Subject Code:303143 Subject: Power Electronics Laboratory

Power Electronics TE Electrical Engg. (2015 Course)

PES Modern college of engineering Department of Electrical Engineering Page 1

Subject Code:303143

Subject: Power Electronics Laboratory Manual

Class: TE Electrical ( 2015 Course)



Teaching and Examination Scheme

Practical: 2 hrs/Week Practical Exam Marks: 50

List of Experiments mentioned in University’s syllabus

Sr.No Name of Experiments Performed

Practical

Group A: Perform any THREE experiments

(Hardware)

1 Static VI characteristic of SCR /GTO 3. 4. 5. 6. 7. 8.

Both) 9.

2 Static VI characteristic of TRIAC ×

3 Single phase Half controlled converter with R and

RL load

4 Single phase fully controlled converter with R load.

5 Single Phase fully controlled converter with and

without Free Wheeling diode with RL load

6 Single phase A.C. voltage regulator with R load

7 Study of DC step down chopper

8 Output and Transfer Characteristic of MOSFET and

IGBT (both) ×

9 Three phase voltage source converter using 1200

and 1800 mode

×

Group B : Perform any THREE experiments

(Hardware/Software)

10 Three phase AC-DC fully controlled bridge

converter R and RL load

11 Three phase voltage source inverter using 1200 and

1800 mode

12 Study of DC step down chopper

13 Single phase A.C. voltage regulator R and RL load ×

14 Design of snubber circuit and verification using

simulation ×

15 Study and Design of single phase VSC ×

Experiment Beyond practical Syllabus

1 Single phase fully controlled converter with RLE

load



EXPERIMENT NO. 1A

AIM: To study static VI characteristics of SCR and determine breakover voltage , on state

resistance, holding and latching current of SCR

APPRATUS:

SCR VI Characteristics Kit(SCR – TY604: 1 No , Wattage Resistors)

DC Milliammeter : 2 NO(0-30mA,0-100mA)

DC power supply: 2No ( 0-15V,2A and 0-30V,2A)

THEORY:

It is four layers (alternate p type and n type silicon semiconductors) , three junctions

(junctions J1,J2 and J3) semiconductor switching device in which two transistors (PNP and

NPN) are connected back to back

It has three terminals – anode, cathode and gate.

To provide greater mechanical strength it is properly braced with tungsten or molybdenum.

Gate terminal is normally kept near to cathode.

SCR’s are solid state devices and are high power controlled device.

WORKING AND V-I CHARACTERISTICS

When anode is made positive with respect to cathode junction, J2 is reverse biased and only

leakage current will flow through the device. The SCR is then said to be in the forward blocking

state or off state.

When cathode is made positive with respect to anode junction, J1 and J3 are reverse biased

and small reverse leakage current will flow through the SCR. This is the reverse blocking state of

devices.

When anode to cathode voltage is increased the reverse biased junction J2 will break down

due to large voltage gradient across the depletion layers. This is known avalanche breakdown. Since

J1 andJ3 are forward biased there will be free carrier movement across all three junctions resulting

in large anode current It. The voltage drop across the device will be ohmic drop in four layers and

the device is said to be in conducting state or ON state.

The V-I characteristics of SCR is a graph of anode current on y axis and anode to cathode

voltage on x axis. The V-I characteristics can be split into four parts namely the reverse blocking

region, forward blocking region, forward conducting region and forward latching region

HOLDING CURRENT (IH): It represents the current that con flow through SCR and still “hold” it

in the ON state. The accompanying voltage is termed as holding voltage Vh. If the forward anode

current is reduced below holding current SCR will be turned off. The holding current is defined for

zero gate current.



LATCHING CURRENT (IL): it is minimum anode current that must flow through SCR to latch it

into the ON state. The latching current is higher than the holding current. The latching current is

important when SCR is being turned ON.

ADVANTAGES:

1. It can handle large voltages, current and power.

2. Easy to turn ON.

3. Triggering circuits are simple.

4. It can be protected with the help of a fuse.

DISADVANTAGES:

1. It can conduct only in one direction.

2. It can turn on accidently due to high dv/dt of the source voltage.

3. It is not easy to turn off the conducting SCR.

4. SCR cannot be used at high frequency.

5. Gate current cannot be negative.

CIRCUIT DIAGRAM:

PROCEDURE:

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

2. The value of gate current IG, is set to convenient value by adjusting VGG.

3. By varying the anode- cathode supply voltage VAA gradually in step-bystep, note down the

corresponding values of VAK & IA. Note down VAK & IA at the instant of firing of SCR and

after firing (by reducing the voltmeter ranges and increasing the ammeter ranges) then

increase the supply voltage VAK. Note down corresponding values of VAK and IA

4. The point at which SCR fires, gives the value of break over voltage VBO.

5. A graph of VAK V/S IA is to be plotted.

6. The on state resistance can be calculated from the graph by using a formula.

7. The gate supply voltage VGG is to be switched off



8. Observe the ammeter reading by reducing the anode-cathode supply voltage VAA. The

point at which the ammeter reading suddenly goes to zero gives the value of Holding

Current IH.

