A Generic Multi-Criteria Design Approach Toward High Power Density and Fault-Tolerant Low-Speed PMSM for Pod Applications

Pod propulsion systems are widely used, since they exhibit high efficiency and reliability, especially when they are combined with permanent magnet synchronous motors (PMSMs). Except from high efficiency, high power density and increased fault-tolerance capability are also the main requirements for a motor in order to be used in such an application. Generally, PMSMs present high power density in high-speed operation. However, in low-speed applications, the achievement of increased power density is not an easy task. Moreover, PMSMs with surface-mounted magnets are characterized by low winding self-inductance which limits the fault-tolerance capability. Thus, this paper presents an effective generic multicriteria PMSM design approach and proposes a global selection strategy for both the slots/poles combination and the motor's airgap diameter to axial length ratio aiming to enhance the two aforementioned characteristics. At the same time, numerous practical and physical constraints have been thoroughly described and taken into account in the proposed process. These constraints are not adequately presented in the relative literature. The derived topologies are validated through finite element method analysis and several important quantities are calculated and used as comparison metrics. Finally, useful conclusions are extracted that could be of great help for designers and manufacturers of pod propulsion systems.