EE2301 Power Electronics Anna University Question Bank Question Paper Model Question Paper Important Questions 2 marks and 16 marks questions
EE 2301 Power Electronics Anna University Question Bank Question Paper Model Question Paper Important Questions 2 marks and 16 marks questions
|
1. Why IGBT is very popular nowadays?
|
a. Lower hate requirements
|
b. Lower switching losses
|
c. Smaller snubber circuit requirements
|
2. What are the different methods to turn on the thyristor?
|
a. Forward voltage triggering
|
b. Gate triggering
|
c. dv/dt triggering
|
d. Temperature triggerin g
|
e. Light triggering
|
3. What is the difference between power diode and signal diode?
|
S.No.
|
Power diode Signal diode
|
1.
|
Constructed with n-layer, called
|
Drift region is not present.
|
drift region between p+ layer and
|
n+ layer.
|
2.
|
The voltage, current and power
|
Lower
|
ratings are higher.
|
3.
|
Power diodes operate at high
|
Operates at higher switching speed.
|
speeds.
|
4. IGBT is a voltage controlled device. Why?
|
Because the controlling parameter is gate-emitter voltage.
|
5. Power MOSFET is a voltage controlled device. Why?
|
Because the output (drain) current can b e controlled by gate-source voltage.
|
6. Power BJT is a current controlled device. Why?
|
Because the output (collector) current can be controlled by base current.
|
7. What is the relation between a and ß?
|
ß = a/1-a
|
a = ß/1- ß
|
8. What are the different types of power MOSFET?
|
a. N-channel MOSFET
|
b. P-channel MOSFET
|
9. How can a thyr istor turned off?
|
A thyristor can be turn ed off by making the current flowing through it to zero.
|
unit-1
|
10. Define latching current.
|
The latching current is defined as the minimum value of anode curr ent which it
|
must attain during turn on process to maintain conduction when gate signal is removed.
|
11. Define holding current.
|
The holding cu rrent is defined as the minimum value of anode current below
|
which it must fall to for turning off the thyristor.
|
12. What is a snubber circuit?
|
It consists of a series combination of a resistor and a capacitor in parallel with the
|
thyristors. It is mainly used for dv / dt protection.
|
13. What losses occur in a thyristor during working conditions?
|
a. Forward conduction losses
|
b. Loss due to leakage current during forward and reverse blocking.
|
c. Switching losses at turn-on and turn-off.
|
d. Gate triggering loss.
|
14. Define hard-driving or over-drivin gate.
|
When gate current is several times higher than the minimum gate cur rent
|
required, a thyristor is said to be hard-fired or over-driven. Hard-firin g o f a thyristor
|
reduces its turn-on time and enhances its di/dt capability.
|
15. Define circuit turn off time.
|
It is defined as the time during which a reverse voltage is applied across the
|
thyristor during its commutation process.
|
16. Wh y circuit turn off time should be greater than the thyristor turn -off time?
|
Circuit turn off time should be greater than the thyristor turn-off time for reliable
|
turn-off, otherwise the device may turn-on at an undesired instant, a process called
|
commutation failure.
|
17. What is the turn-off time for converter gr ade SCRs and inverter grade SCRs?
|
Turn-off time fo r converter grade SCRs is 50 – 100 ms turn-off time for converter
|
grade SCRs and inverter gr ade SCRs and for inverter grade SCRs is 3 – 50 ms.
|
18. What are the adv antages of GTO over SCR?
|
a. Elimination of commutation of commutating components in forced commutation,
|
resulting in redu ction in cost, weight and volume.
|
b. Reduction in acoustic noise and electromagnetic noise due to elimination of
|
commutation chokes.
|
c. Faster turn-off, p ermitting high switching frequencies.
|
d. Improved efficiency of the converters.
|
unit-2
|
9. What is meant by phase controlled rectifier?
|
It convrts fixed ac voltage into variable dc voltage.
|
20. Mention some of the applications of controlled rectifier.
|
a. Steel rolling mills, printing press, textile mills and paper mills employing dc
|
motor drives.
