Sensorless position estimation at low speeds till standstill with reduced filtering requirements for an externally exited synchronous machine

This paper presents a method for sensorless position estimation at low speeds till standstill for an externally exited synchronous machine. The switching of the buck converter, that drives the rotor circuit is used as carrier signal. Normally the stator current controller reduces the signal that is used for the position estimation and so a filter in the current feedback is needed. A method to use the switching of the rotor buck converter as carrier signal without a filter in the stator current feedback is presented.