Position sensing of permanent magnet machine position sensorless drive at high speed with low sample over rotor operating frequency ratio

This paper improves the permanent magnet (PM) machine position sensorless drive specifically for high speed operation. To obtain the rotor position, an approximation is typically assumed on the position estimator where the estimated position is almost equal to the actual position per sample instant. This small signal approximation might not be valid at high speed when the ratio of sampling frequency over the rotor operating frequency is lower than 10. In this paper, the limitation of EMF-based sensorless drive at high speed is analyzed. By modifying the position estimator without the small signal approximation, it is shown that the drive can improve to operate at the speed of 30-krpm with only five sampling points per electrical cycle (fsample/fe=5). A PM machine is experimentally evaluated to verify the proposed estimation method.