The stability analysis for the control strategy of a rotor-transformed brushless doubly-fed induction motor

This paper presents a method of analyzing the stability of brushless doubly-fed motors (BDFIM) in the synchronous mode of operation based on transformed rotor model. Unlike the stability analysis of conventional induction and synchronous motors for which the linearized state equations are time-invariant, the linearized state equations of the BDFIM are time-varying and, consequently, their eigenvalue analysis cannot be performed directly. However, since the system matrix of the linearized equations is a periodic function of time, the generalized theory of Floquet can be applied to transform the time-varying system of equations into an equivalent set of equations with a constant system matrix. Eigenvalue analysis can then be employed to analyze the stability characteristics of given equilibrium points.