Semi-analytical inductance calculation on an axial-field synchronous machine for a flywheel storage system using surfacic permeances

Accurate knowledge of inductance windings is necessary in cases such as optimization calculations. Knowing the right value of reluctance torque, which depends upon the saliency ratio, is particularly important. The use of a fully-analytical calculation is straightforward and provides quick results. While this approach proves to be efficient for electrical motors with a small airgap, such is not true when the airgap becomes large, as is typical of axial-field machines with air-cored windings. After recalling the principle and hypotheses necessary for conducting the correct analytical calculation, through the example of a cylindrical reluctance machine, this paper proposes a 2-D semi-analytical calculation using surfacic permeance for an axial-field motor. It is shown that for a discoid motor, a 2-D analysis is sufficient in spite of 3-D effects due to its specific configuration and that the flux density in the airgap can be written as the product of the surfacic permeance and the MMM. This method is then applied to a new synchronous machine designed for a flywheel accumulator developed in our laboratory. The machine and its corresponding technology are also presented in this paper.