JP2723928B2 - Power converter - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power converter, and more particularly, to a power converter having a frequency conversion circuit for directly converting a high frequency to a low frequency.

[Conventional technology]

2. Description of the Related Art It is known that in a power conversion device, a DC is temporarily converted to a frequency higher than a commercial frequency, and then converted to a commercial frequency after passing through a transformer, thereby reducing the size of the transformer. For example, JP-A-62-44072 and JP-A-62-44073 disclose a configuration in which a high frequency generated by an inverter is passed through a transformer and then two sets of rectifiers are connected in anti-parallel. It has been proposed to convert a high frequency to a commercial frequency by a separately excited converter.

However, in this method, a separately-excited converter is used as a means for converting a high frequency to a commercial frequency. However, during the period when these polarities are different, commutation by the output voltage of the transformer cannot be performed, and there is no other power supply that performs commutation. Atsuta.

Therefore, it is conceivable to use a separately excited converter as a self-excited converter and perform commutation irrespective of the polarity of the output voltage and the output current.
At present, a self-excited converter generally includes an element having a self-extinguishing ability and performs commutation by extinguishing the element by self-extinguishing. As this kind of power converter,
For example, JP-A-61-236371 can be mentioned.

FIG. 3 shows a power conversion device according to the above-mentioned prior art.
In the figure, 1 is a DC power supply, 2 is an inverter configured by using a switching element such as a transistor and a diode, 3 is a transformer, and 4 is a frequency conversion circuit including bidirectional switches 401 and 402 configured by a switching element such as a transistor and a diode. Reference numerals 5 and 6 denote reactors and capacitors of the filter for improving the waveform.

The circuit operation of FIG. 3 will be described with reference to FIG. The inverter 2 forms a high-frequency voltage e ₁ that is pulse-width-modulated so that the output voltage e _out has a sine-wave shape.
Providing a voltage e ₂ shown in FIG. (A). The frequency conversion circuit 4 is e ₂
4 (e) to 4 (e) to turn on and off the switching elements 41 to 44 so as to convert the signal into a pulse train having the polarity shown in FIG. 4 (b).
Outputs e _L such as Fig. 4 is controlled as (h) (c), to obtain a sinusoidal voltage indicated by a broken line in e _out. That is, the bidirectional switch 401 when no changing the polarity of e _2, when inverting the polarity, thereby turning the switch that can flow an output current i ₂ of the bidirectional switch 402. By controlling on / off of the switching element as described above, a commercial frequency voltage can be obtained from a high frequency voltage in the above-described conventional technology.

[Problems to be solved by the invention]

However, in the above prior art, the spike voltage generated at the time of commutation of the frequency conversion circuit has not been considered. That is, in the frequency conversion circuit of the prior art, a spike voltage due to current interruption or a spike voltage due to diode recovery occurs during the switching operation of the bidirectional switch, and there is a possibility that the switching element is destroyed.

Therefore, in the frequency conversion circuit of the related art, it is necessary to suppress the spike voltage generated at the time of commutation and prevent the switching element from being destroyed.

As means for suppressing a spike voltage applied to the switching element, it is generally known to provide a snubber circuit in which a resistor and a capacitor are connected in series with the switching element in parallel. This snubber circuit can suppress the spike voltage by absorbing the energy at the time of commutation in the capacitor, but all the absorbed energy is lost.
Therefore, when the switching frequency is increased, the efficiency is remarkably reduced.

An object of the present invention is to provide a high-efficiency power converter capable of suppressing a spike voltage generated at the time of commutation of a frequency conversion circuit and reducing a circuit loss.

[Means for solving the problem]

In order to achieve the above object, according to the present invention, a spike voltage generated at the time of commutation of a frequency conversion circuit is absorbed by a capacitor, and the capacitor is connected to the transformer in accordance with the polarity of the output of the transformer. Is regenerated to the transformer side.

[Action]

The capacitor that absorbs the spike voltage absorbs the stored energy of the circuit inductance such as the leakage inductance of the transformer when the switching element of the frequency conversion circuit cuts off the current. Thereafter, by connecting the capacitor charge to the transformer in accordance with the polarity of the transformer output, the energy absorbed by the capacitor is regenerated, and the capacitor voltage is clamped to the output voltage of the transformer. There is no exchange of energy and loss can be suppressed.

