Thyristor-assisted commutation in electrical machines

The paper describes how a small number of thyristors can be used to overcome the physical limitations on d.c.-machine output that are due to commutation. The principle on which the proposed scheme is based is a division of the switching action of a conventional commutator into two parts, an entirely off-load switching by a sliding contact, and a complementary and synchronised on-load switching by two pairs of thyristors. This is only possible in practice if the number of segments on the commutator is small, and the paper looks at the effect of this limitation on machine performance. A description of some prototype machines is included.