Research on an Axial-Axial Flux Compound-Structure Permanent-Magnet Synchronous Machine Used for Hybrid Electric Vehicles

A compound-structure permanent-magnet synchronous machine (CS-PMSM) is a solution to realize both the torque and speed control of the internal combustion engine (ICE) for hybrid electric vehicles (HEVs). This article investigates a CS-PMSM that is integrated by two axial flux permanent-magnet synchronous machines (one stator machine (SM) and one double-rotor machine (DRM)). The magnetic coupling between the SM and the DRM is calculated with 3D finite-element method (FEM), and it is found that little magnetic coupling exists. So the SM and the DRM can be analyzed and controlled independently. The methods to improve the torque characteristic are discussed. Although optimal pole arc embrace, optimal magnet skewing angle and ladder-magnet all enable to reduce torque ripple, the effect of pole arc embrace and skewed magnet is much more satisfying. After the two methods are matched and optimized again, a better scheme is obtained.