DC Sensing Circuit Using Switched Inductive Coupling

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Solution Overview

Problem

Current direct current (DC) circuit breakers face challenges in accurately sensing low short circuit currents, particularly in photovoltaic applications, due to the limitations of thermal and magnetic trip units, which can lead to nuisance tripping and high costs associated with electronic trip units.

Innovation Solution

A direct current sensing circuit that divides the current into two portions, using a switching circuit and current sensor with inductive coupling to generate a square wave output proportional to the DC current magnitude, allowing for precise sensing and tripping control through an electronic trip unit.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Device complexity

If thermal and magnetic trip units are used in DC circuit breakers, then the device complexity is reduced and cost is lowered, but measurement precision of low short circuit currents deteriorates leading to nuisance tripping

Engineering Contradiction:

Improvetrip unit structureVSAvoidshort circuit current sensing accuracy

Core Design Contradiction:

Device complexityVSMeasurement precision

Solution Approach 1:

The patent replaces thermal and magnetic mechanical trip units with an electronic trip unit that uses a current sensor (such as a Hall effect sensor) to detect DC current. This substitution enables precise measurement of low short circuit currents in photovoltaic applications while maintaining reasonable device complexity through integrated electronic circuitry.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Measurement precision

If DC electronic trip units are used to improve measurement precision, then sensing accuracy of low short circuit currents improves, but device complexity and cost increase

Engineering Contradiction:

ImproveDC current sensing accuracyVSAvoidelectronic trip unit structure

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The patent designs the electronic trip unit to perform multiple functions: it senses DC current through a current sensor, processes the signal through electronic circuitry, and controls the tripping mechanism. This multi-functional integration reduces overall device complexity by consolidating sensing, processing, and control functions into a single unified system rather than separate components.

Inventive Principle:

Principle #6Universality (Multi-functionality)

3Reliability

If thermal trip units are used, then nuisance tripping is reduced, but tripping time increases which is insufficient for photovoltaic applications with low short circuit currents

Engineering Contradiction:

Improvenuisance tripping reductionVSAvoidtripping time

Core Design Contradiction:

ReliabilityVSDuration of action of moving object

Solution Approach 1:

The patent replaces the slow thermal trip mechanism with an electronic sensing system that can rapidly detect current conditions and trigger tripping within milliseconds. The electronic trip unit processes current signals in real-time and can immediately actuate the tripping mechanism when abnormal conditions are detected, providing both reliability and fast response time required for photovoltaic protection.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

4Device complexity

If magnetic trip units are used, then device complexity is reduced, but calibration difficulty and measurement accuracy deteriorate

Engineering Contradiction:

Improvetrip unit structureVSAvoidcurrent sensing accuracy

Core Design Contradiction:

Device complexityVSMeasurement precision

Solution Approach 1:

The patent replaces magnetic trip units with an electronic trip unit that uses a current sensor (such as Hall effect sensor) to measure DC current. This electronic system provides precise measurement of low short circuit currents without the calibration difficulties inherent in magnetic trip units, while the integrated electronic design keeps overall device complexity manageable.

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 solution provides accurate and efficient sensing of DC currents, reducing nuisance tripping and costs by enabling precise control of circuit breakers in photovoltaic and other DC applications, while being applicable to a wide range of DC voltage circuits.

Implementation Method 1

a first conductor inductively coupled with the current sensor; a second conductor inductively coupled with the current sensor

Methodology Applied

Scientific EffectInductive coupling: Electromagnetic Induction

Data Source

PatentUS9103852B2Direct current sensing circuit and circuit interrupter including the same

Publication Date: 2015.08.11 EATON INTELLIGENT POWER LTD

AI summary

A circuit for sensing a direct current includes a first resistance and a second resistance. A first portion of the direct current flows through the first resistance and a second portion of the direct current flows through the second resistance. The circuit further includes a current sensor having an opening, first and second conductors inductively coupled with the current sensor, and a switching circuit having a pair of switches structured to alternatingly switch in order that the second portion of the direct current alternatingly flows through the first and second conductors. The second portion of the direct current flowing through the first conductor passes through the opening of the current sensor in a first direction and the second portion of the direct current flowing through the second conductor passes through the opening of the current sensor in a second direction opposite to the first direction.