Controlling PEM fuel cell voltage during power transitions and idling
View Patent ↗The controller ( 185 ) of a fuel cell stack ( 151 ) in a vehicle ( 150 ) responds to lower demand to cause a diverter ( 172 ) to direct all air from the cathodes ( 19 ) except as required to generate sufficient power to limit cell voltage to a safe idle voltage threshold, cause storage in an energy storage system ( 201 ) sufficient to limit cell voltage to the idle voltage threshold unless SOC is too high, connects a voltage limiting load ( 220 ) to the stack sized to consume all power not consumed by auxiliary BOP, or, for longer idles, air-starves the stack and powers BOP from storage. In response to increase in a demand signal, the controller causes flow of all air to the cathodes. In response to an off signal ( 223 ) or a start signal ( 193 ) the controller causes a shutdown routine or a startup routine in each of which all generated power is stored to maintain fuel cell voltage below a threshold, or is consumed in the voltage limiting load.
1. A method comprising:
a) operating a fuel cell power plant to provide electric power to a vehicle propulsion system ( 159 );
b) monitoring fuel cell voltage during normal operation of the vehicle propulsion system;
characterized by:
c) in response to fuel cell voltage reaching a predetermined cell voltage threshold, diverting all reactant air except an amount required to generate enough power to cause the fuel cell voltage to not exceed the predetermined cell voltage threshold; and
d) after step c), and until demand of the vehicle propulsion system exceeds a demand threshold, generating enough power to cause the fuel cell voltage to not exceed the predetermined cell voltage threshold while storing electric power output of the fuel cell power plant in an energy storage system ( 201 ) in an amount equal to the difference between the amount of power required to maintain cell voltage below the predetermined cell voltage threshold and the amount of power consumed by auxiliary, balance-of-plant equipment ( 170 , 174 , 183 , 185 ), until the state of charge of the energy storage system reaches a predetermined storage threshold.
2. A method according to claim 1 further characterized by:
during step d), in the event that the state of charge of the energy storage system reaches the predetermined storage threshold, dissipating in a voltage limiting load ( 220 ) an amount of power approximately equal to the difference between the amount of power required to maintain cell voltage below the predetermined cell voltage threshold and the amount of power consumed by auxiliary, balance-of-plant equipment.
3. A method according to claim 2 further characterized by:
if step d) continues for a period of time exceeding a predetermined time threshold, air-starving the fuel cell power plant and operating balance-of-plant using power provided by the energy storage system.
4. A vehicle ( 150 ) comprising:
a fuel cell power plant including:
balance-of-plant ( 170 , 174 , 183 , 185 );
a fuel cell stack ( 151 ) including a plurality of fuel cells ( 12 ), each having a membrane electrode assembly ( 16 ) adjacent to a cathode ( 19 ) with a reactant air flow field, the fuel cell stack having a power output ( 155 , 156 );
an air pump ( 174 ) for providing reactant air to the cathodes;
a diverter valve ( 172 ) connecting the air pump to the reactant air flow fields and configured to selectively divert air from said pump without diverted air passing through said reactant air flow fields;
a voltage limiting load ( 220 ) selectively connectable to the power output of the stack;
said vehicle also comprising:
a vehicle propulsion system ( 159 ) configured to be selectively powered by said stack in response to a demand signal;
an energy storage system ( 201 );
storage control means ( 200 ) for selectively controlling the storage and retrieval of electrical energy to and from the energy storage system;
a controller ( 185 ) for selectively controlling the fuel cell stack, the diverter valve, the storage control means and the voltage limiting load;
characterized by:
the controller, in a run mode, responsive to reduction of power consumed by the vehicle propulsion system during operation, to enter an idle mode in which the controller a) operates the diverter valve so as to divert from the cathodes all air except air required by the fuel cell stack to generate predetermined idle power sufficient to cause voltage of the fuel cells to not exceed the predetermined idle threshold cell voltage, b) causes the fuel cell stack to generate predetermined idle power sufficient to cause voltage of the fuel cells to not exceed a predetermined idle threshold cell voltage, c) causes i) the storage control means to store in the energy storage system the amount of power by which the predetermined idle power exceeds the amount of power consumed by the balance-of-plant, unless the state of charge of the energy storage system exceeds a predetermined state of charge threshold in which case the controller causes ii) the fuel cell stack to generate the predetermined idle power and causes the voltage limiting load to be connected across the power output of the stack, the voltage limiting load dissipating, at the predetermined idle power, approximately the amount of power by which the predetermined idle power exceeds the amount of power consumed by the balance-of-plant.
5. A vehicle ( 150 ) according to claim 4 further characterized in that:
the idle mode continues until demand of the vehicle propulsion system exceeds a demand threshold.
6. A vehicle ( 150 ) according to claim 4 further characterized in that:
if the duration of the idle mode exceeds a predetermined time threshold, the controller ceases causing i) or ii) and instead causes air-starving the fuel cell power plant and operating balance-of-plant using power provided by the energy storage system.
7. A vehicle ( 150 ) according to claim 4 further characterized in that:
the controller ( 185 ) is responsive, in the idle mode, to demand of the vehicle propulsion system ( 159 ) exceeding a predetermined demand threshold to cause the diverter valve ( 220 ) to direct all air to the cathodes ( 19 ).
8. A vehicle ( 150 ) according to claim 7 further characterized in that:
the controller ( 185 ) is responsive, in the idle mode, to demand of the vehicle propulsion system ( 159 ) exceeding a predetermined demand threshold to ensure that the storage of power to control idle voltage ceases and that the voltage limiting load ( 220 ) is disconnected from the stack.
9. A vehicle ( 150 ) according to claim 4 further characterized in that:
the controller ( 185 ) is responsive to an off signal ( 223 ) from the vehicle propulsion system ( 159 ) to initiate a shut down routine ( 268 ) in which the controller causes iii) the storage control means ( 200 ) to store sufficient power in the energy storage system ( 201 ) to cause voltage of the fuel cells ( 12 ) to not exceed a predetermined shutdown threshold voltage unless the state of charge of the energy storage system ( 201 ) exceeds a predetermined state of charge threshold, in which case the controller causes iv) the voltage limiting load ( 220 ) to be connected across the power output ( 155 , 156 ) of the fuel cell stack ( 151 ).
10. A vehicle ( 150 ) according to claim 9 further characterized in that:
the predetermined shutdown threshold voltage is higher than the predetermined idle threshold voltage.
11. A vehicle ( 150 ) according to claim 4 further characterized in that:
the controller ( 185 ) is responsive to a start signal ( 193 ) from the vehicle propulsion system ( 159 ) to initiate a startup routine in which the controller causes v) the storage control system ( 200 ) to store sufficient power in the energy storage system ( 201 ) to cause voltage of the fuel cell ( 12 ) to not exceed a predetermined startup threshold voltage, unless the state of charge of the energy storage system exceeds a predetermined state of charge threshold in which case the controller causes vi) the voltage limiting load ( 220 ) to be connected across the power ( 155 , 156 ) output of the fuel cell stack ( 151 ).
12. A vehicle ( 150 ) according to claim 11 further characterized in that:
the predetermined startup threshold voltage is higher than the predetermined idle threshold voltage.