The coupling between torque and radial force, and between the two radial forces is detrimental to the efficient control and performance improvement of the bearingless switched reluctance motor (BSRM). In the article, an 18/16-pole permanent magnet (PM) biased BSRM with radial force windings driven by a three-phase full-bridge inverter is presented. To solve the coupling between two radial forces in this proposed BSRM, three of its derived decoupled topologies have been developed, and the decoupled characteristics of these structures are proved by the radial force mathematical model and finite element analysis. Further, based on the space vector pulse width modulation (SVPWM) technique for three-phase full-bridge inverters, a one-cycle digital control scheme for the radial force control applicable to four types of BSRMs has been developed. Finally, a BSRM is prototyped and tested for experimental validation of radial levitation.

In the traditional control scheme of a 12/8-pole bearingless switched reluctance motor (BSRM), radial force and torque are usually controlled as a compromise due to the conflict between their effective output areas. Additionally, each phase requires individual power circuits and is excited in turn to produce a continuous levitation force, resulting in high power device requirements and high controller costs. This paper discusses a 12/8-pole single-winding hybrid-rotor bearingless switched reluctance motor (HBSRM) with a hybrid rotor consisting of cylindrical and salient-pole lamination segments. The asymmetric rotor of the HBSRM slightly increases the complexity of its structure and magnetic circuit, but makes it possible to generate the desired radial force at any rotor angular position. A control scheme for the HBSRM is developed to utilize the independent excitation of the four windings in one phase to generate the desired levitation force at any rotor angular position, and it requires only half the number of power circuits used in the conventional control scheme of a 12/8-pole single-winding BSRM. Different from the average torque chosen to be controlled in traditional methods, this scheme directly regulates the instantaneous total torque produced by all excited phases together and presents a current algorithm to optimize the torque contribution of each phase so as to reduce torque pulsation, and the improved performance of this bearingless motor is finally validated by simulation analysis.