JP2010178542A - Power converter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To attain reduction in the leak current that flows into the ground from a power conversion main circuit, by applying resistors for fixing a conductive potential in a power converter. <P>SOLUTION: By electrically connecting the potential of a heat sink (electrically conducting member), wherein an IGBT (semiconductor element) is mounted to a connection between resistors for fixing a conductive potential which are connected to a power conversion DC main circuit, the applied voltage between the ground and the heat sink (conducting member) is reduced, and the leak current that flows into the ground via a floating capacitance can be reduced. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a power conversion device having a circuit configuration for fixing a potential of a conductive member to which a semiconductor element group to be applied is attached.

  A power converter is used to rotate the AC motor at an arbitrary rotational speed. In general, a forward converter that converts an AC voltage into a DC voltage and an inverse converter that converts a DC voltage back into an AC voltage are applied to a power converter. A positive DC power source, a negative DC power source, and a positive DC A smoothing capacitor that smoothes the pulsating flow of the DC voltage is connected to each neutral point DC power source, which is the midpoint between the power source and the negative side DC power source. The positive side DC power source, negative side DC power source, and neutral point DC power source There is a configuration in which the output point is connected via a conversion element. Then, these semiconductor elements are repeatedly turned on and off (hereinafter referred to as switching) to generate a substantial AC voltage, and the AC voltage obtained from the main commercial power supply via the transformer is converted to the DC voltage by the forward converter. Convert to Then, the obtained DC voltage is converted into an AC voltage having an arbitrary frequency and amplitude by an inverse converter, and electric power is supplied to the AC motor, whereby the speed of the AC motor is controlled to be accelerated.

  Further, by switching the semiconductor element, an AC voltage from an AC motor is converted into a DC voltage by an inverse converter, and the obtained DC voltage is converted into an AC voltage of a commercial frequency by a forward converter. The speed of the AC motor is controlled to be reduced by regenerating power to the main commercial power source via the generator.

  By the way, there are various AC motors applied to the steel rolling plant, ranging from several [kW] auxiliary motors to several thousand [kW] main motors depending on the application. Accordingly, there are various power converters for driving the power converter, and when it is used for driving the main motor, a capacity of several thousand [kVA] or more is required.

  As a method of increasing the capacity of the power conversion device, there is a method of increasing the main circuit DC voltage of the power conversion DC main circuit constituting the power conversion device. In order to increase the voltage of the power converter, it is necessary to increase the withstand voltage specification of the semiconductor element connected to the power conversion DC main circuit. For example, in the case of an IGBT (Insulated Gate Bipolar Transistor) module, This corresponds to increasing the withstand voltage specification between the base plate serving as the mounting plate and the collector main terminal and emitter main terminal. The same applies to the diode module, which corresponds to increasing the withstand voltage specification between the base plate as the mounting plate of the diode module and the anode main terminal and cathode main terminal. Here, the withstand voltage is a voltage value at which dielectric breakdown does not occur inside and outside the semiconductor element.

  Since the IGBT module and the diode module are generally mounted on a heat sink that is conductive for cooling the IGBT module and the diode module, the potential of the base plate of the IGBT module and the diode module is electrically connected to the heat sink potential. .

  Here, as a conventional method for realizing high voltage of the power converter, for example, an IGBT module group configured by connecting two IGBT modules in series and a diode module configured by connecting two diode modules in series There is a circuit configuration that allows a group to function as one switch.

  In this conventional circuit configuration, four groups of the IGBT module groups are assigned to each of the U, V, and W phases. The four sets include a positive IGBT module group for outputting the bus potential of the positive DC power source, a first neutral IGBT module group for outputting the bus potential of the neutral DC power source, and a second It consists of a neutral IGBT module group and a negative IGBT module group for outputting the bus potential of the negative DC power supply. These are connected in series between the bus of the positive DC power supply and the bus of the negative DC power supply.

  Two sets of the diode module groups are assigned to each of the U, V, and W phases. Between the connection point of the positive-side IGBT module group and the first neutral-point IGBT module group and the bus of the neutral-point DC power supply, and between the connection point of the negative-side IGBT module group and the second neutral-point IGBT module group A positive-side diode module group comprising a first positive-side diode module and a second positive-side diode module connected in series for outputting the bus potential of the neutral-point DC power source between the buses of the neutral-point DC power source And a negative diode module group composed of a first negative diode module and a second negative diode module.

  The cathode main terminal of the first positive diode module of the positive diode module group is connected to a connection point between the positive IGBT module group and the first neutral IGBT module group. The anode main terminal is connected to the cathode main terminal of the second positive diode module. The anode main terminal of the second positive diode module is connected to a neutral point DC power source.

  The cathode main terminal of the first negative diode module of the negative diode module group is connected to a neutral DC power supply. The anode main terminal is connected to the cathode main terminal of the second negative diode module. The anode main terminal is connected to a connection point between the negative IGBT module group and the second neutral IGBT module group.

  Eight IGBT modules are applied in each of the U, V, and W phases. The collector main terminal of the first series positive side IGBT module which is the positive side IGBT module group is connected to the bus of the positive side DC power supply. The emitter main terminal of the first series positive side IGBT module is connected to the collector main terminal of the second series positive side IGBT module. The emitter main terminal of the second series positive side IGBT module is connected to the collector main terminal of the first series first neutral point IGBT module which is the first neutral point IGBT module group. The emitter main terminal of the first series first neutral point IGBT module is connected to the collector main terminal of the second series first neutral point IGBT module.

  The emitter main terminal of the second series first neutral point IGBT module is connected to the collector main terminal of the first series second neutral point IGBT module which is the second neutral point IGBT module group. The emitter main terminal of the first series second neutral point IGBT module is connected to the collector main terminal of the second series second neutral point IGBT module.

