Two simple flux observers for induction motors

The induction motor has very good qualities-reliability, ruggedness, relati vely low cost, etc., for industrial applications. The reason for this is th at there is no mechanical commutation: the rotor consists simply of closed windings in which currents are induced by a rotating magnetic field set up by the stator, hence creating a torque. But the control of the induction mo tor is not so easy, mainly because of the three following points: the model is rather non-linear, some variables (in particular, the magnetic fluxes, or equivalently, the rotor currents) cannot easily be measured, and some pa rameters (rotor resistance, load torque, inertia) vary a lot in operation. This has motivated a growing literature in the control community. We propose here two simple Aux observers assuming that the rotor velocity a nd the stator currents are measured: the first observer makes use of a natu ral "passivity" property (in fact, it requires only velocity measurements); the second observer [1] relies on a "reparametrization of time" and can be rendered as fast as desired. It is worth mentioning that all the computations are straightforward mainly because they are carried out using the complex variable notation (time-var ying phasor) model of the induction motor. Copyright (C) 2000 John Wiley & Sons, Ltd.