KGCOE MSD Technical Review Agenda
P12407- Clean, Self-Sustained Photovoltaic Energy
Harvesting System
KGCOE MSD Page 1 of 1 Technical Review Agenda
Meeting Purpose:
1. Overview of the project
2. Confirm Engineering Specifications and Customer Needs
3. Review concepts
4. Propose a design approach and confirm its functionality
5. Cross-disciplinary review: generate further ideas
Materials to be Reviewed
1. Project Description
2. Customer Needs
3. Customer Specifications
4. Solar Cells
5. Phase I and II Diagrams
6. Concept Development and Proposed Design – Buck-boost converters
7. Concept Development and Proposed Design – Battery charger
8. Concept Development and Proposed Design – Power monitoring/management
9. Control Diagram
10. MSDI Plan
11. Risk Assessment
Meeting Date: October 27th, 2011
Meeting Location: Senior Design Lab, fourth floor of Building 9
Meeting time: 4:00PM to 5:00PM
Time
10:00
10:05
10:07
10:12
10:14
10:20
10:23
10:27
10:30
10:35
10:37
10:42
Meeting Timeline
Topic of Review
Introduction to the project
Customer Needs
Customer Specifications
Solar Cells
Ascent Solar Panel Concerns
Phase I and II Sketches
Questions, Concerns, Ideas
Concept Development and Proposed Design – Buck-boost
converters
Questions, Concerns, Ideas
Concept Development and Proposed Design – Battery charger
Questions, Concerns, Ideas
Concept Development and Proposed Design – Power
monitoring/management
Required Attendees
Dr. Lyshevski
Dr. Lyshevski
Dr. Lyshevski
Dr. Lyshevski
Dr. Lyshevski
Dr. Lyshevski
Dr. Lyshevski
Dr. Lyshevski
Dr. Lyshevski
Dr. Lyshevski
Dr. Lyshevski
Dr. Lyshevski
10:43
10:45
10:48
10:50
10:55
11:00
Control Diagram
Questions, Concerns, Ideas
Project Plan
Questions, Concerns, Ideas
Risk Assessment
Questions, Concerns, Ideas
Dr. Lyshevski
Dr. Lyshevski
Dr. Lyshevski
Dr. Lyshevski
Dr. Lyshevski
Dr. Lyshevski
Project Description
Expected Project Benefits:
Project Background:
Produce a clean, self-sustained photovoltaic energy
harvesting system from multiple input power sources.
A clean, self-sustained photovoltaic energy
harvesting system is the focus of this project.
Photovoltaics will be used to acquire the energy from
light and this energy will then be sent through an
energy management system to charge a battery or
drive a load.
Core Team Members:



Mike Grolling- EE- Energy Storage
Josh Stephenson-EE- Power Conditioning
Tom Praderio-EE- Power Management
Problem Statement:
Properly manage energy from multiple
sources to charge a battery and drive a load. The
team shall establish and then guarantee efficiency
parameters based on benchmark results. This will
require the team to investigate various applied
technologies, components, and modules to establish
engineering specifications. System and individual
module efficiencies shall approach that of
benchmarked modules where feasible.
Objectives/ Scope:
1.
2.
3.
4.
5.
6.
Generate (average) ~5 W of energy (rated).
Highly
efficient
photonic-to-electrical,
electrical-to-electrical
and
electrical-tophotonic energy conversions.
Superior light harvesting capabilities.
Sufficient energy storage abilities.
Robust voltage stabilization and distribution.
Energy management system with multiple
photovoltaic energy source types.
Deliverables:


Highly efficient energy conversion that meets
customer needs
A functioning portable prototype
Assumptions and Constraints:
The team must obtain a well-rounded understanding
of energy management and harvesting. By using
multiple inputs which have different loading
capabilities, a system must be in place to isolate low
voltage photovoltaics.
Issues & Risks:


Improper battery voltage regulation may lead
to permanent battery damage, swelling, or
explosions
Oversized solar cells may lead to excessive
heat dissipation through the parts and result
in shortened lifetimes or failure
Customer Needs
Customer
Need #
Importance
CN1
CN2
1
1
CN3
CN4
CN5
1
1
1
CN6
CN7
CN8
CN9
CN10
CN11
CN12
1
1
1
1
1
1
1
Description
Design will include safety and component failure
Ability to manage inputs from multiple power sources
Investigate and benchmark technologies, components and
modules
Engineer multiple concepts. Perform tradeoff analysis
System will integrate power management and load distribution.
