Energy Load Management System

Abstract

A system and method for controlling a fuel cell system. An anode tail gas oxidizer (ATO) receives air and fuel exhaust streams from one or more fuel cell stacks of the fuel cell system. The one or more fuel cell stacks provide current to one or more loads. An ATO temperature signal is used to control at least one of a fuel inlet flow to the one or more fuel cell stacks or the current provided to the one or more loads.

What is claimed is: 
     
         1 . A method for controlling a fuel cell system, wherein the fuel cell system comprises one or more fuel cell stacks, the method comprising:
 receiving from a sensor a temperature signal indicative of a temperature of an anode tail gas oxidizer (ATO), wherein the ATO receives air and fuel exhaust streams from the one or more fuel cell stacks and wherein the one or more fuel cell stacks provide current to one or more loads; and   controlling at least one of a fuel inlet flow to the one or more fuel cell stacks or the current provided to the one or more loads using the ATO temperature signal.   
     
     
         2 . The method of  claim 1 , wherein the step of controlling comprises determining by a controller from the temperature signal whether a measured ATO temperature exceeds an ATO set point temperature by a predetermined value, and varying a magnitude of least one of a fuel inlet flow to the one or more fuel cell stacks or the current provided to the one or more loads in response to the ATO temperature signal. 
     
     
         3 . The method of  claim 1 , wherein the step of controlling comprises:
 determining from the temperature signal whether excess fuel is present in the one or more fuel cell stacks; and   at least one of increasing the current to the one or more loads or decreasing the fuel inlet flow rate to the one or more fuel cell stacks when excess fuel is present in the one or more fuel cell stacks   
     
     
         4 . The method of  claim 1 , wherein the step of controlling comprises controlling the fuel inlet flow to the one or more fuel cell stacks. 
     
     
         5 . The method of  claim 4 , wherein: the step of controlling comprises at least one of varying a fresh fuel inlet stream flow rate to the one or more fuel cell stacks or varying a recycling rate of a fuel cell stack anode exhaust stream into the one or more fuel cell stacks. 
     
     
         6 . The method of  claim 5 , wherein:
 the step of controlling comprises at least one of increasing a fresh fuel inlet stream flow rate to the one or more fuel cell stacks or increasing a recycling rate of a fuel cell stack anode exhaust stream into the one or more fuel cell stacks when a measured ATO temperature exceeds an ATO set point temperature by a predetermined value; and   the step of controlling comprises at least one of decreasing a fresh fuel inlet stream flow rate to the one or more fuel cell stacks or decreasing a recycling rate of a fuel cell stack anode exhaust stream into the one or more fuel cell stacks when a measured ATO temperature is less than the ATO set point temperature by a predetermined value.   
     
     
         7 . The method of  claim 1 , wherein the step of controlling comprises controlling the current provided to the one or more loads. 
     
     
         8 . The method of  claim 7 , wherein the step of controlling comprises increasing the current when a measured ATO temperature exceeds an ATO set point temperature by a predetermined value, and decreasing the current when the measured ATO temperature is less than the ATO set point temperature by a predetermined value 
     
     
         9 . The method of  claim 1 , further comprising:
 receiving a current request from the at least one load;   determining from the current request an estimate of a fuel flow ramp to be applied to the fuel inlet flow to meet the current request;   determining from the temperature signal whether excess fuel is present in the one or more fuel cell stacks; and   decreasing the estimated fuel flow ramp by an amount of the excess fuel when excess fuel is present in the one or more fuel cell stacks.   
     
     
         10 . The method of  claim 1 , wherein the ATO receives all of its incoming air from a fuel cell stack cathode exhaust stream and all of its incoming fuel from a fuel cell stack anode exhaust stream. 
     
     
         11 . A system, comprising:
 a fuel cell system, wherein the fuel cell system comprises one or more fuel cell stacks and a anode tail gas oxidizer (ATO), wherein the ATO receives air and fuel exhaust streams from the one or more fuel cell stacks and wherein the one or more fuel cell stacks provide current to one or more loads;   a temperature sensor configured to obtain a temperature signal indicative of a temperature of the ATO; and   a controller configured to perform operations comprising:
 receiving the temperature signal from the sensor; and 
 controlling at least one of a fuel inlet flow to the one or more fuel cell stacks or the current provided to the one or more loads using the ATO temperature signal. 
   
     
     
         12 . The system of  claim 11 , wherein the operation of controlling comprises determining from the temperature signal whether a measured ATO temperature exceeds an ATO set point temperature by a predetermined value, and varying a magnitude of least one of a fuel inlet flow to the one or more fuel cell stacks or the current provided to the one or more loads in response to the ATO temperature signal. 
     
     
         13 . The system of  claim 11 , wherein the controlling operation comprises:
 determining from the temperature signal whether excess fuel is present in the one or more fuel cell stacks; and   at least one of increasing the current to the one or more loads or decreasing the fuel inlet flow rate to the one or more fuel cell stacks when excess fuel is present in the one or more fuel cell stacks.   
     
