An electric motor system that comprises a motor that comprises a rotor having a magnet mounted thereto and a stator that comprises one or more motor phase windings for driving rotation of the rotor when the motor phase windings receive an input voltage from an electrical power supply. The system has a controller that executes a back “EMF” observer that is operable to estimate a rotor angle by observing a back electromotive force induced in the stator by the rotor. Filtering is applied to the back EMF signal to reduce harmonics prior to determining the rotor angle.