ECEN 4517
ECEN 5517
POWER ELECTRONICS AND PHOTOVOLTAIC
POWER SYSTEM LABORATORY
http://ece.colorado.edu/~ecen4517
• Photovoltaic power systems
• Power conversion and control electronics
Prerequisite: ECEN 4797 or ECEN 5797
Instructor: Prof. Bob Erickson
Power Electronics Laboratory
1
Lecture 1
Experiment 1
Direct Energy Transfer System
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Model PV panel
Investigate direct energy transfer system behavior
Investigate effects of shading
Observe behavior of lead-acid battery
Power Electronics Laboratory
2
Lecture 1
Experiments 2 and 3
Maximum Power Point Tracking
• Design and construct dc-dc converter
• Employ microcontroller to achieve maximum power point tracking
(MPPT) and battery charge control
Power Electronics Laboratory
3
Lecture 1
Experiments 4 and 5
Add Inverter to System
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Build your own inverter system to drive AC loads from your battery
Step up the battery voltage to 200 VDC as needed by inverter
Regulate the 200 VDC with an analog feedback loop
Change the 200 VDC into 120 VAC
Power Electronics Laboratory
4
Lecture 1
Mini-Project
ECEE Expo Competition
• Operate your
complete system
• Competition during
ECEE Expo: capture
the most energy with
your system outside
A previous year’s competition poster
Power Electronics Laboratory
5
Lecture 1
Development of Electrical Model
of the Photovoltaic Cell, slide 1
Photogeneration
Semiconductor material absorbs photons and
converts into hole-electron pairs if
Photon energy hn > Egap
(*)
• Energy in excess of Egap is converted to
heat
• Photo-generated current I0 is proportional to
number of absorbed photons satisfying (*)
photon
+
–
Charge separation
Electric field created by diode structure separates holes and electrons
Open circuit voltage Voc depends on diode characteristic, Voc < Egap/q
Power Electronics Laboratory
6
Lecture 1
Development of Electrical Model
of the Photovoltaic Cell, slide 2
Current source I0 models photo-generated current
I0 is proportional to the solar irradiance, also called the “insolation”:
I0 = k (solar irradiance)
Solar irradiance is measured in W/m^2
Power Electronics Laboratory
7
Lecture 1
Development of Electrical Model
of the Photovoltaic Cell, slide 3
Diode models p–n junction
Diode i–v characteristic follows classical
exponential diode equation:
Id = Idss (elVd – 1)
The diode current Id causes the terminal
current Ipv to be less than or equal to the
photo-generated current I0.
Power Electronics Laboratory
8
Lecture 1
Development of Electrical Model
of the Photovoltaic Cell, slide 4
Modeling nonidealities:
R1 : defects and other
leakage current mechanisms
R2 : contact resistance and
other series resistances
Power Electronics Laboratory
9
Lecture 1
Cell characteristic
Cell output power is Ppv = IpvVpv
At the maximum power point
(MPP):
Vpv = Vmp
Ipv = Imp
At the short circuit point:
Ipv = Isc = I0
Ppv = 0
At the open circuit point:
Vpv = Voc
Ppv = 0
Power Electronics Laboratory
10
Lecture 1
Direct Energy Transfer
Power Electronics Laboratory
11
Lecture 1
Maximum Power Point Tracking (MPPT)
• MPPT adjusts DC-DC converter conversion ratio M(D) = Vbatt/Vpv such
that the PV panel operates at its maximum power point.
• The converter can step down the voltage and step up the current.
• Battery is charged with the maximum power available from the PV panel.
Power Electronics Laboratory
12
Lecture 1
Series String of PV Cells
to increase voltage
• To increase the voltage, cells are connected
in series on panels, and panels are
connected in series into series strings.
• All series-connected elements conduct the
same current
• Problems when cells irradiance is not
uniform
Power Electronics Laboratory
13
Lecture 1
Bypass Diodes
Bypass diodes:
• Limit the voltage drop across reversebiased cells or strings of cells
• Reduce the power consumption of
reverse-biased cells
Power Electronics Laboratory
14
Lecture 1
Apparent path of sun through sky
Baseline Rd. is 40˚N
Times are not
corrected for
location of Boulder
in Mountain Time
Zone
Net panel irradiation
depends on cos(j)
with
j = angle between
panel direction and
direction to sun
So take your data
quickly
Power Electronics Laboratory
15
Lecture 1
Experiment 1
Experiment 1: Photovoltaic System
Characterize the SQ-85 PV panels, and find numerical values of model
parameters for use now and later in semester
Test the inverter provided
Charge the battery from the panel, using the Direct Energy Transfer method
Hope for sun!
Experiment 1 to be performed next week
Final report for Exp. 1 due in D2L dropbox by 5:00 pm on Friday Jan. 29
Power Electronics Laboratory
16
Lecture 1
Lab Format
Two-person groups, up to 10 groups per section
This week: lab organizational meetings
Parts kits:
Available from E Store
One kit needed per group
Cost: $180. Contains power and control electronic parts needed for
experiments.
You will also need other small resistors etc. from undergraduate
circuits kit
Lab:
Access via CUID card reader
Computer login via CU Identikey
You may optionally store your parts in your own locked drawer in your lab
bench. Lock and key deposit for the semester at E Store.
Power Electronics Laboratory
17
Lecture 1
Lab reports
• One report per group. Include names of every group
member on first page of report.
• Report all data from every step of procedure and
calculations. Adequately document each step.
• Discuss every step of procedure and calculations
– Interpret the data
– It is your job to convince the grader that you understand
what is going on with every step
– Regurgitating the data, with no discussion or interpretation,
will not yield very many points
– Concise is good
Power Electronics Laboratory
18
Lecture 1
Upcoming assignments
Experiment 1: PV DET system
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Do Exp. 1 in lab next week
Exp. 1 report due in D2L dropbox by 5:00 pm on Friday Jan. 29.
One report per group
Experiment 2: Intro to MSP430 microcontroller
• Do Exp. 2 in lab during week of Jan. 26-28
• Exp. 2 scoresheet initialed by your TA and uploaded to D2L by 5:00
pm on Friday Jan 29
Experiment 3: Buck MPPT converter
• Exp. 3 prelab assignment due in D2L dropbox by 12:00 pm on
Tuesday Feb. 2: Buck converter power stage design.
• Start Exp. 3 during week of Feb. 2-4
Power Electronics Laboratory
19
Lecture 1
Required Work
Your course grade will be based on the following:
Prelab assignments
Lab final reports
Quizzes
Project proposal and report
Expo
Attendance and lab performance
Assignments are due in the appropriate D2L dropbox at the times listed in
the course schedule page. Late assignments will not be accepted.
Weightings for assignments are listed in the course D2L site.
Power Electronics Laboratory
20
Lecture 1