Fuel Cell Stack Cold Start with Current Heating and Pump Delay
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Solution Overview
Problem
Fuel cells, particularly PEMFCs, face issues with reaction product freezing and degradation due to operating temperatures below the freezing point of water, leading to cell damage during cold starts, especially in edge cells without adjacent heat sources.
Innovation Solution
Applying a controlled increasing current to the fuel cell stack to heat it up without using the cooling fluid initially, monitoring to prevent overheating, and adjusting the current and coolant flow to maintain optimal temperatures, allowing the stack to reach operating conditions safely.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a load is applied to the fuel cell stack to generate heat through increasing current, then the temperature of the fuel cell stack increases, but the voltage of the fuel cell stack decreases
Solution Approach 1:
The patent applies parameter changes by dynamically adjusting the current load on the fuel cell stack during cold start. The control unit increases the current from idle to a higher level to generate heat, then reduces it back to idle once the temperature threshold is reached. This temporal variation in electrical parameters resolves the contradiction between needing high voltage (low current) for power and low voltage (high current) for heating.
2Reliability
If the fuel cell stack is heated by applying increasing current, then freezing and degradation are prevented, but overheating may occur causing cell damage
Solution Approach 1:
The patent implements feedback control by continuously monitoring the temperature of the fuel cell stack and adjusting the current load accordingly. The control unit increases current only when temperature is below a threshold, and reduces current when the threshold is reached, preventing both freezing and overheating. This closed-loop feedback resolves the contradiction between preventing harmful freezing and avoiding harmful overheating.
Solution Approach 2:
The patent applies periodic action through cyclic current adjustment during cold start. The current is increased in cycles: raised from idle to generate heat, then reduced back to idle when temperature threshold is met. This periodic modulation of electrical load prevents continuous overheating while ensuring adequate heating during cold conditions, resolving the contradiction between preventing freezing and avoiding overheating damage.
3Object-affected harmful factors
If cooling fluid is pumped through the fuel cell stack during heating, then overheating is prevented, but the heating efficiency is reduced
Solution Approach 1:
The patent applies periodic action by controlling the cooling pump to operate intermittently rather than continuously. The pump is activated only when the temperature approaches the threshold during the heating phase, and deactivated when the threshold is reached. This periodic pumping prevents continuous heat removal that would reduce heating efficiency, while still preventing overheating when necessary.
Solution Approach 2:
The patent applies preliminary action by pre-cooling the cooling fluid before it enters the fuel cell stack during the heating phase. The cooling fluid is cooled in advance in a separate heat exchanger, so when it contacts the fuel cell stack, it removes minimal heat, allowing efficient heating while still providing overheating protection. This preliminary preparation resolves the contradiction between heating efficiency and overheating prevention.
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 method effectively prevents freezing and degradation by uniformly heating the fuel cell stack, ensuring it operates within safe temperature ranges and transitions to normal operation, reducing the risk of cell damage during cold starts.
Implementation Method 1
Fuel cells are typically combined to form so-called fuel cell stacks... Hydrogen is fed as fuel on the anode side and air (or also oxygen) is fed on the cathode side. The reaction produces water as reaction product.
Implementation Method 2
a load is applied to the fuel cell stack so that a first increasing current is taken from the fuel cell stack. This reduces the voltage of the fuel cell stack. At the same time, heating of the entire stack or of the corresponding cells is achieved by this first increasing current.
Data Source
AI summary
The present invention relates to a method for starting a fuel cell stack at temperatures below the freezing point of a reaction product produced during the reaction between an anode-side fuel and a cathode-side fuel. The fuel cell stack comprises a plurality of individual cells having at least one internal cell which is arranged in the stacking direction in the interior of the fuel cell stack and an edge cell which is arranged in the stacking direction at the edge of the fuel cell stack. The fuel cell stack is connected to a cooling circuit having cooling fluid for cooling the fuel cell stack, which cooling fluid can be conducted through the fuel cell stack by a pump arranged in the cooling circuit. The method includes the step of applying a load to the fuel cell stack for drawing a first increasing current from the fuel cell stack, thereby decreasing an output voltage of the fuel cell stack, while the pump does not conduct cooling fluid through the fuel cell stack, until a first predetermined condition is met. In addition, the invention provides a computer program product with computer-executable instructions for carrying out the method and a fuel cell system.