DC-AC FULL BRIDGE CONVERTER.pdf

7/23/2019 DC-AC FULL BRIDGE CONVERTER.pdf

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PROJECT REPORT

Submitted in partial fulfillment of

the requirements for the award of degree of

Bachelor of Technology

In

Electrical and Electronics Engineering

By

V DATTA VISWAS KUMAR (08241A0206)

N KRISHNA MOHAN (08241A0219)

M MANOJ (08241A0222)

B VIKAS NAIK (08241A0254)

P N V G RAJA NARAYANA RAO (07241A0213)

Department of Electrical and Electronics Engineering

Gokaraju Rangaraju institute of Engineering and Technology

(Affiliated to Jawaharlal Nehru Technological University)

Hyderabad

2012


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Department of Electrical and Electronics Engineering

GOKARAJU RANGARAJU INSTITUTE OF ENGINEERING & TECH.

(Affiliated to Jawaharlal Nehru Technological University)

Hyderabad.

CERTIFICATE

This is to certify that the project entitled DC-AC FULL BRIDGE CONVERTER has

been submitted by

V DATTA VISWAS KUMAR (08241A0206)

N KRISHNA MOHAN (08241A0219)

M MANOJ (08241A0222)

B VIKAS NAIK (08241A0254)

P N V G RAJA NARAYANA RAO (07241A0213)

In partial fulfillment of the requirements for the award of degree of

Bachelor of Technology in Electrical and Electronics Engineering from

Jawaharlal Nehru Technological University, Hyderabad.

The results embodied in this project have not been submitted to any other University or

Institution for the award of any degree or diploma.

Guide Head of Department

S. Radhika P.M.Sarma

A. &

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(082410206)

(082410219)

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(072410213)


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Mobility and versatility have become a must for

the fast-paced society today. People can no longer afford to be tied down to a fixed power sourcelocation when using their equipments. Overcoming the obstacle of fixed power has led to the

invention of DC/AC power inverters. While the position of power inverter in the market is

relatively well established, there are several features that can be improved upon.

A comparison analysis of the different power inverter

has been compiled. Aside from the differences in power wattage, cost per wattage, efficiency and

harmonic contend, power inverters can be categorized into three groups: square wave, modified

sine wave, and pure sine wave. A cost analysis of the different types of inverter shows that sine

wave power inverter, though has the best power quality performance, has a big spike in cost per

unit power. Another feature which can be improved is the efficiency of the inverter. The standardsine wave in the market has an average efficiency of 85-90%. Power dissipated due to efficiency

flaws will be dissipated as heat and the 10-15% power lost in the will shorten operational

lifespan of inverters. The quality of the output power could also be improved. It is imperative

that the output signal be as clean as possible. Distortion in the output signal leads to less efficient

output and in the case of a square wave , which has a lot of unwanted harmonics, it will damage

some sensitive equipment.

In designing any type of power supply, it is important to examine the

intended market and place the product in a particular niche market. Our market niche will be todesign a 300watts power inverter that will provide optimum pure sine wave performance with

minimal cost. In meeting the design requirements, there are several technical challenges thatmust be overcome. Our single, most difficult constraint will be to produce power at a lower

power per unit cost than exists in the market. Our efficiency will be greater than 90 percent. Thisinsures that, with a maximum load, less than 10% of power will be dissipated as heat. The total

harmonic distortion will be less than 5 percent. With a total harmonic distortion this low and apure sine wave output, we will be able to power even the most sensitive loads.

The fundamental step in approaching the challenges was to examine the methods used byexisting companies for building power inverters. In examining their methods, many areas were

open for potential improvement. These areas include the DC/DC step up converter, the DC/ACinverter, and the feedback control system.

The DC/DC step up converter in our design will use a high frequency

transformer, enabling us to reduce the size of the converter considerably. The use of a highfrequency transformer will also enable us to meet our efficiency constraint. A high switchingfrequency will improve the efficiency of the inverter. In theory, a 100 percent efficient converter

could be created. However, due to the limitations of actual device material, our efficiency will bebetween 90 and 100 percent. The DC/AC inverter circuit will use a microprocessor to digitally

pulse the transistors. This will allow us to produce a pure sine wave output. This feature will alsoallow us to enter other markets more easily. For instance, in Europe the fundamental frequency is

50 Hz. The frequency can be changed from 60 Hz to 50 Hz by simply editing the source code.


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The feedback control system will be used to regulate the output voltage of the DC/DC converter.This is necessary since the current will vary will the load. The feedback control

system will be accomplished using by sampling the output with an integrated circuit.Most of the design constraints set for the inverter were met. However, the one important

constraint which the power inverter didnt meet was the 300W continuous power, which was

probably because of the transformer and the traces on the PCB. The inverter produces a cleansine wave with 7% of harmonic distortion and has efficiency greater than 90%. Overall, it is awell designed project and a lot has been accomplished over the two semesters. This design if

well marketed, will offer the power inverter market a premium product at a lower cost thanbefore. Future work could be done to further improve efficiency, total harmonic distortion, and

size. With these additional improvements, the standard could be raised forfuture DC/AC power supplies.


