power electronics lab manual
TRANSCRIPT
SUDHARSAN ENGINEERING COLLEGE,
SATHIYAMANGALAM.
DEPARTMENT OF
ELECTRICAL AND ELECTRONICS
ENGINEERING
VII – SEMESTER
POWER ELECTRONICS & DRIVES
SUBJECT CODE: EE 1405
LAB MANUAL
PREPARED BY: APPROVED BY:
Mr. G. SARAVANA VENKATESH
(AP / EEE) (HOD / EEE)
ANNA UNIVERSITY
THIRUCHIRAPALLI
Subject Name : Power Electronics Lab
Subject Code : EE 1405
Semester : VII
Branch : EEE
Course Duration : JULY 2010 – DEC 2010
Staff in – charge : Mr. G.Saravana Venkatesh
LIST OF EXPERIMENTS
1. Single Phase Semi-converter with R and R-L loads for continuous and discontinuous
conduction modes
2. Single Phase Full-converter with R and R-L loads for continuous and discontinuous
conduction modes
3. Three phase full-converter with R-L load
4. IGBT based Single phase inverters.
5. Volts/Hz control of VSI fed three phase induction motor drive.
6. Single phase AC voltage controller
7. Simulation of open loop speed control of converter fed DC motor drive using MATLAB
8. Simulation of open loop speed control of chopper fed DC motor drive using MATLAB
9. Step down chopper
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1. SINGLE PHASE HALF CONTROLLED CONVERTERS WITH R & R-L
LOADS FOR CONTINUOUS AND DISCONTINUOUS CONDUCTION
MODES
AIM:
To study the half controlled and fully controlled converter with Resistive &
Resistive and inductive load.
APPARATUS REQUIRED:
1) Device module.
2) R, RC, UJT/555 firing circuit module.
3) Loading rheostat.
4) Load inductance.
5) CRO.
6) Digital multimeter.
THEORY:
Semi converter
Controlled rectifiers are those whose output voltage can be controlled by
varying the firing angle of the SCR. During the positive half-cycle. SCR1 & D2
are forward biased and starts conducting when trigger pulses are given
simultaneously. During negative half-cycle SCR2& D1 are forward biased and it
starts conducting. In the trigger circuit synchronization must be obtained from the
supply voltage other than SCR voltage and trigger pulse must be continuous
during the conduction period.
PROCEDURE:
Semi converter:
1. Connect the cathodes of SCR1 and SCR3 together, and the anodes of
two diodes together connect the anode of SCR1 and the cathode of diode
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D4 together. Also connect the anode of SCR3 and D2 together.
2) Connect the 24V AC input to the bridge circuit.
3) Connect the load consisting of L and R across the output terminals of the
bridge converter.
4) Connect the gating signals to the SCRs from the bridge firing circuit
module, with G1K1 to SCR1 and G2K3 to SCR3 as marked in the circuit.
5) Switch on + 24AC provided in the firing circuit.
6) Ensure proper connection of the circuit as shown in figure.
7) Switch ON power supply to CRO and the input power module.
8) Connect the CRO probes to observe the waveforms of the input ac
voltage, output voltage and voltage across any one of the SCR.
9) Adjust the firing angle delays to about 600 and plot the waveforms to scale
on a graph sheet.
10) Remove the CRO probes from the circuit and connect them to observe the
load voltage (VL) and load current (IL) waveforms. For this, connect the
CRO ground terminal to (-) end of the load and channel-1 probe to positive
end of the load.channel-2 probe to the common terminal of the inductance
and resistance marked ‘0’ in the circuit. The voltage across the load
resistance is proportional to the load current.
11) Plot the load voltage and load current waveforms to scale in the graph
sheet in time synchronization with the AC input voltage.
12) Measure the average DC output voltage and rms AC input voltage with a
digital multimeter. Switch off power supply to the circuit.
13) Calculate the DC output voltage.
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CIRCUIT DIAGRAM:
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RESULT:
The operation of half controlled and fully controlled converter with
Resistive & Resistive and inductive load have been studied.
Signature of the Staff
SUDHARSAN ENGINEERING COLLEGE, SATHIYAMANGALAM6
2. SINGLE PHASE FULL CONTROLLED CONVERTERS WITH R & R-L
LOADS FOR CONTINUOUS AND DISCONTINUOUS CONDUCTION
MODES
AIM:
To study the half controlled and fully controlled converter with Resistive &
Resistive and inductive load.
