AC-DC Power Converter with Stabilized DC Midpoint

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Solution Overview

Problem

Existing AC-DC power converters for aircraft systems face inefficiencies due to uncommitted reference voltages and imbalanced neutral phases, leading to increased weight and complexity in generators and converters.

Innovation Solution

An AC-DC power converter design that includes an autotransformer connected to an AC feeder, a rectifier connected to the autotransformer, and a DC midpoint terminal connected to the AC source neutral phase, stabilizing the DC midpoint voltage and ensuring symmetrical DC output voltages independent of load imbalances.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If the reference voltage is allowed to float relative to the neutral phases, then the converter can operate with uncommitted reference voltage, but the reference voltage becomes load dependent and causes DC imbalance currents

Engineering Contradiction:

Improvereference voltage flexibilityVSAvoidvoltage stability

Core Design Contradiction:

Adaptability or versatilityVSReliability

Solution Approach 1:

The patent introduces an intermediary connection between the DC midpoint terminal and the AC source neutral phase, which mediates between the floating reference voltage requirement and the need for stable voltage. This connection acts as a mediator that provides voltage reference stability without completely constraining the floating nature of the reference voltage.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent changes the voltage parameter at the DC midpoint terminal by connecting it to the AC source neutral phase, thereby transforming the load-dependent floating voltage into a stable reference voltage that maintains a fixed relationship with the AC source, eliminating DC imbalance currents.

Inventive Principle:

Principle #35Parameter changes

2Power

If the generator and conductors are sized for the 6-pulse non-linear current, then the converter can operate with polyphase AC source, but the generator and converter become more massive

Engineering Contradiction:

Improvepower conversion capabilityVSAvoidconverter weight

Core Design Contradiction:

PowerVSWeight of moving object

Solution Approach 1:

The patent changes the current waveform parameters by introducing the autotransformer with phase shifting, converting the 6-pulse non-linear current into a 12-pulse current with reduced harmonics. This parameter change allows for smaller generator and conductor sizing while maintaining power conversion capability.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The autotransformer acts as an intermediary device between the polyphase AC source and the rectifier, transforming the current characteristics to reduce the mass requirements of the generator and conductors while preserving the power conversion function.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Ease of manufacture

If the voltage difference between neutral phases is imbalanced due to generator winding end turns, then the generator can be constructed, but DC imbalance currents are driven in the converter transformers

Engineering Contradiction:

Improvegenerator constructionVSAvoidDC imbalance currents

Core Design Contradiction:

Ease of manufactureVSObject-generated harmful factors

Solution Approach 1:

The connection between the DC midpoint terminal and the AC source neutral phase acts as an intermediary that blocks the propagation of neutral phase voltage imbalances into the converter transformers, preventing DC imbalance currents while allowing the generator to be constructed with standard winding configurations.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent converts the potentially harmful effect of neutral phase voltage imbalances into a beneficial reference voltage stabilization mechanism, where the AC source neutral phase serves as a stable reference that eliminates DC imbalance currents despite generator construction variations.

Inventive Principle:

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

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 symmetrical DC output voltages at the AC-DC power converter terminals, reducing weight and complexity by stabilizing the DC midpoint voltage, thus improving efficiency and reducing the impact of load imbalances.

Implementation Method 1

an autotransformer connected to the AC feeder

Methodology Applied

Scientific EffectElectromagnetic induction: Electromagnetic Induction

Implementation Method 2

a rectifier connected to the autotransformer

Methodology Applied

Scientific EffectRectification: Diode

Data Source

PatentUS11228254B2Power converters, power distribution systems and methods of converting power

Publication Date: 2022.01.18 HAMILTON SUNDSTRAND CORP

AI summary

A dual-output AC-DC power converter with balanced DC output voltages is described. The DC power source has balanced DC voltage outputs relative to DC midpoint irrespective of DC load imbalance. The input to the power source is three-phase four-wire AC voltage source. Current draws from the AC three-phase voltage source have 12-pulse near sinusoidal waveform. Ripple voltage from DC positive rail to DC negative rail is 12-pulse.