JP2004320977A - Power converter circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To make the size of a power converter circuit small, lengthen its lifetime, and reduce its cost by eliminating the need of a large capacitance electrolytic capacitor and circuits accompanying therewith. <P>SOLUTION: The power converter circuit changes an AC power supply voltage into an AC voltage having a prescribed frequency and voltage by turning on and off a plurality of bilateral semiconductor switches, and supplies the AC voltage to an inductive load. The power converter circuit comprises a first diode bridge 20 whose AC input side is connected to the three-phase AC power supply 10, a second diode bridge 30 whose AC input side is connected to a load, a varistor 71 which is connected between a junction point of positive electrodes of both bridges 20, 30 and a junction point of negative electrodes and can hold as a constant voltage element a lower voltage than the rated voltage of a two-way semiconductor switches 41-43. When all the two-way semiconductor switches 41-43 are off, inductive energy accumulated in the load 60 is consumed by the varistor 71 via both bridges 20, 30. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a power conversion circuit including a protection circuit for protecting a semiconductor switch from a spike voltage due to inductive energy stored in a load.

FIG. 11 equivalently shows a power conversion circuit described in FIG. 2 of Patent Document 1 described later.
In FIG. 11, reference numeral 10 denotes a three-phase AC power supply; 41 to 43, bidirectional semiconductor switches (semiconductor switches capable of interrupting bidirectional current); A single-phase load 20 is connected to the common connection point, a diode bridge 20 is connected on the AC input side to the three-phase AC power supply 10, and has a three-phase full-bridge configuration composed of diodes 21 to 26, and 30 is an AC input. A diode bridge (diode series circuit) composed of diodes 31 and 32 connected in series to one end of a load 60 and connected in series, 51 is both ends on the DC output side of the diode bridges 20 and 30 (the positive poles of the diode bridges 20 and 30). (Between a connection point between the two electrodes and a connection point between the negative electrodes).
Here, as the semiconductor switches 41 to 43, for example, two semiconductor switching elements such as IGBTs are connected in series in the reverse direction, and freewheeling diodes are connected to the respective switching elements in antiparallel.

In this conventional technique, the three-phase AC voltage is converted to a single-phase AC voltage having a predetermined frequency and magnitude and supplied to the load 60 by turning on and off the semiconductor switches 41 to 43 at a predetermined timing. .
The diode bridges 20 and 30 and the capacitor 51 constitute a protection circuit (snubber circuit) for the semiconductor switches 41 to 43. When all the semiconductor switches 41 to 43 are turned off in an emergency or the like, the power supply side and the load are switched. The inductive energy on the side is absorbed by the capacitor 51 via the diode bridges 20 and 30 to protect the semiconductor switches from being applied with a spike voltage.

  In this prior art, as shown in FIG. 12, a voltage detection circuit 52 for detecting that the voltage of the capacitor 51 has reached an allowable voltage, and a drive circuit 53 controlled by an overvoltage detection signal from the detection circuit 52 are provided. And a resistor 55 which is turned on by an output signal of the drive circuit 53 and a resistor 55 (see FIG. 3 of Patent Document 1). When the capacitor 51 becomes overvoltage, the semiconductor switch 54 is turned on and the resistor 55 is connected. By discharging the capacitor 51, the semiconductor switches 41 to 43 of the main circuit are protected.

U.S. Pat. No. 4,697,230 (FIG. 2, FIG. 3)

In the above prior art, a large-capacity capacitor is required to suppress the voltage of the capacitor 51 when the inductive energy on the power supply side or the load side is absorbed to be equal to or lower than the rated voltage of the semiconductor switches 41 to 43. In addition to this, an electrolytic capacitor having a short life is generally used as this type of capacitor, which hinders a longer life of the entire device.
In addition, as described above, a voltage detection circuit 52, a drive circuit 53, a semiconductor switch 54, a resistor 55, and the like for coping with an overvoltage of the capacitor 51 are necessary, including a rush current prevention circuit when the capacitor 51 is initially charged. These have caused the circuit configuration to be complicated, large, and costly.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a power conversion circuit that does not require a large-capacity capacitor and a circuit accompanying the capacitor, and that achieves miniaturization, long life, and low cost.

