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Fuel cell system operation of air compressor in surge for low power

IP.com Disclosure Number: IPCOM000225308D
Publication Date: 2013-Feb-07
Document File: 2 page(s) / 192K

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The IP.com Prior Art Database

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Fuel cell system operation of air compressor in surge at low power

Fuel Cell Systems convert air and hydrogen to electricity and water. In order to provide air as a reactant, an air compressor may be used.     A diagram of a simplified fuel cell system is provided for clarity.  Non-positive displacement air compressor technologies exhibit a surge line, which separates stable and unstable aerodynamic performance. The surge region is characterized by localized stall and reversal of airflow inside the air compressor. This then results in oscillating flow and pressure at the device interfaces. Typically in a fuel cell system, operation avoids the surge region to prevent air compressor damage. Avoiding this surge region requires the fuel cell system to operate the air compressor at a higher air flow rate than necessary.  This can cause higher parasitic losses as well as an inability to maintain humidity targets given the excessively high air flow. The extra parasitic can dramatically reduce fuel cell system efficiencies at low power operation.   For example, a waste gate or stack bypass can be used to prevent excess air at the stack, but there is still extra parasitic loss and system cost (cost of valve).

Figure 1: Block Diagram of the cathode side of a fuel cell system

An alternative method is to intentionally operate the air compressor in the surge region at low to mid compressor speeds.  At compressor speeds less than 50% maximum, the aerodynamic stresses involved in...