JPH01291659A - Gate drive circuit of gto thyristor - Google Patents

Abstract

PURPOSE:To prevent the short-circuit of direct current in starting, by forcibly breaking a forward current supply circuit of the gate of a GTO thyristor in raising the power supply of its gate drive circuit. CONSTITUTION:A gate drive circuit 5A is composed of a power insulating trasformer T1, a rectifier REC, a signal insulating transformer T2, a logic circuit 51, transistors (FET) Q2-Q4, buffer amplifiers BUF 1-2, etc. To this drive circuit 5A a breaking circuit 100, an input terminal M5 of a breaking command signal and a photocoupler PC are provided. When the breaking command signal is inputted from the input terminal M5 to the breaking circuit 100, a light emitting diode LED emits light between them and the transistor Tr is conducting, so that it becomes short-circuiting across the gate and source of the FET Q2 and no FET Q2 will be conducting any longer.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a gate drive circuit for a GTO thyristor, and more specifically, when the power supply in the gate drive circuit is started, the power supply is started and established. The present invention relates to a gate drive circuit for a GTO thyristor, which is equipped with a circuit that prevents the GTO thyristor from being destroyed due to malfunction of the circuit due to an unestablished power supply, although it takes some time to complete the process.

[Conventional technology]

FIG. 3 is a conceptual diagram showing the configuration of a conventional variable speed drive system driven by an induction motor.・In the same figure, 1 is an AC power supply, 2 is a transformer, 3 is an AC/AC converter,
4 is a control circuit, 5 is a gate drive circuit for a GTO thyristor, 6 is an induction motor, CONV is a diode rectifier, C is a capacitor, INV is an inverter constituted by the GTO thyristor, and BATT is a battery. A power converter is composed of a diode rectifier C0NV, a capacitor C, and an inverter INV.

The electric power obtained from the AC power source 1 is converted into AC power of variable voltage and variable frequency by a power converter to drive the induction motor 6 at variable speed. The required drive signal for the GTO thyristor constituting the inverter IN■ is provided by the gate drive circuit 5.
, it is created based on the ignition and extinguishment command signals given from the control circuit 4.

The control circuit 4 performs various adjustments and calculations to control the speed of the induction motor 6, and generates firing and extinguishing command signals for the GTO thyristor. The power required for control circuit 4 is buffer battery B.
Supplied by ATT.

The required power source for the gate drive circuit 5 is a battery BAT which is a power source for the control circuit 4 because it requires a relatively large capacity.
If the power is taken from T, the capacity of the battery BATT increases and is uneconomical, so the configuration is such that it is obtained from the AC power supply 1 via the transformer 2. For that purpose A C/A
A C converter 3 is connected, but this is for the purpose of stabilizing the voltage supplied to the gate drive circuit 5.

The present invention relates to a gate drive circuit for a GTO thyristor used in such a variable speed drive system for an induction motor.

FIG. 4 is a circuit diagram showing details of the gate drive circuit 5 in FIG. 3.

In FIG. 4, terminal M1 is a power input terminal, terminal M2 is an input terminal into which firing and extinguishing command signals for the GTO thyristor are input, terminals M3. M4 is an output terminal that outputs a gate drive signal for the GTO thyristor. The gate drive circuit 5 can be said to be a circuit that amplifies the firing/extinguishing command signal given from the control circuit 4 and supplies it to the gate of the GTO thyristor.

Power isolation transformer TI uses GTO thyristor and AC/ACC
/It is provided for insulation and voltage matching between the motor and the motor 3. REC is a rectifier. Signal isolation transformer T2 is G
It is provided for insulation between the TO thyristor and the control circuit 4. The logic circuit 51 receives the ignition/extinguishing command signal given from the control circuit 4, and then turns on the transistor (
This is a circuit that creates the on/off timing of field effect transistors G2 and G3. Buffer amplifier BUFl,
BUF2 is an amplifier for driving transistors Q2 and G3, respectively.

