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controlled rectifiers

  1. 1. SEMINAR ON AC – DC CONVERTERS BY: ANKUR MAHAJAN M.E. I&C REGULAR -2011 ROLL NO. 112505
  2. 2. GOAL OF THE SEMINAR  SINGLE PHASE HALF WAVE & FULL WAVE CONVERTERS. SEMICONDUCTOR DEVICES – THE HEART OF INDUSTRIAL ELECTRONICS
  3. 3. MY OWN QUOTES :  “THE DEVELOPMENT OF EVERY NATION DEPEND UPON ITS POWER SOURCES, & POWER ELECTRONICS IS A MAGIC WAND WHICH GENERATE POWER SOURCES”  “POWER ELECTRONICS IS A LIFE BLOOD FOR MODERN COMPUTERS, COMMUNICATION & ELECTRONIC SYSTEMS , THUS WITHOUT IT OUR LIFE COMES TO HALT” WHAT IS THE MOST IMPORTANT REASON FOR RAPID DEVELOPMENT IN THE FIELD OF POWER ELECTRONIC DEVICES ?
  4. 4. PIE CHART OF WORL’S ENERGY PRODUCTION LEVEL  IN INDIA 70% OF ELECTRICAL ENERGY COMES FROM COAL ACCORDING TO IEEE JOURNAL ON POWER DELIVERY: WE HAVE NO FOSSIL FUELS NUCLEAR FOSSIL & NUCLEAR FUEL BY THE RENEWABLES END OF 22ND CENTURY. (A)USE EE 87 % EFFICIENTLY. 7% (B) IMPROVE CONVERSION 6 % EFFICIENCY. (C) USE RENEWABLES
  5. 5. INTRODUCTION  WHAT IS RECTIFICATION ?  RECTIFICATION REFERS TO PROCESS OF CONVERTING AN A.C. VOLTAGE OR CURRENT TO D.C. VOLTAGE OR CURRENT.  RECTIFIERS – RECTIFIER REFER TO POWER ELECTRONIC CONVERTERS WHERE THE ELECTRIC POWER FLOWS FROM A.C. SIDE TO THE D.C. SIDE.  NOTE: IN MANY SITUATIONS THE SAME CONVERTER CARRIES ELECTRICAL POWER FROM D.C. SIDE TO A.C. SIDE - INVERTERS
  6. 6. RECTIFIERS CLASSIFICATION
  7. 7. BECAUSE ON & OFF BECAUSE THYRISTOR CAN BE TURNED STATE OF DIODE IS ON BY CONTROL TERMINAL. i.e. GATE DETERMINED BY THE STATE OF THE CIRCUIT.
  8. 8. ASSUMPTIONS :  ALL THE DEVICES & CIRCUIT COMPONENTS ARE IDEAL i.e. Ton =Toff =zero  INPUT IS PURE SINE WAVE CHARACTERISTICS OF AN IDEAL SWITCH
  9. 9. TERMINOLOGIES  LET ‘f’ BE THE INSTANTANEOUS VALUE OF ANY VOLTAGE OR CURRENT ASSOCIATED WITH RECTIFIER CIRCUIT, THEN 
  10. 10. TERMINOLOGIES (CONT.)     Angle at Which SCR starts conducting  Angle at which SCR stops conducting
  11. 11. SINGLE PHASE FULLY CONTROLLED H/W RECTIFIER
  12. 12. FOR PURELY RESISTIVE LOAD  CURRENT FLOWS FROM  TO THROUGH LOAD BECAUSE SCR IS IN FPRWARD CONDUCTION MODE. π-α
  13. 13. CALCULATIONS  Average value of output voltage  1 vav   2vi sin tdt 2  On solving vi vav  (1  cos ) 2
  14. 14. CALCULATION OF RMS VALUE OF VOLTAGE  1 vrms   vo dt 2 2   1 vrms  2   2vi2 sin 2 t dt 1 v 2  Sin t  (1  cos 2t ) 2 vrms   (1  cos 2t )dt 2  i 2 vi 1 sin 2t  1 vrms  [ (t  ) ] 2 2  2
  15. 15. CALCULATION OF RMS VALUE OF VOLTAGE (CONT.)  On solving vi  sin 2 1 vrms  (1   )2 vi 2  2 vav  (1  cos ) 2  Form factor  sin 2 1  (1   ) 2 formfactor  vrms   2 vav 1  cos 
  16. 16. RESISTIVE – INDUCTIVE LOAD α to π π to β
  17. 17. RESISTIVE – INDUCTIVE LOAD Since thyristor does not conduct over the entire input so it is called DISCONTINUOUS CONDUCTION MODE
  18. 18. CALCULATIONS   t   vo  vi  vm sin t  2vi sin t v0  0, otherwise  1 vav  2   2vi sin tdt vi onsolving, vav  (cos   cos  ) 2