APPARATUS REQUIRED:
1) Device module.
2) R, RC, UJT/555 firing circuit module.
3) Loading rheostat.
4) Load inductance.
5) CRO.
6) Digital multimeter.
THEORY:
Fully Controlled Converter
The single phase fully controlled rectifier consists of 4 SCRs and load R.
During the positive half-cycle SCR1&2 are forward –biased and when this SCR is
fired simultaneously at a firing angle the load is connected to the input supply.
During the negative half-cycle the SCRs 3&4 are forward biased and SCRs 1&2
are turned off due to line or natural commutation.
PROCEDURE:
Fully Controlled Converter
1)Form the single-phase bridge circuit. Connect the cathode of SCRs 1&3
together. Connect the anodes of SCRs 2&4 together. Connect the anode
of SCR1 to cathode of SCR4.Connect the anode of SCR3 to the cathode
of SCR2.
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2)Connect the gating signals to the SCRs from the firing circuit module.
Connect 24V ac input to the bridge circuit.
3)Connect the CRO probes to observe the output load voltage and the
voltage across SCR2.
4)Switch on the power supply to CRO and input power module. Switch on
24V ac in the firing circuit module and 24V ac input to the bridge
circuit. Draw the input ac line waveform on a graph sheet to suitable scale,
since SCR2 conducts only during positive half cycles, the output load
voltage waveforms can be easily synchronized with the ac waveform
drawn.
5) Vary the firing angle by adjusting the pot provided in the bridge firing
circuit module and observe the waveform.
6) Adjust the firing angle to 30 degrees. Observe the waveforms. Draw the
voltage waveforms across the load and SCR2, on the graph sheet.
7) Measure the dc output voltage with the digital multimeter and rms value of
the ac voltage to the bridge circuit for various firing angles.
8) Calculate the output dc voltage and compare with the measured one.
CIRCUIT DIAGRAM:
Fully Controlled Converter
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Fully Controlled Converter with Resistive Load
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RESULT:
The operation of half controlled and fully controlled converter with
Resistive & Resistive and inductive load have been studied.
Signature of the Staff
SUDHARSAN ENGINEERING COLLEGE, SATHIYAMANGALAM10
3. THREE- PHASE FULLY CONVERTERS WITH R-L-E LOADS
AIM:
To study the operation of three- phase fully controlled converter with
RLE Loads
APPARATUS REQUIRED:
1) Device module.
2) Firing circuit module.
3) Loading rheostat.
4) Load inductance.
5) CRO.
6) Digital multimeter.
THEORY:
The three-phase circuit consists of two groups of SCRs, positive group
and negative group. The positive group SCRs are turned on when the supply
voltages are positive and negative group SCRs are turned-on when the supply
voltage are negative. If SCR T1 is triggered at a particular instant, it can conduct
provided there is a return path for the current. Since phase B is the maximum
negative, the return path should be to phase B. That means SCR T5 must be
triggered simultaneously with SCR T1. Similarly, when phase B has the highest
value, SCRT2 and T6 and when phase C has the highest T3 must be triggered
simultaneously.
PROCEDURE :
1) Connect the full converter circuit as shown in the circuit.
2) Connect the load across the output terminals of the power citcuit.
3) Keep the MCB in off position.
4) Give the 3- phase supply to control unit. Observe the signals from test
points and from firing pulses terminals with the help of CRO.
5) Connect the firing pulses terminals to gate and cathode terminals of
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respective thyristors.
6) Observe the output waveforms for various firing angle.
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RESULT:
Thus the operation of three- phase fully- controlled converter with RLE load has been
studied.
Signature of the Staff
SUDHARSAN ENGINEERING COLLEGE, SATHIYAMANGALAM 13
4. IGBT BASED SINGLE PHASE PWM INVERTER
AIM:
To study the operation of the single phase bridge inverter using IGBT, with
sinusoidal pulse width modulation.
APPARATUS REQUIRED:
1) Single phase IGBT PWM inverter
2) CRO
3) R-L Load.
