Fuel Cell slow dynamic simulation

Hi people

I'm using the fuel cell model in the SimPowerSystems library of simulink to simulate an stand-alone fuel cell system.I want to see the slow dynamic response of fuel cell to load change that is approved in papers.The problem is that when I change the fuel cell response time in the fuel cell dynamics pane of the Fuel Cell Stack block I see no change in the response time of the fuel cell to load change.Here are the response of fuel cell output power to the load change applied at t=1s.The dynamic response times in the pictures are selected 1sec and 3sec respectively.Why can't I see the dynamic response time effect on the system?

Here is my simulated system that contains Fuel Cell Stack interfaced with a buck converter feeding resistive loads.Buck converter is controlled with two PI voltage an current controllers.