JPS642248B2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a gate turn-off thyristor (hereinafter referred to as
Regarding the turn-off circuit of GTO (referred to as GTO),
This article relates to a turn-off circuit suitable for reducing the size, weight, and cost of GTO gate circuits.

Conventionally, there are two types of GTO turn-off circuits: Direct discharge current of capacitor
There are two methods: one is to supply the off-gate current to the GTO and turn it off (capacitor method), and the other is to supply the off-gate current via a pulse transformer (pulse transformer method).

The capacitor method has the disadvantage that the gate circuit becomes large because each GTO has an independent off-gate power supply. In addition, the off-gate current of a large-capacity GTO reaches a maximum of 100-odd amperes, but the charging voltage of the capacitor that discharges this is limited by the reverse withstand voltage between the gate and cathode of the GTO, so it is selected to be more than 10-odd volts. Can not. If the rise of the GTO's off-gate current is slow, the turn-off time will be long, which will cause problems during high-frequency operation or when implementing overcurrent protection. As described above, a capacitor that discharges an off-gate current is required to have characteristics such as low voltage, quick rise time, and large current flow, and therefore has the drawback of being expensive.

In the pulse transformer method, the off-gate current is supplied through the pulse transformer, so the rise of the off-gate current is delayed due to the leakage inductance of the pulse transformer. To compensate for this, there is a method that uses the discharge of the capacitor charged by the on-gate power supply, but in order to obtain a large off-gate current with a large rise, the charging voltage of the capacitor charged by the on-gate power supply is increased. There is a need to. Furthermore, since GTO requires a larger on-gate current than a normal thyristor, this method increases gate circuit loss.

Another method is to provide power supplies with different voltages, use a high voltage power supply to quickly start up when the off-gate current begins to flow, and then use a low voltage power supply to continue flowing a large current. There is. In this method, the off-gate power supply becomes large and complicated.

An object of the present invention is to provide an off-gate circuit that supplies an off-gate current via a pulse transformer, which eliminates the need for an off-gate power supply with a different voltage, and allows the off-gate power supply to rise quickly without exceeding the reverse withstand voltage between the gate and cathode of a gate turn-off thyristor. The object of the present invention is to provide a gate circuit for a gate turn-off thyristor that is small, lightweight, and inexpensive by supplying current to the gate turn-off thyristor and increasing the utilization rate of a pulse transformer.

The present invention provides a pulse transformer with a first winding _N1 as a means for quickening the rise of the off-gate current, and furthermore, _N1 becomes a part of a winding _N2 that supplies a large current at a low voltage. When the off-gate current begins to flow, _N1 outputs a high voltage for a short time, and then _N2 supplies a low voltage and large current. .

In addition, multiple windings are provided on the output side of the pulse transformer, and each winding is connected to each other via a switch.
By connecting to a GTO and selecting a switch to make it conductive, you can freely decide which GTO to turn off.
The configuration allows each GTO to be turned off at any time, improving the utilization rate of the pulse transformer.

FIG. 1 shows one embodiment of the present invention. In the figure, 1 is a turn-off circuit, and a turn-off power supply 10
1, capacitor 102, charging resistor 103, diode 104, 105, 106, base circuit 10
8, a transistor 109, and a pulse transformer PT, N ₁ and N ₂ are the first and second windings of the pulse transformer, respectively, and N ₃ is an output winding.
2 is a control circuit which issues signals to the turn-off circuit and the turn-off circuit. 3 is a turn-on circuit, and 4 is a gate circuit for the thyristor 6. The thyristor 6 is provided to prevent the on-gate current from the turn-off circuit from flowing into the turn-off circuit. 5 is GTO.

The operation of turn-off circuit 1 will be described next. If the voltage of the turn-off power supply 101 is V _pff , the capacitor 102 is charged to V _pff via the charging resistor 103. Here, when a turn-off signal is issued from the control circuit 2, the base circuit 108 and the gate circuit 4 operate, and the transistor 109 and the thyristor 6
turns on. By turning on the transistor 109, a discharge current flows from the capacitor 102 to the diode 105 and the winding _N1 , and the windings _N2 and _N3
A voltage of the polarity shown is induced. The voltage V _N2 induced in the winding N ₂ immediately after the transistor 109 is turned on is expressed by the following equation.