FIG. 5 is an operational waveform diagram of each part in FIG. 4. Fifth
In the figure, (A) is an ignition/arc extinguishing command signal given from the control circuit 4; when it is on, it is an ignition signal, and when it is off, it is an extinguishing signal. G2 is the ignition/extinction command signal (
A) The logic circuit 51 inputted with the buffer amplifier BU
G3 is a voltage signal outputted to the gate of transistor Q2 via FI, and G3 is a voltage signal similarly outputted by logic circuit 51 to the gate of transistor Q3 via buffer amplifier BUF2.

If the voltage output to transistor Q2 is on, the voltage output to transistor Q3 is off, and if the voltage output to transistor Q2 is off, the voltage output to transistor Q3 is on, so the relationship is always reversed. It will be understood that there are ig is the current waveform that flows in and out of the gate G of the GTO thyristor, the positive waveform is the signal current that flows in and fires the GTO thyristor, and the negative waveform is the signal current that flows out and extinguishes the GTO thyristor. .

The operation of the dot and arc extinguishing circuits will be briefly explained with reference to FIGS. 4 and 5.

When the ignition/extinction command signal (a) is on, the logic circuit 51
is connected to transistor Q2 via buffer amplifier BUF1.
Since an on signal is supplied to the gate of transistor Q2, transistor Q2 becomes conductive, and therefore transistor Q1 also becomes conductive. On the other hand, at this time, the logic circuit 51 supplies an off signal to the gate of the transistor Q3 via the buffer amplifier BUF2, so the transistor Q3 is not conductive.

Therefore, the charge that had been charged in the capacitor C1 becomes a current, which flows along the path shown by the broken line, that is, the transistor Q1, the resistor R2, the output terminal M3, and the gate G1 cathode K of the GTO thyristor.

A forward current (positive waveform of ig) flows through the output terminal M4 to the rectifier REC and fires the GTO thyristor. Resistor R1 and capacitor C3 constitute a speed-up circuit for supplying a large gate current during ignition.

When the ignition/extinction command signal (a) is off, the logic circuit 51
supplies an off signal to the gate of the transistor Q2 via the buffer amplifier BUFI, so the transistor Q2 becomes non-conductive, and therefore the transistor Q1 also becomes non-conductive.

On the other hand, at this time, the logic circuit 51 is connected to the buffer amplifier BUF2.
Since an on signal is supplied to the gate of transistor Q3 through the transistor Q3, the transistor Q3 becomes conductive.

Therefore, the electric charge that had been charged in the capacitor C2 becomes a current, which flows along the path shown by the solid line, that is, through the output terminal M4, the cathode K of the GTO thyristor, the gate G, the output terminal M3, and the transistor Q3, and then flows through the rectifier REC. A reverse current (negative waveform of ig) flows to extinguish the GTO thyristor, causing the GTO thyristor to maintain the cut-off state.

[Problem to be solved by the invention]

The conventional GTO thyristor gate drive circuit as described above has the following problems.

In FIG. 3, when starting up the device (system), when the voltage of the AC power supply 1 rises, the main power supply voltage of the GTO inverter INV and the power supply voltage of the gate drive circuit 5 rise at the same time. The power supply voltage of the gate drive circuit 5 rises while the main power supply voltage (the voltage across the capacitor C) is being generated.

The problem here is that even though the gate drive circuit 5 is given an extinguishing command for the GTO thyristor from the control circuit 4, the logic circuit 51 in the gate drive circuit 5 is not established (transient state at startup)
Due to this, slight malfunctions may occur.
Normally, the GTO thyristor should be held in the extinguished state by outputting an off signal to transistor Q2 and an on signal to transistor Q3, but due to a malfunction, an on signal was output to transistor Q2 and an off signal was output to transistor Q3. There were cases where the GTO thyristor was turned on by outputting the respective outputs.

As a result, a short-circuit accident of the GTO thyristor may occur in the inverter INV, resulting in a problem that the inverter cannot be operated.

An object of the present invention is to provide a gate drive circuit for a GTO thyristor that does not output a firing signal due to malfunction even when the power supply voltage is started up.