  The emitter main terminal of the second series second neutral IGBT module is connected to the collector main terminal of the first series negative IGBT module which is a negative IGBT module group. The emitter main terminal of the first series negative side IGBT module is connected to the collector main terminal of the second series negative side IGBT module. The emitter main terminal of the second series negative IGBT module is connected to the bus of the negative DC power supply.

  The output point of each phase is a connection point between the first neutral point IGBT module group and the second neutral point IGBT module group.

  Six heat sinks for mounting the IGBT module and six heat sinks for mounting the diode module are assigned to each of the U, V, and W phases. The positive side IGBT module group is mounted on one positive side heat sink, the first neutral point IGBT module group is mounted on one first neutral point heat sink, and the second neutral point IGBT is mounted. The module group is mounted on one second neutral point heat sink.

  The negative side IGBT module group is mounted on one negative side heat sink. The positive diode group is mounted on one positive diode heat sink, and the negative diode group is mounted on one negative diode heat sink.

  By connecting the positive side heat sink, the first neutral point heat sink, the second neutral point heat sink, and the negative side heat sink to the connection point of the IGBT modules mounted on the heat sink connected in series, the heat sink potential and The potential of the base plate of the IGBT module is electrically connected to the potential of the emitter main terminal of the first series IGBT module of the IGBT module group and the potential of the collector main terminal of the second series IGBT module, respectively. With this switching, the heat sink potential and the potential of the base plate of the IGBT module change.

  In the case of the heat sink for the positive / negative side diode, the circuit configuration is the same as that of each heat sink for mounting the IGBT module group, and the diode-connected heat sink is connected to the connection point of the diode modules mounted on the heat sink. As a result, the heat sink potential and the potential of the base plate of the diode module fluctuate due to the conduction / cutoff of the diode module. In addition, the voltage applied between the ground and the base plate of each heat sink and each IGBT module and diode module is connected to the ground via the high resistance of the neutral point DC power supply. The applied voltage is added.

  The operation relationship between the positive side IGBT module group, the first neutral point IGBT module group, the second neutral point IGBT module group, and the negative side IGBT module group is the positive side IGBT module group and the first neutral point IGBT module. When the group is conductive, the second neutral IGBT module group and the negative IGBT module group are cut off, and the first neutral IGBT module group and the second neutral IGBT module group are conductive. When the positive-side IGBT module group and the negative-side IGBT module group are in the cut-off state, and when the second neutral-point IGBT module group and the negative-side IGBT module group are in the conductive state, the positive-side IGBT module group and the first neutral-point IGBT module group The point IGBT module group is cut off.

  In the case of the positive heat sink, the voltage between each heat sink potential and the ground in the conduction state of the IGBT module group is represented by Ep as the DC voltage between the positive DC power supply and the neutral DC power supply. When the voltage across the connected high resistance is Erc, it is expressed by equation [1].

Applied voltage between ground and positive heat sink = Ep + Erc ... [1]
(When the positive side IGBT module group is in conduction)

  In addition, in the conductive state of the first neutral point IGBT module group, the voltage applied between the first neutral point heat sink and the ground is determined by the positive side IGBT module group and the first neutral point IGBT module group. The conduction state differs from the case where the first neutral point IGBT module group and the second neutral point IGBT module group are in the conductive state, and the positive side IGBT module group and the first neutral point IGBT module group are conductive. In the case of the state, it is expressed by the equation [2], and when the first neutral point IGBT module group and the second neutral point IGBT module group are in the conductive state, it is expressed by the equation [3].

Applied voltage between ground and first neutral point heat sink = Ep + Erc ... [2]
(When the primary IGBT module group and the first neutral IGBT module group are in conduction)

Applied voltage between ground and first neutral point heat sink = Erc ... [3]
(When the first and second neutral IGBT modules are in conduction)

  On the other hand, in the conductive state of the second neutral point IGBT module group, the voltage applied between the second neutral point heat sink and the ground is the first neutral point IGBT module group and the second neutral point. The DC voltage between the neutral point DC power source and the negative side DC power source is different from that when the IGBT module group is in a conductive state and when the negative side IGBT module group and the second neutral point IGBT module group are in a conductive state. Then, when the first neutral point IGBT module group and the second neutral point IGBT module group are in the conductive state, it is expressed by Equation [4], and the negative side IGBT module group and the second neutral point IGBT are expressed as follows. When the module group is in a conductive state, it is expressed by Equation [5].

Applied voltage between ground and second neutral point heat sink = Erc ... [4]
(When the first and second neutral IGBT modules are in conduction)

Applied voltage between ground and second neutral point heat sink = En + Erc ... [5]
(When the negative IGBT module group and the second neutral IGBT module group are in the conductive state)

  Further, the voltage applied between the negative heat sink and the ground in the conductive state of the negative IGBT module group is expressed by Equation [6].

Applied voltage between ground and negative heat sink = En + Erc ... [6]
(When the negative IGBT module group and the second neutral IGBT module group are in the conductive state)

  Here, in the conductive state of each IGBT module group, the collector main terminal, the emitter main terminal, and the heat sink of each IGBT module have the same potential, and therefore, between the base plate of each IGBT module and the collector / emitter main terminal. No voltage is applied to.

  In the conductive state of the positive / negative diode module group, the voltage applied between each diode heat sink and the ground can be expressed by Equation [7].

Applied voltage between ground and heat sink for positive / negative diode
= Erc ... [7]
(When positive / negative diode modules are in a conductive state)

  Here, since the anode main terminal, the cathode main terminal, and the heat sink potential in the conductive state of each diode module group are all the same potential, no voltage is applied between the base plate of each diode module and the anode / cathode main terminal.

