Weather in a Box Autonomous self-powered energy harvesting interface and power

management system for sensor applications and wireless data transmission

Fritz Huettinger Chair of Microelectronics, University of Freiburg

Maximilian Marx

Daniel Schillinger

Florian Kromer

European Analog Design Contest 2011

Content

Motivation

Fundamentals and idea

System design

Measurement and simulation results

Summary and outlook

22.11.2011 Maximilian Marx, Daniel Schillinger, Florian Kromer - 2 -

22.11.2011 Maximilian Marx, Daniel Schillinger, Florian Kromer - 3 -

Motivation

Distributed wireless sensor nodes

Send measurement data to server

For instance: in- and outdoor weather

monitoring

Energy harvesting generators

Solar cell or vibration driven

No wiring or batteries needed

Low fluctuant output power

Smart power management necessary

Server

Client

(WSN)

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Fundamentals and idea

Generator

Output power depends on load

Matching with internal resistance

Rg

+

-

Vg,oc

generator

+

-

VRLVg

RL

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Fundamentals and idea

Generator

Output power depends on load

Matching with internal resistance

Maximum power point

Voltage on capacitor is controlled

VMPP = kratio Vg,oc

kratio depends on generator type

Vibration-driven generator

kratio = 0.5

Solar cell kratio ≈ 0.7

Rg

+

-

Vg,oc

generator

Cin

+

-

VC,inVg

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System Design

Open circuit voltage sampling

unit (VSU)

Samples Vg,oc

Periodically connected to the

generator

Fast sampling

Low energy loss

Interface circuit is decoupled

during the sampling

Sampling capacitor and voltage

divider to set kratio

Provides reference voltage:

VMPP = kratio Vg,oc

Ambient

Energy

(Sun,

Wind,

Vibrations)

Open-

Circuit

Voltage

Sampling

Unit

(VSU)

Energy

Harvesting

Generator

Vg,oc

LS:

TI SN74AUP1T97

MOSFET:

CSD25401Q3

CSD16301Q2

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System Design

Boost converter

Controlled by load

matching unit

(LMU)

Compares VMPP

with Vcin

Single-step

approach

Input buffer Cin is

charged/discharged

between

upper/lower limit

Storage buffer Cstg

is charged

Vg,oc

Time

Voltage

VCin

VCstg

Ambient

Energy

(Sun,

Wind,

Vibrations)

Open-

Circuit

Voltage

Sampling

Unit

(VSU)

Boost

Converter

(L = 220 µH)

Load

Matching

Unit

(LMU)

Storage

Buffer

(Cstg =

10mF)

Energy

Harvesting

Generator

Input

Buffer

(Cin =

1µF)

Vc,inVg,oc

VMPP

upper limit

lower limit

Comp.: TI TLV3491

AND GATE: TI

SN74AUR2G80

VMPP

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System Design

Buck Converter

VCstg is not regulated

VCstg converted to regulated VCapp

Schmitt-Trigger is used to realize

PFM control

Time

Voltage

VCin

VCstg

VCapp

Comparator: TI TLV3491

LS: TI SN74AUP1T97

VREF: TI REF3312

Ambient

Energy

(Sun,

Wind,

Vibrations)

Open-

Circuit

Voltage

Sampling

Unit

(VSU)

Boost

Converter

(L = 220 µH)

Load

Matching

Unit

(LMU)

Storage

Buffer

(Cstg =

10mF)

Energy

Harvesting

Generator

Input

Buffer

(Cin =

1µF)

Vc,inVg,oc

VMPP

Buck

Converter

(L=560 µH)

Application

Buffer

(Capp =

22mF)

Vc,stg Vc,app

upper limit

lower limit

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System Design

Complete System

MSP430 controls VSU

and buck converter

I²C interface to sensors

Wireless transmission of

sensor data

Voltage supervisor

controls startup

Ambient

Energy

(Sun,

Wind,

Vibrations)

Open-

Circuit

Voltage

Sampling

Unit

(VSU)

Boost

Converter

(L = 220 µH)

Load

Matching

Unit

(LMU)

Storage

Buffer

(Cstg =

10 mF)

Buck

Converter

(L=560 µH)

Application

Buffer

(Capp =

22 mF)

