Fluid flow pulsing for increased stability in PEM fuel cell

Abstract

A fuel cell system includes a fuel cell stack and a flow control device that controls a supply of a first phase fluid flowing through the fuel cell stack. A controller monitors at least one parameter of the fuel cell stack and controls the supply to generate pulses of reactant when the at least one parameter crosses a threshold to flush a second phase fluid from said fuel cell stack.

1 . A fuel cell system, comprising: 
 a fuel cell stack;    a flow control device that controls a supply of a first phase fluid flowing through said fuel cell stack; and    a controller that monitors at least one parameter of said fuel cell stack and controls said supply to generate pulses of fluid when said at least one parameter crosses a threshold to flush a second phase fluid from said fuel cell stack.    
     
     
         2 . The fuel cell system of  claim 1  wherein said pulses are defined by at least one pulse feature selected from pulse duration, interval between pulses and pulse shape, as determined by said controller.  
     
     
         3 . The fuel cell system of  claim 2  wherein said at least one pulse feature is based on an extent by which said at least one parameter varies from said threshold.  
     
     
         4 . The fuel cell system of  claim 1  further comprising at least one voltage sensor sensing voltage of a respective cell of said fuel cell stack and provides a signal to said controller.  
     
     
         5 . The fuel cell system of  claim 4  wherein said parameter includes a cell voltage and said threshold is a minimum cell voltage threshold.  
     
     
         6 . The fuel cell system of  claim 4  wherein said threshold includes a fuel cell voltage fluctuation defined by at least one of a magnitude and a frequency of the individual fuel cell voltage fluctuations.  
     
     
         7 . The fuel cell system of  claim 1  further comprising a voltage sensor that monitors a stack voltage and provides a signal to said controller based on said parameter, which is said stack voltage.  
     
     
         8 . The fuel cell system of  claim 7  wherein said threshold includes a minimum stack voltage.  
     
     
         9 . The fuel cell system of  claim 7  wherein said threshold includes an average voltage fluctuation defined by at least one of a magnitude and a frequency of stack voltage fluctuations.  
     
     
         10 . The fuel cell system of  claim 1  further comprising a pressure sensing system that senses a fluid pressure drop across said fuel cell stack and provides a signal to said controller based on said parameter which is said pressure drop.  
     
     
         11 . The fuel cell system of  claim 10  wherein said threshold value includes a maximum pressure drop.  
     
     
         12 . The fuel cell system of  claim 10  wherein said threshold includes an average pressure drop fluctuation defined by at least one of a magnitude and a frequency of stack pressure drop fluctuations.  
     
     
         13 . The fuel cell system of  claim 1  further comprising a temperature sensing system that senses a fluid temperature change across said fuel cell stack and provides a signal to said controller based on said parameter which is said temperature change.  
     
     
         14 . The fuel cell system of  claim 13  wherein said threshold value includes a maximum temperature change.  
     
     
         15 . The fuel cell system of  claim 13  wherein said threshold includes an average temperature change fluctuation defined by at least one of a magnitude and a frequency of stack temperature change fluctuations.  
     
     
         16 . The fuel cell system of  claim 1  wherein said parameter is a resistance of at least one fuel cell.  
     
     
         17 . The fuel cell system of  claim 1  wherein said parameter is stack load and said threshold value is a minimum stack load.  
     
     
         18 . The fuel cell system of  claim 1  wherein said flow control device is a flow regulator.  
     
     
         19 . The fuel cell system of  claim 1  wherein said controller forms a part of said flow control device.  
     
     
         20 . The fuel cell system of  claim 1  wherein said first phase fluid is a reactant.  
     
     
         21 . The fuel cell system of  claim 1  wherein said first phase fluid is a heat transfer fluid.  
     
     
         22 . A method of operating a fuel cell stack, comprising: 
 supplying flow of a first phase fluid through said fuel cell stack;    monitoring at least one parameter of said fuel cell stack; and    pulsing said flow when said parameter crosses a threshold to flush a second phase fluid from said fuel cell stack.    
     
     
         23 . The method of  claim 22  wherein said pulsing is conducted by varying at least one pulse feature selected from pulse duration, interval between pulses and pulse shape.  
     
     
         24 . The method of  claim 22  wherein said parameter comprises at least one selected from the group consisting of: a voltage of one or more individual cells of said fuel cell stack; a stack voltage; a resistance of one or more individual cells of said fuel cell stack; a stack resistance; a pressure drop across said fuel cell stack; a load on said fuel cell stack; a stack voltage fluctuation; a stack pressure fluctuation; a temperature change across said fuel cell stack; and a stack temperature fluctuation.  
     
     
         25 . The method of  claim 24  wherein said threshold comprises at least one selected from the group consisting of: a minimum cell voltage; a minimum stack voltage; minimum cell resistance; a maximum pressure drop; a maximum pressure drop fluctuation; a minimum load; a maximum stack voltage fluctuation; a maximum pressure fluctuation; a maximum temperature change; and a maximum temperature fluctuation.  
     
     
         26 . The method of  claim 22  wherein said monitoring includes comparing said parameter to said threshold and said pulsing is conducted by varying at least one pulse feature selected from pulse duration, interval between pulses and pulse shape, based on said parameter and said threshold.