Fuel cell voltage control
First Claim
1. A fuel cell power plant, comprising:
- a plurality of fuel cells serially connected in a stack having a pair of external circuit output terminals;
a voltage limiting auxiliary load, disposed to dissipate heat in an element of said fuel cell power plant so as to raise the temperature of said element;
a switch connected in series with said auxiliary load between said terminals; and
switch control means operable during fuel cell stack operation transitions selected from startup and shutdown for causing said switch to alternatively (a) connect said auxiliary load between said terminals, (b) disconnect said auxiliary load from at least one of said terminals, repetitively during at least one of said transitions, in response to electrical output of said fuel cell stack, and operable during periods of time exclusive of start up and shutdown in response to temperature resulting from heat dissipated by said auxiliary load in said element.
6 Assignments
0 Petitions
Accused Products
Abstract
An auxiliary load (148) for a fuel cell stack (102) is alternatively connected and disconnected from the fuel cell external circuit (177, 178) by a switch (200) in response to a switch control (201), repetitively, during startup and shutdown. The switch may be an insulated gate bipolar transistor (208) which is turned on and off by hunting between an upper limit voltage (207) and a lower limit voltage (208), which may be performed by compare circuits (205, 206), by the controller (202), or by commercially available voltage responsive hysteresis switches. Schedules of duty cycle as a function of cell stack voltage for startup (212) and shutdown (213) control a pulse width modulator (215) which operates the switch. Controls (229, 231) may limit the modulation so that the auxiliary load does not overheat, in response to temperature (221) of the load or a voltage/power model (235). The auxiliary load may comprise a heater in a water accumulator (247), an air intake (257) or an enthalpy recovery device (262).
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Citations
19 Claims
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1. A fuel cell power plant, comprising:
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a plurality of fuel cells serially connected in a stack having a pair of external circuit output terminals;
a voltage limiting auxiliary load, disposed to dissipate heat in an element of said fuel cell power plant so as to raise the temperature of said element;
a switch connected in series with said auxiliary load between said terminals; and
switch control means operable during fuel cell stack operation transitions selected from startup and shutdown for causing said switch to alternatively (a) connect said auxiliary load between said terminals, (b) disconnect said auxiliary load from at least one of said terminals, repetitively during at least one of said transitions, in response to electrical output of said fuel cell stack, and operable during periods of time exclusive of start up and shutdown in response to temperature resulting from heat dissipated by said auxiliary load in said element.
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2. A fuel cell power plant, comprising:
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a plurality of fuel cells serially connected in a stack having a pair of external circuit output terminals;
a voltage limiting auxiliary load;
a switch connected in series with said auxiliary load between said terminals; and
switch control means operable during fuel cell stack operation transitions selected from startup and shutdown for causing said switch to alternatively (a) connect said auxiliary load between said terminals and (b) disconnect said auxiliary load from at least one of said terminals, repetitively during at least one of said transitions. - View Dependent Claims (3, 4, 5, 6, 7, 8, 11, 12, 13, 14)
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9. A power plant according to claim 32 wherein:
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said switch control means causes said switch to connect said auxiliary load between said terminals in response to the voltage across said terminals reaching 0.4 volts per cell; and
said switch control means causes said switch to disconnect said auxiliary from at least one of said terminals in response to the voltage across said terminals reaching 0.0 volts per cell.
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10. A power plant according to claim 32 wherein:
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said switch control means causes said switch to connect said auxiliary load between said terminals in response to the voltage across said terminals reaching 0.2 volts per cell; and
said switch control means causes said switch to disconnect said auxiliary from at least one of said terminals in response to the voltage across said terminals reaching 0.1 volts per cell.
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15. A fuel cell power plant, comprising:
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a plurality of fuel cells serially connected in a stack having a pair of external circuit output terminals;
a voltage limiting auxiliary load, disposed to dissipate heat in an element of said fuel cell power plant so as to raise the temperature of said stack;
a switch connected in series with said auxiliary load between said terminals; and
switch control means operable to control said switch (a) during transitions selected from startup and shut down in response to electrical output of said fuel cell stack and (b) during periods of time exclusive of start up and shut down in response to temperature resulting from heat dissipated by said auxiliary load in said element. - View Dependent Claims (16, 17, 18, 19)
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Specification