Brushless D-C excited synchronous motor

SILICON RECTIFIERS have been used for several years to make brushless d-c excited rotating-field synchronous generators. The induced field current and voltage during starting have made similar brushless synchronous motors impractical. The operation and performance of a new brushless synchronous motor, made practical by the development of high-current silicon-controlled rectifiers, are described here. 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.