DC-AC Power Inverter

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DC-AC Power Inverter
Design II, Spring 2004 Midterm Presentation
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Team Members
Min-Chiat Wee Team Leader
Daniel Martin
Faculty Advisor Dr. Yaroslav Koshka
Dustin Bailey
Industrial Advisor Dr. Mark Kinsler
Jason Horner
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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
Name Description
Voltage Convert 12VDC to 120 VAC
Power Provide 300 W continuous
Efficiency gt 90 efficiency
Waveform Pure 60 Hz sinusoidal
Total Harmonic Distortion lt 5 THD
Physical Dimensions 8 x 4.75 x 2.5
Cost 175.00
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Main Components
12 VDC Input (from vehicle battery)
PWM Control Circuit
Half-bridge Converter
Transformer
Full-bridge Inverter
Sinusoidal PWM Controller
Low-pass Filter
120 VAC, 60 Hz, 300 W Output
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PWM Control Circuit
12 VDC Input (from vehicle battery)
PWM Control Circuit
Half-bridge Converter
Transformer
Full-bridge Inverter
Sinusoidal PWM Controller
Low-pass Filter
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
Prototype
Device as Built
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Half-bridge Converter
12 VDC Input (from vehicle battery)
PWM Control Circuit
Half-bridge Converter
Transformer
Full-bridge Inverter
Sinusoidal PWM Controller
Low-pass Filter
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) 0.55O, resulting
  in high power losses.
• Solution
• Chose IRF530 MOSFETs with an Rds(on) 0.16 O

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Half-bridge Oscilloscope Readings
Prototype
Device As Built
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Transformer
12 VDC Input (from vehicle battery)
PWM Control Circuit
Half-bridge Converter
Transformer
Full-bridge Inverter
Sinusoidal PWM Controller
Low-pass Filter
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
Device As Built
Simulation
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Sinusoidal PWM Controller
12 VDC Input (from vehicle battery)
PWM Control Circuit
Half-bridge Converter
Transformer
Full-bridge Inverter
Sinusoidal PWM Controller
Low-pass Filter
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
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Sinusoidal PWM Drive Pulses
Device As Built
Simulation
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Full-bridge Inverter
12 VDC Input (from vehicle battery)
PWM Control Circuit
Half-bridge Converter
Transformer
Full-bridge Inverter
Sinusoidal PWM Controller
Low-pass Filter
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 O

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Simulation vs. Actual (unfiltered)
Simulation
Device As Built
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Frequency Spectrum Before Filtering
Simulation
Device As Built
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Low-pass Filter
12 VDC Input (from vehicle battery)
PWM Control Circuit
Half-bridge Converter
Transformer
Full-bridge Inverter
Sinusoidal PWM Controller
Low-pass Filter
120 VAC, 60 Hz, 300 W Output
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Low-pass Filter

• 2nd 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
Simulation
Prototype
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Frequency Spectrum After Filtering
Simulation
Device As Built
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Component Costs
Item Quantity  (per unit 10,000) Price
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     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?

• ???