power quality improvements using multipulse converters
TRANSCRIPT
11
Seminar Seminar onon
Power Quality Improvements Power Quality Improvements Using Multipulse ConvertersUsing Multipulse Converters
ByBy
Prof. Bhim Singh, Prof. Bhim Singh, Senior Member, IEEESenior Member, IEEE Department of Electrical EngineeringDepartment of Electrical Engineering
Indian Institute of Technology DelhiIndian Institute of Technology Delhi New Delhi-110016, India New Delhi-110016, India
22
Multipulse converters are converters providing Multipulse converters are converters providing more than six pulses of DC voltagemore than six pulses of DC voltage per cycle from per cycle from AC input.AC input.
Or the converter having Or the converter having more steps in AC input more steps in AC input currentcurrent than that of six pulse bridge rectifier supply than that of six pulse bridge rectifier supply current.current.
Bridge rectifier is the basic block required for AC-Bridge rectifier is the basic block required for AC-DC conversion, however, full-wave and half-wave DC conversion, however, full-wave and half-wave rectifiers are also used up to 120kW ratings.rectifiers are also used up to 120kW ratings.
Phase shifting transformers are used to derive Phase shifting transformers are used to derive multiple phase supply from three-phase AC mains multiple phase supply from three-phase AC mains using different combinations of transformer using different combinations of transformer windings such as star, delta, zigzag, fork, polygon, windings such as star, delta, zigzag, fork, polygon, etc.etc.
What are Multipulse AC-DC Converters?
33
Problems in AC-DC ConvertersProblems in AC-DC Converters
The major The major problemsproblems in AC-DC converters are in AC-DC converters are injection of harmonicsinjection of harmonics at input and output at input and output . .
Harmonics causeHarmonics cause dielectric, thermal or dielectric, thermal or voltage stress, which cause voltage stress, which cause premature ageingpremature ageing of electrical insulation.of electrical insulation.
Voltage distortionVoltage distortion at point of common at point of common coupling takes place due to the voltage drop coupling takes place due to the voltage drop of harmonic currents flowing through system of harmonic currents flowing through system impedances.impedances.
Capacitor bank Capacitor bank overloadingoverloading due to system due to system resonance.resonance.
44
Problems in AC-DC ConvertersProblems in AC-DC Converters
Interference Interference on telephone and on telephone and communication lines due to noise induced communication lines due to noise induced from the power conductors.from the power conductors.
Poor power factorPoor power factor.. Equipment damageEquipment damage from voltage spikes from voltage spikes
created by high frequency resonance created by high frequency resonance resulting from notching. resulting from notching.
55
Power Quality Standards in AC-DC Power Quality Standards in AC-DC
ConvertersConverters IEEE Standard IEEE-519.IEEE Standard IEEE-519.
established in 1981 as the “Recommended Practices and established in 1981 as the “Recommended Practices and requirements for Harmonics Control in Electrical Power System” requirements for Harmonics Control in Electrical Power System” giving limits on current and voltage distortion and revised in giving limits on current and voltage distortion and revised in 19921992
IEC 61000 IEC 61000 The electric equipments have been categorized in four groups: The electric equipments have been categorized in four groups: Class- A, B, C and D, for the purpose of harmonic current Class- A, B, C and D, for the purpose of harmonic current limitationlimitation..
IEEE-1531 IEEE-1531 IEEE-1531 (issued in 2003) gives necessary guidelines for IEEE-1531 (issued in 2003) gives necessary guidelines for specifications for the use of passive shunt harmonic filters in low specifications for the use of passive shunt harmonic filters in low and medium voltage electric power systemsand medium voltage electric power systems
66
Current Distortion Limits for General Distribution Systems(120 V Through 69 000 V), IEEE-519 Std.
Maximum Harmonic current Distortion in Percent of IL
Individual Harmonic order (Odd Harmonics)
ISC/ IL<11 11h17 17h23 23h35 35h TDD
<20* 4.0 2.0 1.5 0.6 0.3 5.0
20<50 7.0 3.5 2.5 1.0 0.5 8.0
50<100 10.0 4.5 4.0 1.5 0.7 12.0
100<1000 12.0 5.5 5.0 2.0 1.0 15.0
>1000 15.0 7.0 6.0 2.5 1.4 20.0
Even harmonics are limited to 25% of the odd harmonic limits above.
Current distortion that results in a dc offset, e.g., half-wave converters, are not allowed
*All power generation equipment is limited to these values of current distortion, Regardless of actual ISC/ IL
Where,Isc= maximum short-circuit current at PCC.
IL= maximum demand load current (fundamental frequency component) at PCC
77
Current Distortion Limits for General Subtransmission Systems (69001 V through 161 000 V), IEEE-519 Std.
88
Limits for Class A equipment, IEC-61000 Std.
Harmonic order n
Maximum permissible harmonic Current A
Odd harmonics 3 2.3 5 1.14 7 0.77 9 0.40 11 0.33 13 0.21
15<=n<=39 0.15 15/n Even Harmonics
2 1.08 4 0.43 6 0.3
8<= n <= 40 0.23 8/n
99
Advantages of Multi-pulse AC-DC Advantages of Multi-pulse AC-DC ConvertersConverters
The performance parameters such as total-The performance parameters such as total-harmonic-distortion (THD) of harmonic-distortion (THD) of AC mainsAC mains current and ripple factor of current and ripple factor of output DC output DC voltagevoltage improve, simultaneously. improve, simultaneously.
The improvement is The improvement is independentindependent of supply of supply frequency frequency variation, unlike passive filters.variation, unlike passive filters.
Minimal or no controlMinimal or no control required as Diodes required as Diodes and/or thyristors are mainly used.and/or thyristors are mainly used.
Economic, maintenance free Economic, maintenance free andand efficient efficient..
1010
Phase shifting transformers are used to derive multiple phase supply from three-phase AC mains using different combinations of transformer windings such as star, delta, zigzag, fork, polygon, etc.
1111
Application PotentialApplication Potential
Non-Isolated Uncontrolled Non-Isolated Uncontrolled RectifiersRectifiers : :
Front end of Switched mode Front end of Switched mode powers like-SMPS, UPS, powers like-SMPS, UPS, AC-DC motor drives, dc AC-DC motor drives, dc servo drives.servo drives.
aircraft VSCF (Voltage aircraft VSCF (Voltage source controlled source controlled frequency) systems and frequency) systems and aircraft maintenance aircraft maintenance systems using 60Hz/400Hz systems using 60Hz/400Hz converter systems. converter systems.
Isolated Uncontrolled Isolated Uncontrolled RectifiersRectifiers : :
Railways working on DC.Railways working on DC. The welding equipment The welding equipment
working on high frequencyworking on high frequency
1212
Application PotentialApplication Potential
Non-Isolated Controlled Non-Isolated Controlled Rectifiers:Rectifiers:
DC motor drive system DC motor drive system with regenerative with regenerative capacity.capacity.