In order to solve the above problem, the invention according to claim 1 converts an AC voltage of a power supply into an AC voltage having a predetermined frequency and magnitude by turning on and off a plurality of bidirectional semiconductor switches and supplies the AC voltage to a load. In the power conversion circuit,
A first diode bridge where an AC input side is connected to the power supply, a second diode bridge where an AC input side is connected to the load, and a connection point between positive poles on the DC output side of the first and second diode bridges And a constant voltage element that is connected between a connection point of the negative electrodes and that can hold a voltage equal to or lower than a rated voltage of the bidirectional semiconductor switch,
When the bidirectional semiconductor switch is completely turned off, inductive energy on the power supply side or load side is consumed by the constant voltage element via the diode bridge.

According to a second aspect of the present invention, instead of the constant voltage element in the first aspect, the voltage between the connection point between the positive electrodes and the connection point between the negative electrodes on the DC output side of the first and second diode bridges is changed. Voltage monitoring means for monitoring, a unidirectional semiconductor switch connected between the two connection points, and the unidirectional semiconductor switch such that a voltage between the two connection points is equal to or less than a rated voltage of the bidirectional semiconductor switch. Driving means for turning on the switch in an active state,
When the bidirectional semiconductor switch is completely turned off, inductive energy on the power supply side or the load side is consumed by the unidirectional semiconductor switch in an on state via the diode bridge.

  According to a third aspect of the invention, a series circuit of the unidirectional semiconductor switch and the resistor is provided instead of the unidirectional semiconductor switch of the second aspect.

The invention described in claim 4 is the invention according to claim 2 or 3,
A function in which the functions of the voltage monitoring means and the driving means are realized by a Zener diode in which a cathode is connected to positive poles of first and second diode bridges and an anode is connected to a control terminal of the unidirectional semiconductor switch. It is.

The invention described in claim 5 is the invention according to claim 2, 3 or 4.
A capacitor is connected between the positive electrode and the negative electrode of the first and second diode bridges to prevent the unidirectional semiconductor switch from being accidentally turned on when the voltage between these two electrodes changes suddenly.

According to a sixth aspect of the present invention, in the power conversion circuit according to the first aspect,
A capacitor connected between a connection point between the positive electrodes and a connection point between the negative electrodes of the first and second diode bridges, voltage monitoring means for monitoring a voltage between the two connection points, And a series circuit of a resistor and a first unidirectional semiconductor switch connected to the first unidirectional semiconductor switch and a first unidirectional semiconductor switch such that a voltage between the two connection points is equal to or less than a rated voltage of the bidirectional semiconductor switch. Driving means for turning on,
When the bidirectional semiconductor switch is completely turned off, inductive energy on the power supply side or load side is absorbed by the capacitor via the diode bridge, and the first unidirectional semiconductor switch and the constant voltage element are sequentially turned on. Then, the inductive energy on the power supply side or the load side is consumed by the resistor and the constant voltage element.
Here, the constant voltage element includes, for example, a second unidirectional semiconductor switch connected in parallel to the capacitor and turned on in an active state.

According to a seventh aspect of the present invention, in the power conversion circuit according to the fourth aspect,
A resistor is connected between the anode of the Zener diode and the connection point between the negative electrodes of the first and second diode bridges.
Note that the resistor has a function of discharging the charge accumulated in the control terminal of the unidirectional semiconductor switch that is turned on in the active state.

According to the present invention, a large-capacity capacitor such as an electrolytic capacitor for protecting the semiconductor switch is not required. Along with this, a voltage detection circuit for detecting the voltage of the capacitor and a drive circuit for the semiconductor switch for discharging are not required, which can reduce the size, the life, and the cost of the entire device. it can.
The functions of the voltage monitoring means and the driving means for monitoring the voltage between the positive electrode and the negative electrode of the diode bridge and for turning on the unidirectional semiconductor switch in an active state are defined in the claims. This can be realized by a Zener diode as in the fourth or seventh aspect, and there is no possibility that the circuit configuration is complicated.
According to the invention described in claim 6, it is possible to control the maximum voltage value of the capacitor that has absorbed the inductive energy, and it is possible to reduce the capacitance value of the capacitor. This eliminates the need for a large-capacity capacitor as compared with the prior art, and also eliminates the need for an associated initial charging circuit and the like.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a circuit diagram showing a first embodiment of the present invention corresponding to claim 1. The same components as those in FIG. 11 are denoted by the same reference numerals, and description thereof will be omitted. Will be described.
The difference between FIG. 1 and FIG. 11 is that a varistor as a constant voltage element is connected to both ends on the DC output side of the diode bridges 20 and 30 instead of the capacitor 51 in FIG. Note that a Zener diode (constant voltage diode) can be used as the constant voltage element.
As an overall operation of the power conversion circuit of FIG. 1, the semiconductor switches 41 to 43 are turned on and off at predetermined timings as in FIG. 11 so that the three-phase AC voltage is changed to a single voltage having a predetermined frequency and magnitude. The voltage is converted into a phase AC voltage and supplied to the load 60.

