Dual-Rotor Halbach Machine Layout Without Back-Iron Losses
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Solution Overview
Problem
Conventional single-rotor synchronous machines face inefficiencies due to eddy current losses in back iron, which reduce power and torque density, as increased magnetic flux density leads to increased eddy current losses, and these losses cannot be completely eliminated despite using laminated iron yokes with low electrical conductivity.
Innovation Solution
A dual-rotor synchronous machine design utilizing concentric Halbach arrays for the outer and inner rotors, where the magnetic flux is enhanced in the air gap and minimized on the rotors themselves, eliminating eddy current losses by channeling flux in a way that it only appears on one side of the arrays, and using a stationary stator positioned between the rotors to maximize magnetic field strength and minimize mass.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If magnetic flux density is increased to maximize power and torque density, then power and torque density are improved, but eddy current losses in back iron increase
Solution Approach 1:
The patent divides the rotor structure into two separate rotors (inner rotor and outer rotor) with Halbach arrays positioned at different radii. This segmentation allows the magnetic flux to be channeled through the stator without requiring back iron in the rotor, thereby eliminating eddy current losses while maintaining high magnetic flux density in the air gap for improved power density.
Solution Approach 2:
The patent extracts and eliminates the back iron component from the rotor structure by using Halbach arrays that channel flux through the air gap and stator. This removal of back iron directly eliminates the source of eddy current losses while the Halbach arrays maintain sufficient magnetic flux density for high power density operation.
2Strength
If back iron is used to channel magnetic flux, then magnetic flux density is maintained, but eddy current losses occur due to electrical conductivity of the iron
Solution Approach 1:
The patent extracts and eliminates the back iron component from the rotor structure by using Halbach arrays that channel flux through the air gap and stator. This removal of back iron directly eliminates the source of eddy current losses while the Halbach arrays maintain sufficient magnetic flux density for high power density operation.
Solution Approach 2:
The patent introduces the Halbach array as an intermediary structure that channels magnetic flux through the air gap and stator without requiring conductive back iron. The Halbach array uses permanent magnets arranged in a specific pattern to direct flux, serving as a mediator that achieves flux channeling without the harmful electrical conductivity of iron.
3Device complexity
If conventional single-rotor design is used, then structure is simple, but power and torque density are limited due to eddy current losses
Solution Approach 1:
The patent divides the rotor structure into two separate rotors (inner rotor and outer rotor) with Halbach arrays positioned at different radii. This segmentation allows the magnetic flux to be channeled through the stator without requiring back iron in the rotor, thereby eliminating eddy current losses while maintaining high magnetic flux density in the air gap for improved power density.
Solution Approach 2:
The patent employs a nested configuration where the inner rotor with its Halbach array is positioned inside the outer rotor with its Halbach array. Both rotors share a common stator and rotate about a common axis, creating a compact nested structure that maximizes power density while eliminating the need for back iron in either rotor.
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
The dual-rotor design achieves enhanced magnetic field strength in the air gap with minimal flux on the rotors, resulting in improved power and torque density without eddy current losses, as demonstrated by magnetic field simulations showing approximately 2 Tesla magnetic flux density and 0.5 kJ/m stored energy density.
Implementation Method 1
The inner rotor comprises a first Halbach array, which is mechanically connected to the dual rotor support structure 208. The outer rotor comprises a second Halbach array and is mechanically connected to dual rotor support structure 208
Implementation Method 2
the magnetic flux is enhanced in the air gap and minimized on the rotors themselves, eliminating eddy current losses by channeling flux in a way that it only appears on one side of the arrays
Implementation Method 3
A dual-rotor synchronous machine design utilizing concentric Halbach arrays for the outer and inner rotors, where the magnetic flux is enhanced in the air gap and minimized on the rotors themselves
Data Source
AI summary
A dual-rotor machine comprising a dual rotor support structure rotatably connected to a frame. A stationary stator is disposed between the rotors and is fixed to the frame. An inner rotor and outer rotor, each comprising a permanent magnet Halbach array, are coaxially disposed with the stator and are rotable about the stator. In this configuration, the inner rotor channels its magnetic flux to its outside, while the outer rotor channels its magnetic flux to its inside. The magnetic flux density at the stator for the dual-rotor machine can be as high as 2 Tesla or higher for high-grade neodymium-iron-boron permanent magnet material, and the stored magnetic energy for conversion to mechanical or electrical energy available to the stator may be at least 0.5 kJ/m. The rotor Halbach arrays may comprise monolithic permanent magnets with continuously variable magnetic field direction.