analysis of power converters
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LECTURE NOTES ON
PE2001-ANALYSIS OF POWER CONV
SRM UN
Prepared by
Mr. R. Sridha
Ms. A. Geet
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RECTIFIER CIRCUIT
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INTRODUCTION
IN THYRISTOR BASED RECTIFIERS, OUTPUT VOLTAGE CAN BE CONTROLLED. SO TH
TERMED AS CONTROLLED RECTIFIERS.
CONTROLLED RECTIFIERS PRODUCE VARIABLE DC OUTPUT, WHOSE MAGNITUDE I
PHASE CONTROL.
PHASE CONTROL
DC OUTPUT FROM RECTIFIER IS CONTROLLED BY CONTROLLING DURATION OF T
CONDUCTION PERIOD BY VARYING THE POINT AT WHICH GATE SIGNAL IS APPLI
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CONTROLLED RECTIFIERS ARE OF TWO TYP
1- FULLY CONTROLLED RECTIFIERS
DC CURRENT IS UNIDIRECTIONAL, BUT DC VOLTAGE HAS EITHER POLARITY. WITH
POLARITY, FLOW OF POWER IS FROM AC SOURCE TO DC LOAD---RECTIFICATIO
WITH THE REVERSAL OF DC VOLTAGE BY THE LOAD, FLOW OF POWER IS FROM
TO AC SOURCE---INVERSION.
2- HALF CONTROLLED RECTIFIERSHALF OF SCRS ARE REPLACED BY DIODES.
DC OUTPUT CURRENT AND VOLTAGE ARE UNIDIRECTIONAL. I.E., FLOW OF POW
AC SOURCE TO DC LOAD.
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6
Half-Wave Rectifier with R-L Load
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7
Half-Wave Rectifier with R-L Load (freewheeling diod
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Full controlled Rectifier with R-L Load (freewheeling diode
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9
Full controlled Rectifier with R-L Load
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Full controlled Rectifier with R-L Load with freewheeling diode(Bri
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Full controlled Rectifier with RLE Load(Bridge type)
Continuous current mode Discontinuous c
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Full controlled Rectifier with RLE Load(Bridge type)
Inversion mode of operation
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• IN FULLY-CONTROLLED RECTIFIER, ONLY RECTIFICATION CAN BE OBTAINED
CONNECTING A FREEWHEELING DIODE ACROSS THE OUTPUT TERMINALS OF TRECTIFIER.
• ANOTHER METHOD OF OBTAINING RECTIFICATION IN BRIDGE RECTIFIERS
REPLACING HALF OF THE SCRS WITH DIODES. THESE CIRCUITS ARE CALL
SEMICONTROLLED BRIDGE RECTIFIERS.
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Semi controlled Rectifier with R-L Load
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S i t ll d R tifi ith R L L d ith f h li di d
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Semi controlled Rectifier with R-L Load with freewheeling diode
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S ll d R f h RLE L d (C d )
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Semi controlled Rectifier with RLE Load (Continuous current mode)
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S i ll d R ifi i h RLE L d (Di i d
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Semi controlled Rectifier with RLE Load (Discontinuous current mod
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WHY DUAL CONVERTER……?
• SEMI-CONVERTER ARE SINGLE QUADRANT CONVERTER (I.E) OVER ENTIRE FIRING ANG
LOAD VOLTAGE & CURRENT IS SAME POLARITY
• SEMI-CONVERTER OPERATES ONLY IN RECTIFICATION MODE
• FULL-CONVERTER ARE TWO QUADRANT CONVERTER
• HERE THE CURRENT DIRECTION CANNOT REVERSED DUE TO UNIDIRECTIONAL PROPERT
BUT VOLTAGE CAN BE REVERSED
• Α = 0 TO 90 -(VTG & CT IS + VE)-RECTIFIER
• Α = 90 TO 180 -(VTG IS -VE & CT IS +VE)-INVERTER
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WHAT …..?
