AC DRIVES. There are two type of AC motor Drives : 1. Induction Motor Drives 2. Synchronous Motor Drives

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1 AC DRIVES AC moto Dive ae ued in many indutial and dometic application, uch a in conveye, lift, mixe, ecalato etc. The AC moto have a numbe of advantage : Lightweight (0% to 40% lighte than equivalent DC moto) Inexpenive Low maintenance The Diadvantage AC moto : * The powe contol elatively complex and moe expenive Thee ae two type of AC moto Dive : 1. Induction Moto Dive. Synchonou Moto Dive

2 INDUCTION MOTOR DRIVES Thee-phae induction moto ae commonly ued in adjutable-peed dive (ASD). Baic pat of thee-phae induction moto : Theephae upply Thee-phae winding Stato Ai gap Roto winding Roto m T Stato Roto Ai gap

3 Thee-phae winding Roto winding Theephae upply Stato Ai gap Roto m T The tato winding ae upplied with balanced thee-phae AC voltage, which poduce induced voltage in the oto winding. It i poible to aange the ditibution of tato winding o that thee i an effect of multiple pole, poducing eveal cycle of magnetomotive foce (mmf) o field aound the ai gap. The peed of otation of field i called the ynchonou peed, which i defined by : ω i ynconou peed [ad/ec] N i ynconou peed [pm] o p p i numbe of pole ω i the upply fequency [ad/ec] f i the upply fequency [Hz] 10 f N N m i moto peed p

4 The moto peed The oto peed o moto peed i : ( 1S) m Whee S i lip, a defined a : S m S S O S N S N N S m Thee-phae winding Roto winding Theephae upply Stato Ai gap Roto m T

5 Equivalent Cicuit Of Induction Moto Thee-phae winding Roto winding Whee : Theephae upply I X Stato R Ai gap Roto m X T R i eitance pe-phae of tato winding R i eitance pe-phae of oto winding X i leakage eactance pe-phae of the winding tato X i leakage eactance pe-phae of the winding oto X m i magnetizing eactance Im I R m Reitane eponible fo Coe loe V Xm Rm R / Stato Ai gap moto

6 Pefomance Chaacteitic of Induction Moto I X R X Im I V Xm Rm R / Stato Ai gap moto Stato coppe lo : Roto coppe lo : Coe loe : P P P c cu cu 3I R ' ' 3( I ) R Vm V 3 3 R R m m

7 Pefomance Chaacteitic of Induction Moto - Powe developed on ai gap (Powe fopm tato to oto though ai gap) : ' R Pg 3( I ' ) S - Powe developed by moto : o - Toque of moto : o T d Pd S m P d P d P g P o Pg (1 S) (1 S) g P cu ( 1S) T P g d 3( I ' ) Pd 60 N m R S ' (1 S)

8 Pefomance Chaacteitic of Induction Moto Input powe of moto : P i 3V P c I P cu co P g m Output powe of moto : P o P d P noload Efficiency : Po P i P P c d P P cu noload P g

9 Pefomance Chaacteitic of Induction Moto If P g ( Pc P cu) and Pd P noload o, the efficiency can calculated a : P Pg (1 S) d 1S P P g g

10 Pefomance Chaacteitic of Induction Moto Geneally, value of eactance magnetization X m >> value Rm (coe loe) and alo X m ( R X So, the magnetizing voltage ame with the input voltage : ) V V m Theefoe, the equivalent cicuit i ; I X R X Ii X R X I=I Im I Im I V Xm Rm R / V Pi Xm R / Po Stato Ai gap moto Stato Ai gap oto

11 ) ( ) ( ) ( ' ' ' ' m m m i X X X j S R R S R R jx X X X Z Total Impedance of thi cicuit i : Pefomance Chaacteitic of Induction Moto Stato Ai gap oto V Ii Im I X X R R / Pi Po I=I Xm The oto cuent i : 1 ' ' ' X X S R R V I

12 Ii V Pi Im X R X I=I I R / Po T d S R 3R R S ' ' V X X ' Stato Ai gap oto Tmax Td Tt TL Tm=TL Opeating point S=1 Nm =0 Smax S=Sm m Nm S=0 N Toque peed Chaacteitic

13 Thee egion opeation : 1. Motoing :. Regeneating : 3. Plugging : 0 S S 0 1 S 1 Fowad egeneation Toque Fowad motoing Revee plugging Tmax m m Tt m S=Sm -Smax S=-1 S=0 N Smax =0 S=1 Nm =0 S= -Tmax

14 Stating peed of moto i m = 0 o S = 1, Pefomance Chaacteitic of Induction Moto Stating toque of moto i : ' ' ' 3 t X X S R R V R T Slip fo the maximum toque S max can be found by etting : 0 ds T d d So, the lip on maximum toque i : 1 ' ' max X X R R S

