pe lab manual

Power Electronics Lab
Manual
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Circuit Diagram:
Fig. 1: Circuit diagram for SCR Characterstics

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Expt No. Date: …………….
Study of Characteristics of SCR , MOSFET & IGBT
a)Characteristics of SCR
Aim: To obtain the V-I Characteristics of SCR and to determine the latching current, holding
current.
Apparatus Required:
Table 1
S.No. Name of the equipment Range Qty
Theory:
Silicon Controlled Rectifier: The Silicon Control Rectifier (SCR) consists of four layers of
semiconductors, which form NPNP or PNPN structures. It has three junctions,
labeled J1, J2, and J3 and three terminals. The anode terminal of an SCR is connected to the
P-Type material of a PNPN structure, and the cathode terminal is connected to the N-Type
layer, while the gate of the Silicon Control Rectifier SCR is connected to the P-Type material
nearest to the cathode.
Forward blocking mode: In this mode of operation the anode is given a positive potential
while the cathode is given a negative voltage keeping the gate at zero potential i.e.
disconnected. In this case junction J1 and J3 are forward biased while J2 is reversed biased
due to which only a small leakage current flows from the anode to the cathode until the
applied voltage reaches its breakover value at which J2 undergoes avalanche breakdown and
at this breakover voltage it starts conducting but below breakover voltage it offers very high
resistance to the flow of current and is said to be in off state.
Forward conduction mode: SCR can be brought from blocking mode to conduction mode
in two ways - either by increasing the voltage across anode to cathode beyond
breakover voltage or by applying of positive pulse at gate. Once it starts conducting
no more gate voltage is required to maintain it in on state. There is one way to turn it

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off i.e. Reduce the current flowing through it below a minimum value called holding
current.
Tabular Column:
V-I Characteristics
Table No: 2 Table No: 3
Model graph:
IG1=
VAK (Volts) IA (mA)
IG2=
VAK (Volts) IA (mA)

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Fig. 2:V-I Characteristics of SCR
Reverse blocking mode: SCRs are available with reverse blocking capability. Reverse
blocking capability adds to the forward voltage drop because of the need to have a
long, low doped P1 region. (If one cannot determine which region is P1, a labeled
diagram of layers and junctions can help). Usually, the reverse blocking voltage rating
and forward blocking voltage rating are the same. The typical application for reverse
blocking SCR is in current source inverters.
Latching Current: Latching current (IL) is the minimum principal current required to
maintain the Thyristor in the on state immediately after the switching from off state to
on state has occurred and the triggering signal has been removed.
Holding Current: Holding current (IH) is the minimum principal current required to
maintain the Thyristor in the on state.
Procedure:
V-I Characteristics:-
1. Make all connections as per the circuit diagram.
2. Initially keep V1 & V2 at minimum position and R1 & R2 maximum position.
3. Adjust Gate current Ig to some value(2.5/5.0mA) by varying the V1 or R1.

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4. Now slowly vary V2 and observe anode to cathode voltage VAK and anode current
IA.
5. Tabulate the readings of anode to cathode voltage VAK and anode current IA.
6. Repeat the above procedure for different Gate current Ig.
Gate triggring and finding Vg and Ig:-
1. Keep all positions at minimum.
2. Set anode to cathode voltage VAK to some value say 15V.
3. Now slowly vary the V1 voltage till the SCR triggers and note down the reading of
gate current(IG) and Gate Cathode voltage(VGK) and rise of anode current IA
4. Repeat the same for different Anode to Cathode voltage and find VAK and IG
values.
To find latching current:-
1. Keep R2 at middle position.
2. Apply 20V to the anode to cathode by varying V2
3. Rise the Vg voltage by varying V1 till the device turns ON indicated by sudden
rise in IA . The current at which SCR triggers is the minimum gate current required
to turn ON the SCR.

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4. Now set R2 at maximum position, then SCR turns OFF, if it is not turned off reduce
V2 up to turn off the device and put the gate voltage.
5. Now decrease the R2 slowly, to increase the anode current gradually in steps.
6. At each and every step, put OFF and ON the gate voltage switches V1. If the
Anode current is greater than the latching current of the device, the device stays
ON even after switch S1 is OFF, otherwise device goes to blocking mode as soon
as the gate switch is put OFF.
7. If IA>IL then, the device remains in ON state and note that anode current as
latching current.
8. Take small steps to get accurate latching current value.
To find holding current:-
1. Now increase load current from latching current level by varying R2 & V2
2. Switch OFF the gate voltage switch S1 permanently (now the device is in ON
state)
3. Now increase load resistance(R2), so that anode current starts reducing and at
some anode current the device goes to turn off .Note that anode current as holding
current.

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4. Take small steps to get accurate holding current value.
5. Observe that IH<IL
Precautions:
1.All the connection should be tight.
2. Ammeter is always connected in series in the circuit while voltmeter is parallel to the
conductor.
3. The electrical current should not flow the circuit for long time, Otherwise its
temperature will increase and the result will be affected.
4. It should be care that the values of the components of the circuit is does not exceed
to their ratings (maximum value).
5. Before the circuit connection it should be check out working condition of all the
Component.
Result:

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Viva-voce:
1. Define holding current,latching current, ON state resistance,break down voltage.
2. Write an expression for anode current?
3. Mention the applications of S.C.R?

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Remarks
Signature of the faculty
Circuit Diagram:

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Fig. 3: Circuit diagram for MOSFET Characterstics

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b) Study of MOSFET Characteristics
Aim: To obtain the various characteristics of MOSFET.
Apparatus Required:
Table 4
Theory:
A metal oxide semiconductor field effect transistor is a recent device developed by
combining the areas of field effect concept and technology. It has three terminals called drain,
source and gate. MOSFET is a voltage controlled device. As its operation depends upon the
flow of majority carriers only, MOSFET is uni polar device. The control signal or gate
current less than a BJT. This is because of fact that gate circuit impedance in MOSFET is
very high of the order of 109
Ω. This larger impedance permits the MOSFET gate be driven
directly from microelectronic circuits. Power MOSFETs are now finding increasing
applications in low-power high frequency converters.
The transfer characteristics of MOSFET shows the variation of drain current ID as a
fuction of gate to source voltage VGS. The device is in OFF state upto some voltage called
threshold device voltage. The output characteristics of Power MOSFET indicate the variation
of Drain current ID as a function of Drain source voltage VDS as a parameter. This device
combines into advantages of IGBT and BJT.
Procedure:
Transfer Characteristics:
2. Switch on the regulated power supply. Keep VDS constant say 10V. Vary VGS
in steps and note down the corresponding drain current ID
3. Tabulate the readings in the table.
4. Plot a graph of ID against VGS.

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Observations:
Table 5: Output Charcteristics Table 6: Transfer Charcteristics
S.
No.
VGS1 VGS2
VDS (V) ID(mA) VDS (V) ID(mA)
Model Graphs:
VDS
VGS (V) ID(mA)

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Fig. 4: Output Characterisitcs Fig. 5: Transfer Characterisitcs
Output Characteristics:
1. Make the connections as shown in the circuit diagram.
2. Initially set VGS to some value say 10V.
3. Slowly vary VDS and note down the values of ID and VDS.
4. At particular value of VGS there a pinch off voltage between drain and source. If
VDS< VP device works in the constant resistance region and ID is directly
proportional to VDS. If VDS>VP device works in the constant current region.
5. Repeat above procedure for different values of VGS and draw graph between ID
and VDS.
Precautions:
1.All the connection should be tight.
conductor.
3. The electrical current should not flow the circuit for long time, Otherwise its temperature
will increase and the result will be affected.
4. Care should be taken such that the values of the components of the circuit does not exceed
5. Before the circuit connection , check out the working condition of all the components.
Result:
Viva-voce:
1.What is the difference between MOSFET and BJT?
2.What are the two types of MOSFET?