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CONTENTSPage numbers

ACKNOWLEDGMENTS i

ABSRACT ii - iii

LIST OF TABLES ivLIST OF FIGURES v vi

1 1

1. INTRODUCTION 1

2

2 DESIGN REQUIREMENTS

2.1Technical design constraints

2.2 Practical design constraints

3

3 APPROACH

3.1DC power supplies

3.1.1 power inverters

3.2 Hardware design

3.2.1 PWM control circuit

3.2.2 Sinusoidal PWM control circuit

3.2.3 Full bridge inverters

3.3.4 Low pass filter

3.3 Software design

4

4 EVALUATION

4.1 Test specification

4.2 Test certificate - Simulation

4.3 Test certificate Hardware

4.4 Test certificate- Software


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5

5 SUMMARY

CHAPTER 6

6 PROBLEMS

CHAPTER 7

7 SOFTWARE USED

CHAPTER 8

8 IC DETAILS

8.1 DESCRIPTION OF IC

8.2 OPERATION

8.3 OP-AMP CHARACTERISTICS

8.3.1 ideal op-amps

8.3.2 Real op-amps

8.4 DC IMPERFECTIOS

8.4.1 finite gain

8.4.2 finite input impedance

8.4.3 non-zero output impedance

8.4.4 input current

8.4.5 input off-set voltage

8.4.6 common mode gain8.4.7 output sink current

8.4.8 temperature effects

8.4.9 power supply rejections

8.4.10 drifts


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8.4.11 noise

8.5 AC IMPERFECTIONS

8.5.1 finite bandwidth

8.5.2 input capacitance

8.5.3 common mode gain

8.6 POWER CONSIDERATION

8.6.1 limited output current

8.6.2 limited dissipated power

8.7 LM 339

8.7.1 input voltage range

8.7.2 op-amp voltage comparator

8.7.3 dedicated voltage comparator chip

8.7.4 speed and power

8.7.5 features of LM339

8.7.6 applications of LM339

CHAPTER 9

9 HARDWARE

9.1 DC-AC converter

9.2 Triangular pulse generator

9.3 Complete circuit diagram

CHAPTER 9

9 HARDWARE

CHAPTER 10

10 RESULT


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CHAPTER 11

11 APPENDIX

11.1 DATA SHEETS OF COMPONENTS

CHAPTER 12

12 REFERENCES


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List of figures

Figure 3.1 Block diagram of power inverter.

Figure 3.2 Triangular wave generatorand its wave form

Figure 3.3 Theory of PWM components

Figure 3.4 Full bridge converter

Figure 3.5 unfiltered output

Figure 3.6 Frequency spectrum of unfiltered full

Bridge inverter.

Figure 3.7 Schematic diagram of low pass filter

Figure 3.8 Hand made inductor

Figure 3.9 Circuit diagram

Figure 4.1 Test setup for full bridge inverter

Figure 4.2 Test setup for low pass filter

Figure 4.3 DC/AC inverter

Figure 4.4 simulation certificate for DC/AC inverter

Figure 4.5 Simulation certification of filtered DC/AC inverter

Figure 8.1:An op-amp without negative feedback

Figure 8.2: An op-amp with negative feedback (a non-inverting

Amp)

Figure 8.3 ideal op-amps

Figure 8.4 comparator

Figure 8.5 various comparatorsFigure 8.6 pin diagram of lm 339

Figure 9.1 DC-AC converter

Figure 9.2 Triangular pulse generator

Figure 9.3 Complete circuit diagram

Figure 9.4 Final output


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List of tables

Table 2.1 :Design constraints

Table 2.2: practical constraints

Table 10.1 output result


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1

DC-AC inverters are electronic devices used to produce mains

voltage. AC power from low voltage DC energy mains voltage. AC power from low voltage DCenergy(from a battery or solar panel). This makes them very suitable for when you need to use

AC power tools or appliances but the usual AC mains power is not available. Examples includeoperating appliances in caravans and mobile homes, and also running audio, video and

computing equipment in remote areas.Most inverters do their job by performing two main functions:

first they convert the incoming DC into AC, and then they step up the resulting AC to mains

voltage level using a transformer. And the goal of the designer is to have the inverter performthese functions as efficiently as possible .so that as much as possible of the energy drawn from

the battery or solar panel is converted into mains voltage AC, and as little as possible is wastedas heat.

By switching the two MOSFETs on alternately, the current is madeto flow first in one half of the primary and then in the other, producing an alternating magnetic

flux in the transformers core. As a result a corresponding AC voltage is induced in thetransformers secondary winding, and as the secondary has about 10 times the number of turns in

the primary, the induced AC voltage is much higher: around 170V peak to peak.

Note that because the switching MOSFETs are simply beingturned on and off, this type of inverter does not produce AC of the same pure sinewave. type as

the AC power mains. The output waveform is essentially alternating rectangular pulses. However

the width of the pulses and the spacing between them is chosen so that the ratio between theRMS value of the output waveform and its peak-to-peak value is actually quite similar to that ofa pure sine wave. The resulting wave form is usually called a .modified sine wave., and as the

RMS voltage is close to 230V many AC tools and appliances are able to operate from such awaveform without problems.


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2

There are several factors involving power that can be easily overlooked by the average person.These issues deal primarily with efficiency but are not limited to it. First, the amount of power

consumed by the load must be looked at. Different devices call for different power wattages.Because of this fact, our inverter would not be able to power larger devices that require a lot of

power. This does not affect the efficiency of our device; it is just one of its limitations. Next, thesensitivity of the load being driven should be considered. This means the output signal of the

inverter must provide a cleaner signal without distortion for more sensitive devices. The amountof undesired harmonics present in our output signal would need to be limited.

2.1 :Our five technical design constraints are shown in Table 1. These design constraints will rely heavily on

the pure sine wave output. A pure sine wave output will be obtained through the use of a microprocessor

and high frequency switching.

The DC/AC power inverter being built will be driven using 12 VDC. It will thenconvert this DC voltage in to a functional 120 VAC power source. This power source will be capable of

supplying 300 watts of continuous power and 600 watts of peak power. The output obtained will be as

close as possible to a pure sine wave signal. As mentioned before, the major factor in power is efficiency.

This is directly related to the output signal of the power supply. Due to this fact, it is extremely criticalthat the output be as close to a pure sine wave as possible. Most power inverters do not produce a pure

sine wave output, and their performance is a reflection of that fact.

This power inverter will operate using high frequency switching technology. Theharmonics that are produced using high frequency switching will include those near the range of the

switching frequency, and those that are of a relatively higher order than the 60 Hz frequency. Most of the

harmonics will be the ones that are higher in order than the 60 Hz frequency. These harmonics can beisolated using a small low-pass filter. This translates into a much cleaner output signal. The powerinverter will produce an output signal that contains no more than 5 % of total harmonic distortion. Also,

the use of high frequency switching will minimize the size of parts used for the construction of the

inverter.

NAME DESCRIPTIONVoltage We will convert 12 (V DC) to 12(V AC).

Power We will provide 300 (W) indefinitely. We will provide 600 (W) during apower surge.

Efficiency The inverter will operate at no less than 90 %.

Output This inverter will produce a pure sine wave outputTotal Harmonic

Distortion

The amount of undesirable harmonics present in our output will be less

than 5%.Table 2.1: DESIGN CONSTRAINTS

2.2 :Our five practical design constraints are shown in

Table 2.2. These design constraints will shield the user from unnecessary harm and give the user


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a functional device. The basic economics of a project like this has to do with the price of parts.The price of parts dictates the price of the inverter. The most costly part will be the

microprocessor. By minimizing the parts cost, the price of the inverter should be comparable toother sine wave inverters on the market.