|
b. DC traction
|
c. Electro chemical and electro-metallurgical process
|
d. Portable hand tool drives
|
e. Magnet power supplies
|
f. HVDC transmission system
|
21. What is the function of freewheeling diodes in controlled rectifier?
|
It serves two process.
|
a. It prevents the output voltage from becoming negative.
|
b. The load current is transferred from the main th yristors to the freewheeling diode,
|
thereby allowing all of its thyristors to regain their blocking states.
|
22. What are the adv antages of freewheeling diodes in a controlled in a controlled rectifier?
|
a. Input power factor is improved.
|
b. Load current wav eform is improved and thus the load performance is better.
|
23. What is meant by delay angle?
|
The delay angle is defined as the an gle between th e zero crossin g of the inp ut
|
voltage and the instant the thyristor is fired.
|
24. What are the adv antages of single phase bridge co nverter ov er single phase mid-point
|
converter?
|
a. SCRs are subjected to a peak-inverse voltage o f 2Vm in a fully controlled bridge
|
rectifier. Hence for same voltage and currnt ratin gs of SCrs, power handled by
|
mid-point configuration is about
|
b. In mid-point converter, each secondary winding should be able to supply the load
|
power. As such, the transformer rating in mid-point converter is double the load
|
rating.
|
25. What is commutation angle or overlap an gle?
|
The commutation period when outgoing and incoming thyristors are conducting is
|
known as overlap p eriod. The angular period, when both devices share con duction is
|
known as the commutation angle or overlap angle.
|
26. What are the different methods of firing circuits for line commutated converter?
|
a. UJT firing circuit.
|
b. The cosine wave crossing pulse timing control.
|
c. Digital firing schemes.
|
27. Give an expression for average voltage of single phase semiconverters.
|
Average output voltage V
|
= (V
|
/ p) (1 + cos a ).
|
dc
|
m
|
28. What is meant by input power factor in controlled rectifier?
|
The input power factor is defined as the ratio of the total mean input power to the
|
total RMS input volt-amperes.
|
PF = ( V
|
I
|
cos f
|
) / ( V
|
I
|
where V
|
= phase voltage, I
|
= fundamental
|
)
|
1
|
1
|
1
|
rms
|
rms
|
1
|
1
|
component of the supply current, f
|
= input
|
displacement angle, I
|
= supply rms current.
|
1
|
rms
|
29. What are the adv antages of six pulse converter?
|
a. Commutation is made simple.
|
b. Distortion on the ac side is reduced due to the reduction in lower order harmonics.
|
c. Inductance reduced in series is considerably r educed.
|
30. What is meant by commutation?
|
It is the process of changing the direction of cur rent flow in a particular path of
|
the circuit. This process is used in thyristors for tu rning it off.
|
31. What are the types of commutation?
|
a. Natural commutation
|
b. Forced commutation
|
32. What is meant by natural commutation?
|
Here the current flowing through the thyristor goes through a natural zero and
|
enable the thyristor to turn off.
|
33. What is meant by forced commutation
|
In this commutation, the current flowing through the thyristor is forced to become zero by ex ternal circuitry.
|
34. What is meant by dc chopper?
|
A dc chopper is a high speed static switch used to obtain variable dc voltage from
|
a constant dc voltage.
|
35. What are the applications of dc chopper?
|
a. Battery operated vehicles
|
b. Traction motor control in electric traction
|
c. Trolly cars
|
d. Marine hoists
|
e. Mine haulers
|
f. Electric braking.
|
36. What are the applications of dc chopper?
|
Chopper provides
|
a. High efficien cy
|
b. Smooth acceleration
|
c. Fast dynamic response
|
d. Regen eration
|
37. What is meant by step-up and step-down chopper?
|
In a step- down chopper or Buck converter, the av erage output voltage is less than
|
the input voltage. In a step- up chopper or Boost converter, the average output voltage is
|
more than the input voltage.
|
38. Write down the expression for average output voltage for step do wn chopper.
|
Average output voltage for step down chopper V
|
= a V
|
, a is the duty cycle
|
0
|
s
|
39. Write down the expression for average output voltage for step up chopper.
|
Average output voltage for step down chopper V
|
= V
|
, a is the duty cycle
|
0
|
s
|
1- a
|
40. What is meant by duty- cycle?
|
Duty cycle is defined as the ratio of the on time of the chopper to the total time
|
period of the chopp er. It is denoted by
|
a
|
.
