In this project, sensorless direct torque control (DTC) of three-phase induction motor (IM) drives based on sliding-mode (SM) and integrator backstepping nonlinear control techniques is presented. The IM drive is supplied with a two level space vector modulation (SVM) voltage source inverter. Stator and rotor flux vectors are estimated using two SM flux observers, in which simultaneous determination of rotor flux, rotor speed, and rotor time constant is achieved in one of them. Both proposed controllers are developed in the stationary frame, and ensure a high performance tracking control. A novel model-based (MB) loss minimization approach and an improved search-based (SB) efficiency optimization method are also introduced, which are combined with the motor drive controllers. Sensorless IM drive capable of very low speed operation is also presented. In this region, stator flux vector is determined using a pure integrator developed in the stationary reference frame. An improved method is introduced for offset and drift components compensation. Moreover, feasible solutions are proposed for on line stator and rotor resistances identification to ensure further improvement of drive performance at very low speeds. The proposed control idea is experimentally implemented using a CPLD board synchronized with a personal computer. Simulation and experimental results are presented to verify the effectiveness of the methods proposed. Key Words Induction Motor, Direct Torque Control, Integrator Backstepping, Sliding-Mode, Efficiency Optimization, Stator and Rotor Resistances
