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 (DFO) 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 (SMVMFO) 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. Simulation and experimental results are also used to illustrate features of the proposed observer.