9. Steps No.2, 3, 4, 5, 6, 7, 8 are repeated for another value of the gate current IG.

OBSERVATION TABLE:

IG = IG =

VAK (volts) IA (mA) VAK (volts) IA (mA)

CALCULATIONS:

RON (Avg) = VAK / IA

RESULT TABLE: 1) RON = 2) IH = 3) IL =

1) RON = 2) IH = 3) IL =

CONCLUSION:

ORAL QUESTIONS:

1. Why SCR is called as current controlled device?

2. What are the triggering methods of SCR?

3. What are commutation methods of SCR?

4. How SCR is turned OFF?



EXPERIMENT NO. 1B

AIM: To study static VI characteristics of TRIAC and DIAC

APPRATUS:

TRIAC VI Characteristics Kit

Dual Trace CRO

THEORY:

It is four layers (alternate p type and n type silicon semiconductors) , three junctions

(junctions J1,J2 and J3) semiconductor switching device in which three transistors (PNP

and NPN) are connected back to back

It has three terminals – MT1 , MT2 and gate.

WORKING AND V-I CHARACTERISTICS

TRIAC:

In this thyrister family, after SCR, the triac is the most widely used device for power control. It

is a bilateral device with three terminals and in operation it is equivalent to the two SCR’s

connected antiparallel. As the triac can conduct in both the directions the terms anode and cathode

are not applicable. The two main terminals are designed MT1 and MT2.

The angle is near MT1 when the gate is open the triac, will block with polarities of

voltages(vtg) applied across MT1 and MT2.If magnitude of vtg is less than brkover vtg of device.

The characteristics of TRIAC are similar to those of SCR both in blocking and conducts in only

forward direction whereas TRIAC conducts in both directions. TRIAC can be triggered into



conduction by applying either a + or – vtg to gate of triac wrt MT1 whereas SCR is triggered only

by a + gate signal.

TRIGGERENG MODE OF TRIAC:

When MT2 and gate are + wrt MT1,the TRIAC behaves as conventional SCR with four layers

P1,n1,P2,n2 and cathode connected to layer A2.The device can also be turned by applying – signal

on gate. In this case the device is switched by an operation called junction gate operation.

Initially the layers are turned on by current flowing from terminal MT1 act like cathode gate. When

this left part of layer P2 in contact with n3 will group and because of potential across layer P2 the

current will flow from left to right part of TRIAC. Comparing P1,n1,P2,n2 will turn on. In this

mode the device is switched by remote gate operation. The 4 layers used for this operation are

P1,n1,P2,n2.The reverse biased junction is formed by layers n1P1.It will be broken by layers

P2n1.It will be broken by increasing carrier concentration in layers n1.

In n2P2n1, Since the gate is made + wrt terminal MT1.The transistor will be properly biased and a

+ base current will flow into layer P2.This will increase emitter current and raises the carrier current

in layer n1 and thus lead to breakdown of the reversed biased junction. The device will turn on due

to increased current in layer n but this – gate current mode is made sensitive with previous one.

ADVANT AGES:

1) It is a bidirectional device.

2) It is equivalent to two SCR’s connected back to back.

3) It is more suitable for resistive loads

4) It is more economical than SCR’s

DISADVANTAGES:

1) We can’t use it as a controller rectifier

2) Low di/dt rating

3) Low dv/dt rating



DIAC:

Construction:

1. Its basicaaly a two terminal device. It’s a parallel inverse combination of semiconductor layers

that permits triggering in either direction and DIAC is used in triggering circuits for TRIAC.

2. The arrangements of layers are as shown and terminals MT2 and MT1 are available to the user.

3. When MT1 is positive w.r.t to MT2 the conduction takes place through P1N2P2N3 which is

equivalent to a SCR.

4. Similarly when MT2 is positive w.r.t MT1 , the conduction takes place through P2N2P1N1

which is another SCR.

5. This reflects in the equivalent circuit of the DIAC which shows two SCR’s connected back to

back.

I-V Characteristics:

1. The device can be turned on by either positive or negative cycle of AC supply voltage. For the

positive cycle of supply voltage, if the voltage is less than the forward breakover voltage a very

small current called as the leakage flows through the device.

2. This current is produced due to the drift electrons and the holes at the depletion region and is

not sufficient to cause conduction.

3. Hence the device remains in partially non conducting mode called clocking state.

4. As soon as voltage crossed breakover voltage, device begins to conduct. The device’s current

begins to increase and the voltage decreases.

5. This region is called conduction state and breakover voltage remains unchanged as the gate

terminal is absent here.

