Variable Speed Machine Assembly with Magnetically Geared Generator
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Solution Overview
Problem
Existing wind turbines face inefficiencies and high maintenance costs due to the use of doubly fed induction generators (DFIGs) with partial-rated converters and permanent magnet generators (PMGs) with full-rated converters, which have complex power electronics, large size, and high maintenance requirements.
Innovation Solution
A variable speed machine assembly that includes a power converter with a partial-rated capacity, a magnetically geared generator with two sets of windings and a rotor, and an exciter with a permanent magnet rotor or stator, eliminating the need for slip rings and reducing the power electronics requirements, while maintaining constant frequency electric power output.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a full-rated converter is used in a permanent magnet generator, then efficiency is improved, but device complexity and maintenance requirements increase
Solution Approach 1:
The patent divides the generator into two separate machines: a magnetically geared generator (MGG) that handles the majority of power conversion, and a smaller exciter machine that provides the remaining functionality. This segmentation allows the use of a partial-rated converter instead of a full-rated converter, reducing complexity while maintaining efficiency.
Solution Approach 2:
The patent employs a partial-rated converter that handles only a fraction (e.g., 10-20%) of the total power rating, rather than requiring a full-rated converter. The MGG architecture enables this partial action approach by using the exciter to supplement the converter's capacity, thereby reducing complexity and cost while preserving overall system efficiency.
2Device complexity
If a partial-rated converter is used in a doubly fed induction generator, then device complexity is reduced, but efficiency and reactive power control deteriorate
Solution Approach 1:
The patent introduces an exciter machine as an intermediary component that works in conjunction with the MGG and partial-rated converter. The exciter acts as a mediator that provides the additional reactive power and power factor correction capabilities that would otherwise require a full-rated converter, thereby maintaining efficiency while using a simpler partial-rated converter architecture.
3Adaptability or versatility
If slip rings are used in a doubly fed induction generator, then variable speed operation is enabled, but reliability decreases due to maintenance requirements
Solution Approach 1:
The patent replaces the mechanical slip ring system with a fully integrated MGG architecture where the rotor windings are directly connected to the converter through a rotor bridge. This substitution eliminates the mechanical wear and maintenance issues associated with slip rings while preserving variable speed operation capabilities through the power electronic converter control.
4Loss of energy
If a full-rated converter is used, then efficiency is improved, but cost and size increase
Solution Approach 1:
The patent segments the power conversion function between the MGG and a smaller exciter machine, enabling the use of a compact partial-rated converter instead of a large full-rated converter. The exciter's permanent magnets and windings provide the additional power handling capability in a space-efficient manner, reducing the overall size of power electronics while maintaining high 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
The solution provides efficient energy conversion with reduced power electronics, increased reliability, and improved reactive power control, eliminating the need for slip rings and transformer, and achieving superior efficiency compared to DFIGs.
Implementation Method 1
The second machine includes a rotor, a stator, and one set of windings. The second machine can be referred to herein as an 'exciter' and includes a permanent magnet rotor or a permanent magnet stator.
Implementation Method 2
The first machine is based on a planetary magnetic gearbox and includes two sets of windings and one rotor
Data Source
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AI summary
A variable speed machine assembly (200) includes an input shaft (134), a variable speed magnetically geared generator (202) coupled to the input shaft, an electrical machine (204) coupled to the input shaft, and a power converter (208) coupled to the variable speed magnetically geared generator and the electrical machine. The power converter is configured to use electrical power output by the electrical machine (204) to control a frequency of power output by the variable speed magnetically geared generator (202).