  In the shut-off state of each IGBT module group, the potential of each heat sink and the potential of the base plate of each IGBT module are the same as the potential of the emitter main terminal of the first series IGBT module and the collector main terminal of the second series IGBT module. Therefore, it is applied between the base plate of the first series IGBT module and the collector main terminal of the first series IGBT module, between the base plate of the second series IGBT module and the emitter main terminal of the second series IGBT module. The voltage is equal to the voltage applied between the collector main terminal and the emitter main terminal of each IGBT module.

  In particular, the maximum voltage applied between the base plate of each IGBT module and the collector / emitter main terminal is when each IGBT module cuts off the current, and the jump when each IGBT module cuts off the current. Assuming that the upward voltage is ΔVi, the voltage applied between the base plate of each IGBT module and each heat sink-collector / emitter main terminal can be expressed by Equation [8].

Maximum applied voltage between base plate and collector / emitter main terminal
= Ep (En) / 2 + ΔVi ... [8]

  Here, since the DC voltages Ep and En of the main circuit during normal circuit operation are (Ep) = (En), the positive side IGBT module group, the first neutral point IGBT module group, and the second neutral point In the point IGBT module group and the negative IGBT module group, there is no difference in the voltage applied between the base plate and the collector / emitter main terminal of each IGBT module when the current of the IGBT module group is interrupted.

  Moreover, the voltage applied between each heat sink and the ground in the cutoff state of each IGBT module group can be expressed by Equation [9].

Applied voltage between earth and each heat sink
= Ep (En) / 2 + ΔVi + Erc (9)

  In the positive heat sink, the first neutral point heat sink, the second neutral point heat sink, and the negative IGBT heat sink, there is no difference in the voltage applied between each heat sink and the ground when the current of the IGBT module group is interrupted.

  In the cutoff state of the positive side / negative side diode module group, the voltage applied between the base plate of the first series diode module and the cathode main terminal is between the base plate of the second series diode module and the anode main terminal, It can be expressed by equation [10].

Maximum applied voltage between base plate and anode / cathode main terminal
= Ep (En) / 2 + ΔVd (10)
(However, ΔVd: Bounce voltage due to recovery operation)

  In addition, the voltage applied between each diode heat sink and the ground in the cut-off state of the positive / negative diode module group can be expressed by Equation [11].

Applied voltage between earth and heat sink for each diode
= Ep (En) / 2 + ΔVd + Erc (11)

JP 2003-174882 A JP 2002-171768 A

  In order to reduce the withstand voltage specification between the base plate of each IGBT module and the collector main terminal and emitter main terminal, it is necessary to bring the potential of each heat sink close to the potential of the collector main terminal and emitter main terminal. In order to reduce the withstand voltage specification between the base plate of the module and the anode main terminal and the cathode main terminal, it is necessary to bring the potential of each heat sink close to the potential of the anode main terminal and the cathode main terminal.

  However, when the heat sink potential is brought close to the potential of each main terminal, a voltage is applied between the ground and the heat sink, and a leakage current flows from the heat sink to the ground due to stray capacitance generated between the ground and the heat sink. This leakage current becomes a factor that causes the ground potential to fluctuate. As the voltage applied between the ground and the heat sink increases, the leakage current flowing from the heat sink to the ground also increases, so that the potential fluctuation of the ground also increases.

In the conventional circuit configuration, there has been a problem of adverse effects such as malfunctions on various substrates applied to the power converter and other devices applied to the steel plant due to the potential fluctuation of the ground.
The subject of this invention is providing the power converter device which can reduce the leakage current which flows into a ground from a heat sink, and can reduce the bad influence to other apparatuses.

  In order to solve the above-described problems, a power conversion device according to the present invention includes a power conversion DC main circuit between a positive-side DC power source bus and a neutral-point DC power source bus, and a neutral-point DC power source bus and a negative side. Two heat sink potential fixing resistors connected in series are provided between the bus of the DC power source and between the output point of the power converter and the neutral point DC power source, and the potential of each heat sink is set to the potential between the resistors. did.

  According to the present invention, by reducing the voltage applied between the heat sink and the ground, the leakage current flowing from the power conversion main circuit to the ground can be reduced, and various substrates and steel applied to the power conversion device It is possible to reduce adverse effects such as malfunctions on other equipment applied to the plant.

It is a whole lineblock diagram showing the power converter of a 1st embodiment by the present invention. It is a circuit block diagram which shows an inverse converter (refer FIG. 1) in detail. It is a whole block diagram which shows the power converter device of 2nd Embodiment by this invention. It is a circuit block diagram which shows an inverse converter (refer FIG. 3) in detail.

Embodiments of the present invention will be described with reference to the accompanying drawings.
<First Embodiment>
FIG. 1 is an overall configuration diagram showing a power conversion device 1a according to a first embodiment of the present invention.

  In this power conversion device 1a, the bus P of the positive side DC power source and the neutral point DC power source between the forward converter 500 that converts AC voltage into DC voltage and the inverse converter 510 that converts DC voltage back into AC voltage. Smoothing capacitors Cp and Cn for smoothing the pulsating flow of the DC voltages Ep and En are connected between the bus COM and the bus N of the negative side DC power source, respectively.

  The forward converter 500 converts the AC voltage obtained from the main commercial power supply 800 through the transformer 700 into the DC voltages Ep and En, and charges and discharges the smoothing capacitors Cp and Cn, thereby making the DC voltages Ep and En constant. Control to keep on. The inverse converter 510 converts the DC voltages Ep and En converted by the forward converter 500 into an AC voltage having an arbitrary frequency and amplitude, and supplies / regenerates power to the AC motor 600, whereby the AC motor 600 Variable speed control. Further, the bus COM of the neutral point DC power source is connected to the ground via a high resistance Rc.

  FIG. 2 is a circuit configuration diagram showing in detail the inverse converter 510 (see FIG. 1). The forward converter 500 (see FIG. 1) may have a circuit configuration similar to that of the inverse converter 510.

