CoPEC
Training Electrical Engineers for
Renewable Energy Challenges
Dragan Maksimovic
ECE Department
University of Colorado at Boulder
maksimov@colorado.edu
Background
CoPEC
• Growing interest in Energy Engineering
Environmental and climate change concerns
ƒ Energy independence goals
ƒ A new frontier in Engineering: challenging problems,
opportunities for innovation, entrepreneurship, and
rewarding careers
ƒ
IEEE PELS 2008 Symposium
2
Background
CoPEC
• Growing interest in Energy Engineering
Environmental and climate change concerns
ƒ Energy independence goals
ƒ A new frontier in Engineering: challenging problems,
opportunities for innovation, entrepreneurship, and
rewarding careers
ƒ
9,212 solar panels,
1,600 kW solar
power system at the
Google campus,
Mountain View, CA
IEEE PELS 2008 Symposium
http://www.google.com/corporate/solarpanels/home
3
CoPEC
A New Frontier in Engineering
• New Priorities: “for some job seekers, oil companies are out. Alternative-energy startups are the place to be …” The Wall Street Journal, Oct. 29, 2007, p. R8
• “Greentech could be the largest economic opportunity of the 21st century,” KPCB
Venture Capital, http://www.kpcb.com/initiatives/greentech/index.html
IEEE PELS 2008 Symposium
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CoPEC
Training of Electrical Energy Engineers
• Electrical Engineering started as electric power engineering;
up to 1970’s EE curricula were dominated by traditional
electric power topics
• Over the last 30-40 years, the traditional electric power
theme has diminished in EE/ECE programs
ƒ
Mature technology
ƒ
Fewer research funding opportunities
ƒ
Fewer attractive engineering career options
ƒ
Rapid emergence of many other EE and ECE areas
• Electrical Engineering is now at the core of many existing
and emerging green energy technologies
ƒ
How should we (re)organize EE programs to address the growing
interests, as well as current and anticipated needs?
IEEE PELS 2008 Symposium
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CoPEC
What is Electrical Energy Engineering?
• In the late 19th century Electrical Engineering started the
revolution in generation, transmission and distribution of
Electric Power
Nikola Tesla
Polyphase ac power distribution, and motors/generators based on rotating magnetic field
• In the 20th century, Electrical Engineering revolutionized
Communication and Computing
William Shockley, John Bardeen,
Walter Brattain
Transistor, Bell Labs, Dec 1947
2007 quad-core processor, more
than 500 million transistors
• 21st century Electrical Energy Engineering is
all of the above, and more
IEEE PELS 2008 Symposium
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CoPEC
Electrical Energy Engineering program
at CU Boulder
http://ece.colorado.edu/~ecen2060/energyprogram.html
Sophomore
ECEN2060
Renewable Sources
and Efficient
Electrical Energy
Systems
Junior
ECEN3170
Energy
Conversion
Senior
Graduate
ECEN4797/5797
Intro to Power
Electronics
ECEN5807
Model. and Control of
Power Electronics
ECEN4517/5517
Power Electronics and
PV Systems Lab
ECEN5817
Resonant and Soft
Switch Tech. in
Power Electronics
ECEN4167
Energy Conversion 2
ECEN5017
Conventional
and Renewable
Energy Issues
+EE/ECE fundamentals:
Circuits and microelectronics, semiconductor devices, IC design, EM fields,
programming, digital logic, embedded computing, communications/DSP, control systems
Faculty:
Frank Barnes, Robert Erickson, Ewald Fuchs, Dragan Maksimovic, Regan Zane
IEEE PELS 2008 Symposium
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CoPEC
Electrical Energy Engineering program
at CU Boulder
http://ece.colorado.edu/~ecen2060/energyprogram.html
Sophomore
ECEN2060
Renewable Sources
and Efficient
Electrical Energy
Systems
Junior
ECEN3170
Energy
Conversion
Senior
Graduate
ECEN4797/5797
Intro to Power
Electronics
ECEN5807
Model. and Control of
Power Electronics
ECEN4517/5517
Power Electronics and
PV Systems Lab
ECEN5817
Resonant and Soft
Switch Tech. in
Power Electronics
ECEN4167
Energy Conversion 2
ECEN5017
Conventional
and Renewable
Energy Issues
• New introductory sophomore-level course, first offered in Spring 2008
• Spring 2008 enrollment: 31 students, 2 non-credit continuing education
• Minimal prerequisites, strong technical contents
• Instructors:
Dragan Maksimovic, Robert Erickson, and Regan Zane
IEEE PELS 2008 Symposium
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CoPEC
ECEN 2060 Objectives and Outline
Introduction to Electrical Energy Engineering
Improve generation
Reduce consumption
Renewable Energy
Sources
Energy Efficiency
• Photovoltaic power
systems
• Wind power systems
Transmission,
Distribution,
Conversion
and
Storage