• IN ORDER TO HAVE FOUR QUADRANT OPERATION WITHOUT ANY MECH CHANG
SWITCH WE GO FOR DUAL CONVERTER
• TWO CONVERTERS ARE CONNECTED BACK TO BACK TO THE LOAD CIRCUIT(IE)TW
CONVERTERS IN ANTI-PARALLEL & CONNECTED TO SAME DC LOAD
• BY THIS ARRANGEMENT WE CAN REVERSE BOTH VTG & CT
• THUS FOUR QUADRANT OPERATION IS OBTAINED
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SINGLE PHASE DUAL CONVERTER
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GATING SEQUENCE
1 1
2 2
The average dc output voltage of converter 1 i2
cos
The average dc output voltage of converter 2 i
2 cos
mdc
mdc
V V
V V
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GATING SEQUENCE
0
0
1
In the dual converter operation one
converter is operated as a controlled rectifie
with 90 & the second converter is
operated as a line commutated inverterin the inversion mode with 90
dcV V
2dcSRM UNIVERSITY
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GATING SEQUENCE
1 2 2
1 2
2 1 1
2 1
1 2
2 1
2 2 2cos cos cos
cos cos
or
cos cos cos
or
radians
Which gives
m m mV V V
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OUTPUT WAVEFORM
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PRACTICAL DUAL CONVERTER
• THOUGH THEIR AVG OUTPUT VTG ARE EQUAL ,YET THEIR INST.VTG ARE OUT OF P
RESULT IN VTG DIFFERENCE
• SO LARGE CIRCULATING CT FLOW BETWEEN TWO CONVERTERS BUT NOT THROU
LOAD
• CIRCULATING CT CAN BE LIMITED BY INSERTING A REACTOR BETWEEN THE TWO C
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EXP FOR INST.CIRCULATING CURRENT
• V O1 = INSTANTANEOUS OUTPUT VTG OF CONVERTER 1
• V O2 = INSTANTANEOUS OUTPUT VTG OF CONVERTER 2
• THE CIRCULATING CURRENT IR CAN BE DETERMINED BY INTEGRATING THE INSTANTAN
VOLTAGE DIFFERENCE (WHICH IS THE VOLTAGE DROP ACROSS THE CIRCULATING CUR
REACTOR LR), STARTING FROM T = (2 - 1 ).
• IDEAL CONDTION AS T
AVERAGE OUTPUT VOLTAGES DURING THE INTERVAL T = ( + 1 ) TO (2 - 1 ) ARE
OPPOSITE THEIR CONTRIBUTION TO THE INSTANTANEOUS CIRCULATING CURRENT IR IS
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EXP FOR INST.CIRCULATING CURRENT
1
1
1 2
2
2
1 2
1 2
2
1 1
1 . ;
As the o/p voltage is negative
1. ;
sin for 2 to
t
r r r O O
r
O
r O O
t
r O O
r
O m
i v d t v v v L
v
v v v
i v v d t L
v V t t
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EXP FOR INST.CIRCULATING CURRENT
1 12 2
1
sin . sin .
2cos cos
The instantaneous value of the circulating current
depends on the delay angle.
t t
mr
r
mr
r
V i t d t t d t
L
V i t
L
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EXP FOR INST.CIRCULATING CURRENT
1For trigger angle (delay angle) 0,
the magnitude of circulating current becomes min.
when , 0,2,4,.... & magnitude becomes
max. when , 1,3,5,....
If the peak load current is , one of p
t n n
t n n
I
the
converters that controls the power flow
may carry a peak current of
4,m
p
r
V I
L
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EXP FOR INST.CIRCULATING CURRENT
max
max
where
,
&
4 max. circulating current
m
p L
L
m
r
r
V I I
R
V i
L
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MODES OF OPERATION
•DUAL CONVERTER WITHOUT CIRCULA
CURRENT
•DUAL CONVERTER WITH CIRCULATINGCURRENT
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DUAL CONVERTER WITHOUT CIRCULATIN
CURRENT
• IN THIS MODE ONLY ONE CONVERTER IS OPERATED AT A TIME & NO NEED OF REA
• WHEN CONVERTER 1 IS ON, 0 < 1 < 900
• V DC IS POSITIVE AND IDC IS POSITIVE
• ALLOW 10 TO 20MS TO LOAD CT TO REACH ZERO
• WHEN CONVERTER 2 IS ON, 0 < 2 < 900
• V DC IS NEGATIVE AND IDC IS NEGATIVE
• LOAD CT MAY DISCONTINUOUS OR CONTINUOUS BUT SATISFACTORY OPERATIO
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DUAL CONVERTER WITH CIRCULATING CUR
• IN THIS MODE, BOTH THE CONVERTERS ARE SWITCHED ON AND OPERATED AT THE SA
REACTOR IS INSERTED
• THE TRIGGER ANGLES 1 AND 2 ARE ADJUSTED SUCH THAT ( 1 + 2 ) = 1800 (IE) 2
• WHEN 0 < 1 <900, CONVERTER 1 OPERATES AS A CONTROLLED RECTIFIER AND CON
OPERATES AS AN INVERTER WITH 900 < 2<1800