15 ' max 3 X X R R V T Pefomance Chaacteitic of Induction Moto Toque maximum i : And the maximum egeneative toque can be found a : ' max 3 X X R R V T Whee the lip of moto = - S m

16 ' ' ' 3 d X X S R R S V R T Speed-Toque Chaacteitic : ' ' S R R X X ' ' 3 d X X S V R T ' ' 3 t X X V R T Fo the high Slip S. (tating) So, the toque of moto i : And tating toque (lip S=1) i :

17 R S R X X ' ' d R S V T ' 3 Fo low lip S egion, the moto peed nea unity o ynchonou peed, in thi egion the impedance moto i : So, the moto toque i : 1 ' ' max X X R R S And the lip at maximum toque i : The maximum moto toque i : ' ' ' 3 d X X S R R S V R T

18 Stato Voltage Contol Contolling Induction Moto Speed by Adjuting The Stato Voltage AC Vaiable Voltage Souce V IM Td T d S R 3R R S ' ' V X X ' Td V > V1 > V Tmax Ii X R X I=I Im I V Pi R / Po Tt Tt1 Tt TL Stato ai gap oto S=1 Nm =0 1 S=0 N

19 AC Voltage contolle fo 3 phae Induction Moto

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22 Fequency Voltage Contol Contolling Induction Moto Speed by Adjuting the Fequency of Stato Voltage AC Vaiable Voltage Souce V f IM Td T d S R 3R R S ' V ' X X ' T max T d f < < f1 f Ii X R X I=I T t V f Im I R / T t1 T t T L Pi Po Stato Ai gap oto S=1 m =0 S=0 f 1 S=0 f1 S=0 f

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28 Block diagam of Vaiable fequency peed contol

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30 Voltage ouce invete fed Induction moto dive

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38 Cuent Souce Invete fed Induction moto dive

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42 Compaion of CSI and VSI dive

43 Cycloconvete fed Induction moto dive

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48 CONTROLLING INDUCTION MOTOR SPEED USING ROTOR RESISTANCE (Roto Voltage Contol)

49 Wound oto induction moto application cane

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51 CONTROLLING INDUCTION MOTOR SPEED USING ROTOR RESISTANCE (Conventional Roto Reitance Contol) Equation of Speed-Toque : T d S R 3R R S ' ' V X X ' In a wound oto induction moto, an extenal thee-phae eito may be connected to it lip ing, Stato RX T d 3V S R' Roto RX Thee-phae upply RX

52 Appoximate Toque poduced in thee phae IM i T d KE R R X Extenal eitance i added in each phae of oto though lip ing a hown in the fig. Coeponding toque, ' ' KER Td ' R X ' The tating toque at =1 fo R and can be witten a R T t KE R R X and T KE R ' ' t ' R X

53 The maximum toque condition i.e. R /X We get T max KE X Maximum toque i independent of oto eitance, whateve may be the oto eitance.

54 Thee eito Rx ae ued to contol moto tating and topping anywhee fom educed voltage moto of low hoepowe up to lage moto application uch a mateial handling, mine hoit, cane etc. The mot common application ae: AC Wound Roto Induction Moto whee the eito i wied into the moto econday lip ing and povide a oft tat a eitance i emoved in tep. AC Squiel Cage Moto whee the eito i ued a a ballat fo oft tating alo known a educed voltage tating.

55 The developed toque may be vaying the eitance Rx The toque-peed chaacteitic fo vaiation in oto eitance Thi method inceae the tating toque while limiting the tating cuent. The wound oto induction moto ae widely ued in application equiing fequent tating and baking with lage moto toque (cane, hoit, etc)

56 Advantage: Reduce the tating cuent Inceae the tating toque Powe facto of the line i impoved Thee i no hamonic in the line cuent Speed contol i mooth and of wide ange Diadvantage: Efficiency i educed due to watage of lip enegy in the oto cicuit If oto eitance ae not equal, unbalance in cuent and voltage

57 Static Roto Reitance Contol The thee-phae eito may be eplaced by a thee-phae diode ectifie and a DC choppe. The inducto Ld act a a cuent ouce Id and the DC choppe vaie the effective eitance: Whee k i duty cycle of DC choppe R e R( 1k) The peed can contolled by vaying the duty cycle k, (lip powe) Id Stato D1 D3 D5 Ld Roto Vd GTO R Vdc Thee-phae upply D4 D6 D

58 Slip-Recovey Dive fo Wound-Field Induction Moto The powe in the ai gap potion which i not conveted into mechanical powe i called lip powe. In a wound-field induction moto the lip ing allow eay ecovey of the lip powe which can be electonically contolled to contol the peed of the moto.

59 Slip-Recovey Dive fo Wound-Field Induction Moto (cont d) The oldet and implet technique to invoke thi lippowe ecovey induction moto peed contol i to mechanically vay the oto eitance.

