Publications

JOURNAL PUBLICATIONS

Shipboard Fault Detection through Nonintrusive Load Monitoring: A Case Study. P. Lindahl, D. Green, G. Bredariol, A. Aboulian, J. Donnal, S. Leeb. IEEE Sensors Journal. 2018. ABSTRACT: As crew sizes aboard maritime vessels shrink in efforts to reduce operational costs, ship operators increasingly rely on advanced monitoring systems to ensure proper operation of shipboard equipment. The nonintrusive load monitor (NILM) is an inexpensive, robust, and easy to install system useful for this task. NILMs measure power data at centralized locations in ship electric grids and disaggregate power draws of individual electric loads. This data contains information related to the health of shipboard equipment. We present a NILM-based framework for performing fault detection and isolation (FDI), with a particular emphasis on systems employing closed-loop hysteresis control. Such controllers can mask component faults, eventually leading to damaging system failure. The NILM system uses a neural network (NN) for load disaggregation and calculates operational metrics related to machinery health. We demonstrate the framework’s effectiveness using data collected from two NILMs installed aboard a U.S. Coast Guard (USCG) cutter. The NILMs accurately disaggregate loads, and the diagnostic metrics provide easy distinction of several faults in the gray water disposal system. Early detection of such faults prevents costly wear and avoids catastrophic failures. https://doi.org/10.1109/JSEN.2018.2869115

NILM Dashboard: A Power System Monitor for Electromechanical Equipment Diagnostics. A. Aboulian, D. Green, J. Switzer, T. Kane, G. Bredariol, P. Lindahl, J. Donnal, S. Leeb. IEEE Transactions on Industrial Informatics. 2018. ABSTRACT: Non-intrusive load monitoring (NILM) uses electrical measurements taken at a centralized point in a network to monitor many loads downstream. This paper introduces NILM Dashboard, a machine intelligence and graphical platform that uses NILM data for real-time electromechanical system diagnostics. The operation of individual loads is disaggregated using signal processing and presented as time-based load activity and statistical indicators. The software allows multiple NILM devices to be networked together to provide information about loads residing on different electrical branches at the same time. A graphical user interface provides analysis tools for energy scorekeeping, detecting fault conditions, and determining operating state. The NILM Dashboard is demonstrated on the power system data from two USCG Cutters. https://doi.org/10.1109/TII.2018.2843770

Fuel Cell Stack Emulation for Cell and Hardware-in-the-Loop Testing. P. Lindahl, S. Shaw, S. Leeb. IEEE Transactions on Instrumentation and Measurement. 2018. ABSTRACT: The high costs of fuel cell stacks are often prohibitive for research applications. Instead, researchers tend to either perform tests on individual cells under emulated load conditions, or they use model-based emulated fuel cell stacks to test realistic loads. This paper presents an alternative technique allowing the simultaneous investigation of both cell and hardware. In this technique, an amplifier takes as input the voltage of a reference fuel cell and reproduces the ``scaled up'' voltage that would be provided by a stack of similar cells. The output terminals of this simulated stack can be connected to realistic loads, which are series-connected with the reference cell to maintain a one-to-one correspondence of cell and load currents. This technique allows the simultaneous investigation of stack / load interactions, stack electrochemical performance characteristics, and stack durability under load. The amplifier electronics are independent of the fuel cell thus allowing use with all fuel cell types, e.g., Solid Oxide Fuel Cells (SOFC) or Proton Exchange Membrane Fuel Cells (PEMFC). We demonstrate the emulator using a single planar SOFC and under several real loads. The data collected reveals good steady-state and dynamic accuracy, and the observed electrical interactions highlight the utility of the emulator in cell and hardware-in-the-loop testing. Ultimately, this technique provides fuel cell system researchers and developers a low-cost, easily-implemented tool for rapid assessment of novel fuel cell technologies under real-world loading conditions. https://doi.org/10.1109/TIM.2018.2814070

