I am generally interested in extracting information from physical systems using
novel measurements and analysis procedures. This theme is closely supported
by several classical areas in electrical engineering, including system identification,
control, modeling, optimization, instrumentation and circuit design.
| Current sensing and non-intrusive
fuel cell monitoring |
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Demonstration of far-field current sensing using a regularly spaced and
oriented array of Hall-effect sensors. Relatively simple analog electronics
can be used to extract current measurements from a wire bundle using an array
of Hall effect sensors, even if the sensors do not encircle the conductors.
The best coefficients are derived from the singular value decomposition of the
current to sensor gain matrix. |
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A non-intrusive load monitor (NILM) adapted to measure the interactions
between a molten carbonate fuel cell system and attached load. |
| Micro Mirror Control |
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Two MEMS mirrors mounted and wire-bonded to a TO-5 package. These mirrors
can provide dynamic focus and aberration control in miniature optical instruments,
potentially including confocal microscopy of tissues by catheterized insertion. |
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MEMS mirrors in a optical profilometer stand, showing a portion of the sensing
and control circuitry under development in the laboratory. |
| Tubular Solid Oxide Test Facility |
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Construction is wrapping up on a new off-site test facility to house a Siemens
tubular solid oxide stack. This photograph shows the unit in the process of
installation. |
| High Temperature Energy Conversion
Fuel cell Controls and Instrumentation |
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A multi-source fuel cell control board, using phase-interleaved off-the-
shelf power electronic modules with a modified current sharing control scheme.
Such controls may provide an extra degree of freedom that can be exploited to
increase efficiency, prolong stack life, and introduce stack diagnostics under
load. |
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A FPGA board used to implement transient recognition control for fuel cell
systems. Transient recognition control applies cluster weighted modeling to
estimate long-term behavior of electrical transients in real-time. The real-time
modification, or sequential cluster weighted modeling, involves replacing the "to
be received" portion of the input pattern with the conditional expectation.
The resulting computations are relatively computationally intensive for use
in closed-loop, but feasible. |
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Analog electronics used to create a two-loop control system that allows
fuel cell materials engineers to electronically scale a cell, repeat unit, or
even the middle cells in a short stack to simulate the electrical terminals
of stack with an arbitrary number of cells and area. This instrumentation allows
system designers to study interactions between prototype cells and the full-scale
loads they are proposed to power. This avoids the present necessity of doing
cell development in series with system design. We believe this approach offers
greater insight into electrical terminal interactions than either finite element
cell / stack models or analytical models. |
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Machining a mirror-surface for a fuel cell test platen on an Inconel 600
bar with the Compass 250/1000 lathe and carbide tooling. A recess will be bored
in a subsequent operation to accommodate a tube, which is held in place with
an autogenous TIG weld. |
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Inconel 600 platens at temperature, with SOFC cell under test. |
| PEM Degradation and Control Projects |
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PEM degradation apparatus, showing custom 200+ channel 14 bit data acquisition
system. This apparatus was used for continuous around-the clock monitoring of
160 PEM membranes, under transient loading conditions, at a rate of 2kHz from
installation until failure. |
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A hyperbaric chamber used to explore pressure as a control variable for
a pressurized PEM stack. The bags of PET pellets are being used to move the
dominant pole by reducing the system volume. |
| Degradation oriented control and
diagnostics |
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Anode supported SOFC
Fresh cell ready for testing. |
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Cell on platen
An SOFC about to be sandwiched between inconel 600 platens, with nickel
foam. |
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Inconel 600 platens at temperature, with SOFC cell under test. |
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Failed SOFC on test platen
After observing degradation at the electrical terminals under test, this cell
shows an annular pattern of failure in an early SOFC experiment. The profound
degradation of this cell is accidental, as a result of experimental setup. |
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Connection on SOFC
Low magnification SEM cross-sectional image showing electrical connection between
mesh current collector and solid oxide fuel cell |
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Electrically induced SOFC failure
Mechanical failure at the electrode in an anode-support SOFC, after a few
minutes under electrical degradation conditions. |
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Cathode failure
More electrically induced delimination of an anode-supported SOFC, with cathode
failure. Failure at cathode is probably secondary. |
| Nonlinear Least Squares |
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Converging Parameters
When a user selects an iterative estimation algorithm, criterion, and model
to fit measured data, he or she is really specifying a nonlinear dynamic system
with states that consist of the parameters of the problem. The hope is that
the user-selected initial guess (initial value) lies within the basin of attraction
of the global, optimal solution. The figure shows one such basin of attraction
for a benchmark optimization problem. Initial guesses (states) that will never
converge are shown in black. My group has developed methods that significantly
enlarge the basin of attraction for certain problems, making associated system
identification less sensitive to the initial guess. |
| NSF MRI Spectrometer Development |
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This two-board electronic package compromises high-performance analog electronics
(top) and a DSP that can be dropped into a loop that uses the interference of
a reference laser for control, e.g. the mirror position control loop of a Fourier-transform
infrared spectrometer (FTIR). The DSP estimates the time-variation of the non-ideal
components, such as sensor drift, and can use these estimate to improve the
accuracy of the position control. In addition, even in step-scan mode, the DSP
can create synthetic feedback signals that enhance the analytical frequency
range of the spectrometer for time-resolved spectroscopy experiments. |
| High Performance Solid Oxide Fuelcell
Powered Flight |
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Preparing to collect baseline data on electric powered flight under specific
flight profiles using a conventional remote control plane equipped with an autonomous
data acquisition system. |
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"Wind tunnel" and test stand used for propeller, drive, and controller
testing for solid-oxide fuelcell powered flight. |
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Off-the-shelf brushless DC motor controller, modified for use with SOFC
stack, shock mounted to the test stand cage. Prop is in a pusher configuration. |
