Scholarship & Research
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Item Simulation, design and validation of a solid oxide fuel cell powered propulsion system for an unmanned aerial vehicle(Montana State University - Bozeman, College of Engineering, 2009) Lindahl, Peter Allan; Chairperson, Graduate Committee: Steven R. ShawThis thesis presents a physically-based model for design and optimization of a fuel cell powered electric propulsion system for an Unmanned Aerial Vehicle (UAV). Components of the system include a Solid Oxide Fuel Cell (SOFC) providing power, motor controller, Brushless DC (BLDC) motor, and a propeller. Steady-state models for these components are integrated into a simulation program and solved numerically. This allows an operator to select constraints and explore design trade-offs between components, including fuel cell, controller, motor and propeller options. We also presents a graphical procedure using the model that allows rapid assessment and selection of design choices, including fuel cell characteristics and hybridization with multiple sources. To validate this simulation program, a series of experiments conducted on an instrumented propulsion system in a low-speed wind tunnel is provided for comparison. These experimental results are consistent with model predictions.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 In-situ electrical terminal characterization of fuel cell stacks(Montana State University - Bozeman, College of Engineering, 2010) Seger, Eric Matthew; Chairperson, Graduate Committee: Steven R. ShawThis thesis demonstrates in-situ characterization of a 5kW solid oxide fuel cell (SOFC) stack and a 165W proton exchange membrane fuel cell (PEMFC) stack at the electrical terminals, using impedance spectroscopy and time-domain modeling. The SOFC experiments are performed using excitation from the power electronic ripple current and exogenous excitation generated from several different sources including a hybrid system which uses a secondary power source for the generation of the small-signal currents. The PEMFC experiments are performed using exogenous excitation from a boost converter. In contrast to typical off-line analysis using specialized instrumentation, the measurements are made as the stacks deliver power to their respective loads. The power electronic switching waveform is used as a source of excitation. This technique could be implemented on-line for continuous condition assessment of the stack. The results show typical data from the stack, comparison of model predictions and measured data, and whole-stack impedance spectroscopy results.Item Reversible fuel cell performance and degradation(Montana State University - Bozeman, College of Engineering, 2011) Cornachione, Matthew Aaron; Chairperson, Graduate Committee: Steven R. ShawThis thesis presents the development of a test stand to characterize the performance of reversible solid oxide fuel cells. The test stand was used in two different studies to determine the behavior of commercially available solid oxide fuel cells under varying steam percentage input and to compare the degradation incurred during fuel cell operation to that during electrolysis operation. The development of this test stand included construction of a water vapor delivery system using steam entrained in a hydrogen flow and a circuit built from high power op-amps to allow biasing of the fuel cell in both fuel cell and electrolysis mode. The test stand allows the steady state characteristics to be evaluated over a wide voltage range through current/voltage sweeps and the small signal behavior to be examined in-situ through the use of electrochemical impedance spectroscopy. These tests, as well as post-operation field emission scanning electron microscope observation, were used to determine that the cells perform comparably in both modes of operation though the cell resistance tends to be higher in electrolysis mode. It was also found that during extended operation these cells degrade significantly to the point of mechanical failure in electrolysis mode and thus may not be suitable for long term electrolysis operation. The equipment developed here can perform similar tests on newly designed reversible fuel cells to determine whether different materials choices or cell construction provide superior reversible performance and durability.Item High power, high efficiency, low cost DC/DC converters for laser test equipment and residential fuel cell applications(Montana State University - Bozeman, College of Engineering, 2009) Sternberg, Kyle Matthew; Chairperson, Graduate Committee: Hongwei GaoIn this work two low cost, high efficiency, high power DC/DC converters are developed. The first converter is targeted for industrial laser applications. The converter is designed for a 400 volt input voltage and a 0-36V output voltage and 0-40A output with a maximum power output of 1500 watts at a cost less than $0.30 / watt. To achieve a high efficiency and low cost at this power level a zero-voltage switched