JP2505080B2 - Power converter - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power converter using a self-arc-extinguishing semiconductor element, and more particularly to a power converter having a high voltage and large capacity by connecting a plurality of self-arc-extinguishing semiconductor elements in series. .

[0002]

2. Description of the Related Art FIGS. 7 to 9 are block diagrams of a conventional power converter. In each figure, 1 is an AC power source, 2 is a transformer, and 3 is a converter. The converter 3 is composed of bridge-connected self-extinguishing semiconductor elements, but here, as an example, a case of using a gate turn-off thyristor (hereinafter, simply referred to as GTO) will be described.

A capacitor 20 smoothes the DC output voltage of the converter 3. 211 to 21n are U-phase GTO switches, 221 to 22n are V-phase GTO switches, and 231-2.
3n is a W-phase GTO switch, 241-224n is an X-phase GT
O switch, 251 to 25n are Y phase GTO switches, 2
61 to 26n are Z-phase GTO switches.

Reference numerals 21 to 26 are di / dt suppressing circuits, which are U-phase GTO switches 211 to 21n and V-phase GTO switch 2.
21-22n, W-phase GTO switches 231-23n, X
The phase GTO switches 241 to 24n, the Y phase GTO switches 251 to 25n, and the Z phase GTO switches 261 to 26n are connected in series, respectively. Above U-phase GTO switch
The Z-phase GTO switches 211 to 26n and the di / dt suppressing circuits 21 to 26 are bridge-connected to form the converter 3. Reference numeral 27 is a GTO and 28 is a diode, which functions as a freewheel diode that circulates the circuit current when the X-phase GTO switches 241 to 24n are turned off. A diode 29 guides the current flowing through the GTO 27 to the capacitor 30 when the GTO 27 is turned off. Capacitor 3
0 acts as a so-called snubber capacitor that suppresses the forward voltage increase rate dv / dt of the GTO 27 when the GTO 27 is turned off to be equal to or less than the allowable value of the element. Reference numeral 31 denotes a resistor, which discharges the electric charge of the capacitor 30 when the GTO 27 is turned on. The U-phase GTO switches 211 to 21n are constituted by the above 27 to 31.

The other GTO switches 212 to 26n are similarly constructed. Reference numeral 32 denotes a reactor that suppresses the forward current increase rate di / dt of each GTO when the U-phase GTO switches 211 to 21n are turned on to be equal to or less than the allowable value of the element. 33 is a diode, U-phase GTO switch 211 ~
When turning off 21n, the current flowing in the reactor 32 is led to the resistor 34. The electromagnetic energy trapped in the reactor 32 is consumed by the resistor 34. Next, the operation of the conventional power converter will be described with reference to FIGS. 7 to 9.

7 and 8 show a Z-phase GTO switch 261.
~ 26n is ON, U-phase GTO switch 2
11A to 21n and X-phase GTO switches 241 to 24n are alternately turned on and off to control the U-phase current i2. i1 is a current flowing through the primary side of the transformer 2 corresponding to i2. FIG. 7 shows X-phase GTO switches 241-2.
4n is on. i2 is 2 of the transformer 2
From the next u phase, X phase GTO switches 24n to 241, di
/ Dt suppression circuit 24, di / dt suppression circuit 26 Z-phase GT
The current flows through the closed loop that returns to the secondary w phase of the transformer 2 via the O switches 261 to 26n, and the current increases due to the voltage between the secondary u phase and w phase of the transformer 2. At this time, the capacitor 20
Discharge current iD is supplied to the load side.

FIG. 8 shows X-phase GTO switches 241-24.
n is turned off and U-phase GTO switches 211 to 21n are turned on. i2 is U from the secondary u phase of the transformer 2
A closed loop that returns to the secondary w-phase of the transformer 2 via the phase GTO switches 211 to 21n, the di / dt suppressing circuit 21, the capacitor 20, the di / dt suppressing circuit 26, and the Z-phase GTO switches 261 to 26n. At this time, the voltage between the secondary u-phase and w-phase of the transformer 2 causes the capacitor 20 to operate in a high voltage state, and i2 decreases. In this way, the u-phase secondary current i2 of the transformer 2 is controlled. v phase,
The w phase is controlled similarly.

FIG. 9 shows the X-phase GTO switch 2 in FIG.
It shows a current change caused by turning off 41 to 24n. That is, when the current of FIG. 9 is added to the current of FIG. 7, the current of FIG. 8 is obtained. Therefore, "A" point, "B" point,
A magnetic flux change proportional to the product of the area surrounded by the "C" point, the "D" point and the "E" point and i2 occurs. The change in the electromagnetic energy at this time is absorbed by the snubber capacitors 30 of the X-phase GTO switches 241 to 24n, and then the X-phase GTO switch 2
When turning on 41 to 24n, it is consumed by the resistor 31.

