GB1188017A - Semiconductor Current Converter. - Google Patents

Abstract

1,188,017. Converting. LICENTIA PATENT-VERWALTUNGS G.m.b.H. 21 Nov., 1967 [23 Nov., 1966], No. 52830/67. Heading H2F. Current conductors in an electric current converter are formed into groups of parallel bars such that the sum of the instantaneous current of the bars of each group is zero or a constant value. This prevents incorrect operation due to magnetic fields and reduces eddy current losses. In Fig. 3 a three-phase supply is converted to D.C. (by 11, 12) which is in turn converted by a thyristor bridge 16-19 to single-phase A.C. of frequency substantially above 50 Hertz. Considering one half cycle, current flows from choke 13, through a commutating choke 20 into the central conductor of group 17. From there it flows into the left-hand bar of group 16 through the parallel rectifiers to the right-hand bar and thus to lower terminal of the load. From the upper terminal of the load it continues downwards through the centre bar of 16 through thyristors between the outer bars of 17 back to the supply. In groups 16, for example, the current in the left-hand bar decreases stepwise at each thyristor but correspondingly increases stepwise in the right-hand bar. Thus the sum of the currents in these bars is constant and is equal and opposite to that in the central bar. In addition the current path lengths are equal. Accordingly the magnetic fields substantially cancel. Similar cancellation takes place in each arm and likewise in the bridge arrangement 24 of reactive current diodes, and between the centre and two outer bars of group 23 which connect rectifiers in parallel across choke 13 and in the two intermediate supply bars 22 and 23. The inductor 13, resistor 14 and ignition 15 are protective and smoothing devices. In Fig. 3 (not shown) the outer bars are of channel shape and a flat inner conductor 4 is sandwiched between them. The outer conductors may be hollow to carry cooling fluid.