Drives

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Drives

  1. 1. bgf@ee.iitb.ac.in IIT Bombay Electrical Dept. of Electric Drives Evolution & Overview CEP on Variable Speed Drives, April 9-11’ 20 03
  2. 2. CEP on Variable Speed Drives, April 9-11’ 20 03 Definition of Drive IIT Bombay Electrical Dept. Systems Employed for imparting motion. Evolution of Drive: • Came into being with the invention of wheel in the pro to historic period of around 3500 B.C. • From 3500 B.C. to 17th century not much conscious effort in the control of motion • Conscious effort to control motion:bgf@ee.iitb.ac.in invention of speed governors • Advent of electric motor in the beginning of 19th century led to Electric Drives.
  3. 3. CEP on Variable Speed Drives, April 9-11’ 20 03 Advantages of Electric Drive IIT Bombay Electrical Dept. • All the advantages of Electrical energy over other forms of energy are available • Flexibility in control to negotiate loads • Higher efficiency • Effective non-destructive braking is possible → Regenerative braking is possiblebgf@ee.iitb.ac.in • Longer life, lower noise, lesser maintenance, cleaner operation
  4. 4. bgf@ee.iitb.ac.in IIT Bombay Electrical Dept. Source Motor Structure of Electric Drive Load CEP on Variable Speed Drives, April 9-11’ 20 03
  5. 5. Simplest Drive : Natural CEP on Variable Speed Drives, April 9-11’ 20 03 Characteristics IIT Bombay Electrical Dept. • Speed Torque characteristics TL ω Tmbgf@ee.iitb.ac.in • Control of speed cannot be T accomplished
  6. 6. For controlling speed CEP on Variable Speed Drives, April 9-11’ 20 03 IIT Bombay Electrical Dept. • Control source characteristics: Impractical • To change motor characteristics: Leads to poor performance characteristics Motivation to develop a device which will present the motor load system with abgf@ee.iitb.ac.in variable source characteristic
  7. 7. bgf@ee.iitb.ac.in IIT Bombay Electrical Dept. Source Unit Control Power Command Modulator Unit Sensor Motor Power Modulator Load CEP on Variable Speed Drives, April 9-11’ 20 03
  8. 8. CEP on Variable Speed Drives, April 9-11’ 20 03 IIT Bombay Electrical Dept. • Control Unit Imparts Control Law to be followed • High Performance drive Closed loop Control Sensing • Sensing Protectionbgf@ee.iitb.ac.in
  9. 9. CEP on Variable Speed Drives, April 9-11’ 20 03 DC Motor Drive IIT Bombay Electrical Dept. Ra Ia Eb = K e Ф ω V = E b + I a Ra V Eb Vf T=KeФIa ω = [ V/(K e Ф ) ] – [R a /(K e Ф )2 ] Tbgf@ee.iitb.ac.in
  10. 10. Speed can be varied by varying CEP on Variable Speed Drives, April 9-11’ 20 03 IIT Bombay Electrical Dept. • Resistance connected in series with the armature • Applied voltage • Field fluxbgf@ee.iitb.ac.in
  11. 11. CEP on Variable Speed Drives, April 9-11’ 20 03 Strategy: IIT Bombay Electrical Dept. • Vary Applied Voltage Keep Flux Constant Constant Torque Drive When Rated Speed is reachedbgf@ee.iitb.ac.in • Applied Voltage = Rated Voltage Vary the field flux Constant Power Drive
  12. 12. Methods of Armature Voltage CEP on Variable Speed Drives, April 9-11’ 20 03 Control IIT Bombay Electrical Dept. When the source is AC a) Transformer with tap changer followed by diode bridge b) Line commutated thyristorised AC to DC converter When the source is DC a) Chopper or dc-dc Converterbgf@ee.iitb.ac.in Structure of the power modulator depends on the quadrants in which the drive is intended to operate