[0009]

In order to improve the efficiency of the converter 3 in the conventional power converter having the above-mentioned structure, the points "A", "B", "C", "D" are required. ”
It is necessary to reduce the area surrounded by the points and the "E" points to minimize the so-called leakage inductance.
By the way, when manufacturing a high-voltage large-capacity power converter, for example, the length of a U-phase arm in which U-phase GTO switches 211 to 21n are connected in series is proportional to the voltage. V-phase GTO switch 221-2
Assuming that the insulation distance between the U-phase arm and the V-phase arm composed of 2n is also proportional to the voltage, "A" point, "B" point,
Area surrounded by "C" point, "D" point, "E" point, that is,
The leakage inductance is proportional to the square of the voltage, which has been a major obstacle to manufacturing a high-efficiency, high-voltage, large-capacity converter.

Therefore, the present invention eliminates the above-mentioned drawbacks of the conventional structure by improving the connection of the main circuit,
It is an object of the present invention to provide a high-voltage, large-capacity and efficient power conversion device configured by connecting a large number of GTO switches in series.

[0011]

In order to achieve this object, the present invention provides a first series circuit in which the anode of the first diode is connected to the cathode of the first self-arc-extinguishing semiconductor device. A second series circuit in which the anode of the second self-arc-extinguishing semiconductor element is connected to the cathode of the second diode; the series connection point of the first series circuit; and the second series circuit. A capacitor connected between the circuit and a series connection point of the circuit, and connecting the cathode of the second self-arc-extinguishing semiconductor element and the cathode of the first diode in common, The present invention is characterized in that an arm of a power conversion device is configured by serially connecting a plurality of switch units each having an anode and an anode of the first self-arc-extinguishing semiconductor element connected in common.

[0012]

By configuring the arm of the power converter as described above, assuming that the current flowing in the arm is i, a current of i / 2 is generated in the first series circuit of each switch unit.
A current of i / 2 will also flow in the second series circuit.
Here, in order to turn off the current of the arm, the current change when turning off the first self-extinguishing semiconductor element and the second self-extinguishing semiconductor element of each switch unit is: capacitor → first self-extinguishing semiconductor element. Arc-extinguishing type semiconductor element → second diode →
A current change of i / 2 occurs in the closed loop of the capacitor, the capacitor → the first diode → the second self-extinguishing semiconductor device → the closed loop of the capacitor.

That is, "A", "B", "C",
As indicated by "D" and "C", "D", "E", and "F", the change in current when the current flowing through the GTO is cut off is completed in each switch unit. When the number of switch units in series is n, the voltage in one switch unit is 1 / n, so that the insulation distance can be shortened and the leakage inductance can be reduced.
Further, the leakage inductance of the current loop cut off by one GTO does not change no matter how much the number of series of the switch units is increased, so that it is possible to manufacture a high voltage and large capacity power converter.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the block diagrams of FIGS. In the figure, 1 is an AC power supply,
2 is a transformer and 3 is a converter. The converter 3 is composed of bridge-connected self-extinguishing semiconductor elements, but here, as an example, a case of being composed of GTO will be described. 4 is a DC reactor, 5 and 6 are GTOs, 7 and 8
Is a diode and 9 is a capacitor. More GTO
The U-phase switch unit 111 is composed of 5, 6, diodes 7, 8 and capacitor 9. Similarly, the U-phase switch units 112 to 11n are configured. Similarly, V
Phase switch units 121 to 12n, W phase switch units 131 to 13n, X phase switch units 141 to 1
4n, Y-phase switch units 151 to 15n, and Z-phase switch units 161 to 16n. U above
The converter 3 is configured by connecting the arms including the phase switch unit to the Z phase switch unit in a bridge connection. Next in FIG.
The operation of the present invention will be described with reference to FIGS.

1 and 2 show a U-phase switch unit 11
1 to 11n and Z-phase switch units 161 to 16n are turned on, U-phase switch units 111 to 11
It shows a process in which n is turned off and V phase switch units 121 to 12n are turned on to perform positive commutation from the U phase to the V phase. FIG. 1 shows U-phase switch units 111 to 11n and Z.
This is a state immediately before the start of commutation in which the phase switch units 161 to 16n are turned on. i2 is the secondary u-phase of the transformer 2, the U-phase switch units 111 to 11n, the DC reactor 4, a load not shown, and the Z-phase switch unit 1
It flows through the closed loop returning to the secondary w-phase of the transformer 2 via 61 to 16n. i1 is 1 of the transformer 2 corresponding to i2
This is the current flowing to the next side.

