DETERMINATION OF CONVERTER CONTROL ALGORITHMS FOR BRUSHLESS DOUBLY-FED INDUCTION-MOTOR DRIVES USING FLOQUET AND LYAPUNOV TECHNIQUES

This paper presents a method of analyzing the stability of brushless d oubly-fed machines (BDFM) in the synchronous mode of operation. Unlike the stability analysis of conventional induction and synchronous mach ines for which the linearized state equations are time-invariant, the linearized state equations of the BDFM are time-varying and, consequen tly, their eigenvalue analysis cannot be performed directly. However, since the system matrix of the linearized equations is a periodic func tion of time, the generalized theory of Floquet can be applied to tran sform the time-varying system of equations into an equivalent set of e quations with a constant system matrix. Eigenvalue analysis can then b e employed to analyze the stability characteristics of given equilibri um points. Investigation into the stability of a proof-of-concept BDFM in the synchronous mode of operation using the transformed linearized model shows good correlation between theoretical and experimental res ults. In addition, the possibility of designing a BDFM drive with inhe rent open-loop stability over the entire speed range is demonstrated. Finally, under stable steady state synchronous operation, converter co ntrol methods are discussed and it is shown that scalar control method ologies similar to those for induction motor drives can be applied to the BDFM.