JPH08168263A - Circuit and method for recovering snubber energy of power converter - Google Patents

Abstract

PURPOSE: To suppress the enlargement of a power converter which is isolated from a DC power source and outputs AC power by reducing losses and, at the same time, to improve the efficiency of the power converter by recovering the energy stored in a snubber when the power converter operates. CONSTITUTION: As a switching element 21 constituting a first serial switching circuit 2 operates, the electric charges stored in a snubber capacitor 52 are transferred to a regenerative circuit 12 through a first auxiliary circuit 10 or second auxiliary circuit and further transferred to a first snubber circuit 7 connected in parallel with a power converter, but, since the energy of the snubber circuit 7 is supplied to a load when a switching element 32 constituting a second serial switching circuit 3 is turned on, the electric charges are not consumed by a resistor. In addition, when the turn-on period of the element 32 is set to about 1/2 of the resonance period decided by the capacitance of the capacitor of the snubber circuit 7 and the leakage inductance of a transformer 4, the element 32 is turned off when the current becomes zero or about zero and no switching loss occurs.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the operation of a power converter that outputs AC power insulated from a DC power supply.
The present invention relates to a snubber energy recovery device for a power converter that recovers energy stored in a snubber and a recovery method thereof.

[0002]

2. Description of the Related Art FIG. 9 is a circuit diagram showing a first conventional example of a power conversion device having a snubber and converting a direct current into an alternating current insulated from the direct current. In this first conventional example circuit, one end of a switching element 21 formed by connecting a semiconductor switching element such as an IGBT (insulated gate bipolar transistor) and a diode in reverse parallel to each other is connected to the primary winding of the transformer 4. One end of the switching element 31 having the same structure is connected to one terminal and the other terminal of the primary winding is connected, and the other end of these switching elements 21 and the other end of the switching element 31 are commonly used. The power converter is configured by connecting the negative side of the power source 1 and the positive side of the DC power source 1 to the center tap of the primary winding of the transformer 4.

If only the switching element 21 is turned on, the transformer 4 is excited in the positive direction, and if only the switching element 31 is turned on, the transformer 4 is excited in the negative direction. Therefore, by alternately repeating switching on of the switching element 21 and switching on of the switching element 31, it is possible to take out AC power insulated from the DC power supply 1 from the secondary side of the transformer 4. By the way, when the switching element 21 or the switching element 31 is turned off, a period in which the current and the voltage overlap with each other (that is, a period in which the current flows while the voltage is applied) occurs, and a transient power loss (switching loss) occurs. This switching loss lowers the conversion efficiency of the power conversion device and needs to remove the heat generated due to the loss, which causes a problem such as an increase in size of the device.

Therefore, in the first conventional example circuit of FIG. 9, in order to reduce the switching loss of the elements by reducing the rate of voltage rise when the switching elements 21 and 31 are turned off, it is composed of a capacitor, a diode and a resistor. RD
The C snubber 5 is connected to the switching element 21 in parallel, and the switching element 31 is also connected to the RDC snubber 6 having the same configuration in parallel. Thus, the stored energy of the wiring inductance and the leakage inductance of the transformer is absorbed by the capacitors forming the RDC snubbers 5 and 6 when the switching elements 21 and 31 are turned off, and then the switching elements 21 and 31 are turned on. When RDC
It is consumed by the resistors that form the snubbers 5 and 6.

FIG. 10 is a circuit diagram showing a second conventional example of a power conversion device having a snubber and converting a direct current into an alternating current insulated from the direct current. This second conventional example circuit includes a first series switching circuit 2 including a switching element 21 and a switching element 22 connected in series, and a switching element 31.
And a switching element 32 connected in series to a second series switching circuit 3 that is connected in parallel to form a parallel switching circuit. The connection point between the switching elements 21 and 22 and one terminal of the transformer 4 primary winding And the connection point of the switching elements 31 and 32 is connected to the other terminal of the primary winding. The DC power supply 1 includes the switching element 21.
And the switching element 31 and the center tap of the transformer 4 primary winding. Further, the first snubber circuit 7 including a capacitor is connected in parallel to the parallel switching circuit. The operation of converting the direct current into the alternating current by the power conversion device configured as described above is the same as in the case of the circuit of the first conventional example of FIG. 9 described above, and therefore the description of the operation is omitted.

