Optimum magnetic circuit configurations for permanent magnet aerospace generators

In the design of generators for aerospace applications, it is crucial that the specific output power (power/volume) is as high as possible. In such cases, other factors are relatively minor considerations. As specific output increases with operating speed, many aerospace generators operate at speeds in excess of 12,000 rev/min. Brush wear problems at high speeds, lead to the selection of the permanent magnet (pm) field alternator, which does not use brushes. This alternator has bipolar flux variation in the stator iron and so can be expected to have a high specific output. Magnetic circuit configurations for pm generators are related to radial-field, axial-field, and flux-switching types. The choice of the magnetic circuit configuration is a vital element of the design process. The present paper has the objective to provide for the first time quantitative comparisons of the specific output available from each of several magnetic circuit configurations. It is found that the flux-squeezing configuration has advantages for small sizes.