|
41. What are the two types of control strategies?
|
a. Time Ratio Control (TRC)
|
b. Current Limit Control method (CLC)
|
42. What is meant by TRC?
|
In TRC, the value of T
|
/ T is varied in order to change the average output
|
on
|
voltage.
|
43. What are the two types of TRC?
|
a. Constant frequency control
|
b. Variable frequ ency control
|
44. What is meant by FM control in a dc chopper?
|
In frequency modulation control, the chopping frequency f (or the chopping
|
period T) is varied. Here two controls are possible.
|
a. On-time T
|
is kept constant
|
on
|
unit-3
|
b. Off period T
|
is kept constant.
|
off
|
45. What is meant by PWM control in dc chopper?
|
In this control method, the on time Ton is varied but chopping frequency is kept
|
constant. The width of the pulse is varied and hence this type of control is known as Pulse
|
Width Modulation (PWM).
|
46. Write down the expression for the average output voltage for step down and step up
|
chopper.
|
Average output voltage for step down chopper is V
|
=
|
a
|
V
|
. Average output
|
O
|
S
|
voltage for step up chopper is V
|
=
|
a
|
V
|
x [1/ ( 1-
|
a
|
)].
|
O
|
S
|
47. What are the different types of chopper with respect to commutation process?
|
a. Voltage commutated cho pper.
|
b. Current commutated chopper.
|
c. Load commutated chopper.
|
48. What is meant by voltage commutation?
|
In this process, a charged capacitor momentarily reverse biases the conducting
|
thyristor and turn it off.
|
49. What is meant by current commutation?
|
In this process, a current pulse is made to flow in the reverse direction through
|
the conducting thyristor and when the n et thyristor current becomes zero, it is turned off.
|
50. What is meant by load commutation?
|
In this process, the load current flowing through the thyristor either becomes zero
|
or is transferred to another device from the conducting thyristor.
|
51. What are the adv antages of current commutated chopper?
|
a. The capacitor always remains char ged with the correct polarity.
|
b. Commutation is reliable as load current is less than the peak commutation current
|
I
|
.
|
CP
|
c. The auxiliary thyristor T
|
is naturally commutated as its current passes through
|
A
|
zero value.
|
52. What are the adv antages of load commutated chopper?
|
a. Commutating inductor is not required.
|
b. It is capable of commutating an y amount of load current.
|
c. It can work at high frequencies in the order of kHz.
|
d. Filtering requirements are minimal.
|
53. What are the disadvantages of load commutated chopper?
|
a. For high power applications, efficien cy becomes very low because of high
|
switching losses at high operating frequencies.
|
b. Freewheeling diode is subjected to twice the supply voltage.
|
c. Peak load voltage is equal to twice the supply voltage.
|
d. The commutating capacitor has to carry full load current at a frequency of half
|
chopping frequency.
|
e. One thyristor pair should be turned-on only when the other pair is commutated.
|
This can be realized by sensing the capacitor current that is alternating.
|
54. What is meant by inverter?
|
A device that converts dc power into ac power at desired output voltage and
|
frequen cy is called an inverter.
|
55. What are the applications of an inverter?
|
a. Adjustable speed drives
|
b. Induction heating
|
c. Stand-by aircraft power supplies
|
d. UPS
|
e. HVDC transmission
|
56. What are the main classification of inverter?
|
a. Voltage Source Inverter
|
b. Current Source Inverter
|
57. Wh y thyristors are not preferred fo r inverters?
|
Thyristors require extra commutation circuits for turn off which results in
|
uncreased complexity of the circuit. For these r easons thyristors are not preferred for
|
inverters.
|
58. How output frequen cy is varied in case of a thyristor?
|
The output frequency is varied by varying the turn off time of the th yristors in the
|
inverter circuit, i.e. the delay angle of th e thyristors is varied.
|
59. Give two advantages of CSI.
|
a. CSI does not require any feedback diodes.
