A SIMPLE AND ROBUST ADAPTIVE CONTROLLER FOR DETUNING CORRECTION IN FIELD-ORIENTED INDUCTION MACHINES

This work presents a novel adaptive controller for correcting the rotor time constant estimate used in the slip frequency calculator of indirect field-oriented controllers (IFOC's). The controller is novel in that it possess near digital deadbeat performance and simultaneously maintains its correctness down to zero speed. The robust controller dynamics are based on an operating-point form of digital deadbeat control. In this controller, an operating-point approximate inverse model relates changes in the machine parameters to deviation in the rotor flux components. This allows nearly exact, one-step (deadbeat) prediction of the correction necessary for the slip calculator gain. The correctness down to zero rotor speed is based on the determination of the rotor flux from an accurate air-gap flux estimate obtained from the third harmonic stator phase voltage component introduced by the saturation of the machine stator teeth. Moreover, a function relating the amplitude of the third harmonic air-gap flux component with the value of the magnetizing inductance allows correction of this machine parameter for different flux levels. The proposed adaptive controller is implemented in a digital signal processor, and the experimental results demonstrate its excellent performance for a wide range of rotor speeds, including locked rotor conditions.