Fuel Cell Air Pump Flow Control via Pressure Adjustment
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Solution Overview
Problem
In fuel cell systems using turbo type air pumps with air bearings, achieving the desired air flow rate is challenging, especially when the compressor's rotational speed is near its lowest operational range due to errors in flow-rate sensors and variations in intake air pressure and temperature, leading to increased air flow rates and pressure loss issues.
Innovation Solution
The system incorporates a pressure control mechanism that increases oxidant gas pressure when the actual flow rate exceeds the target flow rate, utilizing a control means to adjust the target pressure and aperture of the back pressure valve, and includes a humidifier bypass to regulate oxidant gas proportions, ensuring appropriate flow rates are maintained by controlling the oxidant-flow regulating means.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the rotational speed of the turbo type air pump is controlled to the lower limit, then power consumption is reduced, but the air flow rate becomes unstable and increases due to air bearing flotation issues
Solution Approach 1:
The control device changes the control parameter from rotational speed only to a combination of rotational speed and discharge pressure. By monitoring the actual air flow rate and comparing it with the target flow rate, the system adjusts the discharge pressure to compensate for flow rate deviations caused by air bearing flotation, thereby maintaining stable air supply while operating at low rotational speeds
Solution Approach 2:
The system implements feedback control by continuously detecting the actual air flow rate, comparing it with the target flow rate, and adjusting the discharge pressure accordingly. When the actual flow rate exceeds the target (indicating air bearing flotation), the control device increases the discharge pressure to reduce the flow rate back to the target value
2Productivity
If the rotational speed is fixed at the lower limit, then the air pump operates efficiently, but the air flow rate greatly increases due to air bearing flotation
Solution Approach 1:
The system introduces discharge pressure as an additional control parameter to regulate the air flow rate. By adjusting the discharge pressure independently of the rotational speed, the system can maintain the rotational speed at the efficient lower limit while controlling the actual air flow rate to match the target flow rate, thus resolving the contradiction between efficiency and flow rate control
3Ease of operation
If feedback control of rotational speed is used, then the air flow rate is regulated, but the control becomes ineffective when the command value is near the lowest rotational speed due to air bearing flotation
Solution Approach 1:
The control device transitions from single-parameter (rotational speed) control to two-parameter (rotational speed and discharge pressure) control. This parameter expansion enables effective flow rate control even when the rotational speed is at the lower limit, because the discharge pressure can be adjusted to compensate for the unstable air bearing flotation effects that occur at low speeds
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 controls the air flow rate to the target value, preventing excessive air feed and maintaining efficient power generation while preventing electrolyte membrane drying, thereby enhancing system reliability and power generation efficiency.
Implementation Method 1
a turbo type air pump (oxidant pump) 21 in which a shaft is supported by an air bearing
Data Source
AI summary
A fuel cell system comprises: a turbo type oxidizing agent pump, the rotary shaft of which is pivotally supported by an air bearing to take in and supply an oxidizing agent gas to a fuel cell by the rotary motion; an actual flow rate detection means for the oxidizing agent gas; a pressure adjustment means for the oxidizing agent gas; a rotary speed monitoring means for the oxidizing agent pump; and a control means which, when the rotary speed of the oxidizing agent pump is within the range of the minimum rotary speed that allows the rotary shaft to be pivotally supported by the air bearing, if the actual flow rate of the oxidizing agent gas is larger than a target flow rate, increases the pressure of the oxidizing agent gas via the pressure adjustment means.