Analytical subdomain model of surface-mounted PM synchronous machine using virtual PM blocks to optimize magnet segmentations for underwater vehicle applications

This paper presents an analytical subdomain model which can consider infinite numbers of virtual permanent magnet (PM) blocks to represent the segmented magnets per pole in any combination of slot and pole numbers of the semi-closed surface-mounted permanent magnet synchronous machines. From the case study discussed in this paper for a three-phase, 6 s/4p surfacemounted PMSM designed specifically for the underwater vehicle applications, the optimum magnet pole-arcs of the two segmented magnets per pole are 147.0° elect. for each magnet pole and 11.3° elect. for the airgap spacing between the magnet segments. The cogging torque and the total harmonic distortion of the phase back-EMF are drastically reduced by 88 % and 26 %, respectively, when comparing the results to the optimum magnet pole-arc of one magnet segment per pole machine, under similar constraint of PM volume. These analytical results are validated by 2D finite element analysis, where good agreement has been achieved.