Download Final Presentation

Department of Electronic Engineering
4th Year Electronic & Computer
Final Year Project Presentation
Supervisor: Dr Maeve Duffy
Co- 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
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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/LCX1220AP
• 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 Cycle
Determine 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 Algorithm
Check Battery
Check Battery
Capacity
Capacity
No
Is V less than
12v (cell<2)
Yes
Start charge cycle
Charge V = 14.7v
(2.45 v/cell)
Start charge timer
Test Cell voltage 2.12 = 100%
No
Ic stable 3 hrs?
Charge time?
Yes
Terminate Charge cycle
Li-poly Battery
•
•
•
•
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•
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 Cycle
Determine a charge cycle
•
•
Current Level
1C for CC stage
0.02C 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
Check Battery
Check Battery
Capacity
Capacity
Is V less than
8.5v (cell<2.8)
Yes
Start Per-condition
Stage
No
No
Start Charge Cycle
Constant Voltage
Is V = 9/9.6
cell 3/3.2
Yes
Start charge cycle
Constant current
I charge = 2 AMPS
Start charge timer
I charge = 0.02C
Timer?
No
Yes
Yes
No
Is V = 12.6
cell 4.2
Terminate Charge cycle
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 Conditions
Value
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 Diagram
L1
C2
D3
13.1uH
1u
D1N4148
D
2
U2
4
V1
24Vdc
L2
13.1uH
C1
R1
C3
22uF
1u
G
1
2
V1 = 0
V2 = 10
TD = 0
TR = 10n
TF = 10n
PW = 1.9u
PER = 3.03u
SI4450DY
S
7.35
1
SEPIC Simulation
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 current
Duty cycle Relationship with output voltage
MSP403x2xx Micro
• Ultra low power 16 RISC mixed signal processor.
• Designed for battery powered measurement applications
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•
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
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Software development tools
• Micro-controllers perpherials used in project.
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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.
Configure
Microcontroller
Firmware Flowchart
Idle
ADC
Interrupt
No
Yes
Truck
truck
Connected
connect
No
Check
Battery
Capacity
No Battery
Charged
Yes
Truck
supply
R:COM
Check
Battery
Capacity
Yes
Battery
supply
R:COM
Yes
Battery
Charged
No
Execute
Charge algorithm
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
+
--
Truck
Battery
Input
Voltage
R:COM
Output Voltage
Back-up Battery System
R:COM Power lines
Switches
Switch Select
Output Voltage PWM Signal
+
--
Back-up
Battery
Charge
Voltage
SEPIC
Micro
Charge control
Signals
Problems Encountered
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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
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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