• IN THIS CASE V DC AND IDC, BOTH ARE POSITIVE• WHEN 900 < 1 <1800, CONVERTER 1 OPERATES AS AN INVERTER AND CONVERTER 2
AS A CONTROLLED RECTIFIER BY ADJUSTING ITS TRIGGER ANGLE 2 SUCH THAT 0 <
• IN THIS CASE V DC AND IDC, BOTH ARE NEGATIVE
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FOUR QUADRANT OPERATION
Conv. 2Inverting2 > 900
Conv. 2
Rectifying
2 < 900
Conv. 1Rectifyin
1 < 900
Conv. 1
Inverting
1 > 900
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MERITS OF DUAL CONVERTER WITH CIRCULAT
• THE CIRCULATING CURRENT MAINTAINS CONTINUOUS CONDUCTION OF BOTH T
CONVERTERS OVER THE COMPLETE CONTROL RANGE, INDEPENDENT OF THE LOA
• ONE CONVERTER ALWAYS OPERATES AS A RECTIFIER AND THE OTHER CONVERTER
AS AN INVERTER, THE POWER FLOW IN EITHER DIRECTION AT ANY TIME IS POSSIB
• AS BOTH THE CONVERTERS ARE IN CONTINUOUS CONDUCTION WE OBTAIN FAS
RESPONSE. I.E., THE TIME RESPONSE FOR CHANGING FROM ONE QUADRANT OPE
ANOTHER IS FASTER
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DEMERITS OF DUAL CONVERTER WITH
CIRCULATING CT
• DUE TO REACTOR, SIZE & COST IS HIGH
• CIRCULATING CT GIVES RISE TO MORE LOSSES IN CONVERTER. SO THE EFFICIENC
FACTOR IS LOW
• THE CONVERTER THYRISTORS SHOULD BE RATED TO CARRY A PEAK CURRENT MUC
THAN THE PEAK LOAD CURRENT
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Effect of source Inductance in single phase rectifier
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Effect of source Inductance in single phase rectifier
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3-phase full controlled rectifier(RL)
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40
• THE LINE-TO-NEUTRAL VOLTAGES ARE:
• THEN THE LINE-TO-LINE VOLTAGES ARE:
)3
2(sin
)3
2
(sin
sin
t V v
t V v
t V v
mcn
mbn
man
)6
5(sin3
)2
(sin3
)6
(sin3
t V vvv
t V vvv
t V vvv
mancnca
mcnbnbc
mbnanab
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3-phase full controlled rectifier(RL)
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• THE AVERAGE OUTPUT VOLTAGE IS FOUND FROM :
• THE RMS VALUE OF THE OUTPUT VOLTAGE IS :
cos
33)(
3 2/
6/
mabdc
V t d vV
2/1
2/12/
6/
2
)2cos4
33
2
1(3
)(
3
mrms
abrms
V V
t d vV
41SRM UNIVERSITY
3-phase full controlled rectifier(RLE)
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3-phase full controlled rectifier(RLE)
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Rectification mode Inversion mode
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Analysis for Rectification mode
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Analysis for Rectification mode
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Effect of source Inductance in three phase rectifier
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Effect of source Inductance in three phase rectifier
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3 phase Dual Converter
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48
Due to instantaneous voltage differences between the output
voltages of converters, a circulating current flows through the
converters.
This circulating current is limited by a reactor.SRM UNIVERSITY
12 PULSE CONVERTER
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a) SERIES CONNECTION
b) PARALLEL CONNECTION
c) TRANSFORMER CONNECTIO
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12 PULSE CONVERTER
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DC-DC CONVERTERS (CHOPPERS)
• THE OBJECTIVE IS TO CONVERT A FIXED DC VOLTAGE TO A VARIABLE
DC VOLTAGE
• IT IS POSSIBLE TO STEP UP AND STEP DOWN VOLTAGE.
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VOLTAGE STEP DOWN (BUCK CONVERTE
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VOLTAGE STEP DOWN (BUCK CONVERTE
First, suppose L=0, E=0.
The diode is not needed.
Va=(ton/T)Vs
VRMS=k
1/2
Vs
Pout=(kVs2)/R
k=ton/T is the duty cycle
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VOLTAGE STEP UP (BOOST) CONVERTER
“On” mode: VL=L(di/dt)
“Off” mode: Assume currentdecreases at a constant rate. Then
Vo=Vs+VL
To ensure continuous current flow, a
capacitor is included.
