Pe Lab Manual_avit_icycle New

AARUPADAI VEEDU

INSTITUTE OF

TECHNOLOGY

P.Rajasekaran, M.E.,(Ph.D)

A.Anitha, B.E

R.Indumathi. B.E., (M.E)

DEPARTMENT OF ELECTRICAL AND

ELECTRONICS ENGINEERING

POWER ELECTRONICS LAB

POWER ELECTRONICS LAB MANUAL

A a r u p a d a i V e e d u I n s t i t u t e o f T e c h n o l o g y

DEPARTMENT OF ELECTRICAL AND ELECTRONICS

ENGINEERING

ISO / WI NO: -Rev: 1 / Effective Date: 10-07-2010

POWER ELECTRONICS LABORATORY

LAB MANUAL / OBSERVATION

V SEMESTER - EEE

Prepared by: Edited by,

P. Rajasekaran M.E (Ph.D) Dr.N.Veerappan M.E,Ph.D.,

A. Anitha B.E HOD EEE&EIE

R. Indumathi B.E (M.E)



PREFACE

This Laboratory manual in Power electronics lab has been revised in order to be up to date with

Curriculum changes, laboratory equipment upgrading.

This Laboratory provides ample opportunity for a good understanding of the power electronic

components and to study the salient features of power diodes, power transistors and other

members of thyristor family. This Laboratory also provides hands on understanding the use of

semiconductor devices in the industrial applications in the field of Electrical, Electronics,

Instrumentation and Control Engineering and the use of Power-electronic components in low as

well as high power electronics.

Every effort has been made to correct all the known errors, if you find any additional errors or

anything else you think is an error, please inform the HOD/EEE at [email protected].

The Authors thank all the staff members from the department for their valuable Suggestions and

contributions.

The Authors

Department of EEE



TABLE OF CONTENTS

S.No Experiment Name Page no

I st Cycle Experiment

1. SCR, MOSFET & IGBT Characteristics - Study.

2. SCR half & fully controlled bridge rectifiers

3. UJT, R, RC Firing circuits for SCR.

4. SCR series inverter.

5. SCR DC Voltage Commutated chopper.

6. IGBT chopper



LABORATORY SAFETY INFORMATION

Introduction

The danger of injury or death from electrical shock, fire, or explosion is present while conducting experiments in this laboratory. To work safely, it is important that you understand the prudent practices necessary to minimize the risks and what to do if there is an accident.

Electrical Shock

Avoid contact with conductors in energized electrical circuits. Electrocution has been reported at dc voltages as low as 42 volts. Just 100ma of current passing through the chest is usually fatal. Muscle contractions can prevent the person from moving away while being electrocuted.

Do not touch someone who is being shocked while still in contact with the electrical conductor or you may also be electrocuted. Instead, press the Emergency Disconnect . This shuts off all power, except the lights.

Make sure your hands are dry. The resistance of dry, unbroken skin is relatively high and thus reduces the risk of shock. Skin that is broken, wet or damp with sweat has a low resistance.

When working with an energized circuit, work with only your right hand, keeping your left hand away from all conductive material. This reduces the likelihood of an accident that results in current passing through your heart.

Be cautious of rings, watches, and necklaces. Skin beneath a ring or watch is damp, lowering the skin resistance. Shoes covering the feet are much safer than sandals.

If the victim isn't breathing, find someone certified in CPR. Be quick! If the victim is unconscious or needs an ambulance, contact the Department Office for help.

Fire

Transistors and other components can become extremely hot and cause severe burns if touched. If resistors or other components on your proto-board catch fire, turn off the power supply and notify the instructor. If electronic instruments catch fire, disconnect the power supply immediately. These small electrical fires extinguish quickly after the power is shut off. Avoid using fire extinguishers on electronic instruments.

Explosion

When using electrolytic capacitors, be careful to observe proper polarity and do not exceed the voltage rating. Electrolytic capacitors can explode and cause injury. A first aid kit is located on the wall near the door. Proceed to Student Health Services, if needed.



GUIDELINES FOR LABORATORY NOTEBOOK

The laboratory notebook is a record of all work pertaining to the experiment. This record should be sufficiently complete so that you or anyone else of similar technical background can duplicate the experiment and data by simply following your laboratory notebook. Record everything directly into the notebook during the experiment. Do not use scratch paper for recording data. Do not trust your memory to fill in the details at a later time.

Organization in your notebook is important. Descriptive headings should be used to separate and identify the various parts of the experiment. Record data in chronological order. A neat, organized and complete record of an experiment is just as important as the experimental work.

1. Heading:

The experiment identification (number) should be at the top of each page.

2.Objective:

A brief but complete statement of what you intend to find out or verify in the experiment should be at the beginning of each experiment

3.Diagram:

A circuit diagram should be drawn and labeled so that the actual experiment circuitry could be easily duplicated at any time in the future. Be especially careful to record all circuit changes made during the experiment.

4.Equipment List:

List those items of equipment which have a direct effect on the accuracy of the data. It may be necessary later to locate specific items of equipment for rechecks if discrepancies develop in the results.

