Asymmetric Phase Shift Autotransformer for AC Motor Weight Reduction

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Solution Overview

Problem

In aircraft and similar applications, AC-AC power converters face a weight penalty due to the high relative power rating of autotransformers, which affects the overall system cost and efficiency, and existing solutions fail to effectively manage common-mode AC voltage without increasing filter component size.

Innovation Solution

An asymmetric phase shift autotransformer/rectifier unit (ATRU) is employed, which generates a common-mode AC voltage that is diverted to ground through a common-mode voltage pull-down circuit, reducing the weight of the autotransformer and filter components while maintaining power quality and electromagnetic interference (EMI) requirements.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Power

If a conventional autotransformer is used to convert AC input to DC output, then power conversion is achieved, but the autotransformer weight increases due to high relative power rating

Engineering Contradiction:

Improvepower conversion capabilityVSAvoidautotransformer weight

Core Design Contradiction:

PowerVSWeight of stationary object

Solution Approach 1:

The patent applies asymmetry by using an asymmetric phase shift autotransformer where the transformer windings are configured with unequal turns ratios and asymmetric phase shifting (e.g., 0° for one phase and 30° for another phase). This asymmetric configuration reduces the relative power rating requirement compared to conventional symmetric autotransformers, thereby reducing weight while maintaining power conversion capability

Inventive Principle:

Principle #4Asymmetry

Solution Approach 2:

The patent changes key parameters including the phase shift angles (0° and 30° instead of conventional equal phase shifts), winding turns ratios, and connectivity configuration. These parameter changes enable the autotransformer to achieve the same power conversion function with reduced relative power rating, directly addressing the weight reduction goal

Inventive Principle:

Principle #35Parameter changes

2Weight of stationary object

If common-mode AC voltage is generated by the autotransformer, then weight reduction is achieved, but EMI and power quality issues arise

Engineering Contradiction:

Improveautotransformer weightVSAvoidcommon-mode voltage EMI

Core Design Contradiction:

Weight of stationary objectVSObject-generated harmful factors

Solution Approach 1:

The patent converts the potentially harmful common-mode voltage into a beneficial element by deliberately generating it through the asymmetric phase shift configuration. The common-mode voltage is then utilized to reduce the relative power rating of the autotransformer, achieving weight reduction. The harmful EMI effect is managed through coordinated control of the DC-AC converter to maintain power quality

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

Solution Approach 2:

The asymmetric phase shift autotransformer performs multiple functions simultaneously: it converts AC to DC, generates common-mode voltage for weight reduction, and the common-mode voltage itself serves as a mechanism for reducing the relative power rating. This multi-functionality resolves the contradiction by making the common-mode voltage a useful feature rather than a harmful byproduct

Inventive Principle:

Principle #6Universality (Multi-functionality)

3Weight of stationary object

If filter component size is reduced to minimize weight, then overall system weight decreases, but power quality and EMI filtering capability may be compromised

Engineering Contradiction:

Improvefilter component weightVSAvoidpower quality and EMI filtering

Core Design Contradiction:

Weight of stationary objectVSReliability

Solution Approach 1:

The patent changes the operating parameters of the DC-AC converter to coordinate with the common-mode voltage generation, adjusting switching frequencies and modulation indices to maintain power quality. These parameter changes enable reduced filter sizing while preserving EMI filtering capability through active control rather than passive filtering alone

Inventive Principle:

Principle #35Parameter changes

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 approach minimizes the weight of the AC-AC power converter by reducing the relative power rating of the autotransformer and effectively manages common-mode voltage, thereby reducing the size of the power quality EMI filter and autotransformer, while maintaining performance.

Implementation Method 1

The common mode voltage is diverted to ground through motor case parasitic capacitance via a common-mode voltage pull-down circuit connected between each phase of the ATRU AC input and the ground

Methodology Applied

Scientific EffectCapacitance: Capacitance

Data Source

PatentUS8729844B2Power converter with asymmetric phase shift autotransformer for alternating current (AC) motor

Publication Date: 2014.05.20 HAMILTON SUNDSTRAND CORP

AI summary

An AC-AC power converter supplies AC power to an AC motor having a plurality of motor windings and a case connected to a ground. The AC-AC power converter architecture includes an asymmetric phase shift autotransformer/rectifier unit (ATRU) that converts an AC input to a DC output, wherein the asymmetric phase shift ATRU generates a common-mode AC voltage across the asymmetric phase shift ATRU. The common mode voltage is diverted to ground through motor case parasitic capacitance via a common-mode voltage pull-down circuit connected between each phase of the ATRU AC input and the ground.