The operation of the first snubber circuit 7 connected in parallel with the parallel switching circuit is as follows. That is, the first
The snubber circuit 7 is clamped to twice the voltage of the DC power supply 1. Here, when the voltage of the switching element 21 or 31 reaches twice that of the DC power supply 1 when the switching element 21 or 31 is turned off, the anti-parallel diode constituting the switching element 22 or 32 becomes conductive, and the switching element 21, 31 is turned on.
The first snubber circuit 7 absorbs energy corresponding to the amount of the jumped-up voltage. here,
For example, when the switching element 32 is turned on while the switching element 21 is on and the transformer 4 is excited in the positive direction, the energy absorbed in the first snubber circuit 7 is changed from the first snubber circuit 7 to the switching element 32. → Transformer 4 → Switching element 21 → Discharge in the path of the first snubber circuit 7. Even when the switching element 31 is on and the transformer 4 is excited in the negative direction, if the switching element 22 is turned on, the energy of the first snubber circuit 7 is discharged by the same operation.

[0007]

In the circuit of the first conventional example shown in FIG. 9, the energy absorbed by the capacitors constituting the RDC snubbers 5 and 6 is released to the resistor when the switching element is turned on next time. It will be lost because it is done. Assuming that the capacitance of the capacitor that constitutes the RDC snubber is C, the DC power supply voltage is E, the jumping voltage of the switching element is ΔV, and the operating frequency of the switching element is f, the loss in the resistance P is expressed by the following formula 1. To be done.

[0008]

[Equation 1] P = {C · (2 · E + ΔV) ² · f} / 2 As the DC power supply voltage E or the operating frequency f increases, the loss generated in the resistor increases. It is necessary to suppress the temperature rise of the resistor by adding the above, so that the size of the RDC snubber becomes large and the conversion efficiency of the power conversion device decreases.

Further, in the second conventional example circuit of FIG. 10, it is not possible to suppress the rate of voltage increase when the switching element is turned off. That is, since the switching loss cannot be reduced by the first snubber circuit 7, the conversion efficiency of the power conversion device is also reduced, and a heat dissipation device or a cooling device for removing heat generated by the generated loss is required. There is an inconvenience that the device becomes large.

Therefore, an object of the present invention is to recover the energy accumulated in the snubber when the power conversion device which outputs the AC power insulated from the DC power supply operates, thereby reducing the generated loss and reducing the generated loss. It is intended to suppress the upsizing of the battery and improve the conversion efficiency.

[0011]

In order to achieve the above-mentioned object, a snubber energy recovery circuit of a power conversion device and a recovery method thereof according to the present invention are provided with two sets of a switching element in which a semiconductor switching element and a diode are connected in antiparallel. Are connected in series to form a series switching circuit, and first and second series switching circuits and at least one set of first snubber circuits including at least a capacitor are connected in parallel to each other in parallel. Constitutes a switching circuit,
A coupling point between switching elements of the first series switching circuit is connected to one end of a transformer primary winding having a center tap, and a coupling point between switching elements of the second series switching circuit is connected to the transformer primary winding. Connect to the other end of the wire, and connect between one end of the parallel switching circuit and the center tap of the transformer primary winding via a DC power supply, or via a DC power supply and a DC reactor connected in series therewith. Then, in the power conversion device that sequentially turns on / off each of the switching elements to extract AC power from the secondary winding of the transformer, the DC power sources of the first and second series switching circuits are connected. A second snubber circuit consisting of a series circuit of a snubber diode and a snubber capacitor is separately connected in parallel to each of the switching elements on the A first auxiliary circuit, which is a series connection of a inductor, an auxiliary diode, and an auxiliary capacitor, is separately connected in parallel to each snubber diode, and the DC power source is not connected to the connection point of the elements forming each of the first auxiliary circuits. It is assumed that each switching element on the side is connected to the side of the parallel connection point separately by a regenerative circuit including a regenerative reactor and a regenerative diode connected in series.

Alternatively, a second snubber circuit composed of a series circuit of a snubber diode and a snubber capacitor is separately connected in parallel to each of the switching elements of the first and second series switching circuits on the side to which the DC power supplies are connected. And a second connection consisting of an auxiliary diode and an auxiliary capacitor connected in series.
An auxiliary circuit is separately connected in parallel between the coupling point between each snubber diode and each snubber capacitor and the center tap of the transformer primary winding, and the coupling point between each auxiliary diode and each auxiliary capacitor and the DC power supply. The parallel connection point side of each switching element on the side not connected with is connected separately by a regenerative circuit that is a series connection of a regenerative reactor and a regenerative diode.

