controlled rectifiers
DESCRIPTION
Controlled Rectifiers in power Electronics. Ankur Mahajan NITTTR ChandigarhTRANSCRIPT
SEMINAR ON AC – DC CONVERTERS
BY:ANKUR MAHAJAN
M.E. I&C REGULAR -2011ROLL NO. 112505
GOAL OF THE SEMINAR SINGLE PHASE HALF WAVE & FULL WAVE
CONVERTERS.
SEMICONDUCTOR DEVICES – THE
HEART OF INDUSTRIAL
ELECTRONICS
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 ?
PIE CHART OF WORL’S ENERGY PRODUCTION LEVEL
FOSSIL FUELSNUCLEAR
RENEWABLES
IN INDIA 70% OF ELECTRICAL ENERGY COMES FROM COAL
ACCORDING TO IEEE JOURNAL ON
POWER DELIVERY: WE HAVE NO
FOSSIL & NUCLEAR FUEL BY THE
END OF 22ND CENTURY.
87%
6%
7%
(A)USE EE EFFICIENTLY.(B) IMPROVE CONVERSION EFFICIENCY.
(C) USE RENEWABLES
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
RECTIFIERS CLASSIFICATION
BECAUSE ON & OFF STATE OF DIODE IS DETERMINED BY THE STATE OF THE CIRCUIT.
BECAUSE THYRISTOR CAN BE TURNED ON BY CONTROL TERMINAL. i.e. GATE
ASSUMPTIONS :
ALL THE DEVICES & CIRCUIT COMPONENTS ARE IDEAL i.e. Ton =Toff =zero
INPUT IS PURE SINE WAVE
CHARACTERISTICS OF AN IDEAL SWITCH
TERMINOLOGIES
LET ‘f’ BE THE INSTANTANEOUS VALUE OF ANY VOLTAGE OR CURRENT ASSOCIATED WITH RECTIFIER CIRCUIT, THEN
TERMINOLOGIES (CONT.)
Angle atWhich SCR starts
conductingAngle at which SCR stops conducting
SINGLE PHASE FULLY CONTROLLED H/W RECTIFIER
CAN BE TURNED ON BY
APPLYING GATE SIGNAL
WHEN SCR IS FORWARD
BIASED.
OPERATION IS ALMOST
SAME AS THAT OF DIODE
CIRCUIT
FOR PURELY RESISTIVE LOAD
CURRENT FLOWS FROM TO THROUGH LOAD BECAUSE SCR IS IN FPRWARD CONDUCTION MODE.
π-α
CALCULATIONS
Average value of output voltage
On solving
ttdvv iav sin22
1
)cos1(2
iav
vv
CALCULATION OF RMS VALUE OF VOLTAGE
tdvv orms
2
2
1
tdtvv irms
22 sin2
2
1
tdtv
v irms
)2cos1(
2
2
2
1
])2
2sin(
1[2
tt
vv irms
)2cos1(2
12 ttSin
CALCULATION OF RMS VALUE OF VOLTAGE (CONT.)
On solving
Form factor
2
1
)2
2sin1(
2
irms
vv
)cos1(2
iav
vv
cos1
)22sin
1( 2
1
av
rms
v
vformfactor
RESISTIVE – INDUCTIVE LOAD
α to π π to β
RESISTIVE – INDUCTIVE LOAD
Thyristor turns ON at ωt= α & voltage appears across Load &
current starts building up. Inductor does not changes
current instantaneously, so load current does not become zero at
ωt = π It continue to flow but the
negative supply voltage decreases its magnitude
At ωt= β current becomes zero and thyristor starts blocking until
again turned ON.
Since thyristor does not conduct over the entire input so it is called
DISCONTINUOUS CONDUCTION MODE
CALCULATIONS t
tvtvvv imio sin2sin
otherwisev ,00
Average value of output voltage
ttdvv iav sin22
1
)cos(cos2
,
iav
vvonsolving
RMS VALUE OF OUTPUT VOLTAGE
2
122 )sin2
2
1( ttdvv irms
21
)2cos1(1
2tdt
vv irms
21
2
2sin
2
2sin(
1
2
irms
vv
21
2
2sin2sin(
2
irms
vv
)2cos1(2
12 ttSin
SINGLE PHASE HALF CONTROLLED BRIDGE
Assume, load is highly inductive Because 90% of loads are inductiveCASE I
T1
T4
D3
D2
LOA
D A B
DURING +VE HALF CYCLE T1 &
D2 ARE FORWARD BIASED.
AT ωt = α, T1 IS TRIGGERED AND ITS
STARTS CONDUCTING.
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
T1
D2
A B
α to π
SINCE LOAD IS HIGHLY INDUCTIVE FREEWHEELING CURRENT FLOWS
THROUGH D2-D3FROM ωt =π To π+α
D3
D2
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.
At ωt = 2π, D2 starts conducting and T4 is OFF, this is called LINE COMMUTATION
D3
T4
A
B
From ωt = 2π to 2π+α, only D2-D3 conducts,
because of load
SINGLE PHASE HALF CONTROLLED BRIDGE
2π+α,α
π
π+α
2π
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
CALCULATIONS
cos1 mav
vV
Vav is +ve and Iav is also +ve so source is supplying power to the load or we can say that load is PASSIVE.
Vav
α
------
----
----
---
1
0.5
π/2
π
Vo
Io
Operation in 1st Quadrant
SINGLE PHASE HALF CONTROLLED BRIDGE
CASE II: CONTINUOUS CONDUCTION MODE
T1 T3
D4 D2
LOAD
DURING α to π OPRATION OS SAME AS THAT OF CASE I.
FROM π to π+α D4 STARTS CONDUCTING & T3 IS IN FORWARD BLOKING MODE. THUS NO CONDUCTION.T1 & D4 CONDUCTS.
A B
α - π
SINGLE PHASE HALF CONTROLLED BRIDGE
FROM π to π+α FROM π+α to 2π
T1
D4
At ωt = π+α, T3 IS TRIGGERED & T1
COMMUTATES ( LINE COMMUTATION)
T3
A B
D4
FROM 2π, D2 STARTS CONDUCTING & T1 IS IN FORWARD BLOKING MODE. THUS NO CONDUCTION.T3 & D2 CONDUCTS.
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
SINGLE PHASE HALF CONTROLLED BRIDGECONTINUOUS CONDUCTION MODE
DISCONTINUOUS CONDUCTION MODE
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.
FULLY CONTROLLED BRIDGE
SINCE THERE ARE TWO PULSESPER CYCLE SO IT ISCALLED :TWO PULSE CONVERTER
AVERAGE VALUE OF OUTPUT VOLTAGE
ttdvV mav
sin1
cos
2 mav
vV
onsolving
Thus, Vav is +ve from o ˂α ˂ π/2 Vav is –ve from π/2 ˂ α ˂ π
Vo
Io
-Vo
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
