CERTC

A d.c. d.c. to d.c. chopper operates from a 48 48 V battery source source into a resistive load of 24 ohms. The frequency of the chopper is set to 250H. !etermine the avera"e and rms load current and load po#er values #hen $a% chopper on& time is ' ms( $b% chopper on&time is ) ms. *ol+n,

ELECS

A d.c. series motor chopper drive has the follo#in" parameters, battery volta"e /V( (Ra + Rf) 0.' ohm( 1 v '0mVA&rads( chopper frequency '25 H. $a% 3alculate the armature speed and torque #ith an avera"e armature current of '00A and a chopper on&time of ms. $b% !etermine the motor speed and armature current at a torque of '0m #ith on&time and off&time as in $a% above. *ol+n,

A d.c. to d.c. chopper has an inductive load of ' ohm resistance and '0mH inductance. *ource volta"e is 24V. The frequency of the chopper is set to '00 H and the on& time time to 5 ms. !etermi !etermine ne the avera"e( avera"e( ma-im ma-imum um and minimum load currents. *ol+n,

A step&up chopper is to deliver ) A into the '0 ohm load. The battery volta"e is '2 V( 20 uH( 3 '00 uH and the chopper frequency is 50 1H. !etermine the on&time of the chopper( the battery current variation and the avera"e battery current. *ol+n,

A small small electric vehicle is po#ered by a / V battery and uses a series #ound motor. 6t has a step&do#n chopper for for#ard drive and a step&up chopper for re"enerative bra1in". The total armatu armature re resis resistan tance ce is 0.' ohm( ohm( and the armatu armature re volta" volta"e e constant is '0m VA&rads. !escendin" a hill in re"eneration mode the motor speed is '000 revmin and the armature current is a constant avera"e value of 80 A. 3alculate the value of the duty cycle required and the available bra1in" po#er.

*ol+n,

CERTC : CEBU-DAVAO

(0932-175-1218) (0932-175-1218)

Page 1

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COACHING 4

CERTC

7hat value of capacitor is required to force commutate a thyristor #ith a turnoff time of 20 us #ith a /V battery and a full&load current of '00A

HA<& <&3=T>=: =:! ! 6!?3T6V: =A!

@>6!9 6!9:

ELECS

76T 76TH

H69H 69H

Avera"e Values Values *ol+n,

*6 *69:&; :&;H HA*: >:3T6<6:>

HA< A<&7AV:

3=T =T>=: :!

3=T>= =:! :! @>6!9 @>6!9: : 76TH 76TH H69H 6!?3T6V: =A!

>oot&mean&square load volta"e( $Vrms% $Vrms%

*69:&;HA*: >:3T6<6:>

T>= =: :! ! >:*6*T6V: =A! Avera"e Values Values

Vrms

3=T>=:!

@>6! @>6!9: 9:

76TH 76TH

A separately e-cited d.c. motor is driven from a 240V( 240V( 50H supply usin" a fully controlled thyristor brid"e. The motor has an armature resistance >a of '.0 ohm( and an armature armature volta"e constant 1v of 0.8 Vrad&s. Vrad&s. The field field current is constant at its rated value. Assume that the armature current is steady. steady. $a% !etermine the values of armature current and torque for an armature speed of '00 revmin and a firin" an"le delay of )00. $b% 3alculate the limits of the firin" an"le delay for this speed.

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COACHING 4

CERTC

A separately e-cited d.c. motor is driven from a 240 V( V( 50 H supply usin" a half&controlled thyristor brid"e #ith a fly&# fly&#heel heel diode diode connec connected ted across across the armatu armature re.. The motor has an armature resistance >a of '.0 ohm( and an armature armature volta"e constant 1v of 0.8 Vrads. Vrads. The field current is constant at its rated value. Assume that the armature current is steady. steady.

ELECS

The three&phase half&controlled converter of :-ample )./ is replac replaced ed by a three& three&pha phase se fully fully contro controll lled ed thyri thyristo stor r converter. oad and supply remain unchan"ed( i.e. hi"hly inductive inductive load of '0fC and a three&phase three&phase supply of 240V at 50H. !etermine the values of avera"e load volta"e and current( rms phase current( load po#er and converter po#er factor for a firin" an"le delay of $a% a )0 0 $b% a B50 $c% 7hat are the ma-imum values of load po#er and converter po#er factor obtainable from the circuit *ol+n,

!etermine the values of armature current and torque for an armature speed of '00 revmin and a firin" an"le delay of $a% )0 0 $b% 00.

A three&phase half&controlled thyristor converter has an hi"hly inductive load of '0 ohm( and a supply of 240V at 50H. !etermine the values of avera"e load volta"e and current( current( rms phase current( current( load po#er and converter converter po#er factor for firin" an"le delay of $a% a )0 0( $b% a B50 $c% 7hat are the ma-imum values of load po#er and converter po#er factor obtainable from the circuit *ol+n,

A half&brid"e inverter #ith a centre&tapped 40V battery has a purely inductive load( 200 mH( and a frequency of '00H. !etermin !etermine e the ma-imum load current and the load current at $a% t )ms( $b% t 5ms( and $c% t 8ms( assumin" that at t 0 the transient had disappeared. *ol+n,

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CERTC

COACHING 4

ELECS

The half&brid"e inverter circuit has a load resistance of '0 ohm and an inductance of '00 mH. The centre&tapped battery has 20V per section. The inverter frequency is '00 H. !etermine the value of l o( and i$t%( $a% ) ms after D' s#itches( and $b% 4ms after D 2 s#itches. *ol+n, A Triac controller provides variable po#er to a 200 ohm resistive load from a 240V( 50H supply. !etermine the values of rms load current( po#er and converter po#er factor for firin" an"le delays of $a% a )0 0 $b% a '500.

