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M. Hofer, Th. Nenning, M. Hutterer, M. Schrödl:
"Current Slope Measurement Strategies for Sensorless Control of a Three Phase Radial Active Magnetic Bearing";
Talk: MagLev 2014, Rio de Janeiro (Brazil); 2014-09-28 - 2014-10-01; in: "Proceedings of The 22nd International Conference on Magnetic Levitated Systems and Linear Drives", (2014), 1 - 14.

This paper discusses the sensorless control of a three phase radial active magnetic bearing (AMB).
Self-sensing or sensorless methods mean, that the electromagnetic actuator itself is used as position sensor
too and the rotor position information is evaluated by electrical quantities as currents and voltages.
Thus, external rotor position sensors can be omitted and allow a simpli cation of magnetic bearing
system architectures. Since many years [7, 11] sensorless AMBs are eld of research to reach performance
parameters as bearing systems with position sensor do have. The proposed self-sensing method
is based on inductance measurement by current slope detection during voltage pulse injection or integrated
in the Pulse Width Modulation (PWM) pattern applied to three phase radial AMBs. Di erent
electrical current slope measurement strategies are investigated regarding self-sensing performance and
accuracy. Two di erent three phase AMB prototype setups are explained and used for experiments.
The measurement results show improvements by di erent current slope detection strategies. Finally
some examples of the behavior during sensorless levitation in a closed loop position control represent
the potential of self-sensing three phase AMBs to industrial applications.

http://publik.tuwien.ac.at/files/PubDat_235823.pdf