Increasing field weakening capability of an axial flux PM machine

In this paper an investigation related with the improvement of the field weakening capability for an axial flux PM machine is carried out. The machine configuration proposed allows us to control the airgap flux, so that field weakening characteristic is obtained based in a negative d-axis current injection. This axial flux topology contains one central stator and two rotors. The stators have 3-phase AC windings allocated in slots. Rotor poles are shaped by a magnet piece, which provide the excitation; and iron pole section, with a reduced d-axis reluctance path. In this manner a reduced amount AC demagnetizing current is required for flux control. Proper design of the rotor yoke, selection of the pole geometry and PM to iron area ratio allows us to increase field weakening capability of the machine.