Embedded Permanent Magnet Rotor Layout for Demagnetization Resistance
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Solution Overview
Problem
Permanent magnet electric motors face demagnetization issues due to large loads, start-up states, or stator winding short-circuits, particularly in rotors with flux barriers and slits, which lead to demagnetization of adjacent magnet areas due to bypassing demagnetization flux.
Innovation Solution
The design includes flux barriers and slits in the rotor core with specific geometric relationships (Lb/La ≥ 2 and Ld/Lc ≥ 1.2) to redirect demagnetization flux away from the magnets, using a rare-earth magnet with reduced dysprosium content to minimize demagnetization risk.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If heavy rare-earth elements such as dysprosium and terbium are added to increase magnetic coercive force, then demagnetization resistance is improved, but cost and procurement difficulty increase
Solution Approach 1:
The invention changes the geometric parameters of the rotor core structure, specifically the distance relationships between slits, flux barriers, and magnet insertion holes. By optimizing parameters La and Lb such that Lb/La ≥ 2, the design achieves improved demagnetization resistance through structural configuration rather than material composition changes, thereby reducing dependence on expensive heavy rare-earth elements.
2Productivity
If flux barriers and slits are formed in the rotor core, then motor efficiency is improved by preventing flux short circuit, but demagnetization flux bypasses these structures causing localized demagnetization
Solution Approach 1:
The invention introduces an intermediary structural relationship between the flux barriers and slits. By positioning the slits at a specific distance Lb from the magnet insertion holes (where Lb/La ≥ 2), the design creates an intermediate zone that allows flux barriers to prevent short-circuit flux while preventing demagnetization flux from directly bypassing to adjacent magnets, thus resolving the conflict between efficiency and demagnetization protection.
3Object-generated harmful factors
If slits extend further in magnet thickness direction than width direction, then harmonic wave components are reduced, but structural complexity increases
Solution Approach 1:
The invention specifies precise parameter relationships for the slit geometry, requiring that slits extend further in the magnet thickness direction than in the width direction. This parameter change effectively reduces harmonic wave components and cogging torque while maintaining manufacturability through clear geometric definitions, balancing performance improvement with structural simplicity.
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 effectively suppresses demagnetization, allowing for high-efficiency operation with reduced rare-earth element usage, lower noise, and enhanced reliability in high-temperature environments, while maintaining motor performance.
Implementation Method 1
flux barriers are formed on both sides of the magnet insertion hole in a circumferential direction; a plurality of slits are formed between each of the magnet insertion holes in the rotor core and a core outer peripheral surface
Implementation Method 2
a corresponding permanent magnet is inserted in each of the plurality of magnet insertion holes
Data Source
Figure 1
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AI summary
A permanent magnet embedded electric motor (1) includes a slit (25) and a flux barrier (23). A hole defining portion of a magnet insertion hole includes an extended portion (11b). The extended portion projects toward an interpolar core portion (11c) in a rotor core (11) in an area positioned further on an outer side of a circumferential direction with respect to a width-direction end surface of a permanent magnet (13). (Lb) is larger than (La), and (Lc) is smaller than (Ld), where the (La) represents a distance between the slit and the core outer peripheral surface; the (Lb) represents a distance between the slit and an outer peripheral-side surface of the permanent magnet; the (Lc) represents a shortest distance between the extended portion and the interpolar core portion; and the (Ld) represents a thickness of the permanent magnet.