The protection operation of the semiconductor switches 41 to 43 in this embodiment will be described. First, it is assumed that all the semiconductor switches 41 to 43 are turned off for some reason from the state where any one of the semiconductor switches 41 to 43 is turned on. .
At this time, since inductive energy is accumulated in the load 60, a current flows between the diode bridges 20 and 30 via the varistor 71, and a voltage between the positive electrode and the negative electrode of the diode bridge 20 (diodes 21, 23 and 23). The voltage between the cathode of the diode 25 and the anodes of the diodes 22, 24 and 26 and the voltage between the positive electrode and the negative electrode of the diode bridge 30 (the voltage between the cathode of the diode 31 and the anode of the diode 32) are the limited voltage (current Is varied, the voltage is clamped by the voltage across the varistor which keeps a substantially constant value.

Accordingly, assuming that the forward voltage drop of the diodes in the diode bridges 20 and 30 is neglected, the overvoltage is applied to the semiconductor switches 41 to 43 by setting the limit voltage by the varistor 71 to be equal to or lower than the rated voltage of the semiconductor switches 41 to 43. There is no danger of application, and these elements can be protected.
At the same time, the inductive energy of the load 60 will be consumed by the current flowing through the varistor 71 via the diode bridges 20,30.

That is, in the present embodiment, the inductive energy of the load 60 is absorbed by the varistor 71, and the voltage between the positive electrode and the negative electrode of the diode bridges 20 and 30 is clamped by the limited voltage of the varistor 71. For the purpose of overvoltage protection of the semiconductor switches 41 to 43, it is necessary to provide a large-capacity capacitor for energy absorption, an inrush current prevention circuit, a voltage detection circuit, a resistor for discharging the capacitor, a semiconductor switch, and a drive circuit thereof. There is no.
For this reason, it is possible to simplify the circuit configuration and reduce the cost by reducing the number of components, and it is possible to extend the life of the entire device by eliminating the need for an electrolytic capacitor and the like.

Next, FIG. 2 is a circuit diagram showing a second embodiment of the present invention corresponding to claim 2.
In this embodiment, a unidirectional semiconductor switch 74 is connected in place of the capacitor 51 in FIG. 11, and a voltage monitoring means 72 for monitoring the voltage between the positive electrode and the negative electrode of the diode bridges 20 and 30 is connected. On the side, driving means 73 for a semiconductor switch 74 that is turned on in an active state (a state in which a current flows while maintaining a voltage) is provided. Here, the case where an IGBT is used as the semiconductor switch 74 is shown, but another type of semiconductor switch may be used.

The protection operation of this embodiment will be described below.
In FIG. 2, it is assumed that all of the semiconductor switches 41 to 43 are turned off for some reason from a state where any of the semiconductor switches 41 to 43 is turned on. It is assumed that the semiconductor switch 74 is off in this state.
At this time, since inductive energy is accumulated in the load 60, current flows through the diode bridges 20 and 30 and the semiconductor switch 74, but since the semiconductor switch 74 is off, the diode bridge 20 is turned off. , 30 are increased.

