Doubly fed operation of cascade-connected machines

A doubly fed cascade-connected machine system may operate either synchronously or asynchronously. The analysis of both modes of operation is considered, and the corresponding equivalent circuits are shown. Use is made of the basic underlying principles of this type of system to develop a practicable stator-fed synchronous machine. The problem of the steady-state stability of this machine is discussed, and simple methods of achieving stable operation are described.