Regulation on radial position deviation for vertical AMB systems

As a source of model uncertainty, gyroscopic effect, depending on rotor speed, is studied for the vertical active magnetic bearing (VAMB) systems which are increasingly used in various industries such as clean rooms, compressors and satellites. This research applies H∞ controller to regulate the rotor position deviations of the VAMB systems in four degrees of freedom. The performance of H∞ controller is examined by experimental simulations to inspect its closed-loop stiffness, rise time and capability to suppress the high frequency disturbances. Although the H∞ is inferior to the LQR in position deviation regulation, the required control current in the electromagnetic bearings is much less than that for LQR or PID and the performance robustness is well retained. In order to ensure the stability robustness of H∞ controller, two approaches, by Kharitonov polynomials and TITO (two inputs & two outputs) Nyquist Stability Criterion, are employed to synthesize the control feedback loop. A test rig is built to further verify the efficacy of the proposed H∞ controller experimentally. Two Eddy-current types of gap sensors, perpendicular to each other, are included to the realistic rotor-bearing system. A four-pole magnetic bearing is used as the actuator for generation of control force. The commercial I/O module unit with A/D and D/A converters, dSPACE DS1104, is integrated to the VAMB, gap sensors, power amplifiers and signal processing circuits. The H∞ is designed on the basis of rotor speed 10 K rpm but in fact it is significantly robust with respect to the rotor speed, varying from 6.5 to 13.5 K rpm.