Design and Analysis of a Fault Tolerant Permanent Magnet Alternator for Aerospace

In this paper, 28 slot - 18 pole and 24 slot - 20 pole permanent magnet alternators (PMA) with soft magnetic composite slot wedges are designed and compared. Power lane separation required due to fault tolerance requirements, means the proposed machines initially do not produce balanced phase voltage and currents, resulting in high ripple on the rectified power output. The alternators are optimised using 2-D finite element analysis (FEA) to get smoother DC power waveform. It is shown that the power ripple might be reduced by about 12
^%
and un-balanced windings can be significantly balanced by thickening up the SMC slot wedges between the sub-machines. Furthermore, no load loss analysis has been conducted at rated speed and it is shown that 28 slot - 18 pole machine generates lower loss on no load condition compared to 24 slot - 20 pole single layer PMA.