department of electronic engineering 4th year electronic & computer final year project...

Department of Electronic Engineering4th Year Electronic & ComputerFinal Year Project Presentation

Supervisor: Dr Maeve DuffyCo- Supervisor: Dr Peter Corcoran

Student: Noel Walsh Date : 13-08-08

Introduction

• The aim of the project was to design an intelligent back-up battery charger capable of charging various battery chemistries.

• The idea for the project was proposed by Ben Kinsella, Hardware Engineering Manager at Blue Tree Systems during my 3rd year PEP.

• The actual circuit itself was to be designed as a rechargeable secondary power source for Blue Trees R:COM device on a dry trailer configuration.

• The structure of the project was broken into the following sections

– Battery Chemistries properties and charge cycles

– DC-DC converters

– Hardware

– Software

– PWM

Battery Chemistries properties and charge cycles

• A Battery is composed of one or more electrochemical cells, which store chemical energy.

• Two types primary and secondary.• There are many battery chemistries available, characteristics vary• Charging algorithms vary for different secondary chemistries.• Selecting the battery for the project was based on:

– Rechargeable– Cost– Capacity– Physical Size– Customer requirements

Sealed Lead Acid

• Low cost battery available in a variety of sizes and designs.• Performs well over a range of temperatures.• Good service life

• Manufactured by panasonic Model number LC-X1220P/LC-

X1220AP • 6 cells connected in series 12v dc output • Capacity is equal to 20Ahours• Charging methods

– Fast charging ( CV/CC, rapid, 2 step CV)

– Slow charging ( CV , trickle, float)

Sealed Lead Acid Charge CycleDetermine a charge cycle

• Current Level

0.4C or smaller CV

0.15C or smaller trickle• Temperature

from 0°C to 40°C • Charge Time

Time CV I < 0.25C

Tch = Cdis / I + (6 to 10)

Trickle 24/48 hours • Capacity

From table

• Overcharging

Shorten battery life

SLA Charging AlgorithmCheck Battery Capacity

No

Yes

Check Battery Capacity

Is V less than 12v (cell<2)

Start charge cycleCharge V = 14.7v

(2.45 v/cell)Start charge timer

Test Cell voltage 2.12 = 100%

Terminate Charge cycle

Ic stable 3 hrs? Charge time?

No

Yes

Li-poly Battery

• Evolved from Lithium.• More robust, lighter and easier to shape.• Manufactured by WorleyParsons Model No. AES 555072.• 3 cell battery, nominal voltage 3.7• 4.2 voltage on terminals when fully charged.• Capacity is rated for 2Ahour.• Preferred charging method is constant current/ constant voltage,

which is composed of 3 stages– Trickle charge

– Fast Charge ( constant current CC)

– Constant voltage (CV)

Li-Poly Charge CycleDetermine a charge cycle

• Current Level1C for CC stage0.02C for end of charge

• Temperature for charging

from 0°C to 45°C • Charge Time

Trickle : < 1Hr Fast : < 1.5Hr CV : < 2Hr

• Capacity ( voltage across terminals)4.2v charged, 3v

discharged • Termination

Current level or timer.

Li-Poly Charge Algorithm

Start Charge CycleConstant Voltage

Start Per-conditionStage

Yes

YesYes

No

No

No

Check Battery Capacity

No

Yes

Check Battery Capacity

Is V less than 8.5v (cell<2.8)

Start charge cycleConstant current

I charge = 2 AMPSStart charge timer

Terminate Charge cycle

Is V = 9/9.6 cell 3/3.2

Is V = 12.6 cell 4.2

I charge = 0.02C Timer?

SEPIC DC to DC converter

• Single Ended Primary Inductance Converter.• Classified as a Switched-mode power supply.• Non-inverting output capable of generating output voltages above or

below the input voltage.• Operates in continuous mode.• The average current in inductor L2 is the same as the load current,

therefore offers low end current sense.

