Power Semiconductor Drives

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Code No:

Code No: R05410R05410202202

Set No. 1

IV

IV B.TB.Tecech I h I SemSemestester er RegRegulaular r ExaExaminminatiationsons, N, Novovemember ber 20020088 POWER SEMICONDUCTOR DRIVES

POWER SEMICONDUCTOR DRIVES (Electrical & Electronic Engineering) (Electrical & Electronic Engineering) T

Tiimmee: : 3 3 hhoouurrs s MaMax x MMaarrkkss: : 8800 Answer any FIVE Questions

Answer any FIVE Questions All Questions carry equal marks All Questions carry equal marks

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1.

1. ExplaiExplain the fundamn the fundamentalentals of thys of thyristor conristor controlled dtrolled drivrives and their oes and their operation. peration. [16][16] 2.

2. ExplaiExplain the Speed n the Speed torque Chatorque Characterisracteristics of a dc sertics of a dc series motor coies motor connected to a thrennected to a threee p

phhaasse e ffuulllly y ccoonnttrroolllleed d ccoonnvveerrtteerr. . [[1166]] 3. Explain brieﬂy the following methods of braking of a D.C Motor

3. Explain brieﬂy the following methods of braking of a D.C Motor (a)

(a) RegeneratRegenerative brakive brakinging (b)

(b) DynamiDynamic brakic brakingng

((cc) ) PPlluuggggiinngg. . [[1166]]

4. Explain the operation of four quadrant chopper fed to the D.C series motor and 4. Explain the operation of four quadrant chopper fed to the D.C series motor and also draw the current and voltage wave forms for continuous current operation.[16] also draw the current and voltage wave forms for continuous current operation.[16] 5.

5. (a) Startin(a) Starting g frofrom m fundfundamenamentaltals s proprove that torque devve that torque develoeloped ped by the Inductiby the Inductionon motor is proportional to square of the supply voltage.

motor is proportional to square of the supply voltage. (b)

(b) DraDraw w the the speed torque curvspeed torque curves es for diﬀerefor diﬀerent voltnt voltages fed ages fed from stator voltfrom stator voltageage

ccoonnttrroolllleerr. . [[88++88]]

6.

6. A 3 A 3 PhasPhase,15e,1500 rpm 00 rpm IndInductiuction motor is develon motor is developioping torque of 3000 Syn. ng torque of 3000 Syn. wawatts attts at an input frequency of 50Hz. If the motor torque is now reduced to 1500 Syn.watts, an input frequency of 50Hz. If the motor torque is now reduced to 1500 Syn.watts, dete

determirmine ne the new the new vvalualue e of of statstator or freqfrequencuencyy. . The motor The motor is operatinis operating g in constanin constantt HP region. Assume constant rotor frequency and neglect eﬀect of rotor resistance. HP region. Assume constant rotor frequency and neglect eﬀect of rotor resistance. [16] [16] 7. A three phase, 460V, 60Hz, 1164 rpm, six pole star connected, wound rotor 7. A three phase, 460V, 60Hz, 1164 rpm, six pole star connected, wound rotor

Induc-tion motor has the following parameters per phase referred to the stator. tion motor has the following parameters per phase referred to the stator. R

R11 = 0.4 ohm, R= 0.4 ohm, R22 = 0.6 ohm, X= 0.6 ohm, X11 = = XX22 =1.8 ohm, X=1.8 ohm, Xmm = 40 Ohm. Stator to rotor= 40 Ohm. Stator to rotor

turns ratio is 2.5. The motor speed is controlled by static rotor resistance control. turns ratio is 2.5. The motor speed is controlled by static rotor resistance control. The ﬁlter resis

The ﬁlter resistanctance e is 0.02 is 0.02 OhmOhm. . The valThe value ue of of extexternaernal l resresistaistance is nce is chchosen sucosen suchh that

that αα = 0 = 0 and the breakdand the breakdowown torque is obtainn torque is obtained at ed at stanstand still. d still. DetDetermiermine thene the

following: following:

(a)

(a) The vThe value of the external resialue of the external resistancestance (b)

(b) αα ffoor r a a ssppeeeed d oof f 99660 0 rrppm m aat t 11..5 5 ttiimmees s tthhe e rraatteed d ttoorrqquuee. . [[1166]]

8. Explain separate control & self control of synchronous motor. 8. Explain separate control & self control of synchronous motor.

[16] [16]

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Code No:

Code No: R05410R05410202202

Set No. 2

IV

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1. Draw and Explain Speed-torque characteristics of semi converter feeding a D.C 1. Draw and Explain Speed-torque characteristics of semi converter feeding a D.C

sseerriiees s mmoottoorr. . [[1166]]

2.

