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F. Demmelmayr:
"Comparison of PM-machines With Ferrite and NdFeB Magnets in Terms of Machine Performance and Sensorless Start-up Control";
Vortrag: IEEE Industrial Electronics Society, Cape Down, South Africa; 25.02.2013 - 27.02.2013; in: "Proceedings IEEE Industrial Electronics Society International Conference on Industrial Technology", (2013), S. 1 - 6.

The costs of rare-earth permanent magnets such
as NdFeB increased rapidly in the last few years. Therefore,
great attention is paid for alternative magnet materials. This
paper compares two permanent magnet synchronous machines
using external rotors with different magnet materials - one with
NdFeB and the other with much cheaper ferrite magnets. The first
section examines the risk of irreversible demagnetization of the
ferrite magnets at inappropriate operating points. Furthermore,
measurements and some numerical-simulation results contrast
characteristics of the machines in terms of no-load voltage, short-
circuit behavior, torque output and efficiency.
Different magnet materials influence position-sensorless tech-
niques based on anisotropic effects especially for start-up control.
The last part of this study compares two methods to estimate
the absolute electrical rotor position at standstill. Reliability
considerations show their quality at the respective machine.

http://publik.tuwien.ac.at/files/PubDat_217334.pdf