Parker EME
Setting up Compax3
192-120113 N08 C3I12T11 - December 2010
219
match between the mathematical model of the observer and the real physical
control section in the fundamental frequency range of the control. This applies in
particular to direct drive systems with fixed moving masses, as otherwise the
mismatch between model and the physical drive system has a destabilizing
influence on the transfer behavior of the speed control. A remedy is to increase the
observer dynamics, however this increases the noise of the observed signals.
Therefore in the case of variable moving masses a compromise has to be found
between the dynamics of the observer and the maximum stiffness of the drive.
Commutation settings of the automatic commutation
In this chapter you can read about:
Display of the commutation error in incremental feedback systems ............................... 220
Prerequisites for the automatic commutation ................................................................. 221
Course of the automatic commutation function .............................................................. 221
Other ............................................................................................................................. 223
Permanently excited synchronous motors can only be operated with an absolute
feedback system (at least for electric motor rotation). The reason is the necessary
commutation information (position assignment of the magnet field generated by the
motor to the motor magnets). Without the commutation information, there is
inevitably the possibility of a positive feedback between position and velocity loop
("running away" of the motor) or of bad motor efficiency (reduced force constant).
Digital hall sensors are the most common aid to prevent this. Due to the
mechanical design it is however impossible or very hard to integrate these sensors
in some motors. The Compax3 automatic commutation function (in the F12 direct
drive device) described below allows however to use incremental feedback
systems without hall sensors.
The functionality implemented in the servo drive establishes the necessary
reference between motor stator field and permanent magnetic field without
additional aids.
The incremental feedback devices are, in contrast to absolute feedback devices,
able to acquire relative distances. It is true that any position can be approached
from a starting point, there would be however no consistency between these
position values and a fixed virtual absolute system. Other than with an absolute
feedback, the correlation between rotor and stator is lost if the position acquisition
is switched off ("the position acquisition zero is lost"). When switching on, the
actual position is randomly taken as zero. A commutation angle error can therefore
absolutely not be excluded. Even a system adjusted before, would show an
angular error, for example after a current failure. Therefore the angular error
occurring randomly upon each new switching on must always be compensated in
an incremental system.
