Controlled Rectifiers in power Electronics. Ankur Mahajan NITTTR Chandigarh

1. SEMINAR ON AC – DC
CONVERTERS
BY:
ANKUR MAHAJAN
M.E. I&C REGULAR -2011
ROLL NO. 112505

2. GOAL OF THE SEMINAR
 SINGLE PHASE HALF WAVE & FULL WAVE
CONVERTERS.
SEMICONDUCTOR
DEVICES – THE
HEART OF
INDUSTRIAL
ELECTRONICS

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. 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. 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. RECTIFIERS CLASSIFICATION

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. ASSUMPTIONS :
 ALL THE DEVICES & CIRCUIT COMPONENTS
ARE IDEAL i.e. Ton =Toff =zero
 INPUT IS PURE SINE WAVE
CHARACTERISTICS OF AN IDEAL SWITCH

9. TERMINOLOGIES
 LET ‘f’ BE THE INSTANTANEOUS VALUE OF ANY
VOLTAGE OR CURRENT ASSOCIATED WITH
RECTIFIER CIRCUIT, THEN


10. TERMINOLOGIES (CONT.)



 Angle at
Which SCR starts conducting
 Angle at which SCR stops conducting

11. SINGLE PHASE FULLY CONTROLLED H/W
RECTIFIER

12. FOR PURELY RESISTIVE LOAD
 CURRENT FLOWS FROM  TO THROUGH
LOAD BECAUSE SCR IS IN FPRWARD
CONDUCTION MODE.
π-α

13. CALCULATIONS
 Average value of output voltage

1
vav   2vi sin tdt
2 
On solving
vi
vav  (1  cos )
2

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. 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. RESISTIVE – INDUCTIVE LOAD
α to π π to β

17. RESISTIVE – INDUCTIVE LOAD
Since thyristor does not conduct over the
entire input so it is called DISCONTINUOUS
CONDUCTION MODE

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. 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. 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. 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. 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. 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. 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. 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. 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. 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. SINGLE PHASE HALF CONTROLLED BRIDGE
CONTINUOUS DISCONTINUOUS
CONDUCTION MODE CONDUCTION MODE

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. FULLY CONTROLLED BRIDGE
SINCE THERE
ARE TWO PULSES
PER CYCLE SO IT IS
CALLED :
TWO PULSE CONVERTER

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. 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