# b-10.dc-ac pure sine wave inverter using bubba oscillator

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DC/AC Pure Sine WaveInverter

Section-B:

Batch No: 10

ANIL .R(07241A0258)MAHENDRA.P(07241A0275)

VAMSI KRISHNA.L(07241A02B4)

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Inverter

Power inverters are devices which can convert

electrical energy of DC form into that of AC.

On the market today are two different types of power

inverters, modified sine wave and pure sine wave

generators. These inverters differ in their outputs,

providing varying levels of efficiency and distortion

that can affect electronic devices in different ways.

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OUR OBJECTIVE

Our goal is to fill a niche which seems to be lacking

in the power inverters market, one for a fairly

efficient, inexpensive inverter with a pure sine wave

output.

Utilizing PWM and analog components, the output

will be a clean sinusoid, with very little switching

noise, combined with the inexpensive manufacturing

that comes with an analog approach.

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COMPOSITION

The major task of generating a pure sine wave is viewedas the summation of outputs obtained from:

Bubba oscillator(Reference sine wave generator)

Carrier wave generator Pulse width modulation

H-bridge with MOSFET drivers

Snubber circuit and filters

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Bubba Oscillator

The Bubba Oscillator is a circuit that provides a

filtered sine wave of any frequency the user desires

based upon the configuration of resistors and

capacitors in the circuit. The circuit completes this task with four operational

amplifiers that either buffer or amplify the signal and

produce a total 180 shift.

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Output

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Carrier Wave Generator

Generating a sine wave at 50Hz requires both the

reference sine wave and a carrier wave at the

switching speed of the power supply.

Carrier waves can be either saw tooth or triangularsignals; in this case, a triangular wave will be used.

The operation of this device is based on basic Schmitt

Trigger and Integrator circuits.

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Output

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Pulse Width Modulation

Analog PWM control requires the generation of both

reference and carrier signals that feed into a

comparator which creates output signals based on the

difference between the signals. The reference signal is sinusoidal and at the

frequency of the desired output signal, while the

carrier signal is often either a sawtooth or triangular

wave at a frequency significantly greater than the

reference.

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When the carrier signal exceeds the reference, the comparator

output signal is at one state, and when the reference

is at a higher voltage, the output is at its second state.

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H-Bridge Configuration

An H-bridge converter is a switching configuration

composed of four switches in an arrangement that

resembles an H.

By controlling different switches in the bridge, apositive, negative, or zero potential voltage can be

placed across a load.

The use of P-channel MOSFETs on the high side and

N-Channel MOSFETs on the low side is easier.

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H-Bridge with N-channel

MOSFETS

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The MOSFET driver on the left side of the bridge will

receive a square wave and the right side will receive the

PWM signal.

Square wave will control the polarity of the output sine wave,

while the PWM signal will control the amplitude.

Now, using an H-Bridge MOSFET configuration, and

utilizing both the above PWM signal and the square wave

generated, we can obtain unfiltered output signal at the load.

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Snubber circuit

One of the major factors in any electronic device is its

ability to protect itself from surges that could damage

the circuitry.

In the case of the inverter, inductive loads can causespecial problems

To combat this problem snubber circuits can reduce

or eliminate any severe voltages and currents.

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Filters

In this inverter , we preferpassive filter than active

filters.

L-C filter

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Block diagram of pure sine wave

inverter

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Total Circuit Diagram

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Final Output at the filter

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Applications

The purpose of a DC/AC power inverter is typically to take

DC power supplied by a battery, such as a 12 volt car battery,

and transform it into a AC power source emulating the power

available at an ordinary household electrical outlet.

Power inverters are used today for many tasks like powering

appliances in a car such as cell phones, radios and televisions.

They also come in handy for consumers who own camping

vehicles, boats and at construction sites where an electric grid

may not be as accessible to hook into.

Inverters allow the user to provide AC power in areas where

only batteries can be made available, allowing portability and

freeing the user of long power cords.

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Simulation part of

the circuits

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Simulation of bubba oscillator

circuit

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Output

R = 33Kohm, C = 100nF then Freq = 50HZ

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R = 26.7Kohm, C = 100nF then Freq = 60HZ

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R = 15Kohm, C = 150nF then Freq = 70HZ

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Simulation of carrier wave circuit

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OutputRtot = 100 Kohm , C = 200 pF, Freq = 2 KHZ

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Rtot = 8.2 Kohm , C = 100 pF, Freq = 50 KHZ

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Rtot = 50 Kohm , C = 150 pF, Freq = 8 KHZ

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Simulation of PWM circuit

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Output

B.O : R=33Kohm, C=100nF

C.G : Rtot = 50Kohm , C= 200pF

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B.O : R=26.7Kohm, C=100nF

C.G : Rtot = 50Kohm , C= 150pF

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B.O : R=15Kohm, C=150nF

C.G : Rtot = 100Kohm , C= 200pF

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B.O : R=15Kohm, C=150nF

C.G : Rtot = 8.2Kohm , C= 100pF

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List of major components

Op amps:

LM348

TL084MC3302

IR2110(Mosfet driver)

IR549P Mosfet

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LM348

Pin diagram : Ratings :

Supply voltage :

Vcc : -18 to +18 V

Input voltage :Vi : -18 to +18 V

Differential Input Voltage :

Vi(Diff) : 36 V

Operating & storage

Temperature :

0 to +70 C & -65 to 150 C

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TL084

Pin Diagram : Ratings :

Supply voltage :

Vcc : -18 to +18 V

Input voltage :

Vi : -15 to +15 V

Differential Input Voltage :

Vi(Diff) : -30 to +30 V

Power Dissipation :

P(tot) : 680mw

Operating & storageTemperature :

0 to +70 C & -65 to 150 C

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MC3302

Pin Diagram : Ratings :

Supply voltage :

Vcc : -15 to +15 V

Input Differential VoltageRange :

Vidr : 30 V

Power dissipation :

Pd: 1 W

Operating & storage

Temperature :

-40 to 85 C & -65 to 150 C

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IR2110

Pin Diagram : Ratings :

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Hardware work

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Bubba Oscillator

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Carrier wave generator

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PWM pulse generator

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H-Bridge configuration of MOSFETS

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Output of bubba oscillator circuit

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Output of carrier wave generator

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Conclusion

After the total connections of internal

circuits,the obtained reference sine wave and

triangular waves are sent to the PWM

generator circuit,from which the accuratePWM pulses are obtained with disturbances

which couldnt properly drive the MOSFET

drivers to give the desired output.

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Scope of the project

This project is a stepping stone to a cheaperand efficient pure sine wave inverter.

Using the data collected in this report as well

as the schematics and recommendations theproduct produced here can be improved

upon.

Simple additions such as circuit protection anda closed loop control system could greatly

improve the performance of this project.