Angle-Sensorless Zero- and Low-Speed Control of Bearingless Machines

Bearingless machines are successfully used for a variety of applications that demand for low mechanical losses, low wear, and low contamination. These machines require exact knowledge of the radial and angular rotor position in order to ensure stable levitation. This information is obtained with different position sensors. Alternatively, a sensorless approach can be used to determine the rotor position. The omission of the angular sensors leads to a reduction in costs and an improvement in reliability and allows to explore new areas of applications for bearingless machines. However, few zero and low-speed sensorless angle estimators are published to this date. Therefore, a novel model-based estimator to determine the rotor angle at zero and at low speeds and, thus, to allow sensorless operation over the whole speed range of the bearingless permanent magnet synchronous machine is proposed in this paper. The observer utilizes the radial position measurements and a model of the bearing force generation to determine the error of the angular position estimation. The method is implemented on a bearingless machine prototype, and the functionality is shown by measurements.