A comprehensive physics-based model for predicting the performance of the miniature wind turbine (MWT) for power
wireless sensor systems was proposed in this paper. An approximation of the power coefficient of the turbine rotor was
made after the turbine rotor performance was measured. Incorporation of the approximation with the equivalent circuit
model which was proposed according to the principles of the MWT, the overall system performance of the MWT was
predicted. To demonstrate the prediction, the MWT system comprised of a 7.6 cm thorgren plastic propeller as turbine
rotor and a DC motor as generator was designed and its performance was tested experimentally. The predicted output
voltage, power and system efficiency are matched well with the tested results, which imply that this study holds promise
in estimating and optimizing the performance of the MWT.
In this paper, a miniature wind turbine (MWT) system composed of commercially available off-the-shelf components
was designed and tested for harvesting energy from ambient airflow to power wireless sensors. To make MWT operate
at very low air flow rates, a 7.6 cm thorgren plastic Propeller blade was adopted as the wind turbine blade. A sub watt
brushless DC motor was used as generator. To predict the performance of the MWT, an equivalent circuit model was
employed for analyzing the output power and the net efficiency of the MWT system. In theory, the maximum net
efficiency 14.8% of the MWT system was predicted. Experimental output power of the MWT versus resistive loads
ranging from 5 ohms to 500 ohms under wind speeds from 3 m/s to 4.5 m/s correlates well with those from the predicted
model, which means that the equivalent circuit model provides a guideline for optimizing the performance of the MWT
and can be used for fulfilling the design requirements by selecting specific components for powering wireless sensors.
In this study, an optimal vibration-based energy harvesting system using magnetostrictive material (MsM) has been
designed to power the Wireless Intelligent Sensor Platform (WISP), developed at North Carolina State University. A
linear MsM energy harvesting device has been modeled and optimized to maximize the power output. The effects of
number of MsM layers and glue layers, and load matching on the output power of the MsM energy harvester have been
analyzed. From the measurement, the open circuit voltage can reach 1.5 V when the MsM cantilever beam operates at
the 2nd natural frequency 324 Hz. The AC output power is 0.97 mW, giving power density 279 μW/cm3. Since the MsM
device has low open circuit output voltage characteristics, a full-wave quadrupler has been designed to boost the rectified
output voltage. To deliver the maximum output power to the load, a complex conjugate impedance matching between the
load and the MsM device has been implemented using a discontinuous conduction mode (DCM) buck-boost converter.
The maximum output power after the voltage quadrupler is now 705 μW and power density reduces to 202.4 μW/cm3,
which is comparable to the piezoelectric energy harvesters given in the literature. The output power delivered to a
lithium rechargeable battery is around 630 μW, independent of the load resistance.
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