Fuel Cell Precharge Circuit Voltage Equalization
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Solution Overview
Problem
In fuel cell systems, a significant voltage difference between smoothing capacitors can lead to excessively high currents when the system is restarted, causing potential damage and inefficiency due to rapid voltage depletion in the secondary battery converter's smoothing capacitor while the fuel cell converter's capacitor remains charged.
Innovation Solution
A fuel cell system with a DC-to-DC converter configuration, including precharge circuits and relays, where a controller manages the charging of smoothing capacitors to equalize voltages before switching on the precharge circuit, reducing current flow and preventing high-capacity relay requirements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the system is restarted after a short stop period, then the fuel cell converter's smoothing capacitor retains high voltage, but the secondary battery converter's smoothing capacitor voltage drops significantly, creating a large voltage difference that causes excessively high current when the relay is switched on
Solution Approach 1:
The patent applies preliminary action by introducing a precharge circuit that equalizes the voltage between the first smoothing capacitor (fuel cell converter) and the second smoothing capacitor (secondary battery converter) before the relay is switched on. This preliminary voltage equalization prevents the harmful high current that would otherwise occur due to the voltage difference between capacitors during system restart after a short stop period.
2Ease of operation
If a relay is provided on the high voltage side to separate the fuel cell system components, then the system can be separated during stop, but the voltage difference between smoothing capacitors causes high current when reconnecting
Solution Approach 1:
The patent uses the precharge circuit as an intermediary between the two smoothing capacitors with different voltages. This intermediary circuit equalizes the voltages before the relay connects the capacitors, thereby preventing the harmful high current during reconnection while maintaining the ease of operation benefits of the relay-based separation system.
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 configuration effectively reduces the electric current during startup, prevents excessive current flow, and allows for the downsizing of relays and precharge circuit components by ensuring voltage equality between capacitors, enhancing system reliability and efficiency.
Implementation Method 1
a first converter (120) connected with the fuel cell (100), the first converter (120) being provided as a DC-to-DC converter and including a first smoothing capacitor (C1) for use in stepping up voltage; a second converter (220) connected with the first converter (120) via high voltage wiring (110) and connected with the secondary battery (200) via low voltage wiring (210), the second converter (220) being provided as a DC-to-DC converter and including a second smoothing capacitor (C2) for use in stepping up voltage
Implementation Method 2
a first precharge circuit (130) connected in parallel to the first relay (140) and configured as a bypass conduction path that is configured to be switched on and off and that includes a reactor or a resistance
Data Source
AI summary
A controller of a fuel cell system performs a starting operation that switches on a first precharge circuit so as to reduce a voltage difference between a first smoothing capacitor and a second smoothing capacitor and subsequently turns on a first relay, when a start switch is turned on in a system off state that the first relay is off. Upon satisfaction of a predetermined condition including at least one of a condition that a difference between the voltage of the first smoothing capacitor and the voltage of the second smoothing capacitor is equal to or greater than a first reference value and a condition that the voltage of the first smoothing capacitor is equal to or higher than a second reference value, the controller uses a second converter to charge the second smoothing capacitor so as to bring the voltage of the second smoothing capacitor closer to the voltage of the first smoothing capacitor, and subsequently switches the first precharge circuit from off to on. This configuration reduces the electric current flowing through a precharge circuit at the time of starting the fuel cell system.