6. Similar characteristics are obtained when the supply voltage goes from positive to negative.

7. The quadrant of operation becomes the 3rd quadrant instead of 1st

8. Breakover voltage ranges from 28-42V and turn on time from 50-500msec.

9. Turn off time is longer. And have a power handling capacity of 300mW to 1W.

Applications:

Lamp dimmer, fan speed regulator, temperature controller.

Advantages:

1. This is a bidirectional device.

2. It is extensively used as a triggering device for the triac ckt.

Disadvantages:



1) It is a low power device. 2)It doesn’t have a control terminal.

Applications:

1) Lamp dimmer. 2) Fan speed regulator 3) Temperature controller

CIRCUIT DIAGRAM:

PROCEDURE:

1. Connect DIAC/TRIAC as DUT (Device Under Test) in socket

2. Put the oscilloscope in x-y mode x gain at 10V and y gain at 0.2V

3. Connect oscilloscope horizontal, vertical and common terminal as shown

4. Turn the gate potmeter fully anticlkwise.

5. Ptu on both unit and the oscilloscope .Along horizontal line should appear on

oscilloscope.

6. Slowly turn the potmeter clkwise. The RHS of the line shall slowly start getting fitted

upwards and tip shall suddenly turn to left. Showing triggering of the SCR displaying V-I

characteristics.

Observation :

A] For DIAC

Characteristic is observed on CRO



B] For TRIAC

Characteristic is observed on CRO

CHARACTERISTICS:

CONCLUSION:

ORAL QUESTIONS:

1. Explain the different working modes of operations of a TRIAC?

2. Why I -mode is more sensitive among all modes?

3. What are the applications of TRIAC



4. Compare SCR, TRIAC & DIAC

5. Why I & II modes are operating in Ist quadrant and III & IV modes are operating in

IIIrd quadrant

EXPERIMENT NO. 2A

AIM: To study of output and transfer Characteristics of N-MOSFET

APPRATUS:

MOSFET Trainer kit

0-30V-2A, DC laboratory regulated power supply – 2 No

DC Milliammeter : 2 No (0-30mA,0-100mA)

CIRCUIT DIAGRAM:

THEORY:

Power MOSFET: 1. It is a unipolar device i.e. current conduction occurs through movement of majority carriers in

the drift region.

2. It is a voltage controlled device and requires only a small input current.

3. It has high input impedance so the gate drive circuit is simplified and reduces the cost.

4. It has fast switching speed so operating frequencies are above 10 KHz and up to 500 KHz.

Basic types of MOSFET are:

1. Depletion Enhancement (DE) MOSFET:

In this mode, the gate is insulated from the channel, either +ve or a –ve gate voltage is

applied. Its type are:

a) Depletion mode( +ve gate voltage is applied)

b) Enhancement mode( -ve gate voltage is applied)



2. Enhancement only(E):

It has no physical channel.

N Channel Enhancement power MOSFET:

On P substrate( or body) , two heavily doped n+ regions are diffused. An insulating layer of

sillicon dioxide(SiO2)is spread on the surface. Metallic terminals of drain and source are embedded

on insulating layer by etching it. A layer of metal is also deposited on SiO2 layer so as to form the

gate of MOSFET.

Principle of Operation:-

1. With Vgs=0 , the MOSFET is equivalent to two diodes connected back to back. The diodes

are formed between n+ and P layers as shown.

2. The structure of MOSFET is similar to that of BJT but the only difference is that a MOS

capacitor isolates the gate from the body region.

3. A positive voltage is applied to the gate w.r.t the source.

4. Due to the presence of P layer (base layer), it is felt that conduction cannot take place through

the MOSFET from drain to source. But practically it is possible due to a phenomenon called

“inversion layer creation”

Formation of Depletion Region:

1. A positive voltage is applied to the drain w.r.t the source and the gate is made positive w.r.t

the body region.

2. P layer of the MOSFET consists of large number of holes but it has holes too which are

sufficiently large in number.

3. Due the positive voltage applied to the gate, the electrons getaccumulated near the Si

layer and produce depletion layer by combining with the holes.



Creation of Inversion layer (Induced channel):

1. If the gate voltage is increased further, the number of electrons accumulated near the Si

layer and it will have less holes.

2. The conductivity of the P layer near the Silicon dioxide layer will change from positive to

negative.

3. This means that a N type sub layer is formed as shown in the figure.

4. This process of creation of the inversion layer and the generation of an inversion layer

due to the externally applied gate voltage is known as the “field effect”

5. The inversion layer is also called as the induced channel.

6. In this a N type channel gets created in the P type body layer and the conduction can take

place through this layer as shown.

7. The MOSFET now acts as a variable resistor wherein the magnitude of the resistance

depends on the gate to body voltage.

8. With the increase in gate to body voltage, the resistance will decrease. However the

resistance cannot decrease below a certain minimum value even with the increase in gate

to body voltage.