• Energy efficient lighting
• Drives in hybrid and
electric vehicles
• Understanding of electrical engineering fundamentals in renewable sources and
energy efficient systems
• Practical knowledge of engineering design issues in system examples
• Background and motivation for follow-up studies
IEEE PELS 2008 Symposium
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ECEN 2060 Syllabus
CoPEC
http://ece.colorado.edu/~ecen2060
• Introduction to electric power
system
• Photovoltaic (PV) power systems
• Energy efficient lighting
• Wind power systems
• Hybrid and electric vehicles
IDC
3øac
øa
n T
Permanentmagnet
synchronous
machine
+
vab(t)
–
øb
ia(t)
Q1
v (t)
ib(t) A A0
B
+
Q5
Q3
vB0(t)
+
–
vC0(t)
VDC
C
øc
Q2
Q4
Q6
–
ic(t)
0
IEEE PELS 2008 Symposium
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ECEN 2060 Syllabus, Spring 2008
CoPEC
• Electric Power System (4 lectures)
ƒ
ƒ
ƒ
Electric utility industry, generation and consumption statistics, cost of electricity
Overview of electricity generation: power plants and polyphase generators
Transmission and distribution of electricity, the US electric power grids
• Photovoltaic Power Systems (16 lectures)
ƒ
ƒ
ƒ
ƒ
ƒ
The solar resource
PV cell physics and efficiency limits, PV technologies, and PV cell electrical model
Grid-connected PV systems
Power electronics
Stand-alone PV systems and lead-acid batteries
• Energy Efficient Lighting (5 lectures)
ƒ
ƒ
ƒ
Lighting technologies, luminous efficiency and cost of lighting
Electronic ballasts for discharge lamps
Solid-state lighting and LED drives
• Wind Power Systems (10 lectures)
ƒ
ƒ
ƒ
ƒ
ƒ
The wind resource and efficiency limits, overview of wind turbines
Wind turbine electrical systems: constant-speed and variable-speed architectures
AC machines
3-phase power electronics
Guest lecture on wind turbine electrical systems and controls by Lee Jay Fingersh (NREL)
• Hybrid and Electric Vehicles (6 lectures)
ƒ
ƒ
ƒ
ƒ
HEV power train architectures: series, parallel and series/parallel
Batteries for HEV, PHEV and EV
Variable-speed AC drives
Operation and sizing of system components
IEEE PELS 2008 Symposium
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CoPEC
ECEN2060 topic example: PV systems
Grid-tie PV power system example
iL
IPV
+
PV
array
L
+ vL −
idc
it
VPV
Cpv
−
−
+
+
+
vt
iac
C
VDC
Single-phase
DC-AC
inverter
AC
vac utility
grid
−
−
vgate
DTs
MPPT controller
•
•
•
•
IEEE PELS 2008 Symposium
Ts
Inverter controller
What is it and how does it work?
Basic physics
Operation and engineering of system components
System engineering and economics
12
(1) Fundamentals of PV technology
CoPEC
• Basic semiconductor
and PV cell physics;
limits of efficiency
• Overview of PV
technologies,
crystalline Si, thin
film, etc
1.8
Full sun: 1,000 W/m2
AM1.5
1.6
Power density p(lambda) [W/m^2/nm]
Ideal photovoltaic output
1.4
Photoelectric output power (ideal):
1.2
λmax
∞
I PV =
1.0
∫p
pv (λ ) dλ
=
0
∫p
= 490 W/m 2
300 nm
η max =
0.8
pv (λ ) dλ
• PV cell circuit model
and characteristics
0.6
IPV
I PV
= 49%
IS
ISC
ID
VD
Rs
Rp
+
VPV
_
0.4
PV cell
0.2
0.0
0
500
1000
1500
2000
2500
Wavelength [nm]
IEEE PELS 2008 Symposium
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(2) PV modules and arrays
CoPEC
• Module and array
characteristics
+
PV
array
idc
+ vL −
it
vt
Cpv
iac
+
+
+
VPV
−
• Maximum power
point (MPP)
L
iL
IPV
Single-phase
DC-AC
inverter
VDC
C
−
AC
vac utility
grid
−
−
vgate
DTs
• Effects of shading
Ts
MPPT controller
Inverter controller
Characteristics of an array of twenty 75 Wp modules (36-cell each) in series
10
1,000 W/m2
(uniform)
1600
3
9
Ppv [W]
1400
2
8
1200
7
Ipv [A]
1000
Ppv [W]
Ipv [A]
6
5
4
900 W/m2
(partial
shading)
800
600
200 W/m2
(uniform)
3
400
2
0
200
1
1
0
50
100
150
Vpv [V]
Vpv [V]
IEEE PELS 2008 Symposium
200
250
0
0
50
100
150
200
250
Vpv [V]
Vpv [V]
14
(3) PV power electronics
CoPEC
10
• Basic operation of
DC-DC converters
and DC-AC inverters
η boost = 96%
3
Ipv [A]
9
8
η boost
= 922%
7
Boost DC-DC
efficiency analysis in
the PV system
• Overview of power
semiconductor
switches
Boost DC-DC converter
averaged model
IPV RL
5
4
3
2
1−D : 1
1
1
+
• Basic averaged
models and efficiency
analysis
Ipv [A]
6
0
VPV
−
0
50
Isw
η boost = 92%
Iout
+
100
VDCVpv [V]
−
150
200
250
Vpv [V]
Boost DC-DC waveforms
iL
IPV
+
PV
array
L
+ vL −
idc
it
VPV
−
Cpv
−
+
+
+
vt
iac
C
VDC
Single-phase
DC-AC
inverter
AC
vac utility
grid
−
−
vgate
DTs
MPPT controller
Ts
Inverter controller
Grid-tie PV system using Boost DC-DC MPP tracker
IEEE PELS 2008 Symposium
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(4) PV system controls
CoPEC
MPP
500
Ppv
Initialize Iref, ΔIref, Pold
450
400
350
300
Measure Ppv
250
200
150
YES
100
Ppv > Pold ?
