1. Satellite Electrical Power System (EPS) Design Review
Hayden Waddle
Joshua Stogsdill
Stephen Maloney
Travis McCullar

2. Abstract
The EPS system will be responsible for several functions including
Boosting input voltages from panels
Regulating battery charging and bus voltages
Sending telemetry to main controller
Commercially available systems - Clyde Space
More features, greater protection
Include same major functions (Voltage regulation, battery charge routines, temperature monitoring)

3. Current Status : Problem Simplification
Simplified Design
Gain traction on building a working prototype by reducing requirements to manageable levels
Add complexity after simplified design is constructed and tested
VBat
5V Regulator
Solar Panels In Parallel
Boost Converter
Battery Charger
Lithium Polymer Batteries 5V
3.3V Regulator
3.3V
Battery Heating System

4. Boost Converter and Voltage Regulation
Solar cells provide V
Battery Charger requires V
Boost converter raps input voltage to a constant 12 V
Voltage Regulation
Current testing - linear voltage regulators.
Production - more efficient switching regulators.

5. Battery Charging Battery Charger - MCP73864 Batteries
Self-contained Li-ion/Li-polymer charger.
Implements most efficient charge cycle.
Provides thermal limits for battery charging.
Batteries
Current testing - smaller scale Li-ion batteries.
Production - Li-polymer batteries with capacity of greater than 1240 mAh.

6. Battery Heating Battery Charger Thermal charging limits.
External heaters and control system
Battery mounted thermistors.
Control through:
Onboard microcontroller.
Main satellite microcontroller.
Heater options:
PCB Traces
Thin Film Heaters
Heat Tape

7. Current Prototype Status
Purchased test boost converter, regulators, battery charger, PIC controller
Tested boost converter and regulators using DC source in lab; 1V->12V
Attempted test using solar panel with flashlight
12V
5V Regulator
DC Source >1 V
Boost Converter 5V
3.3V Regulator
3.3V

8. Future Plans : Complexity Level 1
Replace the boost converter with a peak power tracker
A peak power tracker provides a varying “load” to the outputs of the solar panels
This load specifies the operating point on the solar panel I-V curve
At the knee of this curve, maximum power output from the solar cells is achieved

9. Future Plans : Complexity Level 1
The peak power tracker varies the load efficiently by varying the duty cycle of a boost converter circuit
RIn = ROut(1-D)2
In this way, energy is stored in the magnetic field of the inductor rather than wasted in a resistor

10. Future Plans : Complexity Level 1
Many methods for varying the duty cycle of the boost converter to find peak power exist, such as the “perturb and observe” method
Some assumptions required – if the satellite is spinning very quickly, control will be difficult or impossible
Boost Converter
Load V
Solar Cell I
D/A
A/D
Controller

11. Future Plans : Complexity Level 2
Separate the solar cell panels from their parallel configuration and use a peak power tracker for each panel
This will allow telemetry output of individual panel voltage/current (useful for determining orientation and spin rate)
Telemetry output for battery voltage and charge status
Over-current protection for VBatt

12. Future Plans : Complexity Level 3
Flight pin / footswitch integration
Temperature testing using a NASA weather balloon / Cryo-chamber
Battery coatings to prevent ballooning effect in space – Kapton coating
Design for satellites with more powerful solar panels to continue limited operation after battery death

13. Current Budget Quantity Part Part Number Price 1 Inductor 4590R-473K
$2.07
Schokey Diode
1N5818
$0.39
Battery Charger
MCP73864
$1.56 2
Voltage Regulator
LN1086
$2.42 per Regulator
Boost Converter LT
$5.50
Capacitor ND
$0.95

14. Future Budget Near Future Budget Distant Future Budget Quantity Part
Part Number
Price 1
PIC Processor
PIC18F4550
$4.50 2
Li Polymer Battery
GM045085
$21.60 per Battery
Thermistor
527-C100G104J
$2.16  per Thermistor
Distant Future Budget
Complexity Addition
Estimated Price
Peak to Peak Power Tracking
$15.00*
Mechanical Switches (flight pen and boot switch)
$10.00*
Telemetry Circuit
*Price subject to change due to implementation design.

15. Timeline