JPH0678551A - Converter circuit - Google Patents

Abstract

PURPOSE:To simplify the snubber circuit of an SMR converter which converts an AC input to high-frequency AC with AC switches and applies it to the primary of a transformer, and changes the Ac input current into a sinusoidal wave with a high power factor. CONSTITUTION:AC switches 100 (101 and 102) are connected to AC input terminals U and V through AC reactors ACL1 and ACL2 respectively. This AC switch, in the case of 101 for example, is formed by connecting in parallel a series circuit of diodes D5 and D6, a single-phase bridge inverter circuit IGBT composed of U1, V1, X1, and Y1, and a snubber capacitor C1. Energy stored in the snubber capacitors C1 and C2 is applied to the primary of a transformer 3 through the switching elements of the AC switches, and discharged on its secondary side. In the case of these snubber circuits, it becomes unnecessary to add to the snubber capacitor of each AC switch, a diode bridge or a DC/DC converter for discharging the energy of the snubber capacitor to the secondary of the transformer unlike former ones, and the constitution is simplified.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention converts an AC input voltage into a high frequency AC by an AC switch and applies it to a primary winding of a transformer so that an AC input current can be converted into a sine wave with a high power factor. The so-called SMR (Swit) as an AC / DC converter that produces a direct current by rectifying and smoothing the secondary voltage of this transformer
ing Mode Rectifier) type converter, and more particularly to a converter circuit capable of easily configuring a snubber circuit of an AC switch.

In the following figures, the same reference numerals indicate the same or corresponding parts.

[0003]

2. Description of the Related Art FIG. 7A shows a configuration example of a conventional converter circuit of this type. In the figure, AC switch T1
And T3 are connected in series, and a series circuit in which AC switches T2 and T4 are connected in series are connected in parallel, and the primary winding of the transformer 3 is connected in parallel to this parallel circuit. ing. Both ends of the secondary winding of the transformer 3 are connected to an AC input terminal of a full-wave rectifier circuit 9 composed of diodes D1, D2, D3, D4, and DC output terminals P, N of the full-wave rectifier circuit 9 are connected. Sandenser 4 is connected in between. An AC input terminal U is connected to a connection point between the AC switches T1 and T3 via an AC reactor ACL1.
Similarly, an AC input terminal V is connected to a connection point between the AC switches T2 and T4 via an AC reactor ACL2.

Further, diodes D101, D102, D constituting the snubber circuit are provided at both ends of the AC switch T1.
An AC terminal of the full-wave rectifier circuit 10 including 103 and D104 is connected, and a snubber capacitor Cs1 is connected between the DC output terminals of the full-wave rectifier circuit 10. A DC / DC converter 5 for discharging the stored energy to the secondary side of the transformer 3 is provided across the capacitor Cs1.
Of the DC / DC converter 5 is connected to both electrodes of the capacitor 4.

Similarly, an AC terminal of the full-wave rectifier circuit 11 including diodes D105, D106, D107, and D108 is connected to both ends of the AC switch T2, and a snubber capacitor is provided between the DC output terminals of the full-wave rectifier circuit 11. Cs2 is connected. The input terminals of the DC / DC converter 6 are connected to both ends of this capacitor Cs2,
The output terminal of the DC converter 6 is connected to both ends of the capacitor 4.

Similarly, an AC terminal of the full-wave rectifier circuit 12 including diodes D109, D110, D111, and D112 is connected to both ends of the AC switch T3, and a snubber capacitor is provided between the DC output terminals of the full-wave rectifier circuit 12. Cs3 is connected. The input terminals of the DC / DC converter 7 are connected to both ends of the capacitor Cs3,
The output terminal of the DC converter 7 is connected to both ends of the capacitor 4.

Similarly, an AC terminal of the full-wave rectifier circuit 13 including diodes D113, D114, D115, and D116 is connected to both ends of the AC switch T4, and a snubber is provided between the DC output terminals of the full-wave rectifier circuit 13. Capacitor C
s4 is connected. The input terminals of the DC / DC converter 8 are connected to both ends of this capacitor Cs4, and
The output terminal of the C / DC converter 8 is connected to both ends of the capacitor 4.

