Magnet Shifting for Torque Ripple Reduction in PMSMs
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Solution Overview
Problem
Permanent magnet synchronous motors suffer from significant torque ripple due to the concavity and convexity of their structure and the coupling effect of the magnetic field, limiting their application in demanding applications that require smooth output torque and high operating stability.
Innovation Solution
A method involving magnet shifting, where the rotor and magnets are modularized to form repeating units with consistent torque waveforms and phases, allowing for the calculation of shifting angles to reduce torque ripple by weakening the effects of cogging and reluctance torque, while maintaining torque density.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If skewing is used to reduce torque ripple, then torque ripple is reduced, but manufacturing complexity and production cost increase
Solution Approach 1:
The patent applies asymmetry by optimizing the stator slot opening width to be unequal on different sides of the stator teeth. Specifically, the slot opening width is designed to be larger at the top and bottom of the teeth compared to the middle section, creating an asymmetric magnetic path that reduces cogging torque and torque ripple without requiring mechanical skewing of the stator or rotor components
Solution Approach 2:
The patent changes the geometric parameters of the stator slots, specifically optimizing the slot opening width distribution. By adjusting the slot opening width to different values at different positions (larger at top/bottom, smaller in middle), the magnetic field distribution is optimized to reduce torque ripple while maintaining simple manufacturing processes
2Ease of manufacture
If auxiliary slots or teeth are used to replace skewing, then manufacturing is simplified, but motor efficiency is reduced
Solution Approach 1:
The patent optimizes the slot opening width parameter to achieve a balance between manufacturing simplicity and efficiency. By carefully selecting the slot opening width values at different positions, the design reduces torque ripple through magnetic field optimization while minimizing the impact on motor efficiency, avoiding the need for auxiliary slots that would compromise efficiency
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 method effectively reduces torque ripple, stabilizes motor output, and minimizes vibration and noise, optimizing back-EMF and maintaining nearly original torque output, with fewer harmonic components of radial force density compared to traditional methods.
Implementation Method 1
permanent magnet synchronous motors utilize magnetic material with high magnetic energy
Implementation Method 2
coupling effect of magnetic field
Implementation Method 3
A method involving magnet shifting, where the rotor and magnets are modularized to form repeating units with consistent torque waveforms and phases
Data Source
AI summary
A method named as Magnet Shifting to reduce torque ripple of permanent magnet synchronous motor is disclosed. A way of reasonably choosing the repeating unit of magnetic pole, the shifting ways and the shifting angle calculation of the first and second magnet shifting is described, which are carried on the repeating unit of magnetic poles individually or repeatedly to improve the performance of the motor. The method can be applied to surface, surface-inset and inner-embedded permanent magnet motors, which can reduce torque ripple caused by different torque components, including cogging torque, reluctance torque or permanent magnet torque. It also can quickly calculate the shifting angle of the magnetic pole by choosing repeating unit reasonably. Magnet shifting can effectively enhance the sinusoidal degree of back electrodynamic force (back-EMF) waveform, where the repeating units can offset the torque ripple between the maximum and the minimum value to reduce the different torque harmonics. Also, the output torque can be maintained nearly to the original value while less vibration noise of the motor is inevitably introduced.