THEORY:
DC to AC converters are known as inverters. The function of an inverter is
to change the DC input voltage to a symmetrical output voltage of desired
magnitude & frequency. The output voltage could be fixed or variable at a fixed
or variable frequency. Varying the input DC voltage and maintaining the gain of
the inverter constant can obtain a variable output voltage. On the other hand if
the DC input voltage is fixed and it is not controllable a variable output voltage
can be obtained by varying the gain of the inverter, which is normally
accomplished by pulse width modulation (PWM) controlled within the inverter.
The inverter gain may be defines as the ratio of Ac output voltage to DC input
voltage.
PROCEDURE:
1) Ensure that the circuit breaker and pulse release ON / OFF toggle switch
are in OFF position
2) Connect the R-L load across the output terminals Lo and No provided in
the front panel. Include an ammeter to measure the current and a
voltmeter to measure the voltage.
3) Connect the ac input at the input terminals L and N provided in the front
panel.
4) With the pulse release ON / OFF switch and circuit breaker in OFF
condition give the power to the inverter module. This will ensure the
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control power supply to all control circuitry.
5) Set the amplitude of the reference sine wave to minimum value.
6) Keeping the pulse release ON / OFF switch in OFF position, switch ON
the power supply to the bridge rectifier.
7) Release the gating signals to the inverter switches by turning ON the
pulse release ON / OFF switch.
8) Observe the triangular carrier and the reference sine waveforms on the
CRO. Measure the amplitude and frequency of the triangular carrier
through CRO and note it down. Adjust the sine wave frequency to about
50 Hz.
9) Connect the CRO probes to observe the load voltage and current
waveforms.
10) Observe the load voltage and load current waveforms. Sketch the
waveforms on a graph sheet to scale for one cycle period of the inverter
output frequency. Measure the amplitude of the voltage pulses.
11)Measure the output voltage either by using an analog meter or a digital
multi-meter.
11) Calculate the modulation index ma and the rms output voltage Vo.
m a = V control / V tri
= Amplitude of the sine wave / Amplitude of the triangular wave
Vo = m a Vs / _ 2
1)Increase the amplitude of the reference sine wave and note down its
value.
2)Repeat steps 8 to 13 for various amplitude of reference sine wave and
tabulate the readings. Plot the characteristics of modulation index versus
output voltage.
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SINGLE PHASE PWM INVERTER WAVE FORMS
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RESULT:
The operation of the single-phase bridge inverter using IGBT, with
sinusoidal pulse width modulation has been studied.
Signature of the Staff
SUDHARSAN ENGINEERING COLLEGE, SATHIYAMANGALAM18
5. VOLTS/HZ CONTROL OF VSI FED THREE PHASE INDUCTION
MOTOR DRIVE
AIM:
To control the speed of the induction motor by (a) varying the voltage with
fixed frequency (b) varying the frequency with fixed voltage.
APPPARATUS REQUIRED:
1) Three-phase IGBT PWM inverter kit
2) 1 H.P. – 3- Phase induction motor
3) Braking resistance
4) Isolation transformer
5) CRO
6) Tachometer
THEORY:
Inverters produce a sinusoidal ac output whose magnitude and frequency
can be controlled. The dc voltage is obtained by rectifying and filtering the line
voltage most often by the diode rectifier circuits. In an ac motor load, the voltage
at its terminals is desired to be sinusoidal and adjustable in its magnitude and
frequency. This is accomplished by means of the inverters, which accepts a dc
voltage as the input and produces the desired ac voltage input. In PWM
inverters, the input dc voltage is essentially constant in magnitude. DC voltage is
obtained by a diode rectifier, which is used to rectify the line voltage. The inverter
must control the magnitude and the frequency of the ac output voltages. This is
achieved by PWM of the inverter switches and hence such inverters are called
PWM inverters.
PROCEDURE:
1) Keep the main switch in off position initially.
2) Keep the MCB in off position. Check whether the kit is disconnected
from the supply or not.
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3) Connect the braking resistance to the terminals RB1 and RB2.
4) Connect the 1- HP 3 phase induction motor across the output terminals of
inverter, as per the following procedure:
R phase of motor –U
Y phase of motor –V
B phase of motor –W
5) Switch on the main supply.
6) Switch on the pulse release switch.
