Fuel Cell Insulation Resistance Monitoring via Coolant Compensation

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Solution Overview

Problem

Fuel-cell vehicles face system shutdowns due to increased coolant conductivity from temperature, contamination, and other factors, leading to limited operating temperatures and reduced efficiency, as insulation resistance falls below safety thresholds.

Innovation Solution

A method and device that measure and correct insulation resistance of a fuel-cell system's HV system by using a compensation term to account for coolant conductivity changes, ensuring safe operation even at higher temperatures.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If the coolant temperature is increased to improve system efficiency, then the operating efficiency is improved, but the insulation resistance decreases due to increased coolant conductivity

Engineering Contradiction:

Improvesystem efficiencyVSAvoidinsulation resistance

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

The patent replaces the conventional insulation monitoring method with an equivalent circuit model that separates the HV system insulation resistance from the coolant resistance. Instead of directly measuring total resistance and shutting down when thresholds are exceeded, the system uses a controller to calculate and differentiate between HV system insulation resistance and coolant resistance components, allowing the HV system to be monitored accurately even when coolant conductivity changes with temperature.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Temperature

If the insulation resistance threshold is lowered to allow higher coolant temperatures, then the operating temperature range is expanded, but the safety margin for detecting real insulation faults is reduced

Engineering Contradiction:

Improvecoolant temperature rangeVSAvoidfault detection accuracy

Core Design Contradiction:

TemperatureVSReliability

Solution Approach 1:

The patent segments the total insulation resistance measurement into distinct components: HV system insulation resistance and coolant resistance. By using the equivalent circuit model with multiple measurement paths, the controller can separately determine each resistance component. This segmentation allows the system to maintain accurate fault detection for the HV system while accounting for the variable coolant resistance that changes with temperature and contamination.

Inventive Principle:

Principle #1Segmentation

3Reliability

If a large radiator is used to maintain low coolant temperatures, then the insulation resistance is maintained, but the system cost and complexity increase

Engineering Contradiction:

Improveinsulation resistanceVSAvoidradiator size

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent replaces the mechanical solution of using an oversized radiator with an electrical/electronic solution based on equivalent circuit modeling and resistance separation. Instead of mechanically limiting coolant temperature to maintain insulation resistance, the system uses the controller to mathematically separate HV system insulation resistance from coolant resistance, eliminating the need for excessive cooling capacity while maintaining accurate insulation monitoring.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

4Reliability

If the insulation resistance monitoring is performed continuously, then the safety is improved, but the false shutdowns due to coolant conductivity changes increase

Engineering Contradiction:

ImprovesafetyVSAvoidsystem availability

Core Design Contradiction:

ReliabilityVSProductivity

Solution Approach 1:

The patent replaces the conventional threshold-based monitoring with an equivalent circuit model that continuously calculates HV system insulation resistance by separating it from coolant resistance. The controller performs multiple measurements through different paths and uses the circuit model to isolate the HV system component, enabling continuous safe operation even when coolant conductivity changes due to temperature or contamination, thereby reducing false shutdowns while maintaining safety.

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

This approach widens insulation limits, allowing higher coolant temperatures, reduces radiator costs, and stabilizes vehicle operation by compensating for temperature and contamination effects, preventing unnecessary shutdowns and start failures.

Implementation Method 1

The fluid is routed through the bipolar plates of the fuel-cell and thus contributes significantly to the insulation resistance of the system

Methodology Applied

Scientific EffectElectrical conduction: Conduction (electrical)

Implementation Method 2

Fuel-cells in fuel-cell vehicles have a cooling circuit to dissipate the waste heat of the system

Methodology Applied

Scientific EffectThermal conduction: Conduction (thermal)

Implementation Method 3

This cooling circuit is filled with a liquid, very low conductivity fluid. The fluid is routed through the bipolar plates of the fuel-cell

Methodology Applied

Scientific EffectConvection: Convection

Data Source

PatentUS11092653B2Determination of the insulation resistance of a fuel-cell system

Publication Date: 2021.08.17 AUDI AG

AI summary

The present disclosure relates to a method and a device for determining the insulation resistance of a fuel-cell system.