JPH0365045A - Power converter and snubber circuit - Google Patents

Abstract

PURPOSE:To reduce the size of a transformer by connecting the transformer in parallel with DC terminals through a first capacitor constituting a snubber circuit. CONSTITUTION:Primary winding of a transformer 30 is connected in parallel with the DC diodes 23, 24 of an integrated snubber circuit 20 and the secondary winding of the transformer 30 is connected with DC terminals 16, 17 through a reverse current blocking diode 38. Snubber absorbing energy stored in the first capacitor 21 is discharged to a DC power source or a load which is connected with DC terminals through the primary winding of the transformer 30. Power induced in the secondary winding of the transformer 30 is recovered effectively by a power recovering load such as the DC power source. Snubber absorbing energy stored in the second capacitor 22 is recovered, without passing through the transformer 30, by an AC power source or a load connected with AC terminals and utilized effectively. Since the amount of energy, to be handled by the transformer 30, is reduced the size of the transformer is reduced correspondingly.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a power conversion device, and specifically relates to a snubber circuit that absorbs switching surges of switching elements of a power conversion main circuit. It is particularly suitable for snubber circuits of power converters that use self-extinguishing elements such as GTO (gate turn off) thyristors as main circuit switching elements, and can effectively recover surge energy absorbed by the snubber circuits. Regarding technology.

[Conventional technology]

Conventionally, snubber circuits for power converters have been developed in
Discussed in Publication No. 0-6136. According to this, a snubber circuit consisting of each switching element, a diode, and a capacitor is connected in parallel, and all of the energy stored in the capacitor is recovered to the power source via a transformer.

[Problem to be solved by the invention]

However, the above-mentioned conventional technology does not consider miniaturization of the transformer for snubber energy recovery.

That is, in the conventional example shown in FIG. 19, when the switching element 1 is turned off, the turn-off energy is stored in the capacitor 3. Next, when the switching element 1 is turned on, the stored energy is transferred to the transformer 4 and the switching element 1. All are released through. therefore,
Since all of the energy absorbed by the snubber must be processed by the transformer 4, there is a problem in that the device becomes large.

An object of the present invention is to provide a power conversion device having a snubber circuit configured to release energy absorbed by the snubber without passing through the switching elements of the main circuit.

[Means to solve the problem]

In order to achieve the object described below, the present invention includes a main switching circuit corresponding to each phase, a collective snubber circuit, and a transformer, and each of the main switching circuits includes at least one A positive arm and a negative arm each having a switching element are connected in series, both ends of the series circuit are DC ends, and a common connection point is an AC end, and the collective snubber circuit has a first capacitor and two capacitors. A series circuit of diodes is connected in parallel to the series circuit of the positive and negative arms, and a common connection point of the two diodes is connected to a common connection point of the positive and negative arms via a second capacitor, and the transformer The power converter has a configuration in which the primary side is connected in parallel to the DC end of the main switching circuit via the first capacitor of the collective snubber circuit, and the secondary side is connected to the power recovery load. be.

Note that in order to prevent or suppress magnetic saturation of the transformer, it is desirable to connect a resistor in parallel or in series to the primary winding of the transformer. It is likewise possible to insert a switching element in the primary circuit, thereby interrupting the emission circuit and resetting the excitation current.

Moreover, the recovery load of the snubber absorbed energy can be a DC power source, a control power source, or another power load of the power conversion device.

Further, the present invention can also be applied to a main switching circuit in which each of the positive and negative pole arms has a plurality of switching elements connected in multiple stages to generate a high voltage. In this case, it is desirable to separately provide a conventional snubber circuit for each switching element in addition to the collective snubber circuit. According to this, variations in characteristics of each switching element can be absorbed by the individual snubber circuit.

[Effect]

According to the present invention configured in this manner, the above object is achieved through the following actions.

In other words, since the transformer is connected in parallel to the DC end via the first capacitor that forms the snubber circuit, the snubber absorbed energy stored in the first capacitor is transferred to the primary winding of the current transformer. is discharged to the DC power supply or load connected to the DC end via the DC power supply.

Furthermore, the power induced in the secondary winding of the transformer is effectively recovered by a power recovery load such as a DC power supply.

