Fuel cell power plant with real and reactive power modes

Abstract

An illustrative example fuel cell power plant includes a cell stack assembly having a plurality of fuel cells configured to generate electricity based on an electrochemical reaction. The power plant includes a capacitor, a plurality of inverters, and at least one controller that is configured to control the plurality of inverters in a first mode and a second mode. The first mode includes the cell stack assembly associated with at least one of the inverters. A cell stack assembly and the associated inverter provide real power to a load external to the fuel cell power plant in the first mode. The second mode includes at least a second one of the inverters associated with the capacitor. The capacitor and the second one of the inverters selectively provide reactive power to or receive reactive power from a grid external to the fuel cell power plant in the second mode.

We claim: 
     
         1 . A fuel cell power plant, comprising:
 a cell stack assembly including a plurality of fuel cells configured to generate electricity based on an electrochemical reaction;   a capacitor;   a plurality of inverters; and   at least one controller that is configured to control the plurality of inverters in a first mode and a second mode,   the first mode including the cell stack assembly associated with at least one of the inverters, the cell stack assembly and the at least one of the inverters providing real power to a load external to the fuel cell power plant,   the second mode including at least a second one of the inverters associated with the capacitor, the second one of the inverters and the capacitor selectively providing reactive power to or receiving reactive power from a grid external to the fuel cell power plant.   
     
     
         2 . The fuel cell power plant of  claim 1 , wherein the reactive power of the second mode is the only power output from the fuel cell power plant of the second mode that is external to the fuel cell power plant. 
     
     
         3 . The fuel cell power plant of  claim 1 , wherein more than one of the inverters is associated with the capacitor in the second mode. 
     
     
         4 . The fuel cell power plant of  claim 1 , wherein the capacitor is charged by the reactive power received from the grid in the second mode. 
     
     
         5 . The fuel cell power plant of  claim 1 , wherein
 the first mode includes the capacitor associated with at least one of the inverters; and   the first mode includes the capacitor providing supplemental power output from the fuel cell power plant when there is an increase in a load demand on the fuel cell power plant.   
     
     
         6 . The fuel cell power plant of  claim 1 , wherein the real power is a low voltage power less than or equal to 600 kilowatts. 
     
     
         7 . The fuel cell power plant of  claim 1 , comprising
 a DC bus between the cell stack assembly and the plurality of inverters; and   a switching device that is controlled by the controller to selectively couple the cell stack assembly, the capacitor, and selected ones of the plurality of inverters respectively to the DC bus.   
     
     
         8 . The fuel cell power plant of  claim 8 , comprising
 an output configured to be coupled to a load external to the fuel cell power plant;   an AC bus between the plurality of inverters and the output; and   at least one switching device that is controlled by the controller to selectively couple selected ones of the inverters to the output.   
     
     
         9 . The fuel cell power plant of  claim 1 , wherein the capacitor is the only source of power supplied by the fuel cell power plant external to the fuel cell power plant in the second mode. 
     
     
         10 . The fuel cell power plant of  claim 1 , wherein the second mode includes at least a first one of the inverters associated with the cell stack assembly, the first one of the inverters and the cell stack assembly providing power to at least one other component of the fuel cell power plant. 
     
     
         11 . A method of operating a fuel cell power plant including a cell stack assembly, a capacitor, and a plurality of inverters, the method comprising:
 controlling the plurality of inverters in a first mode and a second mode;   using the cell stack assembly and at least one associated one of the inverters for providing real power to a load external to the fuel cell power plant in the first mode;   and   using the capacitor and at least a second one of the inverters for selectively providing reactive power to or receiving reactive power from a grid external to the fuel cell power plant in the second mode.   
     
     
         12 . The method of  claim 11 , wherein the reactive power of the second mode is the only power output from the fuel cell power plant in the second mode that is external to the fuel cell power plant. 
     
     
         13 . The method of  claim 11 , wherein more than one of the inverters is associated with the capacitor in the second mode. 
     
     
         14 . The method of  claim 11 , comprising charging the capacitor using the reactive power received from the grid in the second mode. 
     
     
         15 . The method of  claim 11 , comprising providing supplemental power output from the fuel cell power plant using the capacitor and at least one of the inverters associated with the capacitor in the first mode when there is an increase in a load demand on the fuel cell power plant. 
     
     
         16 . The method of  claim 11 , wherein the real power is a low voltage power less than or equal to 600 kilowatts. 
     
     
         17 . The method of  claim 11 , wherein the capacitor is the only source of power supplied by the fuel cell power plant external to the fuel cell power plant in the second mode. 
     
     
         18 . The method of  claim 11 , comprising using the cell stack assembly and at least one associated one of the inverters for providing power to at least one other component of the fuel cell power plant in the second mode.