5.Procedure:

In general, lengthy explanations of procedures are unnecessary. Be brief. Short commentaries along side the corresponding data may be used. Keep in mind the fact that the experiment must be reproducible from the information given in your notebook.

6.Data:

Think carefully about what data is required and prepare suitable data tables. Record instrument readings directly. Do not use calculated results in place of direct data; however, calculated results may be recorded in the same table with the direct data. Data tables should be clearly identified and each data column labeled and headed by the proper units of measure.

7.Calculations:

Not always necessary but equations and sample calculations are often given to illustrate the treatment of the experimental data in obtaining the results.



8.Graphs:

Graphs are used to present large amounts of data in a concise visual form. Data to be presented in graphical form should be plotted in the laboratory so that any questionable data points can be checked while the experiment is still set up. The grid lines in the notebook can be used for most graphs. If special graph paper is required, affix the graph permanently into the notebook. Give all graphs a short descriptive title. Label and scale the axes. Use units of measure. Label each curve if more than one on a graph sheet.

9.Results:

The results should be presented in a form which makes the interpretation easy. Large amounts of numerical results are generally presented in graphical form. Tables are generally used for small amounts of results. Theoretical and experimental results should be on the same graph or arrange in the same table in a way for easy correlation of these results.

10.Conclusion:

This is your interpretation of the results of the experiment as an engineer. Be brief and specific. Give reasons for important discrepancies.



CIRCUIT DIAGRAM: CHARACTERISTICS OF SCR

BASE DIAGRAM OF TY604

PINDIAGRAM OF SCR



MODEL GRAPH



OBSERVATION TABLE:

Static V-I Characteristics of SCR

For I g1 = ----- = Constant For I g2 = ----- = Constant

Serial.

No.

Anode to cathode

voltage(Vak) (Volt)

Anode current (I a)

(Ampere)

Serial.

No.

Anode to cathode

voltage(Vak) (Volt)

Anode current (I a)

(Ampere)



EXPT.NO :

DATE :

SCR, MOSFET & IGBT CHARACTERISTICS

SCR CHARACTERISTICS

AIM :

To study the V-I characteristics of S.C.R. and determine the Break over Voltage, Holding current & Latching current

APPARATUS REQUIRED :

Sl.No.

NAME OF THE COMPONENTS

RANGE

QUANTITY

1 SCR,MOSFET,IGBT Characteristics Module

2 Ammeter (0-30)mA 1

3 Voltmeter (0-30)V 1

4 Connecting Wires As required

THEORY:

Silicon Controlled Rectifier (SCR): Thyristor (generally known as SCR) is a four layer,

three junction, pnpn semiconductor switching deivce. It has three terminals; anode, cathode and

gate. Basically, a thyristor consists of four layers of alternate p-type and n-type silicon

semiconductors forming three junctions J1,J2 and J3. A gate terminal is usually kept near the

cathode terminal. The terminal connected to outer p region is called anode (A), the terminated



connected to outer n region is called cathode and that connected to inner p region is called the

gate (G). The symbol of SCR is shown in figure .

A circuit diagram for obtaining static V-I characteristics of a thyristor is shown in Fig . The anode and cathode are connected to main source through the load. The gate and cathode are fed from a source Vs which gives positive gate current from gate to cathode. Fig , shows static V-I characteristics of a thyristor. Va is the anode voltage across thyristor terminals A, K and Ia is the anode current. Fig reveals that a thyristor has three basic modes of operation; namely, reverse blocking mode, forward blocking (off-state) mode and forward conduction (on-state) mode. These three modes of operation are now discussed below.

(a). When cathode is made positive with respect to anode with gate open, thyristor is reverse

biased. Junctions J1, J3 are reverse biased whereas junction J2 is forward biased.



The device behaves like two diodes connected in series with reverse voltage appearing

across them. A small leakage current of the order of a few milliamperes or few microamperes

flows depending upon the SCR rating.. This is reverse blocking mode, called the off state of the

SCR. If the reverse voltage is increase, then at a critical breakdown level, called reverse

breakdown voltage VBR, an avalanche occurs at J1 and J3 and the reverse current increases

rapidly. A large current associated with VBB gives rise to more losses in the thyristor. This may

lead to thyrisstor damage as the junction temperature may exceed its permissible temperature

rise. It should, therefore, be ensured that maximum working reverse voltage across a SCR does

not exceed VBR.

(b). Forward blocking mode: When anode is positive with respect to the cathode with gate circuit

open, SCR is said to be forward biased. During this mode, junctions J1, J3 are forward biased but

junction J2 is reverse biased. In this mode, a small current, called forward leakage current, flows.

In case the forward voltage is increased, ten the reverse biased junction J2 will have an

avalanche breakdown at a voltage called forward breakover voltage VBO.

When forward voltage is less than VBO, thyristor offers high impedance. Therefore, a

SCR can be treated as an open switch even in the forward blocking mode.

