A rotor lamination design for surface permanent magnet retention at high speeds

A major problem in the design and manufacturing of surface mounted permanent magnet machines is reliably holding the permanent magnets in place at high speeds. This paper evaluates a unique rotor lamination design for a high pole number, permanent magnet alternator. This buried magnet design, which is capable of reliably holding the permanent magnets in place at high speeds, offers both easier and cheaper assembly when compared with the methods currently used in surface mounted permanent magnet machines. Finite element analysis is used to compare the buried magnet design with equivalent surface mounted designs and shows that the performance of the alternator is not significantly affected by the iron over the magnets. Experimental results from a prototype alternator further corroborate the FEA and show that the design is capable of operating at high speeds with no other means of magnet retention. In addition, an improvement in the buried magnet design which can reduce the lamination complexity is suggested and examined.