7) Keep the frequency pot of the control voltage is in constant position.
Amplitude pot of the control voltage is the variable one.
Switch on the MCB. Now, voltmeter shows the output voltage of the bridge
rectifier.
8) For particular amplitude of control voltage with fixed frequency, the motor
picks up speed and it runs.
9) Measure the speed of the motor using Tachometer.
10) For various position of amplitude pot of reference sine wave, measure the
speed.
11) Find out the output voltages across u-v, v-w and w-u with the help of
multimeter.
12)Calculate the modulation index and the output voltage. The modulation
index is given by ma = Amplitude of sine wave/ Amplitude of triangular
wave.
13) Increase the amplitude of the reference wave and calculate the
modulation index. Then plot the characteristics of modulation index versus
output voltage.
14)Follow the same procedure keeping voltage as fixed and varying the
frequency. Also, the speed of the motor is controlled by varying both the
voltage and frequency.
15) Also, draw the graph between speed and voltage for voltage control and
speed versus V/f for V/f control.
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TABULAR COLUMN:
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RESULT:
Thus the speed of the induction motor is controlled using IGBT PWM
Inverter was studied.
Signature of the Staff
SUDHARSAN ENGINEERING COLLEGE, SATHIYAMANGALAM22
6. SINGLE PHASE AC VOLTAGE CONTROLLER.
AIM:
To study the operation of single-phase ac voltage regulator with R load.
APPARATUS REQUIRED:
1) Device module
2) R, RC &UJT Firing circuit module
3) CRO
4) R load
THEORY:
The AC regulators are used to obtain a variable AC output voltage from a
fixed AC source. A single phase AC regulator is shown in the figure. It consists of
two SCRs connected in anti-parallel. Instead of two SCRs connected in antiparallel,
a TRIAC may also be used. The operation of the circuit is explained with
reference to RL load. During positive half-cycle SCR-1 is triggered into
conduction at a firing angle _. The current raises slowly due to the load
inductance. The current continues to flow even after the supply voltage reverses
polarity because of the stored energy in the inductor. As long as SCR-1
conducts, conduction drop across it will reverse bias SCR-2.Hence SCR-2 will
not turn on even if gating signal is applied. SCR-2 can be triggered into
conduction during negative half cycle after SCR-1 turns off.
PROCEDURE:
1) Connect the two SCRs in antiparallel as shown in the figure. Connect the
anode of SCR- .to the cathode of SCR-2.Connect the cathode of SCR-1 to
the anode of SCR-2.
2) Connect the load as shown in the figure.
3) Connect 24V AC to the circuit using patch cords.
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4) Connect the gating signals (G1, K1) from the UJT trigger circuit to SCR-1
and (G2, K2) to SCR-2.
5) Switch on 24V AC supply.
6) Connect the CRO probes to observe the input AC voltage and the load
voltage waveforms.
7) Switch on power to CRO and on 24V ac to the circuit.
8) Select suitable voltage sensitivity and time base setting on the CRO. Use
line trigger mode.
9) Observe the waveforms. Vary the firing angle delay and study the
waveforms. For a particular firing angle, plot the waveforms on a graph
sheet to scale. Also plot the load current waveforms in synchronization
with the load voltage.
CIRCUIT DIAGRAM:
MODEL GRAPH:
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RESULT:
The operation of single-phase ac voltage regulator with R, R-L load has been
studied.
Signature of the Staff
SUDHARSAN ENGINEERING COLLEGE, SATHIYAMANGALAM 25
7) SIMULATION OF OPEN LOOP SPEED CONTROL OF CONVERTER FED DC
MOTOR DRIVE USING MATLAB
OBJECTIVE
To simulate and analyze the performance of converter fed dc motor drive using
Matlab/Simulink.
REQUIREMENTS
1. Block parameter: GTO, DC Machine, AC Voltage source, DC voltage source
2. Source Block parameters : Pulse generator, Load Torque (Constant )
3. Function Block parameters: Product, Sum, Bus Selector, Relay, Gain
4. De-multiplexer
5. Connecting Elements
6. Scope
SYSTEM DESCRIPTION
1. Converter is used to get the variable D.C voltage from A.C source of fixed voltage.
2. Converter fed D.C drive also known as Static Ward Leonard drives.
3. II Quadrant operation demands that field winding of the motor is energized from a
single-phase, or three-phase, full converter.