Some power supplies of Some power supplies of large rating also use non-large rating also use non-isolated dual converters isolated dual converters
Isolated Controlled Isolated Controlled RectifiersRectifiers : :
HVDC systems.HVDC systems. Battery energy storage Battery energy storage
systems.systems. Adjustable speed Adjustable speed
synchronous motor drive synchronous motor drive of large power ratings for of large power ratings for applications such as applications such as mining.mining.
Arc furnaces Arc furnaces
1313
Y
Y
harmonic filters
Reactivepower
(closed loop)control
TFS
CAD
Flicker (openloop) control
T1
highvoltage
bus medium voltage bus
PLL
+
-
Reg
actuator
Iarc
V arc
V arc
-
+
V arc
L d
low voltage side
Reg FADIdc
current control of a thyristor bridge
TCR
T2A
T2B
+ +
(TFS = Thyristor firing scheme; CAD = Conduction Angle Determinator; FAD = Firing Angle Determinator; PLL = phase Locked Loop
Typical power supply system of DC arc furnaces
1414
vb
v c
va
N
+
-
Load
Interphase transformer
Rectifiertransformer 34.5
kV / 606 V,2.4MVA
34.5 kV Bus
700 V
A model of twelve pulse railway rectifier system
1515
DiodeRectifier
SmoothingCapacitor
InverterRectifier
&Filter
ArcLoad
ControlCircuits
Premier Stage Secondary Stage
400 V,3-phasesupply
Block schematic of welding inverter power supply system
1616
~ ~
~
~ ~
~
A
B
C
a
b
c
A'
B'
C'
NN
L c
L c
L c
Id
Rectifier (or source sideconverter)
Inverter (or machine sideconverter)
+
-
-
+
v d1v d2
L d
T F
ic
ia
Motor
Inverter
Phase delayand firing
circuit
DC supply
Motor
del * or del '*
f del * or del '
Rotor positionand f *
Rotorpositionsensor
Field
Load commutated current source inverter fed synchronous motor
Brushless DC motor
1717
Six-Pulse Converter with Capacitor Filter
THD =62.3%
1818
Six-Pulse Converter with Inductor-Capacitor Filter
THD =32.7%
1919
PASSIVE WAVESHAPING
LOW COST
RUGGED STRUCTURE
LESS LOSSES
HIGH EFFICIENCY
LESSER RATING TRANSFORMER REQD IN AUTOTRANSFORMER BASED TOPOLOGIES
2020
MULTIPULSE CONVERTERSMULTIPULSE CONVERTERS
CLASSIFICATION OF MULTIPULSE AC-DC CONVERTERS based on phase shift
Pulse Based Configurations
Twelve-Pulse Converters 00 and 300 Phase Shift
Twelve-Pulse Converters Based on +150 and -150 Phase Shift
Twenty-Four-Pulse Converters Based on 150 Phase Shift
Eighteen -Pulse Converters Based on +200 and -200 Phase Shift
Thirty-Pulse Converters Based on 120 Phase Shift
Phase Shift = 60Phase Shift = 6000 / Number of Six-Pulse Converters / Number of Six-Pulse Converters
2121
Full-Wave
AC-DC Converters with reduced harmonics
Controlled (Bi - directional)
multi-pulse converters
Uncontrolled (Uni-directional)
multi-pulse converters
Non-Isolated multi-pulse converters
Non-Isolated multi-pulse converters
Isolated multi-pulse converters
Isolated multi-pulse converters
Bridge-converter
Full-Wave
Bridge-converter
Full-Wave
Bridge-converter
Full-Wave
Bridge-converter
CLASSIFICATION OF MULTIPULSE AC-DC CONVERTERS
2222
Non-Isolated Multipulse AC-DC Non-Isolated Multipulse AC-DC ConvertersConverters
2323
Autotransformer Connection Based Configurations
Star Connected Autotransformer
Delta Connected Autotransformer
Polygon Connected Autotransformer
Delta-Polygon Connected Autotransformer
Hexagon Connected Autotransformer
T- Connected Autotransformer
Zigzag Autotransformer
2424
MULTIPHASE CONVERTERS
CLASSIFICATION OF MULTI-PHASE AC-DC CONVERTERS
Nine-Phase AC-DC Converters
Fifteen-Phase AC-DC Converters
Phase Number Based Configurations
2525
CONVENTIONAL WYE DELTA TRANSFORMER
LARGE KVA RATING OF TRANSFORMER
MORE COST
DIFFICULT TO MAKE IDENTICAL WYE AND DELTA WINDINGS
2626
2727
MODELING AND DESIGN OF MULTIPULSE
AC-DC CONVERTERS Twelve-Pulse Converters Based on +150 and -150 Phase Shift
Star Connected Autotransformer
Va = K1*Va - K2* Vb
Va = K1*Va- K2*Vc Vb’
Va
Va”Va’
Vb
Vb”Vc’
Vc
Vc” N
K1
K2
Va=V00, Vb=V-1200 , Vc = V 1200
Va = V +150 , Vb = V-
1050, Vc = V 1350
Va = 0.816 Va - 0.298 Vb
Va = 0.816 Va - 0.298 Vc
Vb’
VaVa’ Va”
Vb
Vb”Vc’
Vc
Vc”
150150
150
150150
150
K1
K2K2
2828
3 Phase, 415V,50 Hz
isa
IGBT Based Inverter
A
B
C
Cd
-
+a'
b'
c'
a''
b"
c"
Autotransformer
Zs
Zs
Zs
Vb’
Va
Va”Va’
VbVb”Vc’Vc
Vc” N3
phase,VCIMD
+
Vdc
+
6 Pulse Diode Bridge Rectifier
isb
isc
Ld
IPT
IPT
6 Pulse Diode Bridge Rectifier
2929
AC MAINS CURRENT WAVEFORM AND ITS HARMONIC SPECTRUM
FULL LOAD LIGHT LOAD (20%)
Magnetics Rating = 36%THD = 9.89% THD = 15.22%
3030
K1 = 0.8 and K2 = 0.2928.