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AVERAGE VALUE OF THE OUTPUT VOLTAG1
1
0
0
11
1
1
t
a O
t
a S
a S S
a S
V v dt T
V V dt T
t V V ft V T
V kV
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Performance of a step up converter with resistive load
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DC-DC CONVERTER CLASSIFICATION
• FIRST QUADRANT CONVERTER
• SECOND QUADRANT
CONVERTER
• 1ST AND 2ND QUADRANT
CONVERTER
• 3RD AND 4TH QUADRANTCONVERTER
• FOUR QUADRANT CONVERTER
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FIRST QUADRANT CHOPPER
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S QU N C O
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SECOND QUADRANT CHOPPER
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THIRD QUADRANT CHOPPER
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THIRD QUADRANT CHOPPER
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FOURTH QUADRANT CHOPPER
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1-2 AND 3-4 QUADRANT CONVERTERS
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Q
1st quad: S1, D4
2nd quad: S4, D1
3rd quad: S3, D2
4th quad: S2, D3
Polarity of the load EMF is reversed
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FOUR QUADRANT CONVERTER
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FOUR QUADRANT CONVERTER
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FOUR QUADRANT CONVERTER
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FOUR QUADRANT CONVERTER
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LOAD VOLTAGE EXPRESSIONS ARE
OU QU N CONV
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Step-Down/Up (Buck-Boost) Converter
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• The output voltage can be higher or lower than the input voltage
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Buck-Boost Converter: Waveforms
C ti d ti d
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• Continuous conduction mode
Switch closed:
di
dt
V
L
L CC
Switch open:
di
dt
v
L
L o
Inductor Volt-second balance:
D
DV V
L
T DV
L
DT V
CC o
oCC
1
0)1(
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Buck-Boost: Limits of Cont./Discont. Conduct
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• The output voltage is held constant
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Buck-Boost: Discontinuous Conduction
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• This occurs at light loads
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Cuk DC-DC Converter
• The output voltage can be higher or lower than the input voltage
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• Capacitor C1 stores and transfers energy from input to output
• When switch is ON, C1 discharges through the switch and transfers
output
• When switch is OFF, capacitor C1 is charged through the diode by einput and L1
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Cuk DC-DC Converter: Waveforms
• The capacitor voltage is
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• The capacitor voltage is
assumed constant (very large)
• Note phase inversion at the
output
D
D
V
V
d
o
1
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SEPIC Converter
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• Single-ended primary inductance converter (SEPIC)• Can buck or boost the voltage
• Note that output is similar to buck-boost, but without a ph
inversion
• This circuit is useful for lithium battery powered equipmen
D
D
V
V
d
o
1
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SEPIC Converter
Circuits for 2 different switching states
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ZETA CONVERTER
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A Zeta converter performs a non-inverting buck-boost function similar to that of a SEPIC, w
acronym for Single-Ended Primary Inductance Converter. The Zeta topology is also similar to t
in that it uses two inductors, two switches and a capacitor to isolate the output from the input.
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When analyzing Zeta waveforms it is helpful to keep in mind that at equilibrium, L1average curr
average current equals IOUT, since there is no DC current through the flying cap CFLY. Also there is
i h i d Th f CFLY d i l i l f id d VOUT i i h id
ZETA CONVERTER
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either inductor. Therefore, CFLY sees ground potential at its left side and VOUT at its right side, r
across CFLY being equal to VOUT.
When M1 is on, L1 and L2 are energized. D1 sees a potential of VIN+VOUT across it (see figures 3
is off, energy stored in L1 and L2 is released. D1 is forward biased.
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ZETA CONVERTER
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ZETA CONVERTER
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Output voltage is given by the following equation:
Where D is duty cycle. VOUT is plotted as a function of D in figure 6. As
can be seen, for D less than 0.5 the converter performs buck function and
for D larger than 0.5 it is a boost topology.
SRM UNIVERSITY
RESONANT CONVERTER
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INTRODUCTION
CLASSIFICATION
CONCLUSION
RESONANT CONVERTER
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INTRODUCTION
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RESONANT INVERTERS ARE ELECTRICAL INVERTE
ON RESONANT CURRENT OSCILLATION. IT IS KNOWN AS DC TO DC CONV
TO AC PWM INVERTER.
MAIN FUNCTION IS TO REDUCE SWITCHING LOSSES OF THE DEVICES(MO
INTRODUCTION
SRM UNIVERSITY
CLASSIFICATION
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THE RESONANT CONVERTER BROADLY CLASSIFIED INTO EIGHT TYPES. THOS
1. SERIES RESONANT INVERTER
2. PARALLEL RESONANT INVERTER
3. CLASS E RESONANT CONVERTER
4. CLASS E RESONANT RECTIFIER
5. ZERO VOLTAGE SWITCHING(ZVS) RESONANT CONVERTER
6. ZERO CURRENT SWITCHING(ZCS) RESONANT CONVERTER
7. TWO QUADRANT ZVS RESONANT CONVERTER
8. RESONANT DC-LINK INVERTER
SRM UNIVERSITY
SERIES RESONANT INVERTER
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IT IS BASED ON RESONANT CURRENT OSCILLATION.
