A new current model flux observer insensitive to rotor time constant and rotor speed for DFO control of induction machine

Direct Field Orientation (DFO) control for an induction machine is designed and implemented using a new sliding mode technique based current model flux observer. A close loop flux observer, based on the current estimate error is constructed. The flux and current observers include a sliding function, which is derivative of the flux. Therefore, when the estimated current converges to the measured one, the sliding function itself is integrated to calculate the flux magnitude and angle. The flux angle is then used for the DFO control. The flux observer in this technique does not require any knowledge of the rotor time constant and the machine speed because both are included in the sliding mode function, thus making the proposed observer completely insensitive to any error in the rotor time constant or the machine speed information. Simulation and experimental results are presented to show the performance of the proposed observer for the DFO control of an induction motor drive system.