Fuel Cell Bleed-Down Circuit Using Resistor Bypass
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Solution Overview
Problem
Existing fuel cell systems face damage due to open circuit voltage (OCV) during shutdown, which is caused by non-return valves not being leak-proof under temperature and pressure changes, leading to increased system costs and potential freezing issues, and require additional components for air-tight blocking, increasing complexity and costs.
Innovation Solution
A fuel cell system with a second electrical connection as a bypass to the DC/DC converter or in parallel with the fuel cell, incorporating a resistor to discharge residual energy safely, allowing continuous energy discharge during shutdown, independent of the electrical system, and eliminating the need for non-return valves in the cathode path.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If non-return valves are used to block air supply to the cathode chamber during shutdown, then the open circuit voltage can be prevented, but the system complexity and costs increase due to additional components and pressure losses
Solution Approach 1:
The patent removes the non-return valves from the system entirely. Instead of using mechanical blocking components, the invention relies on the electrical circuit configuration where the DC/DC converter automatically stops current flow when the fuel cell voltage drops below its operating threshold, thereby preventing open circuit voltage without requiring additional mechanical components.
Solution Approach 2:
The patent replaces the mechanical non-return valve system with an electrical control mechanism. The DC/DC converter's inherent electrical characteristics (voltage threshold for operation) substitute for the mechanical blocking function of non-return valves, eliminating the need for moving parts and mechanical sealing components.
2Reliability
If non-return valves are used to block air supply, then open circuit voltage can be prevented, but pressure losses increase affecting air compressor design and costs
Solution Approach 1:
The patent eliminates the non-return valves from the air supply path, thereby removing the source of pressure losses associated with these components. The electrical control mechanism does not create flow resistance in the gas paths, maintaining optimal pressure conditions for the air compressor and overall system efficiency.
3Reliability
If non-return valves are used to block air supply, then open circuit voltage can be prevented, but the valves may freeze and become inoperable at temperatures below freezing
Solution Approach 1:
The patent replaces the mechanical non-return valve system with an electrical control mechanism that is not susceptible to freezing. The DC/DC converter's electrical components operate independently of temperature-related mechanical issues, ensuring reliable prevention of open circuit voltage even in sub-freezing conditions.
4Reliability
If a bleed-down switch is used to discharge residual energy, then open circuit voltage can be avoided, but the system requires additional switching components and control complexity
Solution Approach 1:
The patent utilizes the DC/DC converter's inherent operational characteristics to automatically discharge residual energy. When the fuel cell voltage drops below the converter's minimum operating threshold, the converter naturally stops drawing current, creating a self-regulating bleed-down mechanism without requiring external switching components or complex control logic.
Solution Approach 2:
The DC/DC converter serves dual functions: it performs its primary power conversion role during normal operation and simultaneously acts as a bleed-down mechanism during shutdown. This multi-functionality eliminates the need for dedicated bleed-down switching components, reducing overall system complexity.
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 solution reduces the risk of damaging open circuit voltage, extends the fuel cell system's lifespan, simplifies the shutdown process, and lowers system costs by avoiding pressure losses and freezing issues with non-return valves, while ensuring safe and reliable energy discharge.
Implementation Method 1
the second electrical connection is a bypass connection to the DC/DC converter and/or the second electrical connection is a bypass connection in parallel with the fuel cell, wherein at least the residual energy can be discharged by way of the second electrical connection and wherein at least the bypass connection parallel with the fuel cell comprises a resistor
Data Source
AI summary
The invention relates to a fuel cell system (100, 1) comprising: at least one fuel cell (200) which has a cathode (230) with a cathode chamber and has an anode chamber of an anode (210), which anode chamber is separated from the cathode chamber by a membrane, wherein the cathode chamber is connected to a cathode gas source via at least one first fluid connection (240) and the anode chamber is connected to an anode gas source via at least one second fluid connection; and comprising a first electrical connection (3) to a DC/DC converter (450) that electrically connects the anode (210) and the cathode (230) to an energy system (400), wherein in a shut-down phase of the fuel cell system (100, 1), residual energy present in the fuel cell (200) can be discharged. According to the invention, the anode (210) is connected to the energy system (400) and/or the cathode (230) via at least one second electrical connection (2), wherein the second electrical connection (2) is a bypass connection to the DC/DC converter (450) and/or the second electrical connection (2) is a bypass connection parallel to the fuel cell (200), wherein at least the residual energy can be discharged via the second electrical connection (2), and the second electrical connection (2) comprises a resistor (6).