4. Converter with α1 < 90 deg operates the motor in forward motoring mode in
Quadrant I
5. Converter with α1 > 90 deg and with field excitation reversed operates the motor in
forward regenerative braking mode in Quadrant IV.
6. As thyristors are capable of conducting current only in one direction, the rectifier is
capable of providing current only in one direction.
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OPERATION PROCEDURE
Step - 1: Start Matlab and open Simulink
Step - 2 Open New Model Window and save
Step - 3: Drag all the required blocks from the Simulink library
Step - 4: Connect all the blocks and complete the system design
Step - 5: Set firing angles to all the converters with required delay. Set AC source
voltage at 220 V(50 Hz), DC source voltage at ----, simulation stop time at ----s and
Load torque initial and final values at --- N.m., --- N.m respectively.
Step - 6: Start running simulation and wait for the completion of the Simulation stop
time
Step - 7: Observe the behavior of waveforms of the motor speed, armature current,
field current and Electromagnetic torque.
Step - 8: Save the model and waveforms
Step - 9: Close Simulink window and Exit Matlab.
SIMULINK MODEL DIAGRAM
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Figure: Converter fed DC Motor Drive
SIMULATION RESULTS AND ANALYSIS
The following parameters of the Dual converter fed DC motor drive can be observed
on the scope. The parameters are
a. motor speed,
b. Armature current
c. Field current and
d. Electromagnetic torque
1. Converter works as a rectifier and provide control of D.C voltage in either
direction, allow motor control in quadrants I and IV.
2. The rotor speed starts increasing gradually from zero and reaches its maximum
value at the end of simulation time.
3. It is also observed on the scope that field current is constant throughout the
simulation time.
SIMULATION WAVEFORMS
CONCLUSION
In this drive experiment converter fed DC motor Drive has been modeled using
Matlab/Simulink and the performance of the modeled system for the following
parameters have been observer on the scope and the behavior of the system is also
discussed. The parameters are
a. AC Source Voltage : 220 V
b. DC Source Voltage : ------V
c. Load Torque Initial Value : -----N.m.
d. Load Torque Final Value : -----N.m
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e. Simulation time : -----sec
8) SIMULATION OF OPEN LOOP SPEED CONTROL OF CHOPPER FED DC
MOTOR DRIVE USING MATLAB
OBJECTIVE
To simulate and analyze the performance of the chopper fed dc motor drive using
Matlab/Simulink.
REQUIREMENTS
1. Block parameters :Separately Excited DC motor, Voltage source
2. Source block parameters : Constant, Pulse generator
3. GTO
4. Connecting elements
5. Scope
SYSTEM DESCRIPTION
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1. The DC motor is fed by the DC source through a chopper which consists of GTO
thyristor. The motor drives a mechanical load characterized by inertia J, friction
coeficient B, and load torque TL.
2. The hysteresis current controller compares the sensed current with the reference
and generates the trigger signal for the GTO thyristor to force the motor current to
follow the reference.
3. The speed control loop uses a proportional-integral controller which produces the
reference for the current loop. Current and Voltage Measurement blocks provide
signals for visualization purpose. During torque regulation the speed controller is
disabled.
4. Time based generator having a pulse width of 50 with phase delay of 0 sec is used.
This phase delay varies for all the GTO pairs. Time-based is recommended for use
with a variable step solver.
OPERATION PROCEDURE
STEP – 1: Start Matlab and open simulink tool boxes.
STEP – 2: Open new model window and save.
STEP – 3: Draw all the required blocks from simulink library.
STEP – 4: Connect all the blocks and complete the system design.
STEP – 5: Set load torque value at ----Nm, simulation time = -----s.
STEP – 6: Start running the simulation and wait the for completion of the simulation
stop time.
STEP - 7: Using the scope observe the behavior of waveforms of the armature and
field Current, Electromagnetic torque and rotor Speed.
STEP – 8: Save the model and waveform.
STEP – 9 : Close simulink window and exit matlab.
SIMULINK MODEL DIAGRAM
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Figure: Chopper fed dc motor drive
CHOPPER FED DC MOTOR DRIVE SIMULATION
1. In this experiment, a DC supply voltage of ----V is used. The GTO firing angles are
kept at ----deg and -----deg .
