AC/DC Leakage Detector Circuit to Prevent False DC Trips

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Solution Overview

Problem

Existing electric leakage detectors face challenges in achieving improved detection accuracy for both AC and DC leakage currents, particularly in environments like charging control units for electric vehicles, where accurate differentiation between AC and DC leakage is crucial to prevent false alarms and ensure safety.

Innovation Solution

The electric leakage detector incorporates an AC leakage detection section with a correction unit to adjust signal thresholds based on frequency and a DC leakage detection section with an excitation unit and low-pass filter to accurately distinguish between AC and DC components, utilizing a logical OR circuit to combine outputs and enhance detection accuracy.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If a zero-phase current transformer and flux-gate type DC current transformer are used to detect AC and DC leakage currents, then the detector can provide both Type A protection and DC leakage detection, but the detection accuracy deteriorates due to false positives from AC leakage currents being misinterpreted as DC leakage

Engineering Contradiction:

Improvedetection capabilityVSAvoiddetection accuracy

Core Design Contradiction:

Adaptability or versatilityVSMeasurement precision

Solution Approach 1:

The patent divides the leakage current detection into separate AC detection and DC detection pathways. The AC leakage detection section and DC leakage detection section operate independently with dedicated signal processing chains, allowing each to be optimized for its specific detection task without interference from the other type of leakage current

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent introduces intermediary processing stages including correction units and low-pass filters that act as mediators between the raw sensor signals and the final detection decision. These intermediaries condition the signals to prevent AC leakage from being misinterpreted as DC leakage by the DC detection section

Inventive Principle:

Principle #24Intermediary (Mediator)

2Reliability

If the DC leakage detection section uses an excitation coil and flux-gate type transformer, then DC leakage current can be detected, but AC leakage currents with frequencies above a predetermined frequency may be misdetected as DC leakage, reducing detection accuracy

Engineering Contradiction:

ImproveDC leakage detectionVSAvoidfalse positive rate

Core Design Contradiction:

ReliabilityVSMeasurement precision

Solution Approach 1:

The patent applies preliminary signal conditioning actions to the AC leakage detection signal before it reaches the DC detection section. The correction unit pre-processes the AC signal to attenuate high-frequency components that could be misinterpreted as DC leakage, preventing false positives before they occur

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent changes the frequency response parameters of the detection system by introducing correction units with frequency-dependent attenuation characteristics. This parameter modification allows the system to selectively pass relevant AC frequencies while attenuating high-frequency components that would cause false DC leakage detection

Inventive Principle:

Principle #35Parameter changes

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

This configuration significantly improves detection accuracy by reducing false positives from AC leakage currents being misinterpreted as DC leakage, thereby ensuring reliable protection and efficient operation in charging control units.

Implementation Method 1

a secondary coil wound around the first core... outputs a first voltage signal with a signal level corresponding to amplitude of an alternating current flowing through the secondary coil

Methodology Applied

Scientific EffectElectromagnetic induction: Electromagnetic Induction

Implementation Method 2

The low-pass filter is provided between an input terminal of the excitation unit and the excitation coil

Methodology Applied

Scientific EffectElectromagnetic filtering: Filter (electronic)

Implementation Method 3

The excitation unit applies, to the excitation coil, an excitation voltage, having an excitation frequency with a voltage level alternately changing

Methodology Applied

Scientific EffectElectromagnetic induction: Electromagnetic Induction

Data Source

PatentUS10809312B2Electric leakage detector

Publication Date: 2020.10.20 PANASONIC INTELLECTUAL PROPERTY MANAGEMENT CO LTD

AI summary

A first decision unit of an AC leakage detection section outputs a first output signal with a signal level depending on the level of a corrected first voltage signal output from a correction unit relative to a first threshold value. An excitation unit of a DC leakage detection section applies, to an excitation coil, an excitation voltage having an excitation frequency. A DC component detection unit outputs a second voltage signal representing magnitude of a DC component of the voltage obtained by a current-detecting resistor. A second decision unit outputs a second output signal having a voltage level depending on the level of the second voltage signal relative to a second threshold value. The DC leakage detection section includes a low-pass filter provided between an input terminal electrically connected to a connection point between the excitation coil and the current-detecting resistor and the excitation coil.