Single-unit p.a.m. induction frequency convertors

The paper describes the application of the principle of pole-amplitude modulation (p.a.m.) to the well known induction frequency changer. By using a single secondary winding responsive to two fields simultaneously, the need for two separate machines is eliminated. The driving motor and the `excited¿ machine are combined in a single frame of conventional construction. A number of allied developments are described, including a single-unit cascade connection to give a step down in frequency, a single-unit machine with synchronous drive and a method of resistance control for variable-frequency output.