〔Example〕

Hereinafter, the present invention will be described in detail with reference to an embodiment shown in the drawings.

In the following embodiments, a capacitor for absorbing a spike voltage, which is a feature of the present invention, and a means for connecting the capacitor to a transformer according to the polarity are collectively referred to as a clamp circuit.

FIG. 1 shows a first embodiment according to the present invention. In the figure, 700 is a switching element 701 to a switching element such as a transistor.
704, diodes 705 to 708 and a capacitor 709,
A clamp circuit 710 for suppressing a spike voltage applied to the bidirectional switch 401 is a clamp circuit which also includes transistors 711 to 714, diodes 715 to 718, and a capacitor 719 and suppresses a spike voltage applied to the bidirectional switch 402. The other parts are the same as those in FIG. 3, and the description is omitted.

The operation of this embodiment will be described with reference to FIG. The figure shows e
_This shows a commutation operation between the transistors 41 and 43 when both _out and i _L are positive.

Clamp circuit 70 when commutating from transistor 41 to 43
The operation of 0 is as follows. Immediately before the time t ₁ when e ₂ becomes zero, the transistor 43 is conducting, and the capacitor 709 is connected to the peak value E ₂ of the e ₂ via the transistor 43 and the diodes 705 and 708.
It is charged to twice the voltage of _d . To e ₂ but is zero capacitor 709 at time t _1, since there is no discharge path capacitor 709
Is maintained. At time t ₂ , the transistor 41 is turned off and commutated from the transistor 41 to the transistor 43. At this time, the stored energy of the circuit inductance such as the leakage inductance of the transformer 3 is in the path of the diode 707 → the capacitor 709 → the diode 706 → the transistor 43. absorbed into the capacitor 709, the capacitor voltage rises from the energy absorbing amount corresponding 2E _d. As described above, the spike voltage generated in the circuit can be suppressed by absorbing the energy stored in the circuit inductance by the capacitor.

At time t ₄ in conformity to e ₃ is -E _d transistor 701,
When to conduct the 704, the discharge path of the capacitor 709 is formed, to release the load energy absorbed during the t ₂ of t _3, the capacitor voltage is clamped by e ₂ in Natsuta time to 2E _d. If the transistors 701 and 704 are turned off while e ₂ is −E _d after being clamped to e ₂ , the discharge path of the capacitor 709 is eliminated and the capacitor voltage is maintained even when e ₂ becomes zero.

When commutating from the transistor 43 to the transistor 41, the clamp circuit 710 performs the same operation as the clamp circuit 700, thereby suppressing the spike voltage and releasing the absorbed energy to the load. FIG. 2 shows an operation when both e _out and i _L are positive.
If _out is negative, the transistor in the period e ₂ is E _d 7
To conduct 02,703, transistors 71 in the period e ₂ is -E _d
By conducting 2,713, energy can be released to the load in the same manner as shown in FIG. For the polarity of i _L ,
Transistors 701-704, 711-714 only by changing the path for absorbing the energy of the circuit inductance to the capacitor
Is irrelevant to the operation of

In this embodiment, when both of the bidirectional switches 401 and 402 are turned off, the energy stored in the reactor 5 can be absorbed by the capacitor 709 or 719, so that the bidirectional switches 401 and 402 are turned off and the load and the present power conversion device are turned off. Can be cut off.

FIG. 5 shows a second embodiment according to the present invention. This embodiment is different from the clamp circuit of the first embodiment shown in FIG.
700 and 710 are replaced with one clamp circuit 800. FIG. 6 shows the operation of this embodiment. The figure shows a commutation operation between transistors 41 and 43 when both e _out and i _L are positive. Clamp circuit 800 in the present embodiment, e ₂ is E
During the period of _d , the transistors 802 and 803 are turned on, and e ₂ becomes −E _d
By turning on the transistors 801 and 804 during a certain period, the spike voltage can be suppressed and the energy absorbed by the capacitor 811 can be released to the load, as in the embodiment shown in FIG. In this embodiment, when both the bidirectional switches 401 and 402 are turned off, the reactor 5
Can be absorbed by the capacitor 811 via the diode 809 or 810, so that the bidirectional switches 401 and 402 can be turned off to disconnect the load from the power converter. According to the present embodiment, one clamp circuit can be reduced as compared with the first embodiment shown in FIG. 1, so that a small-sized and low-cost power converter can be realized.

