Unbalance Control of Active Magnetic Bearings

Unbalance forces are a major source of undesired vibrations in rotating machinery. Active magnetic bearings (AMBs) with special control algorithms, allow for controlling those forces and counteract appropriately. The two basic principles are UFRC and UFCC. They are known for many years and have been published and patented before. There exist excellent publications treating the closed-loop stability of UFRC but not much can be found on the stability of UFCC. This paper presents an adaptive multi-variable implementation of UFCC, its theoretical background and a proof of control stability. UFCC as described in this paper, has shown excellent stability in practice and it can therefore be engaged over the entire speed range of the machine. However in order to minimize the load on power amplifiers and other components a switching strategy is advised, where UFRC and UFCC are switched on and off in the speed ranges where required. Guidelines for tuning UFCC parameter are also given. The effectiveness of UFCC has been proven in several applications and measurement results are given in this paper.