A. Eilenberger, E. Schmidt, M. Schrödl:
"Sensorless Capability of Permanent Magnet Synchronous Machines Due To Saturation-And Reluctance-Based Coupling Effects";
Talk: IEEE International Symposium on Sensorless Control for Electrical Drives, Padova, Italy; 07-09-2010 - 07-10-2010; in: "Proceeding of IEEE International Symposium on Sensorless Control for Electrical Drives", (2010), 1 - 4.

The paper shows the theoretical derivation of sensorless
capability of a permanent magnet synchronous machine
due to saturation- and/or reluctance-based coupling effects. Only
due to an introduction of coupling terms in the rotor-oriented
inductance tensor a dependency of double the electrical rotor
position can be calculated.

http://publik.tuwien.ac.at/files/PubDat_186962.pdf