A Three-Degree-of-Freedom Bearingless Switched Reluctance Motor With Biased Permanent Magnets

A traditional bearingless switched reluctance motor (BSRM) can only achieve two-degree-of-freedom (2DOF) radial levitation of its rotor shaft. In this article, an 18/16-pole three-DOF (3DOF) BSRM with biased permanent magnets (PMs) are proposed, which allows both axial and radial levitation, and its suspended windings are driven by a four-phase five-bridge-arm power inverter. First, the decoupled characteristics of this 3DOF BSRM are proved by the suspended force model and 3-D finite element analysis. Second, a control scheme consisting of three independent channels for radial force, axial force, and torque is designed for this motor. Then, based on the space vector pulse width modulation (SVPWM), a radial current algorithm for radial force control and an axial current algorithm for axial force control have been developed, respectively. Finally, a PM-biased 3DOF BSRM is prototyped and tested for experimental validation.