JP4696582B2 - Power converter - Google Patents

Description

  The present invention relates to a power conversion device having a function of protecting a semiconductor switch from overvoltage.

FIG. 7 is a configuration diagram in the case where a semiconductor switch protection circuit is added to a matrix converter described in Non-Patent Document 1 described later as a first prior art.
In the figure, AC is a three-phase AC power supply, FR is a filter reactor comprising reactors L1 to L3, FC is a filter capacitor comprising capacitors C1 to C3, and DB1 and DB2 are diodes D1 to D6 and D7 to D12, respectively. A diode bridge, MX is a matrix converter composed of bidirectional semiconductor switches SW1 to SW9, C4 is a capacitor connected between the DC terminals of the diode bridges DB1 and DB2, and LD is a load represented by inductances L4 to L6.

  In this prior art, when the matrix converter MX stops all operations by turning off all the semiconductor switches SW1 to SW9 for some reason, the inductive energy of the load LD or the AC power supply AC is passed through the diode bridges DB1 and DB2. It absorbs by C4 and prevents an overvoltage from being applied to the semiconductor switches SW1 to SW9.

Next, FIG. 9 is a configuration diagram in the case where a protection circuit described in Patent Document 1 below is applied to a matrix converter as a second conventional technique.
In the figure, the same components as those in FIG. 7 are denoted by the same reference numerals. DB11, DB12, DB13 are diode bridges, SD1, SD2, SD3 are diode series circuits, and C41, C42, C43 are capacitors connected to both ends of the diode series circuits SD1, SD2, SD3, respectively. These capacitors C41, C42, and C43 are provided to absorb the inductive energy of the load LD or the AC power supply AC.
Further, each of CNT1, CNT2, and CNT3 is a circuit composed of a diode, a resistor, and a semiconductor switch, and is connected in parallel to capacitors C41, C42, and C43, and the capacitors C41, C42 are turned on and off by the semiconductor switch. , C43 for controlling the voltage of C43.

Steffen Bernet et al. “Desing and Loss Comparison of Matrix Converters and Voltage-Source Converters for Modern AC Drives” IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS. VOL. 49, NO. 2, APRIL2002 pp.304-pp.314 US Pat. No. 4,697,230 (FIG. 2 etc.)

First, the problems of the first prior art will be described with reference to FIGS.
As a precondition for the explanation, it is assumed that all the semiconductor switches SW1 to SW9 are turned off at the moment when the output current of the matrix converter MX flows only in the U phase and the V phase (see FIG. 8). It is assumed that the energy stored in the reactor FR (reactors L1 to L3) is all absorbed by the filter capacitor FC (capacitors C1 to C3) and is not absorbed by the capacitor C4 via the diode bridge DB1.

In the first prior art, after all the semiconductor switches SW1 to SW9 are turned off, the current flowing in the load LD flows through the path 1 in FIG. 8 and flows into the capacitor C4, and absorbs the inductive energy of the load LD. .
Further, when an ideal state is considered, assuming that the voltage of the capacitor C4 is E _d and the voltage between the three-phase AC input terminals R and S of the matrix converter MX is V _RS , for example, the voltage applied to the semiconductor switch SW1 Is determined by V _RS and E _d . Therefore, if this voltage is to design the capacitance value of the capacitor C4 so as not to exceed the rated voltage of the semiconductor switch, or by controlling the voltage E _d of the capacitor C4, to prevent the overvoltage is applied to the device Can do.

