Torsional instabilities in motor-driven turbomachinery

In torsional analyses of motor-driven turbocompressors, the usual approach accounting for forced excitations and dimensioning the train suffices provided that the drive system takes the form of an unregulated electric motor. For variable frequency drive systems, additional stability measures are required only if the vibration frequency controller (VFC) induces negative damping. It appears advisable not to mechanically compensate for this negative damping, but rather to use equipment for the VFC or the impact of the operation parameters on the VFC, which ensure that negative damping does not occur in the first place.