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3. How are MOSFETs suitable for low power high frequency applications?
4. What are the merits of MOSFET?
5. What are demerits of MOSFET?
6.What are the applications of MOSFET?

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Remarks
Circuit Diagram:
Fig. 6: Circuit diagram for IGBT characterstics

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c) Study of IGBT Characteristics
Aim: To obtain the Output and Transfer Characteristics of IGBT.
Apparatus Required:
Table 7
Theory :
It is a new development in the area of power MOSFET technology. This device
combines in to advantages of both MOSFET and BJT. So an IGBT has high input impedance
like as MOSFET and low ON state power like BJT. Further IGBT is free from second
breakdown problem present in BJT. IGBT is also known as metal oxide insulated gate
transistor.
It was also called as insulated gate transistor. The static characteristics or output
characteristics of IGBT shows plot of collector current IC vs collector –emitter voltage VCE
for various values of gate emitter voltage. In the forward direction the shape of output
characteristics is similar to that of BJT and have the controlling parameter is gate-emitter
voltage VGE because IGBT is a voltage controlled device. The device developed by
combining the areas of field effect concept and technology.
Procedure:
Transfer Characteristics:

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2. Initially keep V1 & V2 at minimum position and R1 & R2 middle position.
3. Set VCE to some say 10V.
4. Slowly vary gate emitter voltage VGE by varying V1.
5. Note down IC and VGE readings for each step.
6. Repeat above procedure for 20V & 25V of VCE and plot the graph between IC
& VGE.
Tabular Column:
Table No. 8 Ouput Characteristics
S.No. VGE1 VGE2
VCE (Volts) IC (mAmps) VCE (Volts)
IC
(mAmps)
Table No. 9 Transfer Characteristics
VCE
VGE (Volts) IC (mAmps)
Model Graphs:

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Fig. 7 Output Characteristics Fig. 8 Transfer Characteristics
Output Characteristics:
1. Initially set VGE to some value say 5V by varying V2.
2. Slowly vary V2 and note down IC and VCE readings.
3. At particular value of VCE there will be a pinch off voltage VP between collector and
emitter.
4. Repeat above procedure for different values of VGE and draw graph between IC andVGE.
Precautions:
1. All the connection should be tight.
conductor.
4. It should be care that the values of the components of the circuit is does not exceed to
their ratings (maximum value).
Component.
Result:
Viva Voce:
1. In what way IGBT is more advantageous than BJT and MOSFET?

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2. What are merits of IGBT?
3. What are demerits of IGBT?

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4. What are the applications of IGBT’s?
5. How is IGBT turned off?
6. What is threshold voltage?

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Remarks
Circuit Diagram:
Fig. 1 R-C Triggering circuit

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Expt No: Date: …………
Gate Firing Circuits of SCR
a)R-C Triggering
Aim: To observe the output waveforms of Resistance- Capacitance firing circuit of SCR.
.
Apparatus Required:
Table 1
Theory:
It includes variable resistor, two diodes, SCR (Silicon Controlled Rectifier),
Capacitor, Load resistor.The circuit diagram of an RC Triggering R-C-Diode circuit giving
full half-cycle control (180 electrical degrees).
On the positive half-cycle of SCR anode voltage the capacitor charges to the trigger
point of the SCR in a time determined by the RC time constant and the rising anode voltage.
The top plate of the capacitor charges to the peak of the negative voltage cycle through diode
D2 on the negative half-cycle, resetting it for the next charging cycle.
Procedure:
2. Give the AC power supply from the source.

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3. Connect resistive load of 200Ω between two points.
4. Switch ON Power supply and observe the wave forms of input & output at a time
in the CRO.
5. Slowly vary the control Resistor RC, so that firing angle can vary from 0-180°.
6. Observe various voltage waveforms across load, SCR and other points, by varying the
load resistance.
7. Compare practical obtained voltage waveform swith theoretical waveforms and observe the
firing angle in R-C Triggering.
Waveforms:
(a) (b)
Fig. 2: Output voltage waveforms for RC half wave triggering circuit of (a) high value
j(b) low value of R

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Precautions:
conductor.
Component.
Result:
Viva Voce:
1.What is the maximum firing angle of RC-triggering and why?
2.What are the limitations of RC triggering circuit?

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Remarks
Circuit Diagram:
Fig. 3: Resistance triggering circuit

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b)Resistance Triggering
Aim: To observe the output waveforms of resistance firing circuit of SCR.
Apparatus Required:
Table 2
Theory:
It includes one fixed resistor, variable resistor, diode, SCR(Silicon Controlled
Rectifier), Load resistor. The circuit diagram of an R Triggering consistsof Simple resistor;
diode combinations trigger and control SCRs over the full 180 electrical degree ranges,
performing well at commercial temperatures. These types of circuits operate most
satisfactorily when SCRs have fairly strong gate sensitivities. Since in a scheme of this type a
resistor must supply all of the gate drive required to turn on the SCR, the less sensitive the
gate, the lower the resistance must be, and the greater the power rating.
It provides phase retard from essential zero (SCR full “on”) to 90 electrical degrees of
the anode voltage wave (SCR half “on”).Diode D1 blocks reverse gate voltage on the
negative half-cycle of anode supply voltage. It is necessary to rate blocking to at least the
peak value of the AC supply voltage and the trigger voltage producing the gate current to fire
IGF are in phase. When EAC = Em, at the peak of the AC supply voltage, the SCR can still
trigger with the maximum value of resistance between anode and gate.
Procedure:

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2. Connect the AC power supply from the source indicated in the front panel.
3. Connect Load i.e., Rheostat of 200Ω between two points.
4. Switch ON power supply and observe the wave forms of input & output at a time
in the CRO.
5. Slowly vary the control Resistor R, so that firing angle can vary from 0-90°.
6. Observe various voltage waveforms across load, SCR and other points.
Waveforms:
(a) (b) (c)
Fig. 4: Waveforms across gate, load and SCR for Resistance firing circuit of an SCR in
a half wave circuit at (a) No triggering of SCR (b) α=900
(c) α<900

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7. Compare practical obtained voltage waveforms with theoretical waveforms and
observe the firing angle in Resistance Triggering.
Precautions:
conductor.
Component.
Result:.
Viva Voce:
1. What is the maximum firing angle of R-triggering circuit and why?
2. What are the disadvantages of R triggering?
3. Mention different methods of trigerring SCR?

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4. Why gate triggering is preferred?
Remarks Signature of the facult
Circuit Diagram:
Fig. 5 UJT triggering circuit

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c) UJT Triggering
Aim: To obtain firing of SCR using UJT Relaxation Oscillator and observe the output
wavwforms.
Apparatus Required:
Table 3
Theory:
Uni-Junction Transistor: UJT exhibits negative resistance characteristics; it can be used as
relaxation oscillator. The external characteristics RB1 and RB2 are resistances which are small
in comparison with internal resistances R1 and R2 of the UJT base. The emitter potential V is
varied depending on the charging rate of capacitance C. The charging resistance Rc should be
such that the load line intersects the device only in the negative resistance region. η is called
as the intrinsic standoff ratio. It is defined as
UJT is a highly efficient switch .It’s switching time is in a range of nano seconds. The rise
time output pulse will depend on the switching speed of the UJT and duration will be
proportional to the time constant RB1C of the discharge circuit.
The output pulses of UJT are identical in magnitude and time period
The value of η is specified for each device . For UJT η=0.63

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Procedure:
1. First observe the waveforms at different points in circuit and also trigger output
T1 and T1` observe the pulses are synchronized.
2. Now make the connections as per circuit using AC source, UJT Relaxation
Oscillator, SCR’s and Loads.
3. Observe the waveforms across the load and SCR and other points, by varying the
variable resistor Rc and resistance load, observe firing angle of SCR.
4. Use differential module for observing two waveforms (input and output)
simultaneously in channel 1 and channel 2.
5. Check the waveforms for large value of RC and small value of RC and also
triggering points of SCR.
For Relaxation Oscillator:
1. Short the CF capacitor to the diode bridge rectifier to get filtered AC Output.
2. We get equidistance pulses at the output of pulse transformer.
3. The frequency of pulse can be varied by varying the potentiometer.
4. Observe that capacitor charging and discharging time periods and calculate
frequency and RC time constant of UJT Relaxation Oscillator by using given
formulas
Precautions:
conductor.

