Zero frequency rotor position detection for synchronous PM motors

The paper presents a simple but effective approach to determine the position of the rotor in synchronous PM machines at any operating condition, including very low and zero speed. The proposed approach is based on the addition of a high frequency stator voltage component and on a demodulation of the zero sequence voltage. Compared to previous sensorless schemes, it allows zero speed operations, does not need any initial identification of the rotor position, and can be inexpensively implemented. Experimental tests are shown in order to practically confirm the expected features of the proposed system.