A three&phase Eosfet inverter is connected bet#een a balanced star&connected resistive load #ith > '0 ohm and a 250V d.c. supply. The inverter frequency is set at )) H( and the s#itches have '20 0 conduction periods. 3alculate the load po#er.

A portable electric drill uses a series universal motor and a sin"l sin"le e thyris thyristor tor.. The main supply supply is 240V 240V at 50H. 50H. 3ombined field and armature resistance is ' ohm and the the arma armatu ture re volt volta" a"e e cons consta tant nt is 0.85 0.85 Vra Vrad ds s for for saturated operation. !etermine the avera"e motor current and torque torque #hen #hen the speed is B00 revmin( revmin( the firin" firin" 0 0 an"le delay is )0 and the conduction an"le is '80 .

*ol+n,

A sin"le&phase sin"le&phase full&brid"e full&brid"e inverter is connected bet#een bet#een a 200V d.c. source and a series connected >& load #ith > 20 ohm and 50 mH. The inverter frequency is 50H. !etermine the values of the rms load current( the load po#er and the total harmonic distortion factor( up to the /th harmonic.

A burst&firin" a.c. to a.c. po#er controller is connected bet#een a 250V( 50H supply and a '00 ohm resistive load. !etermine the values of load volta"e( current and po#er #hen #hen $a% tn 40 ms and tf '20 ms( $b% tn '20 ms and tf 40 ms.

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CERTC

A d.c. lin1 inverter has an a.c. mains rms line input of 4'5 V( 50H. The inverter load is a balanced star connection of '00 ohm resistors. !etermine load current and po#er for a converter firin" an"le delay of $a% 50 0 and $b% 850 #ith an inver nverte terr freque equenc ncy y of '00H 00H and and a '20 '200 conduction period of the inverter s#itches.

COACHING 4

ELECS

A thyristor thyristor has a latchin" current of 40mA. 6t is connected in a half&#ave controlled rectifier circuit( bet#een a '20V( 50H 50H a.c. a.c. supp supply ly and and an indu induct ctiv ive e load load of 20 ohm ohm resistance and )0 ohm inductive reactance. !etermine the minim minimum um pulse pulse #idth #idth requir required ed to obtain obtain latchi latchin" n" current #hen the firin" an"le delay is )0 0.

The manufacturer of a selected diode "ives the rate of fall of the the diode diode curr curren entt did didtt 20A 20AIs Is(( and and a reve revers rse e recovery time of trr5 Is. 7hat value of pea1 reverse current do you e-pect

An isolated for#ard $buc1% converter has a d.c. input volta"e of )0V( a ',' transformer and an ideal Eosfet. The induct inductor or value value is '00CH '00CH and and the s#itchin s#itchin" " frequency is 501H. Assume that the output capacitor is lar"e enou"h to hold the load volta"e constant. The converter is required to deliver 4 A into a ) ohm resistive load. !etermine the converter duty cycle( the s#itch on&time and the ripple current ma"nitude.

A thyristor has a linearied "ate&cathode characteristic of slope 25 VA. A "ate current of 200mA turns the thyristor on in ' us. us. The The "ate "ate sour source ce volt volta" a"e e is '0V '0V. The The

A three&phase rectifier has a purely resistive load of >. !etermine a. The efficiency b. The form factor c. The ripple factor e. The pea1 inverse volta"e of each diode and f. The pea1 current throu"h a diode. The rectifier delivers 6 0 A at an output volta"e of Vdc 280.BV and the source frequency is 0 H.

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CERTC

COACHING 4

ELECS

The !3 chopper has a resistive load of >'0 and input volta"e is Vs220V. Vs220V. 7hen the chopper s#itch remains on its volta"e drop 2V( duty cycle 50K and the choppin" frequency frequency is f'1H.det f'1H.determi ermine ne a% The avera"e output output volta"e( b% the rms output volta"e (c% chopper efficiency. efficiency.

The The dc&d dc&dc c conv conver erte terr has has inpu inputt volt volta" a"e e '2 '2 V. The The requ requir ired ed outp output ut volt volta" a"e e is Vo5V o5V and and rippl ripple e outp output ut Volta"e 20mV. The s#itchin" frequency 251H and ripple inductor current is 0.8A. !etermine, a% The duty cycle !( b% The inductance ( c% The filter capacitor.

The sin"le&phase half #ave rectifier has a purely resistive load of > and the delay an"le is J2( determine, a% The efficiency( b% The form factor <<( c% The ripple factor ><( d% The pea1 inverse volta"e ;6V of thyristor. thyristor.

The dc&dc converter has input volta"e 5 V. The required output volta"e is Vo'5V and the avera"e load current 0.5A. 6f the s#itchin" frequency 251H( '50IH and

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CERTC

The sin"le sin"le&ph &phase ase half half brid"e brid"e has a resist resistive ive load load of >2.4M and the dc input volta"e Vdc 24V. !etermine the follo#in", a% The rms value of fundamental component( b% The output po#er( po#er( c% The avera"e and pea1 current of each transistor( transistor( d% The total harmonic distortion TH!( e% The distortion factor !< of third harmonic.

COACHING 4

ELECS

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