RETROFIT ARRANGEMENT
Va = 0.8 Va - 0.2928 Vc
Va = 0.8 Va - 0.2928 Vb
Va = K1*Va - K2* Vb
Va = K1*Va- K2*Vc
3131
Full LoadFull Load Light LoadLight Load
3232
Twelve-Pulse Converters Based on +00 and 300 Phase Shift
Delta Connected Autotransformer
Vb’Va’
Vc’
Vc
Va
Vb
Design of Autotransformer
Va =Va + K1 Vca + K2Vbc
Va=V00, Vb=V-1200 , Vc = V1200
Va = V +300 , Vb
= V-900, Vc = V 1500
K1 =0.0843
K2 = 0.229
Va = Va + 0.0843 Vbc + 0.229 Vca
3333
3 phase,VC
IMD
IGBT Based Inverter
A
B
C
3 Phase, 415V, 50 Hz
+
Vdc
Cd
-
+
+
-
a
b
c
a'
b’
c'
Autotransformer
Zs
Zs
Zs
Vb’Va’
Vc’
Vc
Va
Vb
Ld
THD = 9.51% THD = 15.66%
Full LoadFull Load Light LoadLight Load
3434
Shortfalls in 12-Pulse Converters
High THD of ac mains current
Not within IEEE Standard 519 limits
Use of 18-pulse converters
THD of ac mains current well within IEEE Standard limits
Near unity power factor operation
3535
CONFIGURATIONS
3636
Vb’
Va
Va”Va’
Vb
Vb”Vc’
Vc
Vc” N
K1
K2
Va = K1Va - K2 Vb
Va = K1Va- K2Vc
Va=V00, Vb=V-1200 , Vc = V 1200
Va = V +200 , Vb = V-
1000, Vc = V 1400
K1 =0.7421
K2 = 0.395
Va = 0.7421 Va - 0.395 Vb
Va = 0.7421 Va - 0.395 Vc
3737
IGBT Based Inverter
A
B
C
3 Phase, 460V, 60 Hz
6 Pulse Diode Bridge Rectifier
Cd
-
6 Pulse Diode Bridge Rectifier
+
+
a'
b'
c'
a''
b"
c"
Autotransformer
Zs
Zs
Zs a
b
c
Vb’
Va
Va”Va’
VbVb”Vc’Vc
Vc” N3
phase,VCIMD
+
Vdc
+
IPT
IPT
isa
isb
isc
ica
icb
icc
Ld
3838Magnetics Rating = 41%
THD = 2.71%THD = 4.19%
Full LoadFull Load Light LoadLight Load
3939
Vb’
Va’
Vc’
Vc
Va
Vb
Va”
Vb”
Vc”
0.04
0.040.177 0.177
200 200
K1K2
Vbc
Vab
Vca
Vb”
Va”Va’
Vc’
Vc” Vb’
Vc Vb
Va
Va = Va + K1Vca - K2 Vbc
Va =Va + K1Vab + K2 Vbc
Va=V00, Vb=V-1200 , Vc = V 1200
Va = V +200 , Vb = V-1000, Vc
= V 1400
K1 = 0.0402
K2 = 0.177
Va = Va + 0.0402 Vca - 0.177 Vbc
Va =Va + 0.0402Vab + 0.177 Vbc
4040
IGBT Based Inverter
A
B
C
3 Phase, 460V, 60 Hz
6 Pulse Diode Bridge Rectifier
Cd
-
6 Pulse Diode Bridge Rectifier
+
+
a'
b'
c'
a''
b"
c"
Autotransformer
Zs
Zs
Zs
a
b
c
3phase,VC
IMD
+Vdc
+
IPT
IPT
isa
isb
isc
Ld
Vb’
Va’
Vc’
Va
Vb
Va”
Vb”
Vc”
Vc
4141Magnetics Rating = 22.55%
THD = 4.17% THD = 5.56%Full LoadFull Load Light LoadLight Load
4242
4343
CONFIGURATIONS
4444
Va1 = K1Va 00 - K2 Vb-1200
Va2 = K3Va - K4Vb-1200
Va3 = K1Va00 - K2Vc 1200
Va4 = K3Va 00 - K4Vc1200
Va1 = V 7.50 , Vb1 = V-112.50, Vc1 = V127.50
Va2 = V 22.50, Vb2 = V-97.50, Vc2 = V122.50
Va3 = V -7.50, Vb3 = V-127.50, Vc3 = V112.50 Va4 = V -22.50, Vb4 = V-142.50, Vc4 = V97.50
Va
Vb2
Va2 Va4
VbVc
7.507.50
22.50
22.50
Va1
Vb1
Vb3
Vb4
Vc1
Vc2
Vc3
Vc4
Va3
K1 =0.916, K2 = 0.15069, K3 = 0.7028 and K4 = 0.44189
Vb1
Va
Va1
VbVc
N
Va2
Va3
Va4
Vb2
Vb3Vb4Vc1 Vc2
Vc3
Vc4
K1
K3
K2
K4
4545
Va Va3
22.507.50
K2
K2'
K1
K1'
K3K3'
K4
K4'
Va2
Va2'
Va3'
VbVc
K4’= 0.4256
K1=0.88
24K2
= 0.1451
K3’ = 0.677
Va1’=0.916Va 00 – 0.15069Vb-1200
Va2’ =0.7028Va 00 – 0.44189Vb-1200
Va3’ =0.916Va00 – 0.15069Vc 1200
Va4’ =0.7028Va00 – 0.44189Vc 1200
4646
IGBT Based Inverter
A
B
C3 Phase, 415V,
50 Hz AC Mains
6 Pulse Diode Bridge Rectifiers
Cd
-
+
Zs
Zs
Zs
3 phase,VCIMD
+Vdc
IPT
isa
isb
isc
Ld
+
IPT
+
+
a1
b1
c1
a2
b2
c2
a3
b3
c3
a4
b4
c4
Vb1
VaVa1
VbVc
N
Va2
Va3
Va4
Vb2
Vb3Vb4Vc1 Vc2
Vc3
Vc4
Autotransformer
4747
THD = 3.45% THD = 6.56%
Full LoadFull Load Light LoadLight Load
4848
CURRENT INJECTION IN TWELVE-PULSE AC-DC CONVERTERS
4949
3 Phase, 415V, 50 Hz
isa
IGBT Based Inverter
A
B
C
Cd
+a'
b'
c'
a''
b"
c"Autotransformer
Zs
Zs
Zs
Vb’
Va
Va”Va’
VbVb”Vc’Vc
Vc” N 3phase,VC
IMD
+
Vdc
+
Inter PhaseTransformer
6 Pulse Diode Bridge Rectifier
isb
isc
ZSBT
D1D2
ZSBT
Ld
6 Pulse Diode Bridge Rectifier
Vd1 Vd2
5050
THD = 3.83% THD = 5.25%
Full LoadFull Load Light LoadLight Load
5151
Nine-Phase AC-DC Converters
Delta Connected Autotransformer
Phase shift = 3600/ Number of output phases
Va1
Va
VbVc
Va2
Vb1
Vb2Vc1
Vc2
K1
K2
Va1 = Va + K1Vca - K2 Vbc
Va2 =Va + K1Vab + K2Vbc
Va=V00, Vb=V-1200 , Vc = V1200
Va1 = V 400 , Vb1 = V-800, Vc1 = V1600
Va2 = V -400, Vb2 = V-1600, Vc2 = V800
K1 =0.156 K2 = 0.293
Va1 = Va + 0.156Vca - 0.293 Vbc
Va2 = Va + 0.156Vab + 0.293Vbc
Va
400 400
Vbc
Vab
Vca
Va1
Vc Vb
Va2
Vb1
Vb2Vc1
Vc2
400
400
400400400
400
400
5252
IGBT Based Inverter
A
B
C
3 Phase, 415V, 50 Hz
6 Pulse Diode Bridge Rectifiers
Cd
-
+
+
a1
b1
c1
a2
b2
c2
Autotransformer
Zs
Zs
Zs
a
b
c
3 phase,VC
IMD
+
Vdc
+
IPT
IPT
isa
isb
isc
Ld
Va1
Va
Vb
Vc
Va2
Vb1
Vb2Vc1
