Fuel cell system including wobbe index detector and method of operating same

A method of operating a fuel cell system comprising power modules configured to receive a fuel from a fuel conduit of the system, the power modules each comprising a fuel cell stack and a fuel control valve (FCV) configured to control fuel flow through a module conduit fluidly connecting the FCV to the fuel cell stack, the method comprising:

• detecting a first Wobbe Index (WI) of the fuel in the fuel conduit;
• detecting a second WI of the fuel in each module conduit;
• and
• controlling at least one of the FCV's to change a flow rate of the fuel to the corresponding stack, based on a comparison of the first WI and the corresponding second WI, to maintain a substantially constant fuel utilization before and after a change in the composition of the fuel.