Modeling and Identification of a Solid Core Active Magnetic Bearing Including Eddy Currents
Eddy currents are evident in solid core active magnetic bearings (AMBs) but they are omitted in the commonly used models, leading to a significant error between the analytical model and the real system. Based on the magnetic circuit method, this paper presents an analytical model including the eddy current effects of a solid core AMB under both current drive and voltage drive, after setting up the relationship between the magnetic force and the effective reluctance. A half order term is induced in the effective reluctance due to eddy currents, turning the analytical model to fractional order. The effective reluctance only appears in the coefficient of the s2 term, and affects the system dynamics under current and voltage drives distinctively. The half order term changes the order of the model from 2 to 2.5 under current drive, whereas the order of the model is not changed and is still kept 3 under voltage drive. System identification of a solid core AMB verifies the proposed models, which indicates that the voltage drive can effectively reduce the eddy current effects compared with the current drive. In addition, although the solid core AMB shows fractional order characteristics, it can be described well with an integer order model under voltage drive. As a result, the voltage drive is a more reasonable choice to a solid core AMB, since it avoids the complex fractional order modeling and control.
IEEE/ASME Transactions on Mechatronics