A back-electromotive force (back-EMF) based sensorless technique for surface-mounted permanent magnet synchronous motor (SPMSM) drive systems is considered in this paper. The model of the observer is developed in the Laplace domain and represents an original approach with respect to state-of-art proposals, normally employing a state-state representation. This allows a more intuitive but equivalent design of the observer's gains, based on the standard frequency response, as compared to eigenvalues analysis. Moreover steady-state errors are obtained from a theoretical point-of-view, including the effects of the most common non-idealities affecting the drive system (e.g. offsets) and parameters sensitivity. Full simulation and experimental characterization of the sensor-less drive is provided with reference to a general purpose industrial drive, i.e. both in transient and steady-state conditions and in the whole speed/torque operating range.
