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Power electronics assignment 2

Q1)a) The buck-boost converter is the best choice. This is because, the buck-boost converter operates at steady state. The inductor current is continuousand the converter operates in continuous current mode. oreover, the

capacitor value is su!ciently large so as to assume that a constant supplyvoltage is supplied thus being possible to have a output voltage ripple asnegligible and as small as 1" and lower. This type o# buck converter also canhave an output voltage that is either higher or lower than the source or inputvoltage. $ence, the buck-boost converter absolutely matches the designre%uirements o# the converter that is needed to be designed.

b) &or 's ( 2' * 'o ( 2+', ( 'o /'s 0 'o ( 2+/2 0 2+ ( .+3 &or 's ( 22.4' * 'o ( 2+', ( 'o /'s 0 'o ( 2+/22.4 0 2+ ( .41 5.42&or 's ( 2+' * 'o ( 2+', ( 'o /'s 0 'o ( 2+/2+ 0 2+ ( .4

Thus, the duty ratio range o# the switch is6 .+3 7( 7 .42

c)8e 9rst determine the value o# the load resistance:P ( 'o2;

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d)

&or +.3 uty Cycle

&or 4 uty Cycle

&or 4.2 uty Cycle

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The output voltage is o# the opposite polarity as the input and can be lower orhigher than the input voltage depending upon uty Cycle. This clearly showsthat the circuit design chosen meets the re%uired speci9cations that is to beable to produced the desired output given an input lower than or even higherthan the desired output.

Q2)# ( 4$E, ; ( 12@, B( 2m$, 'dc ( 14', 'amp ( '1( 12'

a)=i) &or bipolar PWM with m# ( 21, The harmonics are 21, 1? and 2< =#rom m# F2)

Computing the #re%uencies: &or n ( n, #n ( n G #1 &or n ( 1, #1 ( 4 &or n ( 1?, #1? ( 4 G 1? ( ?4 $E &or n ( 21, #21 ( 4 G 21 ( 14 $E &or n ( 2

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Computing #or currents, Hn: Hn ( 'nIn ( 'n s%rt=;20 =nwB)2) H1( 12 s%rt==12)20 =1 G 2pi=4) G 2m)2)

( ?.>33>2.< .+++ .

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( .32>?J 5 .32+JH+

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5 ?.3 J H1> ( 21 s%rt==12)20 =1> G 2pi=34) G 2m)2)

( .114++ ( .11J 5 11. mJ H1? ( +.4 s%rt==12)20 =1? G 2pi=?4) G 2m)2)

( .24< ( .24 J 5 2.4 mJ H21 ( +.4 s%rt==12)20 =21G 2pi=14) G 2m)2)

( .1>314 ( .13J 5 1.3 mJH2+

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I2< ( 21 .< (

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olta!e spectrum

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(ii) bipolar PWM with mf = 21

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(iii) unipolar PWM with mf = 1"

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