EI2301-IE_Unit 3_Part A and Part B_With answers.pdf

7/27/2019 EI2301-IE_Unit 3_Part A and Part B_With answers.pdf

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Unit Test 3Industrial ElectronicsQuestion 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 equivalentto an dc transformer with continuously variable turns ratio. Like a transformer it can be usedto 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 ofchopper 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 highoutput frequency, ranging from 200 Hz to 100 KHz. It is commonly used for fixed output

applications such as Ultrasonic generators, Induction heating, Sonar transmitter, FluorescentLighting.


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6. What are the types of PWM control?Single pulse width modulations

Multiple pulse width modulationsSinusoidal pulse width modulations

Modified Sinusoidal pulse width modulations

7.

Compare CSI and VSIVSIIn 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 loadimpedance.

IT requires feedback diodes.

Commutation is complex.

CSIInput 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 loadimpedance.

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 Heatingc. Aircraft power suppliesd. Domestic power suppliese. 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


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Part B1. Explain the working of 3 phase full bridge inverter for 180 conduction and draw the

relevant output waveforms in the graph sheet.


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2. Explain the principle and operation of Current source Inverter.


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3. Explain the working of step up and step down DC chopper with TRC and CLC control.


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4. Explain the different configurations of chopper.Refer class notes for derivation and diagramBookpage no. 229


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5. Explain the voltage control of Inverters using PWM techniquesa. Single-pulse-width modulationb. Multi-pulse-width modulationc. Sinusoidal pulse-width modulation.d. Modified sinusoidal pulse-width modulation


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Single Pulse-Width Modulation

There is one pulse per half-cycle, and its width isvaried.

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The dominant harmonic is the third.

DF increases significantly at a low output

voltage. 1


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The dominant harmonic is the third.

DF increases significantly at a low outputvoltage. 14


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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).

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The following figure shows the harmonic profile

against the variation of modulation index, and

p=5.

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Sinusoidal Pulse-Width

Modulation

Instead of maintaining the width of all pulses

the same, the width of each pulse is varied inproportion to amplitude of a sine wave.

This kind of modulation is known as SPWM.

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The rms output voltage is:

The DF and LOH are reduced significantly, asshown below.

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1

)(

p

m

mso VV

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Modified Sinusoidal Pulse-Width

Modulation

This utilizes a different method of modulation.

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The harmonic profile is shown below.

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6. Explain the working of 3 phase full bridge inverter for 120 conduction and draw therelevant output waveforms in the graph sheet.


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7. Explain the working of AC chopper


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Documents

EI2301-IE_Unit 3_Part A and Part B_With answers.pdf