DC/AC Pure Sine Ware Inverter

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DC/AC Pure Sine Wave

Inverter

Jim Doucet

Dan Eggleston

Jeremy Shaw

MQP Terms ABC 20062007

Advisor: Professor Stephen J. Bitar

Sponsor: NECAMSID

N

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Table of

Table of ContenContentsts

Introduction Introduction...1...1 Problem Statement Problem Statement...2...2 Background Background...3...3 Inverters and Applications

Inverters and Applications...5...5 Pulse Width Modulation

Pulse Width Modulation...7...7 Bubba

Bubba OscillOscillatorator...9...9 HBridge Configuration

HBridge Configuration ...12...12 MOSFET Drivers

MOSFET Drivers...14....14 Circuit

Circuit Protection Protection and and SnubbersSnubbers...15...15 Filtering

Filtering...16...16 Methodology

Methodology...17...17 Sine Wave Generator

Sine Wave Generator...18...18 Carrier Wave Generator

Carrier Wave Generator...20...20 Pulse Width Modulation

Pulse Width Modulation...24...24 HBridge

HBridge...27...27 Filter

Filter...30...30 Implementing the Design

Implementing the Design...32.32 Difficulties

Difficulties...33...33 Sine Wave Generator

Sine Wave Generator...33...33 Filter Design

Filter Design...35.35 Putting the Design to Work

Putting the Design to Work ...37...37 Results Results...38...38 Recommendations Recommendations...40..40 Conclusion Conclusion...42...42 References References...44...44 Appendix A: Switching Frequency Charts

Appendix A: Switching Frequency Charts...46...46 Appendix B: Circuit Diagram

Appendix B: Circuit Diagram...47...47 Appendix C: Flowchart

Appendix C: Flowchart...49...49 Appendix D: PCB Board Diagrams

Appendix D: PCB Board Diagrams...50...50 Appendix E: Parts List

Appendix E: Parts List...52...52

Index of Figures

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Bubba Oscillator Sc

Bubba Oscillator Schematichematic...9...9

RC Filter Schematic... RC Filter Schematic...10...10

Signal at P1... Signal at P1...11..11

HBridge Configuration using NChannel MOSFETs...12

NChannel MOSFET... NChannel MOSFET...14...14

Inductive Load Inductive Load CircuitCircuit...15...15

Inductive Load Inductive Load Circuit Circuit witwith h SnubberSnubber...15...15

Inductive Load Circuit Inductive Load Circuit witwith Snubh Snubber and Zener ber and Zener DiodeDiode...15...15

Block Diagram... Block Diagram...17...17

Bubba Oscillator Bubba Oscillator CircuitCircuit...18...18

Oscillator Signal at P2... Oscillator Signal at P2...19..19

Oscillator Signal at P5... Oscillator Signal at P5...19..19

Triangle Triangle Wave GeneratorWave Generator...20...20

Square Wave Output... Square Wave Output...21...21

Generated Triangle Wave... Generated Triangle Wave...22...22

Square and Triangle Waves... Square and Triangle Waves...22...22

PWM Signal... PWM Signal...24...24

Sine Reference, Triangle Wave, and square wave reference...25

Modified triangle wave, overlaid with sine reference...25

PWM signal and PWM signal and referencreference e sine...sine...26...26

Trilevel P Trilevel PWM signaWM signal...l...26...26

HBridge HBridge with with MOSFET Drivers...MOSFET Drivers...27...27

Typical Conne Typical Connection ction for IR2110 for IR2110 MOSFET Driver...MOSFET Driver...28.28 Frequency plot of losses... Frequency plot of losses...30....30