  The inverse converter 510 according to the first embodiment of the present invention includes power conversion main circuits (311, 312, 313). The power conversion main circuits (311, 312, 313) are U-phase, V-phase, and W-phase power conversion main circuits of three-phase alternating current, and have the same internal configuration.

  In U-phase power conversion main circuit 311, two series-connected U-phase positive IGBT module groups QP 1 and QP 2 and U-phase first neutral point are connected between bus P of positive DC power supply and bus N of negative DC power supply. IGBT module group QPC1, QPC2, U-phase second neutral IGBT module group QNC1, QNC2 and U-phase negative IGBT module group QN1, QN2 are connected.

  Of these, two positive diodes in one diode module are connected between the connection point of the second series positive IGBT module QP2 and the first series first neutral IGBT module QPC1 and the bus COM of the neutral DC power supply. A U-phase positive diode module DCP on which the side diodes DCP1 and DCP2 are mounted is connected. Between the connection point of the second series second neutral point IGBT module QNC2 and the first series negative side IGBT module QN1 and the bus COM of the neutral point DC power supply, two negative sides in one diode module A U-phase negative diode module DCN on which the diodes DCN1 and DCN2 are mounted is connected.

  The U-phase positive IGBT module groups QP1 and QP2 are mounted on the U-phase positive heat sink 211, and the U-phase first neutral IGBT module groups QPC1 and QPC2 are mounted on the U-phase first neutral heat sink 212. . The U-phase second neutral IGBT module group QNC1 and QNC2 are mounted on the U-phase second neutral heat sink 213, and the U-phase negative IGBT module group QN1 and QN2 are mounted on the U-phase negative heat sink 214. . The U-phase positive diode module DCP and the U-phase negative diode module DCN are mounted on the diode heat sink 215.

  Two series-connected U-phase positive heat sink potential fixing resistors RHV11 and RHV12 are connected between the bus P of the positive DC power supply and the bus COM of the neutral DC power supply, and the bus COM of the neutral DC power supply and Two series-connected U-phase negative heat sink potential fixing resistors RHV13 and RHV14 are connected between the buses N of the negative DC power supply. Further, the output point UAC of the U-phase power conversion main circuit 311 which is a connection point between the second series first neutral point IGBT module QPC2 and the first series second neutral point IGBT module QNC1, and the bus COM of the neutral point DC power source Are connected to resistances RHV15 and RHV16 for fixing the U-phase neutral point heat sink potential.

  The U-phase positive heat sink 211 is connected to the connection point of the U-phase positive heat sink potential fixing resistors RHV11 and RHV12. The U-phase first neutral point heat sink 212 and the U-phase second neutral point heat sink 213 are connected to the connection points of the U-phase neutral point heat sink potential fixing resistors RHV15 and RHV16, respectively. The U-phase negative heat sink 214 is connected to the connection point of the U-phase negative heat sink potential fixing resistors RHV13 and RHV14. The diode heat sink 215 is connected to the bus COM of the neutral DC power supply.

  Here, the heat sink potential fixing resistors RHV11, RHV12, RHV13, RHV14, RHV15, and RHV16 all have the same resistance value, and the DC voltage Ep between the positive side DC power source and the neutral point DC power source and the neutral point The DC voltage En of the point DC power supply and the negative DC power supply is (Ep) = (En) during normal circuit operation.

  The potential of the U-phase positive heat sink 211 and the potential of the base plates QP1B and QP2B of the positive IGBT modules QP1 and QP2 in this embodiment are for fixing the positive heat sink potential regardless of the switching of the positive IGBT modules QP1 and QP2. Since the voltage at both ends of the high resistance Rc connected to the neutral DC power supply is Erc because it is fixed at the connection point potential between the resistors RHV11 and RHV12, the voltage applied between the ground and the U-phase positive heat sink 211 Can be expressed by equation [12].

Applied voltage between earth and U-phase positive heat sink 211
= Ep / 2 + Erc ... [12]

  Further, in the conductive state of the positive side IGBT modules QP1 and QP2, the potentials of the collector main terminals and the emitter main terminals of the positive side IGBT modules QP1 and QP2 are the potentials of the bus P of the positive side DC power supply. Respective voltages applied between the base plates QP1B and QP2B of the modules QP1 and QP2 and the collector / emitter main terminal can be expressed by Expression [13].

Applied voltage between base plate and collector / emitter main terminal (when conducting)
= Ep / 2 [13]

  Further, the voltage applied between the base plates QP1B and QP2B of the positive-side IGBT modules QP1 and QP2 and the collector / emitter main terminal at the time of current interruption can be expressed by Expression [14].

Applied voltage between base plate and collector / emitter main terminal (when cut off)
= Ep / 2 + ΔVi [14]

  On the other hand, the potential of the U-phase negative heat sink 214 and the potential of the base plates QN1B and QN2B of the negative IGBT modules QN1 and QN2 are independent of the switching of the negative IGBT modules QN1 and QN2, and the negative heat sink potential fixing resistor RHV13. The voltage applied between the ground and the U-phase negative heat sink 214 can be expressed by Equation [15].

Applied voltage between earth and U-phase negative heat sink 214
= En / 2 + Erc ... [15]

  In the conductive state of the negative side IGBT modules QN1, QN2, the potential of the collector main terminal and the emitter main terminal of each negative side IGBT module QN1, QN2 is the potential of the bus N of the negative side DC power supply. Each voltage applied between the base plates QN1B and QN2B of the modules QN1 and QN2 and the collector / emitter main terminal can be expressed by the equation [16].

Applied voltage between base plate and collector / emitter main terminal (when conducting)
= En / 2 [16]

  Further, the voltage applied between the base plates QN1B and QN2B of the negative side IGBT modules QN1 and QN2 and the collector main terminal and the emitter main terminal when the current is interrupted can be expressed by Expression [17].

