IPM Motor Rotor with Unequal Pole Arc Lengths
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Solution Overview
Problem
Conventional permanent magnet brushless motors with interior permanent magnet (IPM) rotors exhibit non-sinusoidal air-gap magnetic field distribution, leading to non-sinusoidal back emf waveforms, increased torque ripple, noise, and vibration due to repetitive pole structures, which also cause cogging torque.
Innovation Solution
The design incorporates a rotor with pole pieces having different pole arc lengths, specifically a combination of long and short pole pieces with unique geometry and flux barriers to achieve asymmetry, reducing radial forces and unbalanced magnetic pull, thereby enhancing motor performance by improving sinusoidality of the back emf and reducing torque ripple and cogging.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional interior permanent magnet rotors with repetitive pole structures are used, then the motor structure is simple and easy to manufacture, but the air-gap magnetic field distribution becomes non-sinusoidal, causing increased torque ripple, noise, and vibration
Solution Approach 1:
The patent applies asymmetry by configuring pole pieces with unequal pole arc lengths, where adjacent pole pieces have different pole arc lengths. This asymmetric arrangement modifies the air-gap magnetic field distribution to be more sinusoidal, thereby reducing torque ripple and harmful harmonics while maintaining manufacturing feasibility through systematic pole piece design
2Ease of manufacture
If conventional interior permanent magnet rotors with repetitive pole structures are used, then the manufacturing process is straightforward, but the back emf waveform becomes non-sinusoidal, detrimental to motor electronic control
Solution Approach 1:
The asymmetric pole piece configuration with unequal pole arc lengths transforms the air-gap magnetic field distribution, which directly improves the back emf waveform sinusoidality. This enables better electronic control performance while maintaining a straightforward manufacturing process through systematic pole piece arrangement
3Device complexity
If conventional interior permanent magnet rotors with equal pole arc lengths are used, then the rotor design is simple, but cogging torque increases due to repetitive pole structures
Solution Approach 1:
The patent introduces asymmetry by configuring adjacent pole pieces with different pole arc lengths, which disrupts the repetitive pole structure that causes cogging torque. This asymmetric design reduces cogging torque and harmonics while maintaining reasonable rotor design complexity through systematic pole piece configuration
Solution Approach 2:
The patent applies local quality by giving different pole arc lengths to different pole pieces based on their positions. This localized variation in pole piece geometry optimizes the magnetic field distribution in different regions, reducing cogging torque and improving overall motor performance
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 reduces torque ripple, noise, and vibration, while improving motor efficiency and performance by balancing radial forces and harmonics in the air-gap magnetic field, resulting in a more stable and efficient motor operation.
Implementation Method 1
permanent magnet brushless motors that include a rotor that has interior permanent magnets
Implementation Method 2
interior permanent magnets and unequal poles
Data Source
Figure 1
Figure 2
Figure 3~3a
AI summary
An electric machine includes a stator and a rotor core including a first rotor portion positioned adjacent the stator and having an outside diameter. The first rotor portion includes a plurality of elongated slots that define a plurality of poles. The electric machine also includes a plurality of magnets. Each of the plurality of magnets is positioned within one of the slots and arranged such that each of the plurality of poles has a magnetic arc length that is different than a magnetic arc length of any adjacent pole.