New Sine Wave Oscillator Circuit Diagram...34

Two Two Pole Output FilPole Output Filter...ter...35...35

Project on PCB Board... Project on PCB Board...36...36

Closed Loop Closed Loop Flow ChartFlow Chart...37...37

NonInverti NonInverting ng AmplifAmplifier ier BlockBlock...38...38

Frequency plot of Frequency plot of MOSFET lMOSFET losses...osses...41...41

Frequency plot of inductor losses (resistive)...41

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Introduction

This report

This report focuses on focuses on DC DC to AC power inverters, which aim to to AC power inverters, which aim to efficiently transform efficiently transform a a DC powerDC power source to a high voltage AC source, similar to power that would be available at an electrical wall outlet. source to a high voltage AC source, similar to power that would be available at an electrical wall outlet. Inverters are used for many applications, as in situations where low voltage DC sources such as batteries, Inverters are used for many applications, as in situations where low voltage DC sources such as batteries, solar panels or

solar panels or fuel cells mufuel cells must be converted so that st be converted so that devices canrun devices canrun off of AC power. off of AC power. One example of One example of such a situation would be converting electrical power from a car battery to run a laptop, TV or cell such a situation would be converting electrical power from a car battery to run a laptop, TV or cell phone.

phone.

The method in which the low voltage DC power is

The method in which the low voltage DC power is invertedinverted, i, is completed s completed in two sin two steps. teps. The firstThe first being the conversion of the low voltage DC power to a high voltage DC source, and the second step being the conversion of the low voltage DC power to a high voltage DC source, and the second step being the

being the conversion of conversion of the the high DC source to an AC waveforhigh DC source to an AC waveform using pulse width modulatm using pulse width modulation. ion. AnotherAnother method to complete the desired outcome would be to first convert the low voltage DC power to AC, and method to complete the desired outcome would be to first convert the low voltage DC power to AC, and then use a transfor

then use a transformer to boomer to boosst the voltage to 120 volts. t the voltage to 120 volts. This project focused oThis project focused on the n the first methodfirst method described and specifically the transformation of a high voltage DC source into an AC output. described and specifically the transformation of a high voltage DC source into an AC output.

Of the different DCAC inverters on the market today there are essentially two different forms of AC Of the different DCAC inverters on the market today there are essentially two different forms of AC output generated: modif

output generated: modified sine wave, ied sine wave, and and pure sine wavepure sine wave11. . A modifiA modified sine wave ed sine wave can be seen as morecan be seen as more of a

of a square wave than a sine wave; square wave than a sine wave; it passes it passes the high the high DC DC voltage for specified amouvoltage for specified amounts of time so nts of time so that thethat the averag

average power and rms voe power and rms voltage are the same as if it were a sine wave. ltage are the same as if it were a sine wave. These types of inverteThese types of inverters are rs are muchmuch cheaper than pure sine wave inverters and therefore are attractive alternatives.

cheaper than pure sine wave inverters and therefore are attractive alternatives.

Pure sine wave inverters, on the other hand, produce a sine wave output identical to the power Pure sine wave inverters, on the other hand, produce a sine wave output identical to the power coming out of an electrical out

coming out of an electrical outlet. let. These devices are ablThese devices are able to e to run more run more sensisensitive devices that a modifiedtive devices that a modified sine wave may cau

sine wave may cause damage to such se damage to such as: laser printers, laptop computersas: laser printers, laptop computers, power tools, digital clocks , power tools, digital clocks andand medical equip

medical equipment. ment. This forThis form of AC power also reduces audible noism of AC power also reduces audible noise in e in devices devices such as fluorescentsuch as fluorescent lights and runs inductive loads, like motors, faster and quieter due to the low harmonic distortion. lights and runs inductive loads, like motors, faster and quieter due to the low harmonic distortion.

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Problem Statement

In the market of power

In the market of power inverters, inverters, there are many chothere are many choices. ices. They range froThey range from the very expensive m the very expensive toto the very inexpensive, with varying

the very inexpensive, with varying degrees degrees of quality, efficiency, and power output capability along of quality, efficiency, and power output capability along thethe way.

