Asymmetric Delta TRU Topology for Isolated Multi-Pulse Rectification
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Solution Overview
Problem
Conventional Transformer Rectifier Units (TRUs) for aircraft face challenges such as low power quality, high weight, complex assembly processes, and inability to provide galvanic isolation, especially in high current 28V applications, while Auto-Transformer Rectifier Units (ATRUs) lack galvanic isolation and struggle with common-mode voltage issues.
Innovation Solution
The development of an asymmetric delta secondary transformer topology that provides galvanic isolation and efficient 18 or 24 pulse operation, using a standard 3-phase delta or wye primary coupled with a galvanically isolated 3-phase delta secondary, allowing for passive multiphase power factor correction and harmonic cancellation, resulting in reduced weight and cost.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If conventional TRU systems use one primary with two secondaries (wye and delta) to establish 6 AC output phases for 12-pulse rectification, then high current output (200-300 A) is achieved, but interphase transformer is required resulting in increased weight and reduced efficiency
Solution Approach 1:
The patent uses an asymmetric delta-delta transformer configuration where the two delta secondary windings have different turns ratios relative to the primary winding. This asymmetry enables the generation of multiple AC phases (6 or more) from a single primary-winding set, eliminating the need for interphase transformers while achieving 12-pulse or higher rectification. The asymmetric turns ratios create the necessary phase shifts and voltage differences to produce multiple rectified phases without requiring additional transforming stages.
Solution Approach 2:
The transformer design integrates multiple functions into a single device: it provides voltage transformation, galvanic isolation, multiphase power factor correction, and generates multiple AC phases for high-pulse rectification all within one transformer unit. The asymmetric delta-delta configuration with multiple taps on the secondary windings enables the same transformer to serve as both the power transformation element and the multiphase generation element, replacing what would traditionally require separate interphase transformers and PFC circuits.
2Reliability
If multiple transformers with complementary zig-zag secondary windings are used to provide better than 12-pulse power quality, then high output current and excellent power quality are achieved, but manufacturing cost, weight, and complexity significantly increase
Solution Approach 1:
The patent merges the functions of multiple transformers into a single asymmetric delta-delta transformer. Instead of using multiple separate transformer units with zig-zag windings, the invention combines all transformation and multiphase generation functions into one integrated transformer with asymmetric secondary windings. This consolidation reduces the number of discrete components, simplifies the overall system architecture, and lowers manufacturing cost while maintaining the ability to provide 12-pulse or higher power quality through the asymmetric winding configuration.
Solution Approach 2:
The asymmetric delta-delta transformer uses unequal turns ratios in its secondary windings to generate the phase shifts necessary for multi-pulse rectification. This asymmetric configuration replaces the need for complex zig-zag windings across multiple transformers, achieving the same power quality improvement through a simpler, more manufacturable single-transformer design.
3Reliability
If delta primary and hexagonal secondary are used to provide 24-pulse power quality with simpler discrete output inductors, then high performance and weight-competitive solution is achieved for lower current (200 A) applications, but output current capability is limited
Solution Approach 1:
The asymmetric delta-delta transformer extends the successful asymmetric winding concept to accommodate higher current applications. By optimizing the asymmetric turns ratios and adding multiple taps on the secondary windings, the design can generate 6 or more AC phases suitable for 12-pulse or higher rectification while maintaining the ability to handle 200-300 A output currents. This resolves the limitation of previous asymmetric designs that were restricted to lower current applications.
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 solution achieves improved power quality with reduced weight and cost, supporting higher output currents and maintaining reliability and ruggedness for aerospace applications, with efficiency and power density comparable to conventional ATRU technologies.
Implementation Method 1
galvanic isolation between the primary windings and the secondary windings
Implementation Method 2
The transformer provides multiphase Power Factor Correction (PFC), galvanic isolation, and voltage step-down prior to bridge rectification
Implementation Method 3
The bridge rectifier rectifies the transformer AC phase outputs, converting output voltage to DC
Data Source
AI summary
Asymmetric multi-pulse transformer rectifier unit (TRU), and associated systems and methods are described herein. In some embodiments, the transformer includes a 3-phase delta or wye primary coupled to a galvanically isolated 3-phase delta secondary with correction windings placed per the transformer schematic to provide a multi-pulse (e.g., 18-pulse or 24-pulse) asymmetric output. Such construction provides passive multiphase PTC and harmonic cancellation and allows multi pulse rectification. At the TRU level. 3-phase input power is provided to the transformer, which produces an isolated 9-phase or 12-phase output. The isolated multi-phase transformer output may be fed into a bridge rectifier, which converts AC to DC. DC output voltage may be determined by AC input voltage and transformer turns ratio.