AC switches T1, T2, T3, T4
In general, a circuit in which a parallel circuit of a switching element (for example, an IGBT) and a diode is anti-series is used as shown in FIG. 7 (B). FIG. 8 shows operation waveforms of each part of FIG. Next, the operation of FIG. 7 will be described with reference to FIG. When the voltage of the AC input terminal U is higher than the voltage of the AC input terminal V, when the AC switches T1, T2, T3, T4 are turned on, the input end of the primary winding of the transformer 3 is short-circuited,
AC terminal U → AC reactor ACL1 → AC switch T
1 → AC switch T2 → AC reactor ACL2 → AC terminal V path and AC terminal U → AC reactor ACL1
→ AC switch T3 → AC switch T4 → AC reactor ACL2 → Current flows through the path of the AC terminal V, and excitation energy is stored in the AC reactors ACL1 and ACL2. Next, when the AC switches T2 and T3 are turned off, the AC terminal U → AC reactor ACL1 → AC switch T1 →
Transformer 3 → Diode D1 → Capacitor 4 → Diode D4 → Transformer 3 → AC Switch T4 → AC Reactor A
A current flows through the path of CL2 → AC terminal V, and the energy stored in AC reactors ACL1 and ACL2 is released to capacitor 4.

Next, when the AC switches T2 and T3 are turned on, the input terminal of the primary winding of the transformer 3 is short-circuited, and the excitation energy is stored in the AC reactors ACL1 and ACL2. Next, when the AC switches T1 and T4 are turned off, the AC terminal U → AC reactor ACL1 → AC switch T3 → Transformer 3 → Diode D2 → Capacitor 4 →
A current flows through the path of diode D3 → transformer 3 → AC switch T2 → AC reactor ACL2 → AC terminal V, and the energy stored in AC reactors ACL1 and ACL2 is released to capacitor 4. At this time, AC switch T
The polarities of the voltages applied to the transformer 3 are opposite when 1,1 and T4 are on and when T2 and T3 are on, and the transformer 3 is not saturated. However, in the above description, when the energy is supplied to the secondary side of the transformer 3, the electric current is
Although the description has been given in the form of directly penetrating the next space, this is to describe an equivalent current flow for the sake of simplicity of description. Even when the voltage of the AC input terminal V is higher than the voltage of the AC input terminal U, the paths are the same and the operation is the same except that the direction in which the AC reactor current flows is opposite. By repeating such an operation, a voltage having a frequency higher than the frequency of the AC input is applied to the transformer 3, and high frequency insulation conversion is realized. In addition, AC switches T1, T2, T3, T
How to turn on / off 4 AC reactors ACL1, A
The power factor of the AC input becomes approximately 1 by performing the current of CL2 in the same phase as the AC input voltage and in the sinusoidal shape.

In such an operation, the AC switch T
The snubber operation when the AC switches T1 and T4 are turned off (at the time point of FIG. 8) from the state where all 1, T2, T3 and T4 are on will be described. As described above, when the AC switches T1, T2, T3 and T4 are on, the AC terminal U
→ AC reactor ACL1 → AC switch T1 → AC switch T2 → AC reactor ACL2 → AC terminal V route and AC terminal U → AC reactor ACL1 → AC switch T3 → AC switch T4 → AC reactor ACL2
→ Current is flowing in the route of AC terminal V. Next, when the AC switches T1 and T4 are turned off, the AC terminal U → AC reactor ACL1 → AC switch T3 → transformer 3 → diode D2 → capacitor 4 → diode D3 → transformer 3 → A
C switch T2 → AC reactor ACL2 → AC terminal V
Although a current starts to flow in the path of, the transformer 3 has a leakage inductance λt. Therefore, if an attempt is made to flow a current rapidly, a large electromotive force is generated in the inductance λt, and the primary voltage of the transformer 3 is increased. And the sum of electromotive force turned off A
It is applied to the C switches T1 and T4. A snubber circuit (full-wave rectifier circuits 10 and 13 and capacitors Cs1 and Cs4) is connected for the purpose of suppressing this voltage to the allowable voltage of the AC switch or less.

When the AC switches T1 and T4 are turned off,
Current flowing in the transformer 3 (current rises toward the AC reactor current) and AC reactors ACL1, ACL2
The difference current of the currents flowing in the AC terminal U → AC reactor ACL1 → diode D102 → capacitor Cs1 →
Diode D103 → AC switch T2 → AC reactor ACL2 → AC terminal V path and AC terminal U → AC reactor ACL1 → AC switch T3 → Diode D1
14 → capacitor Cs4 → diode D115 → AC reactor ACL2 → AC terminal V, and charges are stored in capacitors Cs1 and Cs4. At this time, the voltages of the AC switches T1 and T4 are clamped to the voltages of the capacitors Cs1 and Cs4, respectively.

