Research on the axial-radial flux compound-structure permanent-magnet synchronous machine (CSPMSM) used for HEV

In this paper, an axial-radial flux compound-structure permanent-magnet synchronous machine (CSPMSM) which consists of one axial-flux PMSM and one radial-flux PMSM is investigated. The purpose of this kind of machine is to keep the internal combustion engine (ICE) operating at maximum efficiency by harmonizing its two machines during all driving cycles in hybrid electric vehicle (HEV), and therewith it can also reduce the emission. In addition, this kind of machine can simplify the structure of a car by replacing the clutch, gearbox and so on. In a word, it integrates the advantages of the series and parallel HEV structures. Firstly, a 3-D finite-element method (FEM) of the axial-radial flux CSPMSM is built. The magnetic coupling between the radial-flux PMSM and axial-flux PMSM is analyzed, and the two motors are matched for a better use in the HEV; Additionally, the structure of the axial-radial flux CSPMSM is optimized by using the 3-D FEM. Fractional-slot winding and tooth-width unequal structure are adopted in the axial-flux PMSM to get a smooth back electromotive force (back-EMF) and reduce the torque ripple. Skewed slots are used in radial-flux PMSM to reduce the cogging torque. The results of the optimization show both of the torques meet the demand.