Fuel Cell Stack Impedance Measurement Under Stable Output Current
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Solution Overview
Problem
Accurately measuring the impedance of a fuel cell stack during vehicle operation is challenging due to difficulties in reaching and maintaining a steady state, and the influence of peripheral components degrades measurement accuracy.
Innovation Solution
A method involving a DC-DC converter switching to buck mode to isolate the fuel cell stack's output current, controlling a COD variable resistor to maintain a desired current value, and monitoring battery state of charge to ensure accurate impedance measurement while minimizing interference from other components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If impedance measurement is performed during vehicle operation, then real-time diagnostic capability is improved, but measurement accuracy deteriorates due to inability to reach steady state and interference from peripheral components
Solution Approach 1:
The patent segments the current path by introducing a bypass switch that can isolate the fuel cell stack from the battery and DC-DC converter. This segmentation allows the measurement system to separate the fuel cell output from other system components, enabling accurate impedance measurement during operation without interference from peripheral devices.
Solution Approach 2:
The patent introduces an ammeter as an intermediary device in the current path between the fuel cell stack and the load. This intermediary allows precise measurement of the fuel cell output current during impedance measurement, enabling accurate determination of impedance values while maintaining system operation.
2Measurement precision
If DC-DC converter is switched to buck mode to isolate fuel cell output, then measurement accuracy is improved, but system complexity increases due to switching control requirements
Solution Approach 1:
The patent employs dynamic switching of the DC-DC converter between buck mode and normal operation mode based on measurement requirements. The bypass switch is activated only during impedance measurement to create a isolated current path, then deactivated during normal operation. This dynamic approach enables accurate measurement without permanently increasing system complexity.
Solution Approach 2:
The control unit automatically manages the switching between measurement mode and normal operation mode based on received measurement requests. The system self-regulates the bypass switch and DC-DC converter states without requiring external intervention, simplifying the overall control architecture while maintaining measurement accuracy.
3Stability of the object's composition
If COD variable resistor is used to maintain constant current, then output current stability is improved, but device complexity increases due to additional control mechanisms
Solution Approach 1:
The patent implements a feedback control mechanism where the control unit continuously monitors the fuel cell output current through the ammeter and adjusts the COD variable resistor accordingly. When the measured current deviates from the target value, the control unit modifies the resistor value to restore the desired current level, ensuring stable operating conditions during impedance measurement.
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 precise impedance measurement of the fuel cell stack at desired and various operating points, maintaining output current stability and ensuring driving safety by adjusting the DC-DC converter mode based on battery SOC.
Implementation Method 1
switching a DC-DC converter connecting the fuel cell stack and a battery to each other to a buck mode when measuring the impedance is requested, thereby blocking output current of the fuel cell stack from flowing to the battery through the DC-DC converter
Implementation Method 2
controlling a resistance value of a COD variable resistor consuming the output current of the fuel cell stack according to the first current value
Data Source
AI summary
A method for accurately measuring the impedance of the fuel cell stack in the vehicle during operation of the vehicle includes determining whether measuring the impedance of the fuel cell stack is requested during driving of the vehicle driven by using a power of a fuel cell stack, switching a DC-DC converter connecting the fuel cell stack and a battery to each other to a buck mode when measuring the impedance is requested, thereby blocking output current of the fuel cell stack from flowing to the battery through the DC-DC converter, determining a first current value of the fuel cell stack for measuring the impedance, controlling a resistance value of a COD variable resistor consuming the output current of the fuel cell stack according to the first current value, and measuring the impedance of the fuel cell stack while the output current of the fuel cell stack is maintained at the first current value.