For practical use,an adapter which will be used to

connect the inverter to the 12 VDC system of an automobile. Appropriate gauge wire willconnect the cigarette lighter adapter to the inverter. A blade style fuse will protect the inverterform over-current conditions. The output will be provided using a single output receptacle to

deliver the 12VAC. For mobility sake the whole inverter will be no larger than 8 long, 4.75wide, and 2.5 high.

TYPE NAME DESCRIPTIONECONOMIC COST The expected retail value of this product is

expectedto be 2000 rupess

PROTECTION SHIELD The inverter will shut down when an input

voltage which is greater than 20 volts isapplied.

FUNCTIONALITY USER

INTERFACE

heavy duty wiring harness will be used to

access a vehicles electrical system, and asingle output receptacle will deliver the

output power.

MANUFACTURABILITY SIZE The physical dimensions will be 8 long,4.75 wide, and 2.5 high.

HEALTH AND SAFETY SAFETY Safety will be given high priority to avoidelectrical fires and shock. This will be

implemented using thermal and short circuit

protectionTable 2.2- Practical constraints of DC-AC inverter.


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3

This section explains the theory that must be

considered along with the approach that has allowed for the successful implementation of thepower inverter. It is worth mentioning that power inverter design requires knowledge of various

areas in electrical and computer engineering including circuit analysis, power electronics,microprocessors, electromagnetic, signals and systems, and feedback controls. A general

knowledge of these areas is critical in order to fully understand the physical behavior of eachcircuit component, as well as the interaction with other components. This section begins with a

general overview of the technology considered in this project and then elaborates on the keydesign issues pertaining to both the hardware and software.

3.1.1 :Though the methods involved in constructing a power inverter

are practically unlimited, they all En compass the common goal of altering an incoming DC

voltage to form a sinusoidal output signal. Regardless of the specific design implementation, aquality power inverter should provide the end-user with desirable voltage, current, and frequency

output characteristics that meet or exceed the standards for specific appliances. Often, consumersare satisfied with the least expensive inverter that will provide an adequate power level to allow

constant operation of particular devices. Regardless of price, a close examination of the outputwaveform can distinguish the quality between particular power inverters. For

example, many inexpensive power inverters create what is called a modified sine wave. Figure3.1 shows an actual power inverter sold inexpensively.

The problem with this type of inverter is the harshness withwhich it switches. Harsh switching causes a high harmonic distortion in the output signal.

Harmonic distortion is simply the amount of power that is contained in other frequencies otherthan the fundamental frequency. The harsh switching actually causes voltage and current spikes

in the output signal. This often reduces the useful life of electronic devices. In many case, theconnected device may fail to operate. This is why a sinusoidal waveform is the preferred and

more expensive output waveform.

3.2 :One of the most important considerations in building a pure

sine-wave inverter is the output signal. As the name implies, a pure sine-wave inverter should

produce an output signal with few fluctuations in DC/AC Power Inverter voltage and current.These signal fluctuations, or harmonics, are generated by rapidly switching the transistors that

are used in creating the final output. In order to meet the 5% total harmonic distortion designrequirement, a pulse width modulated (PWM) switch-mode power supply was chosen over the

square-wave or modified square wave topologies. The PWM method allows for filtering manyunwanted harmonics in the output signal, which is not possible in square-wave and modified

square wave inverters.Choosing parts for the power inverter involved extensive

research of the advantages and disadvantages of particular circuit topologies. Some of the majorfactors that determined the topology of choice for this project include power capabilities,


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efficiency, size, and cost. This project has been broken down into one major circuit topology.The circuit topology DC/AC inverter.

BLOCK DIAGRAM OF DC TO AC CONVERTER:

DC INPUT

Figure 3.1: Block diagram of DC-AC converter

3.2.1: :

It is designed to operate under 5 Volts, but different voltages can be applied as well, takingin account the maximum operation voltage of the OP-AMPS.

The two op-amps currently used are the known 741 chips. Different OP-Amps can be usedas well, and also dual chips for simplicity. The right OP-Amp will operate as an integrator andthe left as a comparator. When power is given to the circuit, the comparator drives it's outputHIGH. This signal is driven to the integrator through the resistor R. The capacitor C then starts tocharge gradually with RC time constant. While the capacitor is charging, the output of theintegrator is also taken to it's low state with the same rate. When the positive input of thecomparator, through the voltage divider that the 47K and 100K resistors perform, is driven lowenough, then it changes state, and the integrator starts operating vice-versa.

It is easily understood that the frequency of oscillation will only have to do with the RC

standard. That is true. A half cycle period is exactly the result of the R x C. A full cycle is twicethis amount. Therefore, the frequency is:

FOSC=1

2 x R x C

In our test circuit, the R resistor is 22K and the C capacitor is 100nF. The oscillationfrequency would be:

FOSC=1

2 x 22x10 x 100x10-


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And that would make 227,27Hz approximately. In real life, the frequency measured wasabout 218Hz. This is a rather small (tiny) difference between the theoretical and the practical

value, considering that the resistors have 5% accuracy and so does the capacitor as well.

Elimination the DC voltage from the output

If you watch the output signal in a oscilloscope, then you will notice that the triangle

waveform is above of the zero voltage. The offset is caused by DC voltage. In order to eliminate

this voltage shift, you should add a capacitor in series to the circuit. The value of the capacitorshould be chosen accordint tot he oscillation frequency of the circuit. For low frequencies, 1-100

Hz, a 4.7uF to 10uF would work just fine. Above you should consider using smaller capacitors.A wrong capacitor selection would cause signal distortion and sometimes will add significant

resistance to the output. The following circuit demonstrates the previous circuit with a seriescapacitor.

Figure 3.2:Triangular wave generator and its waveforms


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As you can see, the waveform right after the capacitor is slightly above the zero voltage,where the waveform before the capacitor is several voltages above, due to the DC voltage shift.

Now the output is easier to be used.

3.2.2 :These circuits compared a small voltage sinusoidal

wave (reference signal) to a small voltage saw-tooth wave (control frequency signal). At eachpoint where the sinusoidal and saw-tooth signals intersect, the output of the comparator toggles

from a high state to a low state. To illustrate the theory behind sinusoidal PWM, Figure 3.5shows the expected output of a sine wave compared to a saw-tooth wave. The duty cycle

Actually varies according to the time between sampling the reference sine wave.

