Modeling and digital control of an active magnetic bearing system

Active Magnetic Bearings (AMB) support a body by magnetic pulling forces, without any mechanical contact. The main advantages of such bearings compared with the traditional solutions are: absence of mechanical friction and wear, lubricant-free operation and therefore suitability for severe environments and applications, active vibration control and unbalance compensation. This paper deals with modeling, simulation and control of radial active magnetic bearing system for a high-speed drive. The system model from previous works [1, 5] has been extended with a model of the power amplifier with PWM control. Hence, dynamic behavior of currents in the bearing windings can also be investigated with this model. Two different controllers are used in the work, i.e. PID and state-space controller. Both will be compared to each other for two cases: a) lift-off of the rotor, and b) unbalance in the rotor which causes periodical disturbance force, which has also to be compensated by the magnetic bearing, additionally to the gravitation force.