way. High quality combined High quality combined with high with high efficieefficiency ncy exists, though it exists, though it is often at is often at a high ma high monetaonetary ry cost. cost. ForFor example,

example, Samlex America Samlex America manufactures manufactures a 600 W, pure sine wave inverter; the cost is $289a 600 W, pure sine wave inverter; the cost is $28922. Meanwhile. Meanwhile GoPower manufactures a 600 W inverter with a modified sine wave output (closer to a square wave); this GoPower manufactures a 600 W inverter with a modified sine wave output (closer to a square wave); this model only fetches $69

model only fetches $6933. . The high end pure sine wave inverters tenThe high end pure sine wave inverters tend to incorporate very expensive, d to incorporate very expensive, highhigh power capable d

power capable digigital compoital componennents. ts. The modified sine wave uniThe modified sine wave units can be very efficientts can be very efficient, , as there is as there is notnot much processing being performed on the output waveform, but this results in a waveform with a high much processing being performed on the output waveform, but this results in a waveform with a high number of harmonics, which c

number of harmonics, which can an affect sensitive equipment such as medaffect sensitive equipment such as medical monitors. ical monitors. Many of the veryMany of the very cheap devices

cheap devices outpoutput a ut a square wave, perhaps square wave, perhaps a sliga slightly modified square wave, with the htly modified square wave, with the proper RMSproper RMS voltage, and close to the right frequency.

voltage, and close to the right frequency.

Our goal is to fill a niche which seems to be lacking in the power inverters market, one for a fairly Our goal is to fill a niche which seems to be lacking in the power inverters market, one for a fairly efficient, inex

efficient, inexpensive inverter wpensive inverter with a puith a pure sine re sine wave wave output. output. Utilizing PWM and analog compoUtilizing PWM and analog components, thenents, the output will be a clean sinusoid, with very little switching noise, combined with the inexpensive

output will be a clean sinusoid, with very little switching noise, combined with the inexpensive manufacturin

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Background

DC and AC Current

In the world today there are currently two forms of electrical

In the world today there are currently two forms of electricaltransmission, Direct Current (DC) andtransmission, Direct Current (DC) and Alterna

Alternatting Curreing Current nt (AC), each with it(AC), each with its own advantages and disadvantages own advantages and disadvantages. s. DC power iDC power is simply thes simply the applic

application of ation of a steady constant voltage across a a steady constant voltage across a circuit resulting in a constant currecircuit resulting in a constant current. nt. A battery is A battery is thethe most common source of DC trans

most common source of DC transmission as current flomission as current flows from one ws from one end of a circuit to the other. end of a circuit to the other. MostMost digital circuitry today is run off of DC power as it carries the ability to provide either a constant high or digital circuitry today is run off of DC power as it carries the ability to provide either a constant high or constan

constant low voltage, enabling digt low voltage, enabling digital logic to process coital logic to process code de executions. executions. HistorHistorically, electricity was ically, electricity was firstfirst commercial

commercially ly transmitted by Thomas Edison, and transmitted by Thomas Edison, and was a DC power was a DC power line. line. HowevHowever, er, this electricity wasthis electricity was low voltage, due to the inability to step up DC voltage at the time, and thus it was not capable of

low voltage, due to the inability to step up DC voltage at the time, and thus it was not capable of transm

transmitting power over long itting power over long distancesdistances44..

V V

=

IR IR

P

P== IV IV == I I 22 R R (1)(1) As can be seen in the equations above, power loss can be derived from the electrical current

As can be seen in the equations above, power loss can be derived from the electrical current squared and the resis

squared and the resistance of a transmisstance of a transmission line. ion line. When the voltage is increased, When the voltage is increased, the current decreasesthe current decreases and concurrently the power loss decreases exponentially; therefore high voltage transmission reduces and concurrently the power loss decreases exponentially; therefore high voltage transmission reduces power loss.

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Electrical transmission has therefore been mainly based upon AC power, supplying most Electrical transmission has therefore been mainly based upon AC power, supplying most American h

American homes with a 120 vomes with a 120 vololt AC t AC source. source. It should be noted that since It should be noted that since 1954 there 1954 there have been manyhave been many high voltage DC trans

high voltage DC transmmission systems implemented aission systems implemented around thround the globe we globe wiith the adventh the advent of DC/DCt of DC/DC converters, allo

converters, allowing the wing the easy seasy stepping utepping up and p and down of down of DC voltagesDC voltages66..

