Insights on Observability and Identifiability Properties of Induction Motors at Steady-State

It has been recently shown in the literature that there exists a local solution to the problem of observing induction motor fluxes and identifying constant load torque and rotor/stator resistances from stator currents/voltages and rotor speed measurements. The corresponding adaptive observer is characterized by persistency of excitation conditions which are guaranteed to be satisfied in the typical case of constant motor speed and flux modulus and non-zero electro-magnetic torque and by sufficient stator resistance identifiability conditions at steady-state. The aim of this paper is to provide an elegant observability/identifiability analysis which interprets those requirements and clearly confirms that, under those conditions, the rotor fluxes and the three critical parameters can be actually (locally) reconstructed from the output measurements.