Rotor Permanent Magnet Gradient Coercive Force
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Solution Overview
Problem
In large permanent magnet rotating machines, especially wind power generators, there is a tradeoff between magnetic coercive force and residual magnetic flux density, leading to reduced electric generating capacity due to demagnetization from diamagnetic fields, particularly during short-circuit events, where existing diffusion methods are not effective for rectangular magnets used in IPM machines.
Innovation Solution
Increasing the magnetic coercive force only in the stator-side surface region of the rotor's permanent magnets through diffusion treatment with Dy or Tb, up to a depth of 3-5 mm, effectively enhances demagnetization resistance and output without significantly reducing residual magnetic flux density.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the magnetic coercive force of the permanent magnet is increased to prevent demagnetization, then the demagnetization resistance is improved, but the residual magnetic flux density decreases, reducing the electric generating capacity
Solution Approach 1:
The patent applies local quality by creating a gradient structure where the magnetic coercive force varies across the magnet thickness. The surface region (within 3-5mm from the surface) has a higher magnetic coercive force due to diffusion treatment with Dy or Tb, while the inner portion maintains a lower magnetic coercive force. This allows the surface region to resist demagnetization from diamagnetic fields during short-circuit events, while the inner portion preserves high residual magnetic flux density for maintaining electric generating capacity.
2Reliability
If Dy or Tb is diffused from the surface to the inside of the sintered magnet to increase magnetic coercive force, then the demagnetization resistance is improved, but the residual magnetic flux density is reduced
Solution Approach 1:
The patent applies local quality by creating a gradient structure where the magnetic coercive force varies across the magnet thickness. The surface region (within 3-5mm from the surface) has a higher magnetic coercive force due to diffusion treatment with Dy or Tb, while the inner portion maintains a lower magnetic coercive force. This allows the surface region to resist demagnetization from diamagnetic fields during short-circuit events, while the inner portion preserves high residual magnetic flux density for maintaining electric generating capacity.
Solution Approach 2:
The patent applies partial action by limiting the diffusion treatment to only the surface region within a specific depth (3-5mm from the surface). This partial treatment is sufficient to protect against demagnetization during short-circuit events, while avoiding excessive diffusion that would reduce the residual magnetic flux density throughout the entire magnet.
3Reliability
If the magnetic coercive force is increased throughout the entire magnet, then the demagnetization resistance is improved, but the output is reduced due to lower residual magnetic flux density
Solution Approach 1:
The patent applies local quality by creating a gradient structure where the magnetic coercive force varies across the magnet thickness. The surface region (within 3-5mm from the surface) has a higher magnetic coercive force due to diffusion treatment with Dy or Tb, while the inner portion maintains a lower magnetic coercive force. This allows the surface region to resist demagnetization from diamagnetic fields during short-circuit events, while the inner portion preserves high residual magnetic flux density for maintaining electric generating capacity.
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 significantly increases the magnetic coercive force in the surface region, enhancing demagnetization resistance and maintaining high residual magnetic flux density, thereby improving the output and reliability of large wind power generators by preventing demagnetization during severe diamagnetic field conditions.
Implementation Method 1
there is a method for increasing a magnetic coercive force without reducing a residual magnetic flux density in which Dy (dysprosium) or Tb (terbium) is diffused from a surface to an inside of a sintered magnet
Implementation Method 2
the permanent magnet in the rotating machine is apt to be demagnetized by the action of diamagnetic fields due to the winding wire
Data Source
Figure 1~2
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Figure 5~6
AI summary
A rotor (11) adapted for a large permanent magnet rotating machine (10) having high output and demagnetization resistance and the permanent magnet rotating machine (10) are provided. More specifically, there is provided a rotor (11) adapted for a permanent magnet rotating machine (10), the machine (10) comprising the rotor (11) and a stator (15) disposed with a clearance from an outer peripheral face of the rotor (11) and formed by winding a winding wire through a stator core (16) having two or more slots, the rotor (11) comprising one or more permanent magnets (13) in each of two or more insertion holes, the insertion holes being formed in a circumferential direction in a rotor core (12), wherein a magnetic coercive force in a stator-side surface region of each of the permanent magnets (13) is greater than that in an inner central portion by 300 kA/m or more, the inner central portion being an inner portion at a depth of at least 5 mm from every outer shape face of the permanent magnet (13).