     
         14 . The system of  claim 11 , wherein the controller is further configured to perform operations comprising:
 receiving a current request from the at least one load;   determining from the current request an estimate of a fuel flow ramp to be applied to the fuel inlet flow to meet the current request;   determining from the temperature signal whether excess fuel is present in the one or more fuel cell stacks; and   decreasing the estimated fuel flow ramp by an amount of the excess fuel when excess fuel is present in the one or more fuel cell stacks.   
     
     
         15 . The system of  claim 11 , wherein the ATO receives all of its incoming air from a fuel cell stack cathode exhaust stream and all of its incoming fuel from a fuel cell stack anode exhaust stream. 
     
     
         16 . The system of  claim 11 , wherein the operation of controlling comprises controlling the fuel inlet flow to the one or more fuel cell stacks. 
     
     
         17 . The system of  claim 11 , wherein the operation of controlling comprises controlling the current provided to the one or more loads. 
     
     
         18 . The system of  claim 11 , wherein the operation of controlling comprises both controlling the fuel inlet flow to the one or more fuel cell stacks and controlling the current provided to the one or more loads. 
     
     
         19 . A method for controlling a fuel cell system, comprising:
 receiving from a load a request for additional current at the fuel cell system;   determining if additional current is available from the fuel cell system based on a smallest of air flow provided to the fuel cell system, a fuel inlet flow provided to the fuel cell system, and a measure of additional current that may be supplied by the fuel cell system;   providing the additional current to the load from the fuel cell system without varying fuel or air flow to the fuel cell system if the additional current is available.   
     
     
         20 . The method of  claim 19 , wherein if the additional current is not available or if the additional current is less than or equal to the requested additional current, then creating an additional current output from the fuel cell system by at least one of increasing the fuel inlet flow to the fuel cell system, increasing a recycling rate of a fuel cell stack anode exhaust stream into the fuel cell stack or decreasing an air inlet stream flow rate to the fuel cell stack. 
     
     
         21 . A method for connecting a load to a fuel cell system, the method comprising:
 receiving by a controller a signal demand signal from a load, wherein the load demand signal is indicative of the load requesting connection to a fuel cell system power output bus;   delaying the connection of the load to the fuel cell system power output bus;   initiating or increasing a fuel inlet flow rate delivered to the fuel cell system in response to the demand signal; and   connecting the load to the fuel cell system power output bus when the fuel inlet flow rate is equal to or greater than a fuel inlet flow rate required to provide power required by the load.   
     
     
         22 . The method of  claim 21 , wherein the delaying step comprises delaying by a predetermined period or a delay period set by a delay timer, and wherein the delay period is based on one or more characteristics of the load. 
     
     
         23 . The method of  claim 21 , wherein the step of delaying comprises delaying until the fuel cell system determines that the fuel inlet flow rate is equal to or greater than a fuel inlet flow rate required to provide power required by the load and sends a load enable signal to connect the load to the fuel cell system power output bus. 
     
     
         24 . The method of  claim 21 , wherein the load is associated with a load profile comprising a load fuel ramp and wherein initiating or increasing a fuel inlet flow rate delivered to the fuel cell system in response to the demand signal comprises increasing the fuel inlet flow rate at a constant rate according to the load fuel ramp. 
     
     
         25 . A method for controlling a connection between a plurality of loads and an output of a fuel cell system, the method comprising:
 receiving a signal indicative of at least one of voltage of a middle bus of a power output bus and a fuel utilization measure of the fuel cell system; and   signaling a relay to connect or disconnect one or more of the plurality of loads from the fuel cell system power output bus in response to the signal.   
     
     
         26 . The method of  claim 25 , wherein the step of signaling comprises:
 signaling the relay to disconnect the one or more loads from the fuel cell system power output bus when the fuel utilization measure is greater than a first threshold value; and   signaling the relay to connect the one or more loads to the fuel cell system power output bus when the fuel utilization measure is less than a second threshold value.   
     
     
         27 . The method of  claim 26 , wherein the middle bus supplies three phase voltage from outputs of a DC-to-AC inverter, and wherein signaling the relay to connect or disconnect the one or more loads from the fuel cell system power output bus in response to the signal comprises connecting or disconnecting the one or more loads according to a predetermined order. 
     
     
         28 . A method for controlling power supplied to a plurality of loads, the method comprising:
 receiving an output voltage of a bus, wherein the bus is supplied power by a plurality of fuel cell modules having different power outputs and wherein the bus supplies power to the plurality of loads;   receiving state information of the plurality of loads;   sending a same single control signal to the plurality of fuel cell modules in response to the output voltage of the bus and state information of the plurality of loads; and   adjusting the power output of one or more of the plurality of fuel cell modules in response to the control signal.