Design of Active Magnetic Radial and Thrust Bearings for High Speed Turbo Aerator

The thrust and radial active magnetic bearing (AMB) designs are presented for a 135 kW vertical axis high speed turbo aerator operating at maximum speed of 27,000 rpm. The thrust AMB is a double acting configuration with upperandlowerstatorsandasinglecoil. TheradialAMBisa12poleE-coredesign. Theresultsofmagneticcircuit design, 2-D finite element, and 3-D finite element modeling are presented, indicating that the simple magnetic circuit model is a good initial design tool for both thrust and radial AMBs. The AMBs were actuated with a steady state bias current and a time varying perturbation (control) current. The current gain and open loop stiffness for the AMBs are evaluated, showing the linearity of the bearings. Also, the coil resistance and inductance were evaluated. The bearings were successfully operated in the initial testing. The rotating AMB components must be attached to the rotor securely using shrink fits. The principal and shear stresses induced in the thrust AMB disk and the radial AMB lamination stack were evaluated and found to be in the safe range.