Download MSAE * 44L Power Electronics - V

MSAE – 44L Power Electronics
M.Sc (Ele) 4th Sem
Sub - POWER ELECTRONICS
Sub Code MSAE – 44L
EXPERIMENT - 1
V-I CHARACTERISTICS OF SCR
Aim:
1. To obtain V-I characteristics and to find on-state forward resistance of given SCR.
2. To determine holding, latching current and break over voltage of given SCR.
Apparatus Required: Trainer kit, Patch cards, Multimeters.
Circuit Diagram:
Fig 1.1(a) Circuit diagram for VI characteristics of SCR.
SCR Specifications:
VBO = Forward break over voltage
VBR = Reverse break over voltage
Ig = Gate current
Characteristic curve:
Fig 1.2(a) Static characteristic of SCR.
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MSAE – 44L Power Electronics
Tabular Column:
Gate current IG = IG1 =…..mA
Sl. no
𝐕𝐀𝐊 (volts)
𝐈𝑨 (mA)
Procedure:
1. Connections are made as shown in the circuit diagram.
2. Set R1 and R 2 to mid position and V1 and V2 to minimum.
3. Set the gate current IG = IG1 (such that forward break over voltage is between 15 to
20 V), by varying R 2 and V2
4. Slowly vary V1 in steps of 2V and note down VAK and IAK at each step till SCR
conducts. (Note down maximum VAK , which is forward break over voltage just
before SCR conducts).
Finding Latching Current:
1. Ensure that the SCR is in the state of conduction.
2. Start reducing ( VAK ) anode voltage in steps of 2V; simultaneously check the state of
SCR by switching off gate supply V2 . If SCR switches off just by removing gate
terminal, and switches on by connecting gate supply, then the corresponding anode
current IA is the latching current( IL ) for the SCR.
Finding Holding Current:
1. Ensure that the SCR is in the state of conduction.
2. Switch off the gate supply permanently.
3. Start reducing ( VAK ) anode voltage in steps of 2V; simultaneously check the state of
SCR. If SCR switches off. Note down the anode current ( IA ) just before it drops to
zero, which will be IH .
4. Reverse the anode voltage polarity.
5.Vary VAK in steps of 5V till 25V and note down VAK and IA values at each step
6. Plot forward and reverse characteristics using the above-tabulated values. Find the
SCR forward resistance using the graph.
7. Repeat the above procedure for the forward and reverse characteristics of SCR for a
gate current Ig = Ig2 .
RESULT: The values of VAK and IAK are noted down, plotted and SCR forward resistance is
found. The values obtained are verified.
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MSAE – 44L Power Electronics
EXPERIMENT - 2
V – I CHARACTERISTICS OF MOSFET
Aim: To draw static characteristic of MOSFET.
Apparatus Required: MOSFET module, Multimeters, patch chords.
Circuit Diagram:
Fig 2.2 (a) Static Characteristics of MOSFET.
Procedure:
(a) Transfer Characteristics:
1. Connect the circuit as shown in the fig 2.1 (a).
2. Set VDS = 10V by varying V1 . Keep R1 slightly more than of the total value.
3. Vary VGS by varying V2 (keep R 2 to minimum position) and note down IDS for every
0.5V variation of VGS till 5V of VGS .
4. Min VGS voltage that is required for conduction is “Threshold voltage” (VTH ).
5. Repeat the above experiment for different values of VDS2 = 15V.
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MSAE – 44L Power Electronics
Tabular Column:
𝐕𝟏 = 𝐕𝐃𝐒𝟏 = 10V
𝐕𝐆𝐒 (volts)
0V
𝐕𝟏 = 𝐕𝐃𝐒𝟐 = 15V or 12V
𝐈𝐃𝐒 (mA)
𝐕𝐆𝐒 (volts)
0V
8V(MAX)
𝐈𝐃𝐒 (mA)
8V(MAX)
(b) Drain Characteristics:
1. Rig up the circuit as shown in the fig 2.1(a).
2. Adjust VG by varying V2 to VTH .
3. Vary VDS by varying V1 in steps of 0.5v and note down IDS (Till IDS is constant).
4. Repeat the above procedure for different values of VGS2 = VTH ± 0.1 V.
Tabular Column:
VDS
𝐕𝐆𝐒 = 𝐕𝐆𝐒𝟏 = 𝐕𝐓𝐇
(V)
𝐈𝐃𝐒 (mA)
𝐕𝐆𝐒 = 𝐕𝐆𝐒𝟐 = 𝐕𝐓𝐇 ± 0.1 V.
