IPM Magnet Magnetic Path Length Demagnetization Resistance
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Solution Overview
Problem
Interior permanent magnet (IPM) motors face demagnetization issues due to high excitation currents, leading to irreversible demagnetization of permanent magnets, especially when field-weakening control is employed, which increases the risk of demagnetization and requires costly solutions like using rare earth elements or increasing magnet thickness/volume.
Innovation Solution
The design incorporates magnets with magnetic paths oriented at angles closer to the d-axis, featuring longer magnetic paths than the magnet thickness, and a manufacturing method that aligns easy axes of magnetization along these paths to enhance demagnetization resistance without increasing material thickness, thereby reducing demagnetization risks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If field-weakening control is employed to increase rotational speed, then the operational range of the motor is extended, but the demagnetization field acting on permanent magnets increases causing irreversible demagnetization
Solution Approach 1:
The patent changes the magnetic path length parameter of the permanent magnet, making it longer than the thickness dimension. This parameter change increases the demagnetization resistance without requiring material composition changes or increased magnet volume, thereby allowing field-weakening control to be performed while preventing irreversible demagnetization.
2Reliability
If magnet thickness is increased to improve demagnetization resistance, then the resistance against demagnetization field is enhanced, but the device volume and material costs increase
Solution Approach 1:
Instead of increasing magnet thickness, the patent changes the magnetic path length parameter to be longer than the thickness dimension. This allows achieving higher demagnetization resistance while maintaining compact magnet volume and avoiding increased material costs.
3Reliability
If rare earth elements are used to enhance demagnetization resistance, then the resistance against demagnetization field is improved, but the manufacturing cost increases significantly
Solution Approach 1:
The patent achieves improved demagnetization resistance through geometric parameter optimization (magnetic path length > thickness) rather than material composition changes. This avoids the need for expensive rare earth elements while maintaining effective demagnetization resistance.
4Power
If high excitation current is applied to increase torque output, then the torque density of the motor is improved, but the demagnetization field strength increases causing magnet demagnetization
Solution Approach 1:
By optimizing the magnetic path length parameter to be longer than the thickness dimension, the patent enables the motor to withstand higher excitation currents without demagnetization. This allows achieving high torque density while maintaining magnet reliability under high current operation.
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 configuration strengthens the magnetic force against demagnetization fields, effectively reducing demagnetization and enhancing the demagnetization resistance of the magnets, thus improving the performance and reliability of IPM motors without increasing material costs.
Implementation Method 1
Each of the magnets has magnetic paths each having a length longer than a thickness dimension of the corresponding one of the magnets between the opposing flux effective surfaces
Implementation Method 2
Each of the magnets has a plurality of easy axes of magnetization; the easy axes of magnetization are oriented to be along the respective magnetic paths
Data Source
AI summary
In a rotary electric machine, magnets provided in a core generate circumferentially arranged magnetic poles. Each magnetic pole defines d- and q-axes. The d-axis represents a center of the corresponding magnetic pole. The rotary electric machine includes an armature including an armature winding. Each magnet includes a magnet body having opposing first and second flux effective surfaces. The first flux effective surface is a surface out of which magnetic flux flows. The second flux effective surface into which magnetic flux flows. The magnet body has a thickness defined as a minimum distance between the first and second flux effective surfaces. The magnet body has easy axes of magnetization. A length of a line along at least one of the easy axes of magnetization between the first and second flux effective surfaces is longer than the thickness of the magnet body.