FIG. 2 shows U-phase switch units 111 to 1
This is a state immediately after all of the 1n GTOs 5 and 6 are turned off and all of the V-phase switch units 121 to 12n GTOs 5 and 6 are turned on to start positive side commutation from the U phase to the V phase. U
In the phase switch units 111 to 11n, i2 flows to the diodes 7 and 8 and the capacitor 9. In the V-phase switch units 121 to 12n, when the GTOs 5 and 6 are all turned on, the voltage of the capacitor 9 becomes GTO5.
6 is added in the forward direction, and the commutation current ic increases in the direction of the arrow.

FIG. 3 shows a current change caused by turning off the GTOs 5 and 6 of the U-phase switch units 111 to 11n in FIG. For example, immediately before turning off the GTOs 5 and 6 of the U-phase switch units 111 to 11n, if the current of i2 / 2 is shunted to each of the GTO 5 and GTO 6, the closed circuit "is turned off by turning off the GTO 5 and GTO 6. A "," B "," C ",
A current change of i @ 2/2 shown by the arrows in "D" and "A" occurs. At the same time closed circuit "C", "D", "E", "F"
A current change of i @ 2/2 shown by an arrow at "C" occurs. Therefore, closed circuits "A", "B", "C", "D", "A"
Then, a magnetic flux change proportional to the product of the area surrounded by the points "A", "B", "C", and "D" and i2 / 2 occurs.

At the same time, the closed circuits "C", "D", "E",
"F", "C", "C" point, "D" point, "E" point,
A magnetic flux change proportional to the product of the area surrounded by the "F" points and i @ 2/2 occurs. The change in electromagnetic energy at this time is
When O5 and 6 are turned off, they are consumed as switching loss. This also applies to other switch units.

FIGS. 4 to 6 are configuration diagrams showing another embodiment of the present invention, and for simplification, only one arm constituting the bridge of the converter is shown. In the figure, 10 to 1
3 is a GTO, 14 to 17 are diodes, and 18 and 19 are capacitors. A switch unit 171 is constituted by the GTOs 10 to 13, diodes 14 to 17 and capacitors 18 and 19 described above. In addition, the switch units 172-17
n is similarly configured. Next, the operation of another embodiment of the present invention will be described with reference to FIGS. FIG. 4 shows a state in which the switch units 171 to 17n are turned on. The arm current i2 is shunted to the left and right elements by i2 / 2.
Shall flow.

FIG. 5 shows the switch units 171 to 17n.
This is a state immediately after all GTOs 10 to 13 are turned off.
The current flowing through the GTOs 10-13 becomes zero, and the current flowing through the diodes 14-17 increases to i2.

FIG. 6 shows the switch units 171 to 17n.
3 shows the current change caused by turning off the GTOs 10 to 13. For example, if the current of i @ 2/2 is shunted to each of the GTOs 10 to 13 immediately before the GTOs 10 to 13 of the switch unit 171 are turned off,
Closed circuit "A" by turning off GTO10-13
I2 / 2 indicated by arrows on "B", "C", "D", and "A"
Change current. At the same time closed circuit "C", "D",
A current change of i @ 2/2 indicated by an arrow is generated at "E", "F" and "C". At the same time closed circuit "E", "F", "G",
A current change of i @ 2/2 indicated by an arrow is generated at "H" and "E". Therefore, the closed circuits "A", "B", "C", "D",
At "A", a magnetic flux change occurs in proportion to the product of the area surrounded by "A" point, "B" point, "C" point, and "D" point and i2 / 2.
At the same time closed circuit "C", "D", "E", "F", "C"
Then, a magnetic flux change proportional to the product of the area surrounded by the "C" point, the "D" point, the "E" point, and the "F" point and i2 / 2 occurs. At the same time closed circuit "E", "F", "G", "H", "E"
Then, a magnetic flux change occurs in proportion to the product of the area surrounded by the "E" point, the "F" point, the "G" point and the "H" point and i2 / 2. The change in electromagnetic energy at this time is consumed as switching loss when the GTOs 10 to 13 are turned off. The same applies to the switch units 172 to 17n.

In the above description, the semiconductor element forming the power conversion device is the GTO, but the present invention is a GTO.
However, the present invention is not limited to this, and similar effects can be obtained by using other types of self-arc-extinguishing semiconductor elements.

Further, in the above description, an example of a power conversion device in which a plurality of switch units are connected in series and the arms are bridge-connected is used. A switch etc. can also be configured.