VDS (V)
𝐈𝐃𝐒 (mA)
Result: The transfer characteristics & collector characteristics are obtained and their
respective graphs are plotted and output resistance and Transconductance are found.
******
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MSAE – 44L Power Electronics
EXPERIMENT - 3
SINGLE PHASE FULLY CONTOLLED BRIDGE CONVERTER WITH
R & RL LOAD
Aim: To study the operation of single phase fully controlled converter using R and RL load
and to observe the output waveforms.
Apparatus Required:
1. Power thyristors
2. Rheostat
3. CRO
4. Transformer (1-phase) 230V/24V
5. Connection wires
Circuit Diagram:
Model Graph:
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MSAE – 44L Power Electronics
Observation Table:
Sl. no
Triggering angle ′𝜶′
degree
Output Voltage 𝐕𝐨𝐚𝐯
(volts)
Time Period
1
2
3
Procedure:
1. Single Phase Fully Controlled Bridge Rectifier
2. Make the connections as per the circuit diagram.
3. Connect CRO and multimeter (in dc) across the load .
4. Keep the potentiometer (Ramp control) at the minimum position (maximum resistance).
5. Switch on the step down ac source.
6. Check the gate pulses at G1 -K1 , G2 -K 2 , G3 -K 3 ,& G4 -K 4 respectively.
7. Observe the waveform on CRO and note the triggering angle ‘α’ and note the
corresponding reading of the multimeter. Also note the value of maximum amplitude Vm
from the waveform.
8. Set the potentiometer at different positions and follow the step given in (6) for every
position.
9. Tabulate the readings in observation column.
10. Draw the waveforms observed on CRO.
Theory:
A fully controlled converter or full converter uses thyristors only and there is a wider control
over the level of dc output voltage. With pure resistive load, it is single quadrant converter. Here,
both the output voltage and output current are positive. With RL- load it becomes a two-quadrant
converter. Here, output voltage is either positive or negative but output current is always positive.
Figure shows the quadrant operation of fully controlled bridge rectifier with R-load. Fig shows
single phase fully controlled rectifier with resistive load. This type of full wave rectifier circuit
consists of four SCRs. During the positive half cycle, SCRs T1 and T2 are forward biased. At
ωt = α, SCRs T1 and T3 are triggered, then the current flows through the L – T1 - R load – T3 –
N. At ωt = π, supply voltage falls to zero and the current also goes to zero. Hence SCRs T1 and
T3 turned off. During negative half cycle (π to 2π).
SCRs T3 and T4 forward biased. At ωt = π + α, SCRs T2 and T4 are triggered, then
current flows through the path N – T2 – R load- T4 – L. At ωt = 2π, supply voltage and
current goes to zero, SCRs T2 and T4 are turned off. The Fig-3, shows the current and voltage
waveforms for this circuit. For large power dc loads, 3-phase ac to dc converters are
commonly used. The various types of three-phase phase-controlled converters are 3 phase
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MSAE – 44L Power Electronics
half-wave converter, 3-phase semi converter, 3-phase full controlled and 3-phase dual
converter. Three-phase half-wave converter is rarely used in industry because it introduces dc
component in the supply current. Semi converters and full converters are quite common in
industrial applications. A dual is used only when reversible dc drives with power ratings of
several MW are required. The advantages of three phase converters over single-phase
converters are as under: In 3-phase converters, the ripple frequency of the converter output
voltage is higher than in single-phase converter. Consequently, the filtering requirements for
smoothing out the load current are less. The load current is mostly continuous in 3-phase
converters. The load performance, when 3- phase converters are used, is therefore superior as
compared to when single-phase converters are used.
VOUT =(2VS )(Cosα)/π
Iavg =Vavg /R
Result:
Thus the operation of single phase fully controlled converter using R and RL load has been
studied and the output waveforms has been observed.
*****
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MSAE – 44L Power Electronics
EXPERIMENT – 4
AC VOLTAGE CONTROLLER USING TRIAC-DIAC COMBINATION.
Aim: i) To observe variation of intensity of light with reference to firing angle.
ii) To plot delay angle a V/S VL Load voltage and Conduction angle b V/S IL Load
current.