Like DC power, there exist many devices such as power tools, radios and TV’s that run off of AC Like DC power, there exist many devices such as power tools, radios and TV’s that run off of AC power.

power. It is tIt is therefoherefore re cruciacrucial that bol that both forms of th forms of electrelectricity ticity transmission exist; the world ransmission exist; the world cannocannot bet be powered wit

powered with one simple form. h one simple form. It then becomes a vital matter for tIt then becomes a vital matter for there to exist easy ways here to exist easy ways to transformto transform DC to AC power and vice

DC to AC power and vice versa in an efficienversa in an efficient mannet manner. r. Without this ability people will be restricted toWithout this ability people will be restricted to what electronic dev

what electronic devices they use depending on the electriciices they use depending on the electricity source available. ty source available. Electrical AC/DCElectrical AC/DC converters and DC/AC inverters al

converters and DC/AC inverters allow people this low people this freedom in freedom in transferring electricalpower between thetransferring electricalpower between the two.

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Inverters and Applications

Power inverters are devices

Power inverters are devices which can convert electrical which can convert electrical energy of DC form into that of AC. energy of DC form into that of AC. TheyThey come in all shapes and sizes, from low power functions such as powering a car radio to that of backing come in all shapes and sizes, from low power functions such as powering a car radio to that of backing up a building in case of power outage.

up a building in case of power outage. Inverters Inverters can come in many different varietcan come in many different varieties, differing in pies, differing in price,rice, power, efficiency

power, efficiency and purpose. and purpose. The purpose The purpose of of a DC/AC power inverter a DC/AC power inverter is typicalis typically to take DC powerly to take DC power supplied by a battery, such as a 12 volt car battery, and transform it into a 120 volt AC power source supplied by a battery, such as a 12 volt car battery, and transform it into a 120 volt AC power source operating at 60 Hz, emulating the power available at an ordinary household electrical outlet.

operating at 60 Hz, emulating the power available at an ordinary household electrical outlet.

Figure 1: Commercial 200 Watt Figure 1: Commercial 200 Watt

Inverter

Inverter 7 7

Figure 1

Figure 1 provides a idea of what a provides a idea of what a small power inverter lsmall power inverter looks like. ooks like. Power inverters are used toPower inverters are used todayday for many tasks like powering app

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A modified sine wave is similar to a square wave but instead has a “stepping” look to it that relates A modified sine wave is similar to a square wave but instead has a “stepping” look to it that relates more in shape to

more in shape to a sine wavea sine wave. . This can be seen This can be seen inin Figure 2,Figure 2, which displays how which displays how a ma modified sine waveodified sine wave tries to emulate the

tries to emulate the sine wave itself. sine wave itself. The waveThe waveform form is easy to producis easy to produce because because e it is just the product of it is just the product of switching between 3 values at set

switching between 3 values at set frequencies, frequencies, thereby leaving out thereby leaving out the more the more compcomplicated circuitrlicated circuitry neededy needed for a pure sine wave.

for a pure sine wave. The modified sine wave inverter The modified sine wave inverter provides a cheap and easy solutiprovides a cheap and easy solution to on to poweripoweringng devices that need AC power.

devices that need AC power. It does hIt does have ave some drawbacks as nsome drawbacks as not all dot all devices evices work properly owork properly on an a modified sin

modified sine wave, e wave, produproducts such as cts such as computercomputers and medis and medical equcal equipipment are not resistant to the distortionment are not resistant to the distortion of the signal and must be run off of a pure sine wave power source.

of the signal and must be run off of a pure sine wave power source.

Figure 2: Square, Modified, and Pure Sine Wave

Figure 2: Square, Modified, and Pure Sine Wave 88

Pure sine wave inverters are able to simulate precisely the AC power that is delivered by a wall Pure sine wave inverters are able to simulate precisely the AC power that is delivered by a wall outlet.