  13. 13. Performance of DC Drives CEP on Variable Speed Drives, April 9-11’ 20 03 IIT Bombay Electrical Dept. Advantages: • Simple Control • Flux and Current are decoupled => Fast response (Electrical) • Generally involves single stage of power conversion Disadvantages: • Fragile Commutator and Brush • Frequent maintenance • Inability to operate at high speed, dusty and contaminated atmosphere • Higher weight, volume and hence slow mechanical responsebgf@ee.iitb.ac.in • Higher cost of the machine
  14. 14. Induction Motor Drive CEP on Variable Speed Drives, April 9-11’ 20 03 IIT Bombay Electrical Dept. Rotating Magnetic field Ns= 120f/P Nr = ( 1 – s ) Ns T = ( 3/ωs )(V2/r’2) s Speed can be controlled by varying: • Magnitude of the stator voltage • Frequency (i. e .N s ) and the magnitude of the statorbgf@ee.iitb.ac.in voltage • Rotor resistance • Injecting a variable voltage in the rotor circuit
  15. 15. Stator Voltage Control CEP on Variable Speed Drives, April 9-11’ 20 03 IIT Bombay Electrical Dept. For a given torque S α 1/V2 TL Implications:: Power out put =(1-s)Pg Power Input = Pg N η = (1-s) V reducing η decreases as speed is reduced T α V2 Tbgf@ee.iitb.ac.in IαV T/I α V T/I ratio falls as speed is reduced Implementation: AC Voltage Controllers
  16. 16. Speed Control by varying f , V CEP on Variable Speed Drives, April 9-11’ 20 03 IIT Bombay Electrical Dept. Ns= 120f/P V = E = 4.44 KωNs f Фp Фp=V/(4.44 KωNs f ) Strategy: • Constant Torque Mode Vary applied voltage in sympathy with f so that V/f= V rated /f rated = Ф rated Once rated voltage is reached keep V= V rated and vary fbgf@ee.iitb.ac.in • Constant Power Mode Flux weakening mode of operation T/I ratio falls
  17. 17. bgf@ee.iitb.ac.in IIT Bombay Electrical Dept. 1) 2) to DC AC converter Cycloconverter to AC DC Implementation inverter I.M I.M CEP on Variable Speed Drives, April 9-11’ 20 03
  18. 18. Performance of V/f control scheme CEP on Variable Speed Drives, April 9-11’ 20 03 IIT Bombay Electrical Dept. • No Commutator brushes • Low weight,volume • Cheaper Motor • Requires complicated and costly power modulator →two stages of power conversion • Control is more involved • Slow response • Drive is costlybgf@ee.iitb.ac.in To overcome the problem of slow response: Vector Controlled Drive Direct Torque Controlled Drive
  19. 19. Slip ring Induction Motor Drive CEP on Variable Speed Drives, April 9-11’ 20 03 IIT Bombay Electrical Dept. For a given torque : r’2 α s Speed can be varied by varying r’2 But η falls with speed η is improved if the rotor power is fed back to the sourcebgf@ee.iitb.ac.in
  20. 20. bgf@ee.iitb.ac.in IIT Bombay Electrical Dept. Source Vd Vi Pg = (1−s)P g+ sPg Static Scherbius Drive CEP on Variable Speed Drives, April 9-11’ 20 03
  21. 21. Performance of wound field CEP on Variable Speed Drives, April 9-11’ 20 03 Induction Motor Drive IIT Bombay Electrical Dept. • Simple control structure • Line commutated converter can be used • Power to be handled by Semiconductor = s Pg • Motor is expensive • Restricted speed range • Poor power factorbgf@ee.iitb.ac.in • Operation mainly in the sub synchronous speed range
