+

DC – DC Converter For a Thermoelectric Generator

Ciaran Feeney4th Electronic Engineering StudentFYP Progress Presentation

Supervisor: Dr. Maeve Duffy

Stove TEG

DC-DCConverter

Battery

+Presentation Overview

Project overview

Progress to date

Future work and timeline

Questions

+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

+System Block Diagram

TEGStove

DC – DC Converter

Battery

Pack

Microcontroller

+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

+Thermoelectric Generator

Single Thermoelectric Couple Full Thermoelectric Generator

+Thermoelectric Generator

+Thermoelectric Generator

Equivalent TEG Circuit Model

+Battery Charge and Discharge Profiles

0 10 20 30 40 50 60 70 802.4

2.5

2.6

2.7

2.8

2.9

3

3.1

3.2

3.3

3.4

3.5

3.6

3.7

Voltage increase with constant current 2A

Vbatt

TIme(mins)

Volt

ge a

cro

ss B

Att

ery

+Battery Charge and Discharge Profiles

0 20 40 60 80 100 120 140 160 180 2002.4

2.5

2.6

2.7

2.8

2.9

3

3.1

3.2

3.3

3.4

Discharge Through 3.3ohm LoadApprox Vload = 2.5Approx Iload = .8

Vbatt

Time (mins)

Volt

age

+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

+DC-DC Converter

SEPIC Topology

SEPIC Converter 1st Prototype Chosen Components

+DC-DC Converter

Input Voltage 4VMatched Voltage 2VOutput Voltage .846V Duty Cycle 41.8%Efficiency 71.4%Resistive Load

+DC-DC Converter

0 2 4 6 8 10 12505254565860626466687072747678808284868890

Efficiency

"Efficiency"

Input Voltage

Effi

icie

ncy %

+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 16uH 10A Wureth .0027ohm €5.83MOSFET NXP MOSFET Power 30V 98A N-CH MOSFETs €0.82MOSFET NXP MOSFET Power 30V 98A N-CH MOSFETs €0.82Coupling Capacitor Aluminum Organic Polymer Capacitors 16V 100uF 7Mohms €0.561Input Capacitor Aluminum Organic Polymer Capacitors 16V 100uF 7Mohms €0.561Output Capacitor Aluminum Organic Polymer Capacitors 16V 100uF 7Mohms €0.561

+DC-DC Converter

New Design Replacing diode with MOSFET

Design includes Equivalent Series Resistances for components

+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

+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

+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

+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

+Timeline

Efficiency Analysis

1st Draft of Mock Circuit Analysed and Deficiencies located. Circuit Optimised to minimise deficiencies.

16th of January 2011

MPPT & ChargeAlgorithm

MPPT & Charge Algorithm decided upon and completed.

14th of February 2011

Final Circuit and Testing

Finished circuit completed incorporating MPPT and charge algorithm. Circuitry tested over full charge and discharge cycle with TEG and battery.7th of March 2011

Bench Demonstration

Final ThesisWeek of the 14th of March 2011 1st of April

2011

+Questions