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MOBILE POWER STATION
IRP Presentation
December 10th 2010
Team:
Brad Jensen
William Klema
Nathan Schares
Advisor:
Dr. Ayman Fayed
Client:
PowerFilm, Inc.
PLANNING
PROBLEM STATEMENT & SOLUTION
Photovoltaic (PV) solar arrays can be used to power mobile devices; however, solar
array output power is non-constant and most mobile device chargers require a constant
voltage and current source.
Team dec1013 purposed building a MPS that would supply a constant voltage and
current to mobile devices, while tracking the maximum power point of a PV solar array.
PLANNING
CONCEPT SKETCH
•
Major Concepts
• MPPT
• DC-DC Charging
• Li-Ion Battery Charging
• Variable Source
Solar Panel
Source
120V AC Source
(with AC/DC Adapter)
MPPT
Charging
circuitry
Batteries,
100W
Power
Distribution
12V DC
PLANNING
MARKET & USERS
•
MPS idea developed from market research by PowerFilm, Inc.
• MPS focused mainly on military market
• Designed to carry in backpack
• Simple user interface
• Connect source
• Foldable solar array
• AC/DC Adapter
• Connect load
• AC inverter
• 12VDC Device
• Light weight
• Efficient
• MPS also valid in consumer market
PLANNING
REQUIREMENTS
FR-01 Solar panel input – 1.2A @ 5.4V (20W) Amorphous Silicon Panel
FR-02 100W minimum Lithium-Ion battery capacity
FR-03 15V DC input (with AC-DC Adapter)
FR-04 12V DC output
FR-05 Operation in temperature range of -20°C and 60°C
FR-06 State of charge indicator
FR-07 Charge Balancing Circuitry to keep Li-Ion Batteries balanced
FR-08 Achieve 80% or greater efficiency
NFR-01 MPS should have a weight of less than 5 pounds
NFR-02 MPS should be manufactured for a cost of under $500 per unit
NFR-03 MPS should easily fit inside a military backpack
DELIVERABLES
•
•
•
MPS prototype PCB with Li-ion batteries
MPS poster
MPS Final Report
PLANNING
SCHEDULE
PLANNING
RESOURCES AND RISKS
•
•
•
•
•
Adequate lab space provided for development
TI Analog Design Contest
• Free analog evaluation modules
PCB fabrication and parts
• ECpE Parts Shop
• PowerFilm, Inc.
Knowledge resources
• Dr. Fayed
• PowerFilm
• Brad Scandrett
• Frank Jeffrey
Risks
• Short circuit
• Li-ion overcharge
• Unavailable parts
DESIGN
SYSTEM DECOMPOSITION
Solar
Panel
Source
Buck Converter
Voltage and
Current
Sense
PWM
Control
Signal
Microprocessor
(MSP430)
Serial Communication
(UART) to PC
Feedback
Voltage/Current
Sense
Li-ion Batteries
(3 series cells
x 8Ah)
Charge Control
(BQ20Z70)
Possible
Loads
5VDC (USB)
12VDC
120VAC
DESIGN
SYNCHRONOUS BUCK CONVERTER
•
•
Synchronous rectification improves efficiency
• Eliminates voltage drop across safety diode D1
Controlled by FET driver IR2104
DESIGN
PSPICE SIMULATION
•
•
•
Functionality
Testing
Parasitic inductance
DESIGN
MPPT & LI-ION CHARGING
Solar I-V Curve
Li-Ion Charge Cycle
DESIGN
MSP430 MICROPROCESSOR
DESIGN
,
HIGH SIDE CURRENT SENSE
DESIGN
,
LOW SIDE CURRENT SENSE
DESIGN
,
VOLTAGE SENSE
DESIGN
GUI & MPS COMMUNICATION
•
UART Comm. (via USB)
• Live reporting & plotting
• Processing (Java)
•
All measured values
• Voltages
• Currents
• Duty cycle
• Charging state
•
Debugging tool
•
Demonstration tool
DESIGN
LI-ION BATTERY BALANCING
•TEXAS INSTRUMENTS - BQ20Z70
•IMPEDANCE TRACK BALANCING ALGORITHM
•BQ EVALUATION SOFTWARE INCLUDED
IMPLEMENTATION & TESTING
BREADBOARD
•
Test functionality of buck converter
• Used signal generator for PWM (100 kHz)
• Successfully bucks DC voltage
• Varying duty cycle
•
Connected buck converter and MSP430
• MSP430 controls duty cycle
• Reset problem
•
Breadboard adapters used for ICs
IMPLEMENTATION & TESTING
BREADBOARD TESTING
•
Voltage transients
• Parasitic Inductance
• MOSFET Switching
• Snubber RC filter
• GROUNDING!
•
Transients caused inaccurate
voltage/current readings
•
Fought issues for three weeks
•
Solution?
• Design and fabricate PCB with large
grounding plane
IMPLEMENTATION & TESTING
PCB REV. 1
•
•
•
•
Designed with EagleCAD
• No solder mask for mods.
Transient voltage problem fixed with
ground plane!
• Accurate voltage and current
readings
• Used low-ESR components
• Surface-mounting components
eliminates noise
Problem with differential amplifier used for
measuring high-side current
• Insufficient common-mode voltage
input range
Solution?
• Differential amplifier with rail-to-rail
common-mode voltage input.
• PCB Rev. 2
IMPLEMENTATION & TESTING
PCB REV. 2
•
PCB Changes:
• Updated high-side current sense
differential amplifier.
• Zener diode protection
• Solder mask
• One connector for both programming
and UART
•
Resume calibration and testing
IMPLEMENTATION & TESTING
CALIBRATION
•
Sweep duty cycle range and record serial
data for:
• Solar input voltage and current
• Battery voltage and current
• Load current (30Ω load resistor)
•
Import data to excel and run macro to take
linear regression and convert serial data to
actual voltage and current readings.
IMPLEMENTATION & TESTING
TESTING
•
Start with power supply:
• Constant V & I
• Variable V & I
• Monitor output V & I
• Measure efficiency
•
Practice charging algorithm on lead-acid battery
(more forgiving)
• Trickle charge if pack voltage is less than 9V
• Constant current mode (≤ 500mA) & MPPT
• Constant voltage mode (12.6V)
• Shut down if:
• Battery pack current (≤ 100mA)
• AND Load current (≤ 100mA)
IMPLEMENTATION & TESTING
TESTING (CONT’D)
•
Connect PowerFilm Solar array
• Power solar array and tested on few
sunny days
• Fine tuned MPPT algorithm
• Verified all charging states
•
Connect Li-ion battery
• Charged pack using MPS
• Monitor cell balancing with TI software
and MPS GUI
•
Power external load
• Warmed resistors
• LED lamp
• Laptop through inverter
FINAL REMARKS
CONCLUSION
•
•
•
Many lessons learned
Technical
• Breadboards are terrible for certain circuits.
Use only to test functionality.
• PCBs, surface mount components, and
large ground plane help transient and noise
problems.
• Never assume parts will work as planned.
• GUIs and Macros are tools that make life
easier.
Management
• Utilize talents.
• Stick to schedule.
• Establish ambitious goals.
• Take lots of picture and screen shots.
• Documentation is just as important as the
product.
MOBILE POWER STATION
Thank You:
• Dr. Ayman Fayed
• Brad Scandrett
• Frank Jeffrey
• Dr. Daji Qiao
• CSG
• PowerFilm Inc.
• ECpE Faculty & Staff
• Texas Instruments
• C2 Development