Very low speed sensorless variable structure control of induction machine drives without signal injection

A variable structure, direct torque controlled, sensorless induction machine drive is presented, in which the principles of Direct Torque Control (DTC), Variable Structure Control, and Space Vector Pulse Width Modulation are combined to ensure high-performance operation, both in the steady state and under transient conditions. The classical DTC transient merits are preserved, while the steady-state behavior is significantly Improved. The full-order Sliding Mode Observer does not require speed information and provides accurate state estimation in wide speed range. The proposed scheme is a complete Variable Structure solution that allows sensorless operation of the drive at very low speeds, including zero and three rpm, full load. Simulations and extensive experimental results confirm the robustness, accuracy, quickness, and low-chattering operation of the drive.