EXPERIMENTS IN THE CONTROL OF UNBALANCE RESPONSE USING MAGNETIC BEARINGS

Unbalance response is a common vibration problem associated with rotat ing machinery. For several years, researchers have demonstrated that t his vibration could be greatly alleviated for machines using active ma gnetic bearings through active control. Many of the control strategies employed fall into a class which the authors have termed adaptive ope n loop control. In this paper, three algorithms in this class are pres ented and their performances are examined experimentally. These algori thms are (1) a non-recursive control law with simultaneous estimation, (2) a recursive control law with simultaneous estimation, and (3) a r ecursive control law with gain scheduling according to operating speed . Each algorithm was coded in C and executed on a high-speed, multi-ta sking digital controller. The advantages and disadvantages of each alg orithm are illustrated by examining experimental results from a labora tory magnetic bearing rotor rig. These results clearly demonstrate the high degree of synchronous vibration attenuation (over 30 dB) which c an be achieved with adaptive open loop methods. The response of these algorithms to a sudden change in ''simulated imbalance'' is used to ev aluate their relative transient performances. These results indicate t he benefits of recursive control laws in adapting the synchronous open loop control currents to cancel the vibration. The ability of each of the algorithms to adapt the open loop control during changes in rotor speed is also examined. On this test, the recursive gain scheduled al gorithm shows superior performance: rotor midspan vibration is almost completely eliminated over the operating speed range, However, surpris ingly, the non-recursive control law shows better performance than the recursive law with simultaneous estimation. This result is explained in terms of the stability of the adaptation process.