V _N2 = n ₂ / n ₁ V _pff ………(1) In equation (1), n ₁ and n ₂ are the windings N ₁ and N ₂ respectively
is the number of turns. Here, if n ₂ > n ₁ , then V _N2 >
V _pff and the diode 104 is reverse biased, so no current flows through the winding _N2 .

At the time when the off-gate current begins to flow through the GTO, the gate and cathode can be considered to be in a substantially short-circuited state, and the discharge current of the capacitor 102 flows to the winding _N3 via the pulse transformer PT. At this time, the equivalent circuit seen from the winding _N1 side is shown in Figure 2. In the figure, resistance is ignored. In the figure, L _l1 is the primary leakage inductance, L _l2 is the secondary leakage inductance, and L _lx is the excitation inductance. L _l2 becomes (n ₁ /n ₃ ) ² L _l2 when viewed from the winding N ₁ side. n ₃ is the number of turns of winding N ₃ . It can be seen from the equivalent circuit that the discharge current i _N1 of the capacitor 102 is expressed by the following equation.

In equation (2), C is the capacitance of the capacitor 102. Further, the time τ _N1 during which i _N1 flows is given by the following equation.

The current i _N3 flowing through the winding N ₃ is given by the following equation.

i _N3 = n ₃ /n ₁・i _N1 (4) i _N3 is the off-gate current of GTO, and in order to make i _N3 rise faster, i _N1 in equation (2) should be increased and (3 )
What is necessary is to reduce τ _N1 in the equation. To this end, (i) choose a large V _pff ;

(ii) Provide the winding in a configuration that reduces L _l1 and L _l2 .

(iii) Select n ₁ /n ₃ to be small.

You can do it like this.

However, the following points must also be considered in the GTO turn-off circuit. In the GTO, as the turn-off operation progresses, the impedance in the reverse direction between the gate and the cathode increases, and eventually the GTO becomes almost open. At this time, the reverse withstand voltage between the gate and cathode is generally about ten or more volts, and if a voltage higher than this is applied from the turn-off circuit, the gate
The avalanche between the cathodes is destroyed. This avalanche loss is greatest when only the gate circuit is operated without anode current flowing through the GTO.
There is an upper limit to conditions (i) and (iii) above because it is necessary to reduce this loss to a value that is allowable or less for GTO. However, by appropriately selecting these values, the rate of increase in off-gate current can be reduced to several tens of amperes/μ・sec.
It can be made large enough.

By the above operation, an off-gate current with a quick rise can be obtained.

In addition, in GTO, it is necessary to extract a large amount of charge from the gate electrode when turning off a large anode current. In order to cover all of this charge by discharging the capacitor 102, a large capacitance must be used.When the anode current of the GTO is small, the GTO is turned off before the capacitor is sufficiently discharged, and the remaining capacitor remains. Avalanche breakdown occurs between the gate and cathode due to voltage. To prevent this, capacitor 10
After the off-gate current is raised in a short time by the discharge of 2, a large current can be supplied at a low voltage by the first winding _N1 and the second winding _N2 , and the gate current is , a large charge can be extracted from the gate without causing avalanche breakdown between the cathodes. This operation will be described next.

The capacitor 102 is discharged and the voltage decreases (1)
When V _N2 expressed by the formula becomes smaller than V _pff , the diode 104 becomes forward biased, and the voltage from the turn-off power supply 101 to the diode 104 to the winding N ₂ ,
Current begins to flow through N ₁ and transistor 109. At this time, the voltage V _N3 induced in the winding _N3
is the value of the following equation when the output is open.

V _N3 = n ₃ / n ₁ + n ₂ · V _pff ...... (5) Select n ₁ , n ₂ , n ₃ , and V _pff so that V _N3 is less than the reverse withstand voltage between the GTO gate and cathode. If, GTO
Once the gate has been turned off, excessive voltage will not continue to be applied between the gate and the cathode, and avalanche losses can be reduced.

Also, the collector current of the transistor 109 is i _c
Then, the current i _N3 flowing through the winding N ₃ is expressed by the following equation.

i _N3 = n ₁ + n ₂ / n ₃ i _c (6) Here, if n ₁ + n ₂ > n ₃ , even if i _c is small, a large i _N3 , that is, a large off-gate current can be obtained. .

