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DC-AC Power Inverter . Design II, Spring 2004 Midterm Presentation. Team Members . Min-Chiat Wee Team Leader. Daniel Martin. Faculty Advisor Dr. Yaroslav Koshka. Dustin Bailey. Industrial Advisor: Dr. Mark Kinsler. Jason Horner. Abstract.

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Dc ac power inverter
DC-AC Power Inverter

Design II, Spring 2004

Midterm Presentation


Team members
Team Members

Min-Chiat Wee

Team Leader

Daniel Martin

Faculty Advisor

Dr. Yaroslav Koshka

Dustin Bailey

Industrial Advisor: Dr. Mark Kinsler

Jason Horner


Abstract
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
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



Main components
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
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
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
PWM Oscilloscope Waveform

Prototype

Device as Built


Half bridge converter
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 converter1
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
Half-bridge Oscilloscope Readings

Prototype

Device As Built


Transformer
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
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 testing
DC-DC Converter Testing

Device As Built

Simulation


Sinusoidal pwm controller
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
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


Software flow diagram

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


Sinusoidal pwm drive pulses
Sinusoidal PWM Drive Pulses

Device As Built

Simulation


Full bridge inverter
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 inverter1
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 vs. Actual (unfiltered)

Simulation

Device As Built


Frequency spectrum before filtering

60 Hz

60 Hz

18 kHz

18 kHz

Frequency Spectrum Before Filtering

Simulation

Device As Built


Low pass filter
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 filter1
Low-pass Filter

  • 2nd order L-C filter

    • Filters to retain a 60 Hz fundamental frequency

    • Few components

    • Handle current

    • Wind inductor (fine tune)



Final output testing
Final Output Testing

Simulation

Prototype


Frequency spectrum after filtering
Frequency Spectrum After Filtering

Simulation

Device As Built



Pcb layout
PCB Layout

Dimensions: 7.5” x 6.5” x 2.5”



Status and goals
Status and Goals

  • Continue working with PCB

  • Fine tune filter

  • Improve packaged appearance

  • Attempt to further reduce costs


Acknowledgements
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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