Components Required: Patch cords, Multimeters, Isolation Transformer, 10:1
probes, lamp, Triac Module.
Circuit Diagram:
Fig. Circuit diagram for AC voltage controller
Waveforms:
Fig. Expected input output waveform
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MSAE – 44L Power Electronics
PROCEDURE:
1. Connect circuit as shown in fig.
2. Connect diac-firing circuit as the triggering source.
3. Vary firing angle and note down the waveform; Vac, IL
4. Use 10:1 probe, which is connected to oscilloscope for measurement.
5. Note the change in brightness of lamp and plot the relevant characteristics.
6. Repeat the experiment with UJT firing circuit.
Tabular Column:
DIAC Firing Circuit : Rmin to Rmax.
𝛼 (Firing Angle)
VL (volts)
IL (amps)
𝜋-𝛼
(Conduction angle 𝛽 )
UJT Firing Circuit:
This firing circuit is based on UJT relaxation oscillator. It generates pulses in synchronization
with the AC supply. A pulse transformer is used to isolate the firing pulses.
Procedure:
1. Connect circuit as shown in diagram.
2.
Vary firing angle and note down the waveform; Vac, IL
3. Use 10:1 probe, which is connected to oscilloscope for measurement.
4. Note the change in brightness of lamp and plot the relevant characteristics.
Tabular Column:
UJT Firing Circuit : Rmin to Rmax.
𝛼 (Firing Angle)
VL (volts)
IL (amps)
𝜋-𝛼
(Conduction angle 𝛽 )
Result: The values of load voltage, firing angle, load current and conduction angle are found
and verified for both Diac firing circuit and UJT firing circuit. Required graphs are plotted.
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MSAE – 44L Power Electronics
EXPERIMENT - 5
SPEED CONTROL OF UNIVERSAL MOTOR
Aim : To study the speed control of a Universal motor by varying armature applied voltage
through phase controlled converter.
Apparatus Required:
i) Universal kit
ii) CRO
iii) Universal motor
This unit consists of two parts:
(a) Firing circuit and (b) Power circuit
Circuit Diagram:
Speed Control of Universal Motor Using AC Voltage Control
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MSAE – 44L Power Electronics
Speed control of DC motor using Single phase Half wave converter
Speed control of DC motor using Single phase full wave converter
Single phase Half controlled bridge rectifier
Tabular Column :
Sl. no
Input Voltage
Vin
Firing
Angle
Output
Voltage Vo
Output
current Io
Speed RPM
a) Firing Circuit:
This unit, generates line synchronized 2 pulse transformer isolated trigger pulses. These
trigger pulses can be used to trigger.
(i) Single phase AC phase control using SCR’s (Antiparallel SCR’s)
(ii) Single phase AC phase control using triac.
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MSAE – 44L Power Electronics
(iii) Single phase Half wave rectifier (single SCR)
(iv) Single phase Full wave rectifier (Two SCR’s)
(v) Single phase Half controlled bridge rectifier (Two SCR’s & Two diodes) power circuits.
The firing circuit is based on zero crossing detector, ramp generator, op-amp comparator and
amplifier / pulse transformer isolation method.
b) Power Circuit:
The power circuit consists of 2 SCR’s, 3 diodes and a Triac. The power devices are mounted
on suitable heat sink for power dissipation. The snubber circuit is connected for dv/dt
protection. A fuse is also provided in series with the devices for short circuit or over current
protection. In the input side a MCB is provided to switch ON/OFF the supply to the power
circuit.
A voltmeter and an ammeter is provided to measure the Input / Output voltage and
current.
Procedure:
1. Make the inter connections in the power circuit as given is the circuit diagram.
2. Switch ON the firing circuit and observe the trigger outputs. Make sure that the firing
pulses are proper before connecting to the power circuit.
3. Then connect the trigger output from firing circuit to corresponding SCR’s / Triac.
4. In the power circuit Initially set the AC input to 30 volts.
5. Switch ON and MCB. Switch ON the Trigger outputs switch.
6. Select the SCR / Triac selection switch and observe the output wave forms across ‘R’
load by varying the firing angle potentiometer.
7. If the output wave form is proper then you can connect the motor & increase the input
voltage to rated value 0-230V gradually.
8. Vary the firing angle and note down output voltage and speed of the motor.
Result:
Thus the speed control of Universal motor is performed by varying armature voltage
through phase controlled converter
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