[0024]

As described above, according to the present invention,
The closed loop of the current change that occurs when the current flowing in the GTO is cut off is completed in each switch unit of the bridge arm that constitutes the converter. That is, in the conventional configuration,
As shown by “A”, “B”, “C”, “D”, and “E” in FIG. 9, when the current flowing in the GTO is cut off, the current change is spread across the arms of other phases. Occurs. Therefore, as the number of GTO switches connected in series is increased to increase the voltage, it is necessary to increase the distance between the arms for insulation. Therefore, the leakage loss increases and the switching loss increases. There was a limit. In contrast, the present invention is shown in FIG.
"A", "B", "C", "D" and "C""D",
As indicated by “E” and “F”, the change in current when the current flowing through the GTO is cut off is completed within each switch unit. Therefore, when the number of switch units in series is n, the voltage in each switch unit is 1 / n, so that the insulation distance can be shortened and the leakage inductance can be reduced.

Further, the leakage inductance of the current loop cut off by one GTO does not change even if the number of series of the switch units is increased, so that a high voltage and large capacity power converter can be manufactured. Become. Further, in the connection of FIG. 4 according to the present invention, since the left element and the right element are all connected in series, the sum of the forward voltage drops of the left element and the forward voltage drop of the right element The sum can be adjusted more accurately. Therefore, the current flowing in the left element and the current flowing in the right element can be more accurately balanced. Also, in FIG. 6, “A”, “B”,
"C", "D" or "C", "D", "E", "F"
As shown in, the change in current when the current flowing through the GTO is cut off is completed in the switch unit, as in FIG. As described above, according to the configuration of the present invention, the number of GTO switches in series can be increased without commutation restrictions. Therefore, a very high voltage power conversion device such as a power conversion device for DC power transmission is manufactured. can do.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a power conversion device showing an embodiment of the present invention.

FIG. 2 is a diagram showing a state in which the energization path of [FIG. 1] is changed to explain the operation of the present invention.

FIG. 3 is a diagram showing a process in which the U-phase arm of FIG. 1 is turned off.

FIG. 4 is a configuration diagram of one arm of a power conversion device showing another embodiment of the present invention.

FIG. 5 is a diagram for explaining a state immediately after the GTO forming the arm in FIG. 4 is turned off.

FIG. 6 is a diagram for explaining a change in current that occurs when the arm of FIG. 4 is turned off.

FIG. 7 is a configuration diagram of a conventional power conversion device.

FIG. 8 is a diagram showing a state in which the energization path of FIG. 7 has changed.

FIG. 9 is a diagram showing an energization path for explaining a defect of a conventional power conversion device.

[Explanation of symbols]

1 ... AC power supply 2 ...
Transformer 3 ... Converter 4 ...
DC reactors 5, 6 ... GTO 7, 8 ...
Diode 9 ... Capacitor 10-13 ...
GTO 14-17 ... diode 18-20 ...
Capacitors 21 to 26 ... Di / dt suppressing circuit 27 ...
GTO 28,29 ... diode 30 ...
Capacitor 31 ... Resistor 32 ...
Reactor 33 ... Diode 34 ...
Resistors 111 ~ 11n ... U-phase switch units 121 ~ 12n ...
V-phase switch units 131 to 13n ... W-phase switch units 141 to 14n ...
X-phase switch units 151 to 15n ... Y-phase switch units 161 to 16n ...
Z-phase switch units 171 to 17n ... Switch units 211 to 21n ...
U-phase GTO switches 221 to 22n V-phase GTO switches 231 to 23n
W-phase GTO switch 241 to 24n ... X-phase GTO switch 251 to 25n ...
Y-phase GTO switch 261-26n ... Z-phase GTO switch

Claims (2)

(57) [Claims] 1. A first series circuit in which an anode of a first diode is connected to a cathode of a first self-arc-extinguishing semiconductor element, and a second self-arc-extinguishing type is connected to a cathode of a second diode. A second series circuit to which the anode of the semiconductor element is connected; a series connection point of the first series circuit; and a capacitor connected between the series connection point of the second series circuit, The cathode of the first diode is commonly connected to the cathode of the second self-arc-extinguishing semiconductor element, and the anode of the second diode and the anode of the first self-arc-extinguishing semiconductor element. A power conversion device in which a plurality of switch units each having a common connection are connected in series to form an arm. 2. A first series circuit in which the anode of the first diode is connected to the cathode of the first self-arc-extinguishing semiconductor element, and the second self-arc-extinguishing type is connected to the cathode of the second diode. A switch including a second series circuit connected to the node of the semiconductor element, a series connection point of the first series circuit, and a capacitor connected between the series connection point of the second series circuit. A plurality of units are provided, the lowermost switch unit commonly connects the first self-extinguishing semiconductor element and the anode of the second diode, and the uppermost switch unit connects the second self-extinguishing semiconductor element and the second diode. The cathodes of the first diode are commonly connected, and the middle switch unit is the first diode of the lower switch unit, the second diode of the upper switch unit, and the second self-extinguishing semiconductor of the lower switch unit. A power converter in which a body element and a first self-extinguishing semiconductor element of an upper switch unit are connected in series to form an arm.