Similarly, even when the AC switches T2 and T3 are turned off, the current flowing through the transformer 3 and the AC reactor ACL are the same.
1, the difference current of the current flowing in ACL2 is AC terminal U →
AC reactor ACL1 → AC switch T1 → diode D105 → capacitor Cs2 → diode D108 → AC reactor ACL2 → AC terminal V path and AC terminal U → AC reactor ACL1 → diode D109 → capacitor Cs3 → diode D112 → AC switch T4
→ AC reactor ACL2 → Absorbed by the capacitors Cs2 and Cs3 along the path of the AC terminal V. AC switch T2, T3
Are clamped to the voltages of capacitors Cs2 and Cs3, respectively.

Even when the voltage at the AC input terminal V is higher than the voltage at the AC input terminal U, the operation is the same except that the flow direction of the AC reactor current is opposite. Capacitor Cs1 ~
The energy stored in Cs4 is insulated and rectified through the DC / DC converters 5, 6, 7, and 8 and is discharged to the capacitor 4, so that the voltages of the capacitors Cs1 to Cs4 are set to predetermined values.

[0014]

However, in the conventional circuit configuration shown in FIG. 7, the rectifier circuits 10, 11, 12, 13 constituting the snubber circuit of the AC switch, the snubber capacitors Cs1, Cs2, Cs3, Cs4, DC / There is a problem that the DC converters 5, 6, 7, and 8 are required for the number of AC switches. Further, the DC / DC converters 5, 6, 7 and 8 have a voltage control function for insulating the input and output from each other and maintaining the voltage of the capacitors Cs1, Cs2, Cs3 and Cs4 at a predetermined value. Since it is necessary, there is a problem that a complicated and expensive circuit is required.

Therefore, an object of the present invention is to provide a converter circuit capable of solving such a problem.

[0016]

In order to solve the above-mentioned problems, a converter circuit according to a first aspect of the present invention converts an N-phase AC input into a high-frequency AC to form a primary winding of a transformer (3 or the like). A converter circuit for applying a direct current by rectifying and smoothing a secondary voltage of this transformer (through a rectifier 9, a capacitor 4, etc.) to generate a direct current.
6) and 4 switching elements (IGB
TU1, V1, X1, Y1, etc.) is connected in parallel between the DC terminals of the single-phase bridge inverter circuit such that the cathode of the diode series circuit is on the positive terminal side of the single-phase bridge inverter circuit. A snubber capacitor (such as C1) or a series circuit of this snubber capacitor and a resistor is connected in parallel to the parallel circuit to form one AC.
A switch (such as 100) is configured, N AC switches (such as 101 to 103) are provided, and each connection point of the diodes of the diode series circuit in the N AC switches is connected directly or to an AC reactor (ACL1). ~
(AC3, etc.) to the terminals (U, V, W, etc.) of the N-phase AC input, and one of the AC output terminals of each single-phase bridge inverter circuit in the N AC switches is connected to the transformer. To connect to one terminal of the primary winding of the transformer, and also to connect the other of the AC output terminals of each of the single-phase bridge inverter circuits to the other terminal of the primary winding of the transformer. .

A converter circuit according to a second aspect is the converter circuit according to the first aspect, wherein capacitors (C12, C23, C31, etc.) are provided between respective connection points of the diodes of the diode series circuit in the N AC switches. To connect. A converter circuit according to a third aspect of the present invention is the converter circuit according to the first or second aspect, in which the AC switch of the AC switch is applied during a period in which the N-phase AC input is applied to the primary winding of the transformer. The switching element of the opposite arm of the single-phase bridge inverter circuit is turned on for a predetermined period, and the energy of the snubber capacitor in the AC switch is discharged to the secondary side thereof via the transformer.

[0018]

Operation: A series circuit of diodes in which the anode of the first diode, the second diode and the cathode are connected (the mutual connection point of these two diodes is P1) and four switching elements Connected bridge circuit (the AC output terminals of this bridge circuit are
2 and P3), a snubber capacitor or a circuit in which a snubber circuit in which this snubber capacitor and a resistor are connected in series are connected in parallel is used as one AC switch, and this AC switch is provided for the number of phases of the AC input power supply. Then, the connection point P1 of each AC switch is connected to each AC input terminal directly or via an AC reactor, and the AC output terminal P2 of each AC switch is collectively connected to one of the transformer primary windings. Similarly, the AC output terminals P3 of the AC switches are collectively connected to the other terminal of the transformer primary winding.

