Passivity properties of induction motors: application to flux observer design

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Abstract
The energy balance equation of the induction motor model is used to establish some passivity properties. The properties are independent of the representation reference frame, and thus can be used to analyze in a unified manner the various control and observation strategies reported in the literature, a task which typically relies strongly on the chosen coordinates. It is shown that the slip frequency control variable does not affect the motor energy balance equation. This fact clarifies, to some extent, the stable behavior of field-oriented control schemes. A general framework is presented for observer design and the derivation of a globally exponentially stable nonlinear flux observer for an induction motor model that includes mechanical and electrical dynamics.