Here, when the voltage between the positive electrode and the negative electrode of the diode bridges 20 and 30 is about to become equal to or higher than the voltage set by the voltage monitoring means 72, the driving means 73 turns on the semiconductor switch 74 in an active state, whereby the diode bridges 20 and 30 are turned on. A current flows through the semiconductor switch 74 in a state where the voltage between the positive electrode and the negative electrode of 30 is clamped to the set voltage by the voltage monitoring means 72. As a result, the inductive energy stored in the load 60 is consumed by the semiconductor switch 74 itself via the diode bridges 20 and 30.
Therefore, assuming that the forward voltage drop of the diodes in the diode bridges 20 and 30 is neglected, by setting the set voltage of the voltage monitoring means 72 to be equal to or less than the rated voltage of the semiconductor switches 41 to 43, the semiconductor switches 41 to 43 It is possible to prevent an overvoltage from being applied.

As described above, in the present embodiment, the semiconductor switch 74 that is turned on in the active state operates as if it were a constant voltage element, and consumes the inductive energy of the load 60. Therefore, there is no need to provide the discharge resistor 55 of the capacitor as in the conventional configuration shown in FIG.
Further, according to this embodiment, similarly to the first embodiment, an effect that a large-capacity capacitor is not required can be obtained.

Here, FIG. 3 shows a specific configuration example for realizing the functions of the voltage monitoring means 72 and the driving means 73, and corresponds to the invention of claim 4.
That is, in this example, both functions of the voltage monitoring means 72 and the driving means 73 are realized by the Zener diode 77 connected between the positive electrodes of the diode bridges 20 and 30 and the gate of the semiconductor switch 74 with the illustrated polarity. I have.

With such a configuration, when the voltage between the collector and the gate of the semiconductor switch 74 tries to become higher than the Zener voltage of the Zener diode 77, the Zener diode 77 conducts and charges the gate of the semiconductor switch 74. Switch 74 operates in the active state.
Therefore, the voltage between the positive electrode and the negative electrode of the diode bridges 20 and 30 can be clamped by the sum of the Zener voltage of the Zener diode 77 and the gate voltage of the semiconductor switch 74, and the overvoltage is applied to the semiconductor switches 41 to 43. It is not applied.
In this case, if the forward voltage drop of the diodes in the diode bridges 20 and 30 is ignored, the sum of the Zener voltage of the Zener diode 77 and the gate voltage of the semiconductor switch 74 is equal to or less than the rated voltage of the semiconductor switches 41 to 43. It is necessary to set to.

Next, FIG. 4 is a circuit diagram showing a third embodiment of the present invention corresponding to claim 3.
In this embodiment, a resistor 75 is connected in series to a semiconductor switch 74 in the second embodiment of FIG. 2, and the functions of the voltage monitoring means 72 and the driving means 73 are the same as those in FIG.

The operation of this embodiment is basically the same as that of the second embodiment, except that the voltage between the positive electrode and the negative electrode of the diode bridges 20 and 30 is clamped to the set voltage by the voltage monitoring means 72, and the semiconductor is connected via the driving means 73. When the switch 74 is turned on, a current flows through a series circuit of the semiconductor switch 74 and the resistor 75, and both of them cause the inductive energy of the load 60 to be consumed.
In this case, since the inductive energy of the load 60 is shared and consumed by the semiconductor switch 74 and the resistor 75, the energy duty of the semiconductor switch 74 can be reduced as compared with the second embodiment. Therefore, a semiconductor switch (semiconductor switch having a large thermal resistance) having a smaller chip size than the semiconductor switch in the second embodiment can be used, which contributes to downsizing of the circuit and cost reduction.

  Next, FIG. 5 shows a specific configuration example of the voltage monitoring means 72 and the driving means 73 corresponding to claim 4, and the functions of the voltage monitoring means 72 and the driving means 73 are realized by the Zener diode 77 as in FIG. It is an example. Since the operation can be easily analogized from FIGS. 3 and 4, the detailed description is omitted.

FIG. 6 is a circuit diagram showing a fourth embodiment of the present invention corresponding to claim 5.
In this embodiment, a capacitor 76 is connected between the positive electrode and the negative electrode of the diode bridges 20, 30 in the third embodiment of FIG. The idea of connecting the capacitor 76 between the positive electrode and the negative electrode of the diode bridges 20 and 30 as described above is also applicable to the configurations of FIGS. 1 to 3 and 5.

