JPH0729750Y2 - GTO inverter - Google Patents

Description

[Detailed Description of the Invention] [Object of the Invention] (Field of Industrial Application) The present invention relates to a GTO inverter provided with a circuit for protecting a GTO used in an inverter circuit from destruction due to a reverse voltage.

(Prior Art) FIG. 3 shows the gate turn-off thyristor of FIG.
A waveform (a) between the anode and the cathode and a current waveform (b) of the snubber capacitor at the time of turn-off.

Until the time t ₁ before, GTO1 is not turned on, the load current I _M
Is flowing. GTO1 starts the turn-off at time t _1,
The current i _C of the snubber capacitor 4 reaches I _M at time t ₂ , then starts decreasing from time t ₃ , and becomes zero at time t ₄ . At this time
The anode-cathode voltage of GTO1 reaches a peak. Time t ₄ after, the snubber capacitor current i _C has a negative value by the recovery current of the snubber diode 2. At time t ₅ the reverse breakdown voltage of the snubber diode 2 starts to rapidly recover, the anode-cathode voltage of the stray inductance 7 of the reactor 5 and line GTO1 rapidly decreases. Due to this rapid decrease in voltage, the anode-cathode voltage becomes a negative value as shown by the broken line in FIG. 3 in the following cases.

FIG. 5 shows a circuit example of an inverter using GTO. Now G
TO1a is on, GTO1b-1d are off, load current I _M
Is circulating through GTO 1a, load 10 and diode 6b. After the GTO 1a is turned off, the recovery current of the snubber diode 2 flows through the snubber diode 2, the diode 6b, the load 10, the reactor 5, and the snubber capacitor 4. When the load 10 includes the stray capacitance 11, the recovery current has a large value and may have a negative value between the anode-cathode voltage of the GTO 1a when the reverse breakdown voltage of the snubber diode 2 is recovered. The reverse voltage of this GTO destroys the GTO when the GTO is an element with a small reverse breakdown voltage (eg, 15V, which has a reverse breakdown voltage in principle). there is a possibility.

In order to suppress the reverse voltage of the GTO, there has been proposed a method of connecting a diode 8 in antiparallel with the GTO 1 as shown in FIG. (JP-A-57-31378) The reverse voltage of GTO1 is clamped by the ON voltage of diode 8.

(Problems to be solved by the invention) When the reverse breakdown voltage of the snubber diode 2 is recovered, a steep rising current flows through the diode 8 connected in anti-parallel to the GTO 1. At this time, the diode 8 in FIG. 6 has a turn-on transient voltage V _fr of 10 to 100 times the on-state voltage in the steady state.
Appears. The turn-on transient voltage V _fr tends to increase as the beak repeating reverse voltage of the diode 8 increases. FIG. 7 is a turn-on transient voltage of a fast recovery type diode used for the diode 8 of FIG.
The characteristic of the peak repetition reverse voltage V _RRM of V _fr is shown.
Here, the current capacities of the diodes are the same. For example, 2500V element has V _fr about 3 times larger than 1200V element. With the recent increase in withstand voltage of GTO, the diode 8 is also required to have a high withstand voltage, but an increase in the turn-on transient voltage V _fr of the diode cannot suppress the reverse voltage of the GTO and may destroy the GTO. Brought. One way to reduce V _fr is to increase the current capacity of the diode, but this increases the cost of the protection circuit and increases the volume.

The diode 8 and the reactor 5 are connected to the load in parallel with the diode 6, and the reactive current of the load is shunted through the diodes 6 and 8. It is generally difficult to make a large difference in the on-voltages of the diodes 6 and 8 in terms of the shunt ratio of both diodes, and it is difficult to identify it because it is affected by the wiring resistance and stray inductance. However, it requires sufficient current capacity, which also increases the cost and size of the GTO protection circuit.

[Constitution of device]

(Means for Solving Problems) In order to solve the above problems, in the present invention, GT
In a GTO inverter equipped with a reverse voltage protection diode for O, at least two protection diodes with a low rated voltage are connected in series, and the forward voltage of the protection diode is higher than the forward voltage of the feedback diode. To provide a GTO inverter characterized by being selected as follows.

(Operation) In the GTO inverter configured in this way,
The turn-on transient voltage V _fr can be made small because a plurality of diodes with a lower rated voltage are connected in series than using one diode with a predetermined rated voltage, and the protection diode is turned on during steady operation Since the voltage can be increased and the reactive current of the load can be prevented from flowing to the protective diode, it is possible to protect the GTO, which does not have reverse blocking capability, from damage due to reverse voltage, and also to reduce the size and cost of the protection circuit. .

(Embodiment) FIG. 1 shows an embodiment of the present invention. Anti-parallel to GTO1 V _fr
Are connected to the small diodes 8a and 8b. 9a and 8b are capacitors for averaging the voltage sharing of the diodes 8a and 8b.

FIG. 2 is a waveform example of the anode / cathode voltage of the GTO according to the present invention. Anode during recovery of reverse breakdown voltage of snubber diode
The cathode-to-cathode voltage V _r (twice the V _fr of the diode 8a if the effect of wiring inductance is ignored) is suppressed below the breakdown voltage of the GTO.

[Effect of device]

As described above, according to the present invention, it is possible to provide a GTO inverter having a small-sized and low-cost protection circuit capable of reducing the reverse voltage between the anode and the cathode when the reverse breakdown voltage of the snubber diode is recovered.

[Brief description of drawings]

FIG. 1 is a connection diagram showing an embodiment of the present invention, FIG. 2 is a waveform diagram showing the effect of the present invention, and FIG. 3 is a diagram showing a conventional example of the waveform change occurring at the turn-off of a gate turn-off thyristor. FIG. 4 is a diagram showing a conventional example of a peripheral circuit of a gate turn-off thyristor, FIG. 5 is a diagram for explaining a voltage applied to the gate turn-off thyristor, and FIG. 6 is a reverse voltage applied to the gate turn-off thyristor. FIG. 7 is a diagram showing a conventional protection circuit for the above, and FIG. 7 is a diagram showing a rising voltage characteristic of a diode. 1,1a, 1b, 1c, 1d ... GTO, 2 ... Snubber diode, 3 ... Snubber resistor, 4 ... Snubber capacitor, 5 ... Reactor, 6,6
a, 6b… diode, 7… stray inductance, 8,8a, 8b
… Protective diode, 9a, 9b… Capacitor, 10… Load reactor, 11… Stray capacitance.

Claims (1)

[Scope of utility model registration request] 1. A GTO (gate turn-off thyristor) and the G
A reactor connected in series with the TO, a feedback diode connected in parallel with the series circuit, a snubber circuit connected in parallel with the GTO, and anti-reverse voltage protection of a predetermined rated voltage provided in the anti-parallel with the GTO. In an inverter circuit having a circuit composed of a diode as a constituent element, the reverse voltage protection diode is composed of a circuit in which two or more diodes having a rated voltage lower than the predetermined rated voltage are connected in series, and the reverse voltage protection diode is connected in series. A GTO inverter characterized in that its forward voltage drop is selected so that the reactive current flowing in the connection circuit is smaller than the reactive current flowing in the feedback diode side.