9. There is limitation on the maximum value of voltage applied between the gate and body.

If it exceeds the silicon dioxide dielectric, it’ll breakdown.

The characteristics are divided into Ohmic, saturation,cut-off region.

When gate circuit is open , no current flows from drain to source and load because of one reverse-

biased n+ p- junction.

gate is made positive w.r.t.source, an electric field is established. Eventually, induced negative

charges in the p-substrate below Silicon dioxide (SiO2) layer are formed. These negative charges

called electrons form N channel and current can flow from drain to source as shown by arrow.

If VGS is made more + ve, n-channel becomes more deep and therefore more current flows from D

to S. This shows that ID is enhanced by the gradual increase of gate voltage , hence the name

enhancement MOSFET.

Advantage:-

1. It is easy to turn ON & OFF the MOSFET.

2. It is very easy to parallel power MOSFET’S without use of external compensation circuit.

3. The secondary breakdown does not take place in MOSFET.

4. Switching speed is very high.

Disadvantage:-

1. The ON state voltage across MOSFET is high.

2. They have asymmetric blocking capacity.

3. They cannot block high reverse voltage.

Applications:-



1. In high frequency inverters.

2. In display drivers.

3. Motor control.

4. In uninterruptible power supplies.(UPS)

5. In switching mode power supplies (SMPS).

PROCEDURE:

1. Plotting output characteristics of N-MOSFET:-

1. Connect N-MOSFET terminals on R.H.S. circuit.

2. Connect on ‘0-30V’ DC & 2A power supply.

3. Connect 0-30V DC voltmeter between D/C & S/E sockets.

4. Connect second 15V DC at more than 100mA power supply circuit in gate, then

connect 10mA DC range multimeter in series with power supply.

5. Set both power supplies to zero volts & switch ON.

6. Now increase & set VGS power supply voltage at 30. Slowly increase VDS power

supply and note ID increase VDS in steps of 2V upto 15V & note values of ID at

every step.

7. Increase setting of V GS in steps of 0-5V upto 6V, plot VDS-ID characteristics.

2. Plotting transfer characteristics:-

1. Connect N-MOSFET in place of OUT.

2. Connect VDS supply.

3. Connect VGS to zero between ‘G’ and oscilloscope GND.

4. Switch ON. Set VDS at 15V.

5. Set VGS to zero, ID will be zero.

6. Start slowly increasing VGS & note voltage at which ID starts flowing. This is

threshold voltage.

7. Increase VGS in steps upto 6V. Note ID at every step. This is transfer characteristics.

8. Calculate the transconductance.

OBSERVATION TABLE:

1. Output Characteristics:

VGS = VGS =

VDS (volts) ID (mA) VDS (volts) ID (mA)



2. Transfer Characteristics:

VDS = 15V VGS (volts) ID (mA)

CALCULATIONS:

RON (Avg) = VAK / IA

RESULT TABLE: 1) RON = 2) IH = 3) IL =

1) RON = 2) IH = 3) IL =

CONCLUSION:

ORAL QUESTIONS:

1. What is Forward Transconductance? 2. Explain working of MOSFET. And state its applications. 3. Explain drawbacks of MOSFET.



EXPERIMENT NO. 2B

AIM: To study of output and transfer Characteristics of IGBT

APPRATUS:

IGBT Trainer kit

0-30V-2A, DC laboratory regulated power supply – 2 No

DC Milliammeter : 2 No (0-30mA,0-100mA)

CIRCUIT DIAGRAM:

THEORY:

CONSTRUCTION:-

The fig. shows basic structure of an IGBT. If it is constructed virtually, it is same manner as

MOSFET. There is a power MOSFET is now substituted in the IGBT by a point layer substrate

called collector C like power MOSFET on IGBT has also thousands of basic structure cells

connected appropriately on a single chip on silicon.



WORKING:-

1.Creation of inversion layer:

When gate is +ve w.r.t. emitter and with gate emitter voltage more than threshold voltage of IGBT,

an N-channel is formed in region of SiO2 layer.

Due to the formation of n-type of layer in the p-type body layer, n-chanel is formed (n+ n n-)

which helps to establish the current

The conductivity modulation of the n- drift layer takes place in IGBT.Due to this, on state

resistance and hence on state power loss decreases in IGBTthan MOSFET.

When forward voltage between collector and emitter i.e.Vce ,the junction J3 is forward biased.Due

to creation of inversion layer ,electrons from the emitter are injected into the n- drift layervia n+ p

n- channel.

As the junction J3 is already forward biased , it will inject holes in the n+ buffer layer.The

electrons injected in the n- drift layer create a space charge which will attract holes from the n+

buffer layer. In this way, double injection takes place into the n- driftregion from both sides. This

increases the conductivity of the drift region and reduces the resistance to its minimum. Thus

conductivity modulation reduces the on state voltage drop across IGBT.

