Design and optimization of dual-permanent-magnet-excited motors and its application

Abstract

Dual-permanent-magnet Vernier electric machine (DPMM) operates based on the flux-modulation effect. It has permanent magnets (PM) located on both the stator and rotor. And it has been developed for several advantages. The first is the decoupling between stator slots and rotor poles. The pole pair of the armature winding does not need to be the same as the rotor pole pairs. Thus, the selection of slot/pole of DPMM is more flexible. Moreover, compared with conventional PM motors, the stator slot number can be further reduced even with large rotor pole pairs with a split-tooth stator. Another advantage is its high torque density. This advantage is because both stator PMs and rotor PMs contribute to the output torque. With appropriate slot/pole combinations, the output torque of DPMM will be significantly improved compared with the conventional motors. Besides, the bidirectional flux-modulation effect in DPMM brings abundant harmonics in the air gap. And through the modulation effect, not only the base harmonic can be used, but also other prominent harmonics. Moreover,the structure of DPMM is relatively simple. The flux modulation effect can be realized with a one-layer air gap. Currently, DPMM is widely investigated for low­speed, high-torque applications. In this thesis, the main contents are as follows: a) A literature review of the flux-modulation machines, especially on DPMMs, is presented. b) A unified operation principle of DPMM and its torque equation is presented in this thesis. The selection guideline for slot/pole combinations of DPMM is also concluded in this thesis. c) Different slot/pole combinations of DPMMs with the split-tooth stator and concentrated winding are investigated. A more general stator topology for the DPMMs is proposed. d) A novel general model for DPMM optimization is proposed in this thesis. Through the proposed general model, DPMMs with different topologies can be generated. And the models that have preferable performances are compared. e) The loss analysis of DPMMs is studied. And the core loss in stator core and rotor core, the eddy current loss in stator PMs and rotor PMs are studied. The thermal field of a DPMM is analyzed. The temperature distribution in the DPMM at stator PMs, rotor PMs, stator core, rotor core, and armature winding are simulated. A prototype is fabricated to validate the simulation. f) Two axial-flux DPMMs, made of soft magnetic composite material with different stator configurations and the same rotor pole pairs, are investigated to apply for an active structure control system.