Fuel Cell Impedance Measurement via Current Cut-off Bypass
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Solution Overview
Problem
In power conditioning systems with fuel cells, accurate impedance measurement is compromised by load variations, leading to potential over-drying or flooding of the fuel cell, and high impedance DC/DC converters cause output loss and heat generation.
Innovation Solution
A power conditioning system with a fuel cell connected in parallel to a high-voltage battery, featuring a current bypass path and a current cut-off unit, allowing the impedance measuring device to measure the fuel cell's impedance by outputting alternating currents between its electrodes, while the DC/DC converter boosts the output voltage during measurement to increase impedance and prevent current backflow.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a DC/DC converter is provided on the battery side to link the battery and fuel cell outputs, then the system can handle load variations, but load variation signals may flow to the fuel cell and interfere with impedance measurement accuracy
Solution Approach 1:
The patent introduces a current cut-off unit as an intermediary component on the bypass path. This unit selectively blocks current flow between the battery and fuel cell based on operational conditions, preventing load variation signals from reaching the fuel cell during impedance measurement while allowing normal power sharing during regular operation
Solution Approach 2:
The bypass path configuration with the current cut-off unit dynamically adjusts the electrical connection state between battery and fuel cell. The cut-off unit switches between conducting and blocking states based on whether impedance measurement is being performed, enabling the system to adapt its topology for different operational requirements
2Measurement precision
If the impedance of the DC/DC converter is increased to suppress load variation flow, then measurement accuracy improves, but output loss increases and heat generation occurs
Solution Approach 1:
The current cut-off unit acts as a mediator that eliminates the need for high DC/DC converter impedance. By blocking the bypass path during measurement, it prevents load variation signals from reaching the fuel cell without requiring the DC/DC converter to present high impedance, thus avoiding power losses and heat generation
Solution Approach 2:
The patent extracts the impedance control function from the DC/DC converter and relocates it to the current cut-off unit on the bypass path. This separation allows the DC/DC converter to maintain low impedance for efficient power transfer while the cut-off unit provides the necessary isolation during measurement
3Measurement precision
If a current bypass path is provided to couple the fuel cell and load, then the DC/DC converter can be bypassed during measurement, but the bypass path may allow current backflow and interfere with measurement
Solution Approach 1:
The current cut-off unit serves as a mediator on the bypass path that selectively permits or blocks current flow. During impedance measurement, it blocks current backflow from the load to the fuel cell, preventing measurement interference while allowing the bypass path to function normally during power operation
Solution Approach 2:
The current cut-off unit applies preliminary anti-action by preemptively blocking the bypass path before impedance measurement begins. This prevents potential current backflow and measurement interference from occurring in the first place, rather than attempting to correct them after they arise
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 configuration enables accurate impedance measurement of the fuel cell, reduces output loss, and improves power generation efficiency by minimizing noise and maintaining high impedance during measurement, while ensuring accurate measurement accuracy.
Implementation Method 1
an impedance measuring device for measuring an impedance of the fuel cell by outputting alternating currents between a positive electrode and an intermediate point of the fuel cell and between the intermediate point and a negative electrode of the fuel cell
Implementation Method 2
a DC/DC converter connected between the fuel cell and the load and converting an output voltage of the fuel cell at a predetermined required voltage ratio
Data Source
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AI summary
A power conditioning system includes a fuel cell connected to a load, a fuel cell converter connected between the fuel cell and the load and converting an output voltage of the fuel cell at a predetermined required voltage ratio, and a battery connected to the load in parallel to the fuel cell and serving as a power supply source different from the fuel cell. The power conditioning system includes an impedance measuring device configured to measure an impedance of the fuel cell by outputting alternating currents between a positive electrode and an intermediate point of the fuel cell and between the intermediate point and a negative electrode of the fuel cell, and a current bypass path configured to couple the fuel cell and the load while bypassing the fuel cell converter. The power conditioning system includes a current cut-off unit configured to provide on the current bypass path, the current cut-off unit electrically cutting off the current bypass path when the impedance of the fuel cell is measured by the impedance measuring device.