ADVANTAGES:-

a) Low on state voltage drop.

b) Low on state power loss.

c) Easy to turn ON and OFF.

d) Does not need Snubber ckt. for its protection.

e) AS It is a voltage controlled device, therefore requires a simpler driver circuit.

f) Large power handling capacity than MOSFET



DISADVANTAGES:-

1) Asymmetric voltage blocking capacity in forward and reverse direction

2) Problem of static and dynamic latch ups.

3) Excess power dissipation can take place at the time of turn off.

APPLICATION:-

1) UPS system.

2) Chopper.

3) Inverter.

4) AC motor controller.

PROCEDURE:

1. Plotting the output characteristic VDS – ID

1) Connect N-IGBT terminals on the R.H.S. circuit plate by links into the appropriate DUT

socket.

2) Connect one 0-30V DC, 2A power supply between S/E & OSC. GND socket with polarities

as shown. Let us call this as VDS power supply. The current meter of this power supply will

act as o-2A ammeter shown between D/C & OSC VERT sockets; hence just connect a short

link between these two sockets.

3) Connect 0-30 V DC voltmeter between D/C & S/E socket with polarities as shown. i.e. –ve

applied to socket S/E.

4) Connect the second 0-15V DC @ more than 100 mA power supply in the gate circuit, as

shown i.e. –ve to S/E. Let us call this as VGE power supply. If the ammeter of this power

supply is much too big to read current upto 10 mA clearly, then connect the 10 mA DC

range of te multimeter in series with this power supply & R2 as shown, otherwise just

connect a short link.

5) Set both the power supplies to 0 volts & switch ON.

6) Now increase & set VGE power supply voltage @3V. Slowly increase VCE power supply

voltage & the point at which the drain current IC starts to flow. Increase VGE in steps of 2V

upto 15V & note the values of IC at every step. Plot the VGE - IC characteristic for every

setting step of VGE.

2. Plotting Transfer or Transconductance Characteristics



1) Connect the N-IGBT in phase of DUT.

2) Connect VDS supply between D/C (+) & OSC. GND (-) & short between D/C & C1.

3) Connect the VGE supply between G (+) & OSC. GND (-).

4) Connect 0-10 mA range of multimeter as shown.

5) Switch ON. Set VCE at 15V.

6) Set VGE to zero, then ID will be zero.

7) Start slowly increasing VGE & note the voltage at which IC starts flowing. This is the

threshold voltage. Plot this point.

8) Increase VGE in steps of 0.5 V till about 6 V. Note IC at every step & plot these points. This

is transfer characteristic. Slope of this curve gives transconductance.

9) Calculate the transconductance.

OBSERVATION TABLE:

4. Output Characteristics:

VGE = VGE =

VCE (volts) IC (mA) VCE (volts) IC (mA)

5. Transfer Characteristics:

VCE = 15V VGE (volts) IC (mA)



CALCULATIONS: Transconductance= IC (mA)/ VGE (volts) = mho

RESULT TABLE:

CONCLUSION:

ORAL QUESTIONS:

1. In what way IGBT is more advantageous than BJT and MOSFET?

2. What are on state conduction losses? How is it low in IGBT?

3. Can we observe the transfer and collector characteristics of IGBT on CRO?



EXPERIMENT NO 03

Study of Single Phase Half Controlled Converter

AIM:

Study of SCRs triggering in half controlled bridge under reactive loads-limitations of simple

UJT triggering circuits

Study of SCR triggering in half controlled bridge under reactive loads using auxiliary SCR

triggering circuit with extended pulse technique

Study of half controlled bridge and action of free wheeling diode

APPARATUS:

Single phase half controlled converter trainer kit.

Lab multimeter to measure output voltages.

Dual scope Oscilloscope.

CIRCUIT DIAGRAM:



THEORY:Converter (Phase Controlled Rectifiers) does AC to DC voltage conversion.

Its classification is as Follows:

In Symmetrical Configeration the cathodes of two SCR’s are at the same potential so their gates can

be connected and a single gate pulse can be used for triggering either SCR. One SCR and one

diode are there in each lag of converter.

In asymmetrical configuration separate triggering circuits are to be used. Two SCRs are

is one leg and two diodes are there in another lag of converter.

Half Controlled Bridge Rectifier

In a phase controlled converter circuit consists of two SCR’s and two diodes are capable of operating

with both positive and negative mean voltages at the DC terminals. The resultant circuit obtained is called as

half controlled bridge rectifier.

Half controlled bridge rectifier is seen with R load, with RL load and with freewheeling diode

action. Waveform are drawn on graph.





Procedure:

Half controlled bridge SCR triggering under reactive loads. Limitation of UJT triggering

circuit:

1. Connect G1-G1A, K1-K1A, G2-G2A and K2-K2A.

2. Put a link in between dotted connections on the board

3. Connect Resistive load across SCR bridge.

4. Connect multimeter and CRO across Resistive load.

5. Initially keep a pot in UJT firing circuit to fully anticlockwise.

6. Switch on the supply and take 2-3 readings of

i) firing angle by varying pot in UJT firing circuit

ii) Avg. output voltage across load by multimeter

iii) Maximum output voltage on CRO.

