Simulation-Based Design Method of Active Magnetic Bearings According to the Criterion of Dynamic Stiffness (DDS)

Applications of magnetically supported rotating machinery are expected to prove, that real loads can be controlled reliably by active magnetic bearings (AMB) during normal operation and disturbances. The basis for the optimal design is firstly the knowledge about the rotor dynamic behavior during operation and secondly the specific load acting on the rotor. Thereby, static and dynamic shares as well as their superpositions must be considered, and also specific process demands (accuracy of rotor position, maximum allowable rotor displacement). Up to now it has ben usual to design active magnetic bearings on the basis of the maximum static load, expected from the application. Often, the dynamic stiffness (as frequency-dependent ratio between disturbance input force and output displacement) is considered only during the start-up phase. At that time the used controller and power amplifier are already determined. Adjustments are merely possible in the setting range of the controller. The tuning of the loop components are not always optimal. In addition, the expenditures for start-up increase. The paper describes a simulation-based method for the AMB Design on the parameter Dynamic Stiffness (DDS). The method is also applicable to the theoretical proof of the reliability performance during normal operation and disturbances. The simulation tool MLDyn was developed by IPM. The dynamic stiffness is determined as a function of the frequency of the real disturbance forces. A necessary dynamic stiffness is introduced as a criterion for the reliability performance and an allowable shaft displacement as the weighting criterion. The proposed DDS method is presented for a process pump in a power plant.