Fuel Cell Stop Control Preventing Open Circuit Voltage Exposure
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Solution Overview
Problem
Fuel cell systems face durability issues due to exposure to open circuit voltage (OCV) during shutdown, leading to unnecessary voltage generation and battery discharge, which degrades the fuel cell and reduces its marketability.
Innovation Solution
A stop control method that manages the high-voltage terminal relay and COD relay to prevent overvoltage by comparing fuel cell voltage with set values, controlling the high-voltage terminal voltage downwardly, and sequencing the relay operations to ensure the fuel cell is not exposed to OCV during shutdown, thereby reducing battery discharge and enhancing durability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the high-voltage terminal relay is opened during fuel cell shutdown, then the fuel cell system can be stopped, but the fuel cell is exposed to open circuit voltage causing overvoltage and durability degradation
Solution Approach 1:
The controller turns on the COD relay before opening the high-voltage terminal relay to preliminarily establish a voltage discharge path. This preliminary action ensures that when the high-voltage terminal relay opens and the fuel cell becomes isolated, the COD relay is already active to consume the open circuit voltage through resistive heating, preventing overvoltage damage to the fuel cell stack
Solution Approach 2:
The COD relay acts as an intermediary component between the fuel cell and the high-voltage terminal. When activated, it provides a controlled discharge path for the fuel cell voltage, mediating the voltage transition during shutdown. The COD heater element serves as the intermediary that dissipates the electrical energy as heat, preventing direct overvoltage exposure to the fuel cell stack
2Object-affected harmful factors
If the COD relay is operated before the high-voltage terminal relay, then overvoltage is prevented, but unnecessary battery current is consumed
Solution Approach 1:
The controller dynamically adjusts the COD relay operation based on real-time voltage comparisons. It monitors the fuel cell voltage and only activates the COD relay when the voltage exceeds a predetermined threshold, rather than operating it continuously or unconditionally. This dynamic control optimizes the balance between overvoltage prevention and energy conservation by engaging the COD heater only when necessary
Solution Approach 2:
The controller changes the operational parameters of the COD relay based on voltage conditions. It monitors the fuel cell voltage parameter and uses this information to determine when to activate or deactivate the COD relay. By changing the operational state of the COD relay based on voltage parameter thresholds, the system prevents overvoltage while minimizing unnecessary energy consumption from the high-voltage battery
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
The method effectively prevents fuel cell exposure to open circuit voltage, reduces battery discharge, and enhances the durability and marketability of the fuel cell system by controlling voltage and relay operations during shutdown.
Implementation Method 1
a COD relay provided between the fuel cell and the COD heater is closed, whereby the voltage of the fuel cell is consumed as heat by the COD heater
Data Source
AI summary
A stop control method for a fuel cell system of a vehicle can include: determining whether a fuel cell of the fuel cell system is shut down when a key-off signal is received; comparing a voltage of the fuel cell with a first set voltage when it is determined that the fuel cell is not shut down; controlling a voltage of a high-voltage terminal downwardly when the voltage of the fuel cell is larger than the first set voltage; turning on a cathode oxygen depletion (COD) relay a first time after controlling the voltage of the high-voltage terminal downwardly; turning off a high-voltage terminal relay a first time after turning on the COD relay, the high-voltage relay disposed between the fuel cell and the high-voltage terminal; and shutting down the fuel cell and performing key-off control after turning off the high-voltage terminal relay.