Modular String Monitor with Reset Current Transformers

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Solution Overview

Problem

Current string monitoring systems for photovoltaic power generation are expensive due to the high cost of transducers for monitoring DC current and voltage, and they can be permanently affected by current surges, leading to inaccurate measurements unless recalibrated.

Innovation Solution

A modular string monitor using reset current transformers and a modular construction with a base unit and sensor modules, where each sensor module includes a microcontroller and current transformers with a controllable voltage source to prevent core saturation and maintain accurate measurements without recalibration.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If traditional transducers are used for monitoring DC current in photovoltaic strings, then measurement capability is provided, but cost increases significantly and measurement accuracy is compromised by current surges

Engineering Contradiction:

ImproveDC current measurement accuracyVSAvoidtransducer susceptibility to current surge damage

Core Design Contradiction:

Measurement precisionVSReliability

Solution Approach 1:

The patent replaces expensive, surge-vulnerable transducers with inexpensive current transformers that can be easily replaced. These CTs are designed to be sacrificial components that protect the main monitoring system from surge damage, aligning with the principle of using cheap, replaceable components to protect against harmful effects.

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

Solution Approach 2:

The patent introduces an intermediary isolation barrier using optical coupling and galvanic isolation. The current transformers measure current without direct electrical connection to the monitoring circuit, and optical isolators prevent surge propagation, serving as mediators that protect the measurement system while enabling accurate monitoring.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Measurement precision

If multiple transducers are deployed for string-level monitoring, then monitoring precision improves, but system cost increases proportionally

Engineering Contradiction:

Improvestring performance monitoring accuracyVSAvoidnumber of transducers required

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The patent replaces expensive transducers with inexpensive current transformers and simple voltage dividers. Each string monitoring point uses low-cost components (CTs, optocouplers, voltage dividers) that dramatically reduce the per-channel cost while maintaining monitoring precision across all strings.

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

Solution Approach 2:

The patent replaces traditional electrical transducers with a measurement system based on current transformers and optical isolation. This substitution eliminates the need for expensive, complex transducer assemblies while achieving the same measurement function through simpler, more reliable electromagnetic induction and optical coupling mechanisms.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Measurement precision

If conventional current monitoring devices are used, then DC current measurement is achieved, but recalibration is required after current surges leading to loss of measurement accuracy

Engineering Contradiction:

Improvecurrent measurement accuracyVSAvoidmaintenance and recalibration requirements

Core Design Contradiction:

Measurement precisionVSEase of manufacture

Solution Approach 1:

The patent places current transformers and optical isolators as protective barriers before the main monitoring electronics. These components absorb and isolate surge effects, cushioning the measurement system from damage that would require recalibration. The isolation architecture prevents surge propagation to sensitive measurement circuits.

Inventive Principle:

Principle #11Beforehand cushioning (Prior cushioning)

Solution Approach 2:

The patent uses inexpensive current transformers as sacrificial protective elements that can be replaced rather than recalibrated after surge exposure. This approach eliminates complex recalibration procedures by using simple, replaceable components that maintain accuracy throughout their service life or are easily swapped if needed.

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

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 modular design reduces costs and maintains measurement accuracy by using reset current transformers that are not affected by power surges, enabling efficient monitoring of DC current and voltage across multiple strings with reduced calibration needs.

Implementation Method 1

a current transformer arranged to sense DC current in a conductor

Methodology Applied

Scientific EffectElectromagnetic induction: Electromagnetic Induction

Implementation Method 2

current transformers with a controllable voltage source to prevent core saturation

Methodology Applied

Scientific EffectMagnetic saturation: Magnetic Saturation

Data Source

PatentUS9214893B2String monitor

Publication Date: 2015.12.15 VERIS INDS LLC

AI summary

A string monitor comprises a modular base unit and one or more sensor modules which may include sensor modules for measuring DC voltage and current.