Converter arrangement for alternating and direct current operation

Claim 2

In a converter arrangement the combination comprising a plurality of thyristor elements connected between a polyphase alternating current supply source and a load for supplying the load with direct current produced by rectification at the thyristors, a pulse generator for producing control pulses, circuit means including a pulse distributor for delivering the pulse output from said generator to the control elements on said thyristors for igniting the same in the proper sequence to produce the desired current rectification, a pulse shifter interposed in said circuit means between said pulse generator and pulse distributor capable of changing over the operation of said thyristor from a rectifier to an inverter mode by a shift in the pulses, means responsive to excess current flow in said direct current load circuit for actuating said pulse shifter to effect the changeover from rectifier to inverter operation, and means operable at the end of a delay following said changeover and provided said excess direct current then still exists for suppressing further delivery of ignition control pulses to said thyristors.

Claim 3

A converter arrangement as defined in claim 1 wherein suppression of further delivery of the ignition control pulses to said thyristors is effected with a delay of from 180* to 270* of the alternating current wave form after the first zero passage of the rectified direct current voltage.

Claim 4

A converter arrangement as defined in claim 1 wherein said means responsive to excess current flow in said direct current load circuit for actuating said pulse shifter includes a trigger member producing an output signal when the excess current appears, and wherein said delayed means operable to suppress further delivery of ignition control pulses to said thyristors comprises a delay-action bistable multivibrator having its input connected to a first output of said trigger member, a first AND member having one input thereto connected to the output of said multivibrator and a second input connecteddirectly to a second output from said trigger, and anegative AND member having one input thereto connected to the output from said first AND member, a second input to said negative iAND member and the output therefrom being included in said circuit means between said pulse generator and pulse distributor.

Claim 5

A converter arrangement as defined in claim 1 wherein said thyristors are arranged in a bridge circuit, wherein said means responsive to excess current flow in said direct currentload circuit for actuating said pulse shifter includes a trigger member producing an output signal when the excess current appears, and wherein said delayed means operable to suppress further delivery of ignition control pulses to said thyristors comprises current transformers provided in each branch of the bridge circuit, said transformers being connected to integrating means for integrating the respective outputs of the current transformers with respect to time, a maximum value device to which the respective outputs from said integrating means are connected for evaluation, said maximum value device serving to transmit from its output only the maximum value of theintegrated currents, a first AND membEr having one input thereto connected directly to the output from said trigger and a second input connected to the output from said trigger and a second input connected to the output from said maximum value device, and a negative AND member having one input thereto connected to the output of said first AND member, a second input to said negative AND member and the output therefrom being included in said circuit means between said pulse generator and pulse distributor.