DC * DC Converter For a Thermoelectric Generator

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Stove
TEG
DC-DC
Converter
Battery
DC – DC Converter For a Thermoelectric Generator
Ciaran Feeney
4th Electronic Engineering Student
FYP Progress Presentation
Supervisor: Dr. Maeve Duffy
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Presentation Overview

Project overview

Progress to date

Future work and timeline

Questions
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Project Overview

Researchers in Trinity College Dublin are developing a
energy harvesting system for use in developing countries.

Generate electricity using a Thermoelectric Generator(TEG)
from excess heat produced during the cooking process.

Store energy generated in a battery

Use stored power in low power applications

This project focuses on providing an impedance match
between the source and load using a DC-DC Converter and
Microcontroller
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System Block Diagram
Stove
TEG
DC – DC
Converter
Microcontroller
Battery
Pack
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Progress To Date

Thermoelectric generator operation understood

Battery charge and discharge profile established

DC-DC converter Topology determined

Basic analysis of 1st SEPIC DC-DC converter circuit complete

Suitable Microcontroller found

Website online and blog regularly updated
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Thermoelectric Generator
Single Thermoelectric Couple
Full Thermoelectric Generator
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Thermoelectric Generator
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Thermoelectric Generator
Equivalent TEG Circuit Model
Battery Charge and Discharge
Profiles
Voltage increase with constant current 2A
3.7
3.6
3.5
3.4
Voltge across BAttery
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3.3
3.2
3.1
3
Vbatt
2.9
2.8
2.7
2.6
2.5
2.4
0
10
20
30
40
TIme(mins)
50
60
70
80
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Battery Charge and Discharge
Profiles
Discharge Through 3.3ohm Load
Approx Vload = 2.5
Approx Iload = .8
3.4
3.3
3.2
Voltage
3.1
3
2.9
Vbatt
2.8
2.7
2.6
2.5
2.4
0
20
40
60
80
100
Time (mins)
120
140
160
180
200
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DC-DC Converter

Require DC-DC converter that can provide an output voltage
above and below input voltage

Variation of Buck Boost topology decided upon

SEPIC DC-DC Converter

Non-inverting output

Isolation between output and input terminals due to coupling
capacitor
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DC-DC Converter
SEPIC Topology
SEPIC Converter 1st Prototype
Chosen Components
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DC-DC Converter
Input Voltage 4V
Matched Voltage 2V
Output Voltage .846V
Duty Cycle 41.8%
Efficiency 71.4%
Resistive Load
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DC-DC Converter
Efficiency
90
88
86
84
82
80
78
Effiiciency %
76
74
72
70
68
"Efficiency"
66
64
62
60
58
56
54
52
50
0
2
4
6
Input Voltage
8
10
12
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DC-DC Converter

Redesigned SEPIC Converter

Switching frequency is now 80kHz

Reduces size of components

Reduces cost

Diode Replaced by MOSFET

Circuit Components
Inductor Coupled
MOSFET
MOSFET
Coupling Capacitor
Input Capacitor
Output Capacitor
16uH 10A Wureth .0027ohm
NXP MOSFET Power 30V 98A N-CH MOSFETs
NXP MOSFET Power 30V 98A N-CH MOSFETs
Aluminum Organic Polymer Capacitors 16V 100uF 7Mohms
Aluminum Organic Polymer Capacitors 16V 100uF 7Mohms
Aluminum Organic Polymer Capacitors 16V 100uF 7Mohms
€5.83
€0.82
€0.82
€0.561
€0.561
€0.561
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DC-DC Converter

New Design Replacing diode with MOSFET

Design includes Equivalent Series Resistances for
components
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Microcontroller


Required characteristics

PWM (Pulse Width Modulation)

Analog Input pins

Low power consumption

Low cost

Easily programmable
Chosen Controller – Arduino Uno

Fulfills all of the above criteria

Cost €24.31

Abundance of information available online
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Future Work

MPPT

Initial Investigation shows that load current should be maximized
as the battery can be viewed as a purely voltage source.

Preliminary investigation into current sensors reveals that a hall
effect sensor should be used instead of a current sense resistor.

Sensor to be placed in series with battery

A hall effect sensor has been singled out for further investigation
The Allegro Microsystems Current Sensor

Rated for 5A

Low series resistance 1.2mΩ

Cost low €6.54

185mV per Amp
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Future Work


Charge Algorithm

Constant current to 3.6V

Constant voltage of 3.6V until charge cut off current is reached or
30 minutes has elapsed

Voltage to be monitored across battery
Yet to be decided whether a constant voltage will be applied

Researchers in Trinity College Dublin to decide this
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Future Work

Implementation of Circuit with

Thermoelectric Generator

Microcontroller implementing MPPT

Simulated cooking profile/Actual cooking duration

Battery

Efficiency analysis over cooking profile

Identify were improvements can be made
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Timeline
Efficiency Analysis
MPPT & Charge
1st Draft of Mock Algorithm
Circuit Analysed
and Deficiencies
located. Circuit
Optimised to
minimise
deficiencies.
16th of January
2011
Final Circuit and Testing
MPPT & Charge
Algorithm
Bench Demonstration
decided upon
Finished circuit
and completed. completed
Final Thesis
th
incorporating MPPT Week of the 14
of March 2011
and charge
th
14 of February algorithm. Circuitry
1st of April 2011
2011
tested over full
charge and
discharge cycle
with TEG and
battery.
7th of March 2011
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Questions
Download
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