An implicit sensorless position/speed estimator for the speed control of a Doubly Fed Induction motor

This paper proposes an implicit sensorless position estimator for the accurate estimation of rotor position and speed for the decoupled control of a Doubly-Fed Induction Machine (DFIM). Here the rotor position is estimated in a straight forward and implicit manner without the need for computing or estimating the stator flux. In particular the rotor current components in the stationary reference frame are computed using measured stator quantities. Instead of computing the stator magnetic flux directly or indirectly, the stator flux vector components in the stationary reference frame are substituted with analytical equivalents in terms of measurable stator and rotor quantities. Although it is an open loop technique, it does not involve the voltage integration, recursive or inverse trigonometric computations in real time. Starting on the fly, accurate estimation near and through the synchronous speed, immunity against fluctuations in the grid voltage and frequency are the other advantages of the algorithm.