Effect of Stator and Rotor Saturation on Sensorless Rotor Position Detection

This paper investigates the impact of the geometry of a permanent-magnet (PM) motor on the capability to detect the rotor position without sensors by means of a high-frequency signal injection. An interior PM motor with three rotor flux barriers is considered, which is characterized by a magnetic saliency, necessary for the sensorless rotor position detection. The objective is twofold: 1) to keep an adequate saliency in all the operating range of the motor, including operations at high current, and 2) to limit the angular error of the rotor detection, which is due to the effect of the cross-saturation between the d- and the q-axes. The phenomenon of iron saturation is deeply analyzed, highlighting how the saturation of both the stator and rotor affects the machine performance, in terms of sensorless rotor position detection capability. To this purpose, the motor geometry is modified so as to achieve a higher iron saturation in the stator and, then, in the rotor. Then, the volume of the PM is changed so as to emphasize the impact of the PM flux. Different rotor geometries are finally compared with the initial one.