Applied voltage between base plate and collector / emitter main terminal (when cut off)
= En / 2 + ΔVi [17]

  The potential of the heat sink 215 for the diode and the potentials of the base plates DCPB and DCNB of each U-phase positive diode module DCP and U-phase negative diode module DCN are related to the conduction / cutoff of the diode modules (DCP1, DCP2, DCN1, DCN2). The voltage applied between the ground and the diode heat sink 215 can be expressed by Equation [18] because the voltage is fixed to the same potential as the bus COM of the neutral DC power supply.

Applied voltage between earth and diode heat sink 215
= Erc ... [18]

  In the conductive state of the U-phase positive side diodes DCP1 and DCP2 or the U-phase negative side diodes DCN1 and DCN2, the anode main terminal and the cathode main terminal are at the potential of the bus COM of the neutral DC power supply. No voltage is applied between the base plate of the diode module DCP and the base plate of the U-phase negative side diode module DCN, and the respective anode main terminals and cathode main terminals.

  The voltage applied between the base plate of the U-phase positive diode module DCP or the U-phase negative diode module DCN, the anode main terminal, and the cathode main terminal when the current is interrupted can be expressed by Equation [19].

Applied voltage between base plate and anode / cathode main terminal (when cut off)
= Ep (En) / 2 + ΔVd (19)
(However, ΔVd: Bounce voltage due to recovery operation)

  The potential of the U-phase first neutral point heat sink 212 and the potentials of the base plates QPC1B and QPC2B of the first neutral point IGBT modules QPC1 and QPC2, the potential of the U-phase second neutral point heat sink 213 and each second neutral point The potentials of the base plates QNC1B and QNC2B of the point IGBT modules QNC1 and QNC2 become the connection point potential between the neutral point heat sink potential fixing resistors RHV15 and RHV16, and vary depending on the potential of the output point UAC of the U-phase power conversion main circuit 311. .

  When the positive side IGBT modules QP1 and QP2 and the first neutral point IGBT modules QPC1 and QPC2 are in a conductive state, the output point UAC becomes the same potential as the potential of the bus P of the positive side DC power supply, and the neutral point heat sink potential is fixed. The connection point potential between the resistors RHV15 and RHV16 is Ep / 2. For this reason, the voltage applied to the base plate QPC1B, QPC2B of each of the ground and U phase first neutral point heat sink 212 and the first neutral point IGBT modules QPC1 and QPC2 and the ground and U phase second neutral point heat sink. The voltage applied to the base plates QNC1B and QNC2B of the second neutral point IGBT modules QNC1 and QNC2 can be expressed by Equation [20].

Applied voltage between ground and U-phase first neutral point heat sink 212 / U-phase second neutral point heat sink 213
= Ep / 2 + Erc ... [20]
(When the primary IGBT module and the first neutral IGBT module are in conduction)

  At this time, between the base plates QPC1B and QPC2B of the first neutral point IGBT modules QPC1 and QPC2 and the collector main terminals and emitter main terminals, and the base plate QNC1B and the collector of the first series second neutral point IGBT module QNC1 Each voltage applied between the main terminals and between the base plate QNC2B of the second series second neutral point IGBT module QNC2 and the emitter main terminal can be expressed by Expression [21].

Applied voltage between base plate and collector / emitter main terminal = Ep / 2 [21]
(When the primary IGBT module and the first neutral IGBT module are in conduction)

  The voltage between the base plate QNC1B and the emitter main terminal of the first series second neutral point IGBT module QNC1 and between the base plate QNC2B and the collector main terminal of the second series second neutral point IGBT module QNC2 is Not applied.

  When the first neutral point IGBT modules QPC1 and QPC2 and the second neutral point IGBT modules QNC1 and QNC2 are in the conductive state, the output point UAC becomes the same potential as the potential of the bus COM of the neutral point DC power source. The connection point potential between the neutral point heat sink potential fixing resistors RHV15 and RHV16 is also the potential of the bus COM of the neutral DC power supply. For this reason, the voltage applied to the base plate QPC1B, QPC2B of each of the ground and U phase first neutral point heat sink 212 and the first neutral point IGBT modules QPC1 and QPC2 and the ground and U phase second neutral point heat sink. The voltage applied to the base plates QNC1B and QNC2B of the second neutral point IGBT modules QNC1 and QNC2 can be expressed by Equation [22].

Applied voltage between ground and U-phase first neutral point heat sink 212 / U-phase second neutral point heat sink 213
= Erc ... [22]
(When the first / second neutral IGBT module is in conduction)

  At this time, between the base plates QPC1B and QPC2B of the first neutral point IGBT modules QPC1 and QPC2 and the collector main terminals and emitter main terminals, and the base plates QNC1B and QNC2B of the second neutral point IGBT modules QNC1 and QNC2 No voltage is applied between each collector main terminal and emitter main terminal.

  On the other hand, when the second neutral point IGBT modules QNC1 and QNC2 and the negative side IGBT modules QN1 and QN2 are in a conductive state, the output point UAC becomes the same potential as the potential of the bus line N of the negative side DC power supply. The connection point potential between the heat sink potential fixing resistors RHV15 and RHV16 is En / 2. For this reason, the voltage applied to the base plate QPC1B, QPC2B of each of the ground and U phase first neutral point heat sink 212 and the first neutral point IGBT modules QPC1 and QPC2 and the ground and U phase second neutral point heat sink. The voltage applied to the base plates QNC1B and QNC2B of the second neutral point IGBT module group QNC1 and QNC2 can be expressed by Equation [23].

