Design and Low-Cost Implementation of an Optimally Robust Reduced-Order Rotor Flux Observer for Induction Motor Control

The aim of this paper is to design and analyze reduced order observers of the rotor flux of induction motors. The design is carried out in two steps. In the first step a boundary of the stability region of the observation error is obtained corresponding to a chosen Lyapunov function. In the second step the boundary is translated into a performance index which is minimized with respect to stator and rotor resistance variations and differences of voltages supplying the motor and those supplying the observer, in order to obtain the largest stability region. Implementation of the observer on a low cost fixed point DSP using look-up tables is described. Experimental results are shown with reference to a prototype consisting of a simple PI controller, the proposed observer and a 2.2 kW induction motor; the implementation of both the controller and the observer are carried out on a DS1104 dSpace microcontroller using the fixed point option.