|
b. Commutation circuit is simple as it involves only thyristors.
|
60. What is the main drawback of a single phase half bridge inverter?
|
It require a 3-wire dc supply.
|
61. Wh y diodes should be connected in antiparallel with thethyristors in inverter circuits?
|
For RL loads, load current will not be in phase with load voltage and the diodes
|
connected in antiparallel will allow the current to flow when the main thyristors are
|
turned off. These diodes are called feedback diodes.
|
62. What types of inverters require feedback diodes?
|
VSI with RL load.
|
63. What is meant a series inverter?
|
An inverter in which the commutating elements are connected in series with the
|
load is called a series inverter.
|
64. What is the condition to be satisfied in the selection of L and C in a series inverter?
|
2
|
R
|
< 4L/C
|
65. What is meant a parallel inverter?
|
An inverter in which the commutating elements are connected in parallel with the
|
load is called a parallel inverter.
|
66. What are the applications of a series inverter?
|
The thyristorised series inverter produces an approximately sinusoidal waveform
|
at a high output frequen cy, ranging from 200 Hz to 100kHz. It is commonly used for
|
fixed output applications such as
|
a. Ultrasonic generator.
|
b. Induction heating.
|
c. Sonar Transmitter
|
unit-4
|
d. Fluorescent lighting.
|
67. How is the inverter circuit classified based on commutation circuitry?
|
a. Line commutated inverters.
|
b. Load commutated inverters.
|
c. Self commutated inverters.
|
d. Forced commutated inverters.
|
68. What is meant by McMurray inverter?
|
It is an impulse commutated inverter which relies on LC cir cuit and an aux iliary
|
thyristor for commutation in the load circuit.
|
69. What are the applications of a CSI?
|
a. Induction heating
|
b. Lagging VAR compensation
|
c. Speed control of ac motors
|
d. Synchronous motor starting.
|
70. What is meant by PWM control?
|
In this method, a fixed dc input voltage is given to the inverter and a controlled
|
ac output voltage is obtained by adjusting the on and off periods of th e inverter
|
components. This is the most popular method of controlling the output voltage and this
|
method is termed as PWM control.
|
71. What are the adv antages of PWM control?
|
a. The output voltage can be obtained without any additional components.
|
b. Lower order harmonics can be eliminated or minimized along with its output
|
voltage control. As the higher order harmonics can be filtered easily, the filtering
|
requirements are minimized.
|
72. What are the disadvantages of the harmonics present in the inverter system?
|
a. Harmonic currents will lead to excessive heating in the induction motors. This
|
will reduce the load carrying capacity of the motor.
|
b. If the control and the regulating circuits are not pr operly shielded, harmonics from
|
power ride can affect their operation and malfunctioning can result.
|
c. Harmonic currents cause losses in the ac system and can even some time produce
|
resonance in the system. Under resonant conditions, the instrumentation and
|
metering can be affected.
|
d. On critical loads, torque pulsation produced b y the harmonic current can be
|
useful.
|
73. What are the methods of reduction of harmonic content?
|
a. Transformer connections
|
b. Sinusoidal PWM
|
c. Multiple commutation in each cycle
|
d. Stepped wave inverters
|
74. Compare CSI and VSI.
|
S. No. VSI CSI
|
1.
|
Input voltage is maintained
|
Input current is constant but
|
constant
|
adjustable
|
2.
|
The output voltage does not
|
The output current does not depend
|
depend on the load
|
on the load
|
3.
|
The magnitude of the output
|
The magnitude of the output voltage
|
current and its waveform
|
and its waveform depends on the
|
depends on the nature of the
|
nature of the load impedance
|
load impedance
|
4.
|
It requires feedback diodes It does not requires feedback diodes
|
5. Commutation circuit is
|
Commutation circuit is simple i.e. it
|
complicated i.e. it contains
|
contains only capacitors.
|
capacitors and inductors.
|
75. What are the disadvantages of PWM control?
|
SCRs are expensive as they must possess low turn-on and turn-off times.
|
76. What does ac voltage controller mean?
|
It is device which converts fixed alternating voltage into a variable voltage
|
without change in frequency.
