7370642 inverter cum charger

Inverter Cum Charger

SYNOPSIS

Today the world is of electronics and computers, the development in

there spheres are unprecedented and there are more and more sophisticated devices

being launched.

Therefore the need for power system with sophisticated and

reliability is also immense.

Power device employing the transistors are being used to cope up the

needs of the sophisticated systems.

This project deals with the design and lubrication of 50 HZ inverter

using power transistors. The report induce the step by step designed of electronic

control circuit.

The results are so obtained the modifications needed for further

improving the performances are also discussed.

Govt. Poly. Washim 1


INTRODUCTION

Inverter is a circuit use to convert a D.C. power into A.C. power at a

designed output voltage and frequency. This conversion can be achieved either by

controlling ON and OFF devices [ eg. BJTs MOSFETs IGBTs, SITs, GTOs etc.]

or by forced commutations thyristors, depending on application. The output

frequency of an inverter is determined by the rate at which the semiconductor

devices are switched ON and OFF by inverter control circuitry.

At present, most power supply system available in the market

provides square wave output, which is unsuitable for powering those equipment

which has rotating machinery such as in induction motors and blowers also for

computer system, which make use of linear power supplies.

Since wave (230 V AC at 50 HZ) inverter (230 V AC at 50 HZ) is the

ideal choice for powering devices such as cordless phone, medical electronics

equipments and even T.V., V.C.R. and Computer etc. during mains failure.

In this report project, a push-pull half bridge inverter is used. The

power transistors are used for switching purpose. During each half cycle only one

of two power transistors conduct and drives the current through half of the primary

winding of output transformer in opposite direction. Thus the alternating current

flows through the primary and also through the secondary of transformer. And this

A.C. output is converted into pure sine wave using OTT filter and sine wave

output of OTT filter is given to A.C.load.



IMPORTANCE OF INVERTER

An inverter circuit is used to convert DC power to AC power. This

conversion can be achieved. Either by transistors or by SCR's. For low and

medium power inputs, transistorized inverters are suitable but for high power

outputs, SCR's should be used. For low power self-oscillating transistor inverters

are suitable but for high power outputs, driven inverters are more common than

self-oscillating one.

Moreover for multiphase Ac output there is no alternative other than

better frequency stability because a separator master oscillator is used for the

purpose for the application in invertors, transistors have some Advantages over

SCR's regarding the switching speed, simplicity in control circuit higher efficiency

and greater reliability. This is mainly due to the fact that SCR's inverters requires

extra circuits to turn SCR's off, moreover additional complex logic circuits may be

required to prevent false, triggering and provide proper commutation.

Transistor invertors are useful in wide variety of applications. They

provide power to the complicated electronic system. They are useful in the

operation and various airbone equipment. More over they find wide applications

in a Ac to Dc converter.



CLASSIFICATION OF INVERTERS

The inverter are classified into two groups namely, voltage source

inverters and current source inverters.

Voltage source inverter is one in which the source has small and

negligible impedance, because of low, impedance, the terminal voltage of VSI

remains substainly constant with variations in load. It is therefore, equally

suitable to single motor and multi motor drives. On the other hand the current

sources inverters is supplied with a controlled current from DC source of high

impedance. Typically a phase controlled SCR's feeds the inverter with revaluated

current through series inductor. Some of important industrial applications of CSI

are in variable speed AC motor drives, HVDC transmission lines, etc.

According to number of phases of load, inverter are classified as

single phase inverter and three phase invertors.

Single phase bridge inverter are again classified as half bridge and

full bridge inverter. 3.1 shows half bridge inverter and figure 3.2 shows full

bridge inverter are classified according to semiconductor devices used, Such as

thyristorised, inverter, transistorized MOSFET based inverter.

The thyristorised inverter are further classified as series inverter,

parallel inverter. Load commutated inverter and force commutated inverter. The

force-commutated inverter are classified again as McMurray and McMurray. Bed

ford inverter. The classification of inverters is summarized in table.



CLASSIFICATION OF THE INVERTERS


Inverter

VSI inverter CSI inverter

Single Phase inverter

Three Phase Inverter

Half Bridge

inverters

Single phase Bridge inverter

Three Phase Bridge Inverter

MOSFET Based

TransistorisedThyristorised

Series Inverter

Parallel Inverter

Load commutation

inverters

Forced commutation

inverter

MC Murrary Bedford

MC Murray


THEORY OF TRANSISTOR

Power transistors have controlled turn ON and turn off

characteristics. The transistors, which are used as switching elements are operated

in the saturation region, resulting in a low on state voltage drop. The switching



speed of modern transistors in much higher than that of thyristors and they are

extensively employed in dc-dc and ac-ac converter, with inverse parallel connected

diodes to provide bi-directional current flows.