2. ExplaiExplain the Speed - n the Speed - torque Charactorque Characteristiteristics of a dc cs of a dc series motor connseries motor connected to a threeected to a three p

phhaasse e ffuulllly y ccoonnttrroolllleed d ccoonnvveerrtteerr. . [[1166]] 3.

3. (a) (a) DiDiscuscuss ss in in detdetaiail l coucountnter er curcurrenrent t anand d dydynamnamic ic brbrakiaking ng opeoperatratioions ns of of D.D.C.C. shunt motors.

shunt motors.

(b) A 400V, 750 rpm, 70A dc shunt motor has an armature resistance of 0.3Ω (b) A 400V, 750 rpm, 70A dc shunt motor has an armature resistance of 0.3Ω when running under rated conditions, the motor is to be braked by plugging when running under rated conditions, the motor is to be braked by plugging with armature current limited to 90A. What external resistance should be with armature current limited to 90A. What external resistance should be conn

connecteected d in series with in series with the armatuthe armature? re? CalCalculculate the ate the iniinitial brakitial braking ng torqtorqueue aannd d iitts s vvaalluue e wwhheen n tthhe e ssppeeeed d hhaas s ffaalllleen n tto o 330000rrppmm. . [[88++88]] 4.

4. (a) (a) DisDistingtinguisuish betweh between class A and class B choppeen class A and class B choppers with suitrs with suitable exaable examplmples of es of speed control of motors.

speed control of motors. (b)

(b) A 220V, 190A dc series motoA 220V, 190A dc series motor r has armathas armature and ﬁeld resisture and ﬁeld resistanceance’s of ’s of 0.03 and0.03 and 0.0

0.02 2 ohmohms s resperespectivctivelyely. . RunRunning on ning on no no loaload d as as a a genegeneratorator r with ﬁeld wininwith ﬁeld winingg connected to a separate source it gave following magnetization characteristic connected to a separate source it gave following magnetization characteristic at 500rpm.

at 500rpm. F

FiieellddCCuurrrreenntt((AA) ) 440 0 880 0 11220 0 11660 0 220000 T

TeermrmiinnalalVVoollttaage ge ((VV) ) 552 2 1108 08 11448 8 17176 6 118989

Motor is controlled by a chopper in dynamic braking with a braking Motor is controlled by a chopper in dynamic braking with a braking resis-tanceof 2Ω.

tanceof 2Ω. i.

i. CalCalculculate motor speed for a ate motor speed for a dutduty ratio of y ratio of 0.6 and motor curr0.6 and motor current of 160A.ent of 160A. ii. What will be the motor speed for a duty ratio of 0.75 and motor torque ii. What will be the motor speed for a duty ratio of 0.75 and motor torque eeqquuaal l tto o hhaallf f oof f rraatteed d ttoorrqquuee? ? [[88++88]] 5. An inverter supplies a six pole three-phase cage Induction motor rated at 415V, 5. An inverter supplies a six pole three-phase cage Induction motor rated at 415V, 50Hz. Determine the approximate voltages required of the inverter for motor speeds 50Hz. Determine the approximate voltages required of the inverter for motor speeds 660000//880000//11550000/ / 1188000 0 rrppmm. . [[1166]] 6. A 3 Ph Star connected Induction motor operating at a frequency of 60 Hz consists 6. A 3 Ph Star connected Induction motor operating at a frequency of 60 Hz consists

of 4 poles. The parameters of the stator and rotor referred to stator side are R of 4 poles. The parameters of the stator and rotor referred to stator side are R11 ==

R

R22 = 0.024 ohm and X= 0.024 ohm and X11 = X= X22 = 0.18 ohm. = 0.18 ohm. If the motor is controlled by the vIf the motor is controlled by the variablariablee

frequency control with v/f constant ratio determine the following parameters at an frequency control with v/f constant ratio determine the following parameters at an opera

operating freqting frequencuency y of 12 of 12 Hz. Hz. StarStarting torquting torque e and rotor currenand rotor current t in terms of in terms of theitheirr v

vaalluuees s aat t rraatteed d ffrreeqquueennccyy. . [[1166]]

1 of 2 1 of 2

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Code No:

Code No: R05410R05410202202

Set No. 2

7. Draw the circuit diagram and explain the operation of rotor- resistance control 7. Draw the circuit diagram and explain the operation of rotor- resistance control using chopper. Mention the advantages and disadvantages of the above method of using chopper. Mention the advantages and disadvantages of the above method of

ccoonnttrrooll.. [[1166]]

8. With suitable circuit diagrams discuss in detail the principle of operation of Self 8. With suitable circuit diagrams discuss in detail the principle of operation of Self

co

conntrtrololleled d SySyncnchrhrononouous s momototor r drdrivive e ememplplooyiying ng a a CyCyclclo o coconnvvererteter. r. [1[16]6]

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Code No:

