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

2. Industrial Advisor: Dr. Mark Kinsler
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: Solution:
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. Total Harmonic Distortion
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

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

20. Sinusoidal PWM Drive Pulses
Device As Built
Simulation

21. (from vehicle battery)
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)
Device As Built

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

25. (from vehicle battery)
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 Item Quantity (per unit 10,000) Price Total $41.19
PIC18F252 1
$2.66
transformer
$2.20
driver 2
$1.80
$3.60
inductor
$1.71
capacitor
$1.59
MC34025
$1.40
MOSFET
$1.17
$2.34
$0.79
$1.58
40 MHz oscillator
$0.70
diode 5
$0.33
$1.65
$0.20
$0.40
$0.11
$0.55
Misc. x
$17.81
$0.10
resistor
$0.02
Total
$41.19

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?
???