Transcript Solar Power Array Management for the Solar Racing Team

Maximum Power Point Tracking
System for Solar Racing Team
Andrew Matteson
Ingrid Rodriguez
Travis Seagert
Giancarlo Valentin
April 25th , 2011
GT Solar Jackets
School of Electrical and Computer Engineering
Georgia Institute of Technology
Project Overview
• Customized smart switching power system
to charge car batteries with solar energy
• For use by the Solar Jackets in the World
Solar Challenge 2011
• Material cost: $121 per unit
Design Goals
• Implemented RS-485 communication interface
• Complied with solar challenge regulations
Proposed
Actual
2 MPPTs in 7” x 9” PCB
2 MPPTs in 6½” x 7½” PCB
> 90% efficiency
to be measured
Multiple PCBs
One PCB
Design Overview
Maximum Power Extraction
Maximum
Power
Point
P = IV
Solar Cell I-V Characteristic
Smart Power Switching Circuit
PIC Microcontroller
Smart Switching Demonstration
Current
Voltage
RS-485 Protocol Implementation
• This standard defines a physical layer
• The protocol was defined by the team
• This standard is responsible for communication
between electrical systems in the car
Safety Precautions:
Fuses and Connectors
• Over-current/voltage protection

Automotive fuse at input
 Cylindrical fuse at output
• Touch-safe connectors
Courtesy of Fall 2010 Solar Power Array Management Group.
Safety Precautions:
Fuses and Connectors Illustration
Safety Precautions: Operational
Maximum
Voltage
Maximum
Current
Input
18 V
9A
Output
105 V
3.5 A
Safety Precautions: Operational
Demonstration
Tested software by giving it simulated inputs that were out of
range. Circuit shut down was indicated by the LED.
Safety Precautions: Zener Diodes
The Zener diodes provide paths for current to
flow in the event of an abrupt disconnection.
PCB Size Changes
Efficiency: Synchronous Rectifier
• Circuit efficiency was improved by replacing standard
components with more efficient alternatives
• The standard diode was replaced by an ideal diode
• The design accommodated both alternatives in the
following way:
Ideal Diode
from Inductor
Losses ~ I2RDS(ON)
Losses ~ VFI
to Battery
Problems and Solutions
o The holes on the PCB were
drilled incorrectly
• Drilled bigger size holes by
hand
o Traces were conducting and
leaking current
• Attempted to fix by hand,
then determined it would be
best to mill another PCB
o Limited RAM on PIC
• Space-conscious coding
Final Cost of Design
Components
Toroid Inductor
Ideal Diode Controller
Diodes (various)
Switches
PIC Microcontroller
Current Sensor
Connectors (various)
MOSFET
Oscillator
Miscellaneous Components
Units
2
2
-3
1
3
-4
1
--
Unit Cost
$ 9.56
$ 3.40
-$ 5.75
$ 4.32
$ 4.52
-$ 2.79
$ 2.13
-TOTAL
Total
$ 19.12
$ 10.20
$ 15.30
$ 17.25
$ 4.32
$ 13.56
$ 11.11
$ 11.16
$ 2.13
$ 16.40
$ 120.55
Deliverables
• One working reproducible
PCB
• PCB layout files and
schematics
• Parts list
• Source Code
• RS – 485 Protocol
Present Status
• Testing PCB with solar array
• Testing efficiency of ideal diode
• Improving software robustness
• Combining algorithm and RS-485 code
Questions