SWITCHING DEVICE ARE PLACED IN SERIES WITH LOAD.
THYRISTOR ARE WORK IN SWITCHING DEVICE.
THIS TYPE OF INVERTER PRODUCES AN APPROXIMATELY SINUSOIDAL W
A HIGH FREQUENCY ,RANGING FROM 200HZ TO 100KHZ.
SRM UNIVERSITY
CIRCUIT DIG OF SERIES RESONANT CONVERTER
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CIRCUIT DIG. OF SERIES RESONANT CONVERTER
Equivalent circuit dig. Waveform
SRM UNIVERSITY
PARALLEL RESONANT INVERT
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PARALLEL RESONANT INVERTER IS DUAL OF SERIES RESONANT INVERTE
CURRENT IS CONTINUOUSLY CONTROLLED , THAT GIVES BETTER SHORT
PROTECTION UNDER FAULT CONDITION
SRM UNIVERSITY
CLASS E RESONANT CONVERT
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IT HAS LOW SWITCHING LOSSES , YIELDING A HIGH EFFICIENCY OF MOR
USED IN LOW POWER APPLICATION & HIGH FREQUENCY ELECTRIC LAMP
CLASS E RESONANT CONVERT
SRM UNIVERSITY
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CIRCUIT DIG. OF CLASS E RESONANT INVERTER & WAVE FORM
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CLASS E RESONANT RECTIFIE
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CLASS E RESONANT RECTIFIER IS BASED ON THE PRINCIPLE OF ZE
SWITCHING(ZVS) .
THE DIODE TURN OFF AT ZERO VOLTAGE.
A HIGH FREQUENCY DIODE RECTIFIER SUFFERS FROM DISADVANT
SWITCHING LOSSES , HARMONIC CONTENT.
SRM UNIVERSITY
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SRM UNIVERSITY
ZERO VOLTAGE SWITCHING(ZVRESONANT CONVERTER
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THE ZVS RESONANT CONVERTER TURN ON & TURN OFF AT ZERO VOLTAG
OUTPUT VOLTAGE CONTROL CAN BE ACHIEVED BY VARYING THE FREQU
OPERATES WITH CONSTANT OFF TIME CONTROL .
RESONANT CONVERTER
SRM UNIVERSITY
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SRM UNIVERSITY
ZERO CURRENT SWITCHING(ZCRESONANT CONVERTER
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ZERO CURRENT SWITCHING(ZCS) RESONANT CONVERTER TURN ON & TU
ZERO CURRENT.
THIS CONVERTER CAN OPERATE AT HIGHER RANGE FREQUENCY THAT IS
2MHZ.
RESONANT CONVERTER
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SRM UNIVERSITY
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SRM UNIVERSITY
TWO QUADRANT ZVS RESONACONVERTER
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IN THIS CONVERTER THE ZVS CONCEPT IS EXTENDED
HERE FO > FS
= 1
2Π
SRM UNIVERSITY
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SRM UNIVERSITY
C S S A O
RESONANT DC-LINK INVERTE
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THE DC LINK INVERTER IS SIMILAR TO THE PWM INVERTER .
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SRM UNIVERSITY
CONCLUSION
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IT IS USED FOR HIGH FREQUENCY APPLICATION.
ZCS&ZVS BECOMES POPULAR AND THEY CAN TURN ON &TURN OVOLTAGE&CURRENT AND ALSO ELIMINATE SWITCHING LOSSES.
IN DC-LINK INVERTERS , A RESONANT CIRCUIT IS CONNECTED B
INVERTER & DC SUPPLY.
SRM UNIVERSITY
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UNIT 4
AC VOLTAGE CONTROLLERS
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INTRODUCTION
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• THE POWER FLOW INTO A LOAD CAN BE CONTROLLED BY VARYING THE RMS VALUE
VOLTAGE.
• THIS CAN BE ACCOMPLISHED BY THYRISTORS, AND THIS TYPE OF POWER CIRCUIT IS
VOLTAGE CONTROLLERS.
