Fuel Cell Voltage Control in Stop-Mode Using Battery Charging
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Solution Overview
Problem
Fuel cell vehicles face challenges in maintaining durability and preventing fuel efficiency reduction during stop-mode, as existing methods either fail to sufficiently decrease fuel cell voltage or lead to reacceleration issues and battery overcharging.
Innovation Solution
A method involving a controller that detects the stop-mode, calculates a voltage command value based on available battery charging power, adjusts the bus terminal voltage using a power converter, and increases power consumption of electric field loads to actively decrease the fuel cell voltage, while preventing battery overcharging and maintaining fuel efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the fuel cell voltage is maintained near open-circuit voltage during stop-mode, then the fuel cell durability deteriorates, but if the voltage is forcibly decreased, the reacceleration deteriorates due to time required for voltage increase
Solution Approach 1:
The system performs preliminary actions by pre-charging the high voltage battery with the fuel cell output during stop-mode before reacceleration is needed. This ensures that when reacceleration occurs, the battery can immediately supply power without waiting for fuel cell voltage to build up, thus resolving the contradiction between maintaining voltage for durability and enabling fast reacceleration
Solution Approach 2:
The high voltage battery acts as an intermediary energy storage device between the fuel cell and the motor. During stop-mode, the battery absorbs excess fuel cell power and maintains voltage at optimal levels for durability. During reacceleration, the battery quickly releases stored energy to the motor, eliminating the delay that would occur if power came directly from the fuel cell
2Reliability
If a resistor is connected to decrease the voltage, then the fuel efficiency reduces, but if the voltage is not decreased, the fuel cell durability deteriorates
Solution Approach 1:
The high voltage battery serves as an intermediary that captures and stores the fuel cell's electrical output during stop-mode instead of dissipating it through a resistor. This converts what would be wasted energy into useful stored energy, simultaneously protecting fuel cell durability by controlling voltage and preventing fuel efficiency loss by recovering rather than wasting the electrical energy
Solution Approach 2:
The system converts the potentially harmful effect of excess voltage (which would require resistive dissipation) into a beneficial outcome by charging the battery. The energy that would have been lost as heat in a resistor is instead stored in the battery for later use, transforming an energy loss scenario into an energy recovery opportunity that improves overall fuel efficiency while maintaining fuel cell durability
3Reliability
If the output of the fuel cell is generated by control of voltage decrease of bus terminal using power converter, then the battery may be overcharged when regenerative braking amount is substantial
Solution Approach 1:
The system employs feedback control by continuously monitoring the battery's charge state and regenerative braking amount. Based on this feedback, the controller dynamically adjusts whether to activate the fuel cell voltage decrease control. When the battery is already substantially charged or regenerative braking is substantial, the system suppresses additional charging requests, preventing overcharging while still enabling voltage control when appropriate to maintain fuel cell durability
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 effectively secures fuel cell durability by rapidly and efficiently decreasing voltage during stop-mode, preventing fuel efficiency reduction and battery overcharging, while ensuring reacceleration is not compromised.
Implementation Method 1
operating a converter connected between the high voltage battery and the bus terminal to adjust the voltage of the bus terminal
Implementation Method 2
consuming the output of the fuel cell by a driving motor
Data Source
AI summary
A method and system for controlling a voltage in a stop-mode of a fuel cell vehicle are provided. The method includes detecting whether a fuel cell enters the stop-mode and calculating a voltage command value of a bus terminal based on available charging power of a battery representing a level of power chargeable in a high voltage battery when the fuel cell enters the stop-mode. A converter connected between the high voltage battery and the bus terminal is operated to adjust the voltage of the bus terminal to be the voltage command value of the bus terminal. Additionally, power consumption of an electric field load of a vehicle is increased when the voltage is adjusted and then the voltage of the fuel cell measured by a voltage sensor is equal to or greater than a reference voltage preset in a memory.