Abstract :
A thorough comparison of the converter performance characteristics for four permanent
magnet (PM) synchronous machine configurations is presented. Two versions of an interior PM
(IPM) machine with distributed windings are included. One version has a maximum back-EMF
limit at the top speed while the second does not have any constraint on back-EMF amplitude.
Two types of surface PM (SPM) machines are also considered, one with fractional-slot concentrated
windings, and another with conventional distributed windings. The target application
is an automotive direct-drive starter/alternator requiring a very wide 10 : 1 constant power speed
ratio (CPSR). Detailed comparisons of the converter performance below and above the base
speed are presented, evaluating significant issues, including the converter switching and conduction
losses, output ripple current, and DC-link current ripple. Study results show that the higher excitation
frequencies required by PM machines with high pole numbers have only a modest impact
on converter efficiency for comparable output current waveform quality. In constrast, the imposition
of maximum back-EMF amplitude constraints at top speed raise the machine rated
current, resulting in elevated converter losses and larger DC-link capacitors.