Microcontroller

MSP430F2274

Pressure

sensor

Bosch

BMP085

Humidity

sensor

Sensirion

SHT21

RF trans-

ceiver

TI

CC2420

Voltage

Supervisor

(SVS)

Energy

Harvesting

Generator

Input

Buffer

(Cin =

1 µF)

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System Design

Complete System

MSP430 controls VSU

and buck converter

I²C interface to sensors

Wireless transmission of

sensor data

Voltage supervisor

controls startup

Simulation and Measurement results

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Spice Simulation

Verify functionality and dimensioning

Using TI Spice models

System Startup

Phase 1: All active devices turned off

Phase 2: Boost converter and LMU is

working to enable system to start with

low Vg,oc

Phase 3: MSP430 and VSU is working,

Vg,oc is sampled and input voltage is

adapted

(1)

(1)

(2)

(2) (3)

(3)

Simulation

Measurement

Measurement results

Load matching

Vg,oc is sampled every 200 ms

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(1) (2) (3)

Measurement results

Load matching

Vg,oc is sampled every 200 ms

VCin is adapted to 0.7 Vg,oc

Vg,oc = 2.65 V VCin = 1.85 V

Supply RF transceiver

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Summary and Outlook

WSN for weather monitoring powered by energy harvesting

generators

Efficient self-startup

Maximum power point tracking

Reliable power management for sensors and RF transceiver

Outlook

Measurements with different generator types

Integrating complete RF protocol

Long-term field test

Integrated circuit (ASIC)

Acknowledgment

We would like to thank:

Texas Instruments

Fritz Huettinger Chair of Microelectronics

Prof. Dr.Ing-Yiannos Manoli

Dominic Maurath

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Thank you for your attention!

VSU

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TI

CSD25401Q3

500 kΩ

Vvsu

DMSP2

5 MΩ

500 kΩ

Cref1

200 nF

Cref2

470 µF

TI

CSD25401Q3

TI

CSD16301Q2

VCstg

500 kΩ

VCapp

5 MΩ

ONSemiconductor

BAT54C

M1

M6

M7

D3

U4

U6

DMSP3

DMSP1

VCstg

Open circuit voltage

sampling unit (VSU)

Levelshifter (I)

TI

SN74AUP1T97

Levelshifter (NI)

TI

SN74AUP1T97

Energy harvesting

generatorInput Buffer

(Cin)

start-up

branch

RVSH1 RVSH2

LMU

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TI TLV3491

VCapp VCapp

DMSP1

1 MΩ

ST1

U2a

Open Circuit

Voltage

Sampling Unit

(VSU)

Boost Converter

Input Buffer

(Cin) VCapp

Voltage

supervisor

TI SN74AUP2G80

Load Matching Unit

U2bDboost,onVvsh

Vin

ST1

Weather in a Box - Circuit

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TI

CSD25401Q3

TI

SN74AUP1T9

7

500 kΩ

MSP1

SI1050x

1

MΩ

Uref 1

Uref 1

TI

TLV3491

MSP2

5 MΩ

500 kΩ

Cref1

470 nF

Cref2

470 µFTI

CSD25401Q

3

TI

CSD16301Q2

Cbuf2

Cbuf2

Cbuf1

1 uF

NSR1020MW2T1G

Cbuf2

10 mF

1 MΩ

NSR1020MW2T1GCbuf3

22 mFMSP430F2274

TI

SN74AUP1T9

7

Cbuf2

MSP4

Cbuf3

TI

TLV3491

Int1

MSP1

MSP2

MSP3

MSP4

500

kΩ

Cbuf3

1 MΩ

Levelshifter (NI)

TI

SN74AUP1T97

Cbuf2

MSP

3

1 MΩ

5 MΩ

ONSemiconduct

or

BAT54C

LS2_Out

ADC

M1

M2

M3

M4

M5

D2

D3

D4

L1 L2

U1

U4

U5

U6

U7

U8BSH20

5

Cbuf3

U2

Cbuf3

TI SN74AUP2G80

ADC

MSP1

Voltage

supervisor

TPS3106E16

Cbuf3

Out 1 Out 2

M6

U9

Voltage

reference

REF3312

1,25 V

U10

+

INPUT

-