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Component.

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Result:
Viva Voce:
1. Why is an UJT used in SCR firing circuit?
2. Why is the isolation needed between Thyristor and firing circuit?
3. What are the applications of UJT trigger circuits?
4. What are the merits of UJT firing circuit over RC triggering circuit?

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Remarks
Circuit Diagrams:
(a) Class-A Commutation (b) Class-B Commutation
(c) Class-C
Commutation
(d) Class-D
Commutation

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(e) Class-E Commutation
Fig. 1: Commutation Circuits
Expt No. Date: …………
Study of Forced Commutation Circuits
Aim: To verify the different types of forced commutation circuits of SCR by connecting
a resistive load.
Apparatus Required:
Table 1
Theory: Commutation is the process of turning off the SCR and it normally causes the
transfer of current flow to other parts of circuit. Commutation can be divided into
a) Natural commutation
b) Forced commutation
a) Natural commutation: If the source voltage is AC, the SCR current goes through a
natural zero and reverse voltage appears across the SCR. The device is automatically turns
off due to the natural behavior of the source voltage. This is known as natural commutation
or line commutation.
b) Forced commutation: In some SCR circuits the input voltage is DC and the
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external or additional circuitry called as commutation circuitry to turn off SCR. This
technique is called forced commutation and normally applied in DC to DC converters .
Forced Commutation circuits can be classified as
i. Class-A Commutation (Series resonant commutation circuit)
ii. Class-B Commutation (Parallel resonant commutation circuit)
iii. Class-C Commutation ( Complementary commutation circuit)
iv. Class-D Commutation (Auxiliary Commutation)
v. Class-E Commutation (External Pulse Commutation.
Waveforms:
Class-A Commutation
Class-B Commutation

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Procedure:
Class-A Commutation:
1. Connect the circuit as shown in the circuit.
2. Connect Trigger output T1 to gate and cathode of SCR T1
3. Switch on the DC supply to the power circuit and observe the voltage waveform
across load.
4. Repeat the same for different values of L,C and R.
Class-B Commutation:
2. Connect Trigger output T1 to gate and cathode of SCR T1
3. Switch on the DC supply to the power circuit and observe the voltage waveform
across load.
4. Repeat the same for different values of L,C and R.
Class-C Commutation:
2. Connect T1 and T2 from firing circuit to gate and cathode of Thyristors T1 and T2.
3. Observe the waveforms across R1,R2 and C by varying frequency and also duty cycle
potentiometer.
4. Repeat the same for different values of C and R.
Class-D Commutation:
2. Connect T1 and T2 gate pulses from the firing circuit to the corresponding SCRs’in
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3. Initially keep the trigger ON/OFF at OFF position initially charge the capacitor, this can be
observed by connecting CRO across the capacitor.
4. Now switch ON the trigger output and observe the voltage waveform across the
load, T1, T2 and capacitor.Note down the voltage waveforms at different frequency of
chopping and also at different duty cycles.
5. Repeat the experiment for different values of load Resistance, commutation inductance
and capacitance.
Class-C Commutation:
Class-D Commutation:

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Class-E Commutation:
2. Connect the trigger output T1 from the firing circuit to the SCR.
3. Connect T2 to the Transistor base and emitter points.
4. Switch on the Power Supply and External DC supply.
5. Switch on the trigger output and observe and note down waveforms. Repeat the
Same by varying frequency and duty cycle.
Precautions:
conductor.

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Component.
Class-E Commutation

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Result:
Viva Voce:
1.What is meant by commutation?
2.What are the different types of commutation techniques?
3.What is meant by impulse commutation?

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4.What is meant by external pulse commutation?
5.When the circuit is said to be under damped circuit?
6.In which type of converter forced commutation is employed?
Remarks
Circuit Diagram:
Fig. 1: Half Controlled Bridge Converter with R load

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Fig. 2: Half Controlled Bridge Converter with R-L load
Single Phase Half Controlled Bridge Converter
Aim: To obtain the output waveform of single phase half controlled bridge converter with R
and RL Loads.
Apparatus Required:
Table 1

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Theory:
The circuit arrangement of a 1-ph converter is shown in figure 1. In the positive half
cycle thyristor T1 is forward biased. When SCR T1 is fired at ωt = α, the load is connected to
the input supply through T1 and D2 during the period from α ≤ ωt ≤ π+α the input voltage is
negative and freewheeling diode DM is forward biased. DM conducts to provide continuously
current in case of inductive loads. In the negative half-cycle of input voltage T2 is forward
biased and triggering of T2 at ωt = π +α will reverse bias DM and is turned OFF. Load is
connected to supply through T2 and D1.
The converter has a better power factor due to the freewheeling diode and is
commonly used in applications up to 15KW where one quadrant operation is acceptable.
The half controlled bridge has the inherent freewheeling action and analysis is more
or less the same with or without a freewheeling diode is connected across the load. In
practical it is always adjustable to provide a freewheeling diode in a half-controlled converter
so that the commutation of SCR’s is assumed inductive loads.
Tabular Column:
Table 2
Model Calculations:
Load
type
Input
Voltage
(Vin)(volts)
Firing
angle in
Degrees
Output voltage (V0) Output Current (I0)
Theoretical(V) Practical(V) Theoretical(A) Practical(A)

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Procedure:
1.Make all connections as per the circuit diagram
2.Connect first 30V AC supply from Isolation Transformer to circuit
3.Connect firing pulses from firing circuit to Thyristors as indication in circuit
4.Connect resistive load 200Ω / 5A to load terminals and switch ON the MCB and
IRS switch and trigger output ON switch
5.Connect CRO probes and observe waveforms in CRO, Ch-1 or Ch-2, across load.
6..By varying firing angle gradually up to 1800
and observe related waveforms
7.Measure output voltage and current by connecting AC voltmeter & Ammeter
Tabulate all readings for various firing angles.
8.For RL Load connect a large inductance load in series with Resistance and observe
all waveforms and readings as same as above.
9.Observe the various waveforms at different points in circuit by varying the Resistive
Load and Inductive Load.
10.Calculate the output voltage and current by theoretically and compare with it
practically obtained values.
Precautions:

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conductor.
Component.
6. Use only isolated power sources (either isolated power supplies or AC power through
isolation power transformers). This helps using a grounded oscilloscope and reduces the
possibility of risk of completing a circuit through your body or destroying the test equipment.
Waveforms:

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Fig. 2 : Single Phase Semi Converter output voltage waveforms
Result:

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Viva Voce:
1. What is meant by half controlled rectifier?
2. What is the effect of adding free wheeling diode?
3.Give at least five application of phase controlled rectifier?
4.What is meant by firing angle?
5.What is other name for single half controlled rectifier?
6.What is meant by pulse number?
Remarks
Circuit Diagram:

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Fig. 1:Fully Controlled Bridge Converter with R load
Fig. 2:Fully Controlled Bridge Converter with R-L load

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Expt No: Date: …………
Single Phase Fully Controlled Bridge Converter
Aim: To observe the output waveforms of a single phase fully controlled bridge converter
with R and RL Loads.
Apparatus Required:
Table 1
S.No. Name of the equipment Range Type Qty
Theory:
A single phase full bridge converter using four SCR’s is shown in figure1. The load is
assumed to be R and RL. Thyristor pair T1 and T2 is simultaneously triggered and π radians
after pair T3 and T4 is gated together.
During the positive half cycle SCR’s T1 and T1
I
are forward biased and when there
two thyristors are fired simultaneously at wt = α, the load is connected to the input through T1
and T1
I
. In this case of inductive loads during the period π <wt < π+α the input voltage is
negative and freewheeling diode Dm is forward biased. Dm conducts to provide the
conductivity of current in the inductive load. The load current is transferred from T1 and T1
I
to DM and thyristors T1 and T1
I
are turned off due to line or natural commutation.
During the negative half cycle of the input voltage thyristors T2 and TI
2 are forward
biased. The firing of thyristors T2 and T2
I
simultaneously at wt = π+α will reverse bias DM. the
diode DM is turned off and the load is connected to the supply through T2 and T2
I
.

