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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?
???