Fuel Cell Voltage Control via Periodic Cathode Flow
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Solution Overview
Problem
In fuel cell systems, when the required power is equal to or smaller than a threshold, the fuel cell is disconnected from load devices, leading to low open circuit voltages, which can result in a deterioration of the actual power response due to insufficient oxygen, necessitating control of cathode gas flow rates to maintain target voltage ranges.
Innovation Solution
A fuel cell system with first and second fuel cells, supply systems for controlling cathode gas flow rates, a switching device, and a control unit that adjusts flow rates at different timings to maintain open circuit voltages within target ranges, preventing both from being in low states and improving power response.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the fuel cell is electrically disconnected to load devices when required power is equal to or smaller than a threshold, then the open circuit voltage can be controlled, but the open circuit voltage becomes too high which causes cathode catalyst elution
Solution Approach 1:
The patent applies periodic action by periodically increasing and decreasing the cathode gas flow rate to the fuel cell when electrically disconnected. This periodic flow rate adjustment creates corresponding periodic variations in open circuit voltage, preventing the voltage from remaining continuously high and thus preventing cathode catalyst elution while still allowing voltage control.
2Reliability
If the flow rate of cathode gas is reduced to control open circuit voltage, then catalyst elution is prevented, but the amount of oxygen remaining inside the fuel cell becomes too small which deteriorates power response
Solution Approach 1:
The patent uses periodic action by periodically increasing the cathode gas flow rate, which periodically increases the oxygen concentration inside the fuel cell. This ensures that when power response is needed, sufficient oxygen is available, improving power response speed while maintaining catalyst stability during the periodic cycles.
Solution Approach 2:
The patent applies preliminary action by maintaining a baseline level of cathode gas flow and oxygen concentration in the fuel cell even when disconnected. This preliminary preparation of oxygen supply ensures that when power demand increases, the fuel cell can respond quickly without catalyst damage from continuous high voltage.
3Reliability
If the flow rate of cathode gas is increased and decreased to converge open circuit voltage within target range, then voltage control is achieved, but both open circuit voltages may be in low states which deteriorates power response
Solution Approach 1:
The patent applies asymmetry by controlling multiple fuel cells with different open circuit voltage characteristics. Instead of applying identical flow rate adjustments to all cells, the system recognizes and exploits the asymmetric nature of individual cell voltages, adjusting each cell's cathode gas flow rate according to its specific characteristics to avoid simultaneous low voltage states.
Solution Approach 2:
The control unit performs preliminary assessment of each fuel cell's open circuit voltage state and predicts potential low voltage conditions. By taking preliminary action to adjust flow rates before all cells simultaneously reach low voltage states, the system maintains at least one cell in a high voltage state, ensuring rapid power response capability.
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 enhances the fuel cell system's response to required power by ensuring open circuit voltages remain within optimal ranges, preventing catalyst elution and maintaining high oxygen concentrations, thus improving power generation efficiency.
Implementation Method 1
a fuel cell unit including first and second fuel cells that supplies electric power to a load device
Implementation Method 2
a cathode catalyst of the fuel cell might be eluted
Data Source
AI summary
A fuel cell system includes: a fuel cell unit; first and second supply systems; a switching device; a switching control unit, when required power of the fuel cell unit is equal to or smaller than a threshold; an open circuit voltage obtaining unit; and a supply system control unit.