[Means to solve the problem]

To achieve the above object, in the present invention, in the gate drive circuit of the GTO thyristor, when the power supply fails, a forward current is supplied to the gate of the GTO thyristor until the power supply is established, and the GTO thyristor is activated. It is equipped with a cutoff circuit that forcibly cuts off the forward current supply circuit for ignition.

[Effect]

In this way, even if the logic circuit in the gate drive circuit malfunctions, no forward current is supplied to the GTO thyristor, so the GTO thyristor will not fire, and therefore a short circuit will not occur.

〔Example〕

FIG. 1 is a circuit diagram showing one embodiment of the present invention.

In this figure, the same parts as in FIG. 4 are given the same reference numerals. In addition, 5A is a gate drive circuit for the GTO thyristor according to the present invention, 100 is a cutoff circuit, M5 is an input terminal for a cutoff command signal, pc is a photocoupler (consisting of a light emitting diode LED and a transistor Tr), R100
, RIOI are each a resistor, and Dlol is a diode.

FIG. 2 is a waveform diagram of various signals in the circuit of FIG. 1. That is, assuming that the main power supply turn-on command is given at time 10, the main power supply voltage starts to rise after a delay of time Δt, and the main power supply voltage is completely established after the time Δt.

Therefore, a timer (not shown) or the like is used to create a shutoff command signal that remains on for a time T (=Δ1+1) from the time to when the main power supply ON command is generated, as shown in FIG. An input is made to the circuit 100 from the input terminal M5.

Then, in the cutoff circuit 100, during that time (only time T)
The light emitting diode LED is emitting light and the transistor Tr
is in a conductive state, so even if the gate G and source S of the transistor Q2 become short-circuited and the logic circuit 51 malfunctions and outputs an ON command via the puffer amplifier BUF1, the transistor Q2 will remain conductive. Therefore, the GTO starter is not fired.

Note that the resistor R101 is connected for decoupling between the photocoupler PC and the buffer amplifier BUF,1.

After time T has elapsed and the main power supply voltage has been established, the light emitting diode LED stops emitting light, so normal driving operation of the GTO thyristor can begin.

〔Effect of the invention〕

According to the present invention, when the power supply voltage of the gate drive circuit of the GTO thyristor is raised, the forward current supply circuit that supplies forward current to the gate of the GTO thyristor is forcibly cut off.
Since the firing signal is not given to the GTO thyristor due to malfunction, the GTO thyristor is
This has the advantage of preventing DC short circuits in the thyristor and preventing failures caused by DC short circuits.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing one embodiment of the present invention, and Fig. 2 is a circuit diagram showing an embodiment of the present invention.
3 is a conceptual diagram showing the configuration of a very ordinary variable speed drive system for an induction motor; FIG. 4 is a circuit diagram showing details of the gate drive circuit 5 in FIG. 3. , FIG. 5 is an operation waveform diagram of each part in FIG. 4,
be. Explanation of symbols 5A...Gate drive circuit of the GTO thyristor according to the present invention, 100...Shutoff circuit, M5...Input terminal for cutoff command signal, PC...Photocoupler (light emitting diode L)
consisting of ED and transistor Tr), R100°R10
1... Resistance, Dlol... Diode Representative Patent Attorney Akio Namiki Representative Patent Attorney Kiyoshi Matsuzaki 112 Figure

Claims (1)

[Claims] 1) When an ignition command is given from the control device, a forward current is supplied to the gate of the GTO thyristor to turn it on, and when an extinguishing command is given from the control device, the gate of the GTO thyristor is turned on. In the gate drive circuit of a GTO thyristor which is turned off by supplying a reverse current to the drive circuit, when the power supply to the drive circuit is turned on, the GTO thyristor is turned off regardless of the command from the control device until the power supply is established.
A gate drive circuit for a GTO thyristor, comprising a cutoff circuit that forcibly cuts off a forward current supply circuit that supplies forward current to the gate of a TO thyristor.