Design, Modelling and Control of MIMO AMB System with 3 Radial Bearing Planes for Megawatt-Range High-Speed Rotor

Abstract

High-speed electric machines require dedicated bearings. Active magnetic bearings (AMBs) provide economical solution for high-power rotors where oil-free operation and low operational costs are crucial. In high-power and high-speed applications benefits of contactless rotor suspension, e.g. compared to traditional rolling element bearings, as well as online monitoring and diagnostics are highly valued. AMBs offer low losses and balancing capabilities in integrated package. The design of the high-speed high-power induction machine rotor is very challenging and cost sensitive. Manufacturing limitations, thermal and cooling constraints, stress and rotor dynamic issues and total efficiency are interdependent. The space and power electronics are limited for bearings and control design, which have to provide robust rotor suspension. This work presents electromagnetic design, modelling, and control of fully levitated AMB-rotor for demanding application. The machine design offers very limited space but 3 radial bearing planes and separate axial AMB are used. The control plant is modelled based on flexible rotor dynamics; while bearing inductances and forces are modelled with 2D and 3D FEM electromagnetic simulations. The presented LQG model-based control is scalable from single axis axial suspension to coupled centralized 3 actuator-sensor pairs radial suspension. The control has to deal with considerable plant parameter variations because of saturation and high destabilizing position stiffness because of small airgaps. The control design is verified in simulations using non-linear engineering models.