Permanent magnet generators for aerospace applications

The primary design consideration for electrical generators used in aerospace applications is the maximisation of the power to weight ratio (power density). Since the gross power available from a generator is directly proportional to its operating speed and the generated frequency is unconstrained in an isolated system, it is natural to operate at high speeds. This high speed operation makes the use of a DC rotor field impractical due to brush wear, and therefore the field excitation is obtained from permanent magnets (PM). Many magnetic circuit configurations have been proposed by various researchers on PM machines, but there have been few attempts at quantitative comparisons. The author aims to provide such comparisons for popular configurations, in the power range 0.25-10 kW and the speed range 10000-100000 RPM suitable for unmanned aircraft and spacecraft. The general approach is to produce approximate designs for each configuration over the power and speed ranges, using formal optimisation methods, and then to compare the power density figures