Active Control of Rotordynamic Instability in Turbomachinery

The onset of rotordynamic instability is a significant challenge to successful design and oper-ation of high speed rotating machinery particularly gas compressors. The use of active magnetic bearings (AMBs) to support gas compressor rotors presents an ideal opportunity for the explo-ration of optimal and robust active vibration control algorithms. A notable advantage of AMBs is their ability to generate optimal support stiffness and damping characteristics. Unlike passive me-chanical bearings, the support characteristics of AMBs may be modified over the operating life of the system without any major hardware changes. The objective of this paper is to demonstrate the expansion of the stability region for an experimental rotor subject to destabilizing cross-coupled stiffness. A model-based control paradigm was followed to develop nominal and uncertain dy-namic models of the rotor-bearing system. Using m -synthesis several robust controllers were designed and implemented on the MBTRI hardware to investigate their effect on the stability threshold. The best controller established a thirty-six percent increase in the stability threshold over an existing benchmark controller. This represented an increase from fifty-six percent of the maximum achievable stability threshold to seventy-six percent. A damping ratio estimation al-gorithm was used to experimentally evaluate the sensitivity of the various controllers to varying cross-coupled stiffness.