Transcript Solar Power Array Management for the Solar Racing Team

Solar Power Array Management
for the Solar Racing Team
Mark Calotes
Ginah Colón
Alemneh Haile
Nidhi Joshi
Michael Lu
December 13, 2010
GT Solar Jackets
School of Electrical and Computer Engineering
Georgia Institute of Technology
Project Overview
• Design a system to charge car batteries
with the energy received from solar cells
• To be used for the Solar Jackets’ solar car
in the World Solar Challenge
• Estimated cost: $151.58
Design Goals
• Implement boost converter to extract power
from solar array
• Implement feedback with microcontroller to
extract maximum power
• Create a compact PCB board with circuit and
microcontroller
• Implement RS-485 communication to transfer
information
Overall System Diagram
Technical Specifications
Characteristic
Specification
Input Voltage Range
0 to 6 V
Input Current Range
0 to 5.5 A
Operating Frequency
15 kHz
External Supply Required
12 V Supply
Input Sources
Power Supply, Solar Array
Output Loads
Resistor, Battery
Average Efficiency
84.6%
Absolute Maximum Limits
Parameter
Maximum Value
Input Current
10 A
Input Voltage
12 V
Output Current
10 A
Output Voltage
14 V
Maximum Switching Frequency
20 kHz
Overall Circuit Diagram
Microcontroller Input Protection
• Voltage on microcontroller pin
 Minimum: -0.6 V
 Maximum: 5.6 V
• Protects Microcontroller
Circuit Protection
• External User Control
 Switch at Input
 Switch at Output
• Over Current Protection
 Automotive Fuse at Input
 Cylindrical Fuse at Output
Preliminary Test Circuit
Preliminary Circuit Output Voltage
Approximate Circuit
Efficiency
Circuit Efficiency
0.92
0.9
0.88
y = -0.071x + 0.8858
R² = 0.7992
0.86
0.84
0.82
0.8
0.78
0.76
0
0.5
1
Input Current (A)
1.5
2
Issues and Solutions
• Current sensor output voltage dropped upon
connection to microcontroller
– Use op-amp between sensor and microcontroller
• Output voltage failed to boost
– Verify gate driver output
• Voltage regulator heated up
– Check for faulty components that draw too much
current
Circuit Future Work
• Adapt system to new solar array and 96 V
battery output
– Components to Modify
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Schottky Diode
Inductor
Fuses
Current Sensor
• Increase efficiency by choosing lower
resistance components and active rectification
MCU Key Benchmarks and Specifications
Component
Specification
Benchmark Testing
PWM/Duty Cycle
Frequency: 15 kHz
Step Size: 0.5%
Used oscilloscope to measure
duty cycle and frequency with
based on known input voltages
TX/RX Serial
Sends measured input
components to console
once per half-second
Viewed console for updated
outputs and used MATLAB
program to verify valid
measurements of all parameters
Integer conversion
to ASCII for serial
and LCD output
One ASCII character
assigned per digit of any
integer with knowledge of
total digits in number
Verified from both LCD display on
Qwik&Low board and serial
console, which must be
programmed digit-by-digit
A/D Conversion
13 analog channels to
accept input data; scales
value from 0 - 210
corresponding to 0-Vdd
Accurate voltage measurements
displayed on LCD display and
serial based on known voltages
from DC Power supply
Microcontroller Issues and Concerns
• Current Issues
– MCU PWM pins from prototype
have burned out due to excessive
current drawn by MOSFET base
– RS-485 communication to other
devices work in progress
– Only functional for one PWM, not
two independent modules
– Can measure output voltage, but no
conditional checking for circuit
protection coded yet
– Performance quality expensive (59%
program memory utilization) and
size results in some lost output data
MPPT Safeguards
• Voltage scaled from 0-1023 so we had to
readjust the scale to be from 0-5
– V = Vr/1023 * 5
• Duty cycle stays between 5% and 95%
– This keeps the PWM from breaking
• Voltage must stay below 5 V
– This keeps the micro-controller from breaking
PIC Microcontroller: Future Work
• Obtain more test data
from circuit to improve
MPPT implementation
• Develop and integrate
RS-485 communication
protocol in code
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Optimize code for less
memory consumption
Develop more objective
way to view input data and
change duty cycle, e.g.
through a moving averager
RS-485 Connection
• Onboard or remote
computer can check on
each board’s status
• Status includes voltage,
current, power, and
whether the PWM is
increasing or decreasing
Printed Circuit Board
PCB Design
• Laid out using DesignSpark PCB
• One MPPT module
• Toggle switches for solar cells and battery
• Automotive fuse for solar cells
• Cylindrical fuse for battery
• RS-485 communication
PCB Issues & Resolutions
• Two-module board too large to print on
campus
– Remove one module
• Pins improperly connected in schematic
– Remove trace and reconnect with flying leads
• Drill hole sizes incorrect
– Re-drilled by Bob House
Future PCB Modifications
• Print two-module board off campus
• Use more accurate PCB footprints
• Use larger soldering pads for easier soldering
• Place switches, fuses, and peripherals along one
side of board for ease of access
• Consolidate components to minimize board size
Cost Analysis
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Total cost: $151.58
Circuit Component Cost: $17.56
Sensors: $10.50
Protection: $15.45
Connectors/Communication: $7.14
Prototyping: $100
Some parts were provided by the lab and
therefore were free.
Modifications Required for Solar Jackets for
Spring 2011
• Finalize Solar Array Characteristics
• Modify Power Switching Circuit to Accept
Higher Voltage and Current Values
• Optimize MPPT algorithm and Memory
Utilization
• PCB with 2 MPPT Modules
• RS 485 communication with Multiple MPPT
boards