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

Experiment 1 Direct Energy Transfer System Model PV panel Investigate direct energy transfer system behavior Investigate effects of shading Observe behavior of lead-acid battery

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

Experiments 4 and 5 Add Inverter to System 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

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

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 (*) Charge separation Electric field created by diode structure separates holes and electrons Open circuit voltage Voc depends on diode characteristic, Voc < Egap/q

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

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.

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

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

Direct Energy Transfer

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.

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

Bypass Diodes Bypass diodes: Limit the voltage drop across reverse- biased cells or strings of cells Reduce the power consumption of reverse-biased cells

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

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

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.

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

Upcoming assignments Experiment 1: PV DET system 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

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.