Noncontact electrical system monitoring on a U.S. Coast Guard cutter. P. Lindahl, G. Bredariol, J. Donnal, S. Leeb IEEE Instrumentation and Measurement Magazine. Vol. 20, No. 4, pp. 11-20, Aug. 2017. ABSTRACT: Modernization in the U.S. Navy and U.S. Coast Guard (USCG) includes an emphasis on automation systems to help replace manual tasks and reduce crew sizes. This places a high reliance on monitoring systems to ensure proper operation of equipment and to maintain safety at sea. Recently developed noncontact current and voltage sensors, [1] combined with nonintrusive load monitoring (NILM) methods [2], provide a nonintrusive, low-cost, and easily installed package for machinery monitoring. This paper presents an application case study using these NILM enabled sensors installed on the main electrical feeders of the USCG Famous Class Cutter SPENCER. The system records the power demand on the ship and disaggregates this demand by identifying transients corresponding to loads changing states, e.g., a pump turning on. Results of this study showcase these novel sensors' ability to monitor both generation and load side equipment while at sea or in port and provide information useful for tracking operation schedules, energy usage, and maintenance needs. https://doi.org/10.1109/MIM.2017.8006388

Untangling Non-Contact Power Monitoring Puzzles. J. Donnal, P. Lindahl, D. Lawrence, R. Zachar, S. Leeb IEEE Sensors Journal. Vol. 17, No. 11, pp. 3542-3550, June 2017. ABSTRACT: Electromagnetic field sensors provide an electronic “stethoscope” that can determine the current and power flowing in the wire without ohmic contact and without the need to physically separate conductors. Isolation is inherent, and non-contact monitors can be installed without special safety precautions. However, the process of reconstructing the detailed conductor currents is an inverse problem subject to subtle and severe complications in real environments. Interference from nearby conductors, incorrect or unconventional wiring, ground leakage, and three-wire connections complicate the interpretation of electric and magnetic fields to infer line currents. Over a year of field monitoring has been conducted to demonstrate signal processing and physical approaches for untangling these problems to produce accurate and reliable multiphase power measurements with non-contact sensors. http://dx.doi.org/https://doi.org/10.1109/JSEN.2017.2696485

A Transmitter-Receiver System for Long-Range Capacitive Sensing Application. P. Lindahl, A. Avestruz, W. Thompson, E. George, B. Sennett, S. Leeb. IEEE Transactions on Instrumentation and Measurement. Vol. 65, No. 10, pp. 2412-2423, Oct. 2016. ABSTRACT: Human occupancy detection and localization are important in a variety of smart building applications including building security, assisted living monitors, and energy-efficient heating ventilation and air cooling and lighting. Current implementation of such systems is limited by motion-sensor technologies, e.g., passive infrared (PIR) and ultrasonic sensors, which substitute as occupancy detectors but ultimately suffer from an inability to detect stationary objects. Capacitive sensing can detect stationary objects, but the technology has almost exclusively been developed for short-range human detection and localization, e.g., touch-screen human interfacing of smart devices. This paper presents a transmitter-receiver platform for research and development of capacitive sensing for long-range human occupancy detection and localization. During testing, the system revealed a detection range of 3.5 m, a typical room dimension in homes. Further, tests of a multitransmitter single-receiver system in a 3.2 m x 3.2 m space showed the system's potential for occupant localization. Ultimately, this system represents an alternative to PIR and ultrasonic motion sensors, and has the potential to increase smart building system implementation. http://dx.doi.org/10.1109/TIM.2016.2575338

Utilizing Spin-Down Transients for Vibration-Based Diagnostics of Resiliently Mounted Machines. R. Zachar, P. Lindahl, J. Donnal, W. Cotta, C. Schantz, S. Leeb. IEEE Transactions on Instrumentation and Measurement. Vol. 65, No. 7, pp. 1641-1650, July 2016. ABSTRACT: This paper presents a vibration measurement and analysis technique for use during a machine’s spin-down procedure. During spin-down, the machine’s operation covers a continuous wide frequency band, from operating speed to standstill, which allows the estimation of the machine’s vibration transfer function (VTF). This transfer function is rich in information for detecting and differentiating not only machinery pathologies but also problems with vibrational mounts. Utilizing a back-electromotive force sensor to infer rotor speed and a single-axis accelerometer for vibration measurements, this technique allows minimally intrusive estimation of a machine’s VTF. Data collected in laboratory and field tests aboard U.S. Navy ships are presented to demonstrate the usefulness of this monitoring technique. http://dx.doi.org/10.1109/TIM.2016.2540944

