Asymmetric Rotor Magnet Layout for Low-Cogging Electric Machines
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Solution Overview
Problem
Conventional synchronous generators experience issues with high cogging torque and output voltage ripple due to the interaction between permanent magnets and stator slots, which can be mitigated but at the cost of increased complexity and reduced running torque.
Innovation Solution
A rotor assembly with a set of first permanent magnets and a set of second permanent magnets alternately spaced about the periphery, where the second magnets are circumferentially offset with respect to the first magnets, reducing harmonic distortion and cogging torque without adding manufacturing complexity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If permanent magnets are arranged in conventional symmetric patterns, then manufacturing is simple, but cogging torque and harmonic distortion increase
Solution Approach 1:
The patent applies asymmetry by arranging permanent magnets with non-uniform spacing around the rotor periphery. Specifically, the angular distance between adjacent magnets varies, creating an asymmetric magnetic field distribution that reduces cogging torque and harmonic distortion while maintaining manufacturing feasibility through standardized magnet components.
Solution Approach 2:
The patent implements local quality by creating different magnetic field characteristics at different angular positions around the rotor. The varying spacing between magnets produces localized magnetic field variations that collectively reduce overall harmonic distortion and cogging torque, allowing each region to contribute differently to the overall performance.
2Object-generated harmful factors
If permanent magnets are arranged in conventional symmetric patterns, then manufacturing is simple, but harmonic distortion increases
Solution Approach 1:
The asymmetric magnet arrangement with varying angular spacing disrupts the periodicity that causes harmonic distortion in conventional symmetric designs. This non-uniform distribution eliminates the regular magnetic field patterns that generate harmonics, reducing distortion in the generated electrical output.
Solution Approach 2:
The patent changes the angular spacing parameter between adjacent magnets from a constant value to a variable value. By modifying this geometric parameter to create non-uniform spacing, the magnetic field distribution changes in a way that reduces harmonic distortion without requiring changes to magnet material or stator design.
3Object-generated harmful factors
If conventional magnet arrangements are used, then manufacturing is straightforward, but output voltage ripple increases
Solution Approach 1:
The asymmetric magnet spacing creates a more uniform electromagnetic interaction with the stator windings throughout the rotation cycle. This eliminates the periodic variations in magnetic coupling that cause voltage ripple in symmetric arrangements, producing smoother output voltage without requiring additional filtering components.
4Object-generated harmful factors
If asymmetric magnet arrangement is implemented, then cogging torque decreases, but manufacturing complexity increases
Solution Approach 1:
The asymmetric arrangement achieves cogging torque reduction through non-uniform magnet spacing while maintaining ease of manufacture by using identical magnet components. The complexity is minimized to only the positioning arrangement, not the magnet fabrication, allowing standard manufacturing processes to be used with simple positioning adjustments.
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 arrangement decreases harmonic distortion, cogging torque, and output voltage ripple, enhancing the efficiency and reducing manufacturing costs by minimizing the use of magnetic materials while maintaining or exceeding the performance of conventional systems.
Implementation Method 1
an electric machine having a stator and a rotor assembly. The rotor assembly can include a rotor core having a set of permanent magnets
Implementation Method 2
a rotor core having a set of permanent magnets and driven to rotate by a source of rotation
Data Source
Figure 1
Figure 2
Figure 3
AI summary
A rotor assembly (212) comprising rotatable element defining a periphery (219), a set of first permanent magnets (221) and a set of second permanent magnets (222) alternately circumferentially spaced about the periphery (219). The first permanent magnets (221) are symmetrically spaced from each other, the second permanent magnets (222) are symmetrically spaced from each other, and each second permanent magnet (222) is disposed between and asymmetrically spaced from a respective pair of immediately adjacent first permanent magnets (221).