Establish highly efficient energy conversion parameters and
design
System must manage energy source variability
Provide data acquisition points for future team's display design
System must be portable
System must include instructions for set-up and use
System must utilize Ascent Solar’s flexible solar modules
Adequate amount of energy storage
Comments/Status
Example: Li-ion Batteries (place in a wooden box when testing)
3-5 solar panel inputs/ do not load low voltage panels
Find efficient battery charging technology
Efficiency is dependent on light conditions
Example: clouds or night-time
Data acquisition is performed by the microcontroller
Ascent Solar competition requirement
Ascent Solar competition requirement
Ascent Solar competition requirement
Project Specifications
Spec. #
Importance
Source
Function
Specification (metric)
S1
1
Power
S2
S3
1
1
CN11
CN3,4,5,
7,8
CN5,7
V Stability
V out
S4
S5
S6
1
1
1
CN7
CN1, 7
CN12
I out
I out
Storage
S7
1
Ability to generate ~5W of energy
Voltage stabilization for battery charging
(~15V ±0.05V)
Output voltage to load of 10V
Full solar delivery, provide a max output
current of 0.5A
Peak output current will meet 5A max
Battery capacity is ~5 A-h
Power load to simulate future display
device at a constant 5W
Load/Display
S8
CN2
Input
S9
S10
CN3
CN4
All
All
S11
S12
S13
S14
S15
CN6
CN8
CN9
CN10
CN6
All
All
Unit of
Measure
Marginal
Value
W
V
V
A
A
A-h
14.95V15.05V
N/A
N/A
W
Multiple solar panels
Benchmark given component's
specifications
Weigh concepts for each function
Calculate, design, measure each
function
List DAQ points
V/A
User's manual
Efficiencies for each function
N/A
Ideal
Value
Comments/Status
5
Average power
15
10
Needs clarification
0.5
5
5
Choose an appropriate battery
5
5V-36V
/ 0A-1A
Efficiencies
N/A
N/A
Proposed Solution Diagrams
Phase 1
0V to 36V
10V
15V
Buck-Boost
Converter
Photovoltaic Panel
10V
Battery Charger
Load
Battery
SPI Bus Interface
Switch ON/OFF
control line
Microcontroller
Voltage and current
sensing circuitry
Figure 1: Single-source testing concept model
0V to 36V
Photovoltaic Panel
Buck-Boost
Converter
Phase 2
10V
15V
Photovoltaic Panel
Buck-Boost
Converter
10V
Battery Charger
Load
Battery
Photovoltaic Panel
Buck-Boost
Converter
Charging current
monitor
SPI Bus interface
Microcontroller
Voltage and current
sensing circuitry
Switch ON/OFF control
lines
Figure 2: Multiple-source concept model
Selection Criteria
Max charge current
Adjustable output
Number of cells supported
Efficiency
Load bypass
Overall Rank
Rating
+
0
+
+
Concept Selection - Battery charger
LTM4006
LM3420
Notes
Rating
Notes
4A
20mA
Preset values
No
4
0
4
96%
0
Yes
No
1
3
Rating
+
+
0
+
-
ADP3806
Notes
3A
Yes
95%
No
2
Table 1: Battery charging concept selection
Selection Criteria
Input voltage range
Output voltage range
Quiescent current
Efficiency at 250mA
Output disconnect
Overall Rank
Rating
+
+
Concept Selection - Buck Boost Converters
LTM4607
ADP1111
Notes
Rating
Notes
4.5V-36V
+
2V-30V
0.8-24V
+
3V-Vin
300uA
85% (12V)
Yes
0
No
1
2
Rating
0
+
+
0
SM74301
Notes
6V-95V
2.5V-Vin
92% (15V)
No
3
Table 2: Buck-boost converter concept selection
Selection Criteria
Voltage sense maximum
Sensor channels per chip
Power consumption
System complexity
Overall Rank
Rating
+
0
-
Concept Selection - Power Management
SM72441
Microconroller ADC (voltage division)
Notes
Rating
Notes
0 to DC supply
+
Depends on division resistors
8
+
24
50mW
+
on the order of uW
Complicated
0
Passive components needed
2
1
Table 3: Power Management concept selection
Rating
0
0
-
ADM1276
Notes
2V to 20V
1
One chip needed per sense line
3
Figure 3: Buck Boost Converter Application diagram
Figure 4: Battery Charger Application diagram
NC
NC
Note: Thermistors used as a precautionary measure against battery overheating
Figure 5: Microcontroller application diagram
3V Battery
Vcc1
From BBC Output Voltage Divider
ADC1
GPIO
From BBC Output Current Sense Amp
ADC2
From Charger Current Monitor
ADC3
MSP430F6638
Microcontroller SPI_MISO
From Load Output Voltage Divider
ADC4
SPI_MOSI
From Load Output Current Sense Amp
ADC5
SPI_CLK
ADC6
SPI_SS
ADC7
UART_TX
To PV Disconnect Switch
GPIO
ADC8
From BBC SPI Data Out
To BBC SPI Data In
To BBC SPI Clock
To BBC SPI XCO
RS232 Level
Shifter
To PC via RS232
UART_RX
GND
Note: All BBC lines will be duplicated for each buck-boost converter in the final design. The MSP430 will support up to eight BBC’s.