  22. 22. Synchronous Motor Drive CEP on Variable Speed Drives, April 9-11’ 20 03 IIT Bombay Electrical Dept. High Power Drive Doubly excited system and hence power factor is controllable Ns= 120f/P) T = (3/ωs) * (V E f/Xs) sin δ Methods of speed control Constant V/f mode of operation below rated speed • True synchronous : Frequency is changed slowly Mode of Control • Self Control Mode : Stator frequency tracks the rotor speed Of operation Permanent Magnet SM Drivebgf@ee.iitb.ac.in Brushless DC Motor Drive Implementation : Same as I.M. Drive
  23. 23. Performance of Synchronous CEP on Variable Speed Drives, April 9-11’ 20 03 Motor Drive IIT Bombay Electrical Dept. • Technically superior when large amount of power is involved • Load commutation simplifies the power circuit configuration • Reduction in inverter rating • Higher efficiency • Better speed regulation • Complicated controlbgf@ee.iitb.ac.in • Bulkier machine • Problems associated with the permanent magnets
  24. 24. Squirrel Cage Induction Motor CEP on Variable Speed Drives, April 9-11’ 20 03 IIT Bombay Electrical Dept. Advantages:- • No commutator and brush • Low weight, volume and cost Disadvantages:- • Requires a complicated and costly power modulator and two stages of power conversionbgf@ee.iitb.ac.in • Control is more involved • Slow response • Drive is costly
  25. 25. Wound Rotor Induction Motor CEP on Variable Speed Drives, April 9-11’ 20 03 Drive IIT Bombay Electrical Dept. Advantages:- • Simple control • Line commutation can be employed Disadvantages:- • Motor is expensivebgf@ee.iitb.ac.in • Routine maintenance is required • Restricted Speed Range
  26. 26. Synchronous Motor Drive CEP on Variable Speed Drives, April 9-11’ 20 03 IIT Bombay Electrical Dept. Advantages:- • Technically superior when large amount of power is involved • When load commutation is employed, thyristors without the conventional commutation circuit can be employed for the inverter and hence the overall cost is less Disadvantages:- • Complicated controlbgf@ee.iitb.ac.in • Costly, bulky and of large volume • Brushes still require considerable amount of maintenance
  27. 27. Permanent Magnet Synchronous CEP on Variable Speed Drives, April 9-11’ 20 03 Motor IIT Bombay Electrical Dept. Brushless D.C. Motor Advantages:- • No brushes • Very high speeds possible • Less maintenance is required Disadvantages:-bgf@ee.iitb.ac.in • Expensive • Problem associated with the permanent magnets
  28. 28. APPLICATION REQUIREMENTS CEP on Variable Speed Drives, April 9-11’ 20 03 IIT Bombay Electrical Dept. 1. TYPE OF LOAD DRIVEN 2. LOAD REQUIREMENT - CONSTANT TORQUE - CONSTANT T, TST, TOVERLOAD 3. HP RATING AND SPEED RANGE - ABOVE NS AND BELOW NS 4. EXISTING MOTOR TO BE USEDbgf@ee.iitb.ac.in 5. ENVIRONMENTAL CONSIDERATIONS
  29. 29. CONCLUSION CEP on Variable Speed Drives, April 9-11’ 20 03 IIT Bombay Electrical Dept. 1. WE ARE LIVING IN TRULY GLOBAL SOCIETY - FREE FROM TRADE BARRIERS - FIERCE INDUSTRIAL COMPETITION - WARS WILL BE FOUGHT ON ECONOMIC RATHER THAN MILITARY FRONTS 2. POWER ELECTRONIC APPLICATIONS WILL SPREAD EVERYWHERE - INDUSTRY, RESIDENTIAL, COMMERCIAL, TRANSPORTATION, MILITARY 3. REDUCED COST AND SIZE, INCREASED PERFORMANCE AND INCREASED ENERGY SAVINGbgf@ee.iitb.ac.in 4. TWO TECHNOGIES WILL BE MOST DOMINATING - COMPUTERS AND POWER ELECTRONICS WITH MOTION CONTROL
