A field-oriented induction motor drive with a nonlinear state observer

Direct field-oriented technique for high-performance control of induction motors requires the use of rotor flux magnitude and angular position. Whenever direct measure of the rotor flux is not available an observer must be included in the control loop to reconstruct the flux using available measurements, like rotor speed and stator currents and voltages. In this paper the use of a nonlinear closed-loop observer in a standard field-oriented controller is investigated As opposed to simplified linear methods, the nonlinear observer fully takes into account for the nonlinear dynamics of the induction motor, providing good performances in the whole range of machine operations. In our implementation the observer provides, as a by-product, also the estimate of the mechanical load