Overview of Permanent Magnet Machines with Ironless Stator

Due to the advantages of high efficiency, good overload capacity, less cogging torque and rotor loss, which result from eliminating magnetic field conductive medium with saturated effect entirely or partly from stators, ironless or slotless stator PM machines have a very wide application prospect in these occasions, such as flywheel energy storage system, wind turbine generation, aerospace servo system and electric propulsion system. Based on the magnetic flux principle, the ironless or slotless stator PM machines are classified into radial flux type, axial flux type and planar flux linear type. Fundamental characteristics and key technology of different topology structures are elaborated, including the ironless winding and cooling, optimization of air-gap magnetic field, the small inductance characteristic for controllers. The development and application of ironless stator PM machines are summarized and discussed. Based on the characteristics of ironless stator PM motor, such as efficiency and torque performance, the development and future of the study on the direction of the key technologies are presented. © 2018 Chin. Soc. for Elec. Eng.