A Delay-Based Frequency Estimation Scheme for Speed-Sensorless Control of Induction Motors

The use of costly speed sensors challenges the overall system reliability in induction motor drives. Hence, speed-sensorless control techniques are desired in high-performance induction motors, where estimating the motor speed is of importance. Distinctive advantages, e.g., structural and control simplicity and acceptable performance, have pushed the synchronization technique (ST)-based estimation schemes popular for motor drives. However, in many ST-based schemes, their performance may be degraded during acceleration and deceleration. To address this, a delay-based frequency estimation (DFE) scheme is explored for speed-sensorless control of induction motors in this article. More specifically, speed estimation in the proposed DFE scheme is achieved by using the estimated rotor flux and its delay signals. Additionally, disturbances like dc offsets are also considered, and thus a closed-loop flux observer is implemented in the proposed DFE scheme to maintain speed estimation. The performance of the proposed DFE scheme is investigated by experimental tests.