A simple method to predict the induced EMF waveform and the d-axis and q-axis inductances of an axial flux interior PM synchronous motor

The paper presents an algorithm to calculate the parameters of an axial flux interior PM (AFIPM) synchronous motor. The proposed procedure is based on a suitable “airgap function”. At each instant, this function describes an equivalent airgap flux line´s length due to the presence of the stator slots and the rotor geometry. Assuming infinite iron permeability, the magnetic potential of the rotor poles generated by the magnets and/or by the stator currents can be calculated. Therefore, for a specific machine radius, it is possible to determine the airgap flux density waveform. The complex AFIPM prototype geometry requires calculation of the flux densities at different machine radii. The performed analyses point out that ten radii values are sufficient to get a good precision. In the paper, the complete calculus procedure is presented. The obtained results are compared with the experimental data, measured directly on the AFIPM motor prototype. The induced EMF waveform is in excellent agreement with the measured one, also the values of the synchronous inductances in the d-axis and in the q-axis confirm the validity of the proposed method