Sinusoidal surface-mounted pm machine drive using a minimal resolution position encoder

This paper presents a high resolution position estimation system for sinusoidal surface PM machines based on a vector-tracking observer and a 90° resolution encoder. It is shown here that this is the minimum amount of resolution needed for sinusoidal PM drives. The key implementation issues of this system are presented, and stability analysis is performed, leading to the definition of local stability limits, within which the actual position is tracked with bounded estimation error. The effect that non-uniform sector widths have on position estimation is also explored and a straightforward compensation method is proposed. Both simulation and experimental testing illustrate the performance and limitations of the proposed observer topology and of the drive when this observer is used for state feedback.