REFERENCE FREQUENCY

CONTROL FREQUENCY

PWM OUTPUT

Figure 3.5: Theory PWM components


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3.2.3 :The full-bridge inverter circuit, as shown in Figure 3.6,

is very simple to construct because it only consists

of four switches. The function of the full-bridge inverter is to convert the 170 VDC link voltagesupplied by the DC-DC converter into a 340 VAC (120 V RMS), 60 Hz sine wave. Thetransistors chosen for the full-bridge inverter circuit were the IRF740As. The IRFZ44A

transistors were chosen because they have the appropriate voltage and current ratings (Vdss =400V, Id = 10A). The two complimentary PWM pulses produced by the sinusoidal PWM

controller circuit are fed into the full-bridge inverter. One signal is sent in parallel to mosfets T1and T4. The other signal is sent in parallel to transistors T2 and T3. Programming the signals into

the microcontroller as compliments of one another allows for transistors T1 and T4 to be onwhile transistors T2 and T3 are off, and vice versa. The basic principle with sinusoidal PWM is

to divide the period of the desired sine wave output into a large number of evenly spacedintervals. In each interval, the control signal remains on for part of the time and off for the other

part of the time. The ratio of the on time to off time at any given instant determines theamplitude of the desired output signal.


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Figure 3.6 Full bridge converter

Figure 3.7 unfiltered output

3.2.4 :In order to eliminate the switching frequency and all multiples

of the switching frequency, a low-pass filter had to be inserted after the output of the full-bridge

inverter. A low-pass filter only allows frequencies below the cutoff-frequency to pass. The filter


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will reject any frequency above the cutoff frequency. The cutoff frequency can be set by thefollowing formula:

Fcutoff 2

= 1/2LC

Figure 3.8 shows the switching harmonics that resulted from an 18 kHz switching frequency. Itshould be noted that the harmonics are located at the switching frequency and multiples of the

switching frequency. The switching frequency was intentionally set at 18 kHz so it would berather distant from the 60 Hz fundamental frequency. This would allow for a high cutoff

frequency, which by equation ??, allows for small LC components. The large distance betweenthe unwanted harmonics and the fundamental frequency is also beneficial because it allows for a

large margin of error in the filter values.

Figure 3.8 Frequency spectrum of unfiltered full bridge output

An L-C low-pass filter was chosen for the power inverter. This topology, as shown in Figure 13,

is simple to build, contains few components, and can handle high currents.


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Figure 3.9 Low pass filter schematic

Figure 3.10 Hand made inductor


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3.3 :

Figure 3.11 circuit diagram


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4

4.1 :The test specifications explain the methods used to showthat design constraints have been met. The power inverter is composed of many components thatrequire testing separately and as a complete system. Testing each component individually helps

to locate unique problems that are specific to each component. Complete system testing willensure that each hardware and software component is fully functional at a mutual level.

4.1.1 :PSIM is a vital circuit simulation environment that allows rapid testing

of parameters such as voltage, current, power, frequency, and total harmonic distortion. PSIM

only generates theoretical circuit output values which would only be observed under idealconditions. Therefore, PSIM will only be used as a guide for the comparison of hand calculatedmeasurements or laboratory experimentations.

The PSIM circuit simulation environment will be used to verify thedesign of the DC-DC converter and the DC-AC inverter. Both circuits and corresponding sub-

circuits will be simulated in a similar manner, with the proper parts selected from existing PSIMlibraries. Most of the analog parts that comprise the power inverter are standard parts and will

pose no problems in simulation; however, the integrated circuits for both the DC-DC converterand the DC-AC inverter will be simulated with the use of ideal sources that will be modified to

duplicate each controllers desired output waveform.The DC-DC circuit contains a half-bridge converter and a transformer

that were simulated in PSIM to compare simulated results with experimental results. For correctoperation of the DC-DC converter, two complementary square wave pulses must constantly

pulse the two MOSFET transistors of the half-bridge circuit. Specifically, these two square-wavepulses were created by selecting vpulse from the PSIM library.

Simulated in PSIM and was used to verify the experimental results.Four N-channel MOSFET transistors were used to construct the full-bridge inverter. To obtain

the necessary sinusoidal PWM signal to switch the four MOSFETs, two comparators with partnumber uA741 were used. Both comparators were set up to compare a 60 Hz sine wave with an

18 kHz saw tooth wave. The PWM output of the comparators was used to switch the transistorsto chop the 170 VDC link voltage supplied by the DCDC converter to an 18 kHz PWMwaveform. An LC low-pass filter was added to the full-bridge inverter to filter frequencies

higher than the 60 Hz fundamental frequency. The complete DC-AC inverter simulation yieldeda voltage of 120 VAC, a frequency of 60 Hz, and a total harmonic distortion of less

than 5%.

4.1.2 :All individual hardware design is tested using an oscilloscope and a digital multi-meter. The keycomponents of the overall power inverter are a PWM control circuit, a half-bridge inverter, a


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transformer, a sinusoidal PWM controller, a full-bridge inverter, and a low-pass filter. Eachcomponent was tested for the desired voltages, currents, efficiencies, and frequencies. The

following sub-sections demonstrate the tests that were performed on the power inverterhardware.

:The test setup for the full bridge inverter is illustrated in Figure 4.3. The procedure for testing thefull bridge inverter is located below the test setup.

Figure 4.1 Test setup for full bridge inverter

1. Connect the circuit shown in Figure 4.1.

2. Feed the outputs from the sinusoidal PWM controller to the four MOSFET transistors.

3. Using the oscilloscope, perform a differential measurement across the 50 load. Note: the10X probes must be used when measuring voltages over 100 VAC.4. Verify that the voltage across the 50 load is a PWM pulse that is 340 V peak-to-peak with a

frequency of 18 kHz.5. Verify that the ammeter reads 2.5 A.

:The test setup for the low-pass filter is illustrated in Figure 4.4. The

procedure for testing the low-pass filter is located below the test setup.


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Figure 4.2 Low pass filter test setup

1. Connect the circuit as shown in Figure 4.2.2. Feed the 340 V peak-to-peak PWM pulse from the full-bridge inverter to the LC filter.

