This book provides a theoretical treatment of the operation, and the excitation systems, of “asynchronized” synchronized (AS) machines — that is, ac motors and generators which have their excitation supplied by an independent slip-frequency source. Such devices are usually called “doubly fed” machines in American practice. Almost the entire book is devoted to the development and analysis of the d and q axes equations of the machine, and consideration of the excitation requirements — including the power that must be supplied by the excitation system.