Yara Huleihel, Alon Cervera, and Shmuel (Sam) Ben-Yaakov
Power Electronics Laboratory, Department of Electrical and Computer Engineering
Ben-Gurion University of the Negev
P.O. Box 653, Beer-Sheva, 84105 Israel
halihal@bgu.ac.il; cervera@bgu.ac.il; sby@ee.bgu.ac.il
Website: www.ee.bgu.ac.il/~pel/
Abstract – A tapped-inductor boost converter for an input
voltage range of 0.3-0.6 V with the output connected to a fixed
voltage of 24V for battery charging, was designed, analyzed and
tested experimentally. The converter is intended to be used as a
harvester for low voltage renewable energy sources such as
thermoelectric generators and bio-reactors. The proposed
converter is capable of achieving a high boost ratio (40-80) with a
reasonable duty-cycle (0.3-0.7). The converter was optimized by
selecting low parasitic resistance components and by applying a
PCB-based flat magnetic core to reduce the leakage inductance.
The operation of the proposed converter was analyzed for
continuous and discontinuous inductor current modes and power
loss and efficiency expressions were derived. Good agreement
was found between circuit simulations, theoretical analysis and
experimental results. The experimental unit reached an
efficiency of about 86% (gate drive losses included) at an input
voltage of 0.5V and output power level of about 1.2W.
Index Terms- Energy harvesting, high-gain DC-DC converter,
boost converter, tapped-inductor, leakage inductance, snubber,
thermoelectric generator, TEG.
I. INTRODUCTION
The issues of global warming and of the anticipated future
shortage of fossil fuels motivate the search for alternative
energy sources. Aside from the major energy alternatives,
such as solar and wind energy, there is growing interest in the
harvesting of small, yet abundant, unexploited energy sources
such as wasted thermal energy, kinetic energy and
electromagnetic energy. This study focuses on the harvesting
of thermal energy that is now dissipated in cars, factories, PV
panels and many other places. Thermal energy can be
converted into usable electrical energy by thermoelectric
devices, which generate a DC voltage as a function of the
temperature gradient between the cold and the hot side of the
plates. A Thermoelectric Generator (TEG) module is
characterized by its high reliability, long life and small size
features. Typically, the generated voltage of a single TEG will
be lower than 1Volt, while the output power will be in the
order of one to several Watts. Hence, there is a need for power
conversion between the output of the TEG and the load,
which could be a car battery or other loads that normally
require higher voltages.
Previous studies have presented various solutions to this
basic conversion problem, but none of them is suitable for
high efficiency power conversion from sources having a sub-
volt output voltage and above 1Watt power level (equivalent
to output currents of a few Amperes).
It is important to mention that in a case of very low input
voltage together with high input current, not only the circuit
design plays an important role, but also choosing the
components has a major effect on the circuit ’s functioning and
efficiency. Therefore, different magnetic body forms should
be examined.
The objective of this study was to examine the expected
losses in high-gain DC-DC converters and to apply the results
of the theoretical analysis to the design of a high voltage-gain
converter that is suitable for the harvesting of wasted thermal
energy by a TEG. The converter was designed to operate at a
power level of about 1Watt with an input voltage of 0.3-0.6V,
and with the output connected to provide a fixed voltage of
24V for battery charging.
II. PROPOSED CONVERTER TOPOLOGY AND OPERATION
ANALYSIS
Fig.1. Proposed high tapped-inductor boost ratio DC-DC
converter
The basic structure of the proposed converter is shown in
Fig.1.
is the input capacitor which is applied in order to
reduce the input ripple; TI is the tapped-inductor with turn
ratio 1:n, which is characterized by primary inductance,
,
secondary inductance,
, and the leakage inductance,
,
seen at the primary side;
is the MOSFET switch;
is the
output diode;
is the output capacitor, which minimizes
the output ripple;
,
and
are the diode,
resistor and capacitor of the snubber unit, respectively. As
discussed below, the snubber is not required in the present
application since the voltage overshoot at the MOSFET’s
drain is minimal thanks to the very low leakage inductance
achieved in the experimental unit.
A High Gain DC-DC Converter for Energy Harvesting
of Thermal Waste by Thermoelectric Generators
1 978-1-4673-4681-8/12/$31.00 ©2012 IEEE
2012 IEEE 27
th
Convention of Electrical and Electronics Engineers in Israel