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Doubly-fed cascade-connected induction machines (CCIMs), whether mounted in a single frame or otherwise, are capable of developing useful torque as brushless synchronous machines over a wide speed range. Such machines exhibit instability within certain regions of operation and may be insufficiently damped within others. This paper presents some of the loci of the dominant eigenvalues of the system equations plotted as functions of the values of various design parameters of the machines. It is shown that, by appropriate design, certain areas of instability may be reduced or removed and the response improved, but that it is not possible, by design changes alone, to remove all such unstable areas, nor can the response be improved in all areas simultaneously.
Date of Publication: March 1983