The power transistors can be classified broadly in to four categories :-

1) Bipolar junction transistors (BJTs)

2) Metal-oxide semiconductor field effect transistor (MOSFETs)

3) Static induction transistors (SITs)

4) Insulated-gate, bipolar transistors (IGBTs)

BJT, or MOSFET's, SIT's or IGBT's can the assumed as ideal

switches to explain the power conversion techniques. A transistors switch is much

simpler then a forward commuted thyristor switch.

POWER BIPOLAR JUNCTION TRANSISTORS

A bipolar junction transistor is a three layer device with emitter (E),

base (B) and collector (C) regions. The term bipolar indicates that current flow

consists of a movement of both positive and negative charges, that is holes and

electrons.



As indicated in figure the N-Type material, separated by a p-type

base region. This is the N-P-N transistor which has the circuit symbol shown. For

high voltage and high current applications. N-P-N transistors are more widely

used because they are easy to manufacture and cheaper.

For a normal transistor operation the base-emitter junction is forward

bias and the emitter acts as a source of mobile carriers which enter the base region,

these injected carriers are electrons in the N-P-N transistor. In general, the emitter

region is made of heavily doped material to increase the number of injected

carriers, which become minority carries when they enter the base. Most of these

minority carriers diffuse through the base region, which is very narrow and arrive

at the collector base junction. This junction is reversed by an external voltage and

hence, the minority base carriers injected by the emitter are swept into the

collector region by the electric field at the collector base junction. Figure shows



the diagrammatic representation of the electron current flow in an N-P-N

transistor. Some electron recombine in the base region and do not reach the

collector. Hence, collector current, IC is slightly less than emitter current, IE. The

difference between these currents is responsible for the small base current IB.


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CIRCUIT DESCRIPTION

A) Inverter control circuit :-

It uses the basic square wave (astable multivibrator) oscillator

employing IC555, with 5.1 supply voltage derived from 12 v. battery by using 5.1v

zener ZD1 in series with a resistance R1. A stable multivibrator is designed for a



frequency of 100 HZ, which can be varied above or below 100 HZ using preset

PR2. The frequency 'f' or of a stable multivibrator is given by the relationship.

f = 1.44/ (RA + 2RB)C HZ.

Where RB = circuit resistance of preset PR1

If RA = 220 Ohms and RB = 15 Kilo-ohms then frequency = 100

HZ. Due to the tolerance of the component values. Observed frequency may not

be exactly equal to 100 HZ and therefore preset PR1 may need to be suitably

adjusted.

The output of the a stable multivibrator is given to pin no-5 the IC

7473, which produces the two 50 HZ square wave outputs at its pin 8 and 9 with a

phase difference of 180 degrees between the two. One of outputs is coupled to the

base of transistor T2 through diode D1 and limiting resistor R4 while the second

output is given to the base of transistor T1 through diode D2 and series resistor R5.


I/P to pin no. 5 of IC - 7473


B) Power Output Stage :-

The power stage includes transistors, output transformer and filters.

The transistors are used in switching applications because of there

inherent high speed turn - ON and turn OFF capabilities. The output pulses

generated from pin no.8 and pin no.9. of IC 7473 are applied to the base of

transistor T1 and T2 which works as a driver circuit for power transistor.

During half cycle, only one of the two transistors, conducts and

drives the current through half the primary winding of transformer.

Thus overall efficiency of inverter is quite high. The efficiency is

further reduced if transformer losses are taken into consideration.

C) Ott Filter :-

The output of the secondary transformer is square wave. In order to

attenuate the harmonic contents. It is necessary to pass them through filter.

The OTT filter performs following important functions.

1) It provides sine wave output, thus the essential elimination of harmonic content

to the load.

2) It maintains a capacitive load to the inverter overlarge range of load power

factor. However it suffers from the disadvantage that the voltage drop across the

circuit is more.



E) Testing and Performance :-

Suitable actual size sided PCB for the circuit of figure (T) is

manufactured and all the component with expect transistors are accommodate on

the PCB the two transistors are to be mounted on appropriate heat sink. A single

heat sink may be used but the transistors should be insulated from the heat sink



using mica insulator and secured using either IC screw/nuts or appropriate Teflon

washers ensuring that the body is not shorted to heat sink. Also use heat sink

compound between the TRANSISTORS body and mica insulators as well as

between mica insulators and heat sink. Precaution by way shorting all three

terminates of transistor together using a thin copper stand and during together may

be taken. When the item is being handled during the assembly. Remove this

shorting only after the assembly and the computer using is over.

