Transcript Summary Lecture - IEEE Real World Engineering Projects

Pico Power Generation for
the Developing World
(Summary Lecture)
Loren Wyard-Scott 1 *
&
Dr. James Andrew Smith 2 *
1
Dept. of Electrical & Computer Engineering
University of Alberta
Edmonton, Alberta, Canada
2
Dept. of Electrical & Computer Engineering
Ryerson University
Toronto, Ontario, Canada
*
Member, IEEE
Outline
•
•
•
•
The Project’s Objectives
Improving the Design Process
Using Technology Closer to its Potential
Super Capacitor Discharging and
Charging
• Knowing the Measurement Tools
• Conclusion
The Project:
Scenario & Goals
• Scenario
– A remote village of 500
people
– No night-time electricity
– Have small low-power
lamps
• Objective
– Build a small power source
– 30 minute lamp operation
– Preferably human-powered
– Night-time discharging
Bas-Ravine, Haiti
The Project’s Objectives
• Were these goals simple to meet?
• Is your project a Success? A Failure?
Do you have enough information to answer these questions? You
are on the path to a solution, but there is still a lot of work to do!
• Many of you may have found that the objectives are
under-specified.
–What process did you go through to better specify your project?
• Designing and evaluating often requires groups to work
in “the grey”.
Improving the Design Process
•
•
Did you get lost on the way to finding a
solution – in “the grey”?
Finding a good solution to any real-world
problem requires:
1. Understanding the problem – from many
perspectives! (e.g. users, manufacturers)
2. Understanding what technology is available
(always changing!): “Product Knowledge”
3. Understanding the principals of operation of
the technologies used.
Improving the Design Process
•
•
Finding your way through any of these three
items can be challenging. It gets simpler with
experience (like this project)!
Tools and protocols that can help:
1.
2.
3.
4.
5.
6.
Correlation matrices: Understanding Design Trade-offs
State Diagrams
Block Diagrams
Multi-discipline Design Teams
Critical Design Review
Putting the Project Through its Paces: Testing
Design: Correlation Matrices
• Real design problems always have tradeoffs. “Cheap, fast, good: pick two.”
• To help understand the tradeoffs and how
they will affect the outcome is important.
• A tool that helps understand the tradeoffs
is a “Correlation Matrix”.
Design: Correlation Matrices
More Storage
Capacity
More Storage
Capacity
User Convenience
Low Cost
User
Convenience
Low Cost
+++
--
(highly positive)
(quite negative)
N/A
Design: Characterizing System
States
A state diagram can help characterize the system!
Design: Block Diagram
• Block diagrams are a great way to
communicate your ideas to fellow designers.
• They provide a simple view of what could be a
complicated system.
Design: Multi-Discipline Design Teams
• Almost every real-world project involves more
than one field of technology.
• Teams that have a wider set of experiences and
knowledge to draw from are typically more
successful.
• Commonly required skill sets:
–
–
–
–
–
–
–
electrical
mechanical
manufacturing
industrial design
technical writing
financial
resource management
Design: Critical Design Review
• In practice it is not always possible to develop a
team that has all skill sets covered.
• A Critical Design Review (CDR) is a standard
stage of project design that can help offset this
lack.
• Once a (usually paper-based) design is
complete, the design is reviewed by people from
all walks of life, including experts.
• The feedback is used to improve the design, or,
in some cases, terminates it: “go” or “no go”.
Design: Testing
• Testing a new product is a complicated
process.
• There are discipline- and technologyspecific courses and books dedicated to
testing.
• Companies that do nothing but this aspect
of project development exist.
• Ensure that the end-user has a chance
to use a product candidate!
Using Technology Closer to its
Potential
• Understanding the options that are at your
disposal when designing is important:
“Product Knowledge” gained from reading
trade publications, journals, etc.
• Your education provides you with the tools
to understand how particular technology
works.
• Device datasheets are key to
understanding the capabilities of a device.
Technology: Options
• On-going developments in science, engineering
and manufacturing are leading to amazing
advances in energy generation, storage and
distribution.
• Keeping an eye on new developments is critical!
• For instance, new storage technologies can
allow power generated during the daytime to be
stored more effectively for night-time use!
– Batteries are not the only way to store electricity
– Capacitors and fuel cells are becoming alternatives
Technology: Options
Source: http://en.wikipedia.org/wiki/Supercapacitor, accessed 29 March 2008.
Technology: Options
Capacitor Technology
Source: http://en.wikipedia.org/wiki/Supercapacitor, accessed 29 March 2008.
Technology: Options
• Adding key components can
boost your device’s
performance substantially!
– Capacitor filters on rectifiers
make the voltage more usable
• Component optimization can
make a design even more
effective
– Tuning the capacitor value
allows optimal performance for
certain generator input speeds
Technology: Options
• Hopefully this has demonstrated to you
that
–Understanding what devices are available;
and
–Understanding how these devices operate
both come into play during design.
Super Capacitor Discharging and
Charging
You may have noted a few things while
testing your design:
– the LED remains on for longer than you
expected;
– there is no (easily) definable time that the
LED turns off – it slowly fades; and
– it takes less time to charge the super
capacitor than to discharge it.
All of these observations have a common
component: time.
Super Capacitor Discharging and
Charging
• Capacitors do not provide a constant voltage until there
is no energy left.
• The decay in the voltage is actually exponential and is
given by:
Vc (t )  Vstart  Vfinish e
t

 Vfinish
where Vstart is the voltage at t=0, Vfinish is the final
(steady-state) voltage, and  is known as the time
constant of the circuit. (You will see a lot more about
time constants in every field of engineering.)
Super Capacitor Discharging and
Charging
• For a circuit with a resistor and a capacitor,
  RC
• The next slide shows a plot of Vc(t) with Vstart = 5V, and
Vfinish=2.0V for two different time constants.
• Why is Vfinish set to 2.0V? (What is the forward voltage
drop of an LED?)
• Can you explain why charging of the capacitor is
quicker than discharging?
Super Capacitor Charging and
Discharging
5
4.5
4
Vc(t)
3.5
Larger Time Constant
3
2.5
2
Smaller Time Constant
1.5
1
Time
Note that real capacitors have a resistance, potentially increasing the time
constant!
Knowing the Measurement Tools
• It is always important to understand the
capabilities and limitations of the test equipment
and measurement processes.
• Understanding these bounds while constantly
asking “is what we are observing consistent with
what we know?” is important to any scientific
process.
Conclusion
• Conventional, limited, sources of energy
are being taxed more heavily as the world
population increases.
• As a result, environmentally- and energyconscious designs are now of paramount
importance.
• The system you developed here has
taught you how some of the emerging
technologies operate.
Conclusion
• You have learned a lot about the design
process, and have hopefully enjoyed yourselves
while doing so.
• Successful completion of the project itself, Pico
Power Generation for the Developing World, will
see underprivileged peoples provided with a
safe power generation and storage system that
can be used to expand their opportunities by
improving productivity and literacy.
For more information
• Light Up The World (LUTW)
– http://www.lutw.org/
• Bicycle Dynamo Rectifiers & Filters
– http://pilom.com/BicycleElectronics/DynamoCircuits.htm
• Super Capacitors
– http://en.wikipedia.org/wiki/Supercapacitor
• Micro Hydro Installations
– http://www.green-trust.org/hydro.htm