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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

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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

  • 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


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

Device As Built

Simulation


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 cross-conduction in full-bridge inverter

  • This Semester:

    • Chose PIC18F252 – fewer unused ports

    • Programmed 500ns between each control pulse


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

Device As Built

Simulation


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


60 Hz

60 Hz

18 kHz

18 kHz

Frequency Spectrum Before Filtering

Simulation

Device As Built


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


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?

???


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