Parker EME Setting up Compax3192-120113 N08 C3I12T11 - December 2010 219match between the mathematical model of the observer and the real physicalcontrol section in the fundamental frequency range of the control. This applies inparticular to direct drive systems with fixed moving masses, as otherwise themismatch between model and the physical drive system has a destabilizinginfluence on the transfer behavior of the speed control. A remedy is to increase theobserver dynamics, however this increases the noise of the observed signals.Therefore in the case of variable moving masses a compromise has to be foundbetween the dynamics of the observer and the maximum stiffness of the drive.Commutation settings of the automatic commutationIn this chapter you can read about:Display of the commutation error in incremental feedback systems ............................... 220Prerequisites for the automatic commutation ................................................................. 221Course of the automatic commutation function .............................................................. 221Other ............................................................................................................................. 223Permanently excited synchronous motors can only be operated with an absolutefeedback system (at least for electric motor rotation). The reason is the necessarycommutation information (position assignment of the magnet field generated by themotor to the motor magnets). Without the commutation information, there isinevitably 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 themechanical design it is however impossible or very hard to integrate these sensorsin some motors. The Compax3 automatic commutation function (in the F12 directdrive device) described below allows however to use incremental feedbacksystems without hall sensors.The functionality implemented in the servo drive establishes the necessaryreference between motor stator field and permanent magnetic field withoutadditional 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 approachedfrom a starting point, there would be however no consistency between theseposition values and a fixed virtual absolute system. Other than with an absolutefeedback, the correlation between rotor and stator is lost if the position acquisitionis switched off ("the position acquisition zero is lost"). When switching on, theactual position is randomly taken as zero. A commutation angle error can thereforeabsolutely not be excluded. Even a system adjusted before, would show anangular error, for example after a current failure. Therefore the angular erroroccurring randomly upon each new switching on must always be compensated inan incremental system.
