Optimal design of a three-pole active magnetic bearing

The active magnetic bearing (AMB) is an important element for high-speed systems, such as semiconductor equipment and machine tools. The most popular AMB has eight magnetic poles. We propose a three-pole AMB here. Compared with the eight-pole configuration, it has the advantages of fewer power amplifiers, lower iron loss, and more space for heat dissipation, coil winding, and sensor installation. As a result, the AMB´s overall cost can be reduced. Here, we study the three-pole AMB´s optimal design, one that minimizes both the number of power amplifiers and the steady-state copper loss. Four design variables are considered: bias current, pole orientation angle, number of coil turns, and pole face. The optimal bias currents minimizing the steady-state copper loss are obtained by the method of Lagrange´s multiplier. The coil turns and pole face area are optimal if they occupy equal available bearing space. The optimal three-pole AMB is Y-shaped, i.e., the pole orientation angle is π/6. With this optimal pole orientation, the AMB´s two upper poles can share the same bias and control currents, but with opposite winding directions. Thus, only two power amplifiers are required for the optimal three-pole AMB. Finally, it is shown that the three-pole AMB possesses lower steady-state copper loss than the eight-pole AMB