Applied voltage between ground and U-phase first neutral point heat sink 212 / U-phase second neutral point heat sink 213
= En / 2 + Erc ··· [23]
(When the second neutral point IGBT module group and the negative IGBT module group are in conduction)

  At this time, between the base plate QPC1B of the first series first neutral point IGBT module QPC1 and the collector main terminal, between the base plate QPC2B of the second series first neutral point IGBT module QPC2 and the emitter main terminal, Each voltage applied between the base plates QNC1B and QNC2B of the second neutral point IGBT modules QNC1 and QNC2 and each collector main terminal and emitter main terminal can be expressed by Expression [24].

Applied voltage between base plate and collector / emitter main terminal = En / 2 (24)
(When the second neutral point IGBT module group and the negative IGBT module group are in conduction)

  The voltage between the base plate QPC1B and the emitter main terminal of the first series first neutral point IGBT module QPC1 and between the base plate QPC2B and the collector main terminal of the second series first neutral point IGBT module QPC2 is Not applied.

  As described above, since the power conversion device 1a of the present embodiment has the formula [8] = the formula [14] with respect to the conventional circuit configuration, the dielectric strength specifications of the positive side IGBT modules QP1 and QP2 are not changed. The voltage applied between the ground and the positive heat sink can be reduced as shown in equations [25] and [26].

(Conventional circuit configuration) − (Circuit configuration of this embodiment)
= Formula [1]-Formula [12]
= Ep / 2 [25]
(When the positive side IGBT modules QP1 and QP2 are in conduction)

(Conventional circuit configuration) − (Circuit configuration of this embodiment)
= Equation [9] −Equation [12]
= ΔVi ・ ・ ・ [26]
(When primary IGBT modules QP1 and QP2 are shut off)

  Further, since the power conversion device 1a of the present embodiment has the formula [8] = the formula [17] with respect to the conventional circuit configuration, the ground breakdown voltage specification of the negative side IGBT modules QN1 and QN2 is not changed. The voltage applied between the negative heat sink and the negative heat sink can be reduced as shown in equations [27] and [28].

(Conventional circuit configuration) − (Circuit configuration of this embodiment)
= Formula [6]-Formula [15]
= En / 2 [27]
(When negative side IGBT modules QN1 and QN2 are conducting)

(Conventional circuit configuration) − (Circuit configuration of this embodiment)
= Formula [9]-Formula [15]
= ΔVi ・ ・ ・ [28]
(When negative-side IGBT modules QN1 and QN2 are off)

  In contrast to the conventional circuit configuration, the power conversion device 1a of the present embodiment has the expression [10] = expression [19], and therefore, the withstand voltage specifications of the positive / negative diode modules (DCP1, DCP2, DCN1, DCN2) Without changing the voltage, the voltage applied between the ground and the heat sink for the diode can be reduced as shown in the equation [29].

(Conventional circuit configuration) − (Circuit configuration of this embodiment)
= Formula [11]-Formula [18]
= Ep (En) / 2 + ΔVd [29]
(When positive / negative side diode modules (DCP1, DCP2, DCN1, DCN2) are cut off)

  At this time, when the positive side / negative side diode modules (DCP1, DCP2, DCN1, DCN2) are in a conductive state, Equation [7] = Equation [18] is satisfied, so that the conventional circuit configuration and the circuit configuration of the present embodiment Then there is no difference.

  On the other hand, in the dielectric strength specifications of the first neutral point IGBT modules QPC1 and QPC2 and the second neutral point IGBT modules QNC1 and QNC2, the circuit configuration of the present embodiment is different from the conventional circuit configuration in the expression [30]. As shown in FIG. 3, the dielectric strength specification can be reduced.

(Conventional circuit configuration)-(Circuit configuration of this embodiment)
= Formula [8] -Formula [21] (or Formula [24])
= ΔVi [30]
(First and second neutral IGBT modules (QPC1, QPC2, QNC1, QNC2))

  Further, in the circuit configuration of the present embodiment, the voltage applied between the ground and the U-phase first neutral point heat sink 212 and the U-phase second neutral point heat sink 213 is expressed by the equation [31]. Or it can reduce as shown in Formula [32], Formula [33], or Formula [34].

(Conventional circuit configuration)-(Circuit configuration of this embodiment)
= Formula [2] -Formula [20] (or Formula [23])
= En (Ep) / 2 ... [31]

(Conventional circuit configuration)-(Circuit configuration of this embodiment)
= Formula [9] -Formula [20] (or Formula [23])
= ΔVi [32]
(U-phase first neutral point heat sink 212 / U-phase second neutral point heat sink 213)

  Therefore, as described above, the circuit configuration of this embodiment reduces the voltage applied between each heat sink and the ground without changing the dielectric strength specification of each IGBT module compared to the conventional circuit configuration. Therefore, the leakage current flowing from each heat sink to the ground can be reduced, and the potential fluctuation of the ground can be reduced. Further, the heat sink potential fixing resistors RHV11, RHV12, RHV13, and RHV14 can be applied as discharge resistors for the smoothing capacitors Cp and Cn during maintenance work.

<Second Embodiment>
A second embodiment according to the present invention will be described.
FIG. 3 is an overall configuration diagram showing a power conversion device 1b according to the second embodiment of the present invention.

  Between the forward converter 400 that converts the AC voltage into a DC voltage and the inverter 410 that converts the DC voltage back into an AC voltage, there is a direct current between the bus P of the positive DC power supply and the bus N of the negative DC power supply. A smoothing capacitor Cdc for smoothing the pulsating flow of the voltage Edc is connected. The forward converter 400 converts the AC voltage obtained from the main commercial power supply 800 through the transformer 700 into the DC voltage Edc, and controls the DC voltage Edc to be kept constant by charging and discharging the smoothing capacitor Cdc. . The reverse converter 410 converts the DC voltage Edc converted by the forward converter 400 into an AC voltage having an arbitrary frequency / amplitude, and supplies / regenerates power to the AC motor 600 so that the speed of the AC motor 600 can be controlled at a variable speed. To do. The bus P of the positive side DC power supply is connected to the ground via a high resistance Rp, and the bus N of the negative side DC power supply is connected to the ground via a high resistance Rn.

