JPS6330229Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an extinguishing circuit for a gate turn-off thyristor that is turned on and off by a gate current.

Gate turn-off thyristors (hereinafter abbreviated as GTO) have a current capacity of 50A.
It can be ignited with a minute gate current of about 100 mA, but to turn it off, a current of about 5 A must normally flow through the gate in the opposite direction.
In this case, the turn-off gain is about 10. Also, GTO with small current capacity, for example, 1 to 5 A
But the turn-off gain is at most 15-20 or less.

Conventionally, the waveforms of the gate current Ig and load current I _L for operating this type of GTO are shown in FIGS. 1a and 1b. Therefore, when a forward voltage is applied to the GTO and an ignition current I _gON is applied to the gate as shown in Figure 1a, the GTO becomes conductive and the load current I as shown in Figure 1b occurs. Run _L. Then the load current I _L
1st in reverse direction to GTO gate to turn off
As shown in Figure a, the load current I _L is turned off by flowing the current I _gOFF . However, this I _gOFF must flow at a value greater than the value determined by the gain, which has the serious drawback of increasing the capacity of the control circuit.

In order to eliminate such drawbacks, the present invention charges a capacitor with a current flowing through the gate turn-off thyristor constituting the main circuit, and discharges the energy of the charged capacitor by a switching element to switch the gate turn-off thyristor off. is used as energy to extinguish the arc, and this enables gate turn-off and
The present invention aims to provide a gate turn-off thyristor arc extinguishing circuit that increases the turn-off gain of the thyristor, and will be described below using embodiments.

Fig. 2 shows an embodiment of the gate turn-off thyristor arc extinguishing circuit according to the present invention. A current transformer 2 is provided for detecting the load current. This current transformer 2 may be a normal current transformer or a saturated current transformer;
It is sufficient to charge the capacitor described later with the current flowing through GTO1, and for that purpose, one end of the output side (secondary winding side) of current transformer 2 is connected to the anode electrode of small capacity auxiliary GTO4 via diode 3. is,
The cathode electrode of this auxiliary GTO 4 is connected to the cathode electrode of the main GTO 1 via a resistor 5. Further, 6 is a capacitor connected between the other end of the output side (secondary winding side) of the current transformer 2 and the cathode electrode of the diode 3, and 7 is a capacitor whose anode electrode is connected to the output side of the current transformer 2. Connected to the other end and the gate electrode of main GTO1, and the cathode electrode is auxiliary.
This Zener diode 7, which is connected to the anode electrode of the GTO 4, is used to suppress the terminal voltage of the capacitor 6 to a constant value. Also, in 8, the anode electrode is GTO4
connected to the connection point between the cathode electrode and the resistor 5,
Further, the cathode electrode is a diode connected to one end of the output side of the current transformer 2, and is used to reset the current transformer 2. In addition, G is the main
Gate terminals of GTO1, g and k are auxiliary GTO4 respectively
These are the gate terminal and cathode terminal.

Based on this configuration, when an ignition current is applied to the gate G of the main GTO 1 to turn on the main GTO 1 and a load current is applied, a current determined by the turns ratio flows through the current transformer 2 to the diode 3 and the capacitor 6. , and the capacitor 6 is charged. And the main GTO
When load current flows through capacitor 1 for a predetermined period of time, capacitor 6 is charged with the polarity shown, and in this state it is auxiliary.
When a firing command pulse is applied to the gate terminal g and cathode terminal k of the GTO 4 with the gate terminal g side being positive, the auxiliary GTO 4 shifts to a conductive state. Therefore, capacitor 6 is discharged, and the current flows from capacitor 6 to
It flows through the loop of auxiliary GTO 4 → resistor 5 → cathode electrode of main GTO 1 → gate electrode of main GTO 1 → capacitor 6, and main GTO 1 shifts to the off state. The resistor 5 connects the current transformer 2 via the diode 8.
A reset current flows through the current transformer 2 in preparation for a charge/discharge cycle of the capacitor 6 similar to that described above in the event that the main GTO 1 fires again. On the other hand, GTO4 is mainly
After the time required for GTO1 to turn off, that is, the turn-off time, the auxiliary GTO4 returns to the off state by passing an extinguishing pulse with the cathode terminal k side being positive between the gate terminal and cathode terminal gk of the auxiliary GTO4. .

