Electromagnetic modelling of Permanent Magnet Axial Flux Motors and Generators

Purpose – To provide a general framework for the electromagnetic analysis of axial flux motors and generators. Design/methodology/approach – The procedure is based on the solution of Maxwell's equation in a cylindrical frame. All field sources (permanent magnets, windings) are subdivided into filamentary windings. The expansion of the 2D air-gap magnetic field into a Fourier series is computed at every radius. The contributions of the harmonics are then added to achieve the expressions of the stator and rotor flux densities, back emf and developed torque. Slotting and skewing are taken into account also. Findings – The model can be written in a compact form by introducing a generalisation of the space vectors theory. The analysis is proved to be in accordance both with the finite element analysis and with experimental data. Research limitations/implications – The model does not take into account eddy-currents and non-linearities. It does not take into account also specifically 3D phenomena, as the radial components of the flux densities. Practical implications – The analysis is of practical interest from the standpoint both of control and of machine design. In this latter occurrence, it represents a valid alternative over computationally heavier 3D finite elements models. Originality/value – Although the procedure is partly based on previous analyses, it is original in the way it exploits the basic theory in order to introduce skewing, slotting, and finite length of the iron. With respect to other models introduced so far, the present one is more compact in the end, its parameters can be easily computed and their physical meaning is easily understood.