  FIG. 4 is a circuit configuration diagram showing the inverse converter 410 (see FIG. 3) in detail. The forward converter 400 (see FIG. 1) may have a circuit configuration similar to that of the inverse converter 410.

  The inverse converter 410 according to the second embodiment of the present invention includes power conversion main circuits 301, 302, and 303. The power conversion main circuits 301, 302, and 303 are three-phase alternating current U-phase, V-phase, and W-phase power conversion main circuits, and the internal configurations thereof are the same.

  In the power conversion main circuit 301, two U-phase positive IGBT module groups QP11 and QP12 and a U-phase negative IGBT module group QN11 are connected in series between the bus P of the positive DC power supply and the bus N of the negative DC power supply. , QN12 are connected. The U-phase positive side IGBT module group QP11, QP12 is mounted on the U-phase positive side heat sink 201. U-phase negative-side IGBT module groups QN 11 and QN 12 are mounted on U-phase negative-side heat sink 202.

  Two high-resistances Rp and Rn connected in series are connected between the bus P of the positive DC power supply and the bus N of the negative DC power supply. The connection point of the high resistances Rp and Rn is connected to the ground.

  The heat sink potential fixing resistors RHV1 and RHV2 are connected between the bus P of the positive DC power supply and the bus N of the negative DC power supply. The U-phase positive heat sink 201 and the U-phase negative heat sink 202 are connected to the connection point of the heat sink potential fixing resistors RHV1 and RHV2. Here, the heat sink potential fixing resistors RHV1 and RHV2 all have the same resistance value in this example.

  In the circuit configuration of the present embodiment, the potential of the U-phase positive heat sink 201 and the potential of the base plates QP11B and QP12B of the positive IGBT modules QP11 and QP12, the potential of the U-phase negative heat sink 202, and the negative IGBT module QN11. , QN12 base plate QN11B, QN12B potential is fixed to the junction point potential between the heat sink potential fixing resistors RHV1, RHV2 regardless of the switching of the positive side IGBT modules QP11, QP12 and the negative side IGBT modules QN11, QN12. The For this reason, it becomes a ground potential virtually, and the voltage applied between the ground and the U-phase positive heat sink 201 and between the ground and the U-phase negative heat sink 202 can be expressed by Equation [33].

Applied voltage between ground and U-phase positive heat sink 201 / U-phase negative heat sink 202 = Edc / 2
= 0 [33]

  Further, in the conductive state of the positive side IGBT modules QP11 and QP12 and the negative side IGBT modules QN11 and QN12, between the base plates QP11B and QP12B of the positive side IGBT modules QP11 and QP12 and the collector / emitter main terminals, and the negative side The voltage applied between the base plates QN11B and QN12B of the IGBT modules QN11 and QN12 and the collector / emitter main terminal can be expressed by Expression [34].

Applied voltage between base plate and collector / emitter main terminal (when conducting)
= Edc / 2 ... [34]

Between the base plates QP11B and QP12B of the positive IGBT modules QP11 and QP12 and the collector main terminals and emitter main terminals, and the base plates QN11B and QN12B of the negative IGBT modules QN1 and QN12 and the collector main terminals and emitters when the current is interrupted The voltage applied between the main terminals can be expressed by Equation [35], where ΔVi is the jumping voltage when the IGBT module cuts off the current.
Applied voltage between base plate and collector / emitter main terminal (when cut off)
= Edc / 2 + ΔVi [35]

  On the other hand, unlike the circuit configuration in the second embodiment according to the present invention, the conventional circuit configuration does not apply the heat sink potential fixing resistors RHV1 and RHV2, and connects the positive side IGBT module group mounted on the positive side heat sink. This is a circuit configuration in which the point and the positive heat sink are electrically connected, and the connection point of the negative IGBT module group mounted on the negative heat sink is electrically connected to the negative heat sink.

  In the conventional circuit configuration, the voltage applied between the ground and the positive side heat sink and between the ground and the negative side heat sink is positive when the DC voltage between the positive side DC power source and the negative side DC power source is Edc. When the side IGBT module group and the negative IGBT module group are in the conductive state, it can be expressed by Equation [36], and when the current is interrupted, it can be expressed by Equation [37].

Applied voltage between ground and positive / negative heat sink (when conducting)
= Edc / 2 ... [36]

Applied voltage between earth and positive / negative heat sink (when shut off)
= Edc / 2 + ΔVi
= ΔVi [37]

  Further, in the conductive state of the positive side IGBT module group and the negative side IGBT module group, between the base plate-collector / emitter main terminals of each positive IGBT module, between the base plate-collector / emitter main terminals of each negative IGBT module. No voltage is applied during the period.

  The voltage applied between the base plate of each positive IGBT module and the collector main terminal and emitter main terminal, and between the base plate of each negative IGBT module and the collector main terminal and emitter main terminal at the time of current interruption [38]

Applied voltage between base plate and collector / emitter main terminal (when cut off)
= Edc / 2 + ΔVi [38]

  As described above, since the power conversion device 1b of the present embodiment has the formula [35] = the formula [38] with respect to the conventional circuit configuration, the positive-side IGBT modules QP11 and QP12 and the negative-side IGBT modules QN1 and QN2 Without changing the withstand voltage specification, the voltage applied between the ground and the U-phase positive heat sink 201 and the voltage applied between the ground and the U-phase negative heat sink 202 are reduced as shown in Equation [39]. it can.