3. Perform a differential measurement on the oscilloscope across the 50 load.4. Verify that the voltage is 340 V peak-to-peak with a frequency of 60 Hz. Note: the 10X probes

must be used when measuring voltages over 100 VAC.

4.2 :The DC/AC power inverter

was simulated in the PSIM environment. The entire project, except for the half-bridge PWMcontrol circuit and the full-bridge sinusoidal PWM control circuit, was simulated using ideal

parts in PSIM. The complexity of the two PWM circuits was such that they could not besimulated effectively or exactly implemented using the available parts in PSIM. The test

procedures written in the test specification section of this document were followed step by stepin order to ensure that the power inverter worked according to theory. The two major circuits

tested in PSIM were the DC/DC converter and the DC/AC inverter, which are discussed below.

/ :

Figure 4.3 shows the PSIM schematic that was used to simulate the output of the DC/ACinverter. The expected output of the DC/AC inverter is a 12 VAC RMS, 50 Hz sine wave.


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Figure 4.3 DC/AC inverter

Figure 4.4 simulation certificate for DC/AC inverter

Figure 4.5 is an 4added simulation test result showing that only the 50 Hz fundamental frequencyremains after filtering with a low-pass filter.


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Figure 4.5 Simulation certification of filtered DC/AC inverter frequency spectrum

4.3 :

:

Figure 4.10 illustrates the prototypeoutput from a breadboard. The results were found using the test procedure located in section4.1.2 of this document. This control circuit is used to pulse the MOSFETs of the half-bridge

converter. The expected output is two complimentary pulses that are 180 out of phase withamplitude of approximately 12 VAC at a frequency of 100 kHz. The results were close enoughto verify that the prototype works correctly.


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Most of the design constraints set for the inverter were met. However, the one importantconstraint which the power inverter didnt meet was the 300W continuous power, which was

probably because of the transformer and the traces on the PCB. The inverter produces a cleansine wave with 7% of harmonic distortion and has efficiency greater than 90%. Overall, it is a

well designed project and a lot has been accomplished over the two semesters. This design if

well marketed, will offer the power inverter market a premium product at a lower cost thanbefore. Future work could be done to further improve efficiency, total harmonic distortion, andsize. With these additional improvements, the standard could be raised for future DC/AC power

supplies.


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6

Power inverters, regardless of size, are typically constructed of

a DC-DC converter and a DC-AC inverter. These are the two major circuit components thatwork together to convert the input voltage from a vehicle battery into a desirable AC output

waveform. In the INDIA, the standard AC output waveform consists of a voltage of 230 VACand a frequency of 50 HZ. Due to this standard, Electronic mobility has always been an issue

when it comes to our mobile environment. Therefore, a mobile means of providing AC voltage isneeded. The majority of portable electronic devices are more easily powered using 230 VAC.

When these devices need to be used in a remote or mobile setting there is a problem. Mostpeople have access to 12 VDC generated by the standard power supply system of a mobile

vehicle, such as an automobile, ATV, or agriculture equipment. A power inverter of DC to AC

type will be needed to convert 12 VDC to 230 VAC with acceptable power output.Power inverters were first invented using a square wave as

the output form. This led to many different problems involving the functionality of devices that

were being powered because they were designed to work with a sine wave instead of a squarewave. There were some changes made to the hardware to eliminate the harsh corners from the

square wave to transform it to a modified sine wave. It was mainly marketers who coined theterm modified sine wave which in all reality is nothing more than a modified square wave.

Power inverters that used a modified sine wave did not eliminate the problems associatedwith square wave inverters. They did however, minimize these problems. Although most peoplewithout a background in electronics do not know the difference, a modified square wave can

have detrimental effects on electrical loads. First of all, abnormal heat will be produced, causing

a reduction in product reliability, efficiency, and useful life. Another disadvantage of a modifiedsine wave is that its choppy waveform can confuse the operation of some digital timing devices.This can cause a device to perform undesirable or abnormal functions. Also, nearly 5 % of

household electronics will not even work with a modified sine wave. The advantages of a truesine wave inverter are usually reflected in the final market price.

Power inverters are usually described as having either ahigh or low switching frequency. Switching frequency refers to the rate at which the input DC

voltage is oscillated to create an AC output. Low frequency inverters oscillate a DC voltage at 50Hz. Then they step that voltage up to the desired amplitude using a bulky and a heavy

transformer. High frequency inverters, on the other hand, use a small and lightweighttransformer. A high frequency inverter will produce many harmonics near the range of the

switching frequency. However, most of the harmonics are relatively higher in order than the 50Hz fundamental frequency. These harmonics can be isolated using a small low-pass filter. In

turn, isolation of harmonics will result in less buzzing in audio equipment and less interference inother electronic equipment such as radios and televisions.

When you think mobility, a unit thats the size of a laptopdoesnt seem awfully large. But consider the trend in electronics these days, a laptop seems

gigantic as compared to some of the microscopic devices and apertures that are being massedproduced. Therefore a trend in electronics, as is has been in the past decades, is miniaturization.


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7

7.1 :PSIM is a vital circuit simulation environment that allows rapid testing

of parameters such as voltage, current, power, frequency, and total harmonic distortion. PSIM

only generates theoretical circuit output values which would only be observed under idealconditions. Therefore, PSIM will only be used as a guide for the comparison of hand calculated

measurements or laboratory experimentations.The PSIM circuit simulation environment will be used to verify the

design of the DC-DC converter and the DC-AC inverter. Both circuits and corresponding sub-circuits will be simulated in a similar manner, with the proper parts selected from existing PSIM

libraries. Most of the analog parts that comprise the power inverter are standard parts and willpose no problems in simulation; however, the integrated circuits for both the DC-DC converter

and the DC-AC inverter will be simulated with the use of ideal sources that will be modified toduplicate each controllers desired output waveform.

The DC-DC circuit contains a half-bridge converter and a transformerthat were simulated in PSIM to compare simulated results with experimental results. For correct

operation of the DC-DC converter, two complementary square wave pulses must constantlypulse the two MOSFET transistors of the half-bridge circuit. Specifically, these two square-wave

pulses were created by selecting vpulse from the PSIM library.simulated in PSIM and was used to verify the experimental results. Four

N-channel MOSFET transistors were used to construct the full-bridge inverter. To obtain thenecessary sinusoidal PWM signal to switch the four MOSFETs, two comparators with part

number uA741 were used. Both comparators were set up to compare a 50 Hz sine wave with an18 kHz saw tooth wave. The PWM output of the comparators was used to switch the transistors

to chop the 15 VDC link voltage supplied by the DC-DC converter to an 18 kHz PWMwaveform. An LC low-pass filter was added to the full-bridge inverter to filter frequencies

higher than the 50 Hz fundamental frequency. The complete DC-AC inverter simulation yieldeda voltage of 120 VAC, a frequency of 50 Hz, and a total harmonic distortion of less

than 5%.