SRM UNIVERSITY
• THE MOST APPLICATION OF AC VOLTAGE CONTROLLERS ARE:
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• INDUSTRIAL HEATING
• ON-LOAD TRANSFORMER TAP CHANGING
• LIGHT CONTROLS
• SPEED CONTROL OF INDUCTION MOTORS
• AC MAGNET CONTROLS
SRM UNIVERSITY
• FOR POWER TRANSFER, TWO TYPES OF CONTROL ARE NORMALLY USED:
• ON-OFF CONTROL
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• PHASE ANGLE CONTROL
• IN ON-OFF CONTROL, THYRISTOR SWITCHES CONNECT THE LOAD TO THE AC SOU
CYCLES OF THE INPUT VOLTAGE AND THEN DISCONNECTED FOR A FEW CYCLES.
• IN PHASE CONTROL, THYRISTOR SWITCHES CONNECT THE LOAD TO THE AC
PORTION OF EACH CYCLE.
SRM UNIVERSITY
• THE AC VOLTAGE CONTROLLERS CAN BE CLASSIFIED INTO TWO TYPES:
• SINGLE-PHASE CONTROLLERS
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• THREE-PHASE CONTROLLERS
• EACH TYPE CAN BE SUBDIVIDED INTO:
• UNIDIRECTIONAL OR HALF-WAVE CONTROL
• BIDIRECTIONAL OR FULL-WAVE CONTROL
• SINCE THE INPUT VOLTAGE IS AC, THYRISTORS ARE LINE COMMUTATED.
SRM UNIVERSITY
PRINCIPLE OF ON-OFF CONTROL
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• THE PRINCIPLE OF ON-OFF CONTROL CAN BE EXPLAINED WITH THE FOLLOWING SIN
FULL-WAVE CONTROLLER.
SRM UNIVERSITY
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SRM UNIVERSITY
• THIS TYPE OF CONTROL IS APPLIED IN APPLICATIONS WHICH HAVE HIGH MECHANIC
HIGH THERMAL TIME CONSTANT.
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•TYPICAL EXAMPLES ARE INDUSTRIAL HEATING AND SPEED CONTROL OF MOTORS.
• IF THE INPUT VOLTAGE IS CONNECTED TO LOAD FOR N CYCLES AND IS DISCONNEC
CYCLES, THE OUTPUT LOAD VOLTAGE IS FOUND FROM:
SRM UNIVERSITY
n
2/12
22
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• NOTE THAT K IS CALLED THE DUTY CYCLE, AND THE POWER FACTOR AND OUTPUT VO
WITH THE SQUARE ROOT OF K.
k V nm
nV V
t d t V mn
nV
s srmso
srmso
2
0
22 )(sin2)(2
SRM UNIVERSITY
PRINCIPLE OF PHASE CONTROL
• THE PRINCIPLE OF PHASE CONTROL CAN BE EXPLAINED WITH THE FOLLOWING CIRC
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SRM UNIVERSITY
• DUE TO THE PRESENCE OF DIODE D1, THE CONTROL RANGE IS LIMITED.
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• THE RMS OUTPUT VOLTAGE CAN ONLY BE VARIED BETWEEN 70.7 TO 100%.
• THE OUTPUT VOLTAGE AND INPUT CURRENT ARE ASYMMETRICAL AND CONTAIN A D
• THIS CIRCUIT IS A SINGLE-PHASE HALF-WAVE CONTROLLER AND IS SUITABLE ONLY F
POWER RESISTIVE LOADS, SUCH AS HEATING AND LIGHTING.
• SINCE THE POWER FLOW IS CONTROLLED DURING THE POSITIVE HALF-CYCLE OF INP
THIS TYPE OF CONTROLLER IS ALSO KNOWN AS UNIDIRECTIONAL CONTROLLER.
SRM UNIVERSITY
• THE RMS VALUE OF THE OUTPUT VOLTAGE IS FOUND FROM:
222
22 (sin2)(sin2[2
1{
s so td t V t d t V V
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• THE AVERAGE VALUE OF THE OUTPUT VOLTAGE IS:
2/1)]
2
2sin2(
2
1[
2
so V V
)1(cos2
2
(sin2)(sin2[2
1 2
so
s sdc
V V
d t V t d t V V
SRM UNIVERSITY
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SRM UNIVERSITY
• THE FIRING PULSE OF T1 AND T2 ARE 180 DEGREES APART.
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• THE RMS VALUE OF THE OUTPUT VOLTAGE IS:
•BY VARYING
Α FROM 0 TO
Π, VO CAN BE VARIED FROM VS TO 0.
2/1
2/122
2
2sin(
1
)(sin22
2
so
so
V V
t d t V V
SRM UNIVERSITY
SINGLE-PHASE AC VOLTAGE CONTROLLERS INDUCTIVE LOAD
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• IN PRACTICE, MOST LOADS ARE INDUCTIVE TO A CERTAIN EXTENT.
• A FULL-WAVE CONTROLLER WITH AN INDUCTIVE LOAD IS SHOWN NEXT.