SEPIC Switching

SEPIC Waveforms

SEPIC Operating ConditionsValue Unit Note

US Truck Battery 12 Volts DC Range 9-14

EU Truck Battery 24 Volts DC Range 20-28

Vin minimum 9 Volts DC

Vin maximum 36 Volts DC

Vout range 14.5-14.9 Volts DC For lead Acid

Vout range 12.3-12.6 Volts DC For Lithium

I out 2 Amps

Switching Frequency 330 KHz

SEPIC circuit DiagramD 3

D 1 N 4 1 4 8

TD = 0

TF = 1 0 nP W = 1 . 9 uP E R = 3 . 0 3 u

V 1 = 0

TR = 1 0 n

V 2 = 1 0

U 2

S I 4 4 5 0 D Y

D

G

S

4

1

2

V 12 4 V d c

R 1

7 . 3 5

2

1

L 1

1 3 . 1 u H

C 1

1 u

C 2

1 u

C 3

2 2 u F

L 2

1 3 . 1 u H

SEPIC Simulation

Duty cycle Relationship with output current

Vin DC volts Duty cycle(usec) Duty Cycle % Vout DC volts

SLA 24 1.2 40 14.7

SLA 12 1.83 60 14.7

Li-Poly 24 1.17 39 12.6

Li-Poly 12 1.72 57 12.6

Duty cycle Relationship with output voltage

MSP403x2xx Micro

• Ultra low power 16 RISC mixed signal processor.• Designed for battery powered measurement applications• The mixed-signal and digital technologies implemented in the MSP430 allow

for simultaneous interfacing to analogue signals, sensors and digital components while maintaining low power

• Hardware development tools

• Software development tools • Micro-controllers perpherials used in project.

– Digitally controlled oscillator DCO

– 10 bit analog-to-digital converter.

– 2 configurable Op-amps

– 4 Digital I/O ports

MSP430x2xx Architecture

MSP430 Firmware

• First task is to configure the microcontroller and initialise some data variables.

• Configures ports, DCO, Timer_A, ADC, Op-amps• Initialise ADC data array, timedelay, PWM period, PWM duty cycle• ADC is interrupt enabled and the ADC ISR executes when this

process is invoked.• ADC value is read in and if required the value in CCR1 is changed

to adjust the PWM duty cycle.• Timer_A is set in up mode and counts to CCR0. • CCR1 is configured to OUTMOD_7, reset/set.

Firmware FlowchartIdle

YesNo

Check Battery

Capacity

ExecuteCharge algorithm

Truck supply R:COM

Battery supply

R:COM

BatteryCharged

truckconnect

TruckConnected

Yes

No

Check Battery

Capacity

BatteryCharged

No

Yes

ConfigureMicrocontroller

Yes

ADCInterrupt

No

Proposed System

• Microcontroller is powered through a buck converter by the back-up battery

• Input voltage from the trucks battery is measured with a voltage divider ( R3 = 13k and R4 = 1k ohms)

• SEPIC output voltage has to compensate fro the sense resistor on the battery and the voltage ripple. ( R1= 7k and R2 = 1k ohms)

• Battery current measured through resistor R sense 2 = 1.25 ohms • SEPIC output current is source with the sense resistor R sense 1

and it equals 1 ohm. Rated for peak current in the inductor L2.• Switching power sources in implemented with two N0channel

MOSFETS connect to pins TB0 and TB1 of Timer_B.

Circuit Block Diagram

Back-up Battery System

SEPIC

Micro

Switches

R:COMTruck

Battery

+ --

Back-upBattery

+ --

Charge controlSignals

PWM Signal

Switch Select

R:COM Power lines

Charge Voltage

Input Voltage

Output Voltage

Output Voltage

Problems Encountered

• Software development tools for the microcontroller• Driving the power MOSFET from the microcontroller.• Simulating with Pspice.• Configuring microcontroller for an interrupt service routine.• Charging algorithms and component ratings.

Conclusion

• Most of the design is finished to enable the system to be built• Charging algorithms difficult to finalise• Lacked a power electronics background.• I am satisfied with the overall outcome of the project as it introduced

me to various new subjects.• The work completed was mostly successful. Wished I had more

time with the microcontroller.• Remain work to do.

– Firmware– Micro interfaces– Test SEPIC