On the other hand, the snubber absorbed energy stored in the second capacitor is recovered to the AC power supply or load connected to the AC terminal without going through the transformer, and is effectively used.

As a result, the amount of energy processed by the transformer is reduced, and the transformer can be made smaller accordingly.

Furthermore, if a resistor or inductance is connected in parallel or in series to the primary winding of the transformer, the transformer's excitation current flows through those resistors and operates to reset the core of the transformer. , can prevent magnetic saturation,
This allows the transformer to be further downsized.

〔Example〕

Hereinafter, the present invention will be explained based on examples.

FIG. 1 shows the main circuit configuration of one phase of a power conversion device according to an embodiment of the present invention. Regarding the operation description, this circuit will be described below as an inverter device using an AC motor as a load, but the five-wire circuit can be applied as is to a converter device.

In this embodiment, as shown in the figure, the main switching circuit 10,
It is configured to include a collective snubber circuit 20 and a transformer 30. The main switching circuit 10 includes a positive arm having a switching element 11 and a negative arm having a switching element 12 connected in series. Each switching element 11,
12 is a GTO thyristor, and freewheel diodes 13 and 14 are connected in antiparallel to each of them. The positive end of the main switching circuit is connected to the positive DC side terminal 16 via the handle 15, the negative end is connected to the negative DC side terminal 17, and the common connection point of the positive and negative arms is connected to the AC terminal 18. It is connected.

On the other hand, the collective snubber circuit 20 includes a first capacitor 21, a second capacitor 22 . It is formed with two diodes 23 and 24 connected in series in the forward direction. The anode of the series diode 23 is connected to the positive end of the main switching circuit via a first capacitor. The cathode of the series diode 24 is connected to the negative terminal of the main switching circuit. A common connection point between the series diodes 23 and 24 is connected to a common connection point between the positive and negative arms via a second capacitor.

Further, the primary winding of the transformer 30 is connected in parallel to the series diodes 23 and 24 of the collective snubber circuit 20, in other words, it is connected in parallel to the DC end of the main switching circuit 10 via the first capacitor 21. has been done. On the other hand, the secondary winding of transformer 3o is.

The DC terminal 16. is connected to the DC terminal 16.
17.

Note that the connection relationship of the collective snubber circuit 20 to the main switching circuit 10 can be modified as shown in FIG. 2, and in this case, a transformer 3° is connected as shown in the same figure.

The operation of the embodiment configured as described above will be explained using FIG. 3 and FIG. 4.

FIGS. 3(a) to 3(e) show the circuit operation from the positive-electrode arm conduction state to the negative-electrode arm conduction state, and then back to the positive-electrode arm conduction state. The same figure (a
), the switching element 11 is in the on state,
A load current iL is supplied from a DC power source to a load. In this state, when an off-gate signal is input to the switching element 11, the iL that had been flowing until then flows through the path shown in FIG. At this time, the switching surge is absorbed, and the energy stored in the capacitor 22 with the polarity shown is released to the load. This diagram (
In state b), since the switching element 12 is switched from off to on, the polarity of the load current iL remains positive (flowing direction), and the polarity of the output voltage switches from positive to negative, so there is an equivalent delay. The power factor is in a slow phase operation state. On the other hand, in Figure (b), the capacitor 21
is overcharged.

Next, as shown in (Q) in the same figure, when the load current iL shifts to the freewheeling mode in which it commutates to the negative pole arm, the charge in the capacitor 21 is discharged along the path shown by the dotted line, and is transferred to the primary side of the transformer 30. A discharge current is flows. As a result, 2 of the transformer 30
A current is2 having a value inversely proportional to the number of turns of the primary winding and the secondary winding flows to the next side, and energy is recovered to the DC side power supply.

Next, as shown in the same figure (d), the switching element 12
After the off-gate signal is input to the switching element 11, when the on-gate signal is input again to the switching element 11, the capacitor 22 is charged and the switching surge is absorbed, and the load current flows into the switching element 11, resulting in the state shown in FIG. Return to the initial state (a).

In the case of commutation operation from CO) to Ce) in the same figure, the output voltage polarity switches from negative to positive while the polarity of the load current remains positive, which equivalently leads to a leading power factor, that is, a leading phase operation state. It has become.