Vc2
5353
THD = 3.79% THD = 7.39%
Full LoadFull Load Light LoadLight Load
5454
Fifteen-Phase AC-DC Converters
Star Connected Autotransformer
Vb1
Va
Va1
VbVc
N
Va2
Va3Va4
Vb2
Vb3Vb4
Vc1Vc2
Vc3
Vc4
K1
K3
K2
K4
Va
Vb2
Va2 Va4
VbVc
Va1
Vb1
Vb3Vb4Vc1
Vc2
Vc3
Vc4
Va3
240240
240
240
240
240
240
240
240240
240
240
240
240240
Va1 = K1Va 00 - K2 Vb-1200
Va2 = K3Va 00 - K4Vb-1200
Va3 = K1Va00 - K2Vc 1200
Va4 = K3Va 00 - K4Vc1200
Va=V00, Vb=V-1200 , Vc = V1200
Va1 = V 240 , Vb1 = V-960, Vc1 = V1440
Va2 = V 480, Vb2 = V-720, Vc2 = V1680
Va3 = V -240, Vb3 = V-1440, Vc3 = V960
Va4 = V -480, Vb4 = V-1680, Vc4 = V720
5555
a1
A
B
C
6 Pulse Diode Bridge Rectifiers
Cd
-
Zs
Zs
Zs
+
Vdc
ia
ib
ic
+
IPT
b1
c1
a2
b2
c2
a3
b3
c3
a4
b4
c4
Vb1
Va
Va1
VbVc
N
Va2Va3
Va4
Vb2
Vb3Vb4Vc1Vc2
Vc3
Vc4
Autotransformer
a
b
c
IPT
+
+
+
+
Load
i
i1
i2
i3
i4
i5
5656
Magnetics Rating = 76%
THD = 2.38%
5757
Three-Phase Unidirectional 12-Pulse Converter
va
vb
vc
ia
ib
ic
La
Lb
Lc
a2
c2
a1
c1
b1o15
b2 o15
Autotransformer
Li1
Li2
vdc
Load
idc
a
bc
a2c2
c1
b1
b2
a1
Cd
Extended Delta Connection Based 12-Pulse AC-Extended Delta Connection Based 12-Pulse AC-DC ConverterDC Converter
5858
Three-Phase Unidirectional 18-Pulse Converter
o20
o20
Autotransformer
va
vb
vc
ia
ib
ic
La
Lb
Lc
o0
Li1
vdc
Load
idc
Li2
Cd
Extended Delta Connection Based Extended Delta Connection Based 18-Pulse AC-DC Converter 18-Pulse AC-DC Converter
5959
Extended Delta Connection BasedExtended Delta Connection Based 18-Pulse AC-DC Converter 18-Pulse AC-DC Converter
LOAD
6060
Harmonic Spectrum of 18-pulse AC-DC Harmonic Spectrum of 18-pulse AC-DC converterconverter
6161
A A six-pulse diode-bridgesix-pulse diode-bridge fed vector-controlled induction fed vector-controlled induction motor drive (VCIMD) and the controller.motor drive (VCIMD) and the controller.
Zs
Zs
Zs
isa
isb
isc
+
-
6- pulse rectifier
Cd Vdc
Ld
IGBT Based Inverter
~~~
PWM Current
Controller
Field Orientation
and Reference Current
Generation
Estimator for
idm* , iqm* , ω2
*
LimiterPI Speed
Controller
Field Weakening
3 Phase IM
3- Phase AC Mains
ima
imb
imc
ima
imb
ima*
imb*
imc*
idm*
iqm*
ω2*
imr
T T*
ωr
ωrωrωr
*
6262
Dynamic response of 6-pulse diode rectifier fed VCIMD with load perturbation--supply phase voltage VA, source current isA, motor currents
Iabc, speed wr, developed electromagnetic torque Te and DC link voltage Vdc.
6363
Input current waveform and harmonic spectrum of 6-pulse AC-DC converter at full-load.
6464
Twelve-pulse AC-DC converter based on fork-transformer configuration.
3-phase AC
Mains
~~~
iA LOAD
+
-
K1
K2
Vdc
idc
K3
6565
Three-phase supply voltage applied to the input of autotransformer as
0sc
0sb
0sa 120VV ,120VV ,0VV
K1+ K2=1
Output voltages of this configuration are expressed as
b3a1a1 VKVKV
c3a1a2 VKVKV
K1=0.8165, K2= 0.1835, K3= 0.2988
6666
Non-Isolated fork-connection based 24-Pulse AC-DC converterNon-Isolated fork-connection based 24-Pulse AC-DC converter
IPR
3-phase AC
Mains
~~~
iA LOAD
+
-
VDC
iDC
DB1
DB2
DB3
DB4
6767
a
bc
a1
a2a3
a4
b1
b2
b3b4c1c2
c3
c4
K4
K7
K6
K5
nVA
VB
VC
DB1
DB2
DB3
DB4
K8
7.5°
7.5°
7.5° 7.5°
a
bc
n
a1
7.5°7.5°
15° 15°
15°15°
a2 a3a4
b1
b2
b3
b4c1
c2
c3
c4
Phasor representation of transformer for 24-pulse AC-DC converter having fork connected windings.
Winding arrangement of transformer for 24-pulse AC-DC converter having fork connected windings.
6868
0sc1
0sb1
0sa1 217.5VV ,5.97VV ,5.22VV
0sc2
0sb2
0sa2 232.5VV ,5.112VV,5.7VV
0sc3
0sb3
0sa3 247.5VV ,5.127VV,5.7VV
0sc4
0sb4
0sa4 262.5VV ,5.142VV ,5.22VV
The four sets of required voltages for the converters DB1 to DB4 are:
6969
b6b5a4a1 VKVKVKV
a7b5a4a2 VKVKVKV
15-VV a2a3
45-VV a1a4
K8 = 1 - K4
K4=0.7029, K5= 0.1507, K6= 0.2912, K7= 0.2132, K8 =0.2971
The output voltages can be expressed as follows:
7070
Matlab model of 24-pulse AC-DC converter with VCIMD load.
7171
15Out43
14Out33
13Out42
12Out32
11Out41
10Out31
9Out23
8Out22
7Out13
6Out12
5
In3
4In2
3Out21
2Out11
1In1 1+
1
+2
2
+3
3
+4
4
+5
5
+6
6
+7
7
+8
8
PhC
1+
1
+2
2
+3
3
+4
4
+5
5
+6
6
+7
7
+8
8
PhB
1+
1
+2
2
+3
3
+4
4
+5
5
+6
6
+7
7
+8
8
PhA
Matlab model of auto-transformer for the 24-pulse AC-DC converter system simulation.
7272
-400-200
0200400
VA
(V)
0
I ac(A
)
-50
0
50
I abc (
A)
0
100200
Time(sec)
wr(r
ps)
-50
050
100150
T e(N-m
)
0.05 0.1 0.15 0.2 0.25 0.30
500
Time (sec.)
