Adaptive Open-loop Control of Magnetic Bearings to Offset Slew Rate Limitation under a Non-synchronous External Disturbance

Magnetic bearings have a limited force slew rate capacity inherent in their electrical nature. This physical limitation is not transparent to the feedback controller, which under certain loads may continue to request unachievable slew rates resulting In eventual instability. Using larger power electronics is one approach to the problem, however it is shown in this paper that slew may be prevented more cost effectively by using the appropriate control methods. The root-cause of failure under slew rate limitation is investigated followed by a proposed solution for non-synchronous external disturbances. An adaptive open loop algorithm is presented including frequency tracking capability. The algorithm is implemented experimentally and performance is demonstrated under different test conditions.