On the other hand, FIG. 4 shows the circuit operation when the negative electrode arm passes through the current flow state, the positive electrode arm flows through the recirculation state, and the negative electrode arm flows back again.

The commutation operations shown in FIGS. 3(a) to 3(d) are slow mode commutation operations, similar to the operations shown in FIGS. 3(a) to (Q).

Also, the operation from (d) to (f) is from (Q) to (
This is a phase-advanced mode commutation operation, similar to the operation in e). When moving from FIG. 4(d) to FIG. 4(e), the energy stored in the capacitor 22 cannot be released to the AC side terminal 18 due to the current flowing from the AC terminal 9, so the switching element 12
When turned on, the current is recovered by the DC power supply through the current paths shown in (e) and (2).

As described above, according to the embodiment shown in FIG. 1, part of the surge energy generated when the switching element is turned off is absorbed by the capacitor of the snubber circuit, and the absorbed energy is used in either the phase-leading or phase-lag operation mode. Even if there is a power supply (
Since there is an operation mode in which the power can be recovered as electric power to the power source (or the load) and is recovered without going through the transformer, the transformer can be made smaller accordingly.

For example, the accumulated energy of the capacitor 22 charged in Fig. 3(d) is calculated by the capacitor capacitance being C1°, as shown in Fig. 3(b).
, this energy is dissipated to the load and thus processed without going through a transformer.

On the other hand, the capacitor 22(e) charged in FIG. 4(c)
At , it is processed through a transformer.

In FIG. 3(Q) and FIG. 4(d), the overvoltage energy accumulated in the capacitor 21 to be processed by the transformer is
If the capacitance of the capacitor 21 is 02□, the ratio a of the energy processed through the transformer to the total energy to be processed is as follows. Therefore, the transformer can be made smaller by this amount. For example, if c, 1 = 10 c, □ is selected, the ΔV poison can be approximately Ed/4, so a'' = 0.69, and the transformer can be downsized to 69%.

Other embodiments of the present invention will be described below.

In FIG. 5, a resistor 31 is connected in parallel to the primary side of the transformer 30, and a part of the discharge current of the snubber recovered energy is transferred to the parallel resistor 31.
It should be collected by diverting it to the other side.

The excitation current of the transformer 30 is quickly attenuated to prevent magnetic saturation of the iron core.

According to this, the excitation current that continues to flow even when the snubber absorbed energy is not recovered can be quickly reset by the resistor 31, so magnetic saturation of the iron core can be prevented and the transformer can be made smaller. It is possible.

In FIG. 6, a resistor 32 is inserted in series in the primary circuit of the transformer 30, and the voltage is shared between them to attenuate the excitation current as quickly as possible in the same manner as in FIG. 5, thereby preventing magnetic saturation.

7 and 8 show that when the excitation current of the transformer 30 is in the state shown in FIG. 3(b) and FIG. 4(e), the excitation current of the transformer 30 is
3.24, there is an inductance 3
This is an example in which 3 or 8 are connected in series. According to this embodiment, when a freewheeling current flows, the transformer 30 is reset by the voltage drop of the inductance 33 or 18 in addition to the forward voltage drop of the diodes 23 and 24, which is effective in preventing magnetic saturation of the iron core.

In addition, as the energy accumulated in the snubber capacitor is recovered to the DC power supply, the switching element 11 or 1
It is possible to suppress the peak value of the current flowing at the time of turn-on.

FIGS. 9(a) to 9(d) show the embodiment using the resistor 31.32 shown in FIGS. 5 and 6, and the embodiment using the inductance 33.18 shown in FIGS. 7 and 8. This is a combination of the two embodiments, and the effects of the respective embodiments can be combined.

FIG. 10 shows an example in which switching elements 34 are connected in series in order to forcibly reset the excitation current of the transformer 30. According to this embodiment, there is an effect that the switching element 34 can be reset at any time by gate control. When using a switching element without reverse voltage blocking ability as the switching element 34, a diode 35 is connected in antiparallel.

