Sensorless Speed and Vector Control of Induction Motor Based on Rotor Slot Harmonics

The paper presents the design of an induction motor speed estimator based on rotor slot harmonics with the focus placed on analyzing its integration within the current and speed control loops. The PLL based estimator consists of the digital adaptive filters and the information is obtained on a sample-by-sample basis at 50 kHz rate. The estimator parameters design is based on the control loop requirements. The main advantages of the presented structure are the transport delay of 10 ms and steady state error below 0.12%. The estimators' outputs are used as a feedback signal for the speed and vector control, as a replacement for typically used rotor position sensors. The experimental results demonstrate the speed and vector sensor-less closed-loop operation on three-phase 2.2 kW induction motor, with 15 Hz speed closed-loop bandwidth. The operation is demonstrated in a wide speed range of the motor, including very low speeds.