As a result, the snubber circuit has a simple structure and only needs to be provided for the number of phases of the AC input power source, and the energy stored in the snubber capacitor is also given to the secondary side thereof through the AC switch and the transformer. The conventional DC / DC converter for each snubber circuit becomes unnecessary.

[0020]

Embodiments of the present invention will be described below with reference to FIGS. FIG. 1 is a circuit diagram showing a configuration as a first embodiment of the present invention. In the figure, diode D5
, A series circuit of diodes formed by connecting the anode of the diode D6 and the cathode of the diode D6, and IGBT U1 and IGBT
X1 connected in series, IGBT V1 and IG
A circuit in which BTY1 is connected in series and a snubber capacitor C1 are all connected in parallel to form an AC switch 100.
It constitutes (101).

Similarly, a series circuit of diodes in which the anode of the diode D7 and the cathode of the diode D8 are connected, a circuit in which the IGBT U2 and the IGBT X2 are connected in series, and a circuit in which the IGBT V2 and the IGBT Y2 are connected in series. And the snubber capacitor C2 are all connected in parallel to form the AC switch 100 (102). The IGBTs U1 to Y2 are respectively connected with diodes for freewheeling in antiparallel.

An AC input terminal U is connected to a connection point of the diodes D5 and D6 via an AC reactor ACL1 and an AC input terminal V is connected to a connection point of the diodes D7 and D8 via an AC reactor ACL2. Has been done. Also IGBT U1 and IGBT
The connection point with X1 is connected to one terminal of the primary winding of the transformer 3 together with the connection point with IGBT U2 and IGBT X2, and similarly, the connection point between IGBTV1 and IGBT Y1 is between IGBT V2 and IGBT Y2. It is connected to the other terminal of the primary winding of the transformer 3 together with the connection point. Further, both ends of the secondary winding of the transformer 3 have diodes D1, D2,
The full-wave rectifier circuit 9 formed of D3 and D4 is connected to the AC input terminal, and the DC output terminals P and N of the full-wave rectifier circuit 9 are connected to the capacitor 4.

FIG. 2 shows operation waveforms of each part of FIG. Next, the operation of FIG. 1 will be described with reference to FIG. By turning on the IGBTs U1, V1, X2, and Y2 while the AC input voltage is positive, the AC input terminal U → AC reactor A
CL1 → diode D5 → IGBT X2 → diode D8 → AC reactor ACL2 path and AC input terminal U1 → AC reactor ACL1 → diode D5 → IG
The primary input terminal of the transformer 3 is short-circuited by the path of BTV1 → IGBTTY2 → diode D8 → AC reactor ACL2, and the excitation energy is stored in the AC reactors ACL1 and ACL2.

Next, when the IGBT V1 and the IGBT X2 are turned off, the AC input terminal U → AC reactor ACL.
1 → Diode D5 → IGBT U1 → Transformer 3 → Diode D1 → Capacitor 4 → Diode D4 → Transformer 3
→ IGBT Y2 → Diode D8 → AC reactor A
A current flows through the path from CL2 to the AC input terminal V, and the energy stored in the AC reactors ACL1 and ACL2 is released to the capacitor 4. However, in order to simplify the description of the current in the transformer 3 portion, the equivalent current flow is also shown without insulation between the primary and secondary windings. It is the same.

Next, when the IGBTs V1 and X2 are turned on, the input end of the primary winding of the transformer 3 is short-circuited again, and the excitation energy is stored in the AC reactors ACL1 and ACL2. Next, when the IGBT U1 and the IGBT Y2 are turned off, the AC input terminal U → the AC reactor ACL
1 → diode D5 → IGBT V1 → transformer 3 → diode D2 → capacitor 4 → diode D3 → transformer 3 →
IGBT X2 → diode D8 → AC reactor AC
A current flows through the path of L2 → AC terminal V, and the energy stored in AC reactors ACL1 and ACL2 is released to capacitor 4. In the above operation, the IGBT U1,
The voltage polarities applied to the transformer 3 are opposite when Y2 is turned on and when the IGBTs V1 and X2 are turned on, and the transformer 3 is not saturated.

