Chopper basically uses a Thyristor for high power applications. The process of turning off a conducting Thyristor is known as commutation. Here Thyristor is turned off by a current pulse that is why it is called a Current Commutated Chopper.
Transients
Voltage surge or Transient Voltage
Types of Power System Transients
Causes of System transients
Overvoltage due to external causes
Overvoltage due to internal causes
Transients in Simple Circuit
D. C. Source & А.С. Source
Travelling Waves on Transmission Line
Wave equation
Travelling wave with open end line & Short Circuited Line
Reflection and Refraction Coefficient
Line Connected to a Cable
Line terminated Through Capacitance
Capacitor Connection at a T.L.
Attenuation of Travelling Waves
Transients
Voltage surge or Transient Voltage
Types of Power System Transients
Causes of System transients
Overvoltage due to external causes
Overvoltage due to internal causes
Transients in Simple Circuit
D. C. Source & А.С. Source
Travelling Waves on Transmission Line
Wave equation
Travelling wave with open end line & Short Circuited Line
Reflection and Refraction Coefficient
Line Connected to a Cable
Line terminated Through Capacitance
Capacitor Connection at a T.L.
Attenuation of Travelling Waves
Inverter is a device which convert a DC input supply voltage into symmetric AC voltage of desired magnitude and frequency at the output side. It is also know as DC-AC converter.
Ideal and practical inverter have sinusoidal and no-sinusoidal waveforms at output respectively.
If the input dc is a voltage source, the inverter is called a Voltage Source Inverter (VSI). One can similarly think of a Current Source Inverter (CSI), where the input to the circuit is a current source. The VSI circuit has direct control over ‘output (ac) voltage’ whereas the CSI directly controls ‘output (ac) current.
Inverter is a device which convert a DC input supply voltage into symmetric AC voltage of desired magnitude and frequency at the output side. It is also know as DC-AC converter.
Ideal and practical inverter have sinusoidal and no-sinusoidal waveforms at output respectively.
If the input dc is a voltage source, the inverter is called a Voltage Source Inverter (VSI). One can similarly think of a Current Source Inverter (CSI), where the input to the circuit is a current source. The VSI circuit has direct control over ‘output (ac) voltage’ whereas the CSI directly controls ‘output (ac) current.
INTRODUCTION
A chopper is a static device which is used to obtain a variable dc voltage from a
constant dc voltage source. A chopper is also known as dc-to-dc converter. The thyristor converter offers greater efficiency, faster response, lower maintenance, smaller size and smooth control. Choppers are widely used in trolley cars, battery operated vehicles, traction motor control, control of large number of dc motors, etc….. They are also used in regenerative braking of dc motors to return energy back to supply and also as dc voltage regulators.
Choppers are of two types
• Step-down choppers
• Step-up choppers.
In step-down choppers, the output voltage will be less than the input voltage
whereas in step-up choppers output voltage will be more than the input voltage.
Classification of Choppers:
(a) Depending upon the direction of the output current and voltage, the converters can be classified into five classes namely Class A [One-quadrant Operation] Class B [One-quadrant Operation] Class C [Two-quadrant Operation] Class D [Two-quadrant Operation] Class E [Four-quadrant Operation]
(b) Based on the output voltage of the output, the choppers are classified as
(i) Step-Down Chopper In this case the average output voltage is less than the input voltage. It is also known as step down converter
(ii) Step-Up Chopper Here the average output voltage is more than the input voltage. It is also known as step up converter
(iii) Step-Up/Down Chopper This type of converter produces an output voltage that is either lower or higher than the input voltage
(c) Depending upon the power loss occurred during turn ON/OFF of the switching device, the choppers are classified into two categories namely
(i) Hard switched Converter Here the power loss is high during the switching (ON to OFF and OFF to ON) as a result of the non zero voltage and current on the power switches.
(ii) Soft switched or resonant converters In this type of choppers, the power loss is low at the time of switching as a result of zero voltage and/or zero current on the switches.
2
PRINCIPLE OF STEP-DOWN CHOPPER
Figure 2.1 shows a step-down chopper with resistive load. The thyristor in the
circuit acts as a switch. When thyristor is ON, supply voltage appears across the load and
when thyristor is OFF, the voltage across the load will be zero. The output voltage and
current waveforms are as shown in figure 2.2.
