Fuel Cell Stack Impedance Measurement Using Relay-Based Load Separation
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Solution Overview
Problem
Existing fuel cell impedance measurement methods suffer from noise interference and accuracy degradation due to energy consumption from the fuel cell stack, which degrades control and measurement precision, especially when high-voltage components like compressors and cooling pumps are driven directly from the fuel cell.
Innovation Solution
A system and method that supply energy from a battery, rather than the fuel cell, to high-voltage components during impedance measurement, using a relay to disconnect the cooling device and high-voltage battery from the fuel cell stack, allowing the impedance measurement unit to apply an AC current and measure impedance with reduced noise and energy consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If energy is supplied from the fuel cell stack to high-voltage components (compressor, cooling pump) during impedance measurement, then the fuel cell operates in energy-producing state, but noise is generated that degrades measurement accuracy
Solution Approach 1:
The system segments the power supply function by introducing a dedicated battery for high-voltage components during measurement, separating it from the fuel cell's measurement function. This segmentation allows the fuel cell to operate in open-circuit voltage state without driving noisy components, while the battery independently powers the compressor and cooling pump.
Solution Approach 2:
The battery acts as an intermediary energy source between the power grid and the high-voltage components during impedance measurement. Instead of the fuel cell directly powering the compressor and cooling pump (causing noise), the battery mediates this energy transfer, isolating the measurement system from electrical noise while maintaining necessary cooling and compression functions.
2Temperature
If the fuel cell stack supplies energy to the cooling device and high-voltage battery, then the fuel cell operates in energy-producing state, but a large amount of heat is generated requiring water-cooling
Solution Approach 1:
The system employs periodic action by switching between two operational modes: during impedance measurement, the battery supplies energy and air cooling is sufficient; during normal operation, the fuel cell supplies energy and water-cooling is activated. This periodic switching between cooling methods reduces the need for continuous complex water-cooling infrastructure.
3Measurement precision
If the fuel cell stack is used for impedance measurement, then direct measurement of fuel cell deterioration is achieved, but control difficulty increases due to noise and energy consumption
Solution Approach 1:
The invention extracts the noisy energy-consuming functions (compressor, cooling pump) from the fuel cell's measurement circuit by powering them from the battery instead. This extraction removes the primary noise sources and control complications from the measurement system, allowing the fuel cell to be measured in a clean open-circuit voltage state without the complexity of controlling loaded operation during 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
This approach minimizes noise and energy consumption during impedance measurement, allowing for more accurate fuel cell stack impedance assessment and increased design flexibility with reduced heat generation, enabling both water and air cooling options.
Implementation Method 1
an impedance measurement unit configured to apply an AC current to the fuel cell stack and to measure the impedance of the fuel cell stack
Implementation Method 2
a relay provided at the main bus end and configured to electrically connect or disconnect the cooling device and the high-voltage battery to or from the fuel cell stack
Implementation Method 3
the cooling device may cool the energy consumption device
Implementation Method 4
a high-voltage battery connected in parallel to a main bus end of a fuel cell stack
Data Source
AI summary
A system and a method for measuring impedance of a fuel cell stack are disclosed. The system includes: an energy consumption device, a cooling device, and a high-voltage battery connected in parallel to a main bus end of a fuel cell stack; a relay provided at the main bus end and configured to electrically connect or disconnect the cooling device and the high-voltage battery to or from the fuel cell stack; an impedance measurement unit configured to apply an AC current to the fuel cell stack and to measure the impedance of the fuel cell stack; and a controller configured to turn off the relay during measurement of the impedance of the fuel cell stack.