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Unit Test 3 – Industrial Electronics – Question Bank
2 Marks
1. What is meant by a dc chopper ?
A dc chopper is a high speed static switch used to obtain variable dc voltage from a constant
dc voltage. It is also known as dc to dc converter. A chopper can be consider as dc equivalent
to an dc transformer with continuously variable turns ratio. Like a transformer it can be used
to step up / down a dc voltage source.
2. What is meant by step down and step up chopper?
The average output voltage Vo is less than the input voltage Vs, ie Vo < Vs this method of
chopper is called step down chopper / buck converter. Average output voltage Vo is greater
than input voltage Vs ie. Vo > Vs, this chopper is called step up chopper/ boost converter.
3. What is meant by PWM control in dc chopper?
In this control method the on time Ton is varied but chopping frequency f is kept constant.
The width of the pulse is varied and this type of control is known as PWM.
4. What is TRC and CLC in terms of chopper?
5. Applications of series inverter.
The thyristorised series inverters produces an approzimately sinusoidal waveform at a high
output frequency, ranging from 200 Hz to 100 KHz. It is commonly used for fixed output
applications such as Ultrasonic generators, Induction heating, Sonar transmitter, Fluorescent
Lighting.
6. What are the types of PWM control?
Single pulse width modulations
Multiple pulse width modulations
Sinusoidal pulse width modulations
Modified Sinusoidal pulse width modulations
7. Compare CSI and VSI
VSI
In VSI input voltage is maintained constant.
The output voltages does not depend on the load
The Magnitude of output current and its waveform depends upon the nature of the load
impedance.
IT requires feedback diodes.
Commutation is complex.
CSI
Input Current is constant but adjustable.
The amplitude of output current does not depend on the load.
The magnitude of output voltage and its waveform depends upon the nature of the load
impedance.
It does not require any feedback diode.
Commutation circuit is simple…….. Contains only capacitors.
8. List the applications of Inverter?
a. Variable speed ac motor drives.
b. Induction Heating
c. Aircraft power supplies
d. Domestic power supplies
e. UPS
9. What are the disadvantages of harmonics present in the inverter system?
Harmonics currents will lead to excessive heating in the induction motors. This will reduce
the load carrying capacity of the motor
10. What are the methods of voltage control in Inverters?
External control of ac output voltage
External control of dc input voltage
Part B
1. Explain the working of 3 phase full bridge inverter for 180 conduction and draw the
relevant output waveforms in the graph sheet.
2. Explain the principle and operation of Current source Inverter.
3. Explain the working of step up and step down DC chopper with TRC and CLC control.
4. Explain the different configurations of chopper.
Refer class notes for derivation and diagram – Book – page no. 229
5.
a.
b.
c.
d.
Explain the voltage control of Inverters using PWM techniques
Single-pulse-width modulation
Multi-pulse-width modulation
Sinusoidal pulse-width modulation.
Modified sinusoidal pulse-width modulation
Single Pulse-Width Modulation

There is one pulse per half-cycle, and its width is
varied.
12

The dominant harmonic is the third.

DF increases significantly at a low output
voltage.
1

The dominant harmonic is the third.

DF increases significantly at a low output
voltage.
14
Multiple-Pulse-Width Modulation

The harmonic content can be reduced by using
several pulses in each half-cycle of output
voltage.

This type of modulation is also known as
uniform-pulse-width modulation (UPWM).
15
16

The following figure shows the harmonic profile
against the variation of modulation index, and
p=5.
18
Sinusoidal Pulse-Width
Modulation

Instead of maintaining the width of all pulses
the same, the width of each pulse is varied in
proportion to amplitude of a sine wave.

This kind of modulation is known as SPWM.
19
20

The rms output voltage is:
 m 1/ 2
)
m 1 
p
Vo  Vs (

The DF and LOH are reduced significantly, as
shown below.
21
Modified Sinusoidal Pulse-Width
Modulation

This utilizes a different method of modulation.
23

The harmonic profile is shown below.
24
6. Explain the working of 3 phase full bridge inverter for 120 conduction and draw the
relevant output waveforms in the graph sheet.
7. Explain the working of AC chopper