Abstract: A thyristor matrix arrangement having four columns, each column being formed of n thyristors connected in series with each other. In one embodiment, the series connected thyristors in respective columns are coupled to one another via heat sinks. The thyristors in each column are poled such that forward conduction current cannot flow through only one of the columns. The heat sinks are cross-connected among the columns to form a current path which is formed of appropriately poled thyristors in different ones of the columns and the column cross-connections. The cross-connections are inductive so as to provide relatively large inductive voltage drops when the thyristors are fired, thereby enabling the firing of thyristors having relatively low firing and forward voltages.

Abstract: A method of operating a cycloconverter which is adapted for use with a load in the form of a parallel resonant circuit and for use with an intermediate d-c link supplied by an a-c voltage source and including a smoothing choke and a controlled rectifier, the cycloconverter including an inverter circuit comprising a bridge circuit having output terminals adapted to be connected to the load and input terminals adapted to be connected to the d-c link, in which starting of the cycloconverter is realized by firing the thyristors of an auxiliary commutating device for a time interval sufficient to charge commutation capacitors to a predetermined voltage and the thyristors of the inverter then fired for a time interval sufficient to result in a current of predetermined magnitude, the latter being held constant by controlling the rectifier in the d-c link, and, thereupon, prior to each zero crossing of the resonant circuit voltage, first firing the thyristors of the auxiliary device followed, after a predetermined ti

Abstract: A parallel resonant circuit frequency converter having input terminals of its inverter bridged by an auxiliary commutating arrangement which consists of a bridge circuit of thyristors, the a-c outputs of which are connected to a capacitor in which thyristors of the auxiliary commutating arrangement are fired until a predetermined capacitor voltage is reached to start up the frequency converter, the thyristors of the inverter then fired until a current of predetermined magnitude flows, which is kept contant by control of the rectifier, and subsequently, the thyristors of the auxiliary commutating arrangement are fired prior to each zero crossing of the resonant circuit voltage and, the thyristors of the inverter, delayed by a constant time span, are fired until the resonant circuit voltage has reached a predetermined value.

Abstract: A parallel resonant circuit frequency converter, in which, through the resonant circuit voltage picked up by a voltage sensor and the inverter output current picked up by a current sensor, a firing instant for the inverter thyristors is determined prior to every zero crossing of the resonant circuit voltage by means of an evaluating circuit, taking into consideration the commutation and the protection time. To detect commutation short circuits, the currents of bridge arms with a common d-c terminal are measured by the current sensor and added up to an a-c current. The current sensor and the voltage sensor are followed by a monitoring device which releases a pulse if between one of the firing instants and the corresponding zero crossing of the resonant circuit voltage the inverter output current and the resonant circuit voltage remain in phase or are in phase opposition after the zero crossing.

Abstract: A method and apparatus for determining the commutating and protection time in the operation of a load controlled inverter, particularly of a parallel resonant circuit frequency converter, in which the firing instant of the thyristors prior to the zero crossing of the resonant circuit voltage is derived from the intersection point of two measured voltages, one proportional to the resonant circuit voltage and the other including the sum of two voltages, one of which leads the resonant circuit voltage by 90.degree. and is proportional to the product of the resonant circuit frequency and the first measured voltage, and the other of which is proportional to the inverter output current, permitting the current dependent commutating time along with the constant protection time to be unequivocally determined.