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Pulse Width Modulation

In electronic power

In electronic power converters converters and and momotors, PWM tors, PWM is used is used extensextensively as a ively as a means of poweringmeans of powering alternating current (AC) devices with an available direct current (DC) source or for advanced DC/AC alternating current (AC) devices with an available direct current (DC) source or for advanced DC/AC conversion. Variation of duty cycle

conversion. Variation of duty cyclein the PWM signal to provide a DC voltage across the load in ain the PWM signal to provide a DC voltage across the load in a specific pattern will appear to the load as an AC signal, or can control the speed of motors that would specific pattern will appear to the load as an AC signal, or can control the speed of motors that would otherwise run only at full spee

otherwise run only at full speed or d or off. off. This is further explained in this section. The pattern at which theThis is further explained in this section. The pattern at which the duty cycle of a PWM signal varies can be created through simple analog components, a digital

duty cycle of a PWM signal varies can be created through simple analog components, a digital microcon

microcontroller, or troller, or specific PWM specific PWM iintegrated circuits.ntegrated circuits. Analog PWM control requires the

Analog PWM control requires thegeneration of both reference and carrier signals that feed into ageneration of both reference and carrier signals that feed into a comparator which createsoutput signals based on the difference between the signals

comparator which createsoutput signals based on the difference between the signals1010. The reference. The reference signal is sinusoidal and at the frequency of the desired output signal, while the carrier signal is often 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 significant

either a sawtooth or triangular wave at a frequency significantly greater than the reference. ly greater than the reference. When theWhen the carrier signal exceeds the reference

carrier signal exceeds the reference, the , the comparator outpucomparator output signal t signal is at is at one sone state, and when tate, and when the referencethe reference is at a

is at a higher voltage, the output is at higher voltage, the output is at its second staits second state. te. This process is This process is shown inshown in Figure 3Figure 3 with thewith the triangular carrier wave in red, sinusoidal reference wave in blue, and modulated and unmodulated sine triangular carrier wave in red, sinusoidal reference wave in blue, and modulated and unmodulated sine pulses

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Figure 3: Pulse Width Modulation Figure 3: Pulse Width Modulation

In order to source an output with a PWM signal, transistor or other switching technologies are used to In order to source an output with a PWM signal, transistor or other switching technologies are used to conne

connect ct the source to the load when the source to the load when the signal is high the signal is high or low. or low. Full or half bridge coFull or half bridge configuranfiguratitions areons are common switching schemes

common switching schemes used used in in power power electronelectronics. Full ics. Full bridbridge coge configuratnfigurations ions require the use of require the use of fourfour switching devices

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Bubba Oscillator

The Bubba Oscillator is a circuit that provides a filtered sine wave of any frequency the user desires The Bubba Oscillator is a circuit that provides a filtered sine wave of any frequency the user desires based upon the confi

based upon the configuratioguration of n of resistors and capacitors resistors and capacitors in the circuiin the circuit. t. The circuiThe circuit completes tht completes this task is task with four operati

with four operationaonal amplifiers that either buffer l amplifiers that either buffer or amplify the sior amplify the signal. gnal. This oscillator is This oscillator is a phase shifta phase shift oscillator, bu

oscillator, but unlike other t unlike other phase shift varieties phase shift varieties thathat require t require phase sphase shifts of hifts of 90 degrees or more, the 90 degrees or more, the bubbabubba oscillator on

oscillator only requily requires a res a 45 degre45 degree e shift in order to function. shift in order to function. This is because of the four op This is because of the four op amps, thatamps, that when placed in series, produce a total 180

when placed in series, produce a total 180°°_shift._shift.