However, in actuality, as shown in FIG. 8, since the wiring inductance L _S 1 exists, it is determined by the wiring inductance L _S 1 and the rate of change of current with respect to time at the moment when all the semiconductor switches SW1 to SW9 are turned off. The induced voltage is generated, and a voltage obtained by superimposing the induced voltage due to the wiring inductance L _S1 on the voltage determined by the above-described V _RS and E _d is applied to the semiconductor switch SW1. This induced voltage is determined by the wiring length of the path 2 in FIG. 8, and the longer the wiring length, the larger the wiring inductance L _S1 , and the larger the voltage induced in the wiring when all the semiconductor switches SW1 to SW9 are turned off. Become.
Therefore, since the wiring length inevitably increases as the device size increases, the induced voltage generated in the wiring cannot be ignored, and this induced voltage increases the possibility that the voltage applied to the semiconductor switch exceeds the breakdown voltage. Reliability will be significantly reduced.

  Next, problems of the second prior art will be described with reference to FIGS. In the description, the same conditions as above are assumed. Here, it is assumed that the energy accumulated in the filter reactor FR is all absorbed by the filter capacitor FC and is not absorbed by the capacitors C41 to C43 via the diode bridges DB11 to DB13.

After all the semiconductor switches SW1 to SW9 are turned off, the current flowing through the load LD flows through the path 3 in FIG. 10 and flows into the capacitor C41, and absorbs the inductive energy of the load LD. Further, when an ideal state is considered, if the voltage of the capacitor C41 is E _d , for example, the voltage applied to the semiconductor switch S1 is E _d . The voltage applied to the other semiconductor switches is also determined by the magnitude of the voltages of the capacitors C41 to C43.
Further, this prior art, prevents by individually controlling the voltage _{E d} of each capacitor by connecting a control circuit CNT1~CNT3 each capacitor C41～C43, the overvoltage is applied to the semiconductor switches SW1~SW9 It is out.

By the way, in this prior art, the induced voltage due to the wiring inductance L _S1 generated when all the semiconductor switches SW1 to SW9 are turned off is determined by the wiring length of the path 4 in FIG. Shorter than the prior art.
Therefore, since the wiring inductance L _S 1 can be reduced as compared with FIG. 8, the induced voltage of the wiring when all the semiconductor switches SW1 to SW9 are turned off can be reduced, and the reliability can be improved.
However, since it is necessary to control circuit CNT1~CNT3 for controlling the voltage _{E d} of the capacitor C41~C43 individually, which leads to increased cost and size of the apparatus.

  Therefore, the problem to be solved by the present invention is to solve the problems of each conventional technique, to prevent the occurrence of overvoltage due to the induced voltage of the wiring, to improve the reliability, and to simplify the circuit configuration and reduce the size and cost of the device. An object of the present invention is to provide a power conversion device that enables the above.

In order to solve the above-mentioned problem, the invention described in claim 1 is a power conversion device in which each phase of an AC power supply is connected to each phase of a load via a plurality of semiconductor switches.
A first diode rectifier circuit in which an AC terminal is connected to a connection point between each phase of the AC power source and the semiconductor switch;
A second diode rectifier circuit in which an AC terminal is connected to a connection point between one phase of the load and the semiconductor switch, and a positive and negative DC terminal is commonly connected to the first diode rectifier circuit;
An additional circuit for one phase is constituted by a capacitor connected between the positive and negative DC terminals,
Connecting the additional circuit by the number of phases between the AC power source and the load; and
One end of each capacitor of each phase is connected to the anode of each diode commonly connected to the cathode, and each other end of the capacitor is connected to the cathode of each diode commonly connected to the anode. Capacitors are connected in parallel with each other, and the on-voltages of all these diodes are substantially equal .

The invention described in claim 2 is a power conversion device in which each phase of an AC power supply is connected to each phase of a load via a plurality of semiconductor switches.
A first diode rectifier circuit in which an AC terminal is connected to a connection point between each phase of the AC power source and the semiconductor switch;
A second diode rectifier circuit in which an AC terminal is connected to a connection point between one phase of the load and the semiconductor switch, and a positive and negative DC terminal is commonly connected to the first diode rectifier circuit;
An additional circuit for one phase is constituted by a capacitor connected between the positive and negative DC terminals,
Connecting the additional circuit by the number of phases between the AC power source and the load; and
One end of each capacitor of each phase is commonly connected via a resistor, and the other end of each capacitor is commonly connected via a resistor to connect the capacitors of each phase in parallel with each other. The resistance values of the resistors are approximately equal .