Vdc
(V
)
Dynamic response of 24-pulse diode rectifier fed VCIMD with load perturbation----- supply phase voltage VA, source current isA, motor currents Iabc, speed wr, developed electromagnetic torque Te and DC link voltage
7373
0.76 0.77 0.78 0.79 0.8-40
-20
0
20
40
I A (
A)
time (s)
0 12 24 36 48 600
20
40
60
80
100
THD = 3.221%
% M
agni
tude
Harmonic order
Input current waveform and harmonic spectrum of 24-pulse AC-DC converter at full-load.
7474
Topo-Topo-logylogy
LoadLoad AC MainsAC MainsCurrent ICurrent I
acac
(A)(A)
% THD of% THD ofIIacac
atat
DistortionDistortionFactorFactor
DFDF
DisplacementDisplacementPower FactorPower Factor
DPFDPF
PowerPowerFactorFactor
PFPF
DC VoltageDC Voltage(V)(V)
LightLight FullFull LightLight FullFull LightLight FullFull LightLight FullFull LightLight FullFull LightLight FullFull
LoadLoad LoadLoad LoadLoad LoadLoad LoadLoad LoadLoad LoadLoad LoadLoad LoadLoad LoadLoad LoadLoad
6-6-pulsepulse
10.5810.58 8.7018.701 19.1219.12 74.6874.68 31.2431.24 0.91100.9110 0.94910.9491 0.97980.9798 0.97680.9768 0.89260.8926 0.92710.9271 552.9552.9 542.8542.8
12-12-pulsepulse
5.2245.224 8.5788.578 18.8718.87 9.6979.697 8.988.98 0.99460.9946 0.99460.9946 0.98930.9893 0.98980.9898 0.98400.9840 0.98450.9845 555.7555.7 549.4549.4
24-24-pulsepulse
3.0363.036 8.3788.378 18.7418.74 3.9743.974 3.2213.221 0.99900.9990 0.99910.9991 0.99310.9931 0.98910.9891 0.99210.9921 0.98820.9882 578.2578.2 570.7570.7
COMPARISON OF POWER QUALITY PARAMETERS OF DIFFERENT AC-DC CONVERTERS.
7575
Comparison of power quality parameters of12-pulse and 24-pulse AC-DC converters with varying load
Topology
Topology
LoadLoad THD of THD of VVacac
(%)(%)
AC AC Mains Mains CurrenCurrent It Iacac
(A)(A)
THD of THD of
IIacac(%)(%)
Distort-Distort-ion ion
Factor, Factor, DFDF
DisplaceDisplacement ment
Power Power Factor, Factor,
DPFDPF
Power Power Factor, Factor,
PFPF
DC DC Voltage Voltage
(V)(V)
Load Load CurreCurrent Int Idcdc
(A)(A)
Ripple Ripple FactorFactor, RF , RF (%)(%)
12-pulse12-pulse
20%20% 2.8512.851 8.5788.578 9.6979.697 0.99460.9946 0.98930.9893 0.98400.9840 555.7555.7 10.2810.28 0.0060.006
40%40% 3.4943.494 11.0311.03 9.5339.533 0.99480.9948 0.98970.9897 0.98460.9846 554.2554.2 13.2113.21 0.0020.002
60%60% 3.9813.981 13.5813.58 9.3639.363 0.99480.9948 0.98990.9899 0.98480.9848 552.6552.6 16.4816.48 0.0040.004
80%80% 4.6744.674 16.2216.22 9.1799.179 0.99460.9946 0.99000.9900 0.98470.9847 551.0551.0 19.8519.85 0.0030.003
100%100% 5.2245.224 18.8718.87 8.988.98 0.99460.9946 0.98980.9898 0.98450.9845 549.4549.4 23.2423.24 0.0020.002
24-pulse24-pulse
20%20% 2.0282.028 8.3788.378 3.9743.974 0.99900.9990 0.99310.9931 0.99210.9921 578.2578.2 10.2510.25 0.0000.00022
40%40% 2.2862.286 10.7310.73 3.7633.763 0.99880.9988 0.99220.9922 0.99100.9910 576.4576.4 13.1413.14 0.0000.00011
60%60% 2.5502.550 13.3113.31 3.5563.556 0.99920.9992 0.99100.9910 0.99020.9902 574.5574.5 16.3316.33 0.0020.002
80%80% 2.7852.785 16.0016.00 3.3763.376 0.99900.9990 0.99010.9901 0.98910.9891 572.7572.7 19.6619.66 0.0030.003
100%100% 3.0363.036 18.7418.74 3.2213.221 0.99910.9991 0.98910.9891 0.98820.9882 570.7570.7 23.0423.04 0.0020.002
7676
MATLAB model of the proposed autotransformer for 24-pulse AC-DC converter
Topology
Load AC MainsCurrent Iac
(A)
% THD ofIac
at
DistortionFactor
DF
DisplacementPower Factor
DPF
PowerFactor
PF
DC Voltage(V)
Light Full Light Full Light Full Light Full Light Full Light Full
Load Load Load Load Load Load Load Load Load Load Load
6-pulse
10.58 8.701 19.12 74.68 31.24 0.9110 0.9491 0.9798 0.9768 0.8926 0.9271 552.9 542.8
12-pulse
5.224 8.578 18.87 9.697 8.98 0.9946 0.9946 0.9893 0.9898 0.9840 0.9845 555.7 549.4
24-pulse
3.036 8.378 18.74 3.974 3.221 0.9990 0.9991 0.9931 0.9891 0.9921 0.9882 578.2 570.7
7777
Input current waveform of 12-pulse AC-DC converters at light load and its harmonic spectrum
7878
Dynamic response of 24-pulse diode rectifier fed VCIMD with load perturbation--supply phase voltage VA, source current isA, motorcurrents Iabc, speed wr, developed electromagnetic torque Te and DC link voltage.
7979
Input current waveforms of 24 pulse AC-DC converter at full load and its harmonic spectrum.
8080
Comparison of magnetic ratings in different AC-DC converters
Sr.Sr.No.No.
