AFPM Machines Without Stator Cores
Depending on the application and operating environment, stators of AFPM machines may have ferromagnetic cores or be completely coreless. A coreless stator AFPM machine has an internal stator and twin external PM rotor (Fig. 1.4d). PMs can be glued to the rotor backing steel discs or nonmagnetic supporting structures. In the second case PMs are arranged in Halbach array (Fig. 3.15) and the machine is completely coreless. The electromagnetic torque developed by a coreless AFPM brushless machine is produced by the open space current-carrying conductor–PM interaction (Lorentz force theorem).
Coreless configurations eliminate any ferromagnetic material, i.e. steel laminations or SMC powders from the stator (armature), thus eliminating the associated eddy current and hysteresis core losses. Because of the absence of core losses, a coreless stator AFPM machine can operate at higher efficiency than conventional machines. On the other hand, owing to the increased nonmagnetic air gap, such a machine uses more PM material than an equivalent machine with a ferromagnetic stator core.
KeywordsRotor Disc Stator Core Core Loss Eddy Current Loss Electromagnetic Torque
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