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. Laminated magnet is regarded as a wise solution to solve the eddy current loss in the surge of high-speed rotating machinery development.

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, stator magnetic field and rotor 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.

About Laminated Magnet

Laminated magnet is 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. Either laminated SmCo magnets or laminated Neodymium magnets are available. Actually, puzzles existing in the development of laminated magnet are the assembly process and consequently high costs. SDM has collected much experience via some axial flux motor projects.

Bomatec AG has also launched their unique Snake Line Technology to achieve reduction of eddy current loss. According to the relevant conclusions, Snake Line Technology has more competitive advantages compared with laminated magnet, especially dimensional accuracy, mechanical properties, and cost.