Multiconverter System Design for Fuel Cell Buffering and Diagnostics Under UAV Load Profiles. J. Cooley, P. Lindahl, C. Zimmerman, M. Cornachione, G. Jordan, S. Shaw, S. Leeb. IEEE Transactions on Power Electronics. Vol. 29, No. 6, pp. 3232-3244, June 2014. ABSTRACT: This paper presents a multisource, multiconverter power system for electrically propelled unmanned aerial vehicles (UAVs) with a focus on promoting fuel cell health. Linearized multiconverter system analysis and the two extra element theorem (2EET) inform a system design for fuel cell current buffering and integral diagnostics. Integral diagnostics is in situ impedance spectroscopy achieved by controlling the power system to superpose a frequency-swept excitation current at the fuel cell terminals. An experimental system demonstrates hybridization of a solid-oxide fuel cell (SOFC) with a lead-acid battery having suitable current buffering and integral diagnostics performance under UAV load profiles. Experimental behavior is demonstrated with an electrically emulated SOFC stack or "reference simulator." Impedance spectroscopy data measured during run-time clearly indicate both degradation and recovery phenomena in the SOFC. http://dx.doi.org/10.1109/TPEL.2013.2274600

A Time-Domain Least Squares Approach to Electrochemical Impedance Spectroscopy. P. Lindahl, M. Cornachione, S. Shaw. IEEE Transactions on Instrumentation and Measurement. Vol. 61, No. 12, pp. 3303-3311, Dec. 2012.ABSTRACT: This paper presents a time-domain method for electrochemical impedance spectroscopy (EIS) analysis using ordinary least squares (OLS). In this approach, an electrochemical device, e.g., fuel cell or battery, is perturbed galvanostatically by a small-signal sinusoid that is logarithmically swept in frequency. Using four-terminal sensing, voltage and current measurements are made over the course of the sweep and fit to swept sinusoid models using OLS. The interrelated amplitude, phase, and instantaneous frequency of the resulting waveforms are analyzed to reveal the device impedance as a function of frequency. The accuracy of the EIS technique was tested on a known resistive-capacitive circuit, and its performance was demonstrated using a single InDEC solid oxide fuel cell. Data from these tests are included and show good accuracy and high precision over the broad range of frequencies tested (100 mHz to 5 kHz). http://dx.doi.org/10.1109/TIM.2012.2210457

Simulation, Design and Validation of a UAV SOFC Propulsion System. P. Lindahl, E. Moog, S. Shaw. IEEE Transactions on Aerospace and Electronic Systems. Vol. 48, No. 3, pp. 2582-2593. July 2012.ABSTRACT: A physically-based model for design and optimization of a fuel cell powered electric propulsion system for an unmanned aerial vehicle (UAV) is presented. 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 present a graphical procedure using this model that allows rapid assessment and selection of design choices, including fuel cell characteristics and hybridization with multiple sources. A series of experiments conducted on an instrumented propulsion system in a low-speed wind tunnel were performed for comparison of individual component and full propulsion system performance with simulation model predictions. Data from these experiments are provided and are consistent with model predictions. http://dx.doi.org/10.1109/TAES.2012.6237610

New Materials for Optical Rectification and Electro-optic Sampling of Ultra-short Pulses in the THz Regime. L. Hayden, A. Sinyukov, M. Leahy, P. Lindahl, J. French, W. Herman, R. Twieg, M. He. Journal of Polymer Science Part B: Polymer Physics. Vol. 41, No. 21, pp. 2492-2500. Nov. 2003.ABSTRACT: The synthesis and nonlinear optical characterization of new electrooptic (EO) materials useful for terahertz (THz) applications is presented. Semiempirical calculations were used to guide the development of a series of chromophores on the basis of 2-dicyanomethylen-3-cyano-4,5,5-trimethyl-2,5-dihydrofuran acceptors acting as guests in polymer films used in the generation of THz radiation via optical rectification. Amorphous films, 65–250 μm thick, with EO coefficients as high as 52 pm/V at 785 nm were used to generate sub-picosecond pulses with bandwidths up to 3 THz. http://dx.doi.org/10.1002/polb.10650

