A Unified and Enhanced Hybrid Flux Observer for Encoderless Control of AC Motors

In recent decades, the application of encoderless techniques for ac motor drives has continuously expanded. However, encoderless control strategy, which achieves wide speed operation with good robustness against converter nonlinearity is highly desirable, yet is lacking. In this work we propose a unified hybrid observer-based encoderless control strategy which is effective to various types of ac motors, achieving wide-speed-range operation requiring no encoder. To mitigate the converter nonlinearity voltage effect, a straightforward adaptive law is introduced. The effectiveness of this approach has been validated by experimental results. In particular, reliable performance with a converter dead-time of 3.2 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${\boldsymbol{\mu}}$</tex-math></inline-formula>s and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${\boldsymbol{\pm}}$</tex-math></inline-formula>50% stator resistance mismatch can be guaranteed.