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Tabular Column:
Table 2
Free wheel
Load
type
Input
Voltage
(V in)
Firing
angle in
Degrees
Theoretical Practical Theoretical Practical
Model Calculations:
Procedure:
1. Make all connections as per the circuit diagram

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2. Connect firstly 30V AC supply from Isolation Transformer to circuit
3. Connect firing pulses from firing circuit to Thyristors as indication in circuit
4. Connect resistive load 200Ω / 5A to load terminals and switch ON the MCB and
IRS switch and trigger output ON switch.
5. Connect CRO probes and observe waveforms in CRO, Ch-1 or Ch-2, across load
and device in single phase half controlled bridge converter.
6. By varying firing angle gradually up to 1800
7. Measure output voltage and current by connecting AC voltmeter & Ammeter
8. Tabulate all readings for various firing angles.
9. For RL Load connect a large inductance load in series with Resistance and
observe all waveforms and readings as same as above.
10. Observe the various waveforms at different points in circuit by varying the
Resistive Load and Inductive Load.
11. Calculate the output voltage and current by theoretically and compare with it
Precautions:
conductor.
Component.
6.Use only isolated power sources (either isolated power supplies or AC power through

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Result:

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Viva Voce:
1.What is a full controlled rectifier?
2. How can we control the output voltage of a single-phase full converter?
3. What is the type of commutation used in a single phase full controlled converter?
4. What is the effect of adding free wheeling diode?
5. What is rectification mode and inversion mode?
6.What are the applications of Single phase fully controlled rectifiers?
Remarks

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Circuit Diagram:
Fig. 1: 1-Ф A.C. Voltage Controller with R load
Fig. 2: 1-Ф A.C. Voltage Controller with R-L load

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Single Phase A.C. Voltage Controller
Aim: To observe the output wave forms of 1-phase A.C.voltage controller with R and RL
loads using anti parallel connection of SCR’s.
Apparatus Required:
Table 1
S.No. Name of the equipment Range Type Qty
Theory: AC voltage controller’s are thyristor based devices ,which converts the fixed Ac
voltage into variable AC voltage with same frequency .The circuit diagram of Single phase
AC voltage controller is shown in figure .It consists of two SCR’s connected in anti parallel.
The input and output voltage waveforms are also shown. The SCR’s are gate controlled and
gate pulses are obtained from firing unit.
For R-Load: For the first half cycle of input voltage waveform SCR T1 conducts and gives
controlled output to load. During the other half cycle of input voltage waveform SCR T2
conducts .During the Positive half cycle T1 is triggered at a firing angle of wt= α .T1 starts
conducting and source voltage is applied to the load from α to π. At wt= π both Vo and Io
falls to zero. Just after wt= π, T1 is reverse biased and therefore it is turned off by self
commutation. During the negative half cycle of T2 is triggered at wt= π+α, then T2 conducts
from wt = π+α.

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Tabular Column:
Table 2: For R-Load
Table 3: For R-L Load
Model Calculations:
Procedure:
AC voltage controller with two thyristors:
S.No.
Input Voltage
(V in)
Firing
angle in
Degrees
Output voltage (V0r) Output Current (I0r)
S.No.
Input Voltage
(V in)
Firing
angle in
Degrees
Output voltage (V0r) Output Current (I0r)

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2.Connect firstly 30V AC supply from Isolation Transformer to circuit
3.Connect firing pulses from firing circuit to Thyristors as indication in circuit
. IRS switch and trigger output ON switch
5.Observe waveforms in CRO, across load by varying firing angle gradually up to
1800
.
7.Tabulate all readings for various firing angles.
A.C. voltage controller with TRIAC:
3.Connect firing pulse from firing circuit to TRIAC as indication in circuit
5.Observe waveforms in CRO, across load by varying firing angle gradually up to
1800
.
7.Tabulate all readings for various firing angles.
practically obtained values
Waveforms: (i) For R-Load

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(ii) For R-L Load
Precautions:

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conductor.
Component.
Result:
Viva Voce:
1.What is ac voltage controller?
2.What are the applications of ac voltage controllers?
3. What are the two types of control?
4. What are the merits and demerits of voltage controllers?

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5. Why is the trigger source for the two Thyristor isolated from each other in a single-phase

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65
voltage controller?
6. What is the difference between cycloconverters and ac voltage controllers?
Remarks
Circuit Diagrams:

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Fig.1: Single Phase Cycloconverter with R-load

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67
Fig. 2: Single phase Cycloconverter with R-L Load
Single Phase Cycloconverter
Aim: To verify the operation of single phase Cyclo Converter with R and RL Loads and to
observe the output and input waveforms.
Apparatus Required:
Table 1

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Theory:
The circuit diagram of 1-φ cyclo converter with R and RL load are shown in fig.
Construction ally there are four SCR’s T1, T2, T3 &T4.Out of them T1, T2 are
responsible for generating positive halves forming the positive group. The other two T3, T4
are responsible for negative haves forming negative group. This configuration and waveforms
are shown for ½ and 1/3 of the supply frequency. Natural commutation process is used to turn
off the SCR’s.
A) For R-Load:
During the half cycle when point A is positive with respect to O, SCR T1 is in
conducting mode and is triggered at wt =α then current flows through positive point A-
T1-load-negative O. In the negative half cycle when B point is positive with respect to the
point O,SCR T1 is automatically turned off due to natural commutation and SCR T2 is
triggered at wt = π+α. In this condition the current flows through B-T2-load-O. The flow
of the current direction is same as in the first case. After two positive half cycles of load
Tabular Column:
Table 2: For R-load
Sl.
No
Input
Voltage
(V in)
Firing
angle in
Degrees
Frequency
Division
V o
(V)
I o
(A)
Input
frequency
f s
Output
frequency
f o=fs /2
f o / f s
Table 3: For R-L Load
Sl.
No
Input
Voltage
(V in)
Firing
angle in
Degrees
Frequency
Division
V o
(V)
I o
(A)
Input
frequency
f s
Output
Frequency
fo=fs /3
f o / f s

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voltage and load current SCR T4 is gated at wt=2π+α when O is positive with respect to
B. In this condition the load current flows through O-load-T4-B.Thus the direction of
load current is reversed. In the next half cycle when O is positive with respect to A when
wt=3π, T4 turnoff due to natural commutation and at wt=3π+α T3 is triggered. In this
condition the load current flows through O-load-T3-A. The direction of load current is
same as previous case. In this manner two negative half cycles of load voltage and load
current, equal to the number of two positive half cycles are generated. Now T1 is again
triggered to fabricate further two positive half cycles of load voltage and so on. Like this
the input frequency 50Hz is reduced to ½ at the output across the load. The input and
output waveforms are shown in figure.
The frequency of the output voltage can be calculated by:
Frequency ( fo )=(Time period)-1
B) For RL-Load:-
When A is positive with respect to O forward biased SCR T1 is triggered at wt=α and
the current start to flow through A-T1-R-L-O. Load voltage becomes zero at wt=π but load