Even when the voltage of the AC input terminal V is higher than the voltage of the AC input terminal U, the IGBTs U1 and X1 and V1 and Y are connected.
The same operation is performed by simply replacing and using 1, U2 and X2, and V2 and Y2. By repeating such operation,
A voltage having a frequency higher than the frequency of the AC input is applied to the transformer 3 to realize high frequency insulation conversion. Also IGB
By turning on and off T U1 to Y2 so that the currents of the AC reactors ACL1 and ACL2 have the same phase as the AC input voltage and become sinusoidal, the power factor of the AC input becomes almost 1.

In such an operation, the IGBT U
1, V1, X2, Y2 is on, IGBT U
The snubber operation when Y1 and Y2 are turned off (time point in FIG. 2) will be described. As already explained, the IGBT
AC input terminals U → when U1, V1, X2 and Y2 are on
AC reactor ACL1 → diode D5 → IGBT
U1 → IGBT X2 → Diode D8 → AC reactor ACL2 path and AC input terminal U → AC reactor ACL1 → Diode D5 → IGBT V1 → IGBT
A current flows in the path of Y2 → diode D8 → AC reactor ACL2.

Next, when the IGBTs U1 and Y2 are turned off, the AC input terminal U → AC reactor ACL1 → diode D5 → IGBT V1 → transformer 3 → diode D2 → capacitor 4 → diode D3 → transformer 3 → IGBT X
2 → Diode D8 → AC reactor ACL2 → Current starts to flow in the path of AC input terminal V, but transformer 3 has leakage inductance λt, so that current cannot flow rapidly, and AC reactors 1 and 2 do not flow quickly. The difference current between the current flowing and the current flowing through the transformer 3 is the AC terminal U → diode D5 → IGBT U1 → reflux diode of the IGBT V2 → capacitor C2 → diode D8 → AC reactor ACL2 → the path of the AC terminal V and the alternating current The electric current is accumulated in the snubber capacitors C1 and C2 through the terminal U → diode D5 → capacitor C1 → reflux diode of the IGBT X1 → IGBT X2 → diode D8 → AC reactor ACL2 → AC terminal V. At this time, the voltages of the IGBT U1 and the IGBT Y2 are clamped to the voltages of the snubber capacitors C1 and C2, respectively.

In this way, the snubber capacitors C1,
The energy stored in C2 is IGBT V1, X respectively
2 is turned on for a part of the period (point in FIG. 2 ~
By turning on the IGBTs X1 and V2,
Capacitor C1 → IGBTTV1 → Primary winding of transformer 3 →
IGBT X1 → path of capacitor C1 and capacitor C2 → IGBT V2 → primary winding of transformer 3 → IGBT
A current flows through the path of X2 → capacitor C2 and is discharged to the secondary side of the transformer 3. At this time, snubber capacitor C
The voltages of 1 and C2 are maintained at the primary voltage of the transformer 3 (the voltage obtained by multiplying the secondary output voltage by the primary / secondary winding ratio of the transformer). This snubber circuit operates similarly when the other IGBTs are turned off.

FIG. 3 shows a configuration as a second embodiment of the present invention. In the figure, the AC input power supply is the power supply terminal U,
It has three phases of V and W, and in comparison with FIG. 1, in addition to the AC switches 101 and 102 connected to the AC input terminals U and V via the AC reactors ACL1 and ACL2, respectively, a configuration similar to this AC switch. AC switch 100 (1
03 is newly provided for the AC input terminal W.

That is, the AC switch 103 has a diode series circuit in which the anode of the diode D9 and the cathode of the diode D10 are connected, and the IGBT U3 and I.
A circuit in which the GBT X3 and the IGBT V3 are connected in series.
And a IGBT Y3 are directly connected to each other, and a snubber capacitor C3 is all connected in parallel. However, IGBTs U3 to Y3 are respectively connected with diodes for freewheeling in antiparallel. And AC switch 1
The AC terminal W is connected to the connection point of the diode D9 and the diode D10 of No. 03 via the AC reactor ACL3.

