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LED Solar Simulator

LED Solar Simulator. Project 4: Zach Klein Kevin Kroeger Micah Sweeney. Objectives. International Electrotechnical Commission (IEC) provides standards for Solar Simulators. OBJECTIVES Illuminate a 6”x6” surface from 6” away Class C uniformity in the center

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LED Solar Simulator

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  1. LED Solar Simulator Project 4: Zach Klein Kevin Kroeger Micah Sweeney

  2. Objectives • International Electrotechnical Commission (IEC) provides standards for Solar Simulators • OBJECTIVES • Illuminate a 6”x6” surface from 6” away • Class C uniformity in the center • Class A-B spectral match in the visible, C in the infrared • Class C for short and long term temporal stability

  3. Initial Design

  4. Design Process Wavelength (nm) Wavelength (nm) • Approximate each LED’s Gaussian curve as a Triangle in Excel

  5. Initial Design Spectrum Theoretical Spectrum of Tungsten Halogens Wavelength (nm) • LEDs fill in the visible spectrum • Tungsten Halogens fill in the infrared • Triangular approximations mean the peaks will be more shallow and the • valleys more filled than is shown in the Excel plot

  6. Spectrum Using LEDs entirely • Spectrum can be matched entirely with LEDs • -19 different colors used • This is not possible with our limitations • High Power Infrared LEDs are very expensive • We only have only 6 channels of control • Number of required LEDs exceeded space • limitations

  7. Improved Initial Design Theoretical Spectrum of Tungsten Halogens Wavelength (nm) • Six different LED colors • -Five Luxeon REBEL LEDs • -One LEDEngin UV LED • Four 300W 2950K Tungsten Halogen lamps • Current control can be used until Visible spectrum is matched • Infrared intensity attuned by adjusting distance of halogen from surface

  8. Lenses and Attaching LEDs • Need • Strong adherence to heat sink • Flexibility to move LEDs • Solution • 10 mm square LXB-RS10 MCPBs designed for Luxeon REBELs • 10 mm square LXT-R-10 thermal adhesive squares designed for use with MCPCBs • LEDs have a 120° viewing angle, causing most power to be lost outside the 6”x6” area • The 10mm Carclo 10412 has a 22° viewing angle and an 85% efficiency

  9. Power Supply • Drive 6 LED strings • Convert mains power • IC power supply • Self-contained unit • 500 W capable

  10. Buck Converter • DC-DC step-down converter • Switching transfers energy through inductor • Output dependent on duty ratio of MOSFET

  11. Implementing Feedback • Controller takes ADC input and compares it to user entered value. • If desired, controller operates with manually entered duty ratio

  12. ADC Tuning • Average Error Magnitude: .612% • Average Absolute Error: 2.03mV for Vin < 2.5V

  13. Feedback Control Accuracy • With a single channel running the DSP is able to track a user defined current well

  14. Initial Implementation • Two-stage converter mockup • Open-loop control • Pre-wound inductor • Red LED and ballast load

  15. Determining the Spacing • A hexagon with • one center LED • provided the most even distribution of light • LEDs were doubled or tripled at their placement points • UV LEDs were 5W and only 3 were used

  16. Heat Sinks and Stand • Needed to • -Connect two 8”x4” heat sinks • -Attach halogens • -Raise LEDs off illumination surface • Stand was built by Machine Shop

  17. The Attachment Process Pick & Place to place each LED Reflow Oven to solder LEDs to MCPCBs Epoxy to attach lenses Adhesive pads to attach LEDs to heat sink Leads were soldered by hand Rotated outer ring to maximize spacing -This caused problems with exact placement

  18. Theoretical Uniformity • Placement asymmetry caused less than ideal uniformity

  19. Realistic Uniformity • A device that measures uniformity is specified by IEC standards to have up to a • 25 mm x 25 mm testing area for a 6”x6” illumination area • Averaging over this area gives class C uniformity within the center 100mm square

  20. DSP Daughterboard • Simplifies the connections to PWM/ADC pins • Locking connector so that connectors cannot be placed on backwards

  21. Comparison of Tuning with Different Loads • Slope and intercept changes as load changes

  22. Stage 1 • Rectifier and 1st-stage buck • On-board, open-loop control • Tunable frequency, duty ratio • Designed for 100V output

  23. Stage 2 • Optocoupler for PWM input • Current-sense resistor for ADC • Capacitor voltage needs

  24. Snubbers Lossy, RCD snubbers used to reduce switch turn-on losses.

  25. Ballast Load • Energy transfer requires current. • Minimum load determines inductor • Ballast sets minimum • Non-linear LED I-V load

  26. Inductors • Resist current change • Sized to avoid Discontinuous Mode • Majority of converter weight • Winding is time intensive

  27. Performance Troubleshooting • Insufficient Current • Demagnetized inductor cores • MOSFET shortage; changed from 400V to 100V devices • Blown MOSFETs • Blown gate-drivers • Rectifier current spikes

  28. Issues with PCB Interface • Issues with interface between PCB and DSP • Circuit limits output voltage to 1.4V to protect DSP

  29. Spectrum Testing • Fiber optic cable captures incoming light which is analyzed and sent to the computer. • Very narrow light aperture and viewing angle. • asdf

  30. Spectrum Testing • The equipment used measures the spectrum in 3 different wavelength • bands. This system is more sensitive to certain wavelengths • Calibration with a known blackbody emitter determines a scaling factor • Once this scaling factor is determined it can be applied to all spectrum • data measured with the device to obtain the true spectrum

  31. Scaled Halogen Spectrum • Applying the scaling factor to the measured Halogen spectrum • gave erroneous results

  32. Uniformity Testing • A camera photographing a piece of paper 6” away from the LEDs was used to analyze uniformity using MATLAB

  33. Uniformity • Class C uniformity was achieved over an approximately 50mm square area

  34. Remaining Control Issues and Potential Solutions • Coupling between ADC channels makes multiple converter operation difficult • Need additional protection circuitry for the DSP ADCs • Possible Solutions: High output impedance buffer between ADC and converters and separating grounds on the daughterboard

  35. Comparison to Existing LED Solar Simulator • 6”x6” illumination surface • 346 LEDs in 8 colors plus halogen • Class A over 60 mm x 60 mm • Class A or B spectral Match

  36. Thanks • Prof. Krein and the Grainger Foundation, Julio Soares, Mark Smart, Tom Galvin, Kevin Colravy, Ali Bazzi, Kieran Levin, Prof. Rockett, ECE Machine Shop, ECE Parts Shop, ECE Store, Allan Correia, Ralph Gottschlag, and more!

  37. References Spectral Distribution of Sunlight plot courtesy of Prof. Angus Rockett Theoretical Spectrum of Tungsten Halogens retrieved on March 15, 2010 from http://zeiss-campus.magnet.fsu.edu/articles/lightsources/tungstenhalogen.html P.T. Krein. Fundamentals of Power Electronics. 1998. ECE 469 Laboratory Instruction Manual. ECE Department, UIUC. Fall 2009 BLISS, M. ... et al, 2009. Towards a higher power, all LED solar simulator closely matching realistic solar spectra. IN: Proceedings of the 24th European Photovoltaic Solar Energy Conference, Hamburg, Germany, 21st-25th September, paper 4AV.3.11.

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