Simultaneous estimation of speed and rotor resistance in sensorless ISFOC induction motor drive based on MRAS Scheme

Usually the estimation of speed is achieved by assuming that the rotor resistance is constant throughout the operating range. In practice, the variation of this resistance depends on the temperature inside the machine. This paper proposes a simultaneous rotor speed and rotor resistance estimation method for a conventional indirect stator flux oriented controlled (ISFOC) induction motor drive. In order to estimate the both parameters, an adaptation algorithm based on the model reference adaptive system (MRAS) scheme for tuning the rotor speed and the rotor resistance is proposed. The reference and adjustable models, developed in stationary stator reference frame, are used in the MRAS scheme to estimate rotor speed and rotor resistance from measured terminal voltages and currents. The Integral-Proportional (IP) speed controller and Proportional-Integral (PI) current controller gains are calculated and tuned at each sampling time according to the new simultaneous estimation. A 3-phase induction motor has been used to verify the accuracy and feasibility of the proposed method. Simulation results show that the proposed method gives accurate estimations of simultaneous rotor speed and rotor resistance for a reference speed of the induction motor drive with nominal load torque is applied.