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8

8.1 :

8.1.1 741:

An operational amplifier("op-amp") is a DC-coupled high-gain electronic voltage amplifierwith a differential input and, usually, a single-ended output.[1]An op-amp produces an outputvoltage that is typically hundreds of thousands times larger than the voltage differencebetweenits input terminals.

Operational amplifiers had their origins in analog computers where they were used in manylinear, non-linear and frequency-dependent circuits. Characteristics of a circuit using an op-ampare set by external components with little dependence on temperature changes or manufacturing

variations in the op-amp itself, which makes op-amps popular building blocks for circuit design.

Op-amps are among the most widely used electronic devices today, being used in a vast array ofconsumer, industrial, and scientific devices. Many standard IC op-amps cost only a few cents inmoderate production volume; however some integrated or hybrid operational amplifiers withspecial performance specifications may cost over $100 US in small quantities.[citation needed]Op-amps may be packaged as components, or used as elements of more complex integrated circuits.

The op-amp is one type of differential amplifier. Other types of differential amplifier include thefully differential amplifier (similar to the op-amp, but with two outputs), the instrumentationamplifier (usually built from three op-amps), the isolation amplifier (similar to the

instrumentation amplifier, but with tolerance to common-mode voltages that would destroy anordinary op-amp), and negative feedback amplifier (usually built from one or more op-amps anda resistive feedback network).

8.2 Operation

8.1:A ( )


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The amplifier's differential inputs consist of a V+input and a Vinput, and ideally the op-ampamplifies only the difference in voltage between the two, which is called the differential inputvoltage. The output voltage of the op-amp is given by the equation:

where V+is the voltage at the non-inverting terminal, Vis the voltage at the inverting terminalandAOLis the open-loop gain of the amplifier (the term "open-loop" refers to the absence of afeedback loop from the output to the input).

The magnitude ofAOLis typically very large10,000 or more for integrated circuit op-ampsand therefore even a quite small difference between V+and Vdrives the amplifier output nearlyto the supply voltage. This is called saturationof the amplifier. The magnitude ofAOLis not wellcontrolled by the manufacturing process, and so it is impractical to use an operational amplifieras a stand-alone differential amplifier. Without negative feedback, and perhaps with positivefeedback for regeneration, an op-amp acts as a comparator. If the inverting input is held at

ground (0 V) directly or by a resistor, and the input voltage Vinapplied to the non-inverting inputis positive, the output will be maximum positive; if Vinis negative, the output will be maximumnegative. Since there is no feedback from the output to either input, this is an open loopcircuitacting as a comparator. The circuit's gain is just theAOL< of the op-amp.

8.2: A ( )

If predictable operation is desired, negative feedback is used, by applying a portion of the outputvoltage to the inverting input. The closed loopfeedback greatly reduces the gain of the amplifier.If negative feedback is used, the circuit's overall gain and other parameters become determinedmore by the feedback network than by the op-amp itself. If the feedback network is made ofcomponents with relatively constant, stable values, the unpredictability and inconstancy of theop-amp's parameters do not seriously affect the circuit's performance. Typically the op-amp'svery large gain is controlled by negative feedback, which largely determines the magnitude of itsoutput ("closed-loop") voltage gain in amplifier applications, or the transfer function required (in


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analog computers). High input impedance at the input terminals and low output impedance at theoutput terminal(s) are important typical characteristics.

For example, in a non-inverting amplifier (see the figure on the right) adding a negative feedbackvia the voltage divider Rf,Rgreduces the gain. Equilibrium will be established when Voutis just

sufficient to reach around and "pull" the inverting input to the same voltage as Vin. The voltagegain of the entire circuit is determined by 1 + Rf/Rg. As a simple example, if Vin= 1V and Rf=Rg, Voutwill be 2V, the amount required to keep Vat 1V. Because of the feedback provided byRf,Rgthis is a closed loopcircuit. Its overall gain Vout/ Vinis called the closed-loop gainACL.Because the feedback is negative, in this caseACLis less than theAOLof the op-amp.

Another way of looking at it is to make two relatively valid assumptions: One, that when an op-amp is being operated in linear mode, the difference in voltage between the non-inverting (+) pinand the inverting (-) pin is so small as to be considered negligible.[3]The second assumption isthat the input impedance at both + and - pins is extremely high (at least several megohms withmodern op-amps). Thus, when the circuit to the right is operated as a non-inverting linear

amplifier, Vin will appear at the + and - pins and create a current i through Rg equal to Vin/Rg.Since Kirchoff's current law states that the same current must leave a node as enter it, and sincethe impedance into the - pin is near infinity, we can assume the overwhelming majority of thesame current i travels through Rf, creating an output voltage equal to Vin + i*Rf. By combiningterms, we can easily determine the gain of this particular type of circuit.


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8.3 Op-amp characteristics

8.3.1

8.3

A .

An ideal op-amp is usually considered to have the following properties, and they are consideredto hold for all input voltages:

Infinite open-loop gain (when doing theoretical analysis, a limit may be taken as openloop gainAOLgoes to infinity).

Infinite voltage range available at the output ( ) (in practice the voltages available

from the output are limited by the supply voltages and ). The power supplysources are called rails.

Infinite bandwidth (i.e., the frequency magnitude response is considered to be flat

everywhere with zero phase shift).

Infinite input impedance(, , ,

).

(..,

).

(.., ,

).

(.., )

( ).

(.., ,

). .

().

.

These ideals can be summarized by the two "golden rules":


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.

.

. .4:177

The first rule only applies in the usual case where the op-amp is used in a closed-loop design(negative feedback, where there is a signal path of some sort feeding back from the output to the

inverting input). These rules are commonly used as a good first approximation for analyzing ordesigning op-amp circuits.

