Automatic Transfer Switch for Off-Grid Inverter Backup

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Solution Overview

Problem

Existing power conversion systems for alternate energy sources, such as wind turbines or photovoltaic cells, face challenges in safely disconnecting from the utility grid during outages to prevent hazardous energy transfer while also providing backup power to consumers.

Innovation Solution

A power conversion system comprising a grid-tied inverter, an energy storage device like batteries, and an off-grid inverter, along with a transfer switch that connects the off-grid inverter to electrical loads during utility grid failures, allowing safe disconnection from the grid and providing backup power.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Loss of energy

If the grid-tied inverter remains connected to the utility grid during power outages, then the alternate energy source can continue to supply energy to the grid, but hazardous energy transfer may occur to utility crews working on the grid

Engineering Contradiction:

Improveenergy transfer to gridVSAvoidhazardous energy transfer

Core Design Contradiction:

Loss of energyVSObject-affected harmful factors

Solution Approach 1:

An automatic transfer switch is introduced as an intermediary device between the grid-tied inverter and the utility grid. The transfer switch monitors grid status and automatically disconnects the inverter during outages, preventing hazardous back-feeding to utility crews while allowing normal energy transfer during grid operation. This intermediary mechanism resolves the contradiction by enabling safe operation in both grid-connected and isolated modes.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Object-affected harmful factors

If the grid-tied inverter is disabled during power outages to prevent hazardous energy transfer, then safety is improved, but the alternate energy source cannot provide backup power to consumer loads

Engineering Contradiction:

Improvehazardous energy transfer preventionVSAvoidbackup power capability

Core Design Contradiction:

Object-affected harmful factorsVSReliability

Solution Approach 1:

The system is segmented into two distinct operational modes: grid-tied mode for normal operation with energy transfer to the utility grid, and off-grid mode for backup power during outages. The automatic transfer switch enables seamless transition between these segments, allowing the inverter to provide backup power to consumer loads during outages while preventing hazardous energy transfer to the grid when disconnected.

Inventive Principle:

Principle #1Segmentation

3Reliability

If an automatic transfer switch is added to enable safe disconnection and backup power capability, then safety and reliability are improved, but device complexity increases

Engineering Contradiction:

Improvebackup power capabilityVSAvoidsystem structure

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The automatic transfer switch incorporates self-service capabilities through automatic grid status detection and autonomous switching operations. The device monitors voltage presence, automatically transitions between grid-tied and off-grid modes, and manages the disconnection/reconnection process without manual intervention. This self-service functionality reduces the need for additional control systems and manual operations, thereby limiting the increase in overall system complexity while maintaining improved reliability and safety.

Inventive Principle:

Principle #25Self-service

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

Enables safe disconnection from the utility grid during outages, preventing hazardous energy transfer while allowing alternate energy sources to supply critical loads, thereby providing energy savings and backup power capabilities.

Implementation Method 1

The grid-tied inverter monitors the utility grid and converts the electrical energy generated by the alternate energy source to a voltage in phase with the utility grid

Methodology Applied

Scientific EffectPower conversion:

Implementation Method 2

A second inverter has an input and an output, where the input is electrically connected to the energy storage device

Methodology Applied

Scientific EffectPower conversion:

Implementation Method 3

A transfer switch selectively connects either the power distribution point or the second inverter to the electrical load

Methodology Applied

Scientific EffectElectrical switching:

Implementation Method 4

An energy storage device, such as a battery, is configured to store energy generated by the secondary power source

Methodology Applied

Scientific EffectEnergy storage:

Data Source

PatentUS9711967B1Off grid backup inverter automatic transfer switch

Publication Date: 2017.07.18 RELIANCE CONTROLS CORPORATION

AI summary

A power conversion system for use with an alternate energy source includes a first inverter, a battery, and a second inverter, each of which receives power from the alternate energy source. The output of the first inverter and the grid are each connected to at least one electrical load via a load center. The battery is charged via a charger connected to the alternate energy source. This stored energy powers a selected portion of the electrical loads during a failure of the utility grid. The second inverter is connected between the battery and a transfer switch. During normal grid operation, the second inverter is disabled and the transfer switch connects the load center to the selected electrical loads. During a failure of the utility grid, the first inverter is disabled, the second inverter is enabled, and the transfer switch connects the second inverter to the selected electrical loads.