Advantages and limitations of the NFO control algorithm

Natural field orientation (NFO) control technique was introduced and patented in 1980s as an alternative low cost control technique for induction motors. It offered some attractive features, including simplicity of control and low sensitivity to the stator resistance error. Some stability issues in regeneration have also been reported. This paper summarises the authors´ experience with the NFO control technique gained from a recent research project. It explains how NFO is different from other control techniques, presents stabilisation strategy proposed by the authors and results of stability analysis. It then explores fundamental limitations of the NFO control and summarises the authors´ views on the NFO control properties and application prospects. The main findings of the paper are illustrated by simulation and experimental results.