M. Hutterer, M. Hofer, Th. Nenning, M. Schrödl:
"LQG Control of an Active Magnetic Bearing with a Special Method to consider the Gyroscopic Effect";
Talk: 14th International Symposium on Magnetics Bearings, Linz; 08-11-2014 - 08-14-2014; in: "Proceedings of 14th International Symposium on Magnetics Bearings", (2014), 54 - 59.

It could be very difficult to find an acceptable
feedback path for coupled differential equations like a FIVE
degree of freedom (DOF) AMB system. This paper describes
a linear quadratic Gaussian (LQG) approach on this problem.
Due to the time variant gyroscopic part of the AMB system
equation the controller could only be optimized for a specific
angular velocity. For this reason a time variant state feedback is
developed and added to the LQG controller in a way that the
system is nearly equal for all angular velocities. The feedback
matrix which is the result of the LQG problem uses all feedback
terms. Compared to a decentralized controller which only uses
the diagonal terms, the LQG method also uses the cross feedback
terms which are able to provide instability. After developing the
LQG method was compared to a decentralized PID controller.

http://publik.tuwien.ac.at/files/PubDat_230387.pdf