In practice, none of these ideals can be perfectly realized, and various shortcomings andcompromises have to be accepted. Depending on the parameters of interest, a real op-amp may

be modeled to take account of some of the non-infinite or non-zero parameters using equivalentresistors and capacitors in the op-amp model. The designer can then include the effects of these

undesirable, but real, effects into the overall performance of the final circuit. Some parametersmay turn out to have negligible effect on the final design while others represent actual limitations

of the final performance,that must be evaluated.

8.3.2

Real op-amps differ from the ideal model in various respects.

8.4 DC imperfections

Real operational amplifiers suffer from several non-ideal effects:

8.4.1

Open-loop gain is infinite in the ideal operational amplifier but finite in real operational

amplifiers. Typical devices exhibit open-loop DC gain ranging from 100,000 to over 1

million. So long as the loop gain (i.e., the product of open-loop and feedback gains) is

very large, the circuit gain will be determined entirely by the amount of negative

feedback (i.e., it will be independent of open-loop gain). In cases where closed-loop gain

must be very high, the feedback gain will be very low, and the low feedback gain causes

low loop gain; in these cases, the operational amplifier will cease to behave ideally.

8.4.2

The differential input impedance of the operational amplifier is defined as the impedance

between its two inputs; the common-mode input impedance is the impedance from each

input to ground. MOSFET-input operational amplifiers often have protection circuits that

effectively short circuit any input differences greater than a small threshold, so the input

impedance can appear to be very low in some tests. However, as long as these operational


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amplifiers are used in a typical high-gain negative feedback application, these protection

circuits will be inactive. The input bias and leakage currents described below are a more

important design parameter for typical operational amplifier applications.

8.4.3

Low output impedance is important for low-impedance loads; for these loads, the voltage

drop across the output impedance of the amplifier will be significant. Hence, the output

impedance of the amplifier limits the maximum power that can be provided. In

configurations with a voltage-sensing negative feedback, the output impedance of the

amplifier is effectively lowered; thus, in linear applications, op-amps usually exhibit a

very low output impedance indeed. Negative feedback can not, however, reduce the

limitations that Rloadin conjunction with Routplace on the maximum and minimum

possible output voltages; it can only reduce output errors withinthat range.

Low-impedance outputs typically require high quiescent (i.e., idle) current in the outputstage and will dissipate more power, so low-power designs may purposely sacrifice low

output impedance.

8.4.4

Due to biasing requirements or leakage, a small amount of current (typically ~10

nanoamperes for bipolar op-amps, tens of picoamperes for JFET input stages, and only a

few pA for MOSFET input stages) flows into the inputs. When large resistors or sources

with high output impedances are used in the circuit, these small currents can produce

large unmodeled voltage drops. If the input currents are matched, and the impedancelooking out of both inputs are matched, then the voltages produced at each input will be

equal. Because the operational amplifier operates on the difference between its inputs,

these matched voltages will have no effect (unless the operational amplifier has poor

CMRR, which is described below). It is more common for the input currents (or the

impedances looking out of each input) to be slightly mismatched, and so a small offset

voltage (different from the input offset voltage below) can be produced. This offset

voltage can create offsets or drifting in the operational amplifier. It can often be nulled

externally; however, many operational amplifiers include offset null or balance pins and

some procedure for using them to remove this offset. Some operational amplifiers

attempt to nullify this offset automatically.

8.4.5

This voltage, which is what is required across the op-amp's input terminals to drive the

output voltage to zero, is related to the mismatches in input bias current. In the perfect

amplifier, there would be no input offset voltage. However, it exists in actual op-amps


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8.4.11

A .

.

, .

8.5 AC imperfections

The op-amp gain calculated at DC does not apply at higher frequencies. Thus, for high-speed

operation, more sophisticated considerations must be used in an op-amp circuit design.

8.5.1

A . ,

. ,

(B). , B 1 5

200 , 1 1 .

B .

, :

.A

. ,

180

. ,

,

.

. A,

.

.

, . ,

; ,

.

, , . Reduced bandwidth also results inlower amounts of feedback at higher frequencies, producing higher distortion,


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noise, and output impedance and also reduced output phase linearity as thefrequency increases.

Typical low-cost, general-purpose op-amps exhibit a GBWP of a few megahertz.

Specialty and high-speed op-amps exist that can achieve a GBWP of hundreds of

megahertz. For very high-frequency circuits, a current-feedback operational amplifier isoften used.

8.5.2 Input capacitance

Most important for high frequency operation because it further reduces the open-loop

bandwidth of the amplifier.

8.5.3

, .

:

,

;

,

,

'

8.5.4

' . , . ,

.

,

.

8.5.5

. .

.

8.6 Power considerations8.6.1

The output current must be finite. In practice, most op-amps are designed to limit the

output current so as not to exceed a specified level around 25 mA for a type 741 IC op-


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Figure 8.4 comparator

8.7.3 :

A dedicated voltage comparator will generally be fasterthan a general-purpose operational amplifier pressed into service as a comparator. A dedicatedvoltage comparator may also contain additional features such as an accurate, internal voltagereference, an adjustable hysteresis and a clock gated input.

A dedicated voltage comparator chip such as LM339 is designed to interface with a digital logic

interface (to a TTL or a CMOS). The output is a binary state often used to interface real worldsignals to digital circuitry (see analog to digital converter). If there is a fixed voltage sourcefrom, for example, a DC adjustable device in the signal path, a comparator is just the equivalentof a cascade of amplifiers. When the voltages are nearly equal, the output voltage will not fallinto one of the logic levels, thus analog signals will enter the digital domain with unpredictableresults. To make this range as small as possible, the amplifier cascade is high gain. The circuitconsists of mainly Bipolar transistors except perhaps in the beginning stage which will likely befield effect transistors. For very high frequencies, the input impedance of the stages is low. Thisreduces the saturation of the slow, large P-N junction bipolar transistors that would otherwiselead to long recovery times. Fast small Schottky diodes, like those found in binary logic designs,improve the performance significantly though the performance still lags that of circuits with

amplifiers using analog signals. Slew rate has no meaning for these devices. For applications inflash ADCs the distributed signal across 8 ports matches the voltage and current gain after eachamplifier, and resistors then behave as level-shifters.

The LM339 accomplishes this with an open collector output. When the inverting input is at ahigher voltage than the non inverting input, the output of the comparator connects to the negativepower supply. When the non inverting input is higher than the inverting input, the output is'floating' (has a very high impedance to ground).