  30. 30. P.M.S.M. & SRM DRIVE CEP on Variable Speed Drives, April 9-11’ 20 03 WHY P.M. MACHINES? •Induction Machine, Synchronous Machine, Permanent IIT Bombay Electrical Dept. Magnet Synchronous Machine •Same Stator •Torque Producing losses + Field Cu losses η • (P.F * ) 20 % for 10 HP & 50% for 1 HP •T/A • Rotor inertia + weight torque / weight “ If the course of future research produces a magnet of greater energy ………. an ideal magnet would retain Br = 12.6 KG and H = 2 K Oe….. the improvement in output, P.F & Efficiency of PMSM would be remarkable” (Merill, 1955)bgf@ee.iitb.ac.in 15 KG . H = 15 K Oe Robust High speed operation !! No Control over Field Current Constant Power Zone ?? Line Start Machine - Cage Design
  31. 31. bgf@ee.iitb.ac.in IIT Bombay Electrical Dept. CEP on Variable Speed Drives, April 9-11’ 20 03
  32. 32. Classification CEP on Variable Speed Drives, April 9-11’ 20 03 IIT Bombay Electrical Dept. 1. Variable Speed • Surface Mount Magnets are mounted on the rotor Large air gap: Armature reaction is negligible No damping action • Interior PMSM Magnets are buried inside the rotor Xd is less than Xq Small air gap : Armature reactionbgf@ee.iitb.ac.in Surface Mount Interior PMSM
  33. 33. bgf@ee.iitb.ac.in IIT Bombay Electrical Dept. CEP on Variable Speed Drives, April 9-11’ 20 03
  34. 34. CEP on Variable Speed Drives, April 9-11’ 20 03 IIT Bombay Electrical Dept. • Two types of Machines – PMSM and BDCM PMSM BDCM Sinusoidal Stator Wdg Concentrated Wdg EMF is sinusoidal EMF is Rectangular 180 degree phase cond. 120 degree phase cond. • Power Density - 15% higher in BDCM • Torque / Inertia - 15% higher in BDCM • Speed Encoder - Expensive in PMSMbgf@ee.iitb.ac.in • Torque Ripple - less in PMSM
  35. 35. * iq ω * r Controller T * Te* ÷ Inverse Transformation CEP on Variable Speed Drives, April 9-11’ 20 03 ωr * id θr IIT Bombay Electrical Dept. Resolver Signal Processor * * * ic ib ia ia Hysteresis Controller & Base Drive T1 T3 T5 Amplifiers D1 D3 D5 ib v c ωrbgf@ee.iitb.ac.in T4 D4T6 D6T2 D2 T1,T2,T3,T4,T5,T6 PMSM and BDCM drive system
  36. 36. CEP on Variable Speed Drives, April 9-11’ 20 03 IIT Bombay Electrical Dept. Back Emf and Current Waveforms of a brushless DC motorbgf@ee.iitb.ac.in PMSM steady state results BDCM steady state results
  37. 37. CEP on Variable Speed Drives, April 9-11’ 20 03 IIT Bombay Electrical Dept. • PMSM Reference current are sinusoidal • BLDC Reference current are Trapezoidal • Absolute position sensor Position of rotor axis with stator d axis • Current is controlled with in hysterisis band Q ⇒ D q-axis id =ia + ib cos 120 + ic cos 120 iabgf@ee.iitb.ac.in iq = −ib sin 120 + ic sin 240 d-axis T ∝ φ ia In DC the flux produces d axis current
  38. 38. bgf@ee.iitb.ac.in IIT Bombay Electrical Dept. MOTOR (S.R.M) DRIVE SWITCHED RELUCTANCE CEP on Variable Speed Drives, April 9-11’ 20 03
  39. 39. Advantages:- CEP on Variable Speed Drives, April 9-11’ 20 03 IIT Bombay Electrical Dept. • All the technical superiority of the Squirrel Cage Induction Motor Drive is obtained or even enhanced at a very low cost due to:- Simple motor construction: Stator consisting of concentrated windings and rotor without any windings Low inertia, volume and cost Simple unipolar power modulator requiredbgf@ee.iitb.ac.in No possibility of Shoot-through fault Due D.C. series motor characteristics wide range of speed control is possible.Suitable for traction load
  40. 40. Disadvantages:- CEP on Variable Speed Drives, April 9-11’ 20 03 IIT Bombay Electrical Dept. Accurate determination the coil inductance is required. Rotor position encoder is employed which curtail some of the robustness of the drive Accurate torque control can be a problem as accurate determination of coil inductance is difficult (due to saturation)bgf@ee.iitb.ac.in
  41. 41. bgf@ee.iitb.ac.in IIT Bombay Electrical Dept. Vdc θ βr βs A B S.R.M. Diagram Rotor Stator coil Stator pole Rotor pole CEP on Variable Speed Drives, April 9-11’ 20 03
  42. 42. bgf@ee.iitb.ac.in IIT Bombay Electrical Dept. Inductance of coil A Lmin Lmax θ0 θ1 θ2 Rotor pole pitch Inductance Profile θ3 θ4 CEP on Variable Speed Drives, April 9-11’ 20 03
  43. 43. Voltage Equation CEP on Variable Speed Drives, April 9-11’ 20 03 v = r i + dϕ IIT Bombay Electrical Dept. dt Assuming r = 0 , d v = dt (Li) = L di + i dL dθ dt d θ dt dθ = angular speed = ω dt v = L di + i dL ω dt dθbgf@ee.iitb.ac.in Transformer Rotational Voltage Voltage term term
  44. 44. Torque Equation CEP on Variable Speed Drives, April 9-11’ 20 03 Assumptions:− IIT Bombay Electrical Dept. Saturation is neglected Linear system Inductance(L) is independent of current Τ = δ ω fld ( i, θ) (1) δθ ω = 1 *F* φ = 1 * N * i * φ (2) fld 2 2 Νοω, L = N φ / i or Nφ =Li Substituting Nφ = Li in (2) ωf1d = 1 Li2bgf@ee.iitb.ac.in (3) 2 Substituting (3) in (1) T = 1 i2 δ L 2 δθ
  45. 45. bgf@ee.iitb.ac.in IIT Bombay Electrical Dept. Diagram of Elementary Torque Production idealistic idealistic torque developed current of torque developed current of coil A coil A θ0 θ0θ0 θ0 θθ1 1 θ1θ θ1 θθ2 θ 2 θ2 θ2 θ 3 θ3θ3 θ3 CEP on Variable Speed Drives, April 9-11’ 20 03
  46. 46. bgf@ee.iitb.ac.in IIT Bombay Electrical Dept. dcVdc1 source1 S R L D dc Vdc2 Primitive Inverter source 2 the motor Vdc1 =V one phase of dc2 CEP on Variable Speed Drives, April 9-11’ 20 03
  47. 47. CEP on Variable Speed Drives, April 9-11’ 20 03 L/Φ/I Diagram IIT Bombay Electrical Dept. Imax one rotor pole pitch i (coil current) φ ( flux) Lmax L(coil inductance) L,i,φ θ0bgf@ee.iitb.ac.in θi θ0 θx θl θn θm rotor angle (θ )
  48. 48. Control Strategy for S.R.M. CEP on Variable Speed Drives, April 9-11’ 20 03 IIT Bombay Electrical Dept. As S.R.M is a singly excited system, T α Φ2 -------------(a) If applied Voltage and dwell angle is kept α constant, Φ α 1/ω --------------(b) By eq. (a) and (b) , T α 1/ω2 and Power α 1/ωbgf@ee.iitb.ac.in ⇒D.C. series motor characteristics ⇒Not desirable for a practical drive
  49. 49. CEP on Variable Speed Drives, April 9-11’ 20 03 IIT Bombay Electrical Dept. • To make it a constant torque drive, voltage applied to the phase is controlled in accordance with the speed • How to control this voltage with speed so that flux remains at its rated value? - Phase current is controlled within a hysteresis band through the chopping control of the phase switchbgf@ee.iitb.ac.in • How to get the values of θi and θx ?