50
0
0
1
2
3
4
5
6
Ipv = Iref
• Perturb and observe maximum
power point tracking algorithm
• DC-AC inverter controls
• DC bus voltage control
• AC grid current shaping;
unity power factor
IEEE PELS 2008 Symposium
NO
Change
direction
Continue
in the
same
direction
ΔIref = −ΔIref
Iref = Iref +ΔIref
Pold = Ppv
16
(5) PV system design and economics
CoPEC
Insolation data: http://rredc.nrel.gov/solar/codes_algs/PVWATTS/
• Solar resource
US “hours of
full sun” map
kWh
m2 day
• System sizing and
basic economics
• Example: a grid-tie
system in Boulder
• Average of 5.5
hours or full sun
iL
IPV
+
PV
array
L
+ vL −
idc
it
VPV
−
Cpv
−
+
+
+
vt
iac
C
VDC
Single-phase
DC-AC
inverter
−
−
vgate
DTs
MPPT controller
IEEE PELS 2008 Symposium
AC
vac utility
grid
Ts
Inverter controller
• 1 Wp (Watts peak)
installed produces
about 1.5 kWh per
year
• Cost: about $8/Wp
(excluding
incentives)
17
ECEN2060 observations
CoPEC
• Energy systems rich in EE contents (e.g. PV, Wind,
Hybrid and Electric Vehicles) are great motivators for
students in an introductory class
• This is not just a survey class: it is possible to introduce
electrical energy engineering topics in significant
technical depths even in an introductory class
ƒ
Basic physics, materials and components
ƒ
Power electronics and electric machines
ƒ
System controls, system design and economics
• Curriculum revisions are under way to open space for
attractive introductory courses such as ECEN2060 at the
sophomore level
IEEE PELS 2008 Symposium
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CoPEC
Electrical Energy Engineering program
at CU Boulder
http://ece.colorado.edu/~ecen2060/energyprogram.html
Sophomore
ECEN2060
Renewable Sources
and Efficient
Electrical Energy
Systems
Junior
ECEN3170
Energy
Conversion
Senior
Graduate
ECEN4797/5797
Intro to Power
Electronics
ECEN5807
Model. and Control of
Power Electronics
ECEN4517/5517
Power Electronics and
PV Systems Lab
ECEN5817
Resonant and Soft
Switch Tech. in
Power Electronics
ECEN4167
Energy Conversion 2
ECEN5017
Conventional
and Renewable
Energy Issues
• Major course revision in Spring 2008
• Spring 2008 enrollment: 33 undergraduates, 11 graduate students
• Objectives: hands-on design and project experience
• Instructors:
Robert Erickson, Regan Zane and Dragan Maksimovic
IEEE PELS 2008 Symposium
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ECEN4517/5517
CoPEC
Power Electronics and PV Systems Lab
http://ece.colorado.edu/~ecen4517
The course begins with basic experiments on:
• Photovoltaic power systems
• Power conversion electronics
The course then culminates in a design
project involving photovoltaics and power
electronics
PV panels, battery, and inverter in the ECEN 4517 laboratory
DC loads
PV
Panel
85 W
Charge control
DC-DC converter
for maximum power
point tracking and
battery charge profile
Battery
Deepdischarge
lead-acid
12 V, 56 A-hr
Inverter
AC
loads
120 V 60 Hz
300 W
true sinewave
Digital control
A basic standalone PV power system in the ECEN 4517 laboratory
IEEE PELS 2008 Symposium
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CoPEC
ECEN4517/5517 Syllabus
1. Basic PV system elements (1 week)
2. Basic converter control circuitry and pulse-width modulator
(1 week)
Buck converter
+
3. Battery charge controller
and PV peak power tracker
using a DC-DC buck
converter (3 weeks)
4. Inverter system (3 weeks)
5. Project (6 weeks)
ECE Expo
PV
–
+
L1
vpv
C2
C1
–
