit can be simplified.

(Fifth embodiment)
FIG. 8 is a circuit diagram of the main part of the reverse voltage application circuit 7 in the power converter according to the fifth embodiment of the present invention. In the fifth embodiment, in contrast to the first embodiment, the drive signal for the reverse voltage application switching element 17 is supplied via a pulse transformer 38.

  In FIG. 8, the reverse voltage application switching control circuit 31 supplies a gate drive signal to the reverse voltage application switching element 17 via a pulse transformer 38. The reverse voltage application switching element gate drive signal g <b> 2 drives the gate of the reverse voltage application switching element 17 while being insulated by the pulse transformer 38.

  According to the fifth embodiment, since the gate drive signal can be isolated by only one pulse transformer 38, a power supply for a dedicated gate drive amplifier is not required. Therefore, the circuit can be simplified by driving with the same power source as the gate drive signals of other phases with a common control potential.

(Sixth embodiment)
FIG. 9 is a circuit diagram of the main part of the reverse voltage application circuit 7 in the power conversion apparatus according to the sixth embodiment of the present invention. This sixth embodiment is different from the first embodiment in that the pulse width of the drive source signal G applied to the main circuit switching elements 4u, 4x output from the control circuit 39 is set to both the main circuit switching elements 4u, 4x is set to be longer than the short pause period in which both are turned off.

  The drive source signal G of the main circuit switching elements 4u, 4x generated from the control circuit 39 usually has a PwM waveform. The control circuit 39 outputs only the drive source signal G whose pulse width is longer than the idle period in which both the main circuit switching elements 4u and 4x are turned off. This is to prevent pulse loss of the gate drive signal g1a of the positive main circuit switching element 4u.

  FIG. 10 is an explanatory diagram of pulse loss of the gate drive signal g1a of the positive side main circuit switching element 4u. As shown in FIG. 10A, the gate drive signal g1a of the positive main circuit switching element 4u is formed as a signal obtained by delaying the rise time of the drive source signal G by the pause period T, and the negative main circuit switching element 4x. The gate drive signal g1b is formed by delaying the rise time of the waveform obtained by inverting the on / off state of the drive source signal G by a pause period.

  In the gate drive signals g1a and g1b formed in this way, as shown in FIG. 10B, when the on-state period of the drive source signal G is shorter than the pause period T, the positive side main circuit switching element 4u The gate drive signal g1a is not turned on and a pulse defect occurs.

  In the negative side reverse voltage application switching element 17b, normally, the current is cut off naturally by the reverse side auxiliary diode 29b being reverse-biased by turning on the positive side main circuit switching element 4u. However, when such a pulse defect occurs, the positive side main circuit switching element 4u is not turned on, so the negative side reverse voltage application switching element 4x is turned off by its own blocking capability, and the negative side reverse voltage application is performed. As a result, the switching loss and surge voltage when the switching element 4x is turned off increase, and as a result, the reverse voltage application switching element 17b has to be selected with a high capability. Therefore, in the sixth embodiment, a pulse width narrower than such a pause period is not output.

  According to the sixth embodiment, in addition to the effects of the first embodiment, the control device 39 does not output the drive source signal G having a pulse width shorter than the pause period T, so that the positive-side main circuit switching element 4u It is possible to prevent the pulse loss of the gate drive signal g1a. For this reason, when the auxiliary diode 29b is reverse-biased, the current of the reverse voltage application switching element 17b is cut off naturally, and as a result, the reverse voltage application switching element 17b does not need to select a high-performance element.

(Seventh embodiment)
FIG. 11 is a circuit diagram of the main part of the reverse voltage application circuit 7 in the power converter according to the seventh embodiment of the present invention. The sixth embodiment is different from the first embodiment in that the seventh embodiment is a negative of the DC power source out of the set of two main circuit switching elements 4u to 4w and 4x to 4z. The reverse voltage application circuit 7 is provided only in the main circuit switching elements 4x to 4z connected to the side. FIG. 11 shows a power converter when used as a three-phase inverter.