Also, the IGBT U1 of the AC switch 101
And the IGBT X1 connection point, I of the AC switch 102
Connection point between GBT U2 and IGBT X2, and AC
The connection points of the IGBT U3 and the IGBT X3 of the switch 103 are both connected to one terminal of the primary winding of the transformer 3, and similarly, the IGBT V1 and the IG of the AC switch 101 are connected to each other.
Connection point with BT Y1, IGBT of AC switch 102
The connection point between V2 and the IGBT Y2 and the connection point between the AC switch 103 and the IGBT V3 and the IGBT Y3 are both connected to the other terminal of the primary winding of the transformer 3. FIG. 3 has the same operation as that of FIG. 1 except that the number of AC switches is changed from two to three for application to a three-phase circuit.

FIG. 4 shows the configuration of a third embodiment of the present invention. 4 is different from FIG. 1 in that in FIG. 4, a capacitor C12 is provided between the connection point of the diodes D5 and D6, the connection point of the diodes D7 and D8, and the full-wave rectification circuit 9 This is the point where a DC reactor 14 is newly connected between the positive electrode output point and the capacitor 4.

In the circuits shown in FIGS. 1 and 3, the input terminals of the primary windings of the transformer 3 are short-circuited by the AC switches 101 to 103 and then opened to open the AC reactor ACL1.
By providing a mode in which the energy stored in ACL3 is discharged to the secondary side of the transformer 3, the circuits of FIGS. 1 and 3 are suitable for a boost converter, but the circuits of FIG. 4 and FIG. The circuit of FIGS. 4 and 5 is suitable for a step-down converter since the mode in which the primary input terminal of the transformer is short-circuited cannot be provided in the circuit due to the presence of the capacitors C12, C23 and C31.

FIG. 5 shows operation waveforms of each part of FIG. Next, the operation of FIG. 4 will be described with reference to FIG. By turning on the IGBTs U1 and Y2 while the AC input is positive, the capacitor C12 → diode D5 → IGBT U
1 → Transformer 3 → Diode D1 → DC Reactor 14 →
Capacitor 4 → Diode D4 → Transformer 3 → IGBTTY
The voltage of the positive electrode is applied to the transformer 3 via the path of 2 → diode D8 → capacitor C12 to supply power to the secondary side thereof.

Further, by turning on the IGBTs V1 and X2, the capacitor C12 → diode D5 → IGB
TV1 → transformer 3 → diode D2 → DC reactor 14 → capacitor 4 → diode D3 → transformer 3 → IG
The voltage of the negative electrode is applied to the transformer 3 along the path of BT X2 → diode D8 → capacitor C12 to supply power to the secondary side thereof. Further, when all the IGBTs are turned off, the current flowing in the DC reactor 14 is the DC reactor 14 → capacitor 4 → diode D3 → diode D1.
→ The path of the DC reactor 14 and the DC reactor 14 →
The secondary voltage of the transformer is short-circuited by flowing through the path of the capacitor 4 → the diode D4 → the diode D2 → the DC reactor 14.

During the period when the AC voltage is negative, the IGBT U1
And X1, V1 and Y1, U2 and X2, and V2 and Y2 are replaced and the same operation is performed. By repeating such an operation, a voltage having a frequency higher than the frequency of the AC input is applied to the transformer 3, and high frequency insulation conversion is realized. In this circuit, for example, the IGBT that was turned on
When U1 and IGBT Y2 are turned off at the time of FIG. 5,
The energy stored in the leakage inductance λt of the transformer is equivalent to the leakage inductance λt → transformer 3 → diode D1 → diode D2 (where D2 is (DC reactor 1
(Current of 4) − (current of leakage inductance λt) is conducting) → transformer 3 → reflux diode of IGBT V1 → capacitor C1 → reflux diode of IGBT X1 → path of leakage inductance λt and leakage inductance λt → Transformer 3 → Diode D3 (for D3, (current of DC reactor 14) − (leakage inductance λt
Current) flows and conducts) → diode D4 → transformer 3 → IGBT V2 freewheeling diode → capacitor C
2 → reflux diode of IGBT X2 → current flows through the path of leakage inductance λt, so that capacitor C
1, absorbed by C2. At this time, IGBT U1, IG
The voltage of BTY2 is the capacitor C for each snubber.
It is clamped to the voltage of 1, C2.

The energy stored in the capacitors C1 and C2 is the IGBT X1 and V2 during a part of the period in which the IGBT V1 and X2 are on (between time points in FIG. 5).
By turning on, the capacitor C1 → IGBT
V1 → primary winding of transformer 3 → IGBT X1 → capacitor C1 path and current flows through a path of capacitor C2 → IGBT V2 → primary winding of transformer 3 → IGBT X2 → capacitor C2, It is discharged to the secondary side of the transformer 3. At this time, the voltage of the capacitors C1 and C2 is maintained at the primary voltage of the transformer 3. This snubber circuit is
The same operation is performed when the BT is turned off.

