Armature current locus based estimation method of rotor position of permanent magnet synchronous motor without mechanical sensor

This paper describes a new method of estimating the initial rotor position of a permanent magnet (PM) motor without turning the rotor. At the stand still, the saliency of the PM motor makes the locus of the armature current-vector an oval when the armature voltage is a 3-phase balanced sine wave applied by a PWM inverter. The major diameter direction of the current-vector locus gives information on the rotor direction. The shift of the current-vector locus caused by magnetic saturation makes it possible to identify the direction of the rotor magnet N-pole. The proposed method to estimate the rotor position was verified by experimental results of a 100 W PM motor.