That is, in FIGS. 4(e) to (f), the transformer 30
The discharge current flowing to the primary side of the battery is as shown in FIG. At the time t□ shown in the figure, the switching element 1 of the positive arm
1 is turned off, and when the switching element 12 of the negative pole arm is turned on at time t2, a discharge current flows due to the charge of the capacitor 22 (mode shown in FIG. 4(e)), and this discharge is completed by the excitation current of the transformer 30. flows along the path of ■ (
mode in FIG. 4(f)). Since this excitation current continues to flow as a circulating current in the closed circuit consisting of the transformer 30 and the diodes 23, 24, a loss occurs in the diodes 23, 24 due to a forward voltage drop. In this embodiment, by turning off the switching element 34, the circulating current can be cut off and loss can be reduced.

FIG. 12 shows an example in which the embodiment shown in FIG. 1 is applied to a three-phase inverter or a three-phase converter. In the case of an inverter, the reference numeral 19 is an AC load, and in the case of a converter, it is an AC power supply. A transformer 30a provided for each phase,
Leakage snubber circuits 20a, 20b, 30b, 30c,
The energy stored in each of 20c is recovered to a DC power source.

According to this embodiment, the accumulated energy of all arms can be recovered, so the total amount of recovered energy is increased.

FIG. 13 is an example in which the transformers for each phase in the embodiment shown in FIG. 12 are integrated. According to this embodiment, transformer 3
Since only one 0 is required, the overall size of the power converter can be further reduced.

In the above embodiments, the energy recovery destination was the DC side terminals 16 and 17 of the power converter main circuit, but as shown in FIG.
As shown in b), the transformer secondary terminal may be connected to a part of the divided DC power supply capacitors 41, 42, 43, etc. In this embodiment, the DC power supply voltage is divided, so the transformer This has the effect that the dielectric strength voltage on the secondary side of the device 30 and the reverse dielectric strength voltage of the diode 38 can be lowered.

For example, if the embodiment shown in FIG. 12 and the embodiment shown in FIG. 14 are combined, for example, as shown in FIG. Connecting to 42.43 also has the effect of increasing the number of parts that can be designed with low dielectric strength.

In the above embodiments, the energy is recovered from the DC power source of the main circuit of the power converter, but other DC power sources may be used. 1st
FIG. 6 shows an embodiment in which the present invention is applied to a DC power supply section 53 used in a gate drive circuit 52 for operating a switching element 51 as a recovery destination. Transformer 3
The secondary side of 0 is connected to both ends of power supply capacitors 54 and 55. The recovered energy is used in the gate drive circuit 52.
It is effectively used as drive energy to supply the

Note that normally, the DC power for the gate drive circuit 52 is supplied by rectifying the AC voltage stepped down by the transformer 58 by the rectifiers 56 and 57. According to this embodiment, since the power supply voltage of the gate drive circuit 52 is usually about several tens of volts,
This has the effect that the transformer 30 can be made smaller, such as by being able to design a smaller number of winding turns and a lower dielectric strength voltage. Similarly, the control circuit power supply can be used as the recovery charging source, and the same effect can be obtained.

The above-mentioned embodiment of the power recovery light has been described as being recovered to a DC power source, etc., but as shown in FIG. It is also possible to convert it into AC power equal to , and recover it to the AC power supply 19 or any AC load.

According to this, the range of use of snubber recovered energy is widened.

FIG. 18 shows an embodiment in which the main switching circuit of the embodiment of FIG. 1 is composed of a plurality of switching elements connected in multiple stages. Such multi-stage design is adopted in response to higher voltage and larger capacity.

As shown in the figure, in addition to the collective snubber circuit 20, each switching element 11a, llb, 12a, 12b is connected in multiple stages.
An individual snubber circuit 70 is provided for each. Each individual snubber circuit is a known type formed from a diode 71, a capacitor 72, and a resistor 73.

According to this embodiment, when the switching elements of each arm turn off, some of the surge energy is absorbed by the snubber circuit 20.
and switching elements lla and 11b (or 1
2a and 12b) can be absorbed by the individual snubber circuits 70, making it possible to equalize the voltage sharing among the switching elements.

〔Effect of the invention〕

According to the present invention, the following effects can be obtained.

In other words, since the transformer is connected in parallel to the DC end via the first capacitor that forms the snubber circuit, the snubber absorbed energy stored in the first capacitor is transferred to the primary winding of the current transformer. is discharged to the DC power supply or load connected to the DC end via the DC power supply.

