8.1 Preliminary Remarks
Sensorless speed control of induction machine (IM) drives has, in the past decade, become a mature technology for a wide speed range [1–3].
The elimination of the rotor speed sensor, without affecting performance, is a major trend in advanced drives control systems . The advantages of speed sensorless AC drives are reduced hardware complexity, lower costs, elimination of the sensor cable, better noise immunity, increased reliability, access to both sides of the shaft, less maintenance requirements, and higher robustness. An encoder is expensive and a problematic factor. The special motor shaft extension increases the drive's price. The use of encoders affects the reliability, particularly in hostile environments. In general, the operation in explosive, corrosive, or chemically aggressive environments requires a motor without a speed sensor.
A variety of different solutions for sensorless AC drives have been proposed, mostly in the past two decades. Their advantages and limits are reviewed in many survey papers [1–60].
Many methods are generally accepted as better solutions for high sensorless performance, for example, model reference adaptive system (MRAS), Kalman Filters, adaptive non-linear flux observer, sliding mode observers, and other improvements [7–14].