Townsend ’s theory
Introduction
Ionization by collision
Townsend’s current growth equation
Current Growth in the Presence of Secondary Processes
Townsend’s secondary ionization coefficient
Townsend’s Criterion for Breakdown
Breakdown in Electronegative Gases
Part of Lecture series on EEE-413, Electrical Drives (DC Drives) delivered by me to students of VIII Semester B.E. (Electrical), Session 2018-19.
Z. H. College of Engg. & Technology, Aligarh Muslim University, Aligarh.
Missing materials will be uploaded shortly.
Please comment and feel free to ask anything related. Thanks!
To turn on a Thyristor, there are various triggering methods in which a trigger pulse is applied at its Gate terminal. Similarly, there are various techniques to turn off a Thyristor, these techniques are called Thyristor Commutation Techniques.
Inverter is a device which convert a DC input supply voltage into symmetric AC voltage of desired magnitude and frequency at the output side. It is also know as DC-AC converter.
Ideal and practical inverter have sinusoidal and no-sinusoidal waveforms at output respectively.
If the input dc is a voltage source, the inverter is called a Voltage Source Inverter (VSI). One can similarly think of a Current Source Inverter (CSI), where the input to the circuit is a current source. The VSI circuit has direct control over ‘output (ac) voltage’ whereas the CSI directly controls ‘output (ac) current.
Inverter is a device which convert a DC input supply voltage into symmetric AC voltage of desired magnitude and frequency at the output side. It is also know as DC-AC converter.
Ideal and practical inverter have sinusoidal and no-sinusoidal waveforms at output respectively.
If the input dc is a voltage source, the inverter is called a Voltage Source Inverter (VSI). One can similarly think of a Current Source Inverter (CSI), where the input to the circuit is a current source. The VSI circuit has direct control over ‘output (ac) voltage’ whereas the CSI directly controls ‘output (ac) current.
INTRODUCTION
A chopper is a static device which is used to obtain a variable dc voltage from a
constant dc voltage source. A chopper is also known as dc-to-dc converter. The thyristor converter offers greater efficiency, faster response, lower maintenance, smaller size and smooth control. Choppers are widely used in trolley cars, battery operated vehicles, traction motor control, control of large number of dc motors, etc….. They are also used in regenerative braking of dc motors to return energy back to supply and also as dc voltage regulators.
Choppers are of two types
• Step-down choppers
• Step-up choppers.
In step-down choppers, the output voltage will be less than the input voltage
whereas in step-up choppers output voltage will be more than the input voltage.
Classification of Choppers:
(a) Depending upon the direction of the output current and voltage, the converters can be classified into five classes namely Class A [One-quadrant Operation] Class B [One-quadrant Operation] Class C [Two-quadrant Operation] Class D [Two-quadrant Operation] Class E [Four-quadrant Operation]
(b) Based on the output voltage of the output, the choppers are classified as
(i) Step-Down Chopper In this case the average output voltage is less than the input voltage. It is also known as step down converter
(ii) Step-Up Chopper Here the average output voltage is more than the input voltage. It is also known as step up converter
(iii) Step-Up/Down Chopper This type of converter produces an output voltage that is either lower or higher than the input voltage
(c) Depending upon the power loss occurred during turn ON/OFF of the switching device, the choppers are classified into two categories namely
(i) Hard switched Converter Here the power loss is high during the switching (ON to OFF and OFF to ON) as a result of the non zero voltage and current on the power switches.
(ii) Soft switched or resonant converters In this type of choppers, the power loss is low at the time of switching as a result of zero voltage and/or zero current on the switches.
2
PRINCIPLE OF STEP-DOWN CHOPPER
Figure 2.1 shows a step-down chopper with resistive load. The thyristor in the
circuit acts as a switch. When thyristor is ON, supply voltage appears across the load and
when thyristor is OFF, the voltage across the load will be zero. The output voltage and
current waveforms are as shown in figure 2.2.