(c). Forward conduction mode: In this mode, SCR conducts currents from anode to cathode with

a very small voltage drop across it. A SCR is brought from forward blocking mode to forward

conduction mode by turning it on by exceeding the forward break over voltage or by applying a

gate pulse between gate and cathode. In this mode, SCR is on state and behaves like a closed

switch. Voltage drop across thyristor in the on state is of the order of 1 to 2V depending on the

rating of thyristor. This voltage drop increases slightly with an increase in anode current.

In conduction mode, anode current is limited by load impedance alone as voltage drop

across thyristor is quite small. This small voltage drop VT across the device is due ohmic drop in

the four layers.



SPECIFIC TERMINOLOGY Break over Current (I BO) − Principal current at the break over point Break over Voltage (VBO) − Principal voltage at the break over point Gate Trigger Current (I GT) − Minimum gate current required to maintain the SCR in the on state Holding Current (I H) − Minimum principal current required to maintain the SCR in the on state Latching Current (I L) − Minimum principal current required to maintain the SCR in the on state immediately after the switching from off state to on state has occurred and the triggering signal has been removed On-state Voltage (VT) − Principal voltage when the SCR is in the on state Gate Trigger Voltage (VGT) − Gate voltage required to produce the gate trigger current On-state Current (IT) − Principal current when the SCR is in the on state

PROCEDURE:

Static V-I Characteristics of SCR 1. Connections as made as per the circuit diagram

2. Connect multimeter across G-K, across the thyristor (anode and cathode),across the supply

terminals Vs to measure gate voltage Vg, Va and Vs. (all in dc mode). An ammeter of the

range (0-50) mA is connected to measure the load current Il.

3. Keep initially the gate potential Vg at very low value say around 0.4 Volts. Vary the supply

voltage Vs in steps and note whether ammeter shows any reading. For every step of Vs note

the ammeter reading. Also note corresponding readings of Va respectively.

4. If the ammeter does’t indicate any reading, increase the gate potential Vg to some higher

value say around 0.6 Volts & follow the procedure given in step no. (3).

5. Further increase the gate potential to some higher values and repeat the procedure followed

in step no. (3).

6. Tabulate the readings in the observation column.

7. Finally a graph is drawn between anode current (Ia = Il = loadcurrent) and the device voltage

Va respectively.



RESULT:

Thus the V-I characteristics of S.C.R. and the Break over Voltage, Holding current. & Latching current have been determined.

QUESTIONS: 1. Explain the working operation of VI characteristics of S.C.R. 2. Define Holding current, Latching current, Break down voltage. 3. Explain the working operation of S.C.R. characteristics by using two transistor analogy. 4. What is meant by forward leakage current 5. Mention the applications of S.C.R.



CIRCUIT DIAGRAM: CHARACTERISTICS OF MOSFET

MODEL GRAPH :

MOSFET



OBSERVATION TABLE :

FOR MOSFET

VGS = ----------- = Constant VGS = ----------- = Constant VGS = ----------- = Constant

Serial No.

Drain to Source voltage

(VDS) (Volt)

Drain current (ID)

(Ampere)

Drain to Source voltage (VDS) (Volt)

Drain current

(ID)

(Ampere)

Drain to Source voltage (VDS) (Volt)

Drain current

(ID)

(Ampere)



MOSFET CHARACTERISTICS

AIM: To obtain the steady state output side characteristics of the given MOSFET, for a

specified value of gate source voltage


Sl.No.


RANGE

QUANTITY



3 Voltmeter (0-30)V 1

4 Connecting Wires as required

THEORY :

METALOXIDE SEMICONDUCTOR FIELD EFFECT TRANSISTOR (M OSFET):

The circuit diagram to obtain the output characteristics is shown in figure.

Power MOSFET is a voltage controlled device because the output current (drain current) can be

controlled by gate source voltage (VGS).

The power MOSFET has three terminals called D, source S and gate G. The symbol of power

MOSFET is shown in Fig. Here the arrow direction indicates the direction of electrons flow.



Power MOSFET is unipolar device because its operation depends upon the flow of majority

carriers onl. It have very high input impedance, in the orde of 109 obm. The gate draws a very

small leakage current, in the order of nano amperes. MOSFETs do not have problems of

secondary breakdown. However, MOSFETs have the problems of electrostatic discharge and

require special care in handling. In addition, it is very difficult to protect them under short –

circuited fault conditions. Power MOSFETs are finding increasing applications in low power

high frequency converters. The V I characteristics of MOSFET is shown in figure.

PROCEDURE:

Static V-I Characteristics Of MOSFET

1. Connections as made as per the circuit diagram.

2. Connect multimeter across G-K, across the MOSFET (source & drain) & across the supply

terminals Vs to measure gate voltage Vg, VDS , and Vs. (all in dc mode) An ammeter of the

range (0-50) mA is connected to measure the load current Il (drain current ID).

3. Keep initially the gate potential Vg at very low value. Vary the supply voltage Vs in steps

and note whether ammeter shows any reading. For every step of Vs note the ammeter

reading. Also note corresponding readings of VDS respectively.

4. If the ammeter doesn’t indicate any reading, increase the gate potential Vg to some higher

value & follow the procedure given in step no. (3).