FIG. 7 shows a third embodiment according to the present invention. In this embodiment, the frequency conversion circuit 4 in the first embodiment shown in FIG. 1 has a configuration in which four bidirectional switches 403 to 406 are bridge-connected, and clamp circuits 720 to 7 are provided for each bidirectional switch.
50 is provided. In this embodiment, the bidirectional switch 40
3,406 is operated at the same timing as the bidirectional switch 401 of the embodiment shown in FIG. 1, and the bidirectional switches 404,405 are operated at the same timing as the bidirectional switch 402, thereby performing the same frequency conversion operation as that of the first embodiment. It can be carried out. The clamp circuits 720 and 750 are operated at the same timing as the clamp circuit 700 in FIG.
By operating the clamp 40 at the same timing as the clamp circuit 710 in FIG. 1, the spike voltage can be suppressed and the energy absorbed by the capacitor can be released to the load. Also, in this embodiment, when all the bidirectional switches 403 to 406 are turned off, the stored energy of the reactor 5 is clamped by the clamp circuit.
Since the power can be absorbed by the capacitors 720 to 750, the load and the present power converter can be separated by turning off all the bidirectional switches 403 to 406. With such a bridge configuration, there is an effect that the breakdown voltage of the switch can be increased and the reliability can be improved.

FIG. 8 shows a fourth embodiment according to the present invention. In the present embodiment, the frequency conversion circuit in the second embodiment shown in FIG. 5 has a configuration in which four bidirectional switches 403 to 406 are bridge-connected. In the present embodiment, by turning on the bidirectional switch 403 and turning off the switches 404 to 406, the energy stored in the reactor 5 can be absorbed by the capacitor 811.
The load and the present power converter can be separated. The connection points of the diodes 809 and 810 are connected to the bidirectional switches 404 and 4
Although it is connected to the connection point side of 06, it may be connected to the connection points of 403 and 405. In this case, to disconnect the load from the power converter, the bidirectional switch 406 is turned on and 403 to 405
Just turn it off. In this way, the configuration shown in FIG.
The same effect as in the case of the drawing can be obtained, and the number of parts can be significantly reduced. FIG. 9 shows a fifth embodiment according to the present invention. This embodiment is different from the clamp circuit of the fourth embodiment shown in FIG. In this embodiment, by turning off all the bidirectional switches 403 to 406, the load and the present power converter can be separated. Therefore, there is an effect that power consumption can be reduced.

FIG. 10 shows a sixth embodiment according to the present invention. The clamp circuit 901 of this embodiment is obtained by omitting the diodes 809 and 810 of the clamp circuit 800 of the second embodiment shown in FIG. The clamp circuit 901 of the present embodiment suppresses spike voltage and releases energy to the load similarly to the clamp circuit of the second embodiment, but processes the energy stored in the reactor 5 when the bidirectional switches 401 and 402 are turned off. Since there is no means, the bidirectional switches 401 and 402 cannot be turned off to disconnect the load from the power converter. In the figure, the diode 80 of the second embodiment shown in FIG.
Although the illustration of 9,810 is omitted, the diode 8 in FIG.
09,810 can be omitted. As described above, according to this method, the cost can be reduced as compared with the circuits shown in FIGS.

