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DC-AC Power Inverter Design II, Spring 2004 Midterm Presentation

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Team Members Daniel Martin Dustin Bailey Min-Chiat Wee Team Leader Jason Horner Faculty Advisor Dr. Yaroslav Koshka Industrial Advisor: Dr. Mark Kinsler

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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

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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

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Design Constraints NameDescription VoltageConvert 12VDC to 120 VAC PowerProvide 300 W continuous Efficiency> 90% efficiency WaveformPure 60 Hz sinusoidal Total Harmonic Distortion< 5% THD Physical Dimensions8” x 4.75” x 2.5” Cost$175.00

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Main Components Full-bridge Inverter Sinusoidal PWM Controller Low-pass Filter PWM Control Circuit Half-bridge Converter Transformer 12 VDC Input (from vehicle battery) 120 VAC, 60 Hz, 300 W Output

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PWM Control Circuit Full-bridge Inverter Sinusoidal PWM Controller Low-pass Filter PWM Control Circuit Half-bridge Converter Transformer 12 VDC Input (from vehicle battery) 120 VAC, 60 Hz, 300 W Output

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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

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PWM Oscilloscope Waveform PrototypeDevice as Built

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Half-bridge Converter Full-bridge Inverter Sinusoidal PWM Controller Low-pass Filter PWM Control Circuit Half-bridge Converter Transformer 12 VDC Input (from vehicle battery) 120 VAC, 60 Hz, 300 W Output

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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

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Half-bridge Oscilloscope Readings Device As Built Prototype

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Transformer Full-bridge Inverter Sinusoidal PWM Controller Low-pass Filter PWM Control Circuit Half-bridge Converter Transformer 12 VDC Input (from vehicle battery) 120 VAC, 60 Hz, 300 W Output

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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

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DC-DC Converter Schematic

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DC-DC Converter Testing Simulation Device As Built

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Sinusoidal PWM Controller Full-bridge Inverter Sinusoidal PWM Controller Low-pass Filter PWM Control Circuit Half-bridge Converter Transformer 12 VDC Input (from vehicle battery) 120 VAC, 60 Hz, 300 W Output

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Sinusoidal PWM Circuit Last Semester: PIC18F452 – too many unused ports Insufficient dead-time in PIC program caused cross- conduction in full-bridge inverter This Semester: Chose PIC18F252 – fewer unused ports Programmed 500ns between each control pulse

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Software Flow Diagram Initialize all variables Count0 = 300 (300 duty cycles) Has duty cycle been reached? Output 1 = high, Output 2 = low Read duty cycle table (increment pointer) Output 1 = low, Output 2 = high 300 duty cycle values? Decrement Count0 by 1 Duty cycle and sampling period timer One Sampling Period? noyes no yes no

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Sinusoidal PWM Drive Pulses Device As Built Simulation

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Full-bridge Inverter Full-bridge Inverter Sinusoidal PWM Controller Low-pass Filter PWM Control Circuit Half-bridge Converter Transformer 12 VDC Input (from vehicle battery) 120 VAC, 60 Hz, 300 W Output

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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

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Simulation vs. Actual (unfiltered) SimulationDevice As Built

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Frequency Spectrum Before Filtering 18 kHz 60 Hz SimulationDevice As Built 60 Hz

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Low-pass Filter Full-bridge Inverter Sinusoidal PWM Controller Low-pass Filter PWM Control Circuit Half-bridge Converter Transformer 12 VDC Input (from vehicle battery) 120 VAC, 60 Hz, 300 W Output

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Low-pass Filter 2 nd order L-C filter –Filters to retain a 60 Hz fundamental frequency –Few components –Handle current –Wind inductor (fine tune)

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DC-AC Full-bridge Inverter Schematic

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Final Output Testing SimulationPrototype

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Frequency Spectrum After Filtering SimulationDevice As Built

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Component Costs ItemQuantity (per unit 10,000)Price PIC18F2521$2.66 transformer1$2.20 driver2$1.80$3.60 inductor1$1.71 capacitor1$1.59 inductor1$1.59 MC340251$1.40 MOSFET2$1.17$2.34 capacitor1$1.17 MOSFET2$0.79$ MHz oscillator1$0.70 diode5$0.33$1.65 capacitor2$0.20$0.40 capacitor5$0.11$0.55 Misc.x$17.81 capacitor2$0.10$0.20 resistor1$0.02 diode1$0.02 Total $41.19

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PCB Layout Dimensions: 7.5” x 6.5” x 2.5”

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Packaging

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Status and Goals Continue working with PCB Fine tune filter Improve packaged appearance Attempt to further reduce costs

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Acknowledgements Dr. Yaraslov Koshka Dr. Mark Kinsler Dr. Mike Mazzola Dr. Raymond Winton Dr. Herb Ginn Jim Gafford Robin Kelley Len Cox Jessie Thomas

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Any Questions? ???

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