PID Tuning Methods for Active Magnetic Bearing Systems

The use of active magnetic bearings (AMBs) in place of traditional mechanical bearings for rotating machinery has been increasing. AMBs have been used not only in research studies, but also in a wide range of industrial applications. One of the key challenges in AMB appli-cations is the design of control systems that maintain stability in the presence of external loads and disturbances. The most commonly used controller for AMB systems is the Proportional-Integral-Derivative (PID) controller, whose design involves the tuning of control coefficients. Since manual tuning of these coefficients is time consuming, different systematic tuning methods have been developed and reported on in the literature. This paper examines some of these tuning methods in AMB control systems. Both simulation and experiments are carried out on an AMB test rig to compare the performance of the closed-loop systems resulting from these tuning meth-ods in terms of steady state accuracy and robustness. Simulation and experiments of each tuning method are conducted at rotational speeds ranging from 2,000 rpm to 11,000 rpm to evaluate the response peak (orbital size). Also, the frequency responses of the sensitivity function (S) under PID controllers tuned with different methods are measured and used to compare the robustness of the closed-loop system.