5. Further increase the gate potential to some higher values and repeat the procedure followed

in step no. (3).


7. Finally a graph is drawn between load current (ID) and the device voltage VDS respectively.



RESULT:

Thus the steady state output side characteristics of the given MOSFET, for a specified

value of gate source voltage has been obtained.

QUESTIONS: 1. What is power MOSFET? 2. What are the applications of power MOSFET? 3. Compare MOSFET & BJT? 4. Compare MOSFET and BJT 5. Explain o/p & transfer characteristics of MOSFET



CIRCUIT DIAGRAM: IGBT CHARACTERISTICS

MODEL GRAPH:

IGBT



OBSERVATION TABLE:

FOR IGBT:

VGE =__________ =Constant VGE =__________ =Constant VGE =__________ =Constant

Serial

No. Collector

Emitter (VCE)

(Volt)

Collector

current (Ic)

(Ampere)

Collector

Emitter

(VCE) (Volt)

Collector

current (Ic)

(Ampere)

Collector

Emitter

(VCE)

(Volt)

Collector current

(Ic)

(Ampere)



IGBT CHARACTERISTICS

AIM:

To obtain the steady state output side characteristics of the given IGBT, for a specified value of base emitter voltage.

APPARATUS REQUIRED:

Sl.No.


RANGE

QUANTITY


1


5 Voltmeter

(0-50)V 1

(0-15)V 1

7 Connecting Wires as required

THEORY:

INSULATED GATE BIPOLAR TRANSISTOR (IGBT):

The circuit diagram to obtain the output characteristics of IGBT is shown in figure.

The symbol of IGBT shown in Fig. IGBT is a new development in the area of power MOSFET

technology. This device combines into it the advantages of both MOSFET and BJT. So an IGBT

has high input impedance like a MOSFET and low-on state power loss as in a BJT. IGBT is free

from second breakdown problem present in BJT. IGBT is also known as metal oxide insulated

gate transistor (MOSIGT), conductively modulated field effect transistor (COMFET) or gain



modulated FET (GEMFET). It is also called insulated gate transistor (IGT). The V I

characteristics of MOSFET is shown in figure.

PROCEDURE

Static V-I Characteristics Of IGBT

1. Connections as made as per the circuit diagram.

2. Connect multimeter across G-K, across the IGBT (collector and emitter), & across the

supply terminals Vs to measure gate voltage VBE , VCE , and Vs (all in dc mode) An

ammeter of the range (0-50) mA is connected to measure the load current Il (collector

current IC).

3. Keep initially the gate potential VBE at very low value. Vary the supply voltage Vs in steps

and note whether ammeter shows any reading. For every step of Vs note the ammeter

reading. Also note corresponding readings of VCE respectively.

4. If the ammeter does’t indicate any reading, increase the gate potential VBE to some higher

value & follow the procedure given in step no. (3).

5. Further increase the gate potential to some higher values and repeat the procedure

followed in step no. (3).


7. Finally a graph is drawn between load current (IC) and the device voltage VCE respectively.



RESULT:

Thus the steady state output side characteristics of the given IGBT, for a specified value of base emitter voltage has been obtained.

QUESTIONS: 1. What is IGBT? 2. What are the applications of IGBT? 3. Compare MOSFET, BJT & IGBT? 4. Explain the working principle of IGBT 5. Explain o/p & transfer characteristics of IGBT.



CIRCUIT DIAGRAM : SINGLE PHASE HALF CONTROLLED BRIDGE RECTIFIER

P

T1 T3

230V, 50Hz

1φ AC Supply

D4 D2

N

230V/12V

Step down Transformer

UJT TRIGGERING CIRCUIT FOR SINGLE PHASE HALF CONTRO LLED BRIDGE CONVERTER



PATCHING DIAGRAM OF UJT TRIGGERING



PATCHING DIAGRAM OF 1 Ώ HALF CONTROLLED CONVERTER



OBSERVATION TABLE:

Half Controlled Bridge Rectifier Using R Load

Vm = ________________

Serial No.

Triggering angle ‘α’ degree

Output voltage

Voav

(volt)

(measured)

Output voltage

Voav

(volt)

(calculated)



MODEL GRAPH:

Half Controlled Bridge Rectifier Using R Load



EXPT.NO :

DATE :

SCR HALF & FULLY CONTROLLED BRIDGE RECTIFIERS

SINGLE PHASE HALF CONTROLLED CONVERTER

AIM :

To study the operation of single phase half controlled converter using R and RL load and

to observe the output waveforms


Sl.No.


RANGE

QUANTITY

1. Thyristor trainer kit

2. SCR Triggering kit

3. CRO

4. Resistive load

5. Multimeter

6 Patch cards

7 CRO probes



FORMULA :

For Single Phase Half Controlled Bridge Rectifier

)cos1( απ

+= mO

VV

THEORY :

Single Phase Half Controlled Bridge Rectifier (Single Phase Semiconverter): A semi converter uses two diodes and two thyristors and there is a limited control over the level of dc output voltage. A semi converter is one quadrant converter. A one-quadrant converter has same polarity of dc output voltage and current at its output terminals and it is always positive. It is also known as two-pulse converter.