|
77. What are the applications of ac voltage controllers?
|
a. Domestic and industrial heating
|
b. Lighting control
|
c. Speed control of single phase and three phase ac motors
|
d. Transformer tap changing
|
78. What are the adv antages of ac voltage controllers?
|
a. High efficien cy
|
b. Flexibility in control
|
c. Less mainten ance
|
79. What are the disadvantages of ac voltage controllers?
|
The main draw b ack is the introduction of harmonics in the supply current and the
|
load voltage waveforms particularly at low output voltages.
|
80. What are the two methods of control in ac voltage controllers?
|
a. ON-OFF control
|
b. Phase control
|
81. What is the difference between ON-OFF control and phase control?
|
ON-OFF control: In this method, the thyristors are employed as
|
switches to connect the load circuit to the source for a few cycles of the load voltage and
|
disconnect it for another few cycles. Phase control: In this method, thyristor switches
|
connect the load to the ac source fo r a portion of each half cycle o f input voltage.
|
82. What is the advantage of ON-OFF control?
|
Due to zero-voltage and zero current switching of thyristors, the harmonics
|
generated by the switching action are reduced.
|
83. What is the disadvantage of ON-OFF control?
|
This type of control is applicable in systems that have high mechanical inertia and
|
high thermal time constant.
|
84. What is the duty cycle in ON-OFF control method?
|
Duty cycle K = n/ (n + m), where n = no. of ON cycles, m = no. of OFF cycles.
|
85. What is meant by unidirectional or half-wave ac v oltage controller?
|
Here the power flow is controlled only during the positive half-cycle of the input
|
voltage.
|
86. What are the disadvantages of unidirectional or half-wave ac voltage controller?
|
a. Due to the presence of diode on the circuit, the control range is limited and the
|
effective RMS output voltage can be varied between 70.7% and 100%.
|
b. The input current and output voltage are asymmetrical and contain a dc
|
component.If there is an input transformer, sdatur ation problem will occur
|
c. It is only used for low power resistive load.
|
unit-5
|
87. What is meant by bidirectional or half-wav e ac vo ltage controller?
|
Here the power flow is controlled during both cycles of the input voltage.
|
88. What is the control range of firing angle inac voltage controller with RL load?
|
The control range is
|
F
|
<
|
a
|
<180
|
°
|
, where
|
F
|
= load power factor an gle.
|
89. What type of gating signal is used in single phase ac voltage controller with RL load?
|
High frequen cy carrier gating signal is used for single ph ase ac voltage controller
|
with RL load.
|
90. What are the disadvantages of continuous gating signal?
|
a. More heating of the SCR gate.
|
b. Increases the size of pulse transformer.
|
91. What is meant by high frequency carrier gating?
|
Thyristor is turned on by using a train of pulses fro m
|
a
|
to
|
p
|
. This type of signal
|
is called as high frequency carrier gating.
|
92. What is meant by sequen ce control of ac voltage regulators?
|
It means that the stages of voltage controllers in parallel triggered in a proper
|
sequence one after the other so as to obtain a variable output with low harmonic content.
|
93. What are the adv antages of sequence control of ac voltage regulators?
|
a. System power factor is improved.
|
b. Harmonics are reduced in the source current and the load voltage.
|
94. What is meant by cyclo-converter?
|
It conv erts input power at one frequency to output power at another frequency
|
with one-stage conv ersion. Cycloconverter is also known as frequency chan ger.
|
95. What are the two types of cyclo-converters?
|
a. Step-up cyclo-conv erters
|
b. Step-down cyclo-converters
|
96. What is meant by step-up cyclo-converters?
|
In these converters, the output frequency is less than the supply frequ ency.
|
97. What is meant by step-down cyclo-con verters?
|
In these converters, the output frequency is more than the supply frequency.
|
98. What are the applications of cyclo-converter?
|
a. Induction heating
|
b. Speed control of high power ac drives
|
c. Static VAR generation
|
d. Power supply in aircraft or ship boards
|
99. What is meant by positive converter group in a cycloconverter?
|
The part of the cycloconverter circuit that permits the flow of current during
|
positive half cycle of output current is called positive converter group.