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current will not become zero at this angle due to inductance. It becomes zero at wt =β which
is called extinction angle. So it is naturally commutated at wt=β. After half cycle point B
positive with respect to point O. Now at angle wt=π+α. T2 is triggered and the load current
takes path from B-T2-R-L_o and its direction is positive as in the previous case. The load
current decays zero at wt =π+β and SCR T2 is naturally commutated. In the half cycle when
O is positive with respect to B point, T4 is triggered instead of T1 at an angle of wt= (2π+α).
Now the load current flows through O-L-R-T4-B but the direction of load current reversed.
When the load current becomes zero at an angle wt= (2π+α) , T4 naturally commutated
because the voltage is already reversed at wt = 3π.When wt = (3π+α) and point O, is positive
with respect to point A,T3 is triggered then the current flows through O-L-R-T3-A , and the
direction of load current is same in previous case. In the next half cycle again T1 will
triggered like this we get one cycle of output frequency for two cycles of input frequency,
when the frequency division switch is at 2. The waveforms of load voltage and load current
are shown in fig.
The frequency of load voltage can be calculated by fo=(Time period)-1
Waveforms:

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71
Fig. 3: Output Voltage waveforms for step down cycloconverter with R load at α=00
and
α=600
Fig. 4: Output Voltage waveforms for step down cycloconverter with R-L load
Procedure:
2. Connect firstly (30V-0-30V) AC supply from Isolation Transformer to circuit
4. Connect resistive load 200Ω / 5A to load terminals.
5. Set the frequency division switch to (2,3,4,…9) your required output
frequency.
6. Switch ON the MCB and IRS switch and trigger output ON switch.
7. Observe waveforms in CRO, across load by varying firing angle gradually up
to 1800
and also for various frequency divisions(2,3,4,…9).
8. Measure output voltage and current by connecting AC voltmeter & Ammeter
9. Tabulate all readings for various firing angles.
10. For RL Load connect a large inductance load in series with Resistance and
observe all waveforms and readings as same as above.

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11. Observe the various waveforms at different points in circuit by varying the
Resistive Load and Inductive Load.
Precautions:
2. Ammeter is always connected in series in the circuit while voltmeter is parallel to
the conductor.
Component.
isolation power transformers). This helps using a grounded oscilloscope and reduces
the possibility of risk of completing a circuit through your body or destroying the test
equipment.

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Result:
Viva Voce:
1. What is meant by cycloconverter?
2. What are the applications of Cycloconverter?

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3. What are the merits of Cycloconverter?
4. What are demerits of Cycloconverter?
Remarks
Circuit Diagram:

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75
Fig. 1: Circuit Diagram for Single Phase Series Inverter
Single Phase Series Inverter with R and RL Loads
Aim: To study the behavior of modified series inverter by varying load resistance at
different frequencies.
Apparatus Required:
Table 1
Theory:
This circuit which converts DC power into AC power is called inverter. If the
thyristor commutation circuit of the inverter is in series with the Load, then the inverter is
called “Series are tightly coupled. In this circuit, it is possible to turn-on-thyristor Tp before
the current through thyristor Tn has become zero and vice-versa. Therefore, the Modifed
Series Inverter can be operated behond the resonance frequency (fr) of the circuit. Inverter is

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operated at the resonance frequency (fr) if the load current waveform has low frequency and
should not have zero current interval. The inverter’s resonance frequency depends on the
values of L, R and C in the circuit.
Procedure:
2. Give the DC power supply 30V to the terminal pins located in the power circuit
5. By varying the frequency pot, observe related waveforms
6. If the inverter frequency is increases above the resonant frequency of the power
circuit commutation fails. Then switch OFF the DC supply , reduce the inverter
frequency and try again.
Tabular Column:
Table 2 For R= , L=
S.No
Input
Voltage(v)
Firing Angle(α)
Output
Voltage(VO)
Output
Current (A)

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7. Repeat the above same procedure for different value of L,C load and also above
the wave forms with and without fly wheel diodes.
8. Total output waveforms entirely depends on the load, and after getting the perfect
wave forms increase the input supply voltage up to 30V and follow the above
procedure.
9. Switch OFF the DC supply first and then Switch OFF the inverter.( Switch OFF
the trigger pulses will lead to short circuit)
Precautions:
the conductor.
Component.
Result:

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Viva Voce:
1.What is meant by inverter?
2.What are the different types of inverters?

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79
3.What are the application of series inverters?
4.In which aspect inverters are classified?
5.What is the other name for series inverter?
6. What are the merits and demerits of series inverter?

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Remarks
Circuit Diagram:
Fig. 1: Circuit Diagram for Parallel Inverter

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81
Single Phase Parallel Inverter with R and RL Loads
Aim: To study the performance of center tapped transformer type parallel inverter at different
frequencies.
Apparatus Required:
Table 1
Theory:
The circuit diagram of 1-ph Parallel Inverter is shown in fig., SCR1 and SCR2 are
main thyristors. Supply voltage Vdc appears across the left half of the transformer primary
winding OA. Terminal O is positive w.r.t.A. By transformer action terminal B will be at
potential of 2Vdc w.r.t A. Thus capacitor C will get charged twice the supply voltage. The
load voltage will be positive and will have a magnitude VL . At the end of half period SCR2
is firing , capacitor C will be immediately apply a reverse voltage of 2Vdc across SCR1 and
turns off it.

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Similarly the Vdc applies to right half of the primary winding and capacitor gets
charged with 2Vdc in reverse direction. Now the load voltage is negative and hence the
current. Since the commutating capacitor is in parallel with SCRs, so it is called parallel
inverter.
Tabular Column:
Table No: 2
VDC(V) TON(Sec) TOFF(Sec) Frequency(HZ) Vload(v)
Waveforms:

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Fig. 2: Waveforms across load and SCR of Parallel Inverter
Procedure:
1. Make all connections as per the circuit, and give regulated power supply 30V/5A.
2. Give trigger pulses from firing circuit to gate and cathode of SCR’s T1 & T2.
3. Set input voltage 15V, connect load across load terminals.
4. Now switch ON the DC supply, switch ON the trigger output pulses.
5. Observe the output voltage waveforms across load by varying the frequency pot.
6. Repeat the above same procedure for different value of L,C load values.
7. Switch off the DC supply first and then switch off the inverter.
(switch off the trigger pulses will lead to short circuit)
Precautions:
the conductor.

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component.
Result:

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85
Viva voce:
1. To what voltage will the capacitor gets charged?
2. What is the need of the transformer is the circuit?
3. What type of commutation is employed in this circuit?

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4. What are the applications of parallel inverter?
5. What are the merits and demerits of parallel inverter?
Remarks
Fig.1:ThreePhaseHalfControlledBridgeConverterwithR-Lload

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87
Expt No. Date:
…………
Three Phase Half Controlled Bridge Converter
Aim: To observe the output waveforms of three phase half controlled bridge converter with
R & RL Load.
Apparatus Required:
Table 1
CircuitDiagram:

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Theory :
For large power dc loads, 3-ph ac to dc converter are commonly used. The various
types of three phase controlled converter are 3-ph half wave converter, 3-ph half wave
converter is rarely used in industry because it introduces de component in the supply circuit.
If diodes are replaced by 3-thyristors, a semi converter bride is obtained.
Free wheeling mode of operation of bridge connected rectifiers can be realized half of
its thyristor with diodes. Therefore, circuit of three phase half-controlled bridge converter
contains three thyristor in three arms and diodes in the other three arms.For α<600
the
continuous conduction mode is possible. For firing angles α>600
the discontinuous
conduction mode occurs. It can be observed from the waveforms that the output voltage
becomes zero during a part of the output voltage period, because of the free wheeling action.
It is easily noted from the waveforms that the freewheeling period is . Therefore the supply
current flows for the period (Π-α) in each half cycle. As α increase the duration of the supply
current pulse decreases. Therefore, the harmonic content in the source current increases
as the firing angle increases.
Tabular Column:
Table 2
S.No.
Input
Voltage (V
in)
Firing
angle in
Degrees
Theoretical(v) Practical(v)
Theoretical
(A)
Practical
(A)
Model Calculations:

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89
For large firing angle delays, commutation failure may take place due to the limited
time available in symmetrical half controlled converter circuit configuration, if the current is
assumed to be continuous. This may result in half weaving effect
Procedure:
3.Connect resistive load 200Ω / 5A to load terminals and switch ON the MCB
4.Observe waveforms in CRO, across load and device in three phase half controlled bridge
converter.
5.By varying firing angle gradually up to 1800
6.Measure output voltage and current by connecting DC voltmeter & Ammeter
7.Now increase the input supply voltage by changing tapping at Isolation Transformer.
Observe waveforms and readings, changing the supply voltage up to 230V. Tabulate all
readings at various angles and various voltages.
8.For RL Load connect a large inductance load in series with Resistance and observe all
waveforms and readings as same as above.