Data Acquisition Points




Output of each photovoltaic panel
o Voltage and current are measured internally by each buck-boost converter
o Data is reported to the microcontroller via an SPI serial bus
Output of each buck-boost converter
o Current is measured by a LTC6102 current sense amplifier
o Voltage is measured by a high-impedance simple voltage divider
o Data is reported to the microcontroller via an ADC channel
Battery charger output
o Measured internally by the battery charger
o Data is reported to the microcontroller via an ADC channel
System output/load
o Current is measured by a LTC6102 current sense amplifier
o Voltage is measured by a high-impedance simple voltage divider
o Data is reported to the microcontroller via an ADC channel
Figure 6: Microcontroller software algorithm for photovoltaic power management
Figure 7: Current Sensing solution application diagram
Action Item
Learn PCB Express
System Design
Review
Order Samples
TI Competition App
Choose devices
Design Passive Comp
Cadence Schematic
Psuedo Coding
BOM
Detailed Review
Update BOM
Order Parts
Contact Ascent Solar
Test Samples
Week 8
Week 9
Week 10
Week 11
Fall Break
Severity
Importance
Table 4: Senior Design I Time Line
Risk Assessment
ID
1
Risk Item
Effect
Cause
Team runs out of
time
Project doesn't get
finished
Poor project
planning
Likelihood
2
5
Action to Minimize
Risk
Follow timeline and
10 manage weekly
updates
2 Parts arrive late
Schedule is delayed
Unreliable
vendor
2
3
Constant
6 communication with
Vendor
Prototype draws too
3 much power or is
inefficient
Photovoltaics
produce
4
insuffient/minimum
power
Poor battery
life/does not meet
customer spec
Poor choice of
technology
1
3
3
Choose low power/high
efficiency electronics
Very low efficiency
and power
generation
Poor pairing of
solar cells with
DC/DC Conv.
2
5
9
Examine energy curves
for different solar cells
Buck Boost converter
incapable of blocking
5
reverse bias
conditions
reverse currents will
drastically lower
efficiency and may
compromise
operation or damage
solar cells
Poor isolation of
energy sources
7
Place diode across each
8 solar cell to dissipate
reverse emf
Internal electronics
produce too much
6
heat/ambient temp
too high
Electronics overheat;
inefficient
Poor choice of
electronics or
casing;
unrealistic goals
2
2
Choose low power
4 electronics with wide
operating temp range
Internal electronics
7 do not produce
acceptable signals
Redesign/ project
goals not met
Low margins of
safety/ high-risk
technology
2
3
6
Work with electronics
that are acceptable
1
8
Requirements change
during the project
Project will not be
able to change in
time
Redesign
required
1
5
5
Verify deliverables with
customer
9
Teammates do not do
assigned work
Team will need to do
the work for the
teammate
Laziness/ not
enough time
1
3
6
Ask for help with
needed
Team will be delayed
and work will be
postponed
Laziness/ not
enough time
2
Assign tasks that have a
4 high likelihood of being
completed
Teammates do not
10
arrive prepared
2
Inability to contact
11 the customer or
guide
May miss vital
information and
requirements
Poor
Communication
2
2
Keep constant info flow
4 with the customer and
guide
Getting wrong
12 information from
customer
Lead to solving an
issue that doesn't
exist
Poor
Communication
2
3
6
Set up meeting s and
communicate often
Arguments between
13
teammates
Will hurt team
morale and cause
conflict between
members
Poor
Communication
2
2
4
Have group focused
and group leader aware
Microcontroller not
14 fast enough to
manage power
Power management
will be ineffective
Poor part
selection
2
2
Microcontroller
5 selected with
appropriate speed
Microcontroller code
15 does execute
properly
Power management
will be ineffective
Poor coding
4
7
8
Code will be thoroughly
tested and debugged