Transcript presentation - Course Website Directory

Power Board for IlliniSat-2
Project
Group 32
Roberto Suarez, Rachit Goel,
Sam Kearney
TA: Kevin Bassett
ECE 445 Spring 2013
IlliniSat-2 Project Background
• Generic bus for a 2 or 3U Cubesat
• Systems to communicate with and power
payloads
–
–
–
–
ADACS
Command & Data Handling
Communications
Power
IlliniSat-2 Bus
Model from IlliniSat-2 website: cubesat.ae.illinois.edu
Power Board Features
• Battery Charging/MPPT
• Battery Protection
– Overvoltage/Undervoltage Protection
– Cell balancing
– Temperature monitoring/regulation
• 16 DC buses
– 8 unregulated (7.4V) buses
– 8 regulated (3.3V) buses
• Current Monitoring/Overcurrent Protection
Top-Level Block Diagram
Power Lines
Signal Lines
PV Cells Input
Voltage
and
Current
Sense
Battery Charging
Circuit (4 switch
buck-boost
converter)
Gate Drive
Circuits
Control
Voltage
and
Current
Sense
Main
Battery
Battery Monitoring/
Switching Circuitry
Backup
Battery
Output to
satellite
subsystems,
payload
Unregulated
Buses x8
Overcurrent
Protection
Buck
Converter
Regulated
(3.3V) Buses x8
Test Boards
• Main board
– Battery charging circuit
– Buck converter (7.4V to 3.3V)
– 2 DC buses (1 unreg, 1 reg) w/ OC protection
– Microcontroller
• Battery board
– Overvoltage/Undervoltage Protection
– Cell balancing
Battery Charging Circuit
• Requirements and specifications:
– Input: Spectrolab 28.3% UTJ Solar Cells
• 7.05 – 21.28 V (depending on # of cells)
• 0 – 1.1 A
– Output: ___ Lithium Ion Battery Pack
• 7.4V nominal, 6.0 – 8.2V safe range
• Max current 2.2 A
– Layout: 2” x 1”
– Over 90% efficiency
4-Switch Buck-Boost Converter
EPC GaN FET
• Advantages:
– Small footprint (1.08 mm x 1.7 mm)
– High efficiency
– low RDS(on) (16 mΩ)
– low QG (2.48 nC)
• Disadvantages:
– Bumped die configuration
very difficult to solder
digikey.com
Microcontroller
• Interfaces:
Implemented on test board
– DC bus enable and current measurement
– Charge enable/discharge enable for batteries
– PWM output for battery charging circuit
– Voltage and current measurement on BCC
– RTD temperature sensing
– Output to Kapton heaters
– Communication with C&DH
Microchip PIC18F87K22
alliedelectronics.com
Maximum Power Point Tracking
Spectrolab UTJ Solar Cells
IV Characteristic
(spectrolab.com)
Testing
~8 V P-P
Future Work
• Replacement gate driver:
– TI LM5113
– Gate-source voltage clamped to 5.2 V
maximum
www.ti.com