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9.Observe the various waveforms at deferent points in circuit by varying the Resistive Load
and Inductive Load.
10.Calculate the output voltage and current by theoretically and compare with it practically
obtained values.
Waveforms:

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91
Fig. 2: Output Voltage Waveforms for 3-Ф Semi Converter at α=00
, 600
, 900

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Precautions:
1.Do not conduct the experiment without three phase isolation transformer. If you try to
conduct experiment without isolation transformer the instrument may be damaged due to
short circuit exists between single phase & three phase supply while making measurement
using CRO.
2.Do not attempt to observe load voltage and input voltage simultaneously, if does so input
voltage terminal directly connected to load terminals due to the non isolation of both channels
of the CRO.
Result:
Viva Voce:
1.What are the advantages of three phase circuit over single phase circuit?
2.What is the total harmonic distortion in a three phase semiconverter?
3. Why output voltage is more at lesser value of firing angle?
4.Whis the difference between three phase semiconverter and three phase fully controlled
converter?
5.What are the application of Three phase semiconverter?
Remarks

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Circuit Diagram:
Fig1: Four Quadrant Chopper Circuit With Field Supply

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Chopper Controlled DC Motor
Aim: To analyze the operation of four quadrant chopper drive by controling the speed
of the dc motor.
Apparatus:
Table 1
Theory:
Chopper converts fixed DC voltage to variable DC voltage through the use of
semiconductor devices. The DC to DC converters have gained popularity in modern
industry. Some practical applications of DC to DC converter include armature voltage
control of DC motors converting one DC voltage level to pulse width modulated voltage,
and controlling DC power for wide variety of industrial processes. The time ratio
controller (TRC) is a form of control for DC to DC conversion.
In four quadrant dc chopper drives, a motor can be made to work in forward-motoring
mode (first quadrant), forward regenerative breaking mode (second quadrant), reverse
motoring mode (third quadrant) and reverse regenerative breaking mode (fourth quadrant).
The circuit shown offers four quadrant operation of a separately-excited dc motor. This
circuit consists of a DC Power Supply, four choppers, four diodes and a dc motor. Its
operation in the four quadrants can be explained as under.
Four Quadrant diagram:

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Fig 2: Four Quadrant Diagram

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Fig 3: Four Quadrant Chopper circuit
Forward motoring mode (I quadrant):
During this mode or first-quadrant operation, chopper CH2, CH3 are kept off,
CH4 is kept on whereas CH1 is operated. When CH1, CH4 are on, motor voltage is
positive and positive armature current rises. When CH1 is turned off, positive armature
current free-wheels and decreases as it flows through CH4, D2. In this manner controlled
operation in first quadrant is obtained.
Forward regenerative breaking mode (II quadrant):
A dc motor can work in the regenerative-breaking mode only if motor generated emf
is made to exceed the dc source voltage. For obtaining this mode CH1, CH3 and CH4 are
kept off whereas CH2 is operated. When CH2 is turned on, negative armature current
rises through CH2, D4, Ea, La, ra. When CH2 is turned off, diodes D1, D4 are turned on
and the motor acting as a generator returning energy to dc source. This results in forward
regenerative-breaking mode in the second-quadrant.

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Reverse motoring mode (III quadrant):
This operating mode is opposite to forward motoring mode. Chopper CH1, CH4
are kept off, CH2 is kept on whereas CH3 is operated. When CH3 and CH2 are on,
armature gets connected to source voltage Vs so that both armature voltage and armature
current iaare negative. As armature current is reversed, motor torque reversed and
consequently motoring mode in third quadrant is obtained. When CH3 is turned off,
negative armature current freewheels through CH2, D4, Ea, La, ra; armature current
decreases and thus speed control is obtained in third quadrant. Note that during this mode
polarity of Ea is opposite to that shown in circuit diagram.
Reverse Regenerative-braking mode (IV quadrant):
As in forward braking mode, reverse regenerative-braking mode is feasible only if
motor generated emf is made to exceed the source voltage. For this operating mode, CH1,
CH2 and CH3 are kept off whereas CH4 is operated. When CH4 is turned on, positive
armature current ia rises through CH4, D2, ra, La, Ea. When CH4 is turned off, diodes D2,
D3 begin to conduct and motor acting as generator returns energy to dc source. This leads
to reverse regenerative-braking operation of the dc separately excited motor in fourth
quadrant.
The chopper circuit provided is made to work in the following manner:
Forward Rotation:
During this mode chopper is operating in I quadrant (Current & Voltage are
positive) however chopper jumped to IV quadrant momentarily because current doesn't
become zero instantaneously. Therefore in forward motoring current is always positive
but voltage may be positive or negative. In this way chopper operated in I and IV
quadrants.
Reverse Rotation:
During this mode chopper is operating in III quadrant (Current & Voltage are
negative) however chopper is jumped to II quadrant momentarily because current doesn't
become zero instantaneously. Therefore in reverse motoring current is always negative but
voltage may be positive or negative. In this way chopper operated in III and II quadrants.

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Procedure:
Keyboard settings
Stop/Set key:
This key is used to stop the process. And also this key is used to move the curser to set
the parameters (frequency, duty cycle and Fw/Rw).
INR key: This key is used to increase the parameters (f, Dcy or Fw/Rw) by one.
DCR key: This key is used to decrease the parameters (f, Dcy or Fw/Rw) by one.
RUN key: This key is used to run at set parameters.
Note: The parameters of the curser positions are varied by pressing INR, DCR keys. The
curser can be brought to different parameters (frequency, duty cycle, Q1&Q4/Q3&Q2) using
SET key. When the process is under RUN the parameters can't be changed (INR, DCR keys
are inactive). The parameters can be changed only after STOP key is pressed and the process
return to SET after wait.When RUN key is pressed the motor goes to RUN mode after wait
mode. The parameters can be changed only after STOP key is pressed. The process return to
SET after wait.
1. Keep the toggle switch to SET QUAD position.
2. Power circuit connections are made as shown in the circuit diagram.
3. Connect motor terminals to respective points in the power circuit as shown in the circuit
diagram. Field of the motor to field terminals of the unit.. Armature to the respective
terminals in the circuit.
4. Voltmeter and ammeter are connected internally as shown in the circuit..
5. Triggering pulses are connected internally to respective IGBTs..
6.Connect the power scope to monitor current and voltage waveforms (if provided) otherwise
use CRO.
7. Check the connections and conform the connections made are correct before switching on
mains supply.
8. Connect three pin power cord from the four quadrant chopper power unit to the single
phase three pin power mains
9. Switch on the field supply to the motor.
10. Switch on the single phase power supply to the four quadrant chopper triggering circuit.
11. Keeping power supply voltage knob to minimum position sett frequency, duty cycle,
directions of the motor..