Townsend ’s theory
Introduction
Ionization by collision
Townsend’s current growth equation
Current Growth in the Presence of Secondary Processes
Townsend’s secondary ionization coefficient
Townsend’s Criterion for Breakdown
Breakdown in Electronegative Gases
Part of Lecture series on EEE-413, Electrical Drives (DC Drives) delivered by me to students of VIII Semester B.E. (Electrical), Session 2018-19.
Z. H. College of Engg. & Technology, Aligarh Muslim University, Aligarh.
Missing materials will be uploaded shortly.
Please comment and feel free to ask anything related. Thanks!
To turn on a Thyristor, there are various triggering methods in which a trigger pulse is applied at its Gate terminal. Similarly, there are various techniques to turn off a Thyristor, these techniques are called Thyristor Commutation Techniques.
A DC-DC converter topology is presented
combining the soft switching effects of the Snubber Assisted Zero
Voltage and Zero Current Transition (SAZZ) topology and the
increased inductor frequency of the dual interleaved boost
converter with interphase transformer. The snubber capacitors
and output capacitances of the main devices are discharged prior
to turn on using a single auxiliary inductor, eliminating turn on
losses. Furthermore, the turn off losses are significantly reduced
since the energy stored in the device output capacitance at turn
off is recovered at turn on. The effectiveness of the topology is
demonstrated on a SiC prototype operating at 12.5 kW, 112 kHz,
reducing the switching losses by 50%.
le roludes the tiofuture research directionsARNABPAL81
ully distributed formation-containment control protocol for networked MASs with timevarying formation reference. Two detailed case studies are considered in Section 4.4 to
show the effectiveness of the proposed methodology. One of them deals with the formationcontainment of a team of networked satellites, and the other one shows experimental validation using nonholonomic mobile robots. Section 4.5 concludes the chapter mentioning the
future research directions
Energy scenario in india and its energy conservation programJyoti Singh
Energy is essential for Economic growth and economic growth is essential for country like India.
Ratio of energy demand and GDP is useful indicator for Economics growth.
Economic growth of country
is depend upon rate of
improvement in per capita
energy consumption.
India is both a major producer and consumer.
India currently ranked 11th greatest energy producer accounting 2.4% of world’s total energy production and as the world’s 6th greatest energy consumer.
Despite its large annual energy production, India is a net energy importer, mostly due to imbalance between oil production and consumption.
The utility electricity sector in India had an installed capacity of 278.734 GW as of 30 September 2015. Renewable Power plants constituted 28% of total installed capacity and Non-Renewable Power Plants constituted the remaining 72%.
During the year 2014-15, the per capita electricity generation in India was 1,010 kWh with total electricity consumption (utilities and non utilities) of 938.823 billion or 746 kWh per capita electricity consumption.
Electric Energy Consumption in agriculture was recorded highest (18.45%) in 2014-15 among all countries.
The optical and infrared spectroscopy industry is undergoing a major transformation akin to the computer industry. The
size and weight of the instruments are shrinking from bench-top size to pocket-size. The cost is decreasing, and the
performance continues to improve beyond just being acceptable. These miniature handheld spectrometers such as near
infrared (NIR) spectrometers are creating new populations of users taking measurements in the field by nontechnical
workers that were previously conducted in the laboratory by technical personnel. The tests are non-destructive and fast,
taking only a few seconds to complete. This capability allows for obtaining real-time results that, in turn, lead to more
efficient decision making. Users include farmers who would use their handheld NIR analyzers for a whole host of
applications from analyzing the nutritional content of their forage for animal feed optimization to analyzing the
nutritional content of their crop for determining the value of their yield, or for analyzing the soil for fertilization
optimization.
Standard Soil Testing Laboratory
time consuming, Laborious, use of chemical and reagents which effect human health and environment, costly, do not consider spatial variation in the field.
Electrochemical Sensing
Ion Selective Electrodes
Ion Sensitive Field Effect Transistor
Optical Spectroscopy
NIR Spectroscopy
(A) By active media
Solid state laser - crystal, or glass, doped with impurities, e.g. ruby laser, Ti:sapphire laser, semiconductor laser.
Gas laser - e.g. He-Ne laser, Ar+ laser, CO2 laser, N2 laser, HCN laser.
Dye laser - active medium: dye molecules in liquid solvent (sometimes in solids also).
(B) By mode of operation
CW
Pulsed
(C) By pumping and laser levels
3-level laser
4-level laser
Conversion of transfer function to canonical state variable modelsJyoti Singh
Realization of transfer function into state variable models is needed even if the control system design based on frequency-domain design method.
In these cases the need arises for the purpose of transient response simulation.
But there is not much software for the numerical inversion of Laplace transform.
So one ways is to convert transfer function of the system to state variable description and numerically integrating the resulting differential equations rather than attempting to compute the inverse Laplace transform by numerical method.
A basic sound system consists of an input device (microphone), a control device (mixer), an amplification device (power amplifier), and an output device (loudspeaker).
The primary goal of the sound system in sound applications is to deliver clear, intelligible speech, and, usually, high-quality musical sound.
Generating a custom Ruby SDK for your web service or Rails API using Smithyg2nightmarescribd
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1. Current Commutated Chopper
Submitted to: Submitted by:
Mrs Shimi S.L Jyoti Singh
Assistant Professor (EE Dept) ME ( Regular-2014)
NITTTR, Chandigarh I & C 2nd Sem
Roll No: 142511
2. What is meant by current
commutation?
• Chopper is used to change the dc level of voltage,
it is dc/dc converter.
• In current commutated chopper , as the name
suggests, chopper is commutated by current
pulse.
• In this process, a current pulse is made to flow in
the reverse direction through the conducting
thyristor and when the net thyristor current
becomes zero, it is turned off.
3. • Some assumption are:
Load current is constant.
SCR and Diodes are ideal switches.
RC is so large such that it can be treated as
open circuit during the commutation
interval.
• The energy for commutation comes from
energy stored in capacitor.
• Capacitor is charges to Edc , so that energy for
commutation is available.
5. • Main thyristor T1 is fired at t=0 so that load
current and output voltage is IO and VS
respectively from t0 to t1 .
• With the turning on of T1 commutation
circuitry remain inactive.
• Commutation process begins with turning on
of T2.
• The commutation process is divided in various
modes as follows.
6. (a) Mode I, t1<t<t2
At t2
At first the T2 is turned on - T2 is fired through gate and
turned on.
Capacitor C is charged to -Edc –
As T2 is on, the capacitor
inductor series circuit is shorted
and so the capacitor is charged
to negative voltage -Edc .
7. (a) Mode II, t2<t<t3
The capacitor C is fully charged, and current reverses,
and so T2 is turned off - When the capacitor is charged,
it provides -Edc voltage reverse bias to T2 thyristor, so T2
is turned off.
Now the current flows opposite through the thyristor
T1 - The capacitor, charged to negative Edc, pushes
current ic opposite to T1. Here ic doesn't not flow
through diode, because the forward voltage of diode is
more than that of drop accross thyristor T1.
8. (a) Mode III, t3<t<t4
T1 is turned off- Now the ic turns off T1.
So the impedance offered by T1 is more
than diode, and the current ic flows
through diode.
9. (a) Mode IV, t4<t<t5
The D1 is reversed biased - The current ic
slowly decrease, and when ic=Io, the diode
D1 is no longer forward biased. So the
diode is turned off.
10. (a) Mode IV, t5<t<t6
C is charged to +Edc : C is
overcharged, free wheeling diode is
forward biased and Eo is reduced to
zero. Io=ic+ifd.
11. The commutation period is
complete. The T1 is turned on
by gate pulse. And again T2 is
turned on, capacitor charges
to negative potential and cycle
repeats.
12. What are the advantages of current
commutated chopper?
• The capacitor always remains charged with the
correct polarity.
• Commutation is reliable as load current is less
than the peak commutation current ICP.
• The auxiliary thyristor T2 is naturally commutated
as its current passes through zero value.
