Consequent-Pole Rotor Assembly for Lower Back-EMF Harmonics
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Alternating-pole permanent magnet synchronous motors face issues with reduced output torque and increased torque ripple due to the asymmetry of adjacent magnetic pole structures and abundant harmonic content in back-EMF, limiting their promotion and application.
Innovation Solution
A rotor assembly with a rotor core featuring alternately arranged permanent magnetic poles and alternating poles, including mounting grooves with permanent magnets and strategically positioned air slots with stepped extensions, which adjust the magnetic lines of force to reduce back-EMF harmonic content and torque ripple by making the back-EMF waveform more symmetrical.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the number of permanent magnets is reduced to half in alternating-pole motors, then the cost is significantly reduced, but the output torque decreases and torque ripple increases
Solution Approach 1:
The patent introduces non-magnetic portions with specific geometric features (steps, width narrowing) at localized positions within the rotor core, creating non-uniform magnetic pathways that improve torque characteristics while maintaining reduced permanent magnet count
Solution Approach 2:
The patent modifies geometric parameters of the rotor core structure, including the shape and position of non-magnetic portions, to optimize the magnetic circuit and improve torque ripple and output torque despite using fewer permanent magnets
2Quantity of substance
If the number of permanent magnets is reduced to half in alternating-pole motors, then the cost is significantly reduced, but the torque ripple increases
Solution Approach 1:
The patent introduces non-magnetic portions with specific geometric features (steps, width narrowing) at localized positions within the rotor core, creating non-uniform magnetic pathways that improve torque characteristics while maintaining reduced permanent magnet count
Solution Approach 2:
The patent employs asymmetric design of non-magnetic portions within the alternating poles, where the non-magnetic portions have unequal widths and positions on either side of the alternating pole, creating balanced magnetic circuits that reduce torque ripple in alternating-pole motors
3Object-generated harmful factors
If the pole-arc coefficient is optimized to improve torque ripple, then the cogging torque ripple is reduced, but the back-EMF harmonic content remains high
Solution Approach 1:
The patent introduces non-magnetic portions with specific geometric features (steps, width narrowing) at localized positions within the rotor core, creating non-uniform magnetic pathways that improve torque characteristics while maintaining reduced permanent magnet count
Solution Approach 2:
The patent modifies geometric parameters of the rotor core structure, including the shape and position of non-magnetic portions, to optimize the magnetic circuit and improve torque ripple and output torque despite using fewer permanent magnets
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
Significantly reduces back-EMF harmonic content and distortion rate, improving motor performance by enhancing the symmetry of air gap magnetic density and reducing torque ripple.
Implementation Method 1
an alternating-pole permanent magnet synchronous motor
Implementation Method 2
permanent magnetic poles and alternating poles that are arranged alternately in a circumferential direction
Data Source
Figure 1
Figure 2~3
Figure 4~6
AI summary
The present disclosure provides a rotor assembly and an alternating-pole motor. The rotor assembly includes a rotor core including permanent magnetic poles and alternating poles that are arranged alternately in a circumferential direction, each permanent magnetic pole includes a mounting groove (2), a permanent magnet (3) is mounted in the mounting groove (2), polarities of the permanent magnets (3) facing an outer periphery of the rotor core (1) are the same, both ends of the mounting groove (2) are respectively provided with a second air slot (5), the second air slot (5) includes a slot body and a first extension part (6) and a second extension part (7) that are extended from the slot body to a center line of a magnetic pole, and the first extension part (6) and the second extension part (7) are sequentially disposed to form a stepped slot with a decreasing radial thickness. According to the rotor assembly of the present disclosure, a problem that an increase in a torque ripple caused by back-EMF harmonic of the alternating-pole motor is resolved, a back-EMF harmonic content is significantly reduced, and motor performance is improved.