On‐line tuning of the rotor resistance in an inverter‐fed induction machine with direct‐self‐control

Abstract

AbstractThis paper describes a simple adaptive torque‐balancing controller/or on‐line tuning the rotor‐temperature dependent rotor resistance in an inverter‐fed induction machine. The identification has been especially designed for use in drives with Direct‐Self‐Control. The basic version works well down to stator frequencies of a few Hz, even under transient conditions and without stator voltage sensors, but only with a DC‐link voltage sensor. It is shown that the basic version can be enhanced to work properly not only at locked rotor but even at stationary zero stator frequency except for no‐load operation. Then the information for tuning the rotor resistance at zero or very low stator frequencies is obtained by low‐frequency modulation of the stator flux magnitude and observation of the torque of a parameter‐sensitive observer concerning modulation frequency related oscillations, which occur only in the case of a mismatched rotor‐resistance parameter. The parameter is tuned via a simple l‐controller until the oscillations vanish. Experimental tests at a standard 66‐kW squirrel‐cage motor prove the excellent performance of the proposed method.