Permanent Magnet Motor Rotor Design for Torque Ripple Reduction
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Solution Overview
Problem
Permanent magnet assisted synchronous reluctance motors with multiple layers of permanent magnets experience increased torque ripple and vibrations due to the high percentage of reluctance torque, which complicates motor manufacturing and limits the effectiveness of existing methods to reduce torque ripple.
Innovation Solution
The design incorporates a stator and rotor with arc-shaped permanent magnet grooves, optimized endpoint angles, and a filling ratio greater than 85% to minimize the reluctance torque ripple by controlling the magnetic flux paths and inductance differences, ensuring the number of stator slots per pole per phase is an integer, and adjusting the width and shape of the flux barriers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If multiple layers of permanent magnets are arranged in the rotor to increase reluctance torque utilization, then motor efficiency and output torque are improved, but torque ripple and vibrations increase
Solution Approach 1:
The patent changes geometric parameters of the permanent magnets including arc-shaped grooves with optimized endpoint angles, filling ratios greater than 85%, and adjusted widths of flux barriers to control the distribution of magnetic flux paths, thereby reducing torque ripple while maintaining high output torque
Solution Approach 2:
The patent applies different properties to different parts of the rotor structure, including varying the shape and dimensions of permanent magnets in different regions, creating arc-shaped grooves with specific endpoint angles, and adjusting flux barrier widths locally to optimize magnetic flux distribution and reduce torque fluctuations
2Power
If the number of stator slots per pole per phase is set to a fraction to increase reluctance torque, then inductance difference is improved, but harmonic content in stator magnetic field increases
Solution Approach 1:
The patent optimizes the stator slot configuration by setting the number of stator slots per pole per phase to an integer value, which reduces harmonic content in the stator magnetic field while maintaining effective reluctance torque through compensated rotor design features
3Speed
If field weakening control is applied to enable high speed operation, then motor speed is improved, but torque ripple increases due to higher reluctance torque percentage
Solution Approach 1:
The patent implements parameter optimizations in the rotor structure including arc-shaped permanent magnet grooves with controlled endpoint angles and adjusted flux barrier dimensions that reduce torque ripple across the entire operating range, including during field weakening control at high speeds
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 significantly reduces torque ripple and fluctuations in inductance, resulting in a more stable and efficient motor operation with reduced electromagnetic torque fluctuations.
Implementation Method 1
The permanent magnetic torque is generated by the rotor permanent magnetic field interacted with the stator magnetic field
Implementation Method 2
The reluctance torque is generated by the stator magnetic field interacted with the rotor iron core whose direct-axis inductance and quadrature-axis inductance are different
Implementation Method 3
reducing the eddy current loss and the torque ripple
Data Source
AI summary
A permanent magnet motor, comprising a stator (1) and a rotor (4); the rotor comprises a rotor iron core (5) and permanent magnets (7a, 7b); in the radial direction of the rotor, each magnetic pole of the rotor iron core is provided with multiple layers of arc-shaped permanent magnet grooves (6a, 6b); a q-axis magnetic flux path is formed between two neighboring magnetic poles; the permanent magnets are disposed in the permanent magnet grooves; two neighboring magnetic poles of the rotor are respectively a first magnetic pole and a second magnetic pole having opposite polarities; an outer endpoint of a permanent magnet in the first magnetic pole is a first outer endpoint, said outer endpoint is farther from the q-axis; an outer endpoint of the permanent magnet in the second magnetic pole is a second outer endpoint, said outer endpoint is farther from the q-axis; an included angle A of the first outer endpoint and the second outer endpoint with respect to the center of the rotor is less than an electrical angle of 80 degrees, the number of stator slots being N, the number of pairs of rotor poles being P, the number of phases of windings being m, and the number of stator slots per pole per phase (N/2P/m) being an integer. As compared with motors having existing structures, the permanent magnet motor dramatically reduces the torque ripple thereof.