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DC-AC Power Inverter Design II, Spring 2004 Midterm Presentation Team Members Min-Chiat Wee Daniel Martin Team Leader Faculty Advisor Dr. Yaroslav Koshka Dustin Bailey Industrial Advisor: Dr. Mark Kinsler Jason Horner Abstract • Design a switch-mode power supply that converts 12 VDC to 120 VAC • Pure sinusoidal waveform with 60 Hz frequency • 300 W continuous output Problem Statement • Problems: – Inexpensive inverters are very inefficient due to a high harmonic content of the output signal – Pure sine wave inverters have a high cost per watt ratio • Solution: – An inexpensive inverter that produces a near perfect sine wave output Design Constraints Name Description Voltage Convert 12VDC to 120 VAC Power Provide 300 W continuous Efficiency > 90% efficiency Waveform Pure 60 Hz sinusoidal Total Harmonic Distortion < 5% THD Physical Dimensions 8” x 4.75” x 2.5” Cost $175.00 Main Components 12 VDC Input (from vehicle battery) PWM Control Circuit Half-bridge Converter Transformer Low-pass Filter Full-bridge Inverter Sinusoidal PWM Controller 120 VAC, 60 Hz, 300 W Output PWM Control Circuit 12 VDC Input (from vehicle battery) PWM Control Circuit Half-bridge Converter Transformer Low-pass Filter Full-bridge Inverter Sinusoidal PWM Controller 120 VAC, 60 Hz, 300 W Output PWM Controller • Produces two complementary pulses to control half-bridge transistors • Problem: – Voltage dropped less than 170VDC when the input voltage was decreased • Solution: – A feedback network was added for voltage regulation PWM Oscilloscope Waveform Prototype Device as Built Half-bridge Converter 12 VDC Input (from vehicle battery) PWM Control Circuit Half-bridge Converter Transformer Low-pass Filter Full-bridge Inverter Sinusoidal PWM Controller 120 VAC, 60 Hz, 300 W Output Half-bridge Converter • Chops the 12 VDC to produce a 12 V, 100 kHz, square pulse • Problem: – IRF740A MOSFETs has an Rds(on) = 0.55Ω, resulting in high power losses. • Solution: – Chose IRF530 MOSFETs with an Rds(on) = 0.16 Ω Half-bridge Oscilloscope Readings Prototype Device As Built Transformer 12 VDC Input (from vehicle battery) PWM Control Circuit Half-bridge Converter Transformer Low-pass Filter Full-bridge Inverter Sinusoidal PWM Controller 120 VAC, 60 Hz, 300 W Output Step Up Transformer • Steps up voltage from 12 VAC to 340 VAC • Problem: – Initial transformer had high internal capacitance leading to failure of device • Solution: – Custom ordered a transformer to fit our design constraints DC-DC Converter Schematic DC-DC Converter Testing Simulation Device As Built Sinusoidal PWM Controller 12 VDC Input (from vehicle battery) PWM Control Circuit Half-bridge Converter Transformer Low-pass Filter Full-bridge Inverter Sinusoidal PWM Controller 120 VAC, 60 Hz, 300 W Output Sinusoidal PWM Circuit • Last Semester: • PIC18F452 – too many unused ports • Insufficient dead-time in PIC program caused crossconduction in full-bridge inverter • This Semester: • Chose PIC18F252 – fewer unused ports • Programmed 500ns between each control pulse Software Flow Diagram Initialize all variables no Count0 = 300 (300 duty cycles) 300 duty cycle values? yes Output 1 = high, Output 2 = low Read duty cycle table (increment pointer) Output 1 = low, Output 2 = high Decrement Count0 by 1 Duty cycle and sampling period timer no no Has duty cycle been reached? yes One Sampling Period? yes Sinusoidal PWM Drive Pulses Simulation Device As Built Full-bridge Inverter 12 VDC Input (from vehicle battery) PWM Control Circuit Half-bridge Converter Transformer Low-pass Filter Full-bridge Inverter Sinusoidal PWM Controller 120 VAC, 60 Hz, 300 W Output Full-bridge Inverter • Converts 170 VDC to a 120 Vrms, 60 Hz, sine wave • IRF740A MOSFETs – Vdss = 400 V – Id = 10 A – Rds(on) = 0.55 Ω Simulation vs. Actual (unfiltered) Simulation Device As Built Frequency Spectrum Before Filtering Simulation 60 Hz Device As Built 60 Hz 18 kHz 18 kHz Low-pass Filter 12 VDC Input (from vehicle battery) PWM Control Circuit Half-bridge Converter Transformer Low-pass Filter Full-bridge Inverter Sinusoidal PWM Controller 120 VAC, 60 Hz, 300 W Output Low-pass Filter • 2nd order L-C filter – Filters to retain a 60 Hz fundamental frequency – Few components – Handle current – Wind inductor (fine tune) DC-AC Full-bridge Inverter Schematic Final Output Testing Simulation Prototype Frequency Spectrum After Filtering Simulation Device As Built Component Costs Item Quantity (per unit 10,000) PIC18F252 1 $2.66 $2.66 transformer 1 $2.20 $2.20 driver 2 $1.80 $3.60 inductor 1 $1.71 $1.71 capacitor 1 $1.59 $1.59 inductor 1 $1.59 $1.59 MC34025 1 $1.40 $1.40 MOSFET 2 $1.17 $2.34 capacitor 1 $1.17 $1.17 MOSFET 2 $0.79 $1.58 40 MHz oscillator 1 $0.70 $0.70 diode 5 $0.33 $1.65 capacitor 2 $0.20 $0.40 capacitor 5 $0.11 $0.55 Misc. x $17.81 $17.81 capacitor 2 $0.10 $0.20 resistor 1 $0.02 $0.02 diode 1 $0.02 $0.02 Total Price $41.19 PCB Layout Dimensions: 7.5” x 6.5” x 2.5” Packaging Status and Goals • • • • Continue working with PCB Fine tune filter Improve packaged appearance Attempt to further reduce costs Acknowledgements • • • • • • • • • Dr. Yaraslov Koshka Dr. Mark Kinsler Dr. Mike Mazzola Dr. Raymond Winton Dr. Herb Ginn Jim Gafford Robin Kelley Len Cox Jessie Thomas Any Questions? 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