Aircraft Rectifier Unit With Shunt APF for Harmonic Mitigation
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Solution Overview
Problem
Aircraft electrical power systems face challenges in reducing harmonic distortion during AC to DC power conversion, particularly with the use of autotransformer-based multipulse converters, which add weight and cost while struggling to meet stringent power quality standards with varying fundamental frequencies.
Innovation Solution
A shunt active power filter (APF) is introduced in parallel with a single 6-pulse rectifier cell, utilizing an adaptive control algorithm and Schur lattice filters to compensate for harmonic currents, eliminating the need for autotransformers and interphase transformers, thereby reducing the rectifier unit's weight and size.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If direct rectification of 3-phase AC power is used, then the conversion is simple and straightforward, but unacceptable levels of current distortion or harmonics are created
Solution Approach 1:
The patent divides the rectification process into multiple 6-pulse rectifier cells (typically three cells for an 18-pulse converter) that process different phase-shifted AC inputs separately and combine their outputs. This segmentation allows each cell to perform simple rectification while the combination achieves low harmonic distortion, resolving the contradiction between simplicity and harmonic reduction.
2Object-generated harmful factors
If autotransformer-based multipulse converters are used, then harmonic distortion is reduced, but considerable weight and cost are added to the aircraft system
Solution Approach 1:
The patent extracts and removes the heavy autotransformer component from the multipulse converter system while retaining the essential functionality of phase-shifting and harmonic reduction through an alternative configuration of smaller transformers and rectifier cells. This extraction eliminates the primary source of weight while maintaining the harmonic mitigation capability.
3Object-generated harmful factors
If ATRU is used to perform phase shifting, then harmonic distortion is reduced, but the device complexity and part count increase
Solution Approach 1:
The patent merges the phase-shifting function and rectification function into an integrated configuration where multiple 6-pulse rectifier cells are directly connected to phase-shifted AC sources. This merging eliminates the need for separate ATRU components and their associated control systems, reducing overall device complexity while maintaining harmonic reduction performance.
4Adaptability or versatility
If fundamental frequency varies over wide range, then adaptability is improved, but power quality issues become more difficult to address
Solution Approach 1:
The patent employs a control system that dynamically adjusts the switching frequencies of the rectifier cells and the active power filter based on the varying fundamental frequency. This dynamic adaptation ensures that the system maintains optimal harmonic cancellation and power quality performance across the entire operating frequency range, from 350 Hz to 800 Hz.
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 effectively mitigates harmonic distortion, meets aerospace power quality standards, and provides redundancy, ensuring reliable power delivery with reduced weight and size compared to traditional systems, while maintaining or improving power quality across a wide frequency range.
Implementation Method 1
a shunt active power filter (APF) is introduced in parallel with a single 6-pulse rectifier cell, utilizing an adaptive control algorithm and Schur lattice filters to compensate for harmonic currents
Implementation Method 2
utilizing an adaptive control algorithm and Schur lattice filters to compensate for harmonic currents
Data Source
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AI summary
A power converter unit comprising a rectifier arranged to receive AC input from a variable or fixed frequency AC power source and an active power filter with an adaptive control algorithm connected as a shunt between the AC input and the rectifier.