Influence of bias current of active magnetic bearing on robustness and dynamic performance of the system

The Bode´s integral is applied to analysis the robustness of active magnetic levitation systems. Based on the linear model, it is found that the unstable pole of open-loop system is determined by the bias current, and larger bias current leads to unstable pole farther away from the imaginary axis. The bias current strongly influences the dynamic performance of the levitation system. Larger bias current is needed to achieve better dynamic performance, such as higher stiffness and larger load capacity, while unstable pole farther away from the imaginary axis implies larger Bode´s integral and worse robustness. The tradeoff between robustness and dynamic performance of the system is studied. The minimum available bandwidth that is necessary to achieve certain peak value of sensitivity function magnitude is derived. Simulation study is carried out to demonstrate the analysis method and to validate the results.