Structural analysis of low-speed axial-flux permanent-magnet machines

Analytical expressions obtained from circular plate, elastic beam and cylindrical shell theory are applied to calculate the structural mass of axial-flux permanent-magnet machines for a range of typical wind-turbine ratings. Finite-element models and data from existing low-speed axial-flux machines have been used to gain confidence in the models presented, such that they can be incorporated into design-office programs to rapidly provide a first-order estimate with a reasonable level of accuracy. Results confirm that the inactive mass is greater than 60% of the machine total mass, and at multimegawatt ratings it is almost 90% of the total mass. Optimisation of the machine must therefore include the link between structural and electromagnetic designs. Results presented illustrate the impact of inactive mass on geometrical design parameters and also show that multistage designs can lead to a reduction in mass.