Embedded Permanent Magnet Rotor Layout for Demagnetization Suppression
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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, leading to demagnetization of magnet areas adjacent to these features.
Innovation Solution
A rotor design with flux barriers and slits where the distance between slits and the magnet surface (Lb) is greater than the distance between slits and the rotor core (La), and the thickness of the magnet (Ld) is larger than the distance between the extended portion and the interpolar core (Lc), with Lb/La ≥ 2 and Ld/Lc ≥ 1.2, to redirect demagnetization flux away from the magnet.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If flux barriers and slits are added to the rotor to improve motor efficiency and reduce cogging torque, then motor efficiency increases and cogging torque decreases, but demagnetization occurs in magnet areas adjacent to these features
Solution Approach 1:
A flux releasing groove is introduced as an intermediary structure between the flux barrier and the permanent magnet. This groove provides a dedicated flux release path that prevents demagnetization flux from directly affecting the magnet, thereby protecting the magnet while maintaining the benefits of flux barriers for improving motor efficiency and reducing cogging torque.
Solution Approach 2:
The rotor structure is segmented into distinct functional zones: flux barriers for improving efficiency and reducing cogging torque, flux releasing grooves for protecting against demagnetization, and proper spacing (Lb > La) for flux management. This segmentation allows each component to perform its specific function without interfering negatively with others.
2Reliability
If heavy rare-earth elements such as dysprosium and terbium are added to increase magnetic coercive force, then demagnetization resistance improves, but procurement difficulty and price increase
Solution Approach 1:
The invention replaces expensive heavy rare-earth elements with a more economical approach using common materials arranged in specific geometries (flux releasing grooves and spaced flux barriers). This achieves demagnetization protection through structural design rather than expensive material composition, significantly reducing procurement costs and difficulty.
Solution Approach 2:
The invention changes the geometric parameters of the rotor structure (introducing flux releasing grooves, optimizing the spacing Lb > La between slits and magnet surface) to achieve demagnetization resistance. This parameter-based solution replaces material composition changes (adding heavy rare-earth elements) with structural optimization, reducing dependency on expensive materials.
3Object-generated harmful factors
If slits are formed close to the magnet surface to reduce harmonic wave components, then cogging torque and vibration decrease, but demagnetization flux bypasses the flux barrier and demagnetization occurs
Solution Approach 1:
The flux releasing groove acts as an intermediary structure between the slits and the permanent magnet. It provides a controlled path for flux while preventing demagnetization flux from directly reaching the magnet, thereby allowing slits to be positioned effectively for reducing cogging torque without compromising magnet protection.
Solution Approach 2:
The invention converts the potentially harmful demagnetization flux that would normally damage the magnet into a beneficial controlled flux path through the flux releasing groove. The groove captures and directs the flux away from the magnet, transforming what would be a harmful effect into a controlled and harmless flux distribution pattern.
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 design effectively suppresses demagnetization, allowing for the use of rare-earth magnets with lower magnetic coercive force, reducing the need for expensive heavy rare-earth elements and enhancing motor efficiency and reliability, especially in high-temperature environments.
Implementation Method 1
a hole for preventing a flux short circuit is formed in a rotor core so as to be brought close to an outer periphery of the rotor core, and the hole for preventing a flux short circuit is formed so as to be brought into contact with a hole for embedding a permanent magnet and an end portion of a permanent magnet to be embedded in the permanent magnet embedding hole
Implementation Method 2
the flux in the end portion of the permanent magnet extends to a stator so as to effectively serve to generate a torque
Data Source
AI summary
A permanent magnet embedded electric motor includes a slit and a flux barrier. A hole defining portion of a magnet insertion hole includes an extended portion. The extended portion projects toward an interpolar core portion in a rotor core 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. (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.