Design and analysis of general rotor-flux-oriented vector control systems

Reduced-order observers for rotor flux estimation of induction motors are considered. The "current" model and "voltage" model are obtained as special cases. It is shown that the flux dynamics form a nonlinear closed-loop system when the flux estimate is used for field orientation. The observer gain selection is extremely critical for good behavior of this system. A framework is developed, in which the properties of any gain selection can easily be assessed. Four candidate gain selections are considered, two of which yield schemes that do not use the rotor speed in their equations (inherently sensorless schemes). It is also shown that for any gain selection, an equivalent synchronous-frame implementation (i.e., indirect field orientation) always exists.