  50. 50. Determination of θi CEP on Variable Speed Drives, April 9-11’ 20 03 IIT Bombay Electrical Dept. Define θ ′ 0 = θ 0 - θ i From the voltage equation : - V = L di/dt + i (dL/d θ ) ω For the period, θ i → θ 0, dL/d θ = 0 and L = L min ∴ V = L min di/dt IL t or, ∫ di 0 = (V/L min ) ∫ dt 0 Where, I L = current at θ 0 for rated torquebgf@ee.iitb.ac.in or, I L = V. t/L min or, t = I L . L min /V Now, θ ′ 0 = ω t therefor e, θ ′ 0 = I L • L min • ω / V Hence , θ i = θ 0 - θ ′ 0 = f ( I L , ω , V )
  51. 51. Determination of θx CEP on Variable Speed Drives, April 9-11’ 20 03 IIT Bombay Electrical Dept. θx is controlled such that θx – θi or θc is kept constant and also θm < θn As base speed is reached => chopper duty ratio = unity => phase voltage saturates Further increase in speed=> T α 1/ω2 For constant horse power operation=> T α 1/ωbgf@ee.iitb.ac.in
  52. 52. CEP on Variable Speed Drives, April 9-11’ 20 03 Flux(Φ) can be increased by increasing θc Beyond ωbase , θc is controlled in such a IIT Bombay Electrical Dept. manner so that the variation of flux with speed satisfies the following relation:- Φ α 1/√ω But , T α Φ2 Hence, T α 1/ω = constant Horse power mode of operation With increase in speed => θc is also increased => Limiting θc is reached, beyond whichbgf@ee.iitb.ac.in the motor enters into the D.C. series mode of operation i.e. now T α 1/ω2
  53. 53. CEP on Variable Speed Drives, April 9-11’ 20 03 Torque Speed Characteristic IIT Bombay Electrical Dept. constant torque region or chopping mode T=constant constant horse Tα 1/ω power mode or θ single pulse mode torque Tα 1/ω2 normal dc series modebgf@ee.iitb.ac.in ωb ωc Speed
  54. 54. 18 18 24 18 CEP on Variable Speed Drives, April 9-11’ 20 03 inductance profile θd = turn on delay angle IIT Bombay Electrical Dept. 42 θd = 60° - θ′0 → F.M. Lmin 60 = 18° → F.B. = 42° - θ′0 → R.M. rotor angle(θ) referance axis for forward referance axis for = 0° → R.B. forward motoring rotation reverse motoring and forward braking and reverse braking θc = dwell angle reverse current profile rotation θc = θ′0 + θx - θ 0 → F.M. for forward motoring = 18° → F.B. = θ′0 + θx → R.M. = 18° → R.B. θ0 θx θmbgf@ee.iitb.ac.in current profile for forward braking rotor angle(θ)
  55. 55. CEP on Variable Speed Drives, April 9-11’ 20 03 IIT Bombay Electrical Dept. chopping current ω∗r P.I. I* level power S.R.M speed Controller modulator command 18 R.M. F.M. 42 F.G. 60 Lminω θ0 F.M. rotor Vdc R.M. θd position 0 encoder R.G. Vdc ω inductance F.M. θc profile ω R.M. θx F.G.bgf@ee.iitb.ac.in R.G. θx 18
  56. 56. CEP on Variable Speed Drives, April 9-11’ 20 03 Diagram of θx and θ’0 IIT Bombay Electrical Dept. constant constant torque horse power torque α 1/ω2 region operation θm θx θ θ0bgf@ee.iitb.ac.in ωb ωc (base speed)(critical speed) ω
  57. 57. CEP on Variable Speed Drives, April 9-11’ 20 03 S.R.M. Inverter Topologies IIT Bombay Electrical Dept. 1. Classic Inverter: 2. Dual Rail Inverter: 3. Inverter for motor having bifilar winding: 4. C – dump Inverter: 5. Miller Inverter:bgf@ee.iitb.ac.in