The invention described in claim 3, Oite power conversion device according to claim 1 or 2, the parallel connection circuit of the capacitor was connected to a single control means for controlling the voltage of the capacitor Is.

  According to the present invention, the wiring inductance can be made smaller than that of the first prior art to prevent the application of overvoltage to the semiconductor switch, and the reliability can be improved. Further, as compared with the second prior art, a single control means for controlling the voltage of the capacitor of each phase is sufficient, so that the cost and size of the apparatus can be reduced.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
Figure 1 is a block diagram showing a reference embodiment of the present invention. The circuit configuration of this reference form is generally common to the second prior art shown in FIG. 9, and different portions are connected in parallel to capacitors C41, C42, C43 of each phase, A single control circuit CNT and a capacitor C44 are connected in parallel.

  1, AC is a three-phase AC power source, FR is a filter reactor including reactors L1 to L3, FC is a filter capacitor including capacitors C1 to C3, and DB11, DB12, and DB13 are diodes D1 to D6, respectively. , D7 to D12 and D13 to D18, MX is a matrix converter consisting of bidirectional semiconductor switches SW1 to SW9, and SD1, SD2 and SD3 are diodes D19, D20 and D21, D22 and D23 and D24, respectively. Diode series circuits C41, C42, and C43 are capacitors connected to both ends of the diode series circuits SD1, SD2, and SD3, respectively, and LD is a load represented by inductances L4 to L6.

  For convenience, the diode bridges DB11, DB12, and DB13 for each phase are all referred to as a first diode rectifier circuit, and the diode series circuits SD1, SD2, and SD3 are all referred to as a second diode rectifier circuit.

  That is, the circuit of FIG. 1 includes a diode bridge DB11 (first diode rectifier circuit) in which an AC terminal is connected to a connection point between each phase of the three-phase AC power supply AC and the semiconductor switches SW1 to SW3, and a load LD. A diode series circuit SD1 (second diode) in which an AC terminal is connected to a connection point between the phase and the semiconductor switches SW1 to SW3, and a positive and negative DC terminal is commonly connected to the diode bridge DB11 (first diode rectifier circuit). Rectifier circuit) and capacitor C41 connected in parallel to the first and second diode rectifier circuits constitute an additional circuit for one phase (for example, U phase), and these additional circuits are connected to AC power supply AC and a load. Connected to the LD for three phases, and all phase capacitors C41 to C43 are connected in parallel to each other, and capacitors C41 to C43 are connected in parallel. The road is composed of a single control circuit CNT and a capacitor C44 for controlling the voltage in parallel connection.

The control circuit CNT is configured by connecting a semiconductor switch Q in series to a parallel connection circuit of a diode D and a resistor R, and a capacitor C44 is connected in parallel to the control circuit CNT.
Here, it is desirable that the capacitance value of the capacitor C44 be larger than the capacitance values of the capacitors C41 to C43.

The operation of this reference embodiment will be described below with reference to FIG. As a precondition, as described above, it is assumed that all the semiconductor switches SW1 to SW9 are turned off at the moment when the output current of the matrix converter MX flows only in the U phase and the V phase, and is stored in the filter reactor FR. It is assumed that all of the energy absorbed by the filter capacitor FC is not absorbed by the capacitors C41, C42, C43 via the diode bridges DB11, DB12, DB13.

After all the semiconductor switches SW1 to SW9 constituting the matrix converter MX are turned off, the current flowing through the load LD flows through the path 3 and the path 5 in FIG. 2, flows into the capacitors C41, C42 and C44, and is loaded into the load LD. Absorbs inductive energy. Further, when an ideal state is considered, if the voltage of the capacitor C41 is E _d , for example, the voltage applied to the semiconductor switch SW1 is E _d . The voltages applied to the other semiconductor switches are also determined by the voltages of the capacitors C41 to C43.
The control circuit CNT operates so as to charge / discharge each of the capacitors C41 to C43 via the capacitor C44 by controlling the semiconductor switch Q on and off, and to control these voltages to a predetermined value.

