A new brushless D-C excited rotating field synchronous motor

SILICON RECTIFIERS have been used for several years to make brushless d-c excited rotating field synchronous generators.1 The induced field current and voltage during starting have made similar brushless synchronous motors impractical. This paper describes the operation and performance of a new brushless synchronous motor which has been made practical by the development of high-current silicon-controlled rectifiers.2 All sliding- and mechanical-type contacts have been eliminated. The synchronizing function and pull-out protection are automatically provided by a simple static circuit which uses two silicon-controlled rectifiers and Zener diodes. The new motor can be started like a squirrel-cage induction motor with a standard full or reduced voltage starter. The adjustable power factor correction of the conventional synchronous motor is retained.