Sensorless control of AC motor — Where are we now?

In the AC machine drives, the rotor position information is the crucial information for high performance drive system. There have been more than 30 years of researches to get the rotor position information without explicit position sensors such as encoders and resolvers. Some research results are commercialized and applied to industrial field. However, still the performance of sensorless drive is limited. In this paper, the overview of the sensorless drive techniques, especially regarding Interior Permanent Magnet Synchronous Machine (IPMSM), are described. Some research topics for future study are suggested.