Maximum torque per ampere control of induction motor drive without mechanical sensor

In this paper, the direct rotor flux field orientation control of speed sensorless induction motor (IM) is presented. In proposed control scheme, the maximum torque per ampere (MTPA) control strategy is achieved using a so-called fast flux search method. Based on this method, for a given load torque and rotor speed, the magnitude of rotor reference flux is adjusted step by step until the effective value (RMS) of stator current becomes minimized finally. In addition, using the IM fifth order model in the stationary reference frame, a nonlinear rotor flux observer is developed which is capable of motor resistances and rotor speed simultaneously estimation. Moreover, a useful method is introduced for DC offset compensation which is a major problem of AC drives especially at low speeds. Simulation and experimental results are presented to confirm the effectiveness of the proposed method.