Code No: R05410R05410202202

Set No. 3

IV

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1. Write down the basic performance equations for a D.C Series motor Sketch 1. Write down the basic performance equations for a D.C Series motor Sketch

char-act

acterieriststicics s of of coconstnstanant t tortorquque e dridrive ve anand d conconstastant nt powpower er drdrivive e regregioionsns. . [1[16]6] 2. The speed of a separately excited dc motor is controlled by means of a 3 phase semi 2. The speed of a separately excited dc motor is controlled by means of a 3 phase semi

conv

converter from a erter from a 3 phase 415V 3 phase 415V 50Hz supply50Hz supply. . The motor constants are inductanceThe motor constants are inductance 10mH, resistance 0.9 ohm and armature constant 1.5v/rad/s.calculate speed of the 10mH, resistance 0.9 ohm and armature constant 1.5v/rad/s.calculate speed of the motor at a torque of 50 Nm when the converter is ﬁred at 45

motor at a torque of 50 Nm when the converter is ﬁred at 4500

. . NegNegleclect losset losses ins in the

the convconverter.erter.

[16] [16] 3. What are the advantages of electric braking over mechanical braking of D.C. 3. What are the advantages of electric braking over mechanical braking of D.C.

mo-tors

tors? ? ExpExplailain n witwith h propeproper r circircuicuit t diadiagram Speed-Tgram Speed-Torqorque ue chcharacaracteriterististics cs of of D.CD.C motor under dynamic braking, for the following types:

motor under dynamic braking, for the following types: (a)

(a) SeparatelSeparately excited dc moty excited dc motoror

((bb) ) SSeerriiees s mmoottoorr. . [[88++88]] 4.

4. (a) (a) ExpExplailain the prinn the principciple of speed cole of speed contntrol of a dc motorol of a dc motor and shor and show how it caw how it can ben be achieved by a chopper.

achieved by a chopper. (b)

(b) A A 230V230V, , 12001200rpm, 15A rpm, 15A sepaseparaterately excitely excited d motomotor r has an has an armaarmature resisture resistanctancee of

of 1.1.2Ω2Ω. . MotMotor or is is operoperateated d ununder der dydynamnamic ic brbrakiaking ng wiwith th chchoppopper er cocontntrolrol.. Braking resistance has a value of 20Ω.

Braking resistance has a value of 20Ω. i.

i. CalCalculculate duty ratio of ate duty ratio of chchopper for motor speed opper for motor speed of 1000rpm and brakiof 1000rpm and brakingng torque equal to 1.5times rated motor torque.

torque equal to 1.5times rated motor torque.

ii. What will be the motor speed for duty ratio of 0.5 and motor torque equal ii. What will be the motor speed for duty ratio of 0.5 and motor torque equal tto o iitts s rraatteed d ttoorrqquuee? ? [[88++88]] 5.

5. (a) (a) ExpExplailain varn variabiable volle voltage chtage charecarecter sticter stics of Inductis of Induction motoron motor (b

(b) ) ExExplplaiain n TTororquque e & & spspeeeed d cchaharerectctererststicics s of of InInduductctioion n momototor. r. [[8+8+8]8] 6. A 400V, 50HZ Star connected Induction motor is fed from a six step inverter which 6. A 400V, 50HZ Star connected Induction motor is fed from a six step inverter which

in turn fed

in turn fed from a from a sixsix-pu-pulse fulllse fully y concontroltrolled rectiled rectifier. fier. The a.c The a.c supsupply mainply mains s areare rated at 440V, 50HZ. What should be the firing angle of the rectifier to operate the rated at 440V, 50HZ. What should be the firing angle of the rectifier to operate the m

moottoor r aat t 550 0 HHZ Z uunnddeer r vv//f f ccoonnttrrooll? ? [[1166]] 7. Explain static motor resistance control for speed control of I.M. Draw speed & 7. Explain static motor resistance control for speed control of I.M. Draw speed &

torque charecterstics. torque charecterstics. [16] [16] 1 of 2 1 of 2

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Code No:

Code No: R05410R05410202202

Set No. 3

8. A 20 kW, 3-phase, 440V, 4 pole, delta connected permanent magnet synchronous 8. A 20 kW, 3-phase, 440V, 4 pole, delta connected permanent magnet synchronous

mot

motor has or has folfollolowinwing g paraparametmeters. ers. XXss = 5 ohm, R= 5 ohm, Rss = 0, rated power factor =1.0.= 0, rated power factor =1.0.