CONFERENCE PUBLICATIONS

Controlling the Input Impedance of Constant Power Loads. M. Gutierrez, P. Lindahl, A. Banerjee, S. Leeb. 2018 IEEE Applied Power Electronics Conference and Exposition (APEC). March 4–8, 2018ABSTRACT: Power electronic circuits often regulate load power and present a constant power load (CPL) to the utility or other electrical source. Because CPLs exhibit a negative incremental input impedance, they pose stability concerns in both DC and AC systems. This paper presents a power converter for a constant power LED lighting load that mitigates these stability concerns by presenting a controllable input impedance to the electrical source. The use of an energy buffer allows the converter to control input power to resemble a resistive load over short times, while still delivering constant output power. Experimental results demonstrate that the converter exhibits a resistive input impedance at frequencies over 0.5 Hz while maintaining constant power to the LED load.  https://doi.org/10.1109/APEC.2018.8341600

Technical Communication Instruction for Graduate Students: The Communication Lab vs. A Course. A. Hanson, P. Lindahl, S. Strasser, A. Takemura, D. Englund, J. Goldstein. 2017 ASEE Annual Conference & Exposition. June 25-28, 2017ABSTRACT: Communication skills are critical to engineers' success in both academia and industry. Nevertheless, a variety of factors keep engineering students from developing those skills while in school, leading to a skills gap between recent graduates' actual preparation and their expected performance. This gap can be especially pronounced with graduate students, yet relatively little research and innovation has targeted this key population. Here we present two initiatives to improve the communication skills of graduate students: a department-level "Communication Lab" using peer tutors, and a for-credit communication course. Each approach is analyzed for pedagogical advantages, resource intensiveness, and general utility to the department. We conclude that the Communication Lab model is an overall effective resource for reaching a large number of students in a way that is cost-effective per-student, pedagogically advantageous, and an efficient use of student time. With appropriate modifications, it may even supply some of the advantages that the communication course offered, namely explicit communication frameworks and peer feedback.https://www.asee.org/public/conferences/78/papers/18458/view

“Stethoscopes” for nonintrusive monitoring. J. Donnal, C. Schantz, J. Moon, P. Lindahl, S. B. Leeb. 2017 IEEE Sensors Applications Symposium (SAS). March 13–15, 2017ABSTRACT: This paper provides a survey of example sensors that can be implemented with nonintrusive electromagnetic measurements. Stray electric and magnetic fields exist around many important components in commercial and industrial processes. For example, power cables operate surrounded by magnetic and electric fields. Flow meters operate with cyclically-varying magnetic fields. And stray electromagnetic fields can serve as an energy source for powering sensors wirelessly. These stray fields provide remarkable opportunities for nonintrusive sensing of industrial processes. Sensed information can be used to establish monitoring in new or retrofit systems, or can be used as a backup or redundant source to verify the operation of an installed sensor network. Three different example sensors are presented in this paper for power monitoring, fluid flow tracking, and electromechanical vibration monitoring. All three sensors make use of a common set of circuits for electric and magnetic field sensing. They illustrate approaches that could be applied for many other sensing applications.  https://doi.org/10.1109/SAS.2017.7894030

Nonintrusive monitoring for shipboard fault detection. J. Nation, A. Aboulian, D. Green, P. Lindahl, J. Donnal, S. B. Leeb, G. Bredariol, K. Stevens. 2017 IEEE Sensors Applications Symposium (SAS). March 13–15, 2017ABSTRACT: This paper presents a case study applying nonintrusive load monitoring (NILM) for fault detection and isolation (FDI) of automated shipboard systems. A NILM system installed on an engine room subpanel of U.S. Coast Guard (USCG) Cutter SPENCER collected aggregated power consumption data for ten automated systems. A correlation-based transient identifier is used to disaggregate this data, identifying specific automated load events, including on/off events of the gray water disposal pump. A two-parameter model is calculated from these events and used for fault detection. Data collected during two operational periods of the SPENCER demonstrate the effectiveness of this model in identifying a pump sensor fault previously undetected by the crew. Early identification of such malfunctions prevents costly wear on the gray water disposal system pumps and avoids eventual catastrophic failure.  https://doi.org/10.1109/SAS.2017.7894029