FIG. 6 shows a fourth embodiment of the present invention. 6 is different from FIG. 3 in that the diode D5 in FIG.
And a diode D6, a capacitor C12 between the connection point between the diode D7 and the diode D8, a connection point between the diode D7 and the diode D8, and a diode D
Capacitor C23 between the connection point of 9 and diode D10
And a connection point between the diode D9 and the diode D10,
A capacitor C31 is connected between the connection points of the diode D5 and the diode D6, and a DC reactor 14 is newly connected between the output point of the full-wave rectifier circuit 9 and the capacitor 4. Since the operation of FIG. 6 is applied to a three-phase circuit, the operation is the same as that of FIG.

In the above embodiment, the AC switch 101
A resistance for vibration damping may be inserted in series with the snubber capacitors C1 to C3 of No. 103, and this is also included in the present invention. Further, AC reactors ACL1 to ACL3 are not essential because the wiring inductance of the AC input line can be replaced when the switching frequency of AC switch 100 (and therefore the carrier frequency) is high.

[0041]

According to the present invention, two series diodes, a series circuit of a snubber capacitor or a snubber capacitor and a resistor, and a single-phase bridge inverter circuit composed of four switching elements are connected in parallel to form one. Since the AC switch is configured and one AC switch is provided for each AC input line, a general snubber such as a capacitor or a series circuit of a resistor and a capacitor can be used as a snubber circuit of the AC switch constituent element. It can be configured and does not require a new snubber energy storage circuit.
Since it can be performed via the C-switch component, the circuit is simpler and the cost is lower than that of the conventional converter circuit. Further, the reliability is improved because the number of parts is reduced. Further, as a component of the AC switch, a generally available 2 in 1 type module having upper and lower arms can be applied, so that the cost of parts can be reduced.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a configuration as a first embodiment of the present invention.

FIG. 2 is a waveform diagram of each part for explaining the operation of FIG.

FIG. 3 is a circuit diagram showing a configuration as a second embodiment of the present invention.

FIG. 4 is a circuit diagram showing a configuration as a third embodiment of the present invention.

5 is a waveform diagram of each part for explaining the operation of FIG.

FIG. 6 is a circuit diagram showing a configuration as a fourth embodiment of the present invention.

FIG. 7 is a circuit diagram of a conventional converter.

8 is a waveform chart of each part for explaining the operation of FIG.

[Explanation of symbols]

 ACL1 AC reactor ACL2 AC reactor ACL3 AC reactor 3 Transformer 4 Capacitor C12 Capacitor C23 Capacitor C31 Capacitor 9 Rectifier 14 DC reactor 100 (101-103) AC switch

Claims (3)

[Claims] 1. A converter circuit for converting an N-phase AC input into a high-frequency AC and applying it to a primary winding of a transformer to rectify and smooth a secondary voltage of the transformer to produce a DC. A series circuit of two diodes of the same polarity is arranged in parallel between the DC terminals of a single-phase bridge inverter circuit composed of four switching elements so that the cathode of the diode series circuit is on the positive terminal side of the single-phase bridge inverter circuit. Connected to this parallel circuit, a snubber capacitor or a series circuit of this snubber capacitor and a resistor is connected in parallel to form one AC switch. N AC switches are provided. Connecting each connection point of the diodes of the diode series circuit to the terminal of the AC input of the N phase directly or via an AC reactor, One of the AC output terminals of each single-phase bridge inverter circuit in each AC switch is connected to one terminal of the primary winding of the transformer, and the AC output terminal of each of the single-phase bridge inverter circuits is also connected. The converter circuit is characterized in that the other terminal is connected to the other terminal of the primary winding of the transformer. 2. The converter circuit according to claim 1, wherein a capacitor is connected between respective connection points of the diodes of the diode series circuit in the N AC switches. 3. The converter circuit according to claim 1, wherein the single-phase bridge inverter in the AC switch is in a period during which the N-phase AC input is applied to the primary winding of the transformer. A converter circuit, wherein a switching element of an opposite arm of the circuit is turned on for a predetermined period of time, and energy of a snubber capacitor in the AC switch is discharged to a secondary side of the snubber capacitor via the transformer.