SRM UNIVERSITY
SINGLE PHASE AC VOLTAGE REGULATOR WITH RL LOAD
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SRM UNIVERSITY
• THE GATING SIGNALS OF THYRISTORS COULD BE SHORT PULSES FOR A CONTROLLE
RESISTIVE LOAD.
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• HOWEVER, THEY ARE NOT SUITABLE FOR INDUCTIVE LOADS.
• WHEN THYRISTOR T2 IS FIRED, THYRISTOR T1 IS STILL CONDUCTING DUE TO THE INDU
SRM UNIVERSITY
• BY THE TIME THE CURRENT OF T1 FALLS TO ZERO AND T1 IS TURNED OFF, THE GATE C
HAS ALREADY CEASED.
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HAS ALREADY CEASED.
• CONSEQUENTLY, T2 WILL NOT BE TURNED ON.
• THIS DIFFICULTY CAN BE RESOLVED BY USING A CONTINUOUS GATE SIGNAL WITH A
Π - Α.
SRM UNIVERSITY
• HOWEVER A CONTINUOUS GATE PULSE INCREASES THE SWITCHING LOSS OF THYR
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• IN PRACTICE A TRAIN OF PULSES WITH SHORT DURATION ARE USED TO OVERCOME
PROBLEM.
SRM UNIVERSITY
• THE RMS VALUE OF THE OUTPUT LOAD VOLTAGE IS FOUND FROM:
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2/1
2/1
22
2
2sin
2
2sin(
1
)(sin22
2
so
so
V V
t d t V V
SRM UNIVERSITY
THREE-PHASE FULL-WAVE CONTROLLERS
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• THE UNIDIRECTIONAL CONTROLLERS, WHICH CONTAIN DC INPUT CURRENT AND HIG
CONTENT DUE TO THE ASYMMETRICAL NATURE OF THE OUTPUT VOLTAGE WAVEFOR
NORMALLY USED IN AC MOTOR DRIVES.
• A THREE-PHASE BIDIRECTIONAL CONTROL IS COMMONLY USED.
SRM UNIVERSITY
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30o
120SRM UNIVERSITY
• FOR 0 < Α < 60O:
2/1
)2sin
(1
6
VV
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• FOR 60O < Α < 90O:
• FOR 90O
< Α < 150O
:
)846
(6
so V V
2/1
)16
2cos3
16
2sin3
12(
16
so V V
)16
2cos3
16
2sin
424
5(
16
so V V SRM UNIVERSITY
THREE-PHASE BIDIRECTIONAL DELTA-CONNECONTROLLERS
IF THE TERMINALS OF A THREE PHASE SYSTEM ARE ACCESSIBLE THE CONTROL ELEME
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• IF THE TERMINALS OF A THREE-PHASE SYSTEM ARE ACCESSIBLE, THE CONTROL ELEME
LOAD MAY BE CONNECTED IN DELTA.
SRM UNIVERSITY
• SINCE THE PHASE CURRENT IN A NORMAL THREE-PHASE DELTA SYSTEM IS ONLY 1/√3
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CURRENT, THE CURRENT RATINGS OF THE THYRISTORS ARE LESS.
• THE FOLLOWING FIGURE SHOWS THE WAVEFORMS FOR A DELAY ANGLE OF 120 D
SRM UNIVERSITY
60o
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SRM UNIVERSITY
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UNIT 5CYCLOCONVERTER
SRM UNIVERSITY
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SINGLE PHASE CYCLOCONVERTER
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INTRODUCTION
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• A DEVICE WHICH CONVERTS INPUT POWER AT ONE FREQUENCY TO THE OUT PU
DIFFERENT FREQUENCY WITH ONE STAGE CONVERSION IS CALLED A CYCLOCON
• TYPES
STEP-UP CYCLOCONVERTER( FO > FS)
STEP-DOWN CYCLOCONVERTER ( FO < FS)
• DUE TO HIGH COST, NOT SPREAD WIDELY IN EARLY DAYS
• NOW WITH ADVENT OF HIGH POWER THYRISTOR, CYCLOCONVERTER BECOME P
SRM UNIVERSITY
APPLICATION OF CYCLOCONVERTER
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• SPEED CONTROL OF HIGH POWER AC DRIVE
• INDUCTION HEATING
• STATIC VAR COMPENSATION
• FOR CONVERTING VARIABLE SPEED ALTERNATOR VTG TO CONT FREQ OUTPUT VT
AS POWER SUPPLY IN AIRCRAFT OR SHIPBOARDS
SRM UNIVERSITY
SINGLE PHASE TO SINGLE PHASE MID POINTSTEP-UP CYCLOCONVERTER WITH R LOA
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SRM UNIVERSITY
WAVEFORM
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SRM UNIVERSITY