Alternatively, a separate auxiliary terminal is provided between the center tap of the transformer primary winding and both ends of the switching element on the side where the DC power supplies of the first and second series switching circuits are connected. A second snubber circuit composed of a series circuit of a snubber diode and a snubber capacitor is separately connected in parallel, and is close to the coupling point of the snubber diode and the snubber capacitor belonging to the first series switching circuit and one end side of the transformer. A second auxiliary circuit, which is a series connection of an auxiliary diode and an auxiliary capacitor, is connected between the auxiliary terminal and a connection point of the snubber diode and the snubber capacitor belonging to the second series switching circuit, and the other end of the transformer. A second auxiliary circuit other than the above is connected between the auxiliary terminal near the side and each auxiliary diode and each auxiliary capacitor. Between the coupling point and the parallel connection point side of the switching elements on the side not connected to the DC power supply shall be separately connected by the regenerative circuit comprising a series connection of the regeneration reactor and regenerative diode.

Alternatively, two sets of switching elements in which a semiconductor switching element and a diode are connected in anti-parallel are connected in series to form a series switching circuit, which includes first and second series switching circuits and at least a capacitor. At least one set of first snubber circuits connected in parallel to each other to form a parallel switching circuit, and a primary winding of a transformer having a center tap at a connection point between switching elements of the first series switching circuit. Connected to one end of a line, connecting a coupling point between switching elements of the second series switching circuit to the other end of the transformer primary winding, and connecting one end of the parallel switching circuit and the center of the transformer primary winding. Via DC power supply between tap and
Alternatively, a series circuit of a snubber diode and a snubber capacitor is connected to a switching element of the first and second series switching circuits on the side connected to the DC power source and a DC reactor connected in series to the DC power source. A second snubber circuit connected in parallel, an auxiliary circuit including a series circuit of an auxiliary reactor, an auxiliary diode, and an auxiliary capacitor connected in parallel to at least the snubber diode, and the auxiliary circuit is not connected to the DC power source. Is connected to a parallel connection point of the DC switching circuit by a regenerative circuit composed of a series circuit of a regenerative reactor and a regenerative diode, and the ON period of the switching element on the side to which the regenerative circuit is connected is changed to the first snubber circuit. Of the capacitance of the capacitor and the leakage inductance of the transformer It is assumed that almost half of the period.

[0015]

According to the first invention, when the switching element on the side where the series circuit (second snubber circuit) of the snubber diode and the snubber capacitor is connected in parallel is turned off, the snubber capacitor raises the voltage of the switching element. The rate is relaxed to reduce the switching loss. At this time, the electric charge stored in the snubber capacitor is transferred to the auxiliary capacitor forming the first auxiliary circuit while the switching element is on. While the switching element facing the switching element (that is, the switching element on the side to which the regenerative circuit is attached) is turned on, the charge transferred to the auxiliary capacitor is absorbed by the regenerative circuit, and the regenerative circuit concerned is absorbed. Transfer this energy to the regenerative reactor that constitutes the circuit. Furthermore, by turning off the switching element on the side to which the regenerative circuit is attached,
The energy stored in the regenerative reactor is absorbed by the first snubber circuit connected in parallel to the parallel switching circuit, so that the current of the regenerative reactor decreases. Then
While the switching element on the side of the regenerative circuit of one of the series switching circuits and the switching element on the side of the other series switching circuit to which the snubber capacitor is attached are simultaneously turned on, the first snubber is turned on. The energy stored in the circuit is released to the secondary side of the transformer. The series switching circuit on one side and the series switching circuit on the other side alternately repeat the above operations, whereby the electric charge absorbed by the snubber capacitor forming the second snubber circuit is given to the load via the transformer. .

In the second invention and the third invention, the leakage inductance of the transformer is utilized during the period in which the charge stored in the snubber capacitor which constitutes the second snubber circuit is transferred to the auxiliary capacitor. That is, while the switching element on the side to which the series circuit of the snubber diode and the snubber capacitor (the second snubber circuit) is attached is on, the charge accumulated in this snubber capacitor is transferred to the second auxiliary circuit and the transformer. It is absorbed by the leakage inductance and is transferred to the auxiliary capacitor forming the second auxiliary circuit. Since the operation thereafter is the same as that of the first invention described above, the description of that part will be omitted.

According to a fourth aspect of the present invention, the period during which the switching element on the side to which the regenerative circuit is attached is on is constituted by the capacitance of the capacitor forming the switching circuit and the transformer leakage inductance. It is set to be approximately half the resonance cycle of the resonance circuit. A sinusoidal current having a period determined by the capacitance and the leakage inductance flows through the switching element on the side to which the regenerative circuit is attached.
Therefore, the ON period of the switching element is set to approximately 1/2 of the resonance period, and the current is cut off near the zero current at the time of turn-off.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a circuit diagram showing a first embodiment of the present invention, which corresponds to claim 1. The DC power supply 1 and the first series switching circuit 2 shown in the first embodiment circuit are shown in FIG. , Second
The names, applications, and functions of the series switching circuit 3, the transformer 4, the snubber circuit 7, and the switching elements 21, 22, 31, 32 have already been described in the conventional circuit shown in FIGS. Is omitted.