According to this reference mode, the wiring length from the capacitor C41 to the semiconductor switches SW1 to SW3 can be shortened, so that the wiring inductance L _S 1 is reduced as in the second prior art (the same applies to other semiconductor switch groups). The induced voltage can also be reduced as compared with the first prior art.
Furthermore, since the induced voltage is small, the capacitances of the capacitors C41 to C43 can be reduced, and a capacitor having a small volume can be used, which contributes to downsizing of the device.
Further, since the number of control circuits for controlling the voltages of the capacitors C41 to C43 is smaller than that of the second prior art, it is possible to reduce the cost and the size of the apparatus.

Next, a first embodiment of the present invention corresponding to claim 1 will be described with reference to FIGS.
This embodiment is different from the reference embodiment in that capacitors C41 to C43 are connected in parallel via diodes D25 to D30 having substantially the same ON voltage as shown in FIG. That is, the anodes of the diodes D25, D27, and D29 are connected to the respective ends of the capacitors C41 to C43, the cathodes are commonly connected to the one end of the capacitor C44, and the cathodes of the diodes D26, D28, and D30 are connected to the capacitors C41 to C41. Connected to the other ends of C43, the anodes are connected in common and connected to the other end of the capacitor C44.

In the reference embodiment described above, when all the semiconductor switches SW1 to SW9 are turned off, a current flows through the path 3 and the path 5 in FIG. In this case, since the current passes through the four diodes in the path 3 and the current passes through the two diodes in the path 5, the current is shunted to the path 3 and the path 5 according to the ratio determined by the ON voltage of the diode.

Here, when all the semiconductor switches SW1 to SW9 are turned off, an induced voltage is generated in the wiring at the steep rise of the current at which the current starts to flow in the path 3 and the path 5, but when the current starts to flow, Due to the difference in the on-voltage ratio of the diode described above, there may be a state in which current flows only through the path 5 and no current flows through the path 3. In this case, since the wiring length of the path 5 is long, the induced voltage generated by the wiring inductance L _S2 in FIG. 2 also increases, and as a result, the voltage applied to the semiconductor switches SW1 to SW9 may exceed the element breakdown voltage. .

However, when the diodes D25 to D30 are added as in the first embodiment of FIG. 3, the current passes through the four diodes in both the path 3 and the path 5, as shown in FIG. The ratios determined are equal.
Therefore, when all of the semiconductor switches SW1 to SW9 are turned off, current flows equally in the path 3 and the path 5, and the induced voltage of the wiring inductance L _S2 due to the current flowing only in the path 5 The influence can be reduced. In this case, in the path 3, since the wiring length from the capacitor C41 to the semiconductor switches SW1 to SW3 is short and the wiring inductance L _S1 is small (the same applies to other semiconductor switch groups), the voltage induced by the wiring inductance is also small. As a result, the voltage applied to the element can be reduced as compared with the first prior art.

Next, a second embodiment of the present invention corresponding to claim 2 will be described with reference to FIG.
In this embodiment, the diodes D25 to D30 in the first embodiment are replaced with resistors R1 to R6 having substantially the same resistance value, and the principle of equalizing the ratio of the flow resistances of the paths 3 and 5 described above is the first. Since it is the same as that of the embodiment and the operation of the entire circuit is the same, detailed description is omitted.

