Torque Improvement and Analysis of a Bearingless Switched Reluctance Motor Under Efficient Levitation Excitation

In a bearingless switched reluctance motor (BSRM), there is a conflict between the output regions of effective radial force and positive torque. So a compromise between radial force and torque is usually applied in a classical control scheme of the BSRM, resulting in under-utilization of its optimal performance of both levitation and motion. For a 12/8-pole BSRM, this paper implements a levitation control in the efficient excitation region to maximize the radial load capacity, performs a torque excitation from the unaligned position to the aligned position and adjusts in real time the instantaneous total torque so as to improve its torque output. In a 12/8-pole BSRM, the efficient levitation excitation region of each phase consists of two equal-width sectors, and a rotor angular position cycle is formed with the six equal-width sectors. Based on the optimal objective within each sector and combined with the derived mathematical models of the radial force and torque, the corresponding current constraint is designed to calculate the five currents in the two-excited phases. Further, the control scheme for a 12/8-pole BSRM under efficient levitation excitation is developed to simultaneously regulate four instantaneous values of two radial forces and two phase torques. Finally, the good performance of the proposed method for the 12/8-pole BSRM under efficient suspension excitation is proved by simulation analysis.