Self-cascaded machine: a low-speed motor or high-frequency brushless alternator

The self-cascaded machine is a single-unit version of two separate induction machines connected in cascade. In construction, however, it closely resembles a conventional induction motor. It may be run asynchronously, with resistance control if required, or synchronously without any external connections to the rotor winding. As a motor it is particularly suited to low-speed duties. With its simple and robust form of rotor construction, and the absence of slip rings or rotating diodes, it is also ideally suited for operation at high speeds as a high-frequency brushless alternator. A general description of the machine, and the underlying principles involved, are presented. A theoretical treatment is included based on doubly stator-fed operation of the machine. General performance equations are derived, and equivalent static networks are obtained for steady-state operating conditions.