As described above, according to this method, the current rises quickly, and an off-gate current of low voltage and large current can be obtained with a simple circuit configuration and low loss. In addition, in FIG. 1, the diode 105 is connected to the winding from the turn-off power supply 101.
This is provided so that when current begins to flow through _N2 , the current that has passed through the winding _N2 does not flow into the capacitor 102 whose voltage has dropped due to discharge. Furthermore, the diode 106 and the resistor 107 are connected to the transistor 10.
When transistor 9 is turned off, it has the role of circulating the energy accumulated in the excitation inductance of pulse transformer PT and preventing overvoltage from being applied to transistor 109.

When the transistor 109 is turned off, a voltage is applied to each winding in a direction opposite to the illustrated polarity, and the thyristor 6 is turned off.

FIG. 3 shows another embodiment. In this example, the first
In the embodiment shown in the figure, the charging resistor 103 of the capacitor 102 is replaced by the reactor 110 and the thyristor 11.
1, the resistor 113 is replaced.

In the embodiment of FIG. 1, when a current flows from the turn-off power supply 101 through the diode 104 and the windings N ₂ and N ₁ , the voltage V _N1 induced across the winding N ₁ is expressed as follows.

V _N1 = N ₁ / N ₂ + N ₁・V _pff (7) Therefore, the voltage at the resistor 103 is expressed by the following formula.
A current that induces V _R flows from the turn-off power supply.

V _R =V _pff (1-N ₁ /N ₂ +N ₁ ) (8) The embodiment shown in FIG. 3 takes this point into consideration and aims to reduce the loss.

A turn-on signal is issued from the control circuit 2,
The turn-on circuit operates and turns on GTO5. At the same time, the gate circuit 112 of the thyristor 111 is also activated, and the thyristor 111 is turned on. This operation turns off the power supply 101.
An oscillating current flows through the reactor 110 and the capacitor 102, and the capacitor 102 is charged. When the oscillating current changes to negative polarity, the thyristor 111 is turned off by applying a reverse voltage between the anode and the cathode.

When a turn-off signal is output from the control circuit 2 at the time when the GTO should be turned off, the transistor 109 is turned on and an off-gate current flows in the same manner as in the embodiment shown in FIG.

According to this embodiment, even when current flows from the turn-off power supply 101 to the windings N ₂ and N ₁ , the thyristor 1
11 is in the off state, there is an effect that the loss caused by the resistance can be reduced as in the embodiment shown in FIG.

In FIG. 3, the resistor 113 absorbs the discharge of the capacitor 102 due to the leakage current of the capacitor 109, after the capacitor 102 is charged and the thyristor 111 is turned off, until the transistor 109 is turned on next time. This is for compensation and can be selected to a sufficiently large value.

FIG. 4 shows another embodiment. In this example, the first
In the embodiment shown in the figure, a plurality of windings _N3 are provided in the pulse transformer PT, so that a plurality of GTOs can be turned off with one pulse transformer.

Since the off-gate current of the GTO has a maximum value that is a fraction of the anode current that turns off, the transistor 109 needs to have a large current capacity, and the pulse transformer PT also needs to be able to flow a large current with a fast rise. becomes. Therefore, transistor 109 and pulse transformer PT can be connected to multiple GTOs.
The key to making devices using GTO smaller and lighter is to increase the utilization rate of transistors and pulse transformers. In the figure, INV is GTO9, 10, 11,
The inverter is composed of 12, 13, and 14, 8 is a power source of the inverter, and 15 is a load.

41, 42, and 43 are thyristor gate circuits. Pulse transformer PT has multiple output windings
N ₃ are provided, each through a thyristor
Connected between the gates and cathodes of GGTO9 to GTO14. In addition, in the figure, GTO11 to GTO1
The winding connected between the gate and cathode of No. 3 is omitted. GTO9, 10, 11 in inverter INV
Since the cathode potentials are different, it is necessary to supply gate current from each insulated winding. Since the GTOs 12, 13, and 14 have the same cathode potential, gate currents can be obtained in parallel from the same winding, but the figure shows a case where independent windings are provided.

When a turn-off signal is output from the control circuit 2, the transistor 109 in the turn-off circuit is turned on. This turn-off signal is also input to an AND circuit that sends a signal to the gate circuits 41 to 43 of the thyristors.