2. The GTO is triggered by applying the phase delay to the pulse generator. To
shorten the starting time, a very light load was chosen. Since only the speed is
controlled, the field current is maintaining at constant.
RESULTS AND ANALYSIS
The following parameters of the chopper fed DC drive can be observe on thescope.
The parameters are
a. Rotor speed,
b. Armature current,
c. Field currents,
d. Electromagnetic torque.
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1. Motor starting: Start the simulation. Observe the motor current, voltage, and speed
during the starting on the scope. The end of the simulation time (----s), the system has
reached its steady-state.
2. The motor is coupled to a linear load, which means that the mechanical torque of
the load is proportional to the speed. The armature current follows the current
reference very well, with fast response time and small ripples.
3. Response to a change in reference load torque:
4. Restart the simulation and observe the drive response to successive changes in
speed reference and load torque.
SIMULATED WAVEFORMS
CONCLUSION
In this experiment, Chopper fed DC motor drive has been modeled using
Matlab/Simulink and the performance of the modeled system for the following
parameters have been observed on the scope and the behaviour of the system is also
discussed.
The parameters are
a. Voltage : 230 V
b. Load torque range : ---- Nm to ---- Nm
c. Firing angle : ----and -----degrees.
d. Simulation time : -----s
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9. A.STEP DOWN CHOPPER
AIM:
To study the Step down chopper. (Buck converter).
APPARATUS REQUIRED:
· VPET 350 module.
· Patch chords.
THEORY:
A buck converter (dc-dc) is a step-down converter. (Shown in Fig.1.). Only
a switch is shown, for which a device belonging to transistor family is used. Also
a diode (termed as free wheeling) is used to allow the load current to flow
through it, when the switch (i.e., a device) is turned off. The load is inductive (RL)
one. In some cases, a battery (or back emf) is connected in series with the
load (inductive). Due to the load inductance, the load current must be allowed a
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path, which is provided by the diode; otherwise, i.e., in the absence of the above
diode, the high-induced emf of the inductance, as the load current tends to
decrease, may cause damage to the switching device. If the switching device
used is a thyristor, this circuit is called as a step-down chopper, as the output
voltage is normally lower than the input voltage. Similarly, this dc-dc converter is
termed as buck one, due to reason given later. The output voltage and current
waveforms of the circuit (Fig. 1) are shown in Fig. 2. The output voltage is same
as the input voltage, i.e. when the switch is ON, during the period, . The switch is
turned on at, and then turned off at . This is called ON period. During the next
time interval, the output voltage is zero, i.e., as the diode, now conducts. The
OFF period is, with the time period being . The frequency is with T kept as
constant, the average value of the output voltage is,
.
Normally, due to turn-on delay of the device used, the duty ratio (k) is not zero,
but has some positive value. Similarly, due to requirement of turn-off time of the
device, the duty ratio (k) is less than 1.0. So, the range of duty ratio is reduced. It
may be noted that the output voltage is lower than the input voltage. Also, the
average output voltage increases, as the duty ratio is increased. So, a variable
dc output voltage is obtained from a constant dc input voltage. The load current
is assumed to be continuous as shown in Fig. 2. The load current increases in
the ON period, as the input voltage appears across the load, and it (load current)
decreases in the OFF period, as it flows in the diode, but is positive at the end of
the time period, T.
PROCEDURE:
1) Initially keep all the switches in the OFF position
2) Initially keep duty cycle POT in minimum position
3) Connect banana connector 24V DC source to24V DC input.
4) Connect the driver pulse output to MOSFET input. (G to G, S to S).
5) Switch ON the main supply.
6) Check the test point waveforms with respect to ground.
7) Switch ON the S1 switch and then Switch ON S2.
8) Vary the duty cycle POT and tabulate the TON , TOFF & output voltage.
9) Trace the waveforms of Vo & iO.
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· Draw the graph for Vo Vs Duty cycle, k
CIRCUIT DIAGRAM:
I. Fig.1.Buck converter
MODEL GRAPH:
Waveforms for CCM
Output Voltage Vs Duty Cycle
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RESULT:
Thus the Buck converter was studied.
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