For example, if main GTO1 has a capacity of 50A and a turn-off gain of 10, the conventional circuit
Although a power source was required to flow a reverse current of 5A or more to the gate of GTO1, in this example circuit, the main GTO1
can be turned off. In this case, for example, if a GTO4 with a current capacity of 5A is used, the ignition current of this GTO4 is about 100mA at most, so
The main GTO 1 can be turned off by applying a 100 mA firing command pulse to the GTO 4. Furthermore, since the gain of the auxiliary GTO 4 is about 20, this GTO 4 can be turned off at 250 mA. Also, the number of firing command pulses for main GTO1 is approximately
100mA is sufficient.

By doing so, a power source for extinguishing the main GTO 1 is not required, and the turn-off gain can be increased by 10 to 100 times or more using an external circuit. In addition, by using current transformer 2, the main
Switching loss can be suppressed when the GTO 1 is turned on, and overvoltage (specifically, dV/dt) can be suppressed by resetting the current transformer 2 when the main GTO 1 is turned off.

Note that in this example, the gate turn-off
Although the auxiliary GTO 4 is used in the thyristor arc extinguishing circuit, the present invention is not limited thereto, and it goes without saying that a switching element such as a transistor or a thyristor may be used instead of using the auxiliary GTO 4.

In addition, in this embodiment, the current transformer 2 is used as the main GTO
Although the present invention is not limited to this, for example, the main GTO
Of course, it is only necessary to connect it to a position such as the cathode electrode side of the main GTO 1, where the load current flowing to the main GTO 1 is detected.

Further, in this embodiment, although the diode 8 for resetting the current transformer 2 is used, depending on the material that constitutes the current transformer 2, it may not be necessary to reset the current transformer 2. may not be necessary. Further, the current limiting resistor 5 may simply become unnecessary. Furthermore, although not shown, the main
Of course, a CR snubber circuit, which is used in ordinary thyristors, is connected between the anode and cathode of GTO1.

As described above, if the gate turn-off thyristor arc extinguishing circuit according to the present invention is used, there is no need for a power source to arc extinguish the gate turn-off thyristor constituting the main circuit, and the gate turn-off thyristor, which has a particularly large current capacity, can be used. For example, the turn-off gain of 10 to 100 can be set in the external circuit.
It can be more than doubled. In addition, according to the present invention, by using a current transformer, gate turn-off and
Suppression of switching loss when the thyristor is turned on, gate turn-off, and overvoltage caused by current transformer reset when the thyristor is turned off (specifically,
dV/dt) suppression can be performed. Furthermore, the charge stored in the capacitor is proportional to the main circuit current, that is, the current flowing between the anode and cathode of the gate turn-off thyristor, so when the main circuit current is large, a large reverse current is passed through the gate to turn it off, reducing the main circuit current. When is small, a small reverse current flows through the gate to turn it off. That is, it is operated with the gain (main circuit current/reverse current) constant. If you want to turn off the reverse current by keeping it constant,
The reverse current must be set to a value that takes into account the overcurrent level, so even low load current levels are turned off at a high reverse voltage, so energy corresponding to the extra reverse voltage is lost at the cathode junction of the gate turn-off thyristor. This not only causes poor efficiency but also causes deterioration of the gate turn-off thyristor. On the other hand, if the reverse current is made to have a magnitude corresponding to the main circuit current as in the present invention, efficiency is high and deterioration can be suppressed.

[Brief explanation of the drawing]

Figures 1a and b are waveform diagrams of gate current and load current, respectively, to explain the operation of a conventional gate turn-off thyristor, and Figure 2 shows an embodiment of the gate turn-off thyristor arc extinguishing circuit according to the present invention. In the circuit shown in the figure, 1 is the main GTO,
2 is a current transformer, 4 is an auxiliary GTO, and 6 is a capacitor.

Claims (1)

[Scope of utility model registration request] A diode is connected to one output terminal of a current transformer that detects the current flowing through the gate turn-off thyristor that constitutes the main circuit, with the anode facing the output terminal, and the cathode of the diode and the other of the current transformer are connected. A switching element is connected between the connection point between the capacitor and the cathode of the diode and the cathode of the gate turn-off thyristor, and the gate of the gate turn-off thyristor is connected between the terminals of the current transformer. An arc extinguishing circuit for a gate turn-off thyristor, characterized in that it is connected to a connection point between the other output terminal and a capacitor.