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CU-Boulder ECEN 4517 - Direct Energy Transfer System

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POWER ELECTRONICS AND PHOTOVOLTAIC POWER SYSTEM LABORATORY ECEN 4517 ECEN 5517 http ece colorado edu ecen4517 Photovoltaic power systems Power conversion and control electronics Prerequisite ECEN 4797 or ECEN 5797 Instructor Prof Bob Erickson TAs Dongxui Li Alex Brissette Andy Hoke 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 Power Electronics Laboratory 1 Lecture 1 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 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 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 Solar Power o p x E d n a n io t i Compet Thursday 4 30 9 a m to noon Herbst Plaza CU Engr Center Featuring Photovoltaics and Power Electronics Laboratory Classes ECEN 4517 and 5517 Awards given to the stand alone solar power system demonstrating the highest efficiency and energy capture Previous year s competition poster Power Electronics Laboratory 5 Lecture 1 Photovoltaic Cell Technologies Wafer based silicon Single crystalline Most of production to date High efficiency but high cost Cut from ingot with saw Needs 20 kg Si per 1 kWpk Multi crystalline Cut from cast polysilicon ingots Cheaper than single crystalline a few percent less efficient Both are normally p n devices 2 Photovoltaic Cell Technologies Thin film Amorphous silicon p i n devices active layer is i Degradation issues low deposition rates CIS Copper Indium diSelenide Cu In Se2 CIGS Copper Indium GalliumdiSelenide CdTe Cadmium Telluride The three above are p type materials A p n diode is constructed with a thin n layer such as CdS Gallium allows tweaking of bandgap to optimize efficiency Cost of Indium Toxicity of Cadmium Thin layers 2 m lead to low cost Deposition on flexible substrate such as stainless steel or polymer sheets 3 Development of Electrical Model of the Photovoltaic Cell slide 1 Photogeneration Semiconductor material absorbs photons and converts into hole electron pairs if Photon energy h 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 e Vd 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 with angle between panel direction and direction to sun So take your data quickly Power Electronics Laboratory 15 Lecture 1 Variations in Solar Irradiance What the pyranometer sees total irradiance Cells that are not in direct sun can still experience substantial irradiance from clouds reflections diffusion T Stoffel 20 years of solar measurements the Solar Radiation Research Laboratory at NREL National Renewable Energy Laboratory SRRL 4 13 05 7 Plugging in numbers panel current panel voltage solar irradiance efficiency panel area If solar irradiance insolation 1 kW m2 Efficiency 10 Panel area 1 m x 1 m 1 m2 Voltage at peak power point 10 V Then current at peak power point is 1000 W m2 10 1 m2 10 V 10 A and Isc is a little greater than 10 A Panel output power at peak power point is 100 W Q how much power can you get out of this panel indoors using ambient lighting 8 Laboratory facilities mobile PV cart Inverter 60 Hz 300 W 120 Vrms 17 2 V at 4 95 A Shell SQ 85P 6 outlet ac power strip PV panel Battery 12 V deep discharge 56 A hr Alarm Battery low voltage Voltmeter Battery voltage Battery Connectors PV panel 85 Wpk 12V Battery charger 12V Off cart on stationary workbench 5V 8 Isolated dc dc converters


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CU-Boulder ECEN 4517 - Direct Energy Transfer System

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Lecture 4

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Lecture 2

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Lecture 1

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Lecture 6

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Battery

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Lecture 3

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Lecture 4

Lecture 4

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