Start up cascaded fuel cell stack

Abstract

A cascaded fuel cell stack ( 9 a ) includes a plurality of groups ( 10 - 12 ) of fuel cells ( 13 ) connected electrically in series by means of conductive separator plates ( 58, 59 ) and current collecting pressure plates ( 56, 57 ). Each group has an inlet fuel distributing fuel inlet manifold ( 17 a, 19 c, 20 c ), a fuel exit manifold ( 19 a, 20 a ) of each group except the last feeding the inlet manifold of each subsequent group. A microcontroller responds to signals from a plurality of voltage sensing devices ( 48 a - 48 c ) to cause corresponding switches ( 50 a - 50 c ) (a) to connect each group, and all preceding groups in the sequence, to a voltage limiting device (VLD) ( 45 ), or (b) to connect each group to its own (VLD ( 45 a - 45 c ), in response to sensing a predetermined average cell voltage across the corresponding group. When normal operation occurs, the microcontroller connects the main load and disconnects the voltage limiting device ( 53 ) ( 25 ).

1 . A cascaded fuel cell stack operable to provide electrical output, comprising: 
 at least two groups of fuel cells, arranged in a sequence having a first group and a last group, in serial fuel relationship so that fuel flows from each group except said last group into the next successive group in said sequence, and so that each group except said first group receives fuel from the next preceding group in said sequence, said groups of fuel cells connected electrically in series between a pair of current collecting pressure plates, one pressure plate connected to said first group and another pressure plate connected to said last group;    a controller;    a main load;    a switch operable by said controller to connect said main load to said pressure plates so that the electrical output of said stack will drive said load; and    characterized by:    one or more voltage limiting devices, said voltage limiting devices selected from (a) an auxiliary resistive load and (b) an energy storage system;    characterized by:    each of said groups of fuel cells having a fuel exit manifold and having an inlet fuel distributing fuel inlet manifold, the fuel exit manifold of each group except said last group connected to the inlet fuel distributing fuel inlet manifold of the next successive group in said sequence, the fuel distributing fuel inlet manifold of each group except said first group connected to the fuel exit manifold of the next preceding group in said sequence;    a conductive separator plate disposed between adjacent ones of said groups;    a plurality of voltage sensing devices, each connected to either (c) two of said separator plates or (d) one of said separator plates and one of said pressure plates, each providing a signal to said controller in response to the presence of a predetermined average cell voltage across a corresponding one of said groups; and    a plurality of switches, one for each of said groups, each operable by said controller in response to said signal from a corresponding one of said voltage sensing devices for electrically connecting a corresponding one of said groups to one of said voltage limiting devices.    
     
     
         2 . A cascaded fuel cell stack operable to provide electrical output, comprising: 
 at least two groups of fuel cells, arranged in a sequence having a first group and a last group, in serial fuel relationship so that fuel flows from each group except said last group into the next successive group in said sequence, and so that each group except said first group receives fuel from the next preceding group in said sequence, said groups of fuel cells connected electrically in series between a pair of current collecting pressure plates, one pressure plate connected to said first group and another pressure plate connected to said last group;    a controller;    a main load;    characterized by:    each of said groups of fuel cells having a fuel exit manifold and having an inlet fuel distributing fuel inlet manifold, the fuel exit manifold of each group except said last group connected to the inlet fuel distributing fuel inlet manifold of the next successive group in said sequence, the fuel distributing, composite fuel inlet manifold of each group except said first group connected to the fuel exit manifold of the next preceding group in said sequence.    
     
     
         3 . A cascaded fuel cell stack operable to provide electrical output, comprising: 
 at least two groups of fuel cells, arranged in a sequence having a first group and a last group, in serial fuel relationship so that fuel flows from each group except said last group into the next successive group in said sequence, and so that each group except said first group receives fuel from the next preceding group in said sequence, said groups of fuel cells connected electrically in series between a pair of current collecting pressure plates, one pressure plate connected to said first group and another pressure plate connected to said last group;    a controller;    a main load;    a switch operable by said controller to connect said main load to said pressure plates so that the electrical output of said stack will drive said load; and    one or more voltage limiting devices, said voltage limiting devices selected from (a) an auxiliary resistive load and (b) an energy storage system;    characterized by:    a conductive separator plate disposed between adjacent ones of said groups;    a plurality of voltage sensing devices, each connected to either (c) two of said separator plates or (d) one of said separator plates and one of said pressure plates, each providing a signal to said controller in response to the presence of a predetermined average cell voltage across a corresponding one of said groups; and    a plurality of switches, one for each of said groups, each operable by said controller in response to said signal from a corresponding one of said voltage sensing devices for electrically connecting a corresponding one of said groups to one of said voltage limiting devices.    
     
     
         4 . A fuel cell stack according to  claim 3  wherein: 
 there is one voltage limiting device, a first side of which is electrically connected to the one of said pressure plates connected to said first group; and    each of said switches is operable by said corresponding signal to electrically connect a corresponding one of said groups and all of said groups which precede said one group in said sequence to a second side of said one voltage limiting device.    
     
     
         5 . A fuel cell stack according to  claim 3  wherein: 
 there is a separate one of said voltage limiting devices for each of said groups; and    each of said switches is operable by said corresponding signal to electrically connect a corresponding one of said groups across a corresponding one of said voltage limiting devices.