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Asea Brown Boveri Ag

Bbc Brown Boveri Ag

Michael Peppel

Theodor Salzmann

Rainer Marquardt

In a method and device, extinction blocking signals for gate-turn-off power semiconductors, particularly GTO thyristors, are formed in static converters in order to suppress unacceptable extinction attempts and to protect the power semiconductors against destruction. An extinction blocking signal is emitted when the sum of the actual load current of one phase of the converter and the product of the derivation with respect to time of the load current and the maximum storage time of one power semiconductor is greater than the maximum periodically interruptible anode current of one power semiconductor. Furthermore, an extinction blocking signal is emitted when the derivation of a branch current of the converter with respect to time exceeds a threshold value proportional to the voltage supplied to the converter and a short-circuit of the converter is therefore present.

Extinction blocking for GTOs

A method for protecting the gate unit for a GTO thyristor includes predetermining a characteristic curve as a time function adapted both to the maximum load capacity possible for a brief time and to the long-term load capacity of a controllable electronic switch of the gate unit connected to the GTO thyristor. The voltage dropping at the electronic switch is detected and compared with the predetermined characteristic curve. The electronic switch is blocked as soon as the detected switching voltage exceeds the predetermined characteristic curve. An erase pulse switches off the GTO thyristor with the controllable electronic switch.

Method for protecting the gate unit for a GTO thyristor

For maintaining the current-blocking switching state of a thyristor that can be turned off, a low-resistance shunt is added between the gate and cathode terminal of the thyristor in the event of a fault, i.e., in case of a failure of the blocking negative gate- cathode voltage. The shunt preferably is a self-conducting field-effect transistor which is kept in the cut-off state, at least with the thyristor turned off by the negative thyristor gate-cathode voltage itself or indirectly by a supply voltage causing this voltage. The drain-source path of the transistor is connected in series with a diode having a low forward voltage in order to prevent undesirable inverse operation of the transistor.

Device for maintaining the cut-off switching state of a thyristor that

This invention concerns a procedure to operate a turn-off thyristor which can be set to a current-conducting state or a current-blocking state as a function of a switch-on command or a switch-off command. To permit particularly reliable and optimal operation of the turn-off thyristor, the voltage between its gate terminal, G, and its cathode terminal, K, is detected and when it drops below a negative threshold current value U.sub.GKS, a status signal, Z, is generated which indicates the current-blocking state of the turn-off thyristor. A further embodiment detects the gate current of the turn-off thyristor and after the appearance of the switch-off command, the status signal is generated as the polarity changes in accordance with the time derivative of the gate current. An overload of the turn-off thyristor is best recognized by having simultaneous to the appearance of the switch-off command, a time function with a preset expiration time initiated, and having a malfunction notification signal, F, generated for protective ignition of the turn-off thyristor if the time function expires prior to the appearance of the status signal.

Procedure and device for detecting the non-conducting state of turn-off

For recognizing the blocked state of a thyristor which can be switched off (GTO thyristor), especially also if it is alloyed through or the driver addressing the thyristor is defective, a state signal indicating the actual advent of the blocked state is generated after the occurrence of a turn-off signal, if the derivative in time of the gate current has exceeded a positive upper limit, which indicates that the thyristor has been turned off successfully. The maxima of the derivative in time of the gate current are almost independent of the actual anode-cathode current to be extinguished. The derivitive in time of the gate current is advantageously determined via a coupling inductance. Preferably, the method and apparatus are used with a mutual adaptive turn-on interlock of GTO thyristors in converter equipment and can be urged to release protective measures in time if permanent conduction (short circuiting) of a thyristor occurs.

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Weinheim, Germany

Michael Peppel