GaN Bidirectional Neutral Former for Compact Off-Grid Power

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Solution Overview

Problem

Conventional neutral forming transformers used in split-phase and three-phase residential connections are physically bulky, costly, and inefficient, making them unsuitable for off-grid facilities and microgrids.

Innovation Solution

A switched-mode neutral forming device utilizing native four quadrant bi-directional switches and a controller that drives the switches at frequencies significantly higher than AC mains frequency, allowing for a compact, lightweight, and cost-effective design.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Volume of moving object

If a conventional line frequency neutral forming transformer is used, then neutral forming function is provided, but the device becomes physically bulky and heavy

Engineering Contradiction:

Improvedevice volumeVSAvoidneutral forming capability

Core Design Contradiction:

Volume of moving objectVSReliability

Solution Approach 1:

The patent transforms the operating frequency parameter from line frequency (50/60 Hz) to high frequency (kHz to MHz range). This parameter change enables the use of miniaturized high-frequency transformers with ferrite cores instead of bulky iron cores, achieving volume reduction of 10-100 times while maintaining neutral forming capability through high-frequency switching of bidirectional switches

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent replaces the passive mechanical transformer system with an active electronic switched-mode system. Bidirectional switches (MOSFETs, IGBTs, or GaN devices) electronically synthesize the neutral point by switching between phase voltages, eliminating the need for large magnetic cores and windings, thereby achieving compact size while preserving neutral forming function

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Ease of manufacture

If a conventional line frequency neutral forming transformer is used, then neutral forming function is provided, but the device becomes costly to manufacture

Engineering Contradiction:

Improvemanufacturing costVSAvoidneutral forming capability

Core Design Contradiction:

Ease of manufactureVSReliability

Solution Approach 1:

By changing the operating frequency to high frequency, the patent enables use of smaller, cheaper magnetic materials (ferrite instead of silicon steel) and reduces copper winding requirements. The high-frequency transformer core and windings cost significantly less than line-frequency equivalents, achieving cost reduction while maintaining neutral forming capability

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The switched-mode neutral forming device can operate in multiple configurations (single-phase, three-phase, split-phase) and can provide additional functions such as active power factor correction and harmonic filtering through the same bidirectional switch network, reducing overall system cost by eliminating separate devices

Inventive Principle:

Principle #6Universality (Multi-functionality)

3Loss of energy

If a conventional line frequency neutral forming transformer is used, then neutral forming function is provided, but the device is inefficient

Engineering Contradiction:

Improveenergy efficiencyVSAvoidneutral forming capability

Core Design Contradiction:

Loss of energyVSReliability

Solution Approach 1:

The patent changes the operating frequency to high frequency, which reduces magnetic core losses (hysteresis and eddy current losses are proportional to frequency but the reduced core size compensates) and copper losses (due to smaller current transformers and optimized switching). High-frequency operation with modern wide-bandgap devices achieves efficiency exceeding 95%, improving upon conventional transformers

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent replaces the passive transformer with an active switched-mode power conversion system that can actively regulate power flow, recover reactive power, and minimize losses through optimal switching strategies. The bidirectional switches enable four-quadrant operation, allowing energy recovery and regenerative braking functions that improve overall system efficiency

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

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 switched-mode neutral forming device achieves a volume reduction of approximately 1,000 times compared to conventional line frequency-based transformers, resulting in a smaller, more efficient, and less costly solution for neutral forming in off-grid facilities.

Implementation Method 1

each switch of the plurality of switches is a gallium nitride bi-directional high electron mobility transistor

Methodology Applied

Scientific EffectField-effect transistor operation:

Implementation Method 2

high electron mobility transistor

Methodology Applied

Scientific EffectElectron mobility:

Data Source

PatentUS12308754B2Gallium nitride bi-directional high electron mobility transistor in switched-mode neutral forming device applications

Publication Date: 2025.05.20 ENPHASE ENERGY INC

AI summary

A switched-mode neutral forming device is provided herein and comprises one or more windings coupled to (i) a plurality of line terminals via a plurality of switches and (ii) a neutral terminal, wherein each switch of the plurality of switches is a native four quadrant bi-directional switch and a controller, coupled to the plurality of switches, for driving the switches at a frequency orders or magnitude greater than an AC mains frequency.