Investigation of Hybrid Excitation Synchronous Machines With Axial Auxiliary Air-Gaps and Non-Uniform Air-Gaps

The hybrid excitation synchronous machine (HESM) with magnetic shunting rotor is a new topology of brushless HESM. To optimize the excitation construction, improve the flux control capability, and decrease the magnet consumption as well, two types of HESMs with different air-gap features are further proposed and investigated in this paper. First, configuration of the HESM with axial auxiliary air-gaps is presented. The comparative study of axial auxiliary air-gap scheme with respect to radial one is carried out. Three-dimensional (3-D) finite-element analysis (FEA) of the HESM is performed to achieve the field distribution, air-gap flux density and flux control characteristic, which indicates the HESM with axial auxiliary air-gaps also has good flux control capability and moreover enlarged excitation housing. Afterwards, construction and flux control principle of the new HESM with axial non-uniform air-gaps are introduced. A prototype HESM is developed, and the experimental results of open-circuit characteristic and terminal characteristic, which agree with the 3-D FEA results, verify the satisfactory field control performance, desirable power output capability, and the improved flux control capability of the HESM at negative excitation current as well.