7. Repeat the same procedure with R-L load and R-L with freewheeling diode.

OBSERVATION TABLE:

A. Single Phase Half Controlled Converter

1. with Resistive Load

Firing Angle (α) Average DC output

voltage

Maximum output

Voltage Firing time in ms Firing time in degrees

2. with RL Load


voltage

Maximum output


3. with free wheeling diode for RL Load


voltage

Maximum output




CALCULATIONS:

single phase half controlled converter

Sr. No. Type of Load Average DC Output

Voltage (Edc)

Observed value

(Edc)

Calculated value

(Edc)

1. Resistive Load

2. RL Load

3. RL Load with

FWD

Graphs:



CONCLUSION:

QUESTIONS:

1. What is conduction angle?

2. What are the effects of adding freewheeling diode in this circuit?

3. What are the effects of removing the freewheeling diode in single phase semi converter?

4. Why is the power factor of semi converters better than that of full converters?

5. What is the inversion mode of converters?

6. What is continuous and discontinuous conduction mode ? What is free wheeling action od

diode in converter circuit?



EXPERIMENT NO 04

Study of Single Phase Fully Controlled Converter

AIM:

To study single phase fully controlled converter with R and R-L load .

APPARATUS:

Single phase full controlled converter trainer kit.

Lab multimeter to measure output voltages.

Dual scope Oscilloscope.

CIRCUIT DIAGRAM:



THEORY:Converter (Phase Controlled Rectifiers) does AC to DC voltage conversion.

Its classification is as Follows:

Full Controlled Bridge Rectifier

The full controlled converter circuit consists of four SCR’s. It can be operated in rectifing mode

when α<900 and intverting mode when α>900.

Procedure:

Fully Controlled Full wave four SCR Bridge.

1. Connect G1B-G1C, K1b-K1C, G2B-G2C, K2b-K2C.

2. Put a link in between dotted connections on the board

3. Connect Resistive load across SCR bridge.

4. Connect multimeter and CRO across Resistive load.

5. Initially keep a pot in UJT firing circuit to fully anticlockwise.

6. Switch on the supply and take 2-3 readings of

iv) firing angle by varying pot in UJT firing circuit

v) Avg. output voltage across load by multimeter

vi) Maximum output voltage on CRO.

7. Repeat the same procedure with R-L load.





OBSERVATION TABLE:

B. Single Phase Fully Controlled Converter

1. with Resistive Load


voltage

Maximum output


2. with RL Load


voltage

Maximum output


3. With R-l-E Load (Experiment beyond practical syllabus)


voltage

Maximum output




CALCULATIONS:

single phase Fully controlled converter

Sr.

No.

Type of Load Observed value

(Edc)

Calculated value

(Edc)

1. Resistive Load

2. RL Load

3. R-L-E Load

Graphs:



CONCLUSION:

QUESTIONS:

1. What is the difference between half wave and full wave rectifier?

2. Explain Rectifyng and inverting mode operation of single phase fully controlled converter.



EXPERIMENT NO. 5

Single Phase AC Voltage Controller

AIM: To perform single phase A.C vtg controller for resistive load.

APPRATUS:

AC voltage controller kit

Connecting wires

CRO and CRO probes

Multimeter

CIRCUIT DESCRIPTION:

A triggering circuit for a tric using diac.fig shows a triac firing ckt employing diac.in this

ckt resistor R is variable.When R is zero R protects from diac and triac gate from getting exposed to

almost full supply vtg resistor R2 limits the c/n in diac and triac gate when diac turn on. The value

of C and potentiometer R are so selected as to give firing angle range given by 0 to 180 degree. In

practice a triggering angle ckt of 0-170 degree is only possible for firing ckt.Variable resistance R

controls the charging time table of the capacitor C and hence the firing angle of triac, when R is

small the charging time is constant equal to (R1+R) C is small. Source voltage charges capacitor C

to diac trigger voltage earlier and firing angle for triac is small, likewise when R1 is high, firing

angle of triac is large. When capacitor C (with upper plate +ve charge to breakdown vtg at diac)

Diac turns on as consequences capacitor discharges rapidly thereby applying capacitance vtg Vc in

the form of pulse across the triac gate to turn it on. After triac turn on at firing angle α, source

votage Vs appears across the load during +ve half cycle for (π-α) radius when Vs become zero at

wt=π triac turn off. After wt=π, Vs becomes –ve the capacitor now charges with lower plate

positive.

Mode-I (0<wt<π)

During the +ve half cycle of the supply voltage, thyrister T1 is in the forward biased condition

whereas thyrister T2 is in the reversed biased condition. Whenever gate signal has been given to

thyrister T1 at wt=α, it starts conducting.