In the first series switching circuit 2 of the first embodiment circuit shown in FIG. 1, the second snubber circuit 17, which is a series connection of the snubber diode 51 and the snubber capacitor 52, is connected in parallel to the switching element 21, and the auxiliary reactor is connected. 101
The first auxiliary circuit 10 formed by connecting the auxiliary diode 102 and the auxiliary capacitor 103 in series is connected in parallel to the snubber diode 51. Further, the regenerative circuit 12 constituted by a series circuit of a regenerative diode 121 and a regenerative reactor 122.
Is inserted between the connection point of the auxiliary diode 102 and the auxiliary capacitor 103 and the parallel connection point of the parallel switching circuit. In the second series switching circuit 3 as well, the second snubber circuit 18, which is a series connection of the snubber diode 61 and the snubber capacitor 62, is connected in parallel to the switching element 31, and is composed of the auxiliary reactor 111, the auxiliary diode 112, and the auxiliary capacitor 113. The first auxiliary circuit 11 is connected in parallel to the snubber diode 61, and the first auxiliary circuit 11 and the parallel connection point of the parallel switching circuit are connected to each other by a regenerative diode.
Connection is made via a regenerative circuit 13 composed of 131 and a regenerative reactor 132.

FIG. 2 is an operation waveform diagram showing the operation of the first embodiment circuit shown in FIG. 1. FIG. 2 (A) is a gate signal waveform of the switching element 21, and FIG. 2 (B) is a switching element. 31 shows the gate signal waveform, FIG. 2 (C) shows the gate signal waveform of the switching element 22, and FIG. 2 (D) shows the switching element 3
2 shows the gate signal waveform, and FIG. 2 (E) shows the switching element 21.
Current / voltage waveform of Fig. 2 (F) is the current / voltage waveform of switching element 31, Fig. 2 (G) is the current / voltage waveform of switching element 22, and Fig. 2 (H) is the current / voltage waveform of switching element 32. 2 (I) is the voltage waveform of the snubber capacitor 52, FIG. 2 (J) is the current waveform of the auxiliary reactor 101, and FIG.
2K shows the voltage waveform of the auxiliary capacitor 103, FIG. 2L shows the current waveform of the regenerative reactor 122, and FIG. 2M shows the voltage waveform of the capacitor of the first snubber circuit 7.

In the following, the charge energy regenerating operation of the snubber capacitor 52 connected in parallel to the switching element 21 will be described. That is, the period is the period in which the switching element 21 is on, but the charge accumulated in the snubber capacitor 52 is the snubber capacitor 52 → the auxiliary reactor 101 → the auxiliary diode 102 → the auxiliary capacitor 103 during this period. → Switching element 21 → Snubber capacitor 52 discharges to auxiliary capacitor 103 (see FIG. 2 (K)). Next, while the switching element 22 is on, the auxiliary capacitor 103
The charge accumulated in the auxiliary capacitor 103 → regenerative diode 121 → regenerative reactor 122 → switching element 22
→ The auxiliary capacitor 103 is discharged through the path and the regenerative reactor
The current of 122 increases (see Fig. 2 (L)). Next, the switching element 22 is turned off, and the current of the regenerative reactor 122 is changed to the regenerative reactor 122 → first snubber circuit 7 → DC power source 1 → transformer 4 → snubber diode 51 → auxiliary reactor 101 → auxiliary diode 102 → regenerative diode 121 → The energy is transferred to the first snubber circuit 7 by flowing through the path of the regenerative reactor 122 (see FIG. 2 (M)), and the regenerative reactor 122
Current decreases (see Fig. 2 (L)).

During the period when the switching element 21 and the switching element 32 are turned on at the same time, the energy stored in the first snubber circuit 7 is transferred to the first snubber circuit 7
→ Switching element 32 → transformer 4 → switching element 21 → first snubber circuit 7 is discharged along the path. The first auxiliary circuit 11 and the regenerative circuit 13 attached to the second series switching circuit 3 also discharge the electric charge accumulated in the snubber capacitor 62 to the transformer 4 by the same operation. By repeating this operation, the electric charges stored in the snubber capacitors 52 and 62 are supplied to the load from the secondary side of the transformer 4.

FIG. 3 shows a first circuit of the first embodiment circuit described above with reference to FIG.
Is a circuit diagram showing an application example of the above, and is different from the above-described first embodiment circuit in that the negative side of the DC power supply 1 is connected to the center tap of the transformer 4 and the positive side is connected to the switching elements 21 and 31. Except for this point, the names, uses, and functions of the respective elements constituting the circuit of the first application example, and the operation of the circuit are all the same as those of the first embodiment described above. It is the same as the circuit. Therefore, the description of the operation of the first application circuit of FIG. 3 is omitted.