|
100.What is meant by negative converter group in a cycloconverter?
|
The part of the cycloconverter circuit that permits the flow of current during negative half
|
cycle of output current is called negative converter group.
|
PART-B
|
1.Draw the two transistor model of SCR and derive an expression for anode current.
|
Ans:
|
•
|
Schematic diagram (2M)
|
•
|
Two transistor model diagram (2M)
|
•
|
Operation (4M)
|
2.Explain the characteristics of SCR
|
Ans:
|
•
|
Equivalent circuit
|
•
|
V-I characteristics
|
•
|
Switching characteristics
|
3.Describe the various methods of thyristor turn on.
|
Ans:
|
•
|
Forward voltage triggering
|
•
|
The dv/dt triggering
|
•
|
Gate triggering
|
•
|
Temperature triggerin g
|
•
|
Light triggering
|
4.Explain the operation of MOSFET
|
Ans:
|
•
|
Basic structure, symbol
|
•
|
Operation
|
•
|
V-I characteristics, Switching characteristics
|
5.Explain the operation of IGBT
|
Ans:
|
•
|
Basic structure, symbol
|
•
|
Operation
|
•
|
V-I characteristics, Switching characteristics
|
6.Derive the expressions for average output voltage and rms output voltage of 1
|
semiconverter.
|
Ans:
|
•
|
1 semiconverter bridge circuit
|
•
|
waveforms of v
|
, i
|
, i
|
, i
|
, V
|
, V
|
o
|
o
|
fd
|
s
|
T1
|
T2
|
•
|
Operation
|
•
|
Average output voltage, rms value of output voltage expression
|
7.Describe the working of 1 fully controlled bridge converter in the Rectifying mode
|
and inversion mode. And derive the expressions for average output voltage and rms
|
output voltage.
|
Ans:
|
•
|
1 full converter bridge circuit
|
•
|
waveforms of v
|
, i
|
, i
|
, i
|
, V
|
, V
|
o
|
o
|
fd
|
s
|
T1
|
T2
|
UNIT-1
|
UNIT-2
|
Operation for a < 90
|
, a > 90
|
Average output voltage, rms value of output voltage expression
|
•
|
•
|
UNIT-2
|
8. Describe the working of 3 fully controlled bridge converter in the Rectif ying mode
|
and inversion mode. And derive the expressions for average output voltage and rms
|
output voltage.
|
Ans:
|
•
|
3 full converter bridge circuit
|
•
|
waveforms of v
|
, i
|
, i
|
, v
|
o
|
o
|
A
|
s
|
•
|
Operation
|
•
|
Average output voltage expression
|
9.Describe the working of 3 semi converter. And derive the expressions for average
|
output voltage and rms output voltage.
|
Ans:
|
•
|
3 semi converter bridge circuit
|
•
|
waveforms of v
|
, i
|
, i
|
, v
|
o
|
o
|
A
|
s
|
•
|
Operation
|
•
|
Average output voltage expression
|
10. Describe the working of Dual converter.
|
Ans:
|
•
|
3 dual converter bridge circuit
|
•
|
waveforms of v
|
, i
|
, v
|
, v
|
, i
|
, i
|
v
|
i
|
o
|
o
|
o1
|
o2
|
1
|
2 ,
|
s ,
|
c
|
•
|
Operation for with circulating current and without circulating current
|
•
|
load voltage expression, peak value i
|
cp
|
11. FOR A Type A chopper (first quad rant), express the following v ariables as a function
|
of Vs, R and duty cycle a in case the load is resistive average output voltage and
|
current.
|
Ans:
|
•
|
chopper circuit
|
•
|
output voltage & current waveforms
|
•
|
Average load voltage expression
|
12.Describe the principle of step-up chopper. Derive an expression for the average output
|
voltage in terms of input dc voltage & duty cycle.
|
Ans:
|
•
|
chopper circuit
|
•
|
output voltage & current waveforms
|
•
|
Average load voltage expression
|
13.Describe the working of four quad rant chopper. .