60 Slip-powe ecovey dive ae ued in the following application: Lage-capacity pump and fan dive Vaiable-peed wind enegy ytem Shipboad VSCF (vaiable-peed/contant fequency) ytem Vaiable peed hydo-pump/geneato Utility ytem flywheel enegy toage ytem

61 The lip powe in the oto cicuit may be etuned to the upply by eplacing the DC convete and eitance R with a thee-phae full convete (invete) Thee-phae upply Id Tanfome Na:Nb Stato D1 D3 D5 Ld T1 T3 T5 Roto Vd Vdc Slip Powe D4 D6 D T T4 T6 Diode ectifie Contolled ectifie/ invete

62 Example: A thee-phae induction moto, 460, 60Hz, ix-pole, Y connected, wound oto that peed i contolled by lip powe uch a hown in Figue below. The moto paamete ae R=0.041, R =0.044, X=0.9, X =0.44 and Xm=6.1. The tun atio of the oto to tato winding i nm=n/n=0.9. The inductance Ld i vey lage and it cuent Id ha negligible ipple. The value of R, R, X and X fo equivalent cicuit can be conideed negligible compaed with the effective impedance of Ld. The no-load of moto i negligible. The loe of ectifie and Dc choppe ae alo negligible. The load toque, which i popotional to peed quae i 750 Nm at 1175 pm. (a) If the moto ha to opeate with a minimum peed of 800 pm, detemine the eitance R, if the deied peed i 1050 pm, (b) Calculate the inducto cuent Id. (c) The duty cycle k of the DC choppe. (d) The voltage Vd. (e) The efficiency. (f) The powe facto of input line of the moto.

63 V volt p x ad / x377 / ad / The equivalent cicuit :

64 The dc voltage at the ectifie output i : V d E I d R SV e I N N d R( 1k) SV n m and Fo a thee-phae ectifie, elate E and Vd a : Vd 1.65 x E E N Uing : E SV SV n N V SV d If P i the lip powe, ai gap powe i : Developed powe i : P d n m 3( P g m P ) P Pg S P 3( S) S 3P (1 S) S

65 Becaue the total lip powe i 3P = Vd Id and So, P d (1 S) V S d I d T L m P d T L T (1 S) L m m Subtituting Vd fom Solving fo Id give : Vd SV n In equation Pd above, o m : TL Id.3394V n m Which indicate that the inducto cuent i independent of the peed. Fom equation : V I R I R( 1k) and equation : So, d d I R( 1k) SV Which give : d e d n m Id R( 1 k) S.3394 SV n m V SV d n m

66 The peed can be found fom equation : m ( 1 S) 1 S IdR(1 k).3394v n m I R( 1 k).3394 SV n d a : m m 1 TL R(1 k) (.3394V n ) m Which how that fo a fixed duty cycle, the peed deceae with load toque. By vaying k fom 0 to 1, the peed can be vaied fom minimum value to m 180 / ad / Fom toque equation : TL K v m x Nm 1175

67 Fom equation : T Id.3394V nm x I d A.3394 x65.58 x 0.9 L The coeponding inducto cuent i : The peed i minimum when the duty-cycle k i zeo and equation : IdR(1 k) m ( 1 S) V n 78.13R ( x65.58 x m ) 0.9 And : R. 3856

68 Speed Contol by Roto Rheotat Recall that the toque-lip equation fo an induction moto i given by: T e P R V 3. R R / ( L L ) e e l l Fom thi equation it i clea that the toque-lip cuve ae dependent on the oto eitance R. The cuve fo diffeent oto eitance ae hown on the next lide fo fou diffeent oto eitance (R 1 -R 4 ) with R 4 >R 3 >R >R 1.

69 Speed Contol by Roto Rheotat (cont d) An electonic choppe implementation i alo poible a hown below but i equally inefficient.

70 Slip powe ecovey cheme

71 Intead of wating the lip powe in the oto cicuit eitance, a bette appoach i to convet it to ac line powe and etun it back to the line. Two type of convete povide thi appoach: 1) Static Kame Dive - only allow opeation at ub-ynchonou peed. ) Static Schebiu Dive - allow opeation above and below ynchonou peed.

72 Static Kame Dive (cont d) A chematic of the tatic Kame dive i hown below:

73 Static Kame Dive (cont d) The machine ai gap flux i ceated by the tato upply and i eentially contant. The oto cuent i ideally a 6-tep wave in phae with the oto voltage.

74 Static Kame Dive (cont d) The moto fundamental phao diagam efeed to the tato i a hown below: V = tato phae voltage, I =tato cuent, I f = fundamental oto cuent efeed to the tato, g = ai gap flux, I m =magnetizing cuent, and =PF angle.