  58. 58. Classic Inverter CEP on Variable Speed Drives, April 9-11’ 20 03 IIT Bombay Electrical Dept. Important features:- • The phase can be controlled independently • Device voltage rating is that of the D.C. link voltage Vd • Total no. of switches are required is as high as two switches per phase of the motor,bgf@ee.iitb.ac.in hence costly
  59. 59. bgf@ee.iitb.ac.in IIT Bombay Electrical Dept. 3− AC L C Vd D2 S1 S2 1 Classic Inverter phase D1 Sn n Sn+1 phase CEP on Variable Speed Drives, April 9-11’ 20 03
  60. 60. CEP on Variable Speed Drives, April 9-11’ 20 03 Dual Rail Inverter IIT Bombay Electrical Dept. Important feature:- • No. of switches required is lowered as now one switch/phase is required • Device voltage rating is twice that of the earlier circuit • Mismatch between the voltages of the upperbgf@ee.iitb.ac.in and lower capacitor affects the performance of the drive
  61. 61. bgf@ee.iitb.ac.in IIT Bombay Electrical Dept. 2Vd Vd Vd 1 S1 D1 n Dual Rail Inverter Sn Dn CEP on Variable Speed Drives, April 9-11’ 20 03
  62. 62. CEP on Variable Speed Drives, April 9-11’ 20 03 Inverter for motor having bifilar IIT Bombay Electrical Dept. winding Important features: • No. of switches required is reduced • Device voltage rating is increased • If the coupling is not perfect, device stresses will be higherbgf@ee.iitb.ac.in • Motor copper utilization is poor
  63. 63. bgf@ee.iitb.ac.in IIT Bombay Electrical Dept. Vd S1 D1 winding bifilar winding Sn Inverter for motor having bifilar Dn CEP on Variable Speed Drives, April 9-11’ 20 03
  64. 64. CEP on Variable Speed Drives, April 9-11’ 20 03 C – dump Inverter IIT Bombay Electrical Dept. Important features: • No. of active devices required is reduced • Phase wave-shape control is possible • Control becomes somewhat complicatedbgf@ee.iitb.ac.in
  65. 65. bgf@ee.iitb.ac.in IIT Bombay Electrical Dept. Vd C L Df S Vc1 C – dump Inverter S1 n Sn CEP on Variable Speed Drives, April 9-11’ 20 03
  66. 66. magnetising demagnetising CEP on Variable Speed Drives, April 9-11’ 20 03 IIT Bombay Electrical Dept. current phase i1 S1turned S1 turned θ on off upper limit Vc1 s turned on lower limit s turned θ offbgf@ee.iitb.ac.in inductor current i1 S turned off S turned θ on
  67. 67. CEP on Variable Speed Drives, April 9-11’ 20 03 Miller Inverter IIT Bombay Electrical Dept. Important features: • No. of switches and passive elements are reduced • Its performance quality is same as that of the classic inverter • Independent control of phases is somewhat lost • So far as the industrial drives are consideredbgf@ee.iitb.ac.in Miller Inverter has a slight edge over other configuration
  68. 68. bgf@ee.iitb.ac.in IIT Bombay Electrical Dept. Vd D S S1 D1 S2 Miller Inverter D2 S3 D3 CEP on Variable Speed Drives, April 9-11’ 20 03
  69. 69. bgf@ee.iitb.ac.in IIT Bombay Electrical Dept. il i (Inductor (Phase current) Vc1 current) S turned onS turned off S1 turned on S1turned off CEP on Variable Speed Drives, April 9-11’ 20 03
  70. 70. bgf@ee.iitb.ac.in IIT Bombay Electrical Dept. CEP on Variable Speed Drives, April 9-11’ 20 03

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