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Tabular Column:
Forward Motoring Mode:
Table No:2
S.No. Duty Cycle Speed In rpm
Reverse Motoring Mode:
Table No: 3
S.No. Duty Cycle Speed In rpm

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12. Enter RUN key.
13. DC power supply voltage must be increased now from 0 up to suitable value (say 100-
150V) by switching on MCB.
14. When RUN key is pressed the chopper is gone for wait mode,, during this mode the
chopper duty cycle is adjusted to less than 10% for a time interval.. After that the
chopper goes to RUN mode, during RUN the chopper duty cycle is adjusted to the sett
value.
15. Observe the speed of the motor in rpm..
16. Now reduce the supply voltage to minimum value..
17. Enter STOP key..
18. When STOP key is pressed the chopper is gone for wait mode,, during this mode the
chopper duty cycle is adjusted to less than 10% for a time interval.. After that the
chopper goes to SET mode, during SET the chopper frequency, duty cycle, chopper
directions (Fw & Rw) can be set.
19. Do the experiment for different duty cycles.
20. Observe the load voltage & load current waveforms using power scope. Load the motor
21. Load the motor slowly (maximum 1A) & study the performance of the motor.
22. Every time reduce the load when you are setting new duty cycle.
23. Release the load. Reduce power supply voltage.
24. Switch OFF power supply.
25. Switch OFF firing circuit & field supply to the motor at the end.
26. Remove the connections
Precautions:
conductor.
Component.

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Result:
Viva Voce:
1.What is meant by step up chopper?
2.Explain how forward motoring operation is attained with four quadrant chopper in a D.C
motor?
3.Explain how forward breaking operation is attained with a four quadrant chopper in a D.C
motor?
4. Explain how reverse motoring operation is attained with a four quadrant chopper in a D.C
motor?
5. Explain how reverse breaking operation is attained with a four quadrant chopper in a D.C
motor?
6.What is meant by step down chopper?
Remarks

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105
Circuit Diagram:
Fig. 1 : Non-Circulating current type Single Phase Dual Converter
Fig. 2 : Circulating current type Single Phase Dual Converter

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Single-Phase Dual Converter
Aim:
To construct a single phase dual converter and to apply reversible voltage to load.
Apparatus Required:
Table 1
Theory:
Dual converter consists of two converters both are connected to the same load. The
purpose of a dual converter is to provide a reversible DC voltage to the load. It is needed for
DC motor drives where reversal is required. Dual converter provides four quadrant operations
hence the name dual. The two modes of operations are the non-circulating current mode and
circulating current mode. In the former only one bridge is triggered. When reversal of output
voltage is required, the firing pulses for concreting bridge are stopped and second bridge is
gated. Since the conducting SCR’s in the first bridge will turn off only when the current goes
to zero, a small dead time must be allowed before the second bridge is gated otherwise: the
AC input will be shorted through the two bridges.
In the circulating current mode, both bridge are gated simultaneously, one operating
in the rectifying mode and the other in the inverting mode to avoid short circuits. This
scheme requires fully controlled bridges. The internal voltage of rectifier is higher and that of
inverter is lower than the output voltage. This can be done by two ways 1) by keeping supply
voltage V constant and firing bridge 1 (P- converter) at α and bridge 2 (N-converter) at (π-α).
By keeping firing angle constant and maintaining supply voltage at rectifier bridge greater
than supply voltage at inverter bridge.
Model Waveforms:

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107
Fig. 3: Voltage waveforms for Non-Circulating current type Dual Converter
Fig. 4: Voltage waveforms for Circulating current type Dual Converter
The dual converters can be operated with or without a circulating current. In this case of
operation without circulating current, only one converter operates at a time and carries the

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load current and the other converter is completely blocked by inhibiting gate pulses.
However, the operation with circulating current has the following advantages.
The circulating current maintains continuous conduction of both converters over the whole
control range, independent of the load.Since one converter always operates as a rectifier and
the other converter operates as an inverter, the power flow in either direction at any time is
possible.Since both converters are in continuous conduction the time response for changing
from quadrant to another is faster.
Procedure:
Dual Converter in Non-Circulatory Current Mode:
I) P-Converter is ON & N-Converter is OFF:
1) Connections are made as per the circuit diagram.
2) Connect rheostat at 50Ω/8A.
3) Connect CRO across load.
4) Apply AC input voltage using isolation transformer.
5) Made P-converter ON & OFF the N-converter.
6) Vary firing angle observe load voltage waveforms on CRO.
7) Note down load voltage in steps by varying firing angle α using multimeter.
II) N-Converter is ON & P-Converter is OFF:
4) Apply AC input voltage using isolation transformer.
5) Made N-converter ON & P-converter OFF.
6) Vary firing angle observe load voltage waveforms on CRO.
Firing angle of N-converter = П – firing angle of P-converter = П – α
Tabular column:
Dual converter in non circulating current mode:

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109
P-converter is ON & N Converter is OFF:
Table 2
S.No Firing angle in degrees
(N-converter) π-α
Load voltage VL(DC)
in volts
N-Converter is ON & P-Converter is OFF:
Table 3
S.No Firing angle in degrees
(N-converter) π-α
Load voltage VL(DC)
In volts
Dual Converter in Circulatory Current Mode:
Table 4
S.No.
Ffiring angle α in
degrees
( P-Converter)
Firing angle П-α
in degrees
(N-converter)
Load voltage VL
(DC) in volts
III) Dual Converter in Circulatory Current Mode:
4) Apply AC input voltage using isolation transformer. Say 30V range.
5) Made N-converter ON & P-converter ON.
6) Vary firing angle, observe load voltage waveforms on CRO.

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Precautions:
conductor.
Component.
Result:
Viva voce:
1.What is meant by dual converter?
2.What are types of dual converters?

Manual
111
3.What is the phase shift we have to provide between each converter in circulating current
mode of operation?
4.What are the application of dual converter?

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Manual
5.what are the merits and demerits of dual converter?
Remarks
Circuit Diagram:

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113
Fig:1 Circuit Diagram for single phase IGBT Based PWM Inverter
Exp no: Date:………….
Single Phase IGBT Based PWM Inverter

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Manual
Aim: To study the operation of IGBT based PWM inverter.
Apparatus Required:
Table 1
S.No. Name of the equipment Range Quantity
Theory:
A device that converts DC power in to AC power at output voltage and frequency is
called an inverter. Some industrial applications of inverters are for adjustable speed AC
drives, inductive heating, stand by aircraft supplies, UPS, HVDC, transmission lines etc.
Schematic diagram of a single phase inverter is given in the fig. The current can be
supplied to the load by proper gating the IGBTs. Only two IGBTs will be on at any one time.
Load voltage is PWM signal.

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Model Waveform:
Fig 2Model waveform for Single phase bridge inverter

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Manual
The power circuit is IGBT based full bridge inverter shown in figure. When T1, T2 conduct,
load voltage is +Vs and when T3, T4 conduct load voltage is –Vs. The frequency of the
output voltage can be controlled by varying the time period. For inductive loads the diodes
connected in anti-parallel with thyristors will allow the current to flow when the main
thyristors are turned off. These diodes are called feedback diodes. The modulation technique
used is sinusoidal pulse width modulation technique. The modulation index can be varied by
the parameter setting through keyboard.
The AC load voltage is controlled by controlling modulation index. Modulation index
is the ratio of maximum amplitude of sine wave to maximum amplitude of triangular wave.
When modulation index is set keeping amplitude of triangular wave constant the amplitude of
sine wave is varied. This will happen in the internal circuit. The speed of the motor can also
be varied by varying the frequency of the inverter circuit. A keyboard is provided to set the
frequency and the modulation index. The various parameters can be displayed by the liquid
crystal display.
Procedure:
Keyboard settings
Stop/Set key: This key is used to stop the process. And also this key is used to move the
cursor to set the parameters (frequency and modulation index).
INR key: This key is used to increase the parameters (f or M) by one.
DCR key: This key is used to decrease the parameters (f or M) by one.
RUN key: This key is used to run at set parameters.
1. Circuit connections are made as shown in the circuit diagram.
2. Connect the required load.
3. Check all the connections and confirm connections made are correct before switching
on the equipment.
4. Keep the DC Voltage knob at minimum position.
5. Switch on firing circuit switch.
6. Switch on the MCB.
7. Set frequency and modulation index at suitable value. Press RUN key.
8. Adjusting input DC voltage to 100V to 200V slowly.
9. Observe the load voltage waveforms using CRO.
10. Record the frequency of the inverter circuit & the variation in AC voltage with reference
to the modulation index.

