Theses and Dissertations at Montana State University (MSU)
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Item Electric terminal performance and characterization of solid oxide fuel cells and systems(Montana State University - Bozeman, College of Engineering, 2013) Lindahl, Peter Allan; Chairperson, Graduate Committee: Steven R. ShawSolid Oxide Fuel Cells (SOFCs) are electrochemical devices which can effect efficient, clean, and quiet conversion of chemical to electrical energy. In contrast to conventional electricity generation systems which feature multiple discrete energy conversion processes, SOFCs are direct energy conversion devices. That is, they feature a fully integrated chemical to electrical energy conversion process where the electric load demanded of the cell intrinsically drives the electrochemical reactions and associated processes internal to the cell. As a result, the cell's electric terminals provide a path for interaction between load side electric demand and the conversion side processes. The implication of this is twofold. First, the magnitude and dynamic characteristics of the electric load demanded of the cell can directly impact the long-term efficacy of the cell's chemical to electrical energy conversion. Second, the electric terminal response to dynamic loads can be exploited for monitoring the cell's conversion side processes and used in diagnostic analysis and degradation-mitigating control schemes. This dissertation presents a multi-tier investigation into this electric terminal based performance characterization of SOFCs through the development of novel test systems, analysis techniques and control schemes. First, a reference-based simulation system is introduced. This system scales up the electric terminal performance of a prototype SOFC system, e.g. a single fuel cell, to that of a full power-level stack. This allows realistic stack/load interaction studies while maintaining explicit ability for post-test analysis of the prototype system. Next, a time-domain least squares fitting method for electrochemical impedance spectroscopy (EIS) is developed for reduced-time monitoring of the electrochemical and physicochemical mechanics of the fuel cell through its electric terminals. The utility of the reference-based simulator and the EIS technique are demonstrated through their combined use in the performance testing of a hybrid-source power management (HSPM) system designed to allow in situ EIS monitoring of a stack under dynamic loading conditions. The results from the latter study suggest that an HSPM controller allows an opportunity for in-situ electric terminal monitoring and control-based mitigation of SOFC degradation. As such, an exploration of control-based SOFC degradation mitigation is presented and ideas for further work are suggested.Item Extended cluster weighted modeling methods for transient recognition control(Montana State University - Bozeman, College of Engineering, 2006) Zhu, Tao; Chairperson, Graduate Committee: Steven R. ShawThis dissertation considers cluster weighted modeling (CWM), a novel non-linear modeling technique for the electric load transient recognition problem. The original version of CWM is extended with a new training algorithm and a real-time CWM prediction method. In the training process, a new training algorithm is derived that is a mixture of expectation maximization (EM) - least mean squares (LMS). The algorithm addresses the singular matrix inversion problem in EM. A recursive EM-LMS algorithm is developed that allows the CWM to adapt to time varying systems. In the prediction process, a sequential version of CWM prediction based on the novel idea of tail prediction is proposed to improve the real-time performance of load transient recognition. This idea also gives rise to a real-time transient overlapping resolution method that is critical for robust online operation. Other aspects of real-time transient processing methods, such as transient scaling, detection under conditions of transient overlap, and off-training set transient indication are also developed and combined into the sequential CWM model. The sequential CWM technique is applied to an electric load transient recognition model for hybrid fuel cell system control. The model provides real-time information about the steady-state behavior of incoming load transients to control and allocate power between the fast sources and the fuel cell. An implementation of this system in a Xilinx FPGA is discussed.Item Modeling and control of hybrid wind/photovoltaic/fuel cell distributed generation systems(Montana State University - Bozeman, College of Engineering, 2006) Wang, Caisheng; Chairperson, Graduate Committee: M. Hashem NehrirDue to ever increasing energy consumption, rising public awareness of environmental protection, and steady progress in power deregulation, alternative (i.e., renewable and fuel cell based) distributed generation (DG) systems have attracted increased interest. Wind and photovoltaic (PV) power generation are two of the most promising renewable energy technologies. Fuel cell (FC) systems also show great potential in DG applications of the future due to their fast technology development and many merits they have, such as high efficiency, zero or low emission (of pollutant gases) and flexible modular structure. The modeling and control of a hybrid wind/PV/FC DG system is addressed in this dissertation. Different energy sources in the system are integrated through an AC bus. Dynamic models for the main system components, namely, wind energy conversion system (WECS), PV energy conversion system (PVECS), fuel cell, electrolyzer, power electronic interfacing circuits, battery, hydrogen storage tank, gas compressor and gas pressure regulator, are developed. Two types of fuel cells have been modeled in this dissertation: proton exchange membrane fuel cell (PEMFC) and solid oxide fuel cell (SOFC).