Segmented NdFeB Magnet Rotor for Eddy Current Reduction
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Solution Overview
Problem
Permanent magnet rotary machines face challenges with demagnetization due to high temperatures and eddy currents, leading to reduced performance and efficiency, especially in high-speed applications, where existing methods to enhance coercive force often compromise remanence or increase manufacturing costs.
Innovation Solution
The use of sintered Nd base magnets divided into pieces with a coercive force profile enhanced by diffusing Dy or Tb from the surface toward the interior via grain boundaries, and assembling these pieces without insulating layers for electrical conduction, allowing for high torque and heat resistance without reducing net magnet volume.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If sintered Nd base magnets are divided into smaller pieces to reduce eddy current loss, then eddy current reduction is improved, but manufacturing cost increases and output decreases due to reduced magnet volume by increased interstices
Solution Approach 1:
The magnet is divided into multiple magnet pieces arranged in a matrix pattern, which interrupts eddy current paths and reduces eddy current loss while maintaining effective magnetic volume through optimized piece dimensions and arrangement
Solution Approach 2:
Dysprosium or terbium is selectively added to specific regions of the magnet pieces, particularly near surfaces and edges where eddy current density is highest, creating local variations in coercive force that prioritize demagnetization resistance where most needed without uniformly reducing remanence throughout the entire magnet volume
2Reliability
If Dy or Tb is substituted for Nd to increase coercive force, then demagnetization resistance is improved, but remanence decreases
Solution Approach 1:
Dysprosium or terbium is selectively concentrated in specific regions of the magnet pieces, particularly near surfaces and edges where eddy current density is highest, creating local variations in coercive force that prioritize demagnetization resistance where most needed without uniformly reducing remanence throughout the entire magnet volume
Solution Approach 2:
Instead of uniformly substituting Dy or Tb throughout the entire magnet, the invention applies partial substitution only in critical regions, achieving sufficient demagnetization resistance with minimal impact on overall remanence
3Loss of energy
If insulating layers are added between magnet pieces to prevent eddy currents, then eddy current loss is reduced, but magnet volume is reduced
Solution Approach 1:
The magnet is divided into multiple magnet pieces arranged in a matrix pattern, which interrupts eddy current paths through the segmentation itself, reducing the need for additional insulating layers and minimizing volume loss
Solution Approach 2:
The invention optimizes the dimensions and arrangement parameters of the magnet pieces to achieve effective eddy current interruption while maximizing the magnetic material volume fraction, balancing energy loss reduction with volume preservation
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach effectively increases coercive force and heat resistance near the surface of magnet pieces, minimizing demagnetization and maintaining high magnetic flux, suitable for high-output and high-revolution applications in IPM or SPM rotary machines, while avoiding the need for insulating layers that reduce magnet volume.
Implementation Method 1
a coercive force profile enhanced by diffusing Dy or Tb from the surface toward the interior via grain boundaries
Implementation Method 2
sintered Nd base magnets are conductors having an electric resistance of 100 to 200 μΩ-cm. As the rotor rotates, the magnet undergoes a variation of magnetic flux density, by which eddy currents flow
Implementation Method 3
Permanent magnets in rotary machines are exposed to high temperature due to the heat generated by windings and cores and have a likelihood of demagnetization by the demagnetizing field from the windings
Data Source
Figure 1
Figure 2A~3B
Figure 4A~4B
AI summary
A permanent magnet rotary machine comprises a rotor comprising a rotor core and a plurality of permanent magnet segments embedded in the rotor core and a stator having a plurality of coils and disposed to define a gap with the rotor, or a permanent magnet rotary machine comprises a rotor comprising a rotor core and a plurality of permanent magnet segments mounted on the surface of the rotor core and a stator having a plurality of coils and disposed to define a gap with the rotor. In the rotor, each permanent magnet segment is an assembly of divided permanent magnet pieces, the coercive force near the surface of the magnet piece is higher than that in the interior of the magnet piece, and the assembly allows for electrical conduction between the magnet pieces.