FIG. 4 shows the second circuit of the first embodiment circuit described above with reference to FIG.
Is a circuit diagram showing an application example of the first embodiment, and is different from the circuit of the first embodiment described above in that a DC reactor 14 is inserted into the positive electrode side of the DC power supply 1 and the DC power supply 1 and the transformer are connected through the DC reactor 14. The center tap of the container 4 is connected, and the names, uses, and functions of the other elements constituting the circuit other than this are exactly the same as those of the circuit of the first embodiment described in FIG.

In the second application circuit shown in FIG. 4, the switching element 21 and the switching element 31 are turned on at the same time to accumulate energy in the DC reactor 14. If the switching element 31 is turned off in this state,
The DC power supply 1 and the DC reactor 14 supply energy to the transformer 4 to excite the transformer 4 in the positive direction. Then, the switching elements 21 and 31 are turned on at the same time, energy is stored in the DC reactor 14 again, and then the switching element 21 is turned off.
And the DC reactor 14 excite the transformer 4 in the negative direction. By repeating this operation alternately, the AC power insulated from the DC power supply 1 can be taken out from the secondary side of the transformer 4.

FIG. 5 is an operation waveform diagram showing the operation of the second application circuit shown in FIG. 4, FIG. 5 (A) being the gate signal waveform of the switching element 21 and FIG. 5 (B) being the switching element. 31 shows the gate signal waveform, FIG. 5 (C) shows the switching element 22 gate signal waveform, and FIG. 5 (D) shows the switching element 3
2 shows the gate signal waveform, Fig. 5 (E) shows switching element 2
1 current and voltage waveform, Fig. 5 (F) shows switching element 31
Current / voltage waveform, Fig. 5 (G) is the current / voltage waveform of switching element 22, Fig. 5 (H) is the current / voltage waveform of switching element 32, and Fig. 5 (I) is the voltage waveform of snubber capacitor 52. 5 (J) is the current waveform of the auxiliary reactor 101, Fig. 5
5K shows the voltage waveform of the auxiliary capacitor 103, FIG. 5L shows the current waveform of the regenerative reactor 122, and FIG. 5M shows the voltage waveform of the capacitor of the first snubber circuit 7.

The energy regenerating operation of the electric charge of the snubber capacitor 52 connected in parallel with the switching element 21 will be described below. That is, the switching element 21
During the period in which the switching element 31 and the switching element 31 are simultaneously turned on, the charge accumulated in the snubber capacitor 52 is
Snubber capacitor 52 → auxiliary reactor 101 → auxiliary diode 102 → auxiliary capacitor 103 → switching element 2
1 → snubber capacitor 52, auxiliary capacitor 10
Discharge to 3 (see Fig. 5 (K)). Next, during the period when the switching element 22 is on, the charge accumulated in the auxiliary capacitor 103 is transferred to the auxiliary capacitor 103 → regenerative diode.
121 → regeneration reactor 122 → switching element 22 → discharged through the path of auxiliary capacitor 103 and regenerative reactor 122
Current increases. Next, the switching element 22 is turned off, and the current of the regenerative reactor 122 is changed to the regenerative reactor.
122 → 1st snubber circuit 7 → DC power supply 1 → transformer 4 → snubber diode 51 → auxiliary reactor 101 → auxiliary diode 102 → regenerative diode 121 → regenerative reactor 122 The energy is transferred to the first snubber circuit 7 by flowing in the path of The current of the regenerative reactor 122 decreases.

During the period when the switching element 21 and the switching element 32 are simultaneously turned on, the energy stored in the first snubber circuit 7 is transferred to the first snubber circuit 7
→ Switching element 32 → transformer 4 → switching element 21 → first snubber circuit 7 is discharged along the path. The first auxiliary circuit 11 and the regenerative circuit 13 attached to the second series switching circuit 3 also discharge the electric charge accumulated in the snubber capacitor 62 to the transformer 4 by the same operation. By repeating this operation, the electric charges stored in the snubber capacitors 52 and 62 are supplied to the load from the secondary side of the transformer 4.