NILM: A Smarter Tactical Decision Aid. LT. G. Bredariol, LT. K. Stevens, J. Nation, A. Aboulian, P. Lindahl, S. Leeb. ASNE Day 2017 Technology, Systems and Ships. February 14–16, 2017.ABSTRACT: This paper presents results from a recent installation of Nonintrusive Load Monitoring (NILM) systems aboard two operational US Coast Guard Vessels. These NILM systems analyze ship energy consumption from a single, centralized measurement point in the electric distribution system and leverage current and voltage measurements taken upstream of loads to extract operational information of individual equipment through automated signal processing and transient identification techniques. In contrast to a distributed load sensor network, the NILM allows the low-cost and robust monitoring of the shipboard electrical system and loads. The NILM systems installed feature novel noncontact current and voltage sensors, which allow easy installation on live-feeder cables with no service disruptions while keeping the installing technicians on the “safe-side” of the feeder cable insulation. Data collected by these NILMs while the ships operated at sea were used to develop new techniques and applications in energy scorekeeping, fault detection, and tactical decision-making. Specifically, this paper discusses NILM use in monitoring and analyzing loading demands of the ship’s service diesel generators, updating theoretical EPLA Load factors using the disaggregated load information, and condition-monitoring of the waste-water system via statistical analysis of associated pump operation. This later application serves as a case study showing the merits of NILM in detecting machinery faults that would otherwise go undetected and preventing complete failure of expensive and mission critical components. As a final application, NILM system data is shown to aid in tactical decision-making when the parsed data is correlated to the equipment and operational status of the vessel. Throughout the paper, representative samples of identified load power transients are presented in detail to illustrate NILM techniques and explain the merits of the NILM operation.http://www.navalengineers.org/Symposia/Past-Symposia/Technology-Systems-Ships-TSS-2017-formerly-ASNE-Day/Program/Bredariol

Noncontact Sensors and Nonintrusive Load Monitoring (NILM) Aboard the USCGC SPENCER. P. Lindahl, LT G. Bredariol, J. Donnal, S. B. Leeb. IEEE Autotestcon 2016. September 12–15, 2016.ABSTRACT: Modernization in the U.S. Navy and U.S. Coast Guard includes an emphasis on automation systems to help replace manual tasks and reduce crew sizes. This places a high reliance on monitoring systems to ensure proper operation of equipment and maintain safety at sea. Nonintrusive Load Monitors (NILM) provide low-cost, rugged, and easily installed options for electrical system monitoring. This paper describes a real-world case study of newly developed noncontact NILM sensors installed aboard the USCGC SPENCER, a Famous class (270 ft) cutter. These sensors require no ohmic contacts for voltage measurements and can measure individual currents inside a multi-phase cable bundle. Aboard the SPENCER, these sensors were used to investigate automated testing applications including power system metric reporting, watchstander log generation, and machinery condition monitoring.  https://doi.org/10.1109/AUTEST.2016.7589633

A Nonintrusive Magnetically Self-powered Vibration Sensor for Automated Condition Monitoring of Electromechanical Machines. J. Moon, P. Lindahl, J. Donnal, R. Zachar, W. Cotta, C. Schantz, S. Leeb. IEEE Autotestcon 2016. September 12–15, 2016.ABSTRACT: This paper presents a nonintrusive and electromagnetically self-powered embedded system with vibration sensor for condition monitoring of electromechanical machinery. This system can be installed inside the terminal block of a motor or generator and supports wireless communication for transferring data to a mobile device or computer for subsequent performance analysis. As an initial application, the sensor package is configured for automated condition monitoring of resiliently mounted machines. Upon detecting a spin-down event, e.g. a motor turn-off, the system collects and transmits vibration and residual back-emf data as the rotor decreases in rotational speed. This data is then processed to generate an empirical vibrational transfer function (eVTF) rich in condition information for detecting and differentiating machinery and vibrational mount pathologies. The utility of this system is demonstrated via lab-based tests of a resiliently mounted 1.1 kW three-phase induction motor, with results showcasing the usefulness of the embedded system for condition monitoring.  https://doi.org/10.1109/AUTEST.2016.7589635