The bubba oscillator offers a few features that other oscillators cannot, the biggest factor is that the The bubba oscillator offers a few features that other oscillators cannot, the biggest factor is that the frequen

frequency cy stability holds while sstability holds while still giving a low ditill giving a low distortion output. stortion output. The reason for tThe reason for this involves the fouhis involves the fourr filters that the signal passes through, providing a clear and stable signal at point P5, as shown in

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Cancel Anytime. Figure 5: RC Filter Figure 5: RC Filter Schematic Schematic V V _out_out==_V_V in in 1 1 j j_C_C R R 11 j j_C_C = = V V inin j j RR_C_C11 When When == 11 RC RC A

A==V V outout

V V _in_in == 1 1 j j11 ∢ ∢_A_A== ∢∢00 ° ° ∢ ∢4545°°=∢=∢4545 ° ° (2) (2)

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A problem that exists in all oscillators is that it is nearly impossible to get an exact amplification of A problem that exists in all oscillators is that it is nearly impossible to get an exact amplification of the signal.

the signal. If the amplification is too small then the oscIf the amplification is too small then the osciillator sigllator signal wnal will decaill decay to noy to nothing, howething, however if itver if it is too large the signal will keep on amplifying until it

is too large the signal will keep on amplifying until it hits the rails of the op amps. hits the rails of the op amps. This means that someThis means that some sort of nonlinear feedback must be implemented with these oscillators so that the signal provided will sort of nonlinear feedback must be implemented with these oscillators so that the signal provided will actually be a stable sine wave.

actually be a stable sine wave. The bubba oscillator (as well

The bubba oscillator (as well as other phase shift oscillaas other phase shift oscillators) solves this problem by tors) solves this problem by the very naturethe very nature of the op amps, when the signal is amplified back into the circuit the signal gets clipped at the peaks of of the op amps, when the signal is amplified back into the circuit the signal gets clipped at the peaks of the sine wa

the sine wave. ve. This is becauThis is because se the amplitude is reachithe amplitude is reaching the ng the rails of the op amp allowing the signal trails of the op amp allowing the signal too stabilize and providing the nonlinear feedback needed.

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HBridge Configuration

An HBridge or fullbridge converter is a switching configuration composed of four switches in an An HBridge or fullbridge converter is a switching configuration composed of four switches in an arrangement t

arrangement that resembles an H. hat resembles an H. By controllBy controlling different switches in the ing different switches in the bridge, bridge, a positive, negative, ora positive, negative, or zeropotential voltage can be placed across a load. When this load is a motor, these states correspond to zeropotential voltage can be placed across a load. When this load is a motor, these states correspond to forward, reverse

forward, reverse, and off. , and off. The use of an HBridge configuration to dThe use of an HBridge configuration to drive a rive a motor is shown inmotor is shown in Figure 7.Figure 7.

Figure 7: HBridge Configuration using Figure 7: HBridge Configuration using

NChannel MOSFETs NChannel MOSFETs

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The switches used to implement an HBridge can be mechanical or built from solid state transistors. The switches used to implement an HBridge can be mechanical or built from solid state transistors. Selection of the proper s

Selection of the proper switches varies greatly. witches varies greatly. The use of PChannel MOSFETs The use of PChannel MOSFETs on the high side on the high side and Nand N Channel MOSFETs on the low side is easier, but using all NChannel MOSFETs and a FET driver, lower Channel MOSFETs on the low side is easier, but using all NChannel MOSFETs and a FET driver, lower “on” resistance can be obtained resul

“on” resistance can be obtained resulting in ting in reduced reduced power loss. power loss. The use of all NChannel MOSFETsThe use of all NChannel MOSFETs requires a driver, since in order to turn on a highside NChannel MOSFET, there must be a voltage requires a driver, since in order to turn on a highside NChannel MOSFET, there must be a voltage higher than the switching voltage (in the case

higher than the switching voltage (in the case of a power of a power inverteinverter, 170V). r, 170V). This difficulty is This difficulty is oftenoften overcome by driver circuits capable

overcome by driver circuits capable of charging an of charging an external external capacitor capacitor to to create create additional potentadditional potential.ial. MOSFET drivers and discussion of how they achieve this higher potential are discussed in the following MOSFET drivers and discussion of how they achieve this higher potential are discussed in the following section.

