In this paper it is shown that the phase self inductance and resistance, both measured at a high frequency, of a permanent magnet (PM) motor with non-salient rotor vary slightly with the rotor position. The origin of these variations is deeply investigated, taking into account typical physical phenomena present in PM motor. Surprisingly, no classical approach can explain these variations. The physical explication is found in the non-linearity of the iron magnetization B-H curve, and more accurately in the local B-H hysteresis loops. In order to exploit these small variations for the rotor position detection, a simple measurement technique is presented.