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Tabular Column:
Table 2
S.No Modulation Index R-Load RL-Load

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11. Reduce the DC voltage to minimum value.
12. Press STOP key.
13. Set new modulation index. Press RUN key.
14. Tabulate the readings in the table.
15. Slowly reduce the DC voltage to zero. Switch off all the switches when the voltage is
completely reduced.
16. Remove the connections.
17. Do the experiments for R-L load.
Precautions:
conductor.
Component.
Result:
Viva Voce:
1.What is the principle of operation of single phase bridge inverter?
2.Explain about PWM?
3.Explain about different types of PWM techniques?

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4.What are merits and demerits of Single phase bridge inverters?
5.What are the applications of single phase bridge inverters?
Remarks

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121
Circuit Diagram:
Fig. 1: DC Jones chopper circuit

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Manual
DC Jones Chopper
Aim: To analyze the “ DC Jones Chopper” with R & RL loads.
Apparatus Required:
Table 1
Theory:
In many industrial applications, it is required to connect a fixed voltage DC source
into a variable voltage DC source. A DC chopper converts directly from fixed DC to variable
DC and is also known as DC to DC converter. A chopper can be considered as DC equivalent
to an AC transformer with a continuously variable turns ratio. Like a transformer, it could be
used to step down or step up a DC voltage source. Choppers are widely used for traction
motor control in electric automobiles, trolley cars, marine hoists, forklift trucks and mine
haulers. They provide smooth acceleration control, high efficiency and fast dynamic
response. Chopper can be used in regenerative braking of DC motors to return energy back to
the supply and this feature results in energy savings for transportation systems with frequent
stops. Chopper can also be in DC voltage regulators.
The Jones chopper is another example of class-D commutation in which a charged
capacitor is switched by an auxiliary SCR to commutate the main SCR.
Tabular Column:
Table 12.2

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Model Calculations:
S.NO VIN(v) TON(Sec) TOFF(Sec)
DUTY CYCLE
δ = TON / T
VO(v) IO(A)

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Manual
Procedure:
2. Give the DC power supply 10V to the terminal pins located in the power circuit
5. By varying the frequency and duty cycle, observe related waveforms
6. Measure output voltage and current by connecting DC voltmeter & Ammeter
7. Observe waveforms and readings, changing the frequency and duty cycle, and
Tabulate all readings
Precautions:
conductor.
Component.

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125
Waveforms:
Fig. 2: Voltage Waveforms across Capacitor, SCR, auxiliary SCR and load

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Manual
Result:
Viva Voce:
1. What are choppers?
2. On what basis choppers are classified in quadrant configurations?
3. What are different control strategies found in choppers?
4. What are the advantages of DC choppers?
5. Explain the principle of operation of a chopper?
6. What are the disadvantages of choppers?
7. What are the applications of dc choppers?

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Remarks
Signature of the
faculty
Fig:1ThreePhaseFullyControlledBridgeConverterWithR-LLoad

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Three Phase Fully Controlled Bridge Converter with R,RL Loads
Aim: To analyze the three phase fully controlled full wave bridge rectifier for
1.R load
2.R-L load.
Apparatus Required:
Table 1
S.No Name of the equipment Specifications Quantity
Theory:
For any current to flow in the load at least one device from the top group
(T1, T3, T5) and one from the bottom group (T2, T4, T6) must conduct. It can be argued
CircuitDiagram:

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as in the case of an uncontrolled converter only one device from these two groups will
conduct.Then from symmetry consideration it can be argued that each thyristor conducts
for 120° of the input cycle. Now the thyristors are fired in the sequence T1 → T2 → T3 →
T4 → T5 → T6 → T1 with 60° interval between each firing. Therefore thyristors on the
same phase leg are fired at an interval of 180° and hence can not conduct simultaneously.
This leaves only six possible conduction mode for the converter in the continuous
conduction mode of operation. These are T1T2, T2T3, T3T4, T4T5, T5T6, T6T1. Each
conduction mode is of 60° duration and appears in the sequence mentioned. The
conduction table shows voltage across different devices and the dc output voltage for each
conduction interval. Each of these line voltages can be associated with the firing of a
thyristor with the help of the conduction table-1. For example the thyristor T1 is fired at
Experimental Observations:
FOR R LOAD: Table No: 2
S. No.
Firing angle
in degrees
Load
voltage VDC
in volts
Current in
amp
FOR R-L LOAD:
Table No: 3
S. No.
Firing angle
in degrees
Load
voltage VDC
in volts
Current in
amp

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Manual
the end of T5T6 conduction interval. During this period the voltage across T1 was vac.
Therefore T1 is fired α angle after the positive going zero crossing of vac. Similar
observation can be made about other thyristors. The phasor diagram also confirms that all
the thyristors are fired in the correct sequence with 60° interval between each firing. shows
the waveforms of different variables
If the converter firing angle is α each thyristor is fired “α” angle after the positive going
zero crossing of the line voltage with which it’s firing is associated. Once the conduction
diagram is drawn all other voltage waveforms can be drawn from the line voltage
waveforms Similarly line currents can be drawn from the output current and the
conduction diagram. It is clear from the waveforms that output voltage and current
waveforms are periodic over one sixth of the input cycle. Therefore this converter is also
called the “six pulse” converter. The input current on the other hand contains only odds
harmonics of the input frequency other than the triplex (3rd, 9th etc.) harmonics.
The advantage of fully controlled bridge rectifier is the capability of wide
voltage variation between Vdcmin minimum to Vdcmax maximum volts. Such rectifiers
find application in DC motor loads for both motoring and electrical braking of the motor.
Procedure:
1. The connections are made as shown in the circuit of fully controlled rectifier with R load using
Isolation transformer and rheostat.
2. Connect input terminals N, R, Y & B of isolation transformer to respective terminals N, R, Y &
B of firing circuit.

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3. Connect output terminals R, Y & B of isolation transformer to respective terminals R, Y & B
of power module.
4.Connect input terminals N, R, Y & B of isolation transformer to respective terminals N, R, Y &
B of firing circuit.
5. Connect CRO across the load. Use 10:1 CRO Probe or Power Scope.
6. The gate cathode terminals of the three SCR’s are connected to the respective points on the
firing unit.
7. Check all the connections and conform connections made are correct before switching on the
instrument.
8. Keep the firing angle knob to minimum position. Switch on three phase supply, power unit as
well as firing unit.
Model Waveforms:
Fig2: Votage and Current Waveforms for a 3-phase Full Converter at different firing
angles

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Manual
9.Vary firing angle gradually. The output wave forms are seen on a CRO.
10. Trace the load voltage waveforms for any one firing angle.
11. The firing angle is varied and DC output voltage is noted.
12. Bring the firing angle knob to minimum (anticlockwise) position.
13. Switch off MCB, firing unit & three phase AC mains.
14. Experiment may be repeated by connecting R-L loads.
Precautions:
1.Do not conduct the experiment without three phase isolation transformer. If you try to conduct
experiment without isolation transformer the instrument may be damaged due to short circuit
exists between single phase & three phase supply while making measurement using CRO.
2.Do not attempt to observe load voltage and input voltage simultaneously, if does so input voltage
terminal directly connected to load terminals due to the non isolation of both channels of the
CRO.
Result:
Viva Voce:
1.What is need of three phase isolation transformer in a three phase fully controlled rectifier?

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133
2.What is the effect of source inductance in a three fully controlled converter?
3.Compare the three phase full controlled and three phase semi converter?
4.What are the applications of three phase fully controlled converter?

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Manual
5.Explain how the triggering pulses are given in a three phase fully converter?

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135
Remarks

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