Improved Sensorless Control of a Modular Three Phase Radial Active Magnetic Bearing

This paper discusses new results and improvements on the sensorless control of a permanent magnet biased three phase radial active magnetic bearing (AMB), which are also known as hybrid magnetic bearings (HMB). Self-sensing methods offer cost potentials because of a more simple bearing system architecture, but show lower performance in accuracy and bandwidth compared to external position sensors. Thus, making selfsensing technologies competitive to systems with position sensors is a broad field of research and as well a goal of this paper. The proposed sensorless method is based on inductance measurement by voltage pulse injection. Applying an oversampling strategy for current slope measurement reduces the noise of the sensorless obtained rotor position significantly. Timing limitations and operational bandwidth can be improved by utilizing alternative voltage pulse sequences. Further, variations of the permanent magnet bias flux of the HMB prototype are investigated to show the influences on the sensorless rotor position detection method and limitations for applications.