Synchronous Machine Rotor Pole with Tapered Permanent Magnets
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Solution Overview
Problem
Synchronous motors and generators face significant armature magnetic reaction issues, leading to net flux loss and increased line voltage total harmonic distortion (THD), particularly at unity power factor, due to the cross-magnetizing effect, which existing mitigation schemes like permanent magnets placement struggle to address effectively.
Innovation Solution
The implementation of a synchronous electrical machine design where permanent magnets on the rotor poles increase radially in thickness smoothly from the leading to the trailing edge, compensating for armature magnetic reaction and reducing air gap flux distortion, thereby improving operational efficiency and reducing line voltage THD.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If permanent magnets are mounted on rotor pole tip surfaces to mitigate armature reaction, then armature magnetic reaction is compensated, but line voltage total harmonic distortion worsens if magnets are not located at correct positions or are too powerful
Solution Approach 1:
The patent applies local quality by varying the radial thickness of permanent magnets across the pole tip surface. The magnets are thinnest at the leading edge and thickest at the trailing edge, creating a non-uniform distribution that locally compensates for armature reaction effects at different pole positions while maintaining sinusoidal flux distribution and avoiding harmonic distortion
Solution Approach 2:
The patent changes the parameter of magnet thickness from uniform to non-uniform across the pole tip surface. This parameter variation allows the magnets to provide optimal compensation for armature reaction at different locations, improving power factor correction while maintaining low harmonic distortion without requiring precise location or power selection
2Ease of manufacture
If permanent magnets with uniform thickness are used, then manufacturing is simplified, but armature reaction compensation is less effective at mitigating air gap flux waveform distortion
Solution Approach 1:
The patent implements local quality by making the permanent magnet thickness vary across the pole tip surface, with the thinnest section at the leading edge and thickest section at the trailing edge. This non-uniform thickness distribution locally optimizes the magnetic field compensation at different pole positions, effectively mitigating air gap flux waveform distortion while remaining manufacturable
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 enhances the sinusoidal nature of the air gap flux, reduces line voltage THD, and increases operational efficiency, making it less dependent on precise magnet placement and power selection, while allowing for retrofitting into existing machines.
Implementation Method 1
each pole carries a row of permanent magnets which extends across the tip surface from one of the side flanks to the other side flank, the permanent magnets compensating for armature magnetic reaction
Implementation Method 2
the radial thickness of the permanent magnets increases smoothly with progressive distance across the tip surface from one of the side flanks to the other side flank... mitigates the level of distortion of the air gap flux waveform to create a more sinusoidal air gap flux
Data Source
AI summary
A synchronous electrical machine includes a stator having a circumferential row of teeth carrying stator windings. The electrical machine further includes a coaxial rotor having a circumferential row of poles carrying field windings. Each pole has first and second side flanks and a tip surface which extends continuously there between to form an air gap to the teeth of the stator. On a transverse cross-section through the machine, one of the side flanks forms a leading edge of the pole, and the other side flank forms an opposite, trailing edge of the pole. Each pole carries a row of permanent magnets which extends across the tip surface from one of the side flanks to the other side flank, the permanent magnets compensating for armature magnetic reaction. The radial thickness of the permanent magnets increases smoothly with progressive distance across the tip surface from one of the side flanks to the other side flank.