From the control circuit 2, along with the turn-on signal,
Among GTO9-14, GTO you want to turn off
OFF command is output. In FIG. 4, when turning off the GTO 9, a command to turn off the GTO 9 is input to an AND circuit that sends a signal to the gate circuit 41, and a signal is sent to the gate circuit 41 by ANDing with the turn-off signal. This operation turns on the thyristor 61, and an off-gate current flows through the GTO 9. Since no signal is input to the gate circuits 42 and 43, the thyristors 62 and 63 maintain an off state, and no off-gate current flows through the GTO, so only the GTO 9 is selected and turned off. GTOs 10-14 can also be turned off by operations similar to those described above. According to this embodiment, 1
Multiple GTOs can be selectively turned off using two turn cuff circuits and one pulse transformer.
Since the utilization rate of the turn-off circuit and pulse transformer can be improved, the gate circuit of the GTO can be made smaller and lighter.

FIG. 5 shows another embodiment. In the figure, a turn-on circuit and a control circuit are omitted.

When a base current flows from the base circuit 108 to the transistor 109, the transistor 109 is turned on.

As a result, the turn-off power supply 1 is connected to the windings N ₁ and N ₂ .
A voltage of 01 is applied. At this time, a voltage V _N2 expressed by the following equation is induced in the winding N ₂ with the polarity shown.

V _N2 = n ₂ / n ₁ + n ₂ · V _pff ...... (9) In equation (9), V _pff is the voltage of the turn-off power supply V _pff , n ₁ ,
n ₂ is the number of turns of the windings N ₁ and N ₂ , respectively. V _N2
is applied to diode 116. Immediately after transistor 109 turns on, due to the voltage V _N2 induced in winding N ₂ , current from turn-off power supply 101 flows through winding N ₁ to charge capacitor 114 as shown, and the voltage of the turn-off power supply becomes Applied to winding _N1 .

From the point in time when the charging voltage of the capacitor 114 becomes equal to the voltage shown by equation (9), the turn-off power supply 1
The current from 01 will now flow through windings _N1 and _N2 .

Therefore, immediately after the transistor 109 is turned on, that is, when the off-gate current begins to flow, the winding
The off-gate current is applied to the GTO by N ₁ and then by windings N ₁ and N ₂ . The current flowing through each winding at this time is equivalent to that in the embodiment shown in FIG.
In this embodiment, as in the embodiment shown in FIG. 1, the current rises quickly, and a low-voltage, large-current off-gate current can be obtained with a simple circuit configuration and low loss.

The illustrated charged capacitor 114 discharges through the resistor 115 when the transistor 109 turns off, and the charging voltage becomes zero by the time the transistor 109 turns on.

FIG. 6 shows another embodiment. This embodiment is the turn-off circuit shown in FIG. 5, in which n output windings are provided on the secondary side of the pulse transformer PT so that n GTOs can be turned off. In the figure, since the control circuit and the output signals of the control circuit are the same as in FIG. 5, they are omitted.

According to this embodiment, multiple GTOs can be selected and turned off using one turn-off circuit and one pulse transformer, and the utilization rate of the turn-off circuit and pulse transformer can be improved, so the GTO gate circuit can be made smaller and lighter. It has the effect of making it more effective.

According to the present invention, in a device using GTO,
It is possible to reduce the number of power supplies for the gate circuit of the GTO, and also to realize a turn-off circuit with a simple configuration and low circuit loss, which can quickly rise without exceeding the reverse withstand voltage between the gate and cathode of the gate turn-off thyristor. This has the effect of allowing a large current to flow through the GTO. In addition, it is possible to improve the utilization rate of turn-off circuits and pulse transformers.
This has the effect of making the GTO gate circuit smaller and lighter.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an embodiment of the present invention, FIG. 2 is an equivalent circuit explaining the operation of the present invention, and FIGS.
The figure shows an embodiment of the present invention. 1, 20...Turn-off circuit, PT...Pulse transformer, 5...GTO, _N1 , _N2 , _N3 ...PT winding, 109...Transistor, 101...Turn-off power supply, 102, 114... capacitor.

Claims (1)

[Claims] 1. In a turn-off circuit that supplies an off-gate current to a gate turn-off thyristor via a pulse transformer, the primary side of the pulse transformer includes a DC power supply for supplying an off-gate current to the gate turn-off thyristor; A capacitor charged by the DC power supply, a first winding for supplying an off-gate current with a steep rise and a narrow width by the discharging current of the capacitor, and an off-gate current supplied by the current flowing from the DC power supply. a second for supplying current;
and a third winding connected to one of the control electrode and the main electrode of the gate turn-off thyristor on the secondary side of the pulse transformer. turn-off circuit.