Research on an axial-axial flux compound-structure PMSM with varying air gap to fulfill field-weakening control

A compound-structure permanent-magnet synchronous machine (CS-PMSM), which integrates two PMSMs, is a hybrid electric vehicle (HEV) power train concept. In order to meet the requirement of wide speed range of HEV, an axialaxial flux CS-PMSM with a new mechanical method of varying air gap to fulfill field-weakening control and to improve the operating speed range is investigated. The field-weakening principle of the axial-axial flux CS-PMSM with varying air gap is analyzed. The electromagnetic performances with air gaps varying are evaluated by 3D finite-element method (FEM). The principle of selecting original air gap is proposed with comprehensive consideration. The field weakening capability by varying air gap is evaluated based on the comparison with two other electric methods.