Figure shows half controlled rectifier with R load. This circuit consists of two SCRs T1 and T2, two diodes D1 and D2. During the positive half cycle of the ac supply, SCR T1 and diode D2 are forward biased when the SCR T1 is triggered at a firing angle ωt = α, the SCR T1 and diode D2 comes to the on state. Now the load current flows through the path L - T1- R load –D2 - N. During this period, we output voltage and current are positive. At ωt = π, the load voltage and load current reaches to zero, then SCR T1 and diode D2 comes to off state since supply voltage has been reversed.

During the negative half cycle of the ac supply, SCR T2 and diode D1 are forward biased. When SCR T2 is triggered at a firing angle ωt = π + α, the SCR T2 and diode D1 comes to on state. Now the load current flows through the path N - T2- R load – D1 -L. During this period, output voltage and output current will be positive.

At ωt = 2π, the load voltage and load current reaches to zero then SCR T2 and diode D1 comes to off state since the voltage has been reversed. During the period (π + α to 2π) SCR T2 and diode D1 are conducting



PROCEDURE :

Single Phase Half Controlled Bridge Rectifier (Single Phase Semi converter)

1. Make the connections as per the circuit diagram.

2. Connect CRO and voltmeter across the load.

3. Keep the potentiometer at the minimum position.

4. Switch on the step down ac source.

5. Check the gate pulses at G1-K1 & G2-K2, respectively.

6. Observe the wave form on CRO and note the triggering angle ‘α’ and

7. Note the corresponding reading of the voltmeter. Also note the value of Maximum amplitude Vm from the waveform.

8. Set the potentiometer at different positions and follow the step given in (6) for every position.


RESULT :

Thus the operation of single phase half controlled converter using R and RL load has

studied and the output waveforms has been observed.

QUESTIONS:

1. What is meant by semiconverter? 2. What is effect of freewheeling diode? 3. What are the advantages using FD? 4. What are fully controlled rectifiers? 5. What is the condition for different quadrant of operation



CIRCUIT DIAGRAM: SINGLE PHASE FULLY CONTROLLED CONV ERTER:

R LOAD

T1 T2

230 V, 50Hz, Single Phase Supply T3 T4

230V/12V Step down

Transformer

UJT TRIGGERING CIRCUIT FOR SINGLE PHASE FULLY CONTR OLLED BRIDGE CONVERTER



PATCHING DIAGRAM OF UJT TRIGGERING FOR 1 φ FULLY CONTROLLED CONVERTER



PATCHING DIAGRAM OF 1 φ FULLY CONTROLLED CONVERTER



OBSERVATION TABLE:

Fully Controlled Bridge Rectifier Using R Load Vm = _________

Serial No.

Triggering angle ‘α’ degree

Output voltage Voav

(volt) (measured)

Output voltage Voav

(volt) (calculated)



MODEL GRAPH:



SINGLE PHASE FULLY CONTROLLED CONVERTER

AIM:

To study the operation of single phase fully controlled converter using R and RL load and to observe the output waveforms

APPARATUS REQUIRED:

Sl.No.


RANGE

QUANTITY

1. Thyristor trainer kit 1

2. SCR Triggering kit 1

3. CRO 1

4. Resistive load 50Ώ,50W 1

5. Multimeter 1

6 Patch cards Required no’s

7 CRO probes 1

THEORY:

SINGLE PHASE FULLY CONTROLLED BRIDGE RECTIFIER

A fully controlled converter or full converter uses thyristors only and there is a wider control over the level of dc output voltage. With pure resistive load, it is single quadrant converter. Here, both the output voltage and output current are positive. With RL- load it becomes a two-quadrant converter. Here, output voltage is either positive or negative but output current is always positive. Figure shows the quadrant operation of fully controlled bridge rectifier with R-load.



Fig shows single phase fully controlled rectifier with resistive load. This type of full wave rectifier circuit consists of four SCRs. During the positive half cycle, SCRs T1 and T2 are forward biased. At ωt = α, SCRs T1 and T3 are triggered, then the current flows through the L – T1- R load – T3 – N. At ωt = π, supply voltage falls to zero and the current also goes to zero. Hence SCRs T1 and T3 turned off. During negative half cycle (π to 2π),

SCRs T3 and T4 forward biased. At ωt = π + α, SCRs T2 and T4 are triggered, then current flows through the path N – T2 – R load- T4 – L. At ωt = 2π, supply voltage and current goes to zero, SCRs T2 and T4 are turned off. The Fig-3, shows the current and voltage waveforms for this circuit.

For large power dc loads, 3-phase ac to dc converters are commonly used. The various types of three-phase phase-controlled converters are 3 phase half-wave converter, 3-phase semi converter, 3-phase full controlled and 3-phase dual converter. Three-phase half-wave converter is rarely used in industry because it introduces dc component in the supply current. Semi converters and full converters are quite common in industrial applications. A dual is used only when reversible dc drives with power ratings of several MW are required.

