Design and Evaluation for High Torque Density Segmental Rotor Type SRM with Reverse Bias Permanent Magnets

To address the challenge of low output torque and efficiency in conventional switched reluctance motors (SRM), this paper proposed a segmental rotor type SRM incorporating reverse bias permanent magnets (PMs). The PMs are embedded in the stator slot-openings and tangentially magnetized. As the armature windings unexcited, the PMs magnetic flux is closed through stator poles and stator yoke, with only a small amount of magnetic flux passing through the air gap. As the armature windings excited, the armature winding magnetic flux is in the opposite direction to that generated by the PMs in the stator, making the PMs magnetic flux have to close through air gap and rotor segments. This results in the armature windings magnetic flux and the PMs magnetic flux generated superimposing at the air gap, which increases the magnetic flux density in the air gap, thereby improving the output torque compared to that of conventional SRMs. To verify the effectiveness of proposed structure, a detailed design of the proposed SRM is present firstly in the paper, then the static and steady-state characteristics of the proposed structure are analyzed by finite element analysis (FEA) and compared with conventional SRM with PMs and segmental rotor type SRM. The comparison results show that the output torque generated by the proposed structure is at least 15% and 25% larger than that of the other two SRMs with the same armature current, and the efficiency of the proposed SRM is at least 2% and 1% higher than that of the other two SRMs with the same load condition, which verifies the effectiveness of the proposed structure.