TopologyTopology Main Main Transformer Transformer
ratingrating(% of load)(% of load)
Interphase Interphase transformer ratingtransformer rating
(% of load}(% of load}
Total Total magnetic rating magnetic rating
(% of load)(% of load)
11 12-pulse12-pulse 28.6828.68 7.507.50 36.1836.18
22 24-pulse24-pulse 49.249.2 7.367.36 56.5656.56
8181
POLYGON CONNECTED AUTOTRANSFORMER BASED 24-PULSE AC-DC CONVERTER
K2
K1
K3K4
Va
VbVc
Va1
Va2
Va3
Va4
Vb1
Vb2
Vb3
Vb4
Vc1
Vc2
Vc3
Vc4
A
BC
K1 K2
K3K4
N
E
Va
Vb2
Va2 Va4
VbVc
7.507.50
22.5022.50
Va1
Vb1
Vb3
Vb4
Vc1
Vc2
Vc3
Vc4
Va3
8282
Va1 = Va - K1 Vbc + K2 Vca (1) Va2 = Va1 - K3 Vbc + K4 Vca (2)Va3 = Va + K1 Vbc - K2 Vab (3) Va4 = Va3 + K3 Vbc - K4 Vab (4)Assume the following set of voltages:Va=V00, Vb=V-1200 , Vc = V1200 (5)Va1 = V 7.50 , Vb1 = V-112.50, Vc1 = V127.50 (6)Va2 = V 22.50, Vb2 = V-97.50, Vc2 = V122.50 (7)Va3 = V -7.50, Vb3 = V-127.50, Vc3 = V112.50 (8)Va4 = V -22.50, Vb4 = V-142.50, Vc4 = V97.50 (9)
K1 =0.07249, K2 = 0.00576,
K3 = 0.123 and K4 = 0.04509
DESIGN
8383
K1 cos 600 +K2 + K3 cos 600 +K4 + N + K1 cos 600 + K2 + K3 cos 600 = 1 (10) 2K2 +2K4 +K1 + K3 + N = 1 (11) N= 0.6987 (12)
Va1 =Va – 0.071Vbc + 0.00855Vca (13)Va2 =Va3 – 0.123 Vbc + 0.04509 Vca (14)
Va3 =Va + 0.071 Vbc – 0.00855 Vab (15)Va4 =Va + 0.123 Vbc – 0.04509 Vab (16)
8484
IGBT Based Inverter
A
B
C3 Phase, 415V,
50 Hz
6 Pulse Diode Bridge Rectifiers
Cd
-
+
Autotransformer
Zs
Zs
Zs
3 Phase,VCIMD
+Vdc
IPT
isa
isb
isc
Ld
+
IPT
+
+
a1
b1
c1
a2
b2
c2
a3
b3
c3
a4
b4
c4
Va
VbVc
A
BC
8585
Va
Vb
Va1
Va2
Va3
Va4
Vb1'
Vb2'
Vb3'
Vb4'
AK1
K2K3
K4
K1'
K2'
K4'
7.50
7.50
22.50
22.50
7.50
K3'
22.50
22.50
K1’= 0.0546
K2’= 0.0347
K3’=0.1175
K4’= 0.04314
N’ = 0.6722
8686
8787
Dynamic response of 6-pulse diode rectifier fed VCIMD with load perturbation.
8888
8989Dynamic response of 24-pulse ac-dc converter based proposed harmonic mitigator fed VCIMD with load perturbation.
9090
Magnetics Rating = 27.5%
9191
Load Load (%)(%)
THD (%)THD (%) CF CF of Iof I
ss
DFDF DPFDPF PFPF VVdcdc
(V)(V)IIss VVtt
2020 5.225.22 1.761.76 1.431.43 .998.998 .989.989 .988.988 557557
4040 4.654.65 1.901.90 1.431.43 .999.999 .990.990 .989.989 553553
6060 4.414.41 2.312.31 1.431.43 .999.999 .989.989 .989.989 551551
8080 4.054.05 2.512.51 1.441.44 .999.999 .988.988 .988.988 547547
100100 3.203.20 2.732.73 1.441.44 .999.999 .988.988 .988.988 546546
9292
Comparison of power quality indices of a VCIMD fed from different converters
Sr. Sr. NoNo
TopoTopologylogy
THD THD of Vof V
ss
(%)f(%)fFLFL
Supply Current Supply Current IIss (A) (A)
Total Total Harmonic Harmonic
Distortion of Distortion of IIss (%) (%)
Distortion Distortion FactorFactor
Displacement Displacement FactorFactor
Power FactorPower Factor DC Link DC Link Voltage(V)Voltage(V)
AverageAverage
FLFL LLLL(20%)(20%)
FLFL LLLL(20%)(20%)
FLFL LLLL(20%)(20%)
FLFL LLLL(20%)(20%)
FLFL LLLL(20%)(20%)
FLFL LLLL(20%)(20%)
1.1. AA 6.536.53 12.5212.52 4.024.02 30.730.7 57.257.2 .955.955 .868.868 .980.980 .959.959 .937.937 .833.833 545545 556556
2.2. BB 2.802.80 10.6210.62 2.332.33 3.263.26 5.175.17 .998.998 .999.999 .989.989 .988.988 .987.987 .987.987 570570 578578
3.3. CC 2.732.73 10.5910.59 2.312.31 3.203.20 5.225.22 .998.998 .999.999 .989.989 .988.988 .988.988 .988.988 546546 557557
9393
An Isolated Fork Connected Transformer Based 24-Pulse AC-
DC Converter
9494
Six-pulse diode bridge rectifiers with delta and star-Six-pulse diode bridge rectifiers with delta and star-connected transformers supply are commonly used.connected transformers supply are commonly used.
3-phase AC
Mains
~~~
iA
1 : a
LOAD
Six-Pulse Diode Bridge
i DC
VDC
+
-
A 6-pulse AC-DC converter using delta/star transformer.
9595
iA
1:a
Load
Six- Pulse Diode Bridge
Vdc
+
-
idc
~~~
Delta/star Transformer
3- phase AC
Mains
A 6-pulse AC-DC converter using delta/star transformer
Twelve-pulse AC-DC converter based on fork-transformer configuration-
3-phase AC
Mains
~~~
iALOAD
+
-
VDC
iDC
1 : a
K1K2
9696
IPR
3-phase AC
Mains
~~~
iA LOAD
+
-
VDC
iDC
1 : aDB1
DB2
DB3
DB4
Twenty four-pulse AC-DC converter based on fork-transformer configuration-
9797
Delta/fork transformer winding arrangement for 24-pulse AC-DC converter.