Machine is controlled by variable frequency control at a constant (V/f) ratio. Machine is controlled by variable frequency control at a constant (V/f) ratio. Cal-culate armature current, torque angle and power factor at half full load torque and culate armature current, torque angle and power factor at half full load torque and

775500 rrppmm.. [[1166]]

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Code No:

Code No: R05410R05410202202

Set No. 4

IV

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1. Derive the Speed, Torque Equations of a fully controlled converter connected to 1. Derive the Speed, Torque Equations of a fully controlled converter connected to separately excited D.C motor with continuous current operation with necessary separately excited D.C motor with continuous current operation with necessary w

waavveeffoorrmmss.. [[1166]]

2. Explain the Speed - torque Characteristics of a separately excited dc motor 2. Explain the Speed - torque Characteristics of a separately excited dc motor

con-n

neecctteed d tto o a a tthhrreee e pphhaasse e sseemmi i ccoonnttrroolllleed d ccoonnvveerrtteerr. . [[1166]] 3.

3. (a) (a) WitWith neat circuih neat circuit diagrat diagram and m and wawaveveformforms, explas, explain dynamin dynamic brakiic braking of ng of sepa sepa--rately excited motor by single phase converter.

rately excited motor by single phase converter. (b)

(b) A dc A dc shshununt t motomotor r has the armaturhas the armature e resresistaistance of nce of 0.00.04Ω and 4Ω and the ﬁeld windithe ﬁeld windingng resi

resistanstance of ce of 10Ω. 10Ω. MotoMotor r is coupleis coupled d to an to an ovover haulier hauling load with a ng load with a torqtorque of ue of 400N-m. Following magnetization curve was measured at 600 rpm:

400N-m. Following magnetization curve was measured at 600 rpm: F

Fiieelld d CCuurrrreenntt, , A A 22..5 5 5 5 77..5 5 110 0 1122..5 5 11..5 5 1177..5 5 220 0 2222..5 5 2255 B

Baacck k eemmff, , V V 225 5 550 0 7733..5 5 990 0 110022..5 5 11110 0 11116 6 11221 1 11225 5 112299 Calculate the value of R

Calculate the value of RBB when the motor is required to hold overhauling loadwhen the motor is required to hold overhauling load

aat t 11220000rrppmm. . [[88++88]]

4.

4. A 220V, 70A D.C series motor has comA 220V, 70A D.C series motor has combined resistabined resistance of armature and field is 0.12nce of armature and field is 0.12 ohms running on no-load with the field winding connected to a separate source. It ohms running on no-load with the field winding connected to a separate source. It gave following magnetization characteristics at 600 rpm

gave following magnetization characteristics at 600 rpm F

FiieellddCCuurrrreenntt((AA) ) 110 0 220 0 330 0 440 0 550 0 660 0 770 0 8800 T

TeerrmmiinnaallVVoollttaagge e ((VV) ) 664 4 11118 8 11550 0 11770 0 11884 4 11994 4 22002 2 221100

Motor is controlled by a chopper with source voltage equal to 220V. calculate Motor is controlled by a chopper with source voltage equal to 220V. calculate

(a)

(a) MotoMotor Speed for a r Speed for a dutduty ratio of 0.6 and motor curry ratio of 0.6 and motor currenent of t of 60A60A

((bb) ) TToorrqquue e ffoor r a a ssppeeeed d oof f 44000 0 rrppm m aannd d dduutty y rraattiio o oof f 00..6655. . [[1166]] 5. Draw the following AC voltage controllers for varying the speed of a 3 phase 5. Draw the following AC voltage controllers for varying the speed of a 3 phase

In-duction motor duction motor

(a)

(a) Star connecteStar connected controld controllerler (b)

(b) Delta connecDelta connected controlted controllerler (c)

(c) Delta connecDelta connected Stator and controlted Stator and controller.ler. D

Diissccuusss s iin n ddeettaaiil l aabboouut t tthhe e aabboovve e ttyyppees s oof f ccoonnttrroolllleerrss. . [[1166]] 6. With neat block diagrams explain closed loop operation of Induction motor drives. 6. With neat block diagrams explain closed loop operation of Induction motor drives. [16] [16]

1 of 2 1 of 2

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Code No:

Code No: R05410R05410202202

Set No. 4

7.

7. (a) (a) WhWhy rotor resy rotor resististance conance control is prtrol is prefereferred in lored in low powew power crane drir crane driveves?s? (b)

(b) What are What are the advanthe advantages of tages of static rotor resistance control ovstatic rotor resistance control over convener conventionaltional meth

method od of of rotorotor r resiresistanstance ce concontroltrol? ? ExpExplailain n its princiits principle of ple of operaoperation withtion with ssuuiittaabblle e cciirrccuuiit t ddiiaaggrraamms s aannd d cchhaarraacctteerriissttiiccss. . [[88++88]] 8.

8. (a) (a) What iWhat is a sels a self conf control mtrol mode of Syode of Syncnchronhronous moous motor?tor? (b)

(b) DraDraw w and explaiand explain n the block diagrathe block diagram m of of a a selself f concontroltrolled syncled synchronhronous motorous motor ffeed d ffrroom m a a tthhrreee e pphhaasse e iinnvveerrtteerr. . [[88++88]]

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