Design and Optimization of a Radial Magnetic Bearing for High-Speed Motor With Flexible Rotor

The industry application of magnetic bearing (MB) has recently extended from rigid rotor system to flexible rotor system; therefore, the design method of MB for flexible rotor is required. To reduce the inductance of the control coils and improve the dynamic performance, a radial MB with novel coil arrangements and connections is proposed in this paper. An optimal design method of the proposed MB is presented, which includes the simultaneous consideration of the MB itself, rotor-dynamics and the characteristics of the controller, and power amplifier (AMP). The equivalent magnetic circuit, which takes eddy current effects into considerations, is used as analytical model; the damping coefficient at resonant frequency is used as the objective function. The influence of the bias flux density on the objective function is analyzed, and the results show that increasing the bias flux density can reduce the burden on the AMP. Practical restrictions are also imposed, such as flux density constraint, maximum supply voltage of AMP, winding space constraint, pole width constraint, and copper wire capacity constraint on the design. By the optimization method of genetic algorithm and branch and bound algorithm, the optimal structure parameters of the proposed MB have been obtained. Finally, a design example is given and a prototype is manufactured. The experimental results demonstrate that the proposed MB and the optimization method are feasible and valid in the application to high-speed flexible rotor.