ibatt
vbatt
–
High side
gate driver
Bootstrap
power supply
Pulse-width
modulator
Experiment 3
12 VDC
Battery
+
Micro
controller
Peak power
tracking and
battery
charge
control
Sensors
Battery
current and
voltage
HVDC: 120 - 200 VDC
DC-DC
converter
DC-AC
inverter
+
Isolated
flyback
H-bridge
vac(t)
AC load
120 Vrms
60 Hz
–
d(t)
Feedback
controller
d(t)
–+
Vref
Digital
controller
Experiment 4
IEEE PELS 2008 Symposium
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Portable PV carts
• 85 W PV panel that can be
wheeled outside
• Deep discharge lead-acid
battery and 300 W inverter
to power test equipment
• Auxiliary DC power supplies
for control circuitry
• One cart per bench, 10 total
Inverter
60 Hz 300 W
120 Vrms
+
PV panel
85 Wpk
Ds
+
6 outlet
ac power strip
PV
panel
17.2 V at 4.95 A
Shell SQ-85P
–
Battery
12 V
deep-discharge
56 A-hr
Alarm
Battery low voltage
–
Voltmeter
Battery voltage
+
Battery
Connectors
CoPEC
–
+
– 12V, 1A
Battery
charger
+
– 12V, 1A
Off cart:
on stationary workbench
Cart schematic
+
– 5V, 2A
Isolated
dc-dc
converters
DC loads
PV
Panel
85 W
Charge control
DC-DC converter
for maximum power
point tracking and
battery charge profile
Battery
Deepdischarge
lead-acid
12 V, 56 A-hr
Inverter
AC
loads
120 V 60 Hz
300 W
true sinewave
Digital control
IEEE PELS 2008 Symposium
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CoPEC
IEEE PELS 2008 Symposium
Experiment 1, Jan. 22-24, 2008
23
ECE Expo, May 1, 2008
CoPEC
MPP tracker based on
digitally controlled Cuk
DC-DC converter
(April 26 College of
Engineering Expo)
20 projects
in power electronics
for PV or energy
efficiency
IEEE PELS 2008 Symposium
Electronic ballast for fluorescent lamps
Cascaded boost
DC-DC
converter
(battery to highvoltage DC
conversion)
24
Research Program
CoPEC
Colorado Power Electronics Center (CoPEC)
13 sponsoring companies, 25 graduate students, Faculty: R.Erickson, D.Maksimovic, Z.Popovic, R.Zane
Smart Power Electronics Technology
• Analog, mixed-signal and digital control techniques
• Mixed-signal integrated circuits for power control
• Converter modeling and design
Energy
Harvesting
Power
Electronics for
Renewable
Energy
Energy Efficiency
Lighting
Switched-mode
power supplies
• Ballasts
• LED
drives
Power for RF
systems
Ipv, Vpv
PV
Ipv, Vpv
Ipv, Vpv
Converter
PV
Controller
Ipv, Vpv
Ipv, Vpv
Converter
Controller
Ipv, Vpv
PV
Converter
PV
Converter
Ipv, Vpv
Controller
Ipv, Vpv
Controller
Converter
PV
Converter
Controller
Ipv, Vpv
Controller
Inverter
Medical systems
Ipv, Vpv
PV
•
•
•
•
•
IEEE PELS 2008 Symposium
PFC
Isolated DC-DC
POL DC-DC
Multi-phase
Low-power
Ipv, Vpv
60 Hz AC
Utility
Ipv, Vpv
25
Conclusions
CoPEC
• Electrical Energy Engineering at CU Boulder
ƒ
ƒ
ƒ
ƒ
EE/ECE fundamentals + materials/devices + systems + economics
More interdisciplinary than other EE areas
Emphasis on technical and engineering fundamentals, even in
introductory courses with minimum prerequisites
Motivated students
• Department strengths and new initiatives
ƒ
ƒ
ƒ
ƒ
ƒ
Energy is a major area of emphasis in the ECE Department
CoPEC research program: very strong industrial support
Related strengths in control systems, remote sensing, materials and
devices, RF/microwave electronics
CU/CSU/CSM/NREL CREW: Colorado Renewable Energy
Collaboratory Center for Research and Education in Wind
Campus-wide energy initiative
IEEE PELS 2008 Symposium
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