INPUT OUTPUT->+ Grounded

+>- Floating

With a pull-up resistor and a 0 to +5V power supply, the output takes on the voltages 0 or +5 andcan interface with TTL logic:


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.

Figure 8.5 various comparators

8.7.4 :While in general comparators are "fast," their circuits are not

immune to the classic speed-power tradeoff. High speed comparators use transistors with largeraspect ratios and hence also consume more power. Depending on the application, select either acomparator with high speed or one that saves power. For example, nano-powered comparators in

space-saving chip-scale packages (UCSP), DFN or SC70 packages such as MAX9027,LTC1540, LPV7215, MAX9060 and MCP6541 are ideal for ultra-low-power, portableapplications. Likewise if a comparator is needed to implement a relaxation oscillator circuit tocreate a high speed clock signal then comparators having few nano seconds of propagation delaymay be suitable. ADCMP572 (CML output), LMH7220 (LVDS Output), MAX999 (CMOSoutput / TTL output), LT1719 (CMOS output / TTL output), MAX9010 (TTL output), andMAX9601 (PECL output) are examples of some good high speed comparators.


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Figure 8.7 LM339 pin diagram

8.7.5 339:

Wide single supply voltage range = 2V

Very low supply current draw (0.8mA) independent of supply. Low input biasing current 25nA Low input offset current +(-) 5 nA Input common-node voltage range includes ground.

Different input voltage range equals to power supply voltage Low output 250mV at 4mA saturation voltage.

Output voltage compatible with TTL, DTL, ECL, MOS, CMOS logic systems.


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CHAPTER 9

HARDWARE

9.1 CIRCUIT OF DC-AC CONVERTER

Figure 9.1 dc-ac converter


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9.2 TRIANGULAR PULSE GENERATOR:

Figure 9.2 triangular pulse generator


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9.3 COMPLETE CIRCUIT DIGRAM:

Figure 9.3 complete circuit diagram


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9.4 TOTAL OUTPUT OF DC-AC CONVERTER:

Figure 9.4 output of DC-AC converter


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10

10.1 :

1 12 12

2 15 17

3 20 23

10.1

10.2 :

For our future purpose by using micro controller we can swich off and on the dc-ac converter.Like when the power is switched off the microcontroller automatically triggers the mosfet and ac

voltage is produced. when power is on the micro controller switches off the triggering of mosfetand normal power supply is used.

This DC-AC converter is further used to switch on leds and tube lights for internal use byusing dc supply.

CHAPTER 11

APPENDIX

11.1 :

11.1.1 (4007):In electronics, a diode is a type of two-terminal electronic

component with nonlinear resistance and conductance (i.e., a nonlinear currentvoltage

characteristic), distinguishing it from components such as two-terminal linear resistors which

obey Ohm's law. A semiconductor diode, the most common type today, is a crystalline piece of

semiconductor material connected to two electrical terminals.[A vacuum tube diode (now rarely

used except in some high-power technologies) is a vacuum tube with two electrodes: a plate and

a cathode.


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11.1.2 :

Diffused Junction

High Current Capability and Low Forward Voltage Drop

Surge Overload Rating to 30A Peak

Low Reverse Leakage Current

Case: DO-41

Case Material: Molded Plastic. UL Flammability Classification

Rating 94V-0

Moisture Sensitivity: Level 1 per J-STD-020D

Terminals: Finish - Bright Tin. Plated Leads Solderable per

MIL-STD-202

Polarity: Cathode Band

Mounting Position: Any

Ordering Information:

Marking: Type Number

Weight: 0.30 grams (approximate)

11.1.3 :

Peak Repetitive Reverse Voltage(V rrm) =50V

Working Peak Reverse Voltage(V rwm) =50V

DC Blocking Voltage(Vr) =40V

RMS Reverse Voltage VR(RMS) =35V

Average Rectified Output Current (Note 1) @ TA = 75C IO 1.0 A

Non-Repetitive Peak Forward Surge Current 8.3ms

single half sine-wave superimposed on rated load IFSM =30 A

Forward Voltage @ IF = 1.0A VFM 1.0 V


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Peak Reverse Current @TA = 25C 50 A

at Rated DC Blocking Voltage @ TA = 100C IRM 5.0

Typical Junction Capacitance (Note 2) Cj 15 8 pF

Typical Thermal Resistance Junction to Ambient 100 K/W

Maximum DC Blocking Voltage Temperature TA +150 C

Operating and Storage Temperature RangeTJ, TSTG -65 to +150 C

11.2 :

The metaloxidesemiconductor field-effect transistor (MOSFET, MOS-FET, or MOS FET)

is a transistor used for amplifying or switching electronic signals.

11.2.1 :

Very Low RDS(on) at 4.5V VGS

Ultra-Low Gate Impedance

Fully Characterized Avalanche Voltage and Current.

11.2.2 :

Drain-to-Source Voltage =30V

Gate-to-Source Voltage =20V

Continuous Drain Current, VGS @ 10V =56A

Continuous Drain Current, VGS @ 10V =39A

Pulsed Drain Current =20A

PD @TC = 25C Maximum Power Dissipation =50W

PD @TC = 100C Maximum Power Dissipation=25W

Linear Derating Factor =0.33W/c


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TJ Operating Junction and

TSTG Storage Temperature Range =-55 to 75c

11.3 339:

Input Bias Current 2 5

Input Offset Current 5 5

Input CommonMode VoltageRange

0 1.5

Supply Current ICCmA

RL = 8 (For AllComparators

RL = 8, VCC = 30Vdc

0.8

1

2

2.5

Voltage Gain 50 200

Large SignalResponse Time

300

Response Time 1.3

Output Sink CurrentISink

6 16

Saturation Voltage 130 400

Output LeakageCurrent

0.1


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CHAPTER 12

REFERENCES

1.

M.H Rashid, Power electronics circuits devices and appliances,prentice hall of India, 2

ndEdition,1998

2. Bimal k.Bose, Modern Power Electronics and AC drives, Prentice

Hall PTR

3. Muhammad H.Rashid, Power electronics handbook, Academic press

4. M.Morris Mano, Digital logic and computer Design, Prentice Hall of

India

5. www.datasheetarchive.com

6. www.intersil.com

7.

www.national.com8.

www.engineersgarage.com

9. www.texasinstruments.com

10.www.eupec.com

11.www.infineon.com

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