Rotor Bridge Elements for Ferrite Magnet Demagnetization Control
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Solution Overview
Problem
Electric machines using ferrite magnets face challenges in achieving high power density while minimizing demagnetization risks under field weakening and short circuit conditions, as ferrite magnets are less expensive alternatives to rare earth magnets but require effective flux management to prevent demagnetization.
Innovation Solution
A rotor design featuring a support frame with elongated flux barrier elements that control magnetic flux leakage, increasing the reluctance of the flux path and reducing magnetic flux leakage into the center section, thereby enhancing flux density and torque characteristics, and incorporating secondary magnets to saturate and inhibit flux leakage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If ferrite magnets are used instead of rare earth magnets, then cost is reduced, but power density and resistance to demagnetization deteriorate
Solution Approach 1:
Bridge elements are introduced as intermediary components between the permanent magnets and the center section. These bridge elements act as mediators that control and manage magnetic flux distribution, preventing excessive flux concentration that would cause demagnetization of ferrite magnets while maintaining structural connectivity.
Solution Approach 2:
The design changes the magnetic flux distribution parameters by introducing bridge elements with specific geometric configurations. This alters the flux density and path characteristics in the center section, creating conditions that protect ferrite magnets from demagnetization while maintaining acceptable performance.
2Reliability
If flux barriers are introduced to control magnetic flux leakage, then demagnetization risk is reduced, but device complexity increases
Solution Approach 1:
The rotor structure is segmented into distinct functional zones: permanent magnets, bridge elements, and center section. The bridge elements are further divided into multiple segments within each spoke, allowing independent optimization of flux control while maintaining manufacturing feasibility through modular construction.
Solution Approach 2:
The bridge elements serve multiple functions simultaneously: they provide structural support connecting the magnets to the center section, control magnetic flux leakage, and prevent demagnetization. This multi-functionality reduces the need for separate dedicated flux barrier components, thereby limiting the increase in overall device complexity.
3Reliability
If bridge elements with small cross-sectional area are used to promote saturation, then flux leakage is reduced, but manufacturing precision requirements increase
Solution Approach 1:
The bridge elements are designed with specific geometric parameters including small cross-sectional area and elongated shape along the flux path. These parameter changes promote magnetic saturation at controlled locations, effectively blocking flux leakage paths while providing clear design criteria that can be manufactured with standard precision capabilities.
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
The rotor design improves torque characteristics and reduces demagnetization risks by concentrating magnetic flux and managing flux leakage, making it suitable for electric machines, including those using ferrite magnets, while maintaining structural integrity and efficiency.
Implementation Method 1
The reluctance of the flux path to the centre section is increased and magnetic flux leakage may be reduced
Implementation Method 2
The first and second bridge elements may become saturated. By controlling the flux leakage into the centre section, the flux density in an airgap between the rotor and a stator may be improved
Implementation Method 3
The torque characteristics of the electric machine may be improved via flux concentration
Data Source
AI summary
The present disclosure relates to a rotor (3) for an electric machine (1). The rotor (3) is composed of a support frame (5) having a centre section (8) and a plurality of spokes (9). The spokes (9) extend outwardly from the centre section (8). The spokes (9) each have at least first and second bridge elements (12A, 12B) formed by one or more flux barrier (13). The first and second bridge elements (12A, 12B) are configured to control magnetic flux leakage into said centre section (8). The present disclosure also relates to an electric machine (1) having a rotor (3) of this type.