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37
5.1.7 Magnetic Levitation Module (MLM)
The Magnetic Levitation Module provides control of the active magnetic levitation hardware.
The Liebert FS has a unique active magnetic levitation system that fully levitates the flywheel-rotat-
ing group, allowing the flywheel to rotate without any physical contact. This has a number of advan-
tages over mechanical bearing systems:
• Reduced drag- Mechanical bearings have a drag that is proportional to the square of the speed.
The levitation system developed by Liebert uses the same power regardless of speed.
• Reliability and zero maintenance- The levitation system ensures there is no contact between the
rotating parts and the housing and therefore there are no components to wear out. This ensures
the unit will operate maintenance free for the life of the system.
The levitation system, works by measuring the displacement using a capacitive sensor, if the distance
needs to be adjusted; the current to the electromagnet is altered to change the displacement, each
axis is measured and controlled separately with its own capacitive sensor, electromagnet and feed-
back loop which, is controlled by the MLM. This is all done using analog control so it is very fast act-
ing and reliable. There are 5 different circuits working independently, these are: Radial: Upper X, Y;
Lower X, Y and Axial: Z Only
The principle of operation is the same in each case. The upper radial Y-axis is shown in Figure 37.
Figure 37 Schematic of the levitation system
Active Magnetic Levitation Hardware
The electromagnets and capacitive displacement sensors that provide the active magnetic levitation
are located within the flywheel module. See 5.1.7 - Magnetic Levitation Module (MLM) for a full
description of their operation.
CONDITIONER
CONTROLLER
DISPLACEMEN
T
SETPOINT
DISPLACEMENT SIGNAL
INFRARED EMITTER
ELECTRO-
MAGNET
AMPLIFIER
ROTOR
ELECTRO
MAGNET
CAPACITIVE
DISPLACEMENT
MEASUREMENT
AMPLIFIER
Z
X
Y