Fractional Modeling and Identification of Active Magnetic Bearings With Laminated and Nonlaminated Structures Including Eddy Currents

Eddy currents are relatively common in active magnetic bearings (AMBs), and the laminated structure can effectively suppress the eddy-current effects, but there are still obvious phase lag and gain decay at high frequencies, leading to significant model errors. This article presents the fractional-order magnetic circuit models of AMBs with laminated structure and nonlaminated structure, including eddy currents, respectively. Compared with the laminated structure, the traditional second-order model of the nonlaminated AMB has a larger error with the actual system, while using the fractional-order model, the two structures of the AMBs have better performance. Considering the eddy currents can reduce the model errors, but due to the presence of nonlinear factors, such as hysteresis and magnetic saturation, it is hard for the magnetic circuit model to accurately fit the dynamic performance of the actual system. Hence, the system identification of the AMBs is carried out based on the fractional-order model structure to obtain a more accurate model. The results show that the identified model based on the fractional-order model structure is a more reliable choice for the modeling of the AMBs, which can accurately describe the dynamic performance of the actual system in full frequency domain.