Control Analysis of Integrated Fuel Cell Systems with Energy Recuperation Devices.

This work is focused on control-oriented analysis of integrated fuel cell systems that incorporate energy recuperation mechanisms. The high complexity of such fuel cell systems calls for precise control and regulation of multiple inputs. The need for robust and efficient steady state and transient operation imposes the need for intelligent control schemes. The models of two fuel cell systems are developed in this work and used for the design of feedback controllers. It is shown, through simulation, that the proposed controllers enhance the performance and meet the operating constraints. The two plants considered in this dissertation are (i) a catalytic partial oxidation fuel processor system (FPS) coupled with a proton exchange fuel cell and a catalytic burner (CB) and (ii) a hybrid solid oxide fuel cell and gas turbine (SOFC/GT) system. Both systems rely on energy recuperation devices (ERDs), such as a catalytic burner or a gas turbine, for achieving high fuel efficiency. Through model-based open loop analysis the FPS is shown to exhibit fuel cell H2 starvation and reactor overheating while the SOFC/GT system is prone to shutdown during load transitions without proper feedback in place. It is identified that the transient issues can be resolved through reactant ratio control and load filtering for the FPS and the SOFC/GT systems, respectively. Using the insights from the open loop analysis, feedback control schemes are designed to address the transient issues. For the FPS, an observer-based linear controller, that utilizes temperature measurements to control the air and fuel flows into the reformer and maintain proper reactant ratios, is proposed. For the SOFC/GT system, a reference governor control scheme is developed to filter the application of the load in order to avoid GT shutdown. For both systems, the designed control schemes utilize measurements from the ERDs, such as shaft speed or catalytic burner temperature and manage to mitigate the transient operating difficulties. Thus, the ERDs, besides increasing the steady state efficiency of the system by reducing the energy losses, also provide vital measurements for feedback control.PhDNaval Architecture & Marine EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/57700/2/djvas_1.pd