Furthermore, the power induced in the secondary winding of the transformer is effectively recovered by a power recovery load such as a DC power supply.

Further, the snubber absorbed energy stored in the second capacitor can be released to the AC side without going through the transformer and used.

As a result, the amount of energy to be processed by the transformer is reduced, so the transformer can be made smaller by that amount, and the entire device can thereby be made smaller.

In addition, if a resistor or inductance is connected in parallel or in series with the primary winding of the transformer, the discharge current or voltage is shunted or divided into the resistors, which prevents magnetic saturation of the transformer and allows the iron core to be made smaller. There is an effect.

[Brief explanation of drawings]

FIG. 1 is a main circuit configuration diagram for one phase of an embodiment of the present invention, FIG. 2 is a configuration diagram of a modification of the embodiment in FIG. 1, and FIGS.
(e) and FIGS. 4(a) to 4(f) are diagrams for explaining the operation of the embodiment in FIG. 1, and FIGS. 5 to 8 show the configurations of other embodiments corresponding to FIG. 1, respectively. Figures 9(a)-(d)
10 is a configuration diagram of an embodiment obtained by combining the embodiments of FIGS. 5 to 8, FIG. 10 is a configuration diagram of still another embodiment corresponding to FIG. 1, and FIG. 12 is a configuration diagram of an embodiment in which the embodiment in FIG. 1 is applied to a three-phase power conversion device; FIG. 13 is a diagram showing a modification of the embodiment in FIG. 12; FIG. 14 is a diagram for explaining the operation. (a), (b) to Fig. 17 are diagrams showing modified examples of the power recovery light, Fig. 18 is a block diagram of an embodiment in which the main switching circuit is composed of multistage switching elements, and Fig. 19 is a conventional snubber circuit. FIG. 10... Main switching circuit, 11.12... Switching element, 16.17... DC terminal, 18... AC terminal, 20
...Bulk snubber circuit, 21...First capacitor, 22...Second capacitor, 23.24...Diode, 3o...Transformer, 38
...Diode, 31.32...Resistor, 33...
Reactor, 70...Individual snubber circuit.

Claims (1)

[Claims] 1. The main switching circuit is configured to include a main switching circuit corresponding to each phase, a collective snubber circuit, and a transformer, and each of the main switching circuits has at least one switching element. A positive pole arm and a negative pole arm are connected in series, and both ends of the series circuit are used as DC ends, and a common connection point is used as an AC end, and the collective snubber circuit is a series circuit of a first capacitor and two diodes. are connected in parallel to the series circuit of the positive and negative arms, and a common connection point of the two diodes is connected to a common connection point of the positive and negative arms via a second capacitor, and the transformer is a primary A power converter device in which the secondary side is connected in parallel to the DC end of the main switching circuit via the first capacitor of the collective snubber circuit, and the secondary side is connected to a power recovery load. 2. The power conversion device according to claim 1, further comprising a resistance element connected in parallel to the primary side of the transformer. 3. The power conversion device according to claim 1, wherein an impedance element is inserted and connected to the primary circuit of the transformer. 4. The power conversion device according to claim 1, wherein a switching element is inserted and connected to the primary circuit of the transformer, and the excitation current is reset by the switching element. 5. Claims 1 and 2, characterized in that the power recovery load is a DC power supply to which the main switching circuit is connected.
4. The power conversion device according to any one of 3 and 4. 6. The positive pole arm and the negative pole arm have a plurality of switching elements connected in series, and a series circuit of a diode and a capacitor is connected in parallel to each switching element, and a resistor is connected in parallel to the diode. 6. The power conversion device according to claim 1, further comprising an individual snubber circuit. 7. First and second capacitors, two diodes,
A snubber circuit for absorbing a switching surge of a main switching circuit in which a positive arm and a negative arm each having at least one switching element are connected in series, the snubber circuit comprising: a transformer; A capacitor is connected in series with the two diodes and in parallel with the main switching circuit, and the second capacitor is connected between a common connection point of the two diodes and a common connection point of the positive and negative arms. a snubber circuit, wherein the primary side of the transformer is connected in parallel to the series circuit consisting of the two diodes, and the secondary side is connected to a power recovery load.