The advantages of three phase converters over single-phase converters are as under:

In 3-phase converters, the ripple frequency of the converter output voltage is higher than in single-phase converter. Consequently, the filtering requirements for smoothing out the load current are less.



The load current is mostly continuous in 3-phase converters. The load performance, when 3-phase converters are used, is therefore superior as compared to when single-phase converters are used.

FORMULA:

For Single Phase Fully Controlled Bridge Rectifier

)cos2 α

πm

O

VV =

PROCEDURE:

1. Single Phase Fully Controlled Bridge Rectifier

2. Make the connections as per the circuit diagram.

3. Connect CRO and multimeter (in dc) across the load .

4. Keep the potentiometer (Ramp control) at the minimum position (maximum resistance).

5. Switch on the step down ac source.

6. Check the gate pulses at G1-K1, G2-K2,G3-K3,& G4-K4 respectively.

7. Observe the waveform on CRO and note the triggering angle ‘α’ and note the corresponding reading of the multimeter. Also note the value of maximum amplitude Vm from the waveform.

8. Set the potentiometer at different positions and follow the step given in (6) for every position.

9. Tabulate the readings in observation column.

10. Draw the waveforms observed on CRO.



RESULT:

Thus the operation of single phase fully controlled converter using R and RL load has

been studied and the output waveforms has been observed.

QUESTIONS:

1. What is meant by semi converter? 2. What is effect of freewheeling diode? 3. What are the advantages using FD? 4. What are fully controlled rectifiers? 5. What is the condition for different quadrant of operation



CIRCUIT DIAGRAM: R – TRIGGERING CIRCUIT

MODEL GRAPH: R – TRIGGERING CIRCUIT

VS

VL

VAK

t

t

t



TABULAR COLUMN (R-TRIGGERING):

S.No. Input Voltage

(V)

Input Cycle Time (Ms)

Resistance Value (K Ω )

O/P Voltage

V rms (V)

Voltage Across

(Anode- Cathode) V rms (V)



CIRCUIT DIAGRAM: RC TRIGGERING CIRCUIT

MODEL GRAPH:RC TRIGGERING CIRCUIT



TABULATOR COLUMN (RC-TRIGGERING):

S.No. Input

Voltage (V)

Input Cycle Time (Ms)

Resistance Value (K Ω )

O/P Voltage

V rms (V)

Voltage Across

(Anode- Cathode) V rms (V)



CIRCUIT DIAGRAM : UJT TRIGGERING CIRCUIT MODEL GRAPH: UJT TRIGGERING CIRCUIT

t

t

Vo

Vc



PATCHING DIAGRAM OF UJT TRIGGERING CIRCUIT



TABULAR COLUMN (UJT-TRIGGERING):

S.No. Resistor value(r)

(ω)

Capacitor voltage Vc (v)

Charging time (ms)

Discharging Time (ms)

Voltage vo

(v)

Time Period (ms)



EXPT.NO :

DATE :

R, R-C AND UJT FIRING CIRCUITS FOR SCR

AIM: To study the operation of resistance, resistance capacitance and UJT triggering circuits of SCR

APPARATUS REQUIRED:

Sl.No.


RANGE

QUANTITY

1. Transformer (230V/12V), 1

2. SCR – TY604 1

3. Resistor (3.3 KΏ, 100Ώ/20W),

4. Decade Capacitance Box

5. UJT firing module 1

6 CRO 1

7 LOAD 1

8 Multimeter



THEORY: RESISTANCE TRIGGERING Resistance trigger circuits are the simplest & most economical method. During the positive half

cycle of the input voltage , SCR become forward biased but it will not conduct until its gate

current exceeds Igmin . Diode D allows the flow of current during positive half cycle only. R2 is

the variable resistance & R is the stabilizing resistance .R1 is used to limit the gate current.during

the positive half cycle current Ig flows. Ig increases and when Ig= Igmin the SCR turns ON .The

firing angle can be varied from 0 — 90° by varying the resistance R.

R —C TRIGGERING By varying the variable resistance R, the firing angle can be varied from 0 —180° .In the

negative half cycle the capacitance C charges through the diode D2 with lower plate positive to,

the peak supply voltage Emax .This Capacitor voltage remains constant at until supply voltage

attains zero value. During the positive half cycle of the input voltage, C begins to charge through

R. When the capacitor voltage reaches the minimum gate trigger voltage SCR will turn on.

UJT TRIGGERING The circuit for UJT trigger consists of UJT relaxation oscillator. The basic UJT relaxation

oscillator is made as a line synchronized trigger circuit, with the addition of a diode rectifier and

a zener diode. A zener diode clip the control voltage to a fixed level. The capacitor will charge

exponentially. When the voltage across the capacitor reaches the unijunction threshold voltage,

the E-B,junction of UJT breaks down and.capacitor C discharges through UJT . SCR get gate

pulse and turns on.

Average value of output voltage [ ]cos α12

+=πmV

RMS value of output voltage =



PROCEDURE: R Firing 1. Connections are made as shown in fig.

