A triple 3-phase fault-tolerant fractional slot concentric winding interior permanent-magnet machine with low space harmonics

Fractional slot concentric winding (FSCW) machine features with short end winding, high torque density and good fault tolerance. However, this type of machine suffers from abundant MMF harmonics which causes high iron loss and partial saturation, etc. Hence, majority of the FSCW adopts surface-mounted PM (SPM) rotor which have large effective airgap to minimize the influence of the MMF harmonics while the interior PM (IPM) rotor is rarely used. The SPM rotor tends to induce high PM flux linkage and cause large fault current when experiencing a short-circuit failure. As a result, this paper presents a triple 3-phase FSCW-IPM for fault-tolerant applications. The triple 3-phase windings facilitate the uninterrupted fault tolerant operation, the more even distributed windings also induce a more sinusoidal MMF which enables the application of IPM rotor. The IPM rotor reduces the PM usage while reluctance torque can be explored to compensate the PM torque reduction which improves the machine fault tolerance. As a result, the proposed machine owns good performance and excellent fault tolerance. The machine is investigated by electromagnetic and thermal finite element analysis and prototyping tests. Both findings confirm that the proposed triple 3-phase FSCW-IPM is a competitive solution for high reliability application.