|
Ans:
|
UNIT-3
|
chopper circuit
|
operation
|
•
|
•
|
14.Explain the working of current commutated chopper with aid of cir cuit diagram and
|
necessary wav eforms. Derive an expression for its output voltage.
|
Ans:
|
•
|
chopper circuit
|
•
|
Modes of operation- equivalent circuit diagrams
|
•
|
Current & voltage waveforms
|
•
|
Design
|
15. Explain the working of voltage commutated chopper with aid of circuit diagram and
|
necessary wav eforms. Derive an expression for its output voltage.
|
Ans:
|
•
|
chopper circuit
|
•
|
Modes of operation- equivalent circuit diagrams
|
•
|
Current & voltage waveforms
|
•
|
Design of C & L
|
16.Describe the operation of series inverter with aid of diagrams. Describe an
|
expression for output frequency, current and voltages. What are the disadvantages of
|
basic series inverter?
|
Ans:
|
•
|
series inverter circuit
|
•
|
Current & voltage waveforms
|
•
|
Operation
|
•
|
Expression for output frequency, V
|
, V
|
L
|
C
|
18. State different methods of voltage control inverters. Describe about PWM control in
|
inverter.
|
Ans:
|
•
|
External control of ac output voltage
|
•
|
External control of dc input voltage
|
•
|
Internal control of Inverter
|
PWM inverter
|
•
|
Single pulse modulation
|
•
|
Multiple pulse modulation
|
•
|
Sinusoidal pulse modulation
|
0
|
19. Explain the operation of 3 bridge inverter for 180
|
degree mode of operation with aid
|
of relevant phase and line voltage wav eforms.
|
Ans:
|
•
|
Inverter circuit
|
•
|
operation- equivalent circuits
|
•
|
Waveforms of phase and line voltage
|
UNIT-4
|
0
|
20. Explain the operation of 3 bridge inverter for 120
|
deeger mode of operation with aid
|
of relevant phase and line voltage wav eforms.
|
Ans:
|
•
|
Inverter circuit
|
•
|
operation- equivalent circuits
|
•
|
Waveforms of phase and line voltage
|
21. Draw the circuit diagram of 1 auto sequential commutated current source inverter
|
and explain its operation with equivalent circuits for diffrent modes and necessary
|
waveforms.
|
Ans:
|
•
|
Inverter circuit
|
•
|
Modes of operation- equivalent circuits
|
•
|
Waveforms of i
|
, v
|
i
|
c
|
c ,
|
o
|
•
|
Expression for t
|
, v
|
, v
|
c
|
c
|
L
|
22.Draw the circuit diagram of 1 capacitor commutated current source inverter
|
and explain its operation with equivalent circuits for differ ent modes and necessary
|
waveforms.
|
Ans:
|
•
|
Inverter circuit
|
•
|
Modes of operation- equivalent circuits
|
•
|
Waveforms of i
|
, v
|
i
|
i
|
i
|
v
|
v
|
c
|
o ,
|
o,
|
T1,
|
T2,
|
T1,
|
T2
|
•
|
Expression for v
|
, v
|
, v
|
i
|
t
|
c
|
L
|
o ,
|
o,
|
c
|
23.Explain the operation of multistage control of AC voltage controllers with neat
|
diagram.
|
Ans:
|
•
|
Circuit diagram
|
•
|
Operation
|
24.Explain the operation of 1 AC voltage controller with RL load.
|
Ans:
|
•
|
Circuit diagram
|
•
|
Operation
|
•
|
Waveforms
|
•
|
25.Explain the operation of sequence control of AC voltage controller..
|
Ans:
|
•
|
Circuit diagram
|
•
|
Operation
|
•
|
Waveforms
|
UNIT-4
|
Ans:
|
•
|
Circuit diagram
|
•
|
Operation
|
•
|
Waveforms
|
27. For a 1 voltage controller, feeding a resistive load, draw the waveforms of source
|
voltage, gating signals, output voltage and voltage across the SCR. Describe the
|
working with reference to wavefo rms drawn.
|
Ans:
|
•
|
Circuit diagram
|
•
|
Operation
|
•
|
Waveforms
|
26. Explain the operation of 1 sinusoidal AC voltage controller..
|