In FIG. 6, the operations of the voltage monitoring means 72, the driving means 73, the semiconductor switch 74, and the resistor 75 are the same as those of the third embodiment, but in this embodiment, particularly when the diode bridge 20 becomes conductive at the time of start-up or the like. The capacitor 76 absorbs a sudden change in voltage caused by the sudden dv / dt generated between the positive electrode and the negative electrode, thereby preventing the semiconductor switch 74 from being turned on by mistake.
The capacitor 76 does not need to have a large capacity like a conventional electrolytic capacitor for inductive energy absorption, and a small-capacity film capacitor or the like can be used. Price can be expected.

  As in the first to fourth embodiments described above, if each constant is selected such that the voltage between the positive electrode and the negative electrode of the diode bridges 20 and 30 is equal to or less than the rated voltage of the semiconductor switches 41 to 43 of the main circuit, the semiconductor The spike voltage can be suppressed from being applied to the switches 41 to 43 to protect them from overvoltage.

The present invention is applicable not only to the power conversion circuit of the three-phase to single-phase conversion method described in each embodiment, but also to a power conversion circuit that generally converts an n-phase AC voltage to an m-phase AC voltage (n and m are integers). Applicable.
Further, the present invention can be applied to a so-called matrix converter that directly converts a multiphase AC voltage.
FIG. 7 shows a matrix converter to which the above-described configuration of FIG. 5 is applied. 35 is a diode bridge of a three-phase full bridge configuration, 41 to 49 are bidirectional semiconductor switches, 61 is a three-phase load, and 80 is a reactor. And an input filter comprising a capacitor. Since the operation of the matrix converter is well known, the description is omitted, and the protection operation of the semiconductor switches 41 to 49 by the Zener diode 77, the semiconductor switch 74, and the resistor 75 is the same as that of FIG.

Next, FIG. 8 is a circuit diagram showing a fifth embodiment of the present invention corresponding to claim 6.
In the embodiment shown in FIG. 3, when the energy that must be processed (the inductive energy of the power supply 10 and the load 60) increases, only a plurality of unidirectional semiconductor switches 74 are connected in parallel to consume the energy. This may not only increase the cost, but also significantly reduce the reliability due to variations in the characteristics of the unidirectional semiconductor switches connected in parallel.
The fifth embodiment has been made in view of the above points.

8 differs from the fourth embodiment shown in FIG. 6 in that a second unidirectional semiconductor switch 91 such as an IGBT is connected between the positive electrode and the negative electrode of the diode bridges 20 and 30 (for convenience, the unidirectional semiconductor switch 91). 74 is a first unidirectional semiconductor switch), a Zener diode 92 as voltage monitoring and driving means is connected between its collector and gate, and a resistor 93 is connected between its gate and emitter. Note that the resistor 93 is for discharging the electric charge stored in the control terminal (gate) of the unidirectional semiconductor switch 91, and by providing the resistor 93, the voltage between the collector and the emitter of the semiconductor switch 91 is provided. Is easier to adjust. The resistor 93 can be connected between the gate and the emitter of the semiconductor switch 74 shown in FIGS. 3, 5, and 7, or between the gate and the emitter of the semiconductor switch 91 shown in FIG.
Further, in the present embodiment, the first unidirectional semiconductor switch 74 driven by the driving means 73 performs a normal semiconductor switch operation (on / off operation in the saturation region and the cutoff region), and performs the second unidirectional semiconductor switch operation. The semiconductor switch 91 is turned on in the active state.

FIG. 9 is a diagram showing operation waveforms of the fifth embodiment, and the operation will be described below.
In FIG. 8, when all of the bidirectional semiconductor switches 41 to 43 are turned off for some reason, the energy stored in the reactor of the load 60 is released through the diode bridge 20, the capacitor 76, and the diode bridge 30, and the voltage of the capacitor 76 is changed. Rise (time t0 to t1 in FIG. 9).

When the voltage of the capacitor 76 becomes equal to or higher than the voltage set by the voltage monitoring means 72 (FIG. 9A), the unidirectional semiconductor switch 74 is turned on by the driving means 73 and the energy stored in the reactor of the load 60 is The current is split and discharged to the resistor 75.
Here, depending on the capacitor 76, the resistor 75, the constant of the load 60, and the current of the load 60, even when the unidirectional semiconductor switch 74 is turned on, the voltage across the capacitor 76 does not decrease but continues to increase (FIG. 9). At times t1 to t2). Also, in the prior art shown in FIGS. 11 and 12, if the capacitance of the capacitor 51 is reduced in order to reduce the size of the device, even if the charge of the capacitor 51 is discharged by the resistor 55, the voltage of the capacitor 51 is reduced. Keeps rising.
In the above period t1 to t2, the energy stored in the reactor of the load 60 is consumed by the resistor 75 while being absorbed by the capacitor 76.