We have readymade transformer with primary voltage specifications

of 12VAC-012VAC (05 amp. Current rating) and secondary voltage rating of 230

V ( 750 MA or higher current ) the supply for the circuit is taken from a single

12V.07 Ah battery which is adequate for supplying about 200 W/load for 2 hours

in absence of main supply. Higher ampere hour battery could be used for

obtaining longer stand by capacity/period.

Figure shows the wiring diagram of different parts of inverter. Multi

stand Teflon isolated wires of suitable current handling capacity for extending the

connection from battery as well as transformer X1 to the transistor terminal the

PCB should be fully tested before connecting the final collector output to

transistors.

The OTT filter which is designed is connected across the secondary

transformer and across the output of OTT filter the load is connected.



In this way all the connections are made by following certain

precautions and circuit is tested.

F) Charger Circuit and Description :-

For charging purpose the supply from the A.C. main is given to the

step down transformer (9-0-9) which steps down the 230 V of A.C. supply to 12

volt. A.C. from the secondary of the step down transformer is given to the diode



rectifier circuit which converts the A.C. to D.C. (12V). This 12 V. D.C. supply is

used for charging the battery.

In rectifier circuit the current limiting resistor is placed to protect the

battery from overcharging.

List of Components

No. Components Specification Quantity1. Inverter xmer 12-0-12 v

5 amp

(Step-up xmer)

1


CHARGER CIRCUIT


2. Charger xmer 0.9 1 amp

step-down - xmer

1

3. Power transistor 2 N 3055 24. Driver transistor SL 100 or CL 100 25. IC 555 and 7473 26. LED 17. Capacitor 0.47 µF, 100v.

0.01 µF, 100 v,

2

8. Zener diode 5 v 19. Preset 22k 1

10. Resistors 100 r

1 r & 80 r

1

11. Heat sink or Heat

absorber

(Metal plate of Aluminium) 1

12. Diode for rectification 1N 4007 413. Resistor 2 W, 0.68 r 114. Diode 1N - 4148 215. Miscellaneous material connecting wire, soldering g rease,

PCB (6 x 4" ),

As per

requirem-

ent.

CHARACTERISTICS OF INVERTER

Characteristics of inverter are as follows :-

1) Provision for over current protection.

2) Capacity to operation inductive load

3) Controlled output

4) Must have sinusoidal output

5) Must be able to work even when load is disconnected.



APPLICATION AND ADVANTAGES

Inverter are used in various applications such as

1. In UPS [ uninterruptible power supplies ] systems.

2. For operating GYROS and airborne equipment.

3. For providing power to complex electronics system of a satellite and cool

astronauts suits.

4. It is useful in luxury buses and car.

5. Very useful in domestic use when supply in off.

6. Variable speed motor AC drives

7. Induction heating wring AC supply.

8. Inverter can used in household application as AC power source.

9. Sine wave inverter is ideal choice for powering devices such as cordless phase,

medical, electronics equipment and even TV, VCR, etc. during mains failure.

FUTURE TRENDS AND MODIFICATIONS

1. With better layout techniques, switching losses can be further minimized,

thus reducing losses on switching transistors.

2. The regulation of the inverter can be improved by using feed back

techniques.



3. If higher switching frequency is used, size of output and filter components

will get reduced, response will be better and correction time will be fast and

also improved step load performance is achieved.

4. The inverter circuitry can made more smart by adding extra circuitry such

as battery deep discharge and no load over load cutoff and battery changing

circuitry.

5. Relays can be used to protect the device.

RESULT AND CONCLUSION

Transistor based inverter is tested and no load voltage is found to be

228 V, A. C. from given input of 12 V, D. C.

The output waveform is found to be quasi square wave and it is

further improved by using OTT filter.



This circuit can be used for a load up to 100 watts.

Now a days, generally this is used in luxury travels and also be use

for emergency light when battery of 12 V. D.C. is available.

BIBLIOGRAPHY

1) Singh and Khanchandani, " Power Electronics"

Tata McGraw Hill ( Pg. 265, 603 )

2) Goyal N. C. and Khetan R. K.

"A Monograph on Electronics Design Principles" Pg. 199



- Khanna Publishers

3) Rashid M. H., " Power Electronics circuit Devices and

Applications". Page. 540

Printice Hall

4) "Power Electronics" P.C. Sen.


7370642 inverter cum charger

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