A
BC
Primary
a1
Secondary
a2a3
a4
b1
b2
b3b4c1
c2
c3
c4
K1
K4
K3K2
n
VA
VB
VC
DB1
DB2
DB3
DB4
9898
Phasor representation of transformer for 24-pulse Phasor representation of transformer for 24-pulse AC-DC converter having fork connected secondary AC-DC converter having fork connected secondary
winding winding
7.5°
7.5°
7.5°
7.5°
Va
VbVc
n
a1
Secondary
7.5°7.5°
15° 15°
15° 15°
a2 a3
a4
b1
b2
b3
b4c1
c2
c3
c4
A
N
BC
Primary
9999
0sC
0sB
0sA 120VV ,120VV ,0VV
Three-phase supply voltage applied to the primary of transformer as
Secondary phase voltages for the transformer with transformation ratio ‘a’ (a= Va/VA)
Four sets of required voltages for the converters DB1 to DB4 are
CcBbAa VaV ,VaV ,VaV
0sc1
0sb1
0sa1 217.5VV ,5.97VV ,5.22VV
0sc2
0sb2
0sa2 232.5VV ,5.112VV,5.7VV
0sc3
0sb3
0sa3 247.5VV ,5.127VV,5.7VV
0sc4
0sb4
0sa4 262.5VV ,5.142VV ,5.22VV
100100
K1=0.7029, K2= 0.15072, K3= 0.29116, K4= 0.21315
b3b2a1a1 VKVKVKV
a4b2a1a2 VKVKVKV
15-VV a2a3
45-VV a1a4 45-VV a1a4
45-VV a1a4
kVA rating = 0.5 ∑ (Vwinding I winding)
TUF= PDC/∑ (Vsec . Isec)
101101
MATLAB model of the 24-pulse AC-DC converter
v+-
Vin2
v+
-
Vin1
In1
In2
In3
Out11
Out21
Out12
Out13
Out22
Out23
Out31
Out41
Out32
Out42
Out33
Out43
Fork24-pulseISO-Xer
Transformer
LOAD
Scope2
Scope
12
LT3
12
LT2
12
LT1
12
LT
i+ -
Iin3
i+ -
Iin2
i+ -
Iin1
i+ -
Iin
A
B
C
+
-
DB4
A
B
C
+
-
DB3
A
B
C
+
-
DB2
A
B
C
+
-
DB1
N
A
B
C
3-Ph
vA
iA
iB
iC
102102
MATLAB model of the proposed transformer for 24-pulse AC-DC converter
15Out43
14Out33
13Out42
12Out32
11Out41
10Out31
9
Out23
8Out22
7Out13 6
Out12
5
In34
In2
3Out21
2Out11
1In1
1+
1
+2
2
+3
3
+4
4
+5
5
+6
6
+7
7
+8
8
PhC
1+
1
+2
2
+3
3
+4
4
+5
5
+6
6
+7
7
+8
8
PhB
1+
1
+2
2
+3
3
+4
4
+5
5
+6
6
+7
7
+8
8
PhA
103103
Comparison of power quality parameters of12-pulse and 24-pulse AC-DC converters with varying
load
TopologyTopology LoadLoad THD of THD of VVacac (%) (%)
AC Mains AC Mains Current ICurrent I
acac
(A)(A)
THD of THD of I I
acac(%)(%)Distortion Distortion Factor, DFFactor, DF
Displacement Displacement Power Factor, Power Factor,
DPFDPF
Power Power Factor, Factor,
PFPF
DC DC Voltage Voltage
(V)(V)
Load Load Current Current IIdcdc (A) (A)
Ripple Ripple Factor, Factor, RF (%)RF (%)
12-Pulse12-Pulse
40%40% 2.0052.005 11.3111.31 10.3710.37 0.99450.9945 0.99150.9915 0.98600.9860 297.8297.8 26.4726.47 1.0281.028
60%60% 2.6562.656 16.7716.77 9.9279.927 0.99480.9948 0.99050.9905 0.98530.9853 295.5295.5 39.4039.40 0.90520.9052
80%80% 3.2173.217 22.1322.13 9.6869.686 0.99480.9948 0.98900.9890 0.98390.9839 293.2293.2 52.1252.12 0.85390.8539
100%100% 3.6793.679 27.4227.42 9.249.24 0.99500.9950 0.98760.9876 0.98270.9827 290.9290.9 64.6464.64 0.82870.8287
24-Pulse24-Pulse
40%40% 1.5051.505 11.3411.34 4.4614.461 0.99890.9989 0.99150.9915 0.99040.9904 299.3299.3 26.6026.60 0.32320.3232
60%60% 1.9881.988 16.8816.88 4.5424.542 0.99880.9988 0.99210.9921 0.99090.9909 297.8297.8 39.739.7 0.35540.3554
80%80% 2.3652.365 22.3122.31 4.1434.143 0.99890.9989 0.99250.9925 0.99140.9914 296.3296.3 52.6752.67 0.38080.3808
100%100% 2.7012.701 27.7327.73 2.7042.704 0.99870.9987 0.99230.9923 0.99100.9910 294.8294.8 65.565.5 0.44870.4487
104104
Comparison of power quality parameters of Comparison of power quality parameters of the 12-Pulse and 24-Pulse AC-DC converters the 12-Pulse and 24-Pulse AC-DC converters
with 6-Pulse AC-DC Converter with 6-Pulse AC-DC Converter
Topology
Topology
LoadLoad AC MainsAC MainsCurrent ICurrent I
ac ac (A)(A)% THD of% THD of
IIacac at atDistortionDistortionFactor DFFactor DF
DisplacementDisplacementPower Factor Power Factor
DPFDPF
PowerPowerFactor PFFactor PF
DC VoltageDC Voltage(V)(V)
LightLightLoadLoad
FullFullLoadLoad
LightLightLoadLoad
FullFullLoadLoad
LightLightLoadLoad
FullFullLoadLoad
LightLightLoadLoad
FullFullLoadLoad
LightLightLoadLoad
FullFullLoadLoad
LightLightLoadLoad
FullFull
6-pulse6-pulse
4.724.72 5.8945.894 27.9927.99 27.6427.64 24.1324.13 0.9630.963 0.9710.971 0.9940.994 0.9750.975 0.9580.958 0.9470.947 30033003 290.6290.6
12-pulse12-pulse
3.6793.679 5.7565.756 27.4227.42 10.8110.81 9.249.24 0.9930.993 0.9950.995 0.9900.990 0.9870.987 0.9840.984 0.9820.982 300.2300.2 290.9290.9
24-pulse24-pulse
2.7012.701 5.7775.777 27.7327.73 4.874.87 2.702.70 0.9980.998 0.9980.998 0.9840.984 0.9920.992 0.9830.983 0.9910.991 300.8300.8 294.8294.8
105105
Waveforms of 6-pulse AC-DC converter at full-load.
Input current waveform of 6-pulseAC-DC converter at full-load and its harmonic spectrum.
106106
Input current waveform of 12-pulse AC-DC converters at light load and its harmonic spectrum
Waveforms of 12-pulse AC-DC converter at full-load.
107107
Input and output voltage and currentwaveforms of 24-pulse AC-DC converter at full load.
Input current waveforms of 24 pulse AC-DC converter at full loadand its harmonic spectrum.
108108
Comparison of magnetic ratings in different AC-DC converters
Sr.Sr.No.No.
TopologyTopology Main Main TransforTransfor
mer mer ratingrating
(% of load)(% of load)
Interphase Interphase transformer transformer
ratingrating(% of load}(% of load}
Total Total magnetic magnetic
rating rating (% of (% of load)load)
11 6-pulse6-pulse 102.73102.73 -- 102.73102.73
22 12-pulse12-pulse 108.78108.78 8.088.08 116.86116.86
33 24-pulse24-pulse 106.63106.63 7.367.36 113.99113.99
109109
A 36-Pulse AC-DC Converter for Line Current Harmonic Reduction
110110
iA
1:a
Load
Six- Pulse Diode Bridge
Vdc
+
-
idc
~~~
Delta/star Transformer
3- phase AC
Mains
A 6-pulse AC-DC converter using delta/star transformer
Proposed Fork
Based36-pulse
Transfor-mer
3-Phase AC
Mains
18 Pulse Diode Bridge Rectifier,
DB1
18 Pulse Diode Bridge Rectifier,
DB2
~~~
Zs
Zs
Zs
iA
iB
iC
Ld
IPR
IPR
+
-
LoadVdc
B11
B19
B21
B29
Proposed delta/fork transformer based 36-pulse AC-DC converter.