FIG. 11 shows a seventh embodiment according to the present invention. In the present embodiment, the transistors 801 to 804 of the clamp circuit 800 of the second embodiment shown in FIG. 5 are omitted, and a resistor is provided in parallel with the capacitor. The clamp circuit of the present embodiment
Although the spike voltage is suppressed in the same manner as in the clamp circuit shown in the figure, the absorbed energy is released to the resistor, so the efficiency is slightly lower than in the second embodiment.
~ 804 can be eliminated, so the cost can be reduced. In the figure,
The transistor of the clamp circuit shown in FIG. 5 is omitted,
The one in which a resistor is provided in parallel with the capacitor is shown.
Similarly, in the clamp circuits of the embodiments shown in FIGS. 5, 5, 7, 8, 9, and 10, the transistors are omitted and the resistance of the spike voltage is reduced by providing a resistor in parallel with the capacitor. Suppression is possible.

FIG. 12 shows an eighth embodiment according to the present invention. In the figure, reference numeral 7 denotes a clamp circuit configured by using switching elements 70 to 73 such as GTO, diodes 74 to 77, and capacitors 78 and 79, and for reducing a spike voltage applied to the switching elements 41 to 44 of the frequency conversion circuit 4. .

The operation of the clamp circuit 7 in this embodiment will be described with reference to FIG. The figure shows the commutation operation from switching elements 42 to 44 when e _out is positive and i _L is negative. Immediately before time t ₆ is conducting the switching-element 42, a capacitor
79 is charged to the polarity shown at twice the voltage of the peak value E _d of e ₂ through the switching-element 42 and the diode 77. Although the e ₂ is zero at the time of t _6, the voltage of the capacitor 79 because there is no path for discharging is maintained. At time t _7, turns off the switching-element 42 performs commutation from switching-element 42 to 44, but the circuit inductance stored energy, such as leakage inductance of this time transformer 3, transformer 3 → switching-element 44 → Capacitor 79 → Diode 76 → Transformer 3
Is absorbed in the path of the capacitor 79, commutation is completed t ₈ the energy of the inductance becomes zero. At this time capacitor 79, the energy absorbing portion voltage rises from 2E _d.

Commutation period t ₇ ~t _8, since the diode 76 is conducting, since t ₈ ~t ₉ is that the diode 76 has a voltage is applied after completion commutation capacitor 79 is off in the switching-element 42 No voltage is applied to the switching element 42. Times of Day
to t ₉ in conformity to the voltage is generated in e ₂ switching-element 72
When to conduct, capacitor 79, the energy absorbed in the current period t ₇ ~t ₈ capacitor 79 → switching-element 44
→ released in the path of the transformer 3 → switching-element 72 → capacitor 79, the voltage clamping the voltage at the point becomes such 2E _d. When commutating from element 44 to element 42, 3 →
The energy stored in the circuit inductance is absorbed by the capacitor 79 in the path of 42 → 79 → 77 → 3, and the energy is released in the path of 79 → 42 → 3 → 73 → 79. The voltage of the capacitor 79 is 2E _d
Is clamped to. Furthermore, when e _out is negative and i _L is positive
In the commutation from 41 to 43, the energy stored in the inductance is absorbed in the path of 3 → 74 → 78 → 43 → 3, and 78 → 70 → 3 →
43 → 78 route release energy at the voltage of the capacitor 78 is clamped to 2E _d. In the commutation from the element 43 to the element 41, the stored energy of the circuit inductance is absorbed in the path of 3 → 75 → 78 → 41 → 3, and the energy is released in the path of 78 → 71 → 3 → 41 → 78. the voltage is clamped to 2E _d.

In the present embodiment in this manner, but be regenerated after absorbing circuit inductance, such as the transformer leakage inductance in the capacitor, the capacitor voltage is clamped by e _2, while reducing the spike voltage at the time of switching-element-off, Since the energy stored in the inductance can be processed with low loss, a highly efficient power converter can be provided.

A ninth embodiment according to the present invention is shown in FIG. In the present embodiment, the frequency conversion circuit 4 shown in FIG. 12 has a configuration in which four bidirectional switchings 401 to 404 are bridge-connected.

