High speed flexible rotor active magnetic bearing control
Abstract
The School of Electrical, Electronic and Computer Engineering at the North-West University is in the
process of establishing a knowledge base on Active Magnetic Bearings (AMBs). In support of this
initiative this project is aimed at characterising an in-house developed double radial heteropolar AMB
system.
Before characterising the AMB system the acoustic noise problem of the system had to be addressed and
reduced to an acceptable level. To reduce the acoustic noise of the system a noise analysis was done to
determine the source of the noise. The analysis revealed radiated noise from the electromagnets and
power amplifiers (PA) and conducted noise on the signals to and from the controller. The conducted noise
is reduced by using anti-aliasing (AAF) and anti-imaging filters (AIF) before and after the controller. The
effect of the radiated noise is reduced by synchronising the sampling of the sensor signals with the
switching of the PAS.
The characterisation of the AMB system starts with a Mass-Spring-Damper (MSD) simulation which is
a linear representation of the AMB system. This simulation is used to understand the basic principles of a
second order system and to compare its response to the nonlinear AMB simulation. The following step in
characterising the AMB system is to determine the effect of filters on the nonlinear AMB simulation and
to determine the simulation characteristics. These characteristics are compared to the MSD simulation
and the actual AMB system. The characteristics compared between the MSD and AMB simulations are
the static, second order and dynamic stiffness.
The actual AMB system was characterised before and after the AAF and AIF were implemented. This
provided the opportunity to determine the effects of the filters on the actual system and not just from
simulations. The characteristics measured on the actual AMB system include the static stiffness, dynamic
stiffness, rotor dynamics and system sensitivity. The stiffness characteristics of the actual AMB system
showed good correlation with the linear and nonlinear simulations. The measured results showed a
decrease in static stiffness and an increase in system sensitivity because of the AAF, AIF and controller
pole. It also showed that the effects of the filters can be reduced by moving the controller pole to a higher
frequency.
The characterisation of the double radial heteropolar AMB system provides a fundamental understanding
of the AMB performance aiding the AMB design process.
Collections
- Engineering [1403]