75 Static Kame Dive (cont d) The voltage V d i popotional to lip, and the cuent I d i popotional to toque. At a paticula peed, the invete fiing angle can be deceaed to deceae the voltage V I. Thi will inceae I d and thu the toque. A implified toque-peed expeion fo thi implementation i developed next.

76 Expeion fo toque and peed Voltage V d (neglecting tato and oto voltage dop) i given by: V d 1.35V L n whee =pe unit lip, V L = tato line voltage and n 1 =tato-to-oto tun atio. The invete dc voltage V I i given by: 1

77 Expeion fo toque and peed The invete dc voltage V I i given by: V I 1.35V L co n whee n =tanfome tun atio (line ide to invete ide) and =invete fiing angle.

78 Expeion fo toque and peed(cont d) Fo invete opeation, /<<. In teady tate V d =V I (neglecting loe in inducto) n n 1 co The oto peed i given by: n 1 (1 ) e (1 co ) e (1 co ) e n if n 1 =n

79 Expeion fo toque and peed(cont d) Thu oto peed can be contolled by contolling invete fiing angle,. At =, =0 and at =/, = e.

80 Expeion fo toque and peed(cont d) Neglecting loe, the powe equation can be witten a P V I g I d Pm (1 ) P g Tem Tee (1 ) P Whee P =ai gap powe, P =mechanical g m output powe, P= numbe of pole

81 Expeion fo toque and peed (cont d) We know that the toque P Pg Te The toque may be expeed a: P 1.35V L Te Id n e e 1

82 The below figue how the toque-peed cuve at diffeent invete angle.

83 Static Kame Dive (cont d) At zeo peed (=1) the moto act a a tanfome and all the eal powe i tanfeed back to the line (neglecting loe). The moto and invete only conume eactive powe. At ynchonou peed (=0) the powe facto i the lowet and inceae a lip inceae. The PF can be impoved cloe to ynchonou peed by uing a tep-down tanfome. The invete line cuent i educed by the tanfome tun atio -> educed PF.

84 Static Kame Dive (cont d) A futhe advantage of the tep-down tanfome i that ince it educe the invete voltage by the tun atio, the device powe ating fo the witching device in the invete may alo be educed.

85 AC Equivalent Cicuit of Static Kame Dive(cont d) The pe-phae equivalent cicuit deived fom thee equation (efeed to the oto) i hown below:

86 Toque Expeion The aveage toque developed by the moto = total fundamental ai gap powe ynchonou peed of moto T e ' P Pgf PIf RA 3 3 e whee P gf = fundamental fequency pe-phae ai gap powe.

87 Toque Expeion (cont d) The toque equation in tem of cicuit paamete ' P V RA Te 3 ' R ' A e R X l X l

88 Static Schebiu Dive The tatic Schebiu dive ovecome the fowad motoing only limitation of the tatic Kame dive. Regeneative mode opeation equie the lip powe in the oto to flow in the evee diection. Thi can be achieved by eplacing the diode bidge ectifie with a thyito bidge. Thi i the baic topology change fo the tatic Schebiu dive fom the tatic Kame dive.

89 Static Schebiu Dive (cont d)

90 Mode of Opeation Fou mode of opeation of a Schebiu dive Mode 1: Subynchonou motoing Mode : Supeynchonou motoing Mode 3: Subynchonou egeneation Mode 4: Supeynchonou egeneation

91 Mode-1:Subynchonou motoing Identical to Static Kame ytem Stato I/P o ai gap powe(p g ) i +ve Slip powe (P g ) i +ve and Retun back to line Line upplie P m =(1-)P g conumed by the haft Slip fequency cuent ceate RMF in the ame diection a in the tato

92 Mode 3: Subynchonou egeneation The haft i diven by load mechanical enegy conveted into electical enegy and pumped out of tato With ve toque, mech. Powe i/p P m inceae with peed Slip i +ve and P g i ve -ve lip powe i fed to the oto

93 Mode :Supeynchonou motoing Speed inceae beyond ynchonou peed Slip i ve Slip powe abobed by the oto The phae equence of lip fequency i eveed o RMF i oppoite to that of tato

94 Mode 4: Supeynchonou egeneation P g emain contant but additional mech powe i/p i eflected a lip powe o/p Cycloconvete phae equence i now eveed o that the oto field otate in oppoite diection

95 Static Schebiu Dive (cont d) One of the limitation of the peviou topology i that line commutation of the machine-ide convete become difficult nea ynchonou peed becaue of exceive commutation angle ovelap. A line commutated cycloconvete can ovecome thi limitation but add ubtantial cot and complexity to the dive.

96 (a) Subynchonou motoing (b) Subynchonou egeneation

97 (c) Supeynchonou motoing (d) Supeynchonou egeneation

98 Static Schebiu Dive (cont d) Anothe appoach i to ue a double-ided PWM voltage-fed convete ytem a hown below: