Fuel Cell Bus Voltage Control via DC Boost Feedback
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Solution Overview
Problem
In fuel cell vehicles, when a high voltage battery fails, the supervisory controller may allow power draws that exceed the fuel cell stack's capabilities, leading to stack degradation due to measurement inaccuracies and lag times, causing voltage and power transients.
Innovation Solution
A system and method that determines if the high voltage battery has failed, disconnects it from the bus, and uses a DC boost circuit to adjust the high voltage bus set-point based on fuel cell stack voltage, with a supervisory controller setting media flow and determining voltage limits to prevent excessive power draws, employing algorithms to limit loads and maintain operational limits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the supervisory controller allows power draws based on battery voltage limits, then the system can operate with standard voltage control, but measurement inaccuracies and lag times cause power draws to exceed fuel cell stack capabilities leading to stack degradation
Solution Approach 1:
The system implements a feedback mechanism where the actual fuel cell stack voltage is continuously measured and used to adjust the high voltage bus set-point. The DC boost circuit controller receives feedback about the stack voltage and dynamically adjusts the bus voltage to prevent excessive power draws that would degrade the stack, resolving the contradiction between measurement precision and reliability.
Solution Approach 2:
The DC boost circuit acts as an intermediary between the fuel cell stack and the high voltage bus. It decouples the direct voltage relationship, allowing the bus voltage to be adjusted based on actual stack conditions rather than relying solely on battery voltage limits. This intermediary function prevents power draws that would exceed stack capabilities while maintaining proper voltage levels.
2Device complexity
If a fixed high voltage bus set-point is used after battery failure, then the control system is simple, but the fuel cell stack cannot meet system power demand during transient conditions
Solution Approach 1:
The system transitions from a fixed high voltage bus set-point to a dynamic set-point that adjusts based on actual fuel cell stack voltage measurements. The DC boost circuit controller continuously modifies the bus voltage target to match changing stack conditions, enabling the system to meet varying power demands during transient conditions while maintaining manageable control complexity through the use of a lookup table for voltage set-point determination.
3Stability of the object's composition
If the high voltage bus operates independently of fuel cell stack voltage, then the bus voltage is stable, but the fuel cell boost circuit cannot respond to changes in stack voltage during battery failure
Solution Approach 1:
The system uses feedback control where the DC boost circuit controller continuously monitors the actual fuel cell stack voltage and adjusts the high voltage bus set-point accordingly. This feedback mechanism maintains bus voltage stability by dynamically adapting the set-point to match changing stack conditions, resolving the contradiction between stability and adaptability.
Solution Approach 2:
The control system uses the fuel cell stack's own voltage characteristics to determine the appropriate bus set-point. By using the actual stack voltage measurement as the basis for setting the bus voltage target, the system allows the stack to effectively set its own operating conditions, ensuring the boost circuit responds appropriately to stack voltage changes while maintaining overall system stability.
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 effectively confines the load on the high voltage bus and fuel cell stack within desired limits, preventing degradation by dynamically adjusting the bus voltage set-point and ensuring power balance, even during transient conditions.
Implementation Method 1
DC boost circuit that converts the measured voltage to a voltage set-point value for the DC boost that sets the voltage on the high voltage bus
Data Source
AI summary
A system and method for controlling the voltage on a high voltage bus in a fuel cell system in response to a failed high voltage battery. The method includes determining if the high voltage battery has failed, and disconnecting the battery from the high voltage bus in response to a failure. The method measures the voltage of the fuel cell stack by a DC boost circuit and converts the measured voltage to a voltage set-point value that sets the voltage on the high voltage bus, where the voltage set-point value changes as the measured voltage changes. A supervisory controller sets the media flow to the fuel cell stack and determines a minimum stack voltage limit value based on the stack maximum current draw that is used to determine a high voltage bus lower limit value.