Next, when the voltage between the positive poles of the diode bridges 20 and 30 and the gate of the unidirectional semiconductor switch 91 reaches the Zener voltage of the Zener diode 92, the Zener diode 92 conducts and activates the unidirectional semiconductor switch 91. Turn on in the state. Thus, the voltage across the capacitor 76 is clamped to the sum of the Zener voltage of the Zener diode 92 and the gate voltage of the semiconductor switch 91 (FIG. 9B) (time t2 to t3 in FIG. 9).
That is, the Zener diode 92 and the semiconductor switch 91 substantially function as the constant voltage element in the first aspect.
In this period t2 to t3, the energy stored in the reactor of the load 60 is consumed by the resistor 75 and the unidirectional semiconductor switch 91.

  Eventually, when the energy of the reactor of the load 60 decreases with the lapse of time and the voltage of the capacitor 76 decreases as the stored energy of the capacitor 76 is consumed by the resistor 75, the energy consuming operation of the semiconductor switch 91 starts. Ends (time t3 to t4 in FIG. 9). Then, the operation of consuming the energy by the resistor 75 while absorbing the energy by the capacitor 76 again is performed, and finally all the energy stored in the reactor of the load 60 is processed.

  If each constant is selected so that the voltage between both ends of the capacitor 76 is equal to or less than the rated voltage of the bidirectional semiconductor switches 41 to 43, the spike voltage of the bidirectional semiconductor switches 41 to 43 can be suppressed, and overvoltage protection can be prevented. It becomes possible.

According to this embodiment, it is possible to control the maximum value of the voltage of the capacitor 76 that has absorbed the inductive energy. Therefore, it is possible to reduce the capacitance value of the capacitor 76 as compared with the related art of Patent Document 1. it can. This eliminates the need for a large-capacity capacitor as compared with the related art, and also eliminates the need for an initial charging circuit and the like associated therewith.
In addition, since the inductive energy of the power supply 10 or the load 60 consumed by the unidirectional semiconductor switch 91 can be significantly reduced as compared with the embodiment shown in FIG. 3 and the like, only a plurality of unidirectional semiconductor switches 91 are connected in parallel. Such a measure is not required.
Therefore, in this embodiment, cost reduction and size reduction are possible, and reliability is also improved.

In addition, the present embodiment is applicable not only to the power conversion circuit shown in FIG. 8 but also to, for example, a matrix converter as shown in FIG.
10, the same components as those in FIGS. 7 and 8 are denoted by the same reference numerals, and the protection operation of the bidirectional semiconductor switches 41 to 49 is the same as that in FIG.

FIG. 2 is a circuit diagram showing a first embodiment of the present invention. It is a circuit diagram showing a second embodiment of the present invention. FIG. 9 is a circuit diagram illustrating a specific configuration of a second embodiment of the present invention. It is a circuit diagram showing a third embodiment of the present invention. FIG. 11 is a circuit diagram illustrating a specific configuration of a third embodiment of the present invention. It is a circuit diagram showing a fourth embodiment of the present invention. FIG. 6 is a circuit diagram of a matrix converter to which the configuration of FIG. 5 is applied. It is a circuit diagram showing a fifth embodiment of the present invention. FIG. 9 is an operation waveform diagram of the embodiment of FIG. 8. FIG. 9 is a circuit diagram of a matrix converter to which the configuration of FIG. 8 is applied. FIG. 9 is a circuit diagram showing a conventional technique. FIG. 12 is an explanatory diagram of a circuit added to the conventional technique of FIG. 11.