full bridge converter is used. This technology increases the efficiency of the converter past 90% while reducing the size of the components. The converter was built and tested and achieved a 91.5% efficiency at full load. The total cost was $0.28 / watt. This converter met all the design goals while exceeding the cost goals. The second converter is targeted for residential fuel cell applications. This converter utilizes the technology developed for the industrial converter. This residential converter is designed for an input of 26-42 volts at 190 amps and an output of 400 volts and 12 amps at a power level of 5000 watts while maintaining a $40/kilowatt cost goal. To achieve the low cost and high efficiency design goals the converter uses several technologies in its construction. Like the converter for industrial applications this converter utilizes zero voltage switching full bridge converter. To compensate for the high input current a unique multiphase design was designed for the application. A unique parallel input / series output topology and three interleaved converters split the input current to increase the efficiency of the converter. This unique topology increases the switching frequency on the secondary side which reduces the side of the passive components, reducing cost. The converter was built and tested at a light load to verify its operation versus the theory. An estimated 96% efficiency at full load is possible using this topology. The total cost was $39 / kilowatt.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).Item Non-intrusive fuel cell load interaction monitoring(Montana State University - Bozeman, College of Engineering, 2006) Lackey, John David; Chairperson, Graduate Committee: Steven R. ShawThis thesis presents the development of a non-intrusive method for monitoring fuel cells. The instrumentation demands that only the readily accessible AC output terminals of the fuel cell be monitored, making it easy to install on an existing fuel cell. The monitoring hardware senses the current and voltage output of the fuel cell and converts the measurements into the digital domain. The original algorithm to process the data was the Non-Intrusive Load Monitor (NILM) system which detects specific events, classifies and stores them. The software that is described in this thesis is a data specific compression algorithm that is used to store a continuous stream of measurements so that it can be processed off line. This gives the user the ability to search for critical interactions between the fuel cell and loads in the system after the fact, rather than demanding that load and interaction dynamics be known before the monitor is installed.Item A new DC-DC converter for fuel cell powered residential power generation systems(Montana State University - Bozeman, College of Engineering, 2006) Sharma, Rahul Rajiv; Chairperson, Graduate Committee: Hongwei GaoThis thesis presents a new topology for an isolated DC-DC converter for low voltage to high voltage conversions at high power. The proposed converter is targeted for use in fuel cell powered residential power generation systems, where low voltage to high voltage conversion at high power (>5KW) and isolation between input and output are required. Conventional DC-DC converters like forward, half bridge and full bridge for such applications need to have high turn ratio in their power transformers, to enable the high voltage boosting. This high turns ratio of the transformers results in high leakage inductance which reduces the converter's efficiency and increases the difficulty in control. The proposed converter overcomes this problem by utilizing the leakage inductance for energy conversion instead of considering it as a parasite. This reduces the problems of low efficiency and difficulty of control, caused by the leakage inductance.Item Modeling and transient degradation of proton exchange membrane fuel cells(Montana State University - Bozeman, College of Engineering, 2006) Pasricha, Sandip; Chairperson, Graduate Committee: Steven R. ShawThis thesis presents a model based approach to describe proton exchange membrane (PEM) fuel cell degradation with time. This degradation study involves analysis of voltage and current profiles of PEM membranes under transient load conditions. The data is collected from 80 membranes in an Independence1000 1000W PEM system over the life span of the membrane. The thesis also presents PEM fuel cell models developed and validated on a 500W SR-12 commercial PEM stack. Several static models from the literature are reviewed in terms of physical effects, parameterized for identification, and compared using measured data from the commercial PEM stack. The dynamic model is obtained by extending static current voltage profiles to include temperature dependence, and by dynamically modeling the temperature of the membrane. After inspecting all these models a simplified model is used for analyzing PEM fuel cell degradation and changes in physical phenomena in fuel cell observed over a period of time.