Stability and stabilisation of doubly-fed single-frame cascade induction machines

This paper presents a theoretical and experimental study of the dynamic performance of a doubly-fed single-frame cascade induction machine which can operate synchronously from rest over a wide speed range. The dynamic electromechanical-system equations are developed and theoretical performance boundaries for stable operation are found and compared with experimental results. The nature of its instability and an easily implemented feedback control which stabilises its operation are both described. It is shown that the machine can be operated as a stable variable-speed brushless machine with controllable dynamic response. Its mechanical construction is potentially only a little more complicated than that of a squirrel-cage induction machine.