Fuel Cell Coolant Conductivity Estimation Without Contactor Disconnection
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Solution Overview
Problem
In fuel cell systems, the increasing conductivity of cooling fluids due to impurities and degradation poses a challenge for maintaining high voltage isolation, leading to time-consuming diagnostic processes when faults are detected, as existing methods require extensive testing to identify the cause of isolation loss.
Innovation Solution
A method that estimates the conductivity of the cooling fluid by measuring isolation resistances and voltages at different power levels, calculating the stack coolant resistance, and determining the cooling fluid conductivity without the need to close and open contactors, allowing for targeted replacement of the cooling fluid.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional diagnostic methods are used to detect cooling fluid conductivity faults, then fault detection accuracy is maintained, but diagnostic time and labor increase significantly
Solution Approach 1:
The patent replaces traditional mechanical diagnostic procedures (manual isolation resistance testing, contactor operations, extensive component testing) with an electrical measurement system that uses voltage and current measurements during normal operation to calculate cooling fluid conductivity. The controller computes isolation resistance values and determines coolant conductivity without physical intervention, substituting complex mechanical diagnostic workflows with automated electrical measurements and calculations.
Solution Approach 2:
The system performs self-diagnosis by automatically measuring voltages and currents during normal fuel cell operation, calculating isolation resistance values, and determining cooling fluid conductivity without requiring external diagnostic equipment or technician intervention. The fuel cell system monitors its own cooling fluid condition using its existing sensors and control capabilities, enabling autonomous fault detection during operation.
2Measurement precision
If contactors are closed and opened to measure isolation resistance, then accurate resistance measurements are obtained, but system operation is disrupted and diagnostic complexity increases
Solution Approach 1:
The patent performs isolation resistance measurements during normal fuel cell operation before any fault conditions develop or system shutdowns occur. By utilizing measurements taken during regular operation at different power levels, the system obtains accurate cooling fluid conductivity data without needing to preemptively disconnect components or disrupt system operation. The diagnostic information is gathered as part of normal system monitoring.
Solution Approach 2:
The system measures isolation resistance dynamically during varying operational conditions, specifically at different power levels (first and second operating conditions). By taking measurements across multiple dynamic operating states rather than requiring static test conditions, the system maintains measurement accuracy while allowing the fuel cell system to operate continuously without disruption.
3Measurement precision
If extensive component testing is performed to identify isolation loss causes, then diagnostic accuracy is maintained, but labor and time requirements increase
Solution Approach 1:
The patent extracts the specific diagnostic function of cooling fluid conductivity measurement from the broader, more complex isolation loss diagnostic process. By directly measuring and calculating cooling fluid conductivity through isolation resistance measurements during operation, the system isolates and addresses the specific cause (coolant contamination) without needing to perform extensive testing of other potential isolation loss sources. This extraction focuses diagnostic efforts on the most probable and critical failure mode.
Solution Approach 2:
The system performs a limited set of measurements (voltage and current at two different power levels) that provides sufficient information to determine cooling fluid conductivity, rather than performing exhaustive testing of all possible isolation pathways. This partial action approach achieves adequate diagnostic accuracy for the specific application of monitoring coolant degradation without the excessive time and labor requirements of complete system isolation testing.
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 efficient detection and replacement of the cooling fluid, reducing diagnostic time and labor by directly identifying conductivity-related faults, thus optimizing fuel cell system operation and hydrogen usage.
Implementation Method 1
The cooling fluid flowing through cooling channels in the fuel cell stack to cool the bipolar plates could provide an electrical connection between the fuel cell stack and the vehicle chassis
Implementation Method 2
A hydrogen fuel cell is an electro-chemical device that includes an anode and a cathode with an electrolyte therebetween
Implementation Method 3
measuring a positive to chassis isolation resistance at a high system power level, measures the positive to chassis isolation resistance at a low system power level, measures fuel cell stack voltage and battery voltage at the two power levels
Data Source
AI summary
A system and method for monitoring the conductivity of a cooling fluid flowing in a fuel cell system on a vehicle including a chassis. The fuel cell system includes a fuel cell stack electrically coupled to a stack bus and a battery electrically coupled to a propulsion bus. The method includes operating the fuel cell system, measuring a first isolation resistance at the first power level, measuring a first stack voltage, and measuring a first battery voltage. The method also includes operating the fuel cell system at a second power level, and measuring a second isolation resistance, measuring a second stack voltage, and measuring a second battery voltage. The method calculates a stack coolant resistance using the first and second isolation resistances, the first and second stack voltages, and the first and second battery voltages, which is then used to calculate the cooling fluid conductivity.