Rotor unbalance in the primary cause of unacceptable vibration in rotating machinery. Over the last decade, researchers have explored different methods of taking advantage of the active nature of magnetic bearings to attenuate unbalance response including both feedback and adaptive open loop methods. An important issue in the application of this technology to industrial machines is the robustness of the unbalance control algorithm. The stability and performance robustness of a promising adaptive open loop control algorithm is examined. Expressions are derived for a number of unstructured uncertainties. Experimental results are then presented, which evaluate the algorithm's robustness with respect to three variations: gain schedule errors, random additive errors, and feedback loop gain. The robustness exhibited in these tests was quite good and, along with the excellent vibration attenuation obtained, recommend the algorithm for further testing and industrial application. The experimental results indicate that the theoretical robustness expressions do provide an upper bound on actual performance, however this bound is not tight. Although the conservatism in the results is partly due to the variations considered and the worst-case nature of the performance robustness guarantees, the results also indicate that further research is needed on unstructured performance robustness for this method of rotor vibration control.
This paper presents test results from the application of Adaptive Vibration Control (AVC) to a magnetic bearing equipped 6-stage hydrogen process compressor which operates at 20.6 MPa (3000 psi). This application represents the first time AVC has been demonstrated on a fully functional industrial machine. The results demonstrate the reduction in vibration levels possible with AVC operating in each of the two vibration control modes: synchronous position reduction which reduces the synchronous displacement of the shaft as measured at the bearing and synchronous current reduction which reduces the synchronous control effort by the bearings, allowing the shaft to rotate about its inertial center. A discussion is also included on future developments planned for AVC.
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