Galvanic Isolation for Fuel Cell Earth Fault Prevention
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Solution Overview
Problem
High temperature fuel cell systems in marine applications face challenges with earth fault currents, which are not tolerable and require significant added mass, volume, and power losses due to the need for isolating transformers or well-isolated electrical heaters.
Innovation Solution
An isolating DC-DC converter with galvanic isolation and bi-directional power flow capabilities is used to supply heating resistors beyond the fuel cell's power output, preventing earth fault currents from escaping, and incorporating active control for modulation to manage heating resistors effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If isolating transformers are used to prevent earth fault currents in marine applications, then reliability is improved, but weight and volume increase significantly
Solution Approach 1:
The patent replaces the mechanical/electromagnetic isolation system (isolating transformer) with an electrical control system based on galvanic isolation and active fault current injection. The DC-DC converter with galvanic isolation stage provides electrical separation, while the control unit actively manages fault currents through electronic means, eliminating the need for heavy transformer-based isolation.
Solution Approach 2:
The patent changes the operational parameters of the heating resistor by controlling its voltage and current through the DC-DC converter. By adjusting the power delivery parameters dynamically and using bi-directional power flow, the system achieves both heating function and fault current prevention without requiring traditional isolating transformers.
2Reliability
If isolating transformers are used to prevent earth fault currents, then reliability is improved, but device complexity increases
Solution Approach 1:
The DC-DC converter is designed to perform multiple functions: it provides galvanic isolation, controls the heating resistor, enables bi-directional power flow, and actively prevents fault currents. This multi-functional approach consolidates what would otherwise require separate components (transformer, heater controller, fault protection device) into a single integrated system.
Solution Approach 2:
The patent merges the heating control function and fault current prevention function into a single integrated system. The control unit combines the heating resistor control and fault current injection capabilities, while the galvanic isolation stage serves both power conversion and electrical isolation purposes, reducing overall system complexity.
3Ease of operation
If electrical heaters are used for heat management, then ease of operation is improved, but earth fault currents are generated
Solution Approach 1:
The galvanic isolation stage acts as an intermediary between the electrical heater and the fuel cell system. It provides electrical separation that blocks the path for earth fault currents while allowing controlled power transfer to the heating element. The control unit serves as another intermediary that actively manages and compensates for any fault currents through bi-directional power flow control.
4Power
If power output level is exceeded to supply heating resistors, then heating performance is improved, but power management complexity increases
Solution Approach 1:
The system employs dynamic power flow control through the bi-directional DC-DC converter. The converter can adapt its operation mode based on real-time power demands, switching between power delivery to heating resistors and power recovery from the fuel cell system. This dynamic capability allows the system to exceed nominal power output levels when needed while maintaining overall power balance.
Solution Approach 2:
The control unit implements feedback control to manage the bi-directional power flow. It monitors the power status of the fuel cell system and adjusts the heating resistor power consumption accordingly, enabling the system to safely exceed its nominal power output when external conditions permit, while maintaining stability and preventing overheating.
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 provides reliable and cost-effective protection against earth fault currents without the need for additional transformers, reducing mass, volume, and power losses, especially in marine applications.
Implementation Method 1
said converter comprising a galvanic isolation stage and power electronic switching means for performing bi-directional power flow through the galvanic isolation stage
Implementation Method 2
at least one heating resistor connected to the fuel cell stack side of the galvanic isolation stage, and active control means for performing modulation controlling of the at least one heating resistor
Data Source
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AI summary
The object of the invention is an arrangement for avoiding earth fault currents in electrically heated fuel cell systems, each fuel cell in the fuel cell device comprising an anode side (100), a cathode side (102), an electrolyte (104) between the anode side and the cathode side, the fuel cells being arranged in a form of fuel cell stacks (103), and the arrangement comprises means (132) for determining essential temperature information of the fuel cells. The arrangement comprises at least one isolating DC-DC (Direct Current-Direct Current) converter (130) for loading of the stacks (103), said converter comprising a galvanic isolation stage (135) and power electronic switching means (137) for performing bi-directional power flow (144) through the galvanic isolation stage (135), at least one heating resistor (138) connected to the fuel cell stack (103) side of the galvanic isolation stage (135), and active control means (136) for performing modulation controlling of the at least one heating resistor (138). The arrangement also comprises said active control means (136) for utilizing the means (137) for performing bi-directional power flow (144) through the galvanic isolation stage (135) to supply power to the at least one heating resistor (138) by exceeding at least occasionally the power output level of the fuel cell stacks (103).