The clamp circuit 7 controls the switching elements 70 to 73 as in the eighth embodiment. Thereby, in the commutation from 42,48 to 44,46 when e _out is positive and i _L is negative, 3 → 46 → 79 →
In the path of 76 → 3, the energy stored in the leakage inductance of the transformer 3 is absorbed by the capacitor 79, and 79 → 46 → 3 → 72 → 79
The energy is regenerated in a path, the voltage of 79 is clamped by e _2. Also, in the commutation from 44,46 to 42,48, 3 → 42
The energy stored in the leakage inductance is absorbed by the capacitor 79 in the path of 79 → 77 → 3, and the energy is regenerated in the path of 79 → 42 → 3 → 73 → 79. Furthermore, when e _out is negative and i _L is positive, in the commutation from 41,47 to 43,45, 3 → 74 → 78 → 45 → 3
The energy stored in the leakage inductance is absorbed by the capacitor 78 through the path, and the energy is regenerated through the path 78 → 70 → 3 → 45 → 78. In the commutation from 43,45 to 41,47, 3 → 75 →
The energy stored in the leakage inductance is absorbed in the route of 78 → 41 → 3, and the energy is regenerated in the route of 78 → 71 → 3 → 41 → 78.

According to the present embodiment, the switching elements 41 to 48, 70 to 73,
Diodes 74 to 77, the voltage applied to the capacitor 78 and 79, since the normal E _d, can be applied a small breakdown voltage of the device than the embodiment shown in Figure 1. Note that capacitor 7
Although the connection points of 8,79 are connected to the connection points of the switching elements 41,42,45,46, they may be the connection points of 43,44,47,48. Further, another clamp circuit 7 may be provided and connected to the connection point side of the capacitor elements 43, 44, 47 and 48.

FIG. 15 shows the output voltage e in the embodiment shown in FIG.
₇ shows operation waveforms when _out is controlled by the frequency conversion circuit 4. In this method, a high frequency voltage having a constant pulse width is formed by the inverter 2 and a voltage e ₂ shown in FIG. 15A is applied to the secondary side of the transformer 3. The frequency conversion circuit 4 switches the switching elements 41 to 44 so that the output voltage e _out becomes sinusoidal.
On, and outputs a voltage e _L shown by the solid line in FIG. 15 performs phase control with respect to e ₂ as off FIG. 15 (d) ~ (g) ( b), by a broken line in e _out Obtain the sinusoidal voltage shown. The operation of the clamp circuits 700 and 701 in this method will be described with reference to FIG. Figure 16 is that shown an enlarged operation in the period of time t _a ~t _b of Figure 15. Also in this embodiment, as in FIG. 2, the stored energy of the circuit inductance such as the leakage inductance of the transformer 3 when the switching elements 41 to 44 of the frequency conversion circuit 4 are turned off is stored in the capacitor 709 or 719.
Absorb. Then, the switching elements 701 to 704 or 711 to 711 to 704 to connect the capacitor 709 or 719 to the bidirectional switch 401 or 402 so that the voltage polarity applied to the bidirectional switch 401 or 402 and the voltage polarity of the capacitor 709 or 719 become the same. The 714 is turned on and off to regenerate the energy absorbed by the capacitor 709 or 719.
By this operation, the spike voltage applied to the switching element can be suppressed, and at the same time, the loss at the time of commutation can be suppressed. Although the case where the control of the applied voltage is performed by the phase control of the frequency conversion circuit by taking the circuit of the embodiment of FIG. 1 as an example has been described, FIGS. 5, 7, 8, 9 and No.
It goes without saying that the same applies to the case where the phase control is performed in the circuits shown in FIGS. 10, 11, 12, and 14.

FIG. 17 shows a tenth embodiment of the present invention. In the present embodiment, an uninterruptible power supply (hereinafter referred to as UPS) configured by using the present invention is configured. In the figure, 7 is an AC power supply such as a power system, 8 is an AC switch, 10 is a rectifier for converting AC to DC, and 11 is a battery that supplies power to the load when the AC current 7 is out of power. In the UPS, usually, the AC switch 8 is opened, and power is supplied to the load via the DC power supply 1, the inverter 2, the transformer 3, and the frequency conversion circuit 4. However, when the output current becomes overcurrent due to a load short circuit or the like, the AC converter 8 is closed and the power converter is separated from the load at the same time to protect the power converter. In this embodiment, if both the bidirectional switches 401 and 402 are turned off, the energy stored in the reactor 5 is dissipated by the diode 809, the capacitor 811, the diode 806 (808), the transformer 3, the capacitor 6, or the capacitor 6 Vessel 3-diode
It can be absorbed by the capacitor 811 through the path of 807 (805) -the capacitor 811-the diode 810. Therefore, bidirectional switches 401, 4
Since the power converter can be separated from the load by the 02, the AC switch conventionally provided between the load and the power converter can be omitted. In FIG. 15, the UPS is constituted by the power converter shown in FIG.
Of course, the same UPS as that of FIG. 15 can be constituted by the power converter shown in FIGS. 7, 7, 8, 9, 10, 12, and 14.

