Differential RC Coupling Path for AC Power Isolation

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Solution Overview

Problem

Current electrical power measurement systems face challenges in achieving affordable and high-performance isolation methods, with existing solutions like pulse transformers being costly and susceptible to magnetic tampering, and optical isolators having limited operation speed and high costs.

Innovation Solution

A differential resistor-capacitor (RC) coupling path is implemented for communication between a host device and a line side device, using sensors like voltage dividers and Rogowski coils, with A/D converters and a transceiver to convert and transmit signals, providing effective common mode signal attenuation and bi-directional data transfer.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If pulse transformer is used for isolation, then electrical isolation between host device and line side device is achieved, but cost increases and susceptibility to magnetic tampering occurs

Engineering Contradiction:

Improveelectrical isolationVSAvoidcost

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

The patent replaces the traditional pulse transformer (magnetic field-based isolation) with a capacitive coupling structure using PCB trace capacitors. This substitution eliminates the need for bulky magnetic components while achieving the same electrical isolation function through electric field coupling, thereby reducing cost and magnetic tampering susceptibility.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent creates an electrical equivalent of the isolation function by using capacitive coupling that replicates the transformer's isolation effect without requiring magnetic cores. The capacitive structure on PCB traces provides the same galvanic isolation functionality through a different physical mechanism, reducing manufacturing complexity.

Inventive Principle:

Principle #26Copying

2Reliability

If optical isolator is used for isolation, then electrical isolation is achieved, but operation speed is limited and cost is high

Engineering Contradiction:

Improveelectrical isolationVSAvoidoperation speed

Core Design Contradiction:

ReliabilityVSSpeed

Solution Approach 1:

The patent replaces optical isolation mechanisms with direct electrical capacitive coupling. This substitution enables much faster signal transmission speeds compared to optical isolators, as the capacitive coupling operates in the electrical domain without the speed limitations of light conversion and transmission through optical media.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Object-affected harmful factors

If differential RC coupling path is used, then common mode signal attenuation is achieved, but component mismatch may occur

Engineering Contradiction:

Improvecommon mode signal interferenceVSAvoidresistor and capacitor value matching

Core Design Contradiction:

Object-affected harmful factorsVSManufacturing precision

Solution Approach 1:

The patent introduces a common ground reference as an intermediary that provides a stable reference point for both sides of the differential coupling. This ground reference acts as a mediator that compensates for component mismatches by providing a consistent baseline, thereby maintaining common mode rejection performance even when resistor and capacitor values vary within tolerance ranges.

Inventive Principle:

Principle #24Intermediary (Mediator)

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 differential RC coupling path offers a cost-effective and high-performance solution for electrical power measurement, effectively eliminating common mode signal interference and ensuring robust communication, even with slight mismatches in resistor and capacitor values, while providing surge protection and maintaining system performance under various impairments.

Implementation Method 1

Capacitor electrodes form a capacitive structure directly on a printed circuit board's opposing sides. The PCB substrate intermediate the electrodes functions as the capacitive structure's dielectric material.

Methodology Applied

Scientific EffectCapacitance: Capacitance

Implementation Method 2

The PCB substrate intermediate the electrodes functions as the capacitive structure's dielectric material.

Methodology Applied

Scientific EffectDielectric: Dielectric

Implementation Method 3

The host coupling resistors are smaller in resistance value than the resistor of the coupling links to attenuate a differential signal and a common mode signal of the coupling links.

Methodology Applied

Scientific EffectCommon mode signal attenuation:

Data Source

PatentEP3106886B1Method of communicating between phases of an ac power system

Publication Date: 2021.09.01 SILERGY SEMICON HONG KONG LTD

Figure 1~2
Figure 3
Figure 4a~4b

AI summary

A differential coupling path is provided for power measurement communication between a host device and a line side device. The line side device couples to AC power grid to extract voltage signals and current signals using various voltage and current sensors. The extracted voltage signal and current signal are converted to digital signals by internal A/D converters within the line device and then sent to the host device through the differential coupling path coupled between the host device and the line side device. The host device may couple to one or more line side devices via multiple differential coupling paths.