Five-phase version of 12slots/8poles three-phase Synchronous Machine for Marine-propulsion

Abstract

Multiphase machines are widely used in electric marine propulsion especially because of their fault-tolerance which allows to guarantee the propulsion even if a fault occurs in the electrical system. Besides, the 12 slots/8 poles three-phase machine (12/8/3 machine) with fractional slot concentrated windings is known for its low level of permanent Magnet eddy currents losses, making it adequate for compact high speeds applications. Since this interesting property is due to a 0.5 value for the number of slots per pole and per phase (spp=0.5), then the paper examines a five-phase 20 slots/8poles (20/8/5 machine) fault tolerant machine whose spp=0.5. Using an analytical model, the copper losses and an estimation of the magnet losses for the two machines are presented and a comparison is done between the two machines. The results show that the 20/8/5 has more Joules losses than 12/8/3 but lower magnet eddy current losses. Since the Joules losses can be easily evacuated more than the magnet losses, the 20/8/5 machine can be considered as the fault tolerant version of the 12/8/3 machine. Finally, the overall losses for the two machines are computed, the losses in 20/8/5 machine are less than in 12/8/3 machine. A finite element calculation is carried out in order to validate the analytical predictions.