1, 5, 7, 8, 9, and 9.
Although the embodiment shown in FIGS. 10, 11, 12, and 14 shows a single-phase circuit, it is needless to say that the embodiment can be applied to a three-phase circuit or another multi-phase circuit. 1 and FIG.
Figure 7, Figure 7, Figure 8, Figure 9, Figure 11, Figure 12,
In the embodiment shown in FIG. 14 and FIG. 14, the switching elements of the inverter, the frequency conversion circuit, and the clamp circuit are transistors or GTOs, but it is needless to say that other self-extinguishing elements such as MOSFETs and IGBTs can be applied. .

〔The invention's effect〕

According to the present invention, a spike voltage generated at the time of commutation of the frequency conversion circuit can be absorbed by the capacitor and the absorbed energy can be regenerated, so that the spike voltage can be reduced with low loss, and high-efficiency power conversion can be achieved. The device can be realized.

[Brief description of the drawings]

FIG. 1 is a diagram showing a first embodiment of a power converter of the present invention, FIG. 2 is an explanatory diagram of the operation of the first embodiment, FIG. 3 is a diagram showing a power converter according to the prior art, FIG. FIG. 5 is a diagram illustrating the operation of the power converter of FIG. 3, FIG. 5 is a diagram illustrating a second embodiment of the power converter of the present invention, FIG. 6 is a diagram illustrating the operation of the second embodiment, FIG. FIG. 8, FIG. 9, FIG. 10, FIG. 11, FIG.
FIG. 12 shows the third, fourth, fifth, sixth, seventh, and seventh embodiments of the power converter of the present invention.
FIG. 13 is a diagram showing an eighth embodiment, FIG. 13 is a diagram for explaining the operation of the eighth embodiment, FIG. 14 is a diagram showing a ninth embodiment of the power converter of the present invention, FIG. 15 and FIG. Is an explanatory diagram of the operation of the first embodiment,
FIG. 17 is a diagram showing a tenth embodiment of the power converter of the present invention. 1 DC power supply 2 Inverter 3 Transformer 4
…… Frequency conversion circuit, 401,402 …… Bidirectional switch, 5
…… Reactor, 6 …… Capacitor, 700,710 …… Clamp circuit.

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor: Hisao Amano 3-2-1 Sachimachi, Hitachi City, Ibaraki Prefecture Within Hitachi Engineering Co., Ltd. (56) References JP-A-61-236371 (JP, A) Sho-59-104632 (JP, U)

Claims (4)

(57) [Claims] 1. A power converter comprising: an inverter for converting DC to AC; a transformer connected to the output side of the inverter; and a self-excited frequency conversion circuit connected to the output side of the transformer. A capacitor for absorbing a spike voltage generated at the time of commutation of the conversion circuit, and means for connecting the capacitor to the transformer in a direction to regenerate charge of the capacitor to the transformer in accordance with the polarity of the output of the transformer. A power converter, comprising: 2. A power converter according to claim 1, wherein said connection means connects said capacitor to said transformer in a direction opposite to an output polarity of said transformer. 3. The power converter according to claim 1, wherein said connection means connects said capacitor to said transformer during a zero output period of said transformer. 4. The connecting means according to claim 1, wherein an anti-parallel circuit of a switch and a diode is bridge-connected, and an AC side of the bridge is connected to an output side of the transformer to constitute the connection means. A power converter in which a capacitor is connected between the DC terminals of the bridge.