Abstract: A self-excited induction motor variable speed drive using a known self-excitation method in which a capacitor is connected in parallel with the motor. Power is supplied by a supply convertor, a D.C. link and a motor convertor, the latter running at the motor frequency. The motor convertor includes a current bypass switching circuit comprising a capacitor bank connected to the motor terminals and to a neutral point between a pair of thyristors connected across the D.C. link.

Abstract: A rectifier system in which the harmonic content of the A.C. current is reduced in a particularly efficient manner. Two or more 3-phase thyristor bridges are connected in parallel to the A.C. supply, and to the DC output by way of interphase-transformers. For the positive thyristors, and for the negative thyristors separately, the conduction transitions within each bridge are staggered from one bridge to the next so that the total conduction on each phase follows a stepped characteristic approaching a sine wave and thus having a smaller harmonic content than a comparable arrangement having uniform firing angles from bridge to bridge.