(Conventional circuit configuration) − (Circuit configuration of this embodiment)
= Expression [37] −expression [33]
= ΔVi ・ ・ ・ [39]

  Therefore, as described above, the circuit configuration of the present embodiment is different from the conventional circuit configuration in that the dielectric breakdown voltage specification of each IGBT module is not changed, and the voltage applied between the positive heat sink and the ground and the negative heat sink Since the voltage applied between each of the heat sinks and the ground can be reduced, the leakage current flowing from each heat sink to the ground can be reduced, and the potential fluctuation of the ground can be reduced.

  Here, as a conventional circuit configuration, two smoothing capacitors connected in series are connected between the bus of the positive side DC power source and the bus of the negative side DC power source, the connection point of the smoothing capacitor, the positive side heat sink and the negative side heat sink. However, by applying the circuit configuration of the present embodiment to this conventional circuit configuration, an inexpensive power converter 1b can be provided.

500 forward converter (first embodiment)
510 Inverter (first embodiment)
400 forward converter (second embodiment)
410 Inverter (second embodiment)
600 AC motor 700 Transformer 800 Main commercial power supply AC AC circuit

Ep, En, Edc DC voltage P Positive side DC power supply bus COM Neutral DC power supply bus N Negative side DC power supply bus Cp, Cn, Cdc Smoothing capacitors QP1, QP2, QP11, QP12, QPC1, QPC2, QNC1, QNC2, QN1, QN2, QN11, QN12 Power conversion element module QP1B, QP2B, QP11B, QP12B, QPC1B, QPC2B, QNC1B, QNC2B, QN1B, QN2B, QN11B, QN1B2 Power conversion element module base plate DCP1, DCN2, DCN1, DCN2, Clamp diode DCP, DCN Clamp diode module DCPB, DCNB Clamp diode module base plate 211, 212, 213, 214, 215 Conductive member (first embodiment)
RHV11, RHV12, RHV13, RHV14, RHV15, RHV16 Conductive member potential fixing resistor (first embodiment)
311, 312, 313 Power conversion main circuit (first embodiment)
UAC, VAC, WAC Output points of power conversion main circuit 201, 202 Conductive member (second embodiment)
301, 302, 303 Power conversion main circuit (second embodiment)
Rp, Rn Grounding resistance (second embodiment)
RHV1, RHV2 Conductive member potential fixing resistor (second embodiment)
Rc Ground resistance (first embodiment)
Erc Voltage across ground resistance (first embodiment)

Claims (2)

In a power converter that forward-converts and reverse-converts a DC voltage and an AC voltage having an arbitrary frequency and amplitude,
A bus of a positive DC power source and a bus of a negative DC power source that connect in parallel between a forward converter that converts the AC voltage into the DC voltage and an inverter that converts the DC voltage back into the AC voltage. A positive-side semiconductor element group in which a plurality of semiconductor elements for outputting the bus potential of the positive-side DC power supply are connected in series, and a plurality of outputs for outputting the bus-line potential of the negative-side DC power supply And a negative semiconductor element group in which the semiconductor elements are connected in series,
The positive side semiconductor element group and the negative side semiconductor element group are connected in series,
The positive semiconductor element group is attached to a positive conductive member,
The negative semiconductor element group is attached to a negative conductive member,
The positive side conductive member and the negative side conductive member are two series connected first conductive member potential fixing pins connected between the positive side DC power source bus and the negative side DC power source bus. Fixed at a potential between the resistor and the second conductive member potential fixing resistor,
The power converter characterized by the above-mentioned. A power converter that forward-converts and reverse-converts a DC voltage and an AC voltage having an arbitrary frequency and amplitude,
The bus of the positive side DC power supply that connects in parallel between the forward converter that converts the AC voltage into the DC voltage and the reverse converter that converts the DC voltage back into the AC voltage, A bus and a negative DC power source are installed,
A positive-side semiconductor element group in which a plurality of semiconductor elements for outputting a bus-line potential of the positive-side DC power source are connected in series between the positive-side DC power source bus and the negative-side DC power source bus; A first neutral point semiconductor element group and a second neutral point semiconductor element group in which a plurality of semiconductor elements for outputting a bus potential of the neutral point DC power supply are connected in series; and the negative DC power supply A negative-side semiconductor element group in which a plurality of semiconductor elements for outputting the bus potential is connected in series,
The positive side semiconductor element group and the first neutral point semiconductor element group, the second neutral point semiconductor element group and the negative side semiconductor element group are connected in series,
A positive diode group is connected between a connection point of the positive semiconductor element group and the first neutral semiconductor element group and a bus of the neutral DC power supply;
A negative diode group is connected between a connection point of the negative side semiconductor element group and the second neutral point semiconductor element group and a bus of the neutral point DC power supply;
The connection point of the first neutral point semiconductor element group and the second neutral point semiconductor element group is an output point of the power converter,
The positive side diode group and the negative side diode group are attached to the same diode conductive member,
The positive semiconductor element group is attached to a positive conductive member,
The first neutral point semiconductor element group is attached to a first neutral point conductive member;
The second neutral point semiconductor element group is attached to a second neutral point conductive member;
The negative semiconductor element group is attached to a negative conductive member,
The diode conductive member is connected to a bus of the neutral point DC power source,
The positive-side conductive member includes a second series-connected first positive-side conductive member potential fixing resistor and a second resistor connected between the bus of the positive-side DC power source and the bus of the neutral-point DC power source. Fixed to the potential between the positive side conductive member and the potential fixing resistor,
The negative-side conductive member includes a first series-connected first negative-side conductive member potential fixing resistor and a second resistor connected between the neutral-point DC power source bus and the negative-side DC power source bus. The negative side conductive member is fixed at a potential between the potential fixing resistor and
The first neutral point conductive member and the second neutral point conductive member are connected in two series connected between an output point of the power converter and a bus of the neutral point DC power source. A potential is fixed between the first neutral point conductive member potential fixing resistor and the second neutral point conductive member potential fixing resistor.
The power converter characterized by the above-mentioned.

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