IPM Motor Rotor End Surface Resistivity for Eddy Current Loss Reduction
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Solution Overview
Problem
In IPM motors, the protrusion of the rotor's end surface beyond the stator's end surface leads to magnetic flux perpendicular components, causing eddy currents and efficiency deterioration due to eddy current losses.
Innovation Solution
The end surface portion between the permanent magnet and the air gap in the rotor is made of a material with higher electrical resistivity than the main body portion, specifically using a pressed powder compact of soft magnetic powder, to prevent eddy currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the rotor length is designed to be longer than the stator length so that the rotor end surface protrudes further than the stator end surface, then motor characteristics are improved, but eddy current losses occur in the rotor end surface portion leading to efficiency deterioration
Solution Approach 1:
The patent applies local quality by making the electrical resistivity of the rotor core material non-uniform along the axial direction. Specifically, the end surface portion (protruding part) has higher electrical resistivity than the main body portion, which prevents eddy currents from forming in the high-resistivity region while maintaining the beneficial protruding structure for motor characteristics.
Solution Approach 2:
The patent changes the electrical resistivity parameter of the rotor core material along the axial direction. By increasing the electrical resistivity in the end surface portion compared to the main body portion, the patent suppresses eddy current formation in the protruding region while preserving the motor performance benefits of the extended rotor length.
2Loss of energy
If the electrical resistivity of the end surface portion is increased to prevent eddy currents, then efficiency is improved, but the uniformity of the rotor core structure is reduced
Solution Approach 1:
The patent deliberately introduces non-uniformity in the rotor core by assigning different electrical resistivity values to different axial regions. The end surface portion has higher electrical resistivity to prevent eddy currents, while the main body portion maintains lower electrical resistivity for optimal magnetic performance, creating a functionally optimized non-uniform structure.
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 significantly reduces eddy current losses, enhancing motor efficiency by minimizing eddy current occurrences, as demonstrated by finite element analysis.
Implementation Method 1
at least a first portion of the end surface portion which is positioned between the permanent magnet and an air gap between the rotor and the stator as seen from the axial direction of the rotor has a higher electrical resistivity than an electrical resistivity of the main body portion
Data Source
AI summary
In an IPM motor, since an end surface portion which is a pressed powder compact made of soft magnetic powder has a higher electrical resistivity than an electrical resistivity of a main body portion made of a laminated steel sheet, compared to when the electrical resistivity of the end surface portion is the same as the electrical resistivity of the main body portion, the occurrence of an eddy current in the end surface portion is further prevented. For this reason, in the IPM motor, a deterioration in efficiency caused by an eddy current loss is prevented, and an improvement in efficiency is realized.