This paper proposes a five-degree-of-freedom (5-DOF) hybrid magnetic bearing (HMB)\nfor direct-drive wind turbines, which can realize suspension in the 4-DOF radial and 1-DOF axial\ndirections. Only two sets of radial control windings are employed in the proposed HMB because only\none set of radial control windings can achieve the 2-DOF suspension in the radial direction. Unlike the\ntraditional active thrust magnetic bearings, this paper uses a cylindrical rotor core without a large\nthrust disc in the novel HMB. The numbers of the controller, power amplifier and system volume\ncan be reduced in the magnetic suspension system. This paper also presents the structure and basic\ncharacteristics of the proposed magnetic bearing. A precision equivalent magnetic circuit analysis of\nthe permanent magnet ring and control magnetic field is conducted in this study, in consideration of\nthe non-uniform distribution of magnetic density. Accordingly, the mathematical models, including\nthe suspension force expression, are derived based on the accurate equivalent magnetic circuit.\nThe basic principle of the structure parameter design is presented, based on the given key parameters.\nThe accuracy of the analytical method is further validated by 3D finite element analysis.
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