Although not shown, the positive side of the DC power supply 1 is connected to the connection point between the switching element 21 and the switching element 31, and the negative side of the DC power supply 1 is connected to the DC reactor 1.
Of course, even if the center tap connection of the transformer 4 is performed through the circuit 4, the same operation as that of the second application example circuit described above with reference to FIG. 4 is performed. FIG. 6 is a circuit diagram showing a second embodiment of the present invention and corresponds to claim 2. This second embodiment circuit is the first auxiliary circuit in the second application circuit already described in FIG. Second auxiliary circuit 1 instead of 10 (comprised of auxiliary reactor 101, auxiliary diode 102 and auxiliary capacitor 103)
5 (consisting of auxiliary diode 152 and auxiliary capacitor 153)
With a snubber diode 51 and a snubber capacitor 52.
Between the connection point and the center tap of the transformer 4
The connection of the auxiliary circuit 15 and the first auxiliary circuit 11
A second auxiliary circuit 16 (made up of the auxiliary diode 162 and the auxiliary capacitor 163) is provided instead of the (made up of the auxiliary reactor 111, the auxiliary diode 112, and the auxiliary capacitor 113), and the connection point between the snubber diode 61 and the snubber capacitor 62 and the transformer. The difference is that this second auxiliary circuit 16 is connected to the center tap of No. 4, and the names, applications, and functions of the other circuit components are the same. Therefore, the description of the same parts will be omitted.

In the second embodiment circuit of FIG. 6, the leakage inductance of the transformer 4 is utilized when transferring the energy stored in the snubber capacitors 52 and 62 to the auxiliary capacitors 153 and 163. That is, the period in which the switching element 21 and the switching element 31 are simultaneously turned on (see FIG.
(See (A) and (B)), the charge accumulated in the snubber capacitor 52 is transferred to the snubber capacitor 52 → the auxiliary diode 152.
→ Auxiliary capacitor 153 → Transformer 4 → Transformer leakage inductance 171 → Switching element 21 → Snubber capacitor 52 Discharge to auxiliary capacitor 153 along the path. Then, during the period when the switching element 22 is on (see FIG. 5 (C)), the charge accumulated in the auxiliary capacitor 153 is
The auxiliary capacitor 153 → regenerative diode 121 → regenerative reactor 122 → switching element 22 → transformer 4 → auxiliary capacitor 153 discharges in the path, and the current of the regenerative reactor 122 increases. Further, the switching element 22 is turned off, and the current of the regenerative reactor 122 is changed to the regenerative reactor 122 → the first snubber circuit 7 → the DC power supply 1 → the DC reactor 14 → the transformer 4 → the snubber diode 51 → the auxiliary diode 152 → the regenerative diode 121 → the regenerative diode 121 → the regenerative diode. It flows in the path of the reactor 122, transfers energy to the first snubber circuit 7, and regenerates the reactor 12
2 current is reduced. The energy stored in the first snubber circuit 7 is stored in the switching element 32 and the switching element 2
When 1 and 1 are on, or when switching element 31 and switching element 22 are on, they are discharged to transformer 4. The second auxiliary circuit 16 provided in the second series switching circuit 3 also operates in the same manner. By repeating these operations, the charges accumulated in the snubber capacitors 52 and 62 are supplied to the load from the secondary side of the transformer 4.

Contrary to the circuit of the second embodiment described in FIG. 6, the positive side of the DC power supply 1 is connected to the connection point between the switching element 21 and the switching element 31, and the negative side of the DC power supply 1 is the DC reactor. Of course, even if the circuit configuration is such that it is connected to the center tap of the transformer 4 via 14, the same operation as that of the second embodiment circuit is performed. FIG. 7 is a circuit diagram showing a third embodiment of the present invention and corresponds to claim 3. This third embodiment circuit has auxiliary terminals on both sides of a center tap instead of the transformer 4. To provide a transformer 8,
To connect one end of the second auxiliary circuit 15 to one auxiliary terminal of the transformer 8 and connect one end of the second auxiliary circuit 16 to the other auxiliary terminal of the transformer 8, the second auxiliary circuit described in FIG. The circuit of the third embodiment is different from that of the third embodiment, but is otherwise the same as the second embodiment of FIG. 6, and the operation thereof is also the same, so that the description of the operation of the third embodiment is omitted.

Contrary to the circuit of the third embodiment of FIG. 7, the positive side of the DC power source 1 is connected to the connection point between the switching element 21 and the switching element 31, and the negative side of the DC power source 1 is connected via the DC reactor 14. Even if the circuit configuration is such that it is connected to the center tap of the transformer 4, the same operation as the circuit of the third embodiment is of course performed. FIG. 8 is an operation waveform diagram showing the operation of the present invention and corresponds to claim 4, FIG. 8 (A) is a gate signal waveform of the switching element 22 or 32, and FIG.
Represents the current waveform of the switching element 22 or 32.

