Direct Field Oriented Control of Induction Motor without Speed Sensors using Adaptive Flux Observer

The field oriented control method is widely used for induction motor drives. In these applications, a speed sensor such as a shaft encoder is used. However, a speed sensor cannot be mounted in some cases such as motor drives in a hostile environment and high speed motor drives. Several field oriented control methods without speed sensors have been proposed. Most of them can be applied to only the indirect field oriented control but the direct field oriented control. And a stability has not been explained clearly.Therefore, a new method of estimating the induction motor speed based on the adaptive control theory is proposed. Characteristics of the direct field oriented control system with the proposed speed estimation scheme are verified by experiments. Further, the influence of the stator and rotor resistance variations on the speed estimation is analyzed, and its compensation method is also proposed.