In each of the embodiments described above, a diode (for example, D1 to D6, D19, and D20) and a capacitor (C41) are connected to a semiconductor switch group for one phase including three semiconductor switches (for example, SW1 to SW3). Although the configuration has been described, the present invention can also be applied to a case where a diode and a capacitor are connected to the input / output side of each semiconductor switch, for example, as in another embodiment shown in FIG. It is.
In FIG. 6, D101 and D211 are diodes constituting the first diode rectifier circuit on the input side of the semiconductor switch SW1, D191 and D201 are diodes constituting the second diode rectifier circuit on the output side, and D102 and D212 are semiconductors. A diode constituting the first diode rectifier circuit on the input side of the switch SW2, D192 and D202 are diodes constituting the second diode rectifier circuit on the output side, and D103 and D213 are first diodes on the input side of the semiconductor switch SW3. Diodes constituting the rectifier circuit, D193 and D203 are diodes constituting the second diode rectifier circuit on the output side, 411, 412, and 413 are capacitors, and R11, R21, R12, R22, R13, and R23 are resistors.
Although not shown, peripheral circuits are similarly configured for the other semiconductor switches SW4 to SW6 and SW7 to SW9, and these peripheral circuits are connected in parallel to the parallel connection circuit of the control circuit CNT and the capacitor C44. Just connect.

It is a block diagram of the reference form of this invention. It is operation | movement explanatory drawing of a reference form. It is a block diagram of 1st Embodiment of this invention. It is operation | movement explanatory drawing of 1st Embodiment. It is a block diagram of 2nd Embodiment of this invention. It is a block diagram of other embodiment of this invention. Is a block diagram showing the first of the slave come technology. It is operation | movement explanatory drawing of a 1st prior art. It is a block diagram which shows a 2nd prior art. It is operation | movement explanatory drawing of a 2nd prior art.

Explanation of symbols

AC: Three-phase AC power supply FR: Reactor for filter FC: Capacitor for filter DB11, DB12, DB13: Diode bridge MX: Matrix converter SW1-SW9: Semiconductor switch SD1, SD2, SD3: Diode series circuit C41-C44: Capacitor R: Resistance D: Diode Q: Semiconductor switch CNT: Control circuit LD: Load D25-D30: Diode R1-R6: Resistance

Claims (3)

In the power conversion device in which each phase of the AC power source is connected to each phase of the load via a plurality of semiconductor switches,
A first diode rectifier circuit in which an AC terminal is connected to a connection point between each phase of the AC power source and the semiconductor switch;
A second diode rectifier circuit in which an AC terminal is connected to a connection point between one phase of the load and the semiconductor switch, and a positive and negative DC terminal is commonly connected to the first diode rectifier circuit;
An additional circuit for one phase is constituted by a capacitor connected between the positive and negative DC terminals,
Connecting the additional circuit by the number of phases between the AC power source and the load; and
One end of each capacitor of each phase is connected to the anode of each diode commonly connected to the cathode, and each other end of the capacitor is connected to the cathode of each diode commonly connected to the anode. A power conversion device characterized in that capacitors are connected in parallel to each other, and the on-voltages of all these diodes are substantially equal . In the power conversion device in which each phase of the AC power source is connected to each phase of the load via a plurality of semiconductor switches ,
A first diode rectifier circuit in which an AC terminal is connected to a connection point between each phase of the AC power source and the semiconductor switch;
A second diode rectifier circuit in which an AC terminal is connected to a connection point between one phase of the load and the semiconductor switch, and a positive and negative DC terminal is commonly connected to the first diode rectifier circuit;
An additional circuit for one phase is constituted by a capacitor connected between the positive and negative DC terminals,
Connecting the additional circuit by the number of phases between the AC power source and the load; and
One end of each capacitor of each phase is commonly connected via a resistor, and the other end of each capacitor is commonly connected via a resistor to connect the capacitors of each phase in parallel with each other. The power converter characterized by making resistance value of resistance of substantially equal . In the power converter device according to claim 1 or 2 ,
A power conversion apparatus, wherein a single control means for controlling the voltage of these capacitors is connected to the parallel connection circuit of the capacitors .

Images