While the switching element 21 and the switching element 32 are turned on at the same time, or the switching element 31 and the switching element 22 are turned on at the same time, the switching element 22 or the switching element 32 has a first snubber. A sinusoidal current having a period determined by the capacitance of the capacitor that constitutes the circuit 7 and the leakage inductance of the transformer 4 or the transformer 8 flows. Therefore, the ON period of the switching element 22 or the switching element 32 is set to approximately half the resonance period of the capacitance of the capacitor and the leakage inductance of the transformer. That is, the first
Assuming that the capacitance of the capacitor of the snubber circuit 7 is C and the leakage inductance of the transformer is L, a period of about 1/2 of the resonance period T shown in the figure is expressed by the following mathematical formula 2.

[0034]

## EQU2 ## T = π (LC) ^1/2 Due to this, the switching element is turned off in the vicinity of zero current. Therefore, the switching loss when the switching element 22 or the switching element 32 is turned off is reduced.

[0035]

EFFECTS OF THE INVENTION When the switching element which constitutes the power conversion device is turned off, the electric charge stored in the snubber capacitor attached to this switching element is consumed by the resistor and becomes a loss in the past. However, according to the present invention, the charges accumulated in the snubber capacitor are recovered and supplied to the load from the secondary side of the transformer, so that the loss in the first snubber circuit hardly occurs. As a result, the conversion efficiency of the power conversion device is improved, heat generation due to loss is avoided, and the cooling device for heat dissipation can be simplified, so that the device can be downsized. Further, in the operation of discharging the energy stored in the first snubber circuit, the switching element is operated so as to match approximately half the resonance period of the circuit, thereby turning off the switching element in the vicinity of almost zero current. Since the switching loss can be made almost zero, the conversion efficiency can be improved and the cooling device can be simplified to obtain a smaller device.

[Brief description of drawings]

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

2 is an operation waveform diagram showing the operation of the first embodiment circuit shown in FIG.

FIG. 3 is a circuit diagram showing a first application example of the first embodiment circuit described above with reference to FIG.

FIG. 4 is a circuit diagram showing a second application example of the circuit of the first embodiment described above in FIG.

5 is an operation waveform chart showing the operation of the second application circuit shown in FIG.

FIG. 6 is a circuit diagram showing a second embodiment of the present invention.

FIG. 7 is a circuit diagram showing a third embodiment of the present invention.

FIG. 8 is an operation waveform diagram showing the operation of the present invention.

FIG. 9 is a circuit diagram showing a first conventional example of a power conversion device that includes a snubber and converts direct current into alternating current that is insulated from the direct current.

FIG. 10 is a circuit diagram showing a second conventional example of a power conversion device that includes a snubber and converts direct current into alternating current that is insulated from the direct current.

[Explanation of symbols]

 1 DC power supply 2 1st series switching circuit 3 2nd series switching circuit 4,8 Transformer 5,6 RDC snubber 7 1st snubber circuit 10,11 1st auxiliary circuit 12,13 Regeneration circuit 14 DC reactor 15,16 2nd Auxiliary circuit 17,18 Second snubber circuit 21,22 Switching element 31,32 Switching element 51,61 Snubber diode 52,62 Snubber capacitor 101,111 Auxiliary reactor 102,112 Auxiliary diode 103,113 Auxiliary capacitor 121,131 Regenerative diode 122 , 132 Regenerative reactor 152, 162 Auxiliary diode 153, 163 Auxiliary capacitor 171, 172 Transformer leakage inductance

Claims (4)