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MOSFET Drivers

When utilizing NChannel M

When utilizing NChannel MOSFETs to switch a DC OSFETs to switch a DC voltage across a load, the voltage across a load, the drain termidrain terminals of thenals of the high side MOSFETs are often connected to the highest voltage in the system.

high side MOSFETs are often connected to the highest voltage in the system. This creates a difficulty, asThis creates a difficulty, as the gate terminal must be approximately 10V higher than the drain terminal for the MOSFET to conduct. the gate terminal must be approximately 10V higher than the drain terminal for the MOSFET to conduct. Often, integrated circui

Often, integrated circuit det devices known as vices known as MOSFET MOSFET drivers drivers are utilized to are utilized to achieve this differenceachieve this difference through charge pumps or bootstrappi

through charge pumps or bootstrapping techniques. These chips are cng techniques. These chips are capable of quickly apable of quickly charging the inputcharging the input capacitance of the MOSFET

capacitance of the MOSFET (Cgiss) (Cgiss) quickly before the potential difference is reached, causing the gatequickly before the potential difference is reached, causing the gate to source voltage to be the highest system voltage plus the capacitor voltage, allowing it to conduct. A to source voltage to be the highest system voltage plus the capacitor voltage, allowing it to conduct. A

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Circuit Protection and Snubbers

One of the major factors in any electronic device is its ability to protect itself from surges that could One of the major factors in any electronic device is its ability to protect itself from surges that could damage the circuitry.

damage the circuitry. In the case of the In the case of the inverterinverter, , inductive loads can cause special problems because aninductive loads can cause special problems because an inductor cannot instantly stop conducting current, it must be dampened or diverted so that the current inductor cannot instantly stop conducting current, it must be dampened or diverted so that the current does not tr

does not try to flow thry to flow throough the open switch. ugh the open switch. If not dampened the surges can cause trouble in theIf not dampened the surges can cause trouble in the MOSFETs used to produce the output

MOSFETs used to produce the output sine wave; when a sine wave; when a MOSFET is turned off the MOSFET is turned off the indinductive load stilluctive load still wants to push current thro

wants to push current throuugh the switch, as it has no whgh the switch, as it has no where ere else to goelse to go. . This action can causThis action can cause e the switchthe switch to be put under considerable stress, the high dV/dt, dI/dt, V and I associated with this problem can cause to be put under considerable stress, the high dV/dt, dI/dt, V and I associated with this problem can cause

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Filtering

Filters come in many

Filters come in many different different packages, with many different packages, with many different advantages – and advantages – and disadvandisadvantages. tages. ForFor example, a digital filter is easily reconfigurable and

example, a digital filter is easily reconfigurable andcan have almost any frequency response desired. If can have almost any frequency response desired. If the response is simply lowpass/highpass/bandpass behavior with a set frequency, an active filter can be the response is simply lowpass/highpass/bandpass behavior with a set frequency, an active filter can be made to have a very sharp edge at the cutoff, resulting in enormous reductions in noise and very little made to have a very sharp edge at the cutoff, resulting in enormous reductions in noise and very little attenu

attenuation of ation of the signal. the signal. These, however, require These, however, require opamps. opamps. Opamps capable Opamps capable of filtering of filtering a 120V RMSa 120V RMS sine wave exist, but are expensive and lossy, since the opamp must be able to source hundreds of watts, sine wave exist, but are expensive and lossy, since the opamp must be able to source hundreds of watts, and must be very

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Methodology

The construction of the pure sine wave inverter can be complex when thought of as a whole but The construction of the pure sine wave inverter can be complex when thought of as a whole but when broken up into smal

when broken up into smaller projects and divisler projects and divisions it beions it becomes a comes a much easier to manamuch easier to manage ge project. project. TheThe following sections detail each specific part of the project as well as how each section is constructed and following sections detail each specific part of the project as well as how each section is constructed and interacts with other blocks to resu

interacts with other blocks to result in the prolt in the productduction of a 120 volt pure sine wave power inverter.ion of a 120 volt pure sine wave power inverter.

Block Diagram

Analog

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Sine Wave Generator

The first step to creating an accurate pulse width modulation signal using analog circuitry is to The first step to creating an accurate pulse width modulation signal using analog circuitry is to

ntation

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