During the +ve half cycle of the supply voltage, the power gets deliver to load from source during

the period α to π. At π, both output voltage and current falls to zero. At this instant, T1 is subjected

to reverse bias and therefore it gets turnedoff naturally.

Mode-I (0<wt<2π)



During the -ve half cycle of the supply voltage, thyrister T2 is in the forward biased condition

whereas thyrister T1 is in the reversed biased condition. Now,whenever gate signal has been given

to thyrister T2, at wt=π+α, immediately it gets turn on and hence conduct from (π+α) to 2π. T2 is

subjected to reverse bias at wt=2π and it is therefore line commutated at this instant.

CIRCUIT DIAGRAM:

OBSERVATION TABLE:

Input Voltage Firing Angle Output Voltage

across RL In msec In degrees

OBSERVED WAVEFORMS:



CONCLUSION:

ORAL Questions:

1. What are the advantages and the disadvantages of phase control?

2. What is phase control?

3. What are the advantages of bidirectional controllers?



EXPERIMENT NO. 6

EXPERIMENT NO. 7

Three Phase AC-DC Fully Controlled Bridge Converter

AIM: Simulation of Three Phase AC-DC Fully Controlled Bridge Converter

APPRATUS:

MATLAB Software

CIRCUIT DESCRIPTION:

A DC motor represented by a simplified RL-E model is fed from an inductive three-phase source

through a six-pulse thyristor bridge. A pulse generator synchronized on the source voltages

provides the trigger pulses for the six thyristors.

The converter output current is controlled by a PI current regulator built with Simulink® blocks. A

step signal is applied to the reference input to test the dynamic response of the current regulator.

In order to allow further signal processing, signals displayed on the Scope block are sampled at

1/60/512 s (512 samples/ cycle) and stored in a variable named 'psbconveter_str' ('structure with

time' format) .

PROCEDURE:

Start simulation and observe current and voltage waveforms on the Scope block.

When simulation is completed, open the Powergui and select FFT Analysis to display the 0 - 2000

Hz frequency spectrum of signals saved in the 'psbconverter_str' structure. The FFT will be

performed on a 2-cycle window starting at t = 0.1 - 2/60 (last 2 cycles of recording). Input labeled

'Ia & Ib' and signal number 1 (Ia) should be already selected. Click on Display and observe the

frequency spectrum of last two cycles of Ia. Harmonic currents (6n+/-1) are displayed in % of the

fundamental component .

The value of the fundamental current (magnitude = 27.48 A peak) and the Total Harmonic

Distortion (THD) are also displayed. Harmonics in the 0 - 2000 Hz range contribute to 29% in

THD. If you specify a 0-4000 Hz frequency range, notice that contributions of harmonics above

2000 Hz are negligible in the current THD.

Now select the input labeled Vd and display its spectrum. The DC voltage contains harmonics (6n)

and its DC component is 145.4 V.



CIRCUIT DIAGRAM:

Use the Powergui FFT tool to display

the spectrum of Scope signals stored in

the 'psbconverter_str' structure.

208 V rms L-L

3-phase Source

Three-Phase Thyristor Converter

PI Current Regulator

DC motor equivalent circuit

Synchronization Voltages

Continuous

i+

-

iB

i+

-

iA

v+-

Vd

v+-

Vca

Vc

v+-

Vbc

Vb

v+-

Vab

Va

g

A

B

C

+

-

Thyristor Converter

alpha_deg

AB

BC

CA

Block

pulses

Synchronized

6-Pulse Generator

Scope

Mux

Mux

1

s

Id_Reference

i+

-

Id

5

100

?

Double click here for more info

90

0

iA & iB

Id & Id_ref

Vd

OBSERVED WAVEFORMS:

1. With Resistive load (R= Ω)

2. With R-L load (R= Ω & L= H)

3. With R-L-E load (R= Ω, L= H & E= V)



Figure: Waveform for R load



Figure: Waveform for R-L load



Figure: Waveform for R-L-E load



CONCLUSION:-

Sr.No Type of load Output voltage Output Current

1 Resistive load

2 R-L load

3 R-L-E load

ORAL QUESTIONS:



Experiment No. 8

AIM:- Simulation of three phase voltage source Inverter using 180 degree and 120 degree

conduction mode using Software PSIM

THEORY:

Three phase voltage source inverter are supplied with two possible switching schemes:

1. 180 degree conduction mode 2. 120 degree conduction mode:

180 degree conduction mode:

In this scheme, six transistors( BJT/MOSFET/IGBTs) are switched at every 60 degree

intervals and once one transistor starts to conduct , it will remain on for 180 degree and

then it is turned off.

At a time three devices are in ON state. They are from positive and negative group of

bridge.


In this scheme, six transistors( BJT/MOSFET/IGBTs) are switched at every 60 degree

intervals and once one transistor starts to conduct , it will remain on for 120 degree and then

it is turned off.