[Claims] 1. A series switching circuit is configured by serially connecting two sets of switching elements in which a semiconductor switching element and a diode are connected in anti-parallel, and includes first and second series switching circuits and at least a capacitor. And at least one set of the first snubber circuits connected in parallel to each other to form a parallel switching circuit.
The connecting point between the switching elements of the series switching circuit is connected to one end of the transformer primary winding having a center tap, and the connecting point between the switching elements of the second series switching circuit is connected to the other side of the transformer primary winding. Connected to an end, between one end of the parallel switching circuit and the center tap of the transformer primary winding via a DC power supply, or via a DC power supply and a DC reactor serially connected thereto, In a power conversion device for sequentially turning on / off each switching element to extract AC power from a secondary winding of the transformer, a switching on a side connecting the DC power sources of the first and second series switching circuits. A second circuit comprising a series circuit of a snubber diode and a snubber capacitor for each element
The snubber circuits are separately connected in parallel, and the first auxiliary circuit, which is a series connection of an auxiliary reactor, an auxiliary diode, and an auxiliary capacitor, is separately connected in parallel to each of the snubber diodes,
Separately by a regenerative circuit consisting of a series connection of a regenerative reactor and a regenerative diode between the coupling point of the elements forming each of the first auxiliary circuits and the parallel connection point side of the switching elements on the side not connected to the DC power supply. Snubber energy recovery circuit of a power conversion device, characterized in that it is connected to. 2. A series switching circuit is configured by serially connecting two sets of switching elements in which a semiconductor switch element and a diode are connected in anti-parallel, and includes a first and a second series switching circuit and at least a capacitor. And at least one set of the first snubber circuits connected in parallel to each other to form a parallel switching circuit.
The connecting point between the switching elements of the series switching circuit is connected to one end of the transformer primary winding having a center tap, and the connecting point between the switching elements of the second series switching circuit is connected to the other side of the transformer primary winding. Connected to an end, between one end of the parallel switching circuit and the center tap of the transformer primary winding via a DC power supply, or via a DC power supply and a DC reactor serially connected thereto, In a power conversion device for sequentially turning on / off each switching element to extract AC power from a secondary winding of the transformer, a switching on a side connecting the DC power sources of the first and second series switching circuits. A second circuit comprising a series circuit of a snubber diode and a snubber capacitor for each element
A snubber circuit is separately connected in parallel, and a second auxiliary circuit formed by connecting an auxiliary diode and an auxiliary capacitor in series is provided between the coupling point of each snubber diode and each snubber capacitor and the center tap of the transformer primary winding. Connected separately in parallel, and between the connection point of these auxiliary diodes and auxiliary capacitors and the parallel connection point side of each switching element on the side not connected to the DC power supply, the regenerative reactor and regenerative diode are connected in series. A snubber energy recovery circuit for a power conversion device, which is separately connected by a regenerative circuit consisting of 3. A series switching circuit is configured by serially connecting two sets of switching elements in which a semiconductor switching element and a diode are connected in anti-parallel, and includes a first and a second series switching circuit and at least a capacitor. And at least one set of the first snubber circuits connected in parallel to each other to form a parallel switching circuit.
The connecting point between the switching elements of the series switching circuit is connected to one end of the transformer primary winding having a center tap, and the connecting point between the switching elements of the second series switching circuit is connected to the other side of the transformer primary winding. Connected to an end, between one end of the parallel switching circuit and the center tap of the transformer primary winding via a DC power supply, or via a DC power supply and a DC reactor serially connected thereto, In a power conversion device for sequentially turning on / off each switching element to extract AC power from a secondary winding of the transformer, a separate auxiliary terminal is provided between a center tap and both ends of the transformer primary winding. , A snubber diode and a snubber capacitor in each of the switching elements of the first and second series switching circuits which are connected to the DC power source. The second snubber circuit consisting of a series circuit with the
A connection between the snubber diode and the snubber capacitor belonging to the first series switching circuit and the auxiliary terminal near one end of the transformer is connected by a second auxiliary circuit that is a series connection of an auxiliary diode and an auxiliary capacitor. The connection point between the snubber diode and the snubber capacitor belonging to the second series switching circuit and the auxiliary terminal near the other end of the transformer are connected by a second auxiliary circuit different from the above, Separately connect the connection point of each auxiliary diode and each auxiliary capacitor and the parallel connection point side of each switching element on the side not connected to the DC power supply with a regenerative circuit consisting of a series connection of a regenerative reactor and a regenerative diode. A snubber energy recovery circuit for a power conversion device. 4. A series switching circuit is configured by serially connecting two sets of switching elements in which a semiconductor switch element and a diode are connected in anti-parallel, and includes a first and a second series switching circuit and at least a capacitor. And at least one set of the first snubber circuits connected in parallel to each other to form a parallel switching circuit.
The connecting point between the switching elements of the series switching circuit is connected to one end of the transformer primary winding having a center tap, and the connecting point between the switching elements of the second series switching circuit is connected to the other side of the transformer primary winding. Connected to an end, between one end of the parallel switching circuit and the center tap of the transformer primary winding via a DC power supply, or via a DC power supply and a DC reactor serially connected thereto, A second snubber circuit, which is a series circuit of a snubber diode and a snubber capacitor, is connected in parallel to the switching elements of the first and second series switching circuits on the side to which the DC power source is connected, and the auxiliary reactor,
An auxiliary circuit composed of a series circuit of an auxiliary diode and an auxiliary capacitor is connected in parallel to at least the snubber diode, and a regeneration reactor is provided between the auxiliary circuit and the parallel connection point of the DC switching circuit on the side not connected to the DC power supply. Connected by a regenerative circuit consisting of a series circuit with a regenerative diode, the ON period of the switching element on the side to which the regenerative circuit is connected, the capacitance of the capacitor that constitutes the first snubber circuit and the A snubber energy recovery method for a power conversion device, characterized in that the resonance period is set to be approximately 1/2 of a resonance period due to leakage inductance.