Eddy current is one of the biggest difficulties in the motor industry which will give rise to the temperature of permanent magnets and caused demagnetization, then affected the working efficiency of the motor. We named it “Eddy Current Loss of Permanent Magnets”
In most cases, the eddy current loss of permanent magnets is much lower than iron loss and copper loss of the motor, but it will generate a large temperature rise in the high-speed motor and the high power density motor.
Ideally, rotor magnetic field and stator magnetic field of PMSM are rotating synchronously, or relatively static, thus permanent magnets without eddy current loss in such case. In fact, there are a series of space and time harmonics are existing in the air gap magnetic field, and these harmonic components are stemming from cogging effect, non-sinusoidal distribution of magnetomotive force and phase current. The harmonic magnetic field will link with rotor magnetic field and hence generated eddy current and caused relevant eddy current loss. It should be also noted that the harmonic magnetic field and eddy current loss will rise with increasing motor speed.
Laminated magnets are regarded as a wise solution to solve the eddy current loss in the surge of high-speed rotating machinery development.
Laminated magnets are made by bonding several pieces of thin magnets together via special isolation glue which also be called magnet segmentation technology, and thus dramatically reduce the eddy flux loss of the magnets without changing the structure and performance of the motors. Actually, puzzles existing in the development of laminated magnets are the assembly process and consequently high costs. U-Polemag has collected much experience via some axial flux motor projects.
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