DC-AC Power Inverter

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

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

3. 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

4. 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

5. Design Constraints

6. 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

7. 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

8. 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

9. PWM Oscilloscope Waveform Prototype Device as Built

10. 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

11. 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

12. Half-bridge Oscilloscope Readings Prototype Device As Built

13. 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

14. 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

15. DC-DC Converter Schematic

16. DC-DC Converter Testing Device As Built Simulation

17. 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

18. 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

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

20. Sinusoidal PWM Drive Pulses Device As Built Simulation

21. 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

22. 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

23. Simulation vs. Actual (unfiltered) Simulation Device As Built

24. 60 Hz 60 Hz 18 kHz 18 kHz Frequency Spectrum Before Filtering Simulation Device As Built

25. 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

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

27. DC-AC Full-bridge Inverter Schematic

28. Final Output Testing Simulation Prototype

29. Frequency Spectrum After Filtering Simulation Device As Built

30. Component Costs

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

32. Packaging

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

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

35. Any Questions? ???