Ground Fault Detection Offset Voltage Divider Circuit

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Solution Overview

Problem

Existing ground fault detection apparatuses with flying capacitors face challenges in measuring insulation resistance when the capacitor is charged with reverse polarity, and additional circuits or diodes can complicate the configuration or prevent accurate measurement.

Innovation Solution

A ground fault detection apparatus with an offset voltage divider circuit that allows measurement of charge voltage regardless of the capacitor's charge direction, using a set of switches and a control device to calculate insulation resistance based on voltages measured across different paths, and an offset voltage divider circuit to adjust and offset the voltage range for accurate measurement.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If a conventional flying capacitor type ground fault detection apparatus is used, then the insulation resistance can be measured, but the measurement fails when the capacitor is charged with reverse polarity due to diode blocking

Engineering Contradiction:

Improveinsulation resistance measurement accuracyVSAvoidmeasurement capability under reverse polarity condition

Core Design Contradiction:

Measurement precisionVSAdaptability or versatility

Solution Approach 1:

The patent applies inversion by reversing the diode orientation to create a second diode (D2) that conducts when the first diode (D1) is reverse-biased. This allows the measurement circuit to function regardless of the capacitor's charge polarity, converting the limitation of single-directional conduction into a bidirectional measurement capability.

Inventive Principle:

Principle #13The other way round (Inversion)

Solution Approach 2:

The patent introduces an intermediary mechanism (the second diode D2 and associated switching circuitry) that mediates the measurement process when the primary measurement path is blocked. This intermediary allows the system to switch between two measurement paths depending on the capacitor's charge state, ensuring continuous measurement capability.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Adaptability or versatility

If additional circuits or diodes are added to enable reverse polarity measurement, then the measurement capability is improved, but the circuit configuration becomes complicated

Engineering Contradiction:

Improvemeasurement capability under reverse polarity conditionVSAvoidcircuit configuration complexity

Core Design Contradiction:

Adaptability or versatilityVSDevice complexity

Solution Approach 1:

The patent achieves universality by designing a measurement circuit that can handle both normal and reverse polarity conditions using a unified approach. The added diode D2 and switching mechanism create a universal measurement system that automatically adapts to either charge state, making the circuit equally effective in all operating conditions without requiring fundamentally different circuit topologies.

Inventive Principle:

Principle #6Universality (Multi-functionality)

3Reliability

If diodes are added to the circuit to prevent reverse polarity issues, then the measurement reliability is improved, but the diode may prevent accurate measurement when reverse voltage occurs

Engineering Contradiction:

Improvemeasurement reliabilityVSAvoidcharge voltage measurement accuracy

Core Design Contradiction:

ReliabilityVSMeasurement precision

Solution Approach 1:

The patent applies dynamics by making the circuit configuration adaptive rather than static. The switching mechanism dynamically reconfigures the measurement path based on the capacitor's charge state, allowing the circuit to transition between different operational modes (normal polarity measurement vs. reverse polarity measurement) to maintain both reliability and precision under varying conditions.

Inventive Principle:

Principle #15Dynamics

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 simple and accurate measurement of charge voltage across the flying capacitor, regardless of its charge direction, thereby ensuring reliable detection of ground faults without complicating the circuit configuration.

Implementation Method 1

A capacitor C1 functioning as a flying capacitor is charged in a path formed by turning on and off of switches S1-S4, and its charge voltage is measured by a control device 510

Methodology Applied

Scientific EffectCapacitance: Capacitance

Implementation Method 2

V0 is a value corresponding to a voltage of the battery B measured with a path formed by turning on the switch S1 and the switch S2

Methodology Applied

Scientific EffectElectrical conduction: Conduction (electrical)

Data Source

PatentUS11073571B2Ground fault detection apparatus

Publication Date: 2021.07.27 YAZAKI CORP

AI summary

A ground fault detection apparatus includes a capacitor, switches for switching between a V0 charge path including the battery and the capacitor, a Vcn charge path including the battery, the capacitor and negative-side insulation resistance as insulation resistance between negative side of the battery and ground, a Vcp charge path including the battery, the capacitor and positive-side insulation resistance as insulation resistance between positive side of the battery and ground, and a charge voltage measurement path including the capacitor and a measurement resistor, an offset voltage divider circuit that divides and offsets voltage produced at the measurement resistor, a control device that controls the switches and calculates the insulation resistance using output voltage of the offset voltage divider circuit as a measured value, based on V0 measured at the V0 charge path, Vcn measured at the Vcn charge path and Vcp measured at the Vcp charge path.