SINGLE PHASE TO SINGLE PHASE BRIDGE TSTEP-UP CYCLOCONVERTER WITH R LOA
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SRM UNIVERSITY
WAVEFORM
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SRM UNIVERSITY
1-Φ TO 1-Φ MID POINT TYPE STEP-DOWCYCLOCONVERTER WITH R LOAD
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SRM UNIVERSITY
OUTPUT VOLTAGE (VO) AND CURRENT (IO) WAV
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SRM UNIVERSITY
1-Φ TO 1-Φ MIDPOINT TYPE STEP-DOWCYCLOCONVERTER WITH R-L LOAD
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SRM UNIVERSITY
OUTPUT VOLTAGE (VO) AND CURRENT (IOWAVEFORM FOR DISCONTINUOUS CONDUC
MODE
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SRM UNIVERSITY
OUTPUT VOLTAGE (VO) AND CURRENT (IOWAVEFORM FOR CONTINUOUS CONDUCTION
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SRM UNIVERSITY
1-Φ TO 1-Φ BRIDGE TYPE STEP-DOWNCYCLOCONVERTER WITH R LOAD
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SRM UNIVERSITY
OUTPUT VOLTAGE (VO) AND CURRENT (IOWAVEFORM
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SRM UNIVERSITY
1-Φ TO 1-Φ BRIDGE-TYPE STEP-DOWNCYCLOCONVERTER WITH R-L LOAD
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SRM UNIVERSITY
OUTPUT VOLTAGE (VO) AND CURRENT (IOWAVEFORM FOR DISCONTINUOUS CONDUC
MODE
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SRM UNIVERSITY
OUTPUT VOLTAGE (VO) AND CURRENT (IOWAVEFORM FOR CONTINUOUS CONDUCTION
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SRM UNIVERSITY
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THREE PHASE CYCLOCONVERTER
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THREE PHASE TO SINGLE PHASE CYCLOCONVTOPOLOGY 1
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SRM UNIVERSITY
TOPOLOGY 2
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SRM UNIVERSITY
OUTPUT VOLTAGE
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THE INPUT AND OUTPUT VOLTAGES ARE ADJUSTED TO BE EQUAL AND THE LOAD CU
FLOW IN EITHER DIRECTION. THUS,
WHERE VD0 IS THE DC OUTPUT VOLTAGE OF EACH CONVERTER AT ZERO FIRING A
P AND N ARE THE INPUT AND OUTPUT FIRING ANGLES. FOR A 3 HALF-WAVE
VD0 =0.675VL AND VD0 = 1.35VL FOR THE BRIDGE CONVERTER (VL IS THE RMS LIN
0 0 0cos cosd d p d nV V V V
SRM UNIVERSITY
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THREE PHASE TO THREE PHASE CYCLOCONV
EACH PHASE GROUP FUNCTIONS AS A DUAL CONVERTER BUT THE FIRING ANGLE
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• EACH PHASE GROUP FUNCTIONS AS A DUAL CONVERTER BUT THE FIRING ANGLE
GROUP IS MODULATED SINUSOIDALLY WITH 2/3 PHASE ANGLE SHIFT -> 3 BAVOLTAGE AT THE MOTOR TERMINAL.
• AN INTER-GROUP REACTOR (IGR) IS CONNECTED TO EACH PHASE TO RESTRICT CI
CURRENT.
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TOPOLOGY 1
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WAVEFORM
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SRM UNIVERSITY
TOPOLOGY 2
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SRM UNIVERSITY
REFERENCES
• 1 RASHID M H "POWER ELECTRONICS CIRCUITS DEVICES AND APPLICATIONS"
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1. RASHID M.H., POWER ELECTRONICS CIRCUITS, DEVICES AND APPLICATIONS ,
HALL INDIA, THIRD EDITION, NEW DELHI, 2011.
• 2. P.C. SEN, “MODERN POWER ELECTRONICS”, WHEELER PUBLISHING CO, THIRD E
DELHI, 2008.
• 3. NED MOHAN, UNDELAND AND ROBBIN, “POWER ELECTRONICS: CONVERTERS,
AND DESIGN”, JOHN WILEY AND SONS.INC, NEWYORK,REPRINT - 2009.
•4. CYRIL W.LANDER, “POWER ELECTRONICS”, THIRD EDITION, MCGRAW HILL- 199
• www.nptel.ac.in, www.ieee.com, www.ocw.mit.edu
SRM UNIVERSITY