  In FIG. 11, a positive DC bus 1a and a negative DC bus 1b extend from the DC voltage source 1, and are connected to the positive main circuit switching elements 4u to 4w between the positive DC bus 1a and the negative DC bus 1b. The IGBT is applied, and the MOSFET is applied to the negative main circuit switching elements 4x to 4z.

  The negative side main circuit switching elements 4x to 4z use MOSFETs in which freewheeling diodes 5x to 5z are incorporated, whereas the positive side main circuit switching elements 4u to 4w have freewheeling diodes 5u to 5w. Since no IGBT is used, free-wheeling diodes 5u to 5w having a short reverse recovery time and a small reverse recovery loss are connected in parallel to the positive main circuit switching elements 4u to 4w. Therefore, the reverse voltage application circuit 7 is not required for the positive side main circuit switching elements 4u to 4w.

  That is, although the reverse voltage application circuits 7x to 7z are connected to the negative side main circuit switching elements 4x to 4z, the reverse voltage application circuit 7 is not connected to the positive side main circuit switching element 4u. The negative voltage main circuit switching elements 4x to 4z have reverse voltage application circuits 7x to 7z in which only one low voltage DC voltage power supply 8 is commonly applied to a circuit for three phases. This is because one power line of the x-phase to z-phase reverse voltage application circuit 7 can be shared with the negative DC bus 1 b of the DC voltage source 1.

  According to the seventh embodiment, in addition to the effects of the first embodiment, the reverse voltage application circuits 7x to 7z are applied only to the negative main circuit switching elements 4x to 4z. On the other hand, it is not necessary to prepare a low-voltage DC voltage power supply 8 for each phase, and only one unit is required for each phase. Further, since only one low voltage DC voltage power supply 8 is required, the circuit can be simplified.

(Eighth embodiment)
FIG. 12 is a circuit diagram of the main part of the reverse voltage application circuit 7 in the power conversion apparatus according to the eighth embodiment of the present invention. The eighth embodiment is different from the first embodiment in that the voltage change for adjusting the voltage of the drive signal of the main circuit switching element 4 so as to suppress the temporal change of the output voltage of the main circuit switching element 4 is suppressed. A rate suppression circuit 20 is provided.

  In FIG. 12, the voltage change rate suppression circuit 20 is configured by connecting a voltage change rate suppression capacitor 21 and a voltage change rate suppression resistor 22 in series, and the drain terminal of the main circuit switching element 4 and the main circuit switching element. 4 is connected to the gate terminal.

  At the time of reverse recovery of the freewheeling diode 5, the freewheeling diode 5 is rapidly turned off by the operation of the reverse voltage applying circuit 7. Therefore, the temporal change rate of the drain-source voltage of the main circuit switching element 4 increases. Therefore, when the drain voltage of the main circuit switching element 4 starts to rapidly decrease, the gate voltage of the main circuit switching element 4 is lowered by the action of the voltage change rate suppression circuit 20, and as a result, the on-speed of the main switching element is reduced. To do.

  According to the eighth embodiment, in addition to the effects of the first embodiment, since the on-speed of the main switching element 4 is reduced, the voltage change rate of the main circuit switching element 4 is suppressed, and the electromagnetic interference wave Generation of (noise) is suppressed.

(Ninth embodiment)
FIG. 13 is a circuit diagram of the main part of the reverse voltage application circuit 7 in the power conversion device according to the ninth embodiment of the present invention. In the ninth embodiment, a MOSFET designed with priority given to lowering of the on-resistance is used as the main circuit switching element 4 with respect to the first embodiment, and the bipolar element 23 is provided in the main circuit switching element 4. They are connected in parallel. The bipolar element 23 is turned on almost simultaneously with the main circuit switching element 4 and is turned off somewhat earlier than the main circuit switching element 4 is turned off.

