An efficient rotor suspension with active magnetic bearings having viscoelastic control law

Research on active magnetic bearings (AMBs) has received good attention as such bearings not only provide electromagnetic forces over an air-gap to levitate or bear a rotor-shaft system, but at the same time, such bearings may also be used for providing active suspension forces to obtain the desired position of a rotor inside the bearing as well as the desired dynamic behaviour of rotor-shaft systems. The proportional, integral, derivative (PID) control law, as well as a few nonlinear control laws can be found in the literature, of which the former is very common. This paper attempts to study, theoretically and experimentally, the influence of a simple proportional and high-frequency band limited derivative control law (PDhfbl), proposed in this work as the viscoelastic control law to generate viscoelastic semisolid-like behaviour of the AMB, on the dynamic behaviour of a rigid rotor-shaft system. It is observed that within the same limits of control current, the (PDhfbl) control law is much more efficient than the PID in positioning the rotor within closer tolerances and reducing the rotor response amplitude due to unbalance.