Automatic Watchstander Through NILM Monitoring. LT G. Bredariol (USCG), J. Donnal, P. Lindahl, S. B. Leeb. ASNE Day 2016. March 2–3, 2016.ABSTRACT: Widespread modernization in the Navy, Coast Guard, and commercial maritime industries have placed a large emphasis on electronic control and monitoring of systems. Crew sizes continue to decrease as there is a shift to optimally and minimally manned crews that complete more complex and varied mission sets. Crews rely on sensors and automatic operation to perform a host of duties once completed manually. This places a large amount of reliance on monitoring systems to ensure proper operation of equipment and maintain safety at sea. Modern monitoring systems generally rely on individual sensors at a machinery level. Multiple equipment level sensors are appealing as they can easily monitor each piece of machinery, however these systems require a large infras- tructure of sensors, wires, and intermediate panels. This makes them heavy, expensive, and maintenance intensive when at sea conditions including vibrations, water intrusion, temperature gradients, and other environmental factors are introduced. Because they rely on scores of sensors, communications losses and sensor failures can become common place. With fewer technicians available due to optimum manning there may not be enough man hours available to fix these issues, leaving crews to operate without monitoring equipment.  [Read more at link below...] http://www.navalengineers.org/Symposia/Past-Symposia/ASNE-Day-2016/Program/ASNE-Day-2016-Bredariol

Solid Oxide Fuel Cell Degradation, Recovery, and Control Via the Electrical Terminals. P. Lindahl, M. Cornachione, J. Wold, X. Hu, S. R. Shaw. ASME 2014 12th International Conference on Fuel Cell Science, Engineering and Technology. Boston, MA. June 30–July 2, 2014.ABSTRACT: This paper presents results from an investigation concerning load-induced degradation, recovery, and control of solid oxide fuel cells (SOFCs). In this study, commercially available SOFCs were subject to extended over-current conditions, followed by periods of open-circuit operation. During times of current loading, degradation was observed in the cells’ electrical performance through polarization and electrochemical impedance spectroscopy (EIS) measurements. These measurements showed an increase in the polarization curve’s ohmic region slope, i.e. large-signal resistance, as well as an increase in the cell’s small-signal low-frequency impedance. The degradation was temporary however, as the electrical performance recovered during times of open-circuit operation. These results, attributed to electrochemically-induced oxidation and reduction of nickel in the anode, suggest the degradation phenomenon is controllable via the electrical terminals. As such, an additional test was performed on an SOFC powering a pulse-width modulated load, with the load’s duty-cycle negatively proportional to the cell’s large-signal resistance. Polarization and EIS measurements taken during this test showed that despite the controlled load, degradation occurred throughout the test. However, post-test scanning electron microscope images revealed cracks in the cell’s cathode along the boundary between the active and bulk layers. This type of cracking was not observed in the original degradation and recovery tests, suggesting that the degradation observed in the controlled load test was irreversible and caused by a separate phenomenon. http://dx.doi.org/10.1115/FuelCell2014-6650

A Reference Based Fuel Cell Stack Simulator. P. Lindahl, S. R. Shaw. ASME 2010 8th International Conference on Fuel Cell Science, Engineering and Technology. June, 2010. ABSTRACT: This paper provides 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. The simulation allows an operator to select constraints and explore design trade-offs between components, including fuel cell, controller, motor and propeller options. We also present a graphical procedure using this model that allows rapid assessment and selection of design choices, including fuel cell characteristics and hybridization with multiple sources. A series of tests conducted on an instrumented propulsion system in a low-speed wind tunnel reveal good correlation to the simulated results and validate the simulation model and design techniques. http://dx.doi.org/10.1115/FuelCell2010-33315

Simulation, Design and Validation of a UAV SOFC Propulsion System. P. Lindahl, E. Moog, S. R. Shaw. IEEE 2009 Aerospace Conference. Big Sky, MT. March, 2009.ABSTRACT: This paper provides 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. The simulation allows an operator to select constraints and explore design trade-offs between components, including fuel cell, controller, motor and propeller options. We also present a graphical procedure using this model that allows rapid assessment and selection of design choices, including fuel cell characteristics and hybridization with multiple sources. A series of tests conducted on an instrumented propulsion system in a low-speed wind tunnel reveal good correlation to the simulated results and validate the simulation model and design techniques. http://dx.doi.org/10.1109/AERO.2009.4839597

PROJECT REPORTS

Propulsion and Power Rapid Response R&D Support. Deliver Order 0002: Power-Dense, Solid Oxide Fuel Cell Systems: High-Performance, High-Power-Density Solid Oxide Fuel Cells - Materials and Load Control. S. Sofie, S. Shaw, P. Lindahl, L. Spangler. Air Force Research Laboratory Propulsion Directorate. April, 2010 ABSTRACT: High-Performance, High-Power-Density Solid Oxide Fuel Cells: Materials - Solid oxide fuel cell electrodes based on catalyst coatings offer substantial potential for creating more effective anode and cathode structures. Infiltrated anodes based on nickel metal can yield finer catalyst phase distribution at volumetric concentrations well below percolation for traditional cermets. The coarsening of nickel after high temperature thermal treatment poses substantial degradation to the deposited structure; therefore, methods of anchoring the nickel metal to the YSZ scaffold have been evaluated to stabilize fine scale electro-catalyst particles. Aluminum titanate was introduced into the porous YSZ anode scaffold to facilitate a step-wise chemical reaction to anchor the nickel metal catalyst. SEM observation of thermally treated nickel infiltrated scaffolds indicates excellent preservation of the nickel network at 800 °C for 100 hours. Electrochemical tests show not only decreased degradation rates, but also increased initial performance levels due to the additive. High Performance, High-Power-Density Solid Oxide Fuel Cells: Load Control - With currently foreseeable technology, a fuel cell stack capable of supplying the dynamic power requirements for turns, climb, and sprint maneuvers is so heavy as to negate the advantage of using a fuel cell in level flight. This essentially requires the hybridization of the fuel cell using a zero-average power source such as a battery or capacitor. In this report, we discuss the development of an extremely simple hybrid controller that combines the current/voltage characteristics of a battery and fuel cell. This controller could be readily adapted to current fuel cell powered vehicles. http://oai.dtic.mil/oai/oai?verb=getRecord&metadataPrefix=html&identifier=ADA526583

Propulsion and Power Rapid Response R&D Support Delivery Order 0041: Power Dense Solid Oxide Fuel Cell Systems: High Performance, High Power Density Solid Oxide Fuel Cells - Materials and Load Control. S. Sofie, S. Shaw, P. Lindahl, L. Spangler. Air Force Research Laboratory Propulsion Directorate. Dec., 2008 ABSTRACT: High Performance, High Power Density Solid Oxide Fuel Cells: Materials: The current geometry and materials set of the state-of-the-art anode supported cell (ASC) yields several deficiencies that limit the performance and robustness of the cell/stack under demanding aero based operational requirements. These deficiencies are embodied in poor gas transport through mechanically strong anodes, the limited use of cerium oxide in the anode due to unfavorable thermal expansion, and the poor thermal stability of ultra fine nickel catalyst under higher temperature operation for maximum output. These deficiencies are being addressed with the development of engineered porous substrates, additives to tailor thermal expansion in ceria based anode systems, and methods for complete infiltration of anode catalysts. Novel ceramic anodes were synthesized and fabricated at Montana State University and characterized through electron microscopy, dilatometry, thermal gravimetry, x-ray diffraction, and electrochemical testing. Modified processing techniques have generated a means for preparing controlled pore morphologies over large areas by freeze casting suitable for anode supported cell fabrication. The use of aluminum titanate additives has demonstrated a 30% decrease in thermal expansion in nickel/ceria anodes and the addition of aluminum titanate to nickel/zirconia porous scaffolds has shown to limit nickel coarsening from high temperature exposure. This report provides a physically-based model for design and optimization of a fuel cell powered electric propulsion system for an unmanned aerial vehicle. Components of the system include a solid oxide fuel cell providing power, motor controller, brushless DC motor, and a propeller. The simulation allows an operator to select constraints and explore design trade-offs between components, including fuel cell, controller, motor, and propeller options. http://oai.dtic.mil/oai/oai?verb=getRecord&metadataPrefix=html&identifier=ADA499591

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