2. Switch on the power supply to the CRO .

3. Set the CRO to the line trigger mode.

4. Switch on power supply to the SCR trainer.

5. Observe the waveform on the CRO.

6. Study the waveforms for various firing angle by varying the pot in R trigger circuit.

7. Observe the range of firing angle control.

8. For any one particular firing angle plot the waveforms of the ac voltage, voltage across the

load and the SCR.

9. Measure the average dc voltage across the load and rms value of the ac input voltage using a

digital multimeter.

10. Calculate the dc output voltage using the equation.

V - Vrms value of ac input voltage

Vm - .\/2Vrms

And compare the measured value

RC FIRING

1. Connections are made as shown in fig.

2. Switch on the power supply to the CRO .

3. Set the CRO to the line trigger mode.

4. Switch on power supply to the SCR trainer.

5. Observe the waveform on the CRO.

6. Study the waveforms for various firing angle by varying the pot in R trigger circuit.

7. Observe the range of firing angle control.



8. For any one particular firing angle plot the waveforms of the ac voltage, voltage across the

load and the SCR.

9. Measure the average dc voltage across the load and rms value of the ac input voltage usin g' a

digital multimeter.

10. Calculate the dc output voltage using the equation.

UJT FIRING 1. Connect a.k terminal of UJT triggering circuit to the gate cathode terminals of SCR.

2. Give a 24 V ac supply .

3. Observe the waveforms and plot it for one particular firing angle by adjusting the

potentiometer and observe the range over which firing angle is controllable.

4. Observe that capacitor voltage is set at every half cycle.

RESULT:

Thus the operation of resistance, resistance capacitance and UJT triggering circuits of SCR has

been studied.

QUESTIONS:

1. What are all the methods to trigger SCR.

2. Which one is the most common & accurate method to turn on the SCR.

3. Explain the working of resistance firing circuit.

4. Explain the working of resistance- capacitor firing circuit.

5. What is meant by ramp control



CIRCUIT DIAGRAM: SERIES INVERTER



PATCHING DIAGRAM OF SINGLE PHASE SERIES INVERTER



MODEL GRAPH

OBSERVATION TABLE

S.No Amplitude (volt) Ton (ms) Toff (ms)



EXP NO:

DATE:

SERIES INVERTER

AIM: To obtain variable AC from DC ripple input. APPARATUS REQUIRED:

Sl.No.


RANGE

QUANTITY

1. SCR Series Inverter Module 1

2. Resistive Load 50Ώ/50w

3. CRO 1

4. Patching Chords

THEORY:

In the series inverter, the commutating inductance and capacitance are in Series with the load. Thus the commutation circuit is part of the load.

Fig shows the circuit diagram of series inverter. L and C are commutating components. T and T carry load current in positive and negative half cycles Operation of the circuit can be understood through following modes.

Mode - I

At the beginning of this mode, capacitor is charged to negative voltage as shown in waveforms of Fig. At t1 SCR T is triggered. The output current starts flowing through T and L-C-R circuit equivalent circuit-I in Fig show the current path. Because of the RLC circuit, the current increases sinusoid ally. The current becomes maximum when capacitor voltage is equal to Vdc. Then the current reduces. At t current becomes zero. Hence T turns-off. The capacitor charges to the value higher than Vdc. This charge is hold by the capacitor.



Mode - II

This mode begins when SCR T is triggered at t3 Equivalent circuit-II in Fig shows the current path. The current starts flowing in opposite direction. Fig shows the negative half cycle of the current. The capacitor starts discharging in the RLC circuit. The current becomes maximum when capacitor voltage is zero. The current then starts reducing and becomes zero at t4 Therefore T2 turns off at t4. The Capacitor is charged to negative voltage. This charge is hold by the capacitor. The cycle repeats when T1 is triggered again. Fig shows output voltage waveform. Note that it is similar to output current for resistive load.

PROCEDURE:

1. To begin with switch on the power supply to the firing circuit check that Trigger pulses

by varying the frequency.

2. Connections are made as shown in the circuit diagram.

3. Now connect trigger outputs from the firing circuits to gate and cathode of SCRs T1 &

T2.

4. Connect DC input from a 30v/2A regulated power supply and switch on the input DC

supply.

5. Now apply trigger pulses to SCRs and observe voltage waveform across the load.

6. Measure Vrms & frequency of o/p voltage waveform.



RESULT :

Thus the variable AC from DC ripple input has been obtained.

QUESTIONS:

1. What is meant by series inverter?

2. Give the classification of series inverter.

3. Give the frequency range at which the series inverter operate.

4. Explain the working of series inverter.

5. What are all the applications of series inverter.



CIRCUIT DIAGRAM: SCR DC VOLTAGE COMMUTATED CHOPPER

50Ώ/50W (0-30V)

L

O

A

D



WAVEFORM:



PATCHING DIAGRAM OF VOLTAGE COMMUTATED CHOPPER



OBSERVATION TABLE:

OUTPUT ACROSS CAPACITOR

S.NO Vs (volts) Ip=VsVl/L Main SCR turn on time Main SCR turn off time

OUTPUT ACROSS LOAD

S.NO Vs (volts) Ip=VsVl/L Main SCR turn on time Main SCR turn off time



OBSERVATION TABLE:

S.NO

Vs in volts

T auxiliary time

Ton (ms) Toff (ms)

S.NO

Amplitude

T auxiliary time

Ton (ms) Toff (ms)

NOTATIONS USED

Ig- gate current

It- thyristor current

Ic- capacitor current

Vc- capacitor voltage

Vt- thyristor voltage

Vo- output voltage

Ita- auxiliary thyristor current



EXP NO:

DATE:

SCR DC VOLTAGE COMMUTATED CHOPPER

AIM:

To observe the operation of class D commutated technique.