15. Design Consideration : Finding values of L & C
(i) Peak Commutating Current ICP > Load Current IO. The oscillating current
in commutation circuit is given by
……….. (1)
(ii) Circuit turn off time must be greater than turn off time of main Thyristor.
tIt
L
C
Vi oCPosc sinsin osCP I
L
C
VI
os xI
L
C
V
o
CP
I
I
x
xI
I
II
t
ttt
o
CP
oCP
co
c
1
sinsin
sin
2
11
1
1
1
34
16. Circuit turn off time for main Thyristor
………………. (2a)
………………..(2b)
The above relation reveals that as load current Io increases , turn off time of
main thyristor decreases. So,
……………....(3)
Substitution of above value in eq (1)
…………………(4)
)sin2(
1
)2(
1
1
0
1
CP
o
c
o
c
I
I
t
t
L
t
C
LCt
x
c
xc
)](sin2[
)](sin2[
11
11
)](sin2[
)](sin2[
11
11
xo
cs
o
x
cs
xI
tV
L
xI
t
L
V
17. • From eq. (3)
• Subsituting this value in eq (1)
……………….(5)
C
tL
x
c
)](sin2[
11 11
)](sin2[
)](sin2[
11
11
xs
co
x
c
s
o
V
txI
C
C
t
V
xI
18. Total Communication Interval:
(t6-t1)= (t2-t1) + (t4-t2) + (t5-t4) + (t6-t5)
• (t2-t1): time period of half cycle of oscillating current
• (t4-t2) : Sine current waveform of ic is examined
• (t5-t4) : Increase in voltage across C during (t5-t4) = Vs - Vs sin(90-θ1)
LC
o
LC
o
)( 1
1
o
s
o
s
ss
o
I
CV
I
CVtt
tt
VV
CI
11
45
45
1
cos1)90sin(1
)(
)(
)90sin(
19. • (t6-t5) : ic is assumed to be Iocosωot.
• (t6-t1) : total commutation interval
LCtt
o 22
1
)( 56
o
s
o
s
I
CVLC
I
CVLC
2sin
2
2
5
cos1
2
5
1
2
1
1
1
Turn off time: for main thyristor
For auxilary thyristor
LC
LCtt
x
11
134
sin2
2
LCLCttt xC
11
1124 sin
20. Peak Capacitor Voltage
• Maximum capacitor VCP is reached at t6 which is equal to voltage at t5 +
voltage rise due to the energy transfer from L to C during t6 - t5
• At t5 energy in L is ½ L Io
2 and at t6 this energy is transferred to C. Thus
C
L
IVV
C
L
IV
LICV
osCP
oc
oc
22
2
1
2
1
21. Numerical problems
a) For a current commutated chopper, peak commutating current is twice
the maximum possible load current. The source voltage is 230 V dc and
main SCR turn off time is 30 µsec. For a maximum load current of 200A,
calculate
(i) The values of the commutating inductor and capacitor.
(ii) Maximum capacitor voltage and
(iii) The peak commutating current.
SOLUTION:
Given x=2, tq = 30 µsec
tC = tq + Δt
taking Δt= 30 µsec, tC =(30+30) µsec=60 µsec
(i) Value of inductor
)](sin2[ 11
xo
cs
xI
tV
L
22. Value of capacitor
(ii) Peak capacitor voltage
(iii) Peak commutating current
HL
473.16
)](sin2[2002
1060230
2
11
6
FC
V
txI
C
xs
co
822.49
)](sin2[230
sec302002
)](sin2[
2
11
11
voltsV
C
L
IVV
CP
osCP
345
822.49
473.16
200230
AxII oCP 4002002
23. b. A current commutated chopper is fed from a dc source of a 230V. Its
commutating components are L=20µH and C=50µF. Is a load current of 200A
is assumed constant during commutating process, then compute the
following;
(i) Turn off time of main thyristor
(ii) Total commutation interval
(iii) Turn off time of auxiliary thyristor
SOLUTION:
(i) Peak commutating current
Turn off time of main thyristor
8183.1
200
33.363
33.363
50
20
230
CP
O
CP
sCP
I
I
x
AI
L
C
VI
sec52.62105020)](sin2[
)](sin2[
12
8183.1
11
11
c
xc
t
LCt
24. (ii) Total commutation interval
(iii) Turn off time of auxiliary
O
CP
O
I
I
365.33
33.363
200
sinsin 11
1
sec427.239
10477.91095.229
200
363.33cos1
2301050101000
180
365.33
2
5
66
66
O
sec931.80101000
180
365.33
sin
6
11
1
LCLC x