Speed-Adaptive Observer Design for Sensorless Induction Motor Drives in Ultra-Low Speed Region With Graphical Method

In the traditional speed adaptive full-order observers of induction motor (IM), since the actual value of rotor flux is unattainable, the flux error term is usually ignored in the speed adaptive law. This would cause instability at low-speed during regenerating load. To mitigate this issue, an improved speed adaptive law strategy is proposed by introducing the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</i>-axis current error term. Compared with the conventional speed adaptive law, the studied method maintains stability across the wide speed range based on the Routh–Hurwitz stability criterion. Notably, the studied method necessitates only a single parameter design, enhancing its practical applicability. Furthermore, the formula of the improved speed adaptive law is solely dependent on the motor inductance parameter. Consequently, even with variations in inductance, it can still retain its stable operation area. Experimental results from a 2.2 kW IM platform validate the effectiveness of the studied method.