Operation Principle and Improved Topology of a Triple-Degree-of-Freedom Seven-Phase Motor

In this paper, a novel triple-degree-of-freedom sevenphase motor (TDOF-SPM) is proposed to improve traditional multi-motor systems, pursuing higher integration. The investigated motor belongs to the multi-mechanical port motor, which comprises a single set of seven-phase armature winding and three axially arranged permanent magnet rotors. The principle of decoupled operation for three rotors in the TDOF-SPM is revealed basing on the electrical pole changing (EPC) for the multi-phase motor. Thus, the basic topology of 14-slot 4/8/12-pole is constructed, which is also general for motors with other degree-offreedoms. Furthermore, to reduce the torque ripple induced by EPC, the flux modulation effect is introduced and the improved topology of 14-slot 88/92/96-pole is proposed. Accordingly, the improvement mechanism is analyzed, and the comparison between the improved topology and the basic one is carried out. Meanwhile, through the finite-element-analysis (FEA), EPC, flux modulation effect, and axial magnetic field decoupling for the TDOF-SPM are analyzed. Finally, the prototype of improved topology is fabricated and experimented to validate the FEA results and operation principle of the TDOF-SPM.