At a time two devices are in ON state. One device from positive group and another will be

from negative group.

CIRCUIT DISCRIPTION:

1. A circuit is drawn in PSIM worksheet which consists of following:

1. DC source,

2. 6 MOSFET switches,

3. 6 gating signals

4. Three phase balanced resistive load

5. Voltmeters are connected to measure phase and line voltages. The

inverter is built with the MOSFET/Diode block which is the basic

building block of all VSC’s.



Input DC voltage (Vdc=100V), Load resistance / phase=10ohm. The three phase 4 wire star

connected load is used. The gating block of each MOSFET is connected with a following sequence:


For T1 switching point: From 0 degree to 180 degree.




For T5 switching point: From 240 degree to 360 degree and 0 to 60 degree

For T6 switching point: From 300 degree to 360 degree and 0 to 120 0 degree

The voltmeters are connected to measure the line voltages and phase voltages in the circuit.

The total simulation time given is of 0.1 sec in the step of 0.0001 sec.







For T6 switching point: From 0 degree to 60 degree and 300 degree to 360 degree

The voltmeters are connected to measure the line voltages and phase voltages in the circuit.

The total simulation time given is of 0.1 sec in the step of 0.0001 sec.

Procedure:

1.Run the simulation and observe the following two waveforms on the SIMVIEW.

Vab: +100V to -100V

Van:+50V to -50V

Vbc:+100V to -100 V

Vbn:+50V to -50 V



Vca:+100V to -100 V

Vcn:+50V to -50 V

CIRCUIT DIAGRAM:-

SIMULATION RESULTS:-

1. Phase voltages and linevoltages are observed.





CONCLUSION:

ORAL QUESTIONS:-

1. COMPARE 180 degree conduction mode and 120 degree conduction

mode:



EXPERIMENT NO.9

DC Step Down Chopper

AIM: Simulation of DC Step Down Chopper using PSIM Software

THEORY:

DC step down Chopper is also known as DC-DC converter. In step down chopper, output voltage

across load is less than input voltage by following formula:

Vo = α * Vs

CIRCUIT DIAGRAM:

PROCEDURE:

Run the simulation and observe the following two waveforms on the SIMVIEW.

SIMULATION RESULT:



CONCLUSION:

ORAL Questions:

1. Explain the types of choppers in detail.

2. What are output voltage control techniques of chopper?



EXPERIMENT NO.10

Aim: Design of snubber circuit

A snubber circuit consists of a series combination of resistance Rs and capacitance in product with

thyristor.

Working:

When switch ‘S’ is used a snubber voltage appears across the circuit. Capacitance Cs behaves like

short circuit since voltage across SCR is zero.With passage time voltage across Cs builds up at slow

rate that across Cs in one.

Hence voltage across SCR is less, and then specified min, rating at device. Actually Cs is

sufficient to prevent unwanted triggering of SCR.Then what is the use of putting Rs in series

with Cs.Before SCR is fired gate pulses Cs changing to full voltage.

When SCR is tuned ON capacitor discharge through SCR & sends current equal to Vs resistance of

load path forward by Cs. Therefore to limit magnitude of discharge current is relatively small &

turn ON is reduced.

Procedure to design snubber circuit:

1. When switch‘s’ is closed capacitor be like short circuit & SCR in forward block state offers

very high resistance. Hence equivalent circuit differs switch ‘s’ is closed. It is shown in fig,

for this circuit voltage equation is



----------------------(i)

Then solution of equation

Where,

T=time constant

=

2. In (i) T is measured in second from instant of closing circuit. Circuit parameters should

be such that across Cs during changing is less than specified rating of SCR. &

Discharge current of turn ON OFF SCR is within reasonable limit.

Normally & Cs & load circuit parameter from an under damped circuit so that is limited

acceptable value

=

The value of is max. When t=0

= -------------------- (ii)



L=

3. The voltage across SCR is given by

-------------------- (iii)

4. From (iii) & (ii)

----------------------- (iv)

---------------------- (v)

The above circuit consists of should fully analyses to determine optimum value of snubber

circuit parameter

It is given by

Damping factor or Damping ratio

In order to limit peak voltage over short across thyristor state value damping factor it in range 0.5 to

1 is used.

For optimum solution problem ‘r’ is taken

Cs=

From fig (2) When switch ‘s’ is closed capacitor Cs charged to dc supply voltage before SCR is

triggered.

When SCR turn ON capacitor Cs will discharge through max Current through capacitor will be

The current spike is less than the respective current reading of SCR



If is small then current spike is large in order to reduce this current spike is taken queater than

what req. to limit

At same time value also reduced. So that energy stored in is small snubber discharge done not

harm SCR.

It is turn ON.

Thus

For AC circuit max value of voltage is given in (iii) to calculate value of R

Documents

Subject Code:303143 Subject: Power Electronics Laboratory