  19. 19. RMS VALUE OF OUTPUT VOLTAGE  1 1 vrms ( 2   2vi2 sin 2 tdt ) 2   i   v 1 1 vrms 2   (1  cos 2t )dt 2 sin 2 sin 2  i  (     v 1 1 vrms  2 2  2 2 1    sin 2  sin 2 Sin t  (1  cos 2t ) 2 vi (  1 vrms   2 2 2  2
  20. 20. SINGLE PHASE HALF CONTROLLED BRIDGE Assume, load is highly inductive Because 90% of loads are inductive CASE I T1 D3 LOAD A B T4 D2
  21. 21. SINGLE PHASE HALF CONTROLLED BRIDGE At ωt =π, D3 starts conducting and -ve voltage appear across T1 & it starts blocking voltage. THIS PROCESS IS CALLED LINE COMMUTATION SINCE LOAD IS HIGHLY INDUCTIVE FREEWHEELING CURRENT FLOWS T1 THROUGH D2-D3 FROM ωt =π To π+α A B D3 D2 D2 α to π
  22. 22. SINGLE PHASE HALF CONTROLLED BRIDGE  At ωt = π, T4 is in forward blocking mode at ωt = π +α T4 is triggered & +ve voltage appears across D2 and it stops conducting. A D3 T4 B  At ωt = 2π, D2 starts conducting and T4 is OFF, this is called LINE COMMUTATION
  23. 23. SINGLE PHASE HALF CONTROLLED BRIDGE 2π+α,α π 2π π+α Since thyristor does not conduct over the entire input so it is called DISCONTINUOUS CONDUCTION MODE Avg. current rating of thyristor is < that of diode, which is not desirable
  24. 24. CALCULATIONS Vav  vm 1 cos   Vav is +ve and Iav is also +ve so source is supplying power to the load or we can say that load is PASSIVE. Operation in 1st Vo Quadrant Vav 1 0.5 ------ Io π/2 π α
  25. 25. SINGLE PHASE HALF CONTROLLED BRIDGE  CASE II: CONTINUOUS CONDUCTION MODE α-π DURING α to π OPRATION OS SAME AS T1 T3 THAT OF CASE I. A B LOAD FROM π to π+α D4 STARTS CONDUCTING & T3 D4 D2 IS IN FORWARD BLOKING MODE. THUS NO CONDUCTION. T1 & D4 CONDUCTS.
  26. 26. SINGLE PHASE HALF CONTROLLED BRIDGE  FROM π to π+α FROM π+α to 2π T3 T1 A B D4 D4 At ωt = π+α, T3 IS TRIGGERED & T1 FROM 2π, D2 STARTS CONDUCTING & T1 IS IN FORWARD COMMUTATES ( LINE BLOKING MODE. COMMUTATION) THUS NO CONDUCTION. T3 & D2 CONDUCTS.
  27. 27. SINGLE PHASE HALF CONTROLLED BRIDGE 2π+α,α 2π π π+α Since thyristor conducts over the entire input so it is called CONTINUOUS CONDUCTION MODE
  28. 28. SINGLE PHASE HALF CONTROLLED BRIDGE CONTINUOUS DISCONTINUOUS CONDUCTION MODE CONDUCTION MODE
  29. 29. FULLY CONTROLLED BRIDGE ASSUMPTIONS: a) LOAD CURRENT IS CONSTT. & RIPPLE FREE. b) Io IS CONTINUOUS. IN THE +VE HALF, T1 T2 ARE FORWARD BIASED. IN THE NEGATIVE HALF T3 T4 ARE FORWARD BIASED. TI & T2 CONTINUE TO CONDUCT TILL T3 & T4 ARE TRIGGERED.
  30. 30. FULLY CONTROLLED BRIDGE SINCE THERE ARE TWO PULSES PER CYCLE SO IT IS CALLED : TWO PULSE CONVERTER
  31. 31. AVERAGE VALUE OF OUTPUT VOLTAGE   1 v Vo Vav  sin tdt  m  onsolving 2vm Io Vav  cos  Thus, Vav is +ve from o ˂ ˂ α π/2 -Vo Vav is –ve from π/2 ˂ ˂ α π
  32. 32. REFERENCES  M.H.RASHID,POWER ELECTRONICS: CIRCUITS, DEVICES & APPLICATIONS, PENTICE HALL OF INDIA,(IIIRD Ed.),2004  CYRIL LANDER, POWER ELECTRONICS, MCGRAW HILLS CO. ,(IIIRD Ed.), 1993  B.K. BOSE, MODERN POWER ELECTRONICS & A.C. DRIVES, PEARSON EDUCATION INC.,2002

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