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A. Schulz, M. Schneeberger, J. Wassermann:
"A Reliable Switching Amplifier driving an Active Magnetic Bearing - Experimental Results";
Talk: IEEE International Conference on Industrial Technology (ICIT2005), Hong Kong; 2005-12-14 - 2005-12-17; in: "Proc. of 2005 IEEE Int. Conf. on Industrial Technology", (2005), ISBN: 0-7803-9484-4; 6 pages.

Active magnetic bearings (AMBs) offer some advantages
over conventional bearings (contact-free suspension,
variation of suspension parameters like stiffness and damping
during operation, etc.). A lower reliability caused by a fairly
complex assembly of the controller, sensors, electromagnets and
amplifiers, however, is one major reason for the rather low
industrial acceptance of AMBs.
Based on a study on failures in AMB-suspended turbomachines
a concept for an AMB with high reliability has been developed by
the authors, providing a spatial and galvanic isolation between the
controller and the power elements along with a reliable switching
amplifier (RSA), implemented in a modular redundant way.
Depending on the required reliability, a RSA consists of two or
more left and right hand switching amplifier half-bridges. These
so called "Hot-Swap Modules" (HSMs) are connected in parallel,
each with its own error detection and decoupling circuitry. If
an error occurs in a HSM, it is autonomously switched off and
disconnected from the AMB-electromagnets, while the remaining,
fully functioning HSMs take over the required current. The faulty
HSM can be replaced by a functioning one during full operation
of the AMB in a hot-swap procedure.
In this paper the AMB test rig and measurement results
of the complete laboratory version of the RSA during induced
component errors and the hot-swap of a HSM are presented.
Severe half-bridge component errors (IGBT short circuit, open
circuit of a free-wheeling diode) were induced for demonstration
purposes, normally causing a breakdown of the complete AMB
when conventional switching amplifiers are used. An analysis of
the RSA output currents of this new concept shows, that there
nevertheless remains an undisturbed bearing functionality despite
of these manually induced errors.

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