COMBINATION AXIAL AND RADIAL ACTIVE MAGNETIC BEARING WITH IMPROVED AXIAL BANDWIDTH

Homopolar Permanent-Magnet-Biased. Combination Axial and Radial Electromagnetic Actuators used in Active Magnetic Bearings (AMBs) have several advantages over arrangements of separate axial and radial actuators including shorter length, lower part count, lower cost and better rotordynamic response. However, these actuators may require higher-order compensators in applications with significant dynamic axial loads due to somewhat lower axial bandwidth. One of the reasons for a lower axial bandwidth is having the axial magnetic control flux flowing through an opening in a radial actuator assembled from insulated electrical-steel laminations stacked axially. Whenever this flux changes in time, it induces an electrical current in each lamination which is responsible for the dynamic axial force reduction and an additional phase lag. In an improved actuator design, a current path in each lamination is interrupted by a single slot located between two radial control poles. In order to maintain structural integrity of the stack and magnetic conductivity between the radial poles, the slot position is rotated by 90 degrees between each subsequent lamination in the stack. The solution has been evaluated in a test actuator with 3000N axial and 1200N radial load capacities. 7dB gain improvement and 15 degrees phase improvement at 30Hz have been demonstrated.