Elimination of the stator resistance sensitivity and voltage sensor requirement problems for DFO control of an induction Machine

This paper focuses on a method for achieving robust direct field orientation control of an induction machine using a closed-loop voltage model flux observer that is insensitive to stator resistance variation and does not require voltage signal information, thereby eliminating the need for a voltage sensor. In contrast, the conventional voltage model observer topology requires voltage sensors and is highly sensitive to stator resistance variation, especially at low speed. The closed-loop sliding-mode voltage model flux observer presented here is based on current estimation error including a sliding-mode function which is a derivative of the stator flux. The newly designed sliding-mode function will not only drive the estimated current to the measured one, it will also directly give the estimation results for the terms (stator flux) replaced by the sliding-mode function. The constructed observer and chosen sliding-mode function also do not require information about parameters contained in the terms replaced by the sliding-mode function, i.e., voltage signal and stator resistance. The observer stability is verified in the paper. Simulation and experimental results are also used to illustrate features of the proposed observer.