111111
VB
VA
K1
K2K3
K4
K5
K6
A
BC
Primary
a1
Secondary
a2a3 a4
b1
b2
b3b4
c1
c2c3
c4
n
VC
DB1
DB2
a5
a6
b5
b6
c5
c6
B11B12
B13
B14
B15
B16
B17
B18
B19
B21B22
B23
B24
B25
B26
B27B28
B29
iAB
iBC
iCA
iA
iB
iC
50
50
300
300
300
300300
300
300
300
300
100
100
100
100
100
50
5050
50
100
VB11
VB21
VB12
VB13
VB14
VB15
VB16
VB17
VB18
VB19
VB22
VB23
VB24
VB25
VB26
VB27
VB28
VB29
VsBVsC
VsAVsA= VR
Graphical representation of delta/polygon transformer secondary for 36-pulse AC-DC converter and phasor diagram.
Delta/fork transformer winding arrangement for 36-pulse AC-DC converter.
112112
527VV ,523VV ,195VV
,155VV,115VV ,75VV
,35VV ,5VV ,45VV
RB19RB18RB17
RB16RB15RB14
RB13RB12RB11
528VV ,524VV ,205VV
,165VV,125VV ,85VV
,45VV ,5VV ,35VV
RB29RB28RB27
RB26RB25RB24
RB23RB22RB21
)VKK(VKV sB54sA1B11
VK)VKK(V sB4sA31B21
VKV)KK(V sB6sA21B12
sC6sA21B22 VKV)KK(V
VK)VKK(V sC4sA31B13
)VKK(VKV sC54sA1B23
0.1006K , 1542.0K
0.6623,K 0.1891,K 0.6471,K 0.2988,K
65
4321
113113
v+-
Vab2
v+-
Vab1
LOAD
Scope2
Scope1
i+-
Iin3
i+-
Iin2i+-
Iin1
i+-
Iin
Conn1
Conn2Conn3
IPR2
Conn1
Conn2Conn3
IPR
C1
C2
C3
C4
C5
C6
C7
C8
C9
C10
C11
D3
C1
C2
C3
C4
C5
C6
C7
C8
C9
C10
C11
D1
In1
In2
In3
Out1
Out2
Out3
Out4
Out5
Out6
Out7
Out8
Out9
OutB1
OutB2
OutB3
OutB4
OutB5
OutB6
OutB7
OutB8
OutB9
Fork36pulse
Xer
36-pulse Fork Xer
N
A
B
C
3-Ph Source
MATLAB model of the 36-pulse AC-DC converter
114114
21
OutB9
20
OutB8
19
OutB7
18
OutB6
17
OutB5
16
OutB4
15
OutB3
14
OutB2
13
OutB1
12
Out9
11
Out8
10
Out7
9
Out6
8
Out5
7
Out4
6
Out3
5
Out2
4
Out1
3
In32
In2
1
In11+
1
2+
2
3+
3
4+
4
5+
5
6+
6
7+
7
+8
8
+9
9
+10
10
+11
11
PhC
1+
1
2+
2
3+
3
4+
4
5+
5
6+
6
7+
7
+8
8
+9
9
+10
10
+11
11
PhB
1+
1
2+
2
3+
3
4+
4
5+
5
6+
6
7+
7
+8
8
+9
9
+10
10
+11
11
PhA
MATLAB model of the proposed transformer for 36-pulse AC-DC converter
115115
LoadLoad THD THD VVacac
(%)(%)
AC AC Mains Mains
Current Current IIacac (A) (A)
THD of THD of
IIacac(%)(%)
Distortion Distortion Factor,Factor,
DFDF
DisplaceDisplace-ment -ment
Factor,Factor,DPFDPF
Power Power Factor,Factor,
PFPF
DC DC VoltagVoltage (V)e (V)
Load Load Current Current IIdcdc (A) (A)
Ripple Ripple Factor (%)Factor (%)
20%20% 0.75710.7571 5.7875.787 3.013.01 0.99950.9995 0.99840.9984 0.99790.9979 302.9302.9 13.4613.46 0.23770.2377
40%40% 1.0741.074 11.4611.46 2.1692.169 0.99970.9997 0.99720.9972 0.99690.9969 301.8301.8 26.8326.83 0.32790.3279
50%50% 1.1551.155 14.2814.28 1.8551.855 0.99980.9998 0.99670.9967 0.99650.9965 301.3301.3 33.4833.48 0.37530.3753
60%60% 1.1931.193 17.0917.09 1.6051.605 0.99980.9998 0.99620.9962 0.99600.9960 300.8300.8 40.1040.10 0.42230.4223
80%80% 1.2101.210 22.6822.68 1.3141.314 0.99990.9999 0.99510.9951 0.99500.9950 299.6299.6 53.2753.27 0.52170.5217
100100%%
1.2141.214 28.2128.21 1.1971.197 0.99980.9998 0.99370.9937 0.99350.9935 298.4298.4 66.3066.30 0.62410.6241
Comparison of power quality parameters of proposed 36-pulse AC-DC converters with varying load
116116
Comparison of power quality parameters of Comparison of power quality parameters of the 36-Pulse AC-DC converters With 6-Pulse the 36-Pulse AC-DC converters With 6-Pulse AC-DC Converter at full-load and light load AC-DC Converter at full-load and light load
TopologTopologyy
%THD%THDVVacac
% THD of % THD of IIacac, at, at
Distortion Distortion FactorFactor
DisplacemeDisplacement Factornt Factor
Power Power FactorFactor
DC VoltageDC Voltage(V)(V)
FullFullLoadLoad
LightLightLoadLoad
FullFullLoadLoad
LightLightLoadLoad
FullFullLoadLoad
LightLightLoadLoad
FullFullLoadLoad
LightLightLoadLoad
FullFullLoadLoad
LightLightLoadLoad
6-pulse6-pulse 4.0564.056 24.8124.81 27.9327.93 .9815.9815 .9943.9943 .9698.9698 .9630.9630 .9519.9519 .9575.9575 279.2279.2 294.4294.4
36-pulse36-pulse 1.2141.214 1.1971.197 3.013.01 .9998.9998 .9995.9995 .9737.9737 .9984.9984 .9935.9935 .9979.9979 298.4298.4 302.9302.9
117117
The instantaneous values of input phase voltage (vA), input AC mains current (iA), primary winding currents (iAB and iCA), winding-currents of secondary (iK1 to iK6), a bridge output current (idc1) of 36-pulse AC-DC converter.
118118
Input current waveform of 6-pulse AC-DC converter at light-load andits harmonic spectrum
Input current waveform of 6-pulse AC-DC converter at full-load andits harmonic spectrum
Input and output voltage and current waveforms of 36-pