Energy harvesting is becoming increasingly important in low-power applications where energy
from the environment is used to power the system alone, or to supplement a
battery. For example, pulse oximeter sensors inside helmets of road racing cyclists
are powered by the sun. These sensors have become smaller and more practical
without the limitation of a finite energy supply. Harvested energy from
an energy transducer (solar, piezoelectric,
etc.) must be maximized to ensure these devices can survive periods where
environmental energy is scarce.
The conversion process from the transducer to usable power for the
device is not perfectly efficient. Specifically, the output voltage of a solar
cell is a function of the light intensity, and by extension the load it powers.
A small perturbation of the light source quickly diminishes the available power.
The wasted power reduces the energy
available for the application, and can be improved using an approach called maximum
power point tracking (MPPT). This technique maximizes harvesting efficiency by
dynamically impedance matching the transducer to its load.
This report introduces the Maximum Efficient Solar Harvester (MESH),
an MPPT algorithm tuned for a
specific Wireless Sensor Network (WSN) application.
MESH specifically controls the operation
of the DC-DC converter in a solar power management unit (PMU). The control is
done by monitoring the available light and feeding that information to choose
the optimal operating point DC-DC converter. This operating point has a direct dependency on
the overall efficiency of the system.
For MESH to be practical, the cost and power overhead of adding this
functionality must be assessed. Empirical results indicate
that MESH improves the maximum efficiency
of the popular Texas Instruments (TI) RF2500-SEH WSN platform
by an average of 20%, which far exceeds
the power overhead it incurs. The cost is also found to be minimal,
as WSN platforms already include a large portion of the hardware required
to implement MESH.
The report was done in collaboration with Shahil Rais. It covers the
hardware components and the bench automation environment; Rais's companion
report focuses on software implementation and MESH architecture definition. / text
| Identifer | oai:union.ndltd.org:UTEXAS/oai:repositories.lib.utexas.edu:2152/ETD-UT-2010-12-2420 |
| Date | 21 February 2011 |
| Creators | Kobdish, Stephen Matthew |
| Source Sets | University of Texas |
| Language | English |
| Detected Language | English |
| Type | thesis |
| Format | application/pdf |
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