APPARATUS REQUIRED:

S.No Name of the apparatus Type Range Quantity

1 Force commutation trainer kit

1

2 Patch chord Required no’s

3 CRO

THEORY:

MODE-1

Main SCR is triggered to make source current to flow in two path one is load current and other path with triggering of SCR load get connected to supply and load voltage.

MODE-2

At a desired instant the auxiliary SCR is to be triggered for turning OFF the main SCR T1 with the switch ON, T2 reverse capacitance voltage appears across T1 which reverse biases it and turn it OFF.

MODE-3

SCR T2 turn OFF since the capacitance is slightly changed after the freewheeling diode set frequently forward biased.



PROCEDURE:

1) Patch the voltage commutated chopper as per the circuit diagram

2) Connect the CRO probe across the commutated chopper

3) Give the input dc voltage (0-30)v, 2amps from the external power supply.

4) Switch ON the trainer then switch ON the input dc suuply circuit breaker.

5) After then switch ON the trigger OFF-ON position

6) From the capacitor output waveform we can measure the turn on time and turn off time of main SCR as well as auxiliary SCR

7) Verify the unity and frequency of the triggering circuit using parts provided on the triggering circuit.

8) Also observe the voltage across main SCR and auxiliary SCR and load

9) Take the turn on and turn off time at main so auxiliary SCR from the capacitor waveform at various values of unity cycle and frequency and tabulate them

10) Also find out the peak value of current through the capacitor.



RESULT:

Thus the operation of class D commutated technique has been obtained.

QUESTIONS:

1. What is meant by commutation?

2. What are all the methods of commutation?

3. What is meant by voltage commutation?

4. Explain the working of voltage commutated chopper.

5. What are all the advantages and disadvantages of voltage commutated chopper



CIRCUIT DIAGRAM OF IGBT CHOPPER (I & IV QUADRANT OP ERATION)

CIRCUIT DIAGRAM OF IGBT CHOPPER (II & III QUADRANT OPERATION)



FRONT PANEL DIAGRAM OF IGBT CHOPPER POWER CIRCUIT



EXP NO:

DATE:

IGBT CHOPPER

AIM:

To conduct the operation of Two quadrants IGBT chopper with bipolar switching

APPARATUS REQUIRED:

S.No Name of the apparatus Type Range Quantity

1 IGBT module

2 Chopper control module

3 CRO

4 Rheostat

5 Multimeter

THEORY:

The type of chopper is obtained by connectivity type A type B chopper is parallel. The output voltage Vo is always positive because of the presence of freewheeling diode across the load. When chopper CH2 ON free wheeling diode conduct output voltage Vo=0 and incase chopper CH2 is ON or diode.

PROCEDURE:

For bipolar switching

1. Using the chopper module, and referring to the mimic diagram, connect the circuit as per the circuit diagram.

i) Connect B11 to V+1 using patch chords.

ii) Connect B12 to B21 using patch chords.

iii) Connect B23 to V-1 using patch chords.



iv) Connect V+2 to B31 using patch chords.

v) Connect B32 to B41 using patch chords.

vi) Connect V-2 to B43 using patch chords.

2. Connect the R-load between B12 to B33.

3. Connect the gating signals from the chopper control module to the chopper module using the signal cable provided.

4. Connect the power cables for both the modules.

5. Select bipolar voltage switching mode, modeIII by setting SW3 in the control module at position.

6. Keeping pulse release ON/OFF switch SW4, in the control module in the off position. Switch ON ac mains to the CRO, control module and chopper module.

7. Switch ON SW! in chopper module to establish dc link voltage.

8. Release the gating signals by switching on SW$ in the control module.

9. Observe the load voltage waveforms through CRO.

10. Vary the duty cycle ratio and measure Ton, Toff, average dc output voltage and tabulate them.



TABULATION: FIRST AND FOURTH QUADRANT

S.NO Vo Ton (ms) T (ms) α = Ton/T Vo=

TABULATION: SECOND AND THIRD QUADRANT

S.NO Vo Ton (ms) T (ms) α = Ton/T Vo=



RESULT:

Thus the four quadrant chopper was constructed and the operation of the chopper has been obtained from the output waveform.

QUESTIONS:

1. Explain the principle of dc chopper operation

2. Describe the various types of chopper configuration

3. What is meant by IGBT CHOPPER?

4. Explain the working of IGBT chopper

5. Where we are using this two quadrant IGBT chopper.

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