Diode-assisted commutation

Abstract

The use of diodes to assist commutation in d.c. machines is not new, and the basic principles were described as long as 40 years ago. However, attempts to construct such machines have always suffered from problems of current collection from a surface consisting of alternate active and inactive segments. Thyristorassisted commutation was introduced a few years ago as a means of avoiding the major surface-damage problem. Diode-assisted commutation is very much simpler, however, and the letter describes how recent work using carbon-fibre brushes has now largely overcome the particular contact problems of the diodecommutated machine.