Application of nonlinear observers for rotor position detection on an induction motor using machine voltages and currents

The principles and operation of a unique, terminal properties-based speed and position sensing approach for induction machines are demonstrated. A closed-loop nonlinear observer is proposed which uses an analytical model to calculate, in real time, the mechanical states of rotor speed and position given the torque command to the system and the induction motor terminal voltages and line currents. The uniqueness of this observer is that it uses inherent machine magnetic saliency and winding asymmetry to develop a magnetic encoder model of the machine itself. The error between the measured and calculated spatial harmonic EMFs is then used to drive the observer to accurate position and speed estimates in the presence of model parameter errors. Experimental data are included which show harmonic flux terms identified, measured and compared with an analytical model using a slip-ring induction motor with the rotor windings open and short circuited.>