Explanation of reference numerals

10: Three-phase AC power supply 41-49: Bidirectional semiconductor switch 20, 30, 35: Diode bridge 21-26, 31, 32: Diode 60: Single-phase load 61: Three-phase load 71: Varistor (constant voltage element)
72: Voltage monitoring means 73: Driving means 74, 91: Unidirectional semiconductor switch 75, 93: Resistor 76: Capacitor 77, 92: Zener diode 80: Input filter

Claims (7)

In a power conversion circuit for converting an AC voltage of a power supply into an AC voltage having a predetermined frequency and magnitude by turning on and off a plurality of bidirectional semiconductor switches and supplying the AC voltage to a load,
A first diode bridge having an AC input connected to the power supply;
A second diode bridge having an AC input connected to the load;
A constant voltage element connected between a connection point between the positive electrodes of the first and second diode bridges and a connection point between the negative electrodes, and capable of holding a voltage equal to or lower than a rated voltage of the bidirectional semiconductor switch; With
When the bidirectional semiconductor switch is completely turned off, inductive energy on a power supply side or a load side is consumed by the constant voltage element via the diode bridge. In a power conversion circuit for converting an AC voltage of a power supply into an AC voltage having a predetermined frequency and magnitude by turning on and off a plurality of bidirectional semiconductor switches and supplying the AC voltage to a load,
A first diode bridge having an AC input connected to the power supply;
A second diode bridge having an AC input connected to the load;
Voltage monitoring means for monitoring a voltage between a connection point between the positive electrodes of the first and second diode bridges and a connection point between the negative electrodes,
A unidirectional semiconductor switch connected between the two connection points,
Driving means for turning on the unidirectional semiconductor switch in an active state so that the voltage between the two connection points is equal to or less than the rated voltage of the bidirectional semiconductor switch,
A power conversion circuit, wherein when the bidirectional semiconductor switch is completely turned off, inductive energy on a power supply side or a load side is consumed by the unidirectional semiconductor switch in an on state via the diode bridge. In a power conversion circuit for converting an AC voltage of a power supply into an AC voltage having a predetermined frequency and magnitude by turning on and off a plurality of bidirectional semiconductor switches and supplying the AC voltage to a load,
A first diode bridge having an AC input connected to the power supply;
A second diode bridge having an AC input connected to the load;
Voltage monitoring means for monitoring a voltage between a connection point between the positive electrodes of the first and second diode bridges and a connection point between the negative electrodes,
A series circuit of a resistor and a unidirectional semiconductor switch connected between the two connection points,
Driving means for turning on the unidirectional semiconductor switch in an active state so that the voltage between the two connection points is equal to or less than the rated voltage of the bidirectional semiconductor switch,
A power conversion circuit, wherein when the bidirectional semiconductor switch is completely turned off, inductive energy on a power supply side or a load side is consumed by the resistor and the unidirectional semiconductor switch in an on state via the diode bridge. . The power conversion circuit according to claim 2 or 3,
The functions of the voltage monitoring means and the driving means are realized by a Zener diode in which a cathode is connected to the positive electrodes of the first and second diode bridges and an anode is connected to the control terminal of the unidirectional semiconductor switch. A power conversion circuit characterized by the above-mentioned. The power conversion circuit according to claim 2, 3 or 4,
Power conversion, characterized in that a capacitor for preventing erroneous ON operation of the unidirectional semiconductor switch is connected between a connection point between the first and second diode bridges and a connection point between the negative electrodes. circuit. The power conversion circuit according to claim 1,
A capacitor connected between a connection point between the positive electrodes of the first and second diode bridges and a connection point between the negative electrodes,
Voltage monitoring means for monitoring the voltage between the two connection points,
A series circuit of a resistor and a first unidirectional semiconductor switch connected between the two connection points;
Driving means for turning on the first unidirectional semiconductor switch so that the voltage between the two connection points is equal to or less than the rated voltage of the bidirectional semiconductor switch;
With
When the bidirectional semiconductor switch is completely turned off, inductive energy on the power supply side or load side is absorbed by the capacitor through the diode bridge, and the first unidirectional semiconductor switch and the constant voltage element are sequentially connected. A power conversion circuit characterized by turning on to consume inductive energy on a power supply side or a load side by the resistor and the constant voltage element. The power conversion circuit according to claim 4,
A power conversion circuit, wherein a resistor is connected between an anode of the Zener diode and a connection point between the negative electrodes of the first and second diode bridges.

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