MICROPROCESSOR CONTROLLED A.C.

INVERTER

Kyle Merkert

ECE 791/792 Senior Design Project

October 2009 – May 2010

Faculty Advisor: Dr. Wayne Smith

Introduction

We depend on electricity but we use a system that often involves long distance distribution rather than localized power:

Introduction

Power distribution as it is today isn’t always reliable.

Problem Statement

My solution is a high power inverter for producing a sine wave at 110V RMS from electricity stored in 12V batteries.

Design Goals

At least 400 Watts Output Power Integrated Overload Protection Circuits Sine Wave Output with < 10% THD Smooth Switching Between Grid and Inverter Informs User of Errors and Warnings Able to Power Inductive Loads

Design ConsiderationsStep up voltage before or after forming sine wave?

This implementation steps up voltage first, then uses a network of transistors to create a sine wave with this high voltage input.

Design Considerations

This alternate implementation creates a sine wave with the 12 volt input and then steps up the voltage with a high power transformer.

Design ConsiderationsSine wave production: Pulse Width Modulation (PWM) or Digital to Analog Conversion (DAC)?

PWM

DAC

Implementing/Testing Plan1. Protective circuitry

2. Microprocessor programming for 60Hz sine wave output

3. Amplitude adjustment

4. Voltage step-up experimentation

5. Error reporting and increased current capabilities

6. Final user interface and load control

Budget (High Estimate) Deep Cycle Batteries $200 High Voltage Capacitors $40 Power Transistors $50 Power Resistors $10 Misc. Parts as Needed $100 Unexpected Costs

(Damaged Parts, Etc.) $100

Total Cost (High Estimate): $500

Design Goals By MonthNovember: Decide on PWM or DAC. Program sine wave output of microprocessor. Experiment with stepping up voltage and determine if sine

wave should be formed before or after voltage step-up.

December: Build protection circuits. Construct first prototype of inverter for very low load

conditions. Build amplitude regulation circuit. Program power monitoring of grid power. Complete progress Report

Design Goals By MonthJanuary: Add error reporting circuits. Increase output power capabilities. Optimize THD of sine wave to resistive loads.

February: Maintain sine wave with inductive loads. Determine maximum safe output power. Program software to prevent loads from drawing too much

power.

Design Goals By MonthMarch: Add user interface: Battery life and power usage monitoring.

April: Finish and optimize anything that does not meet design

goals. Prepare UNH-URC Poster Presentation

May: Have finished product completed Prepare and present final report