In FIG. 13, a bipolar element 23 is connected in parallel to the main circuit switching element 4. The gate signal delay circuit 24
Upon receiving the original gate drive signal from the main circuit switching control circuit 30, the gate drive signal to the main circuit switching element 4 and the base drive signal to the bipolar element 23 are distributed, and the gate drive signal of the main circuit switching element 4 is turned off. The timing is somewhat delayed from the off timing of the base drive signal of the bipolar element 23.

  A gate drive signal to the main circuit switching element 4 is input to the main circuit switching element 4 via the gate drive amplifier 27 and the gate resistor 19 of the base drive circuit 9. Similarly, a base drive signal to the bipolar element 23 is input to the bipolar element 23 via the gate drive amplifier 28 and the gate resistor 26 of the base drive circuit 25.

  FIG. 14 shows a trend curve of the on-resistance and reverse recovery time of the element characteristics of a general power MOSFET. In FIG. 14, when the MOSFET is designed so that the on-resistance becomes small, the reverse recovery time becomes long. As a result, the loss due to the reverse recovery also becomes large, and conversely, when the MOSFET is designed so that the on-resistance becomes large. The recovery time is shortened, and as a result, the loss due to reverse recovery tends to decrease.

  Therefore, in the ninth embodiment, the power MOSFET used for the main circuit switching element 4 is designed with a preferentially low on-resistance, and is turned on almost simultaneously with the main circuit switching element 4 to switch the main circuit. Bipolar elements 23 that turn off somewhat earlier than element 4 turns off are connected in parallel.

  Thereby, parallel operation with the bipolar element 23 having an accumulation time can be realized. When on, a large amount of current flows through the low-resistance bipolar element 23, so that on-loss can be reduced. Further, at the time of turn-off, the off-timing of the bipolar element 23 is somewhat earlier, so that the main circuit switching element 4 is turned off after the bipolar element 23 having the accumulation time is completely turned off, so that the turn-off loss can be reduced.

  According to the ninth embodiment, the chip area of the power semiconductor can be reduced and the generated loss can be reduced, so that a low-cost and high-efficiency power conversion device can be realized.

The circuit diagram of the power converter device concerning the 1st Embodiment of this invention. The circuit diagram of the principal part of the reverse voltage application circuit in the power converter device concerning the 1st Embodiment of this invention. Explanatory drawing of the gate drive signal from the main circuit switching control circuit in the 1st Embodiment of this invention, and the gate drive signal from a reverse voltage application switching control circuit. The circuit diagram of the principal part of the reverse voltage application circuit in the power converter device concerning the 2nd Embodiment of this invention. The circuit diagram which shows an example of the current suppression circuit in the 2nd Embodiment of this invention. The circuit diagram of the principal part of the reverse voltage application circuit in the power converter device concerning the 3rd Embodiment of this invention. The circuit diagram of the principal part of the reverse voltage application circuit in the power converter device concerning the 4th Embodiment of this invention. The circuit diagram of the principal part of the reverse voltage application circuit in the power converter device concerning the 5th Embodiment of this invention. The circuit diagram of the principal part of the reverse voltage application circuit in the power converter device concerning the 6th Embodiment of this invention. Explanatory drawing of the pulse defect | deletion of the gate drive signal of the main circuit switching element of the positive side in the 6th Embodiment of this invention. The circuit diagram of the principal part of the reverse voltage application circuit in the power converter device concerning the 7th Embodiment of this invention. The circuit diagram of the principal part of the reverse voltage application circuit in the power converter device concerning the 8th Embodiment of this invention. The circuit diagram of the principal part of the reverse voltage application circuit in the power converter device concerning the 9th Embodiment of this invention. The graph of the tendency curve of on-resistance and reverse recovery time of the element characteristic of general power MOSFET. The circuit diagram which shows an example of the conventional inverter circuit. The current waveform figure which shows the reverse recovery characteristic of a freewheeling diode. The circuit diagram which shows an example of the conventional power converter device.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... DC voltage source, 1a ... Positive side DC bus, 1b ... Negative side DC bus, 2 ... Smoothing capacitor, 3 ... Inverter main circuit, 4 ... Main circuit switching element, 5 ... Free-wheeling diode, 6 ... Load, 7 ... Reverse Voltage application circuit, 8 ... Low voltage DC voltage power supply, 8a, 8b ... Power supply line, 9 ... Base drive circuit, 9a, 9b ... Power supply line, 10 ... Current suppression circuit, 11 ... Load terminal, 12 ... Auxiliary power supply, 13 ... Diode, 14 ... capacitor, 15 ... capacitor, 16 ... diode, 17 ... reverse voltage application switching element, 18 ... base drive circuit, 19 ... gate resistance, 20 ... voltage change rate suppression circuit, 21 ... voltage change rate suppression capacitor, 22 ... Voltage change rate suppression resistor, 23 ... Bipolar element, 24 ... Gate signal delay circuit, 25 ... Base drive circuit, 26 ... Gate resistance, 27 ... Gate Drive amplifier, 28 ... Gate drive amplifier, 29 ... Auxiliary diode, 30 ... Main circuit switching control circuit, 31 ... Reverse voltage application switching control circuit, 32 ... High frequency capacitor, 33 ... Bootstrap circuit, 34 ... Gate drive Amplifier 35 ... Gate resistance 36 ... Bootstrap diode 37 ... Bootstrap capacitor 38 ... Pulse transformer 39 ... Control circuit

Claims (9)

A pair of main circuit switching elements connected in series to a DC voltage source for supplying power to a load, freewheeling diodes connected in reverse parallel to these main circuit switching elements, and when each freewheeling diode is shut off, A reverse voltage application circuit for applying a reverse voltage smaller than the DC voltage source to each freewheeling diode,
The reverse voltage application circuit includes an auxiliary power supply having a voltage value lower than that of the DC voltage source, a reverse voltage application switching element that is turned on during reverse recovery of the freewheeling diode and has a withstand voltage lower than that of the main circuit switching element, and is reverse to the freewheeling diode. It consists of a series connection with a fast recovery diode with a short recovery time,
Main circuit switching control for switching the main circuit switching elements with a short pause period in which both the main circuit switching elements are turned off when the two main circuit switching elements are switched between the on state and the off state. Circuit,
And a reverse voltage application switching control circuit for turning on the reverse voltage application switching element during an idle period starting from the time when the main circuit switching element is turned off, and turning off after the elapse of the idle period. . The auxiliary power source suppresses a main circuit current that flows in the low voltage DC voltage power source during reverse recovery of the freewheeling diode connected in series with the low voltage DC voltage power source that is lower than the voltage of the DC voltage source. a current limit circuit, the power of claim 1, wherein the internal impedance in the connected high-frequency range in parallel with the series circuit of a low voltage DC voltage power supply and the current suppressing circuit has a low high-frequency capacitor Conversion device.
  The power converter according to claim 1 or 2, wherein the low-voltage DC voltage power source is used as a power source for driving the main circuit switching element.   4. The power conversion device according to claim 1, wherein a driving power source for the reverse voltage application switching element is supplied from a driving power source for the main circuit switching element by a bootstrap circuit. 5.   4. The power conversion device according to claim 1, wherein the drive signal for the reverse voltage application switching element is supplied via a pulse transformer. 5.   6. The power conversion device according to claim 1, wherein a pulse width of a drive source signal applied to the main circuit switching element is made longer than the pause period.   7. The reverse voltage application circuit is provided only in a main circuit switching element connected to the negative side of a DC power source among a set of two main circuit switching elements. The power converter described.   8. A voltage change rate suppression circuit for adjusting a voltage of a drive signal of the main circuit switching element so as to suppress a temporal change in the output voltage of the main circuit switching element. A power conversion device according to claim 1.   As the main circuit switching element, a MOSFET designed with priority given to a decrease in on-resistance is used, and a bipolar element that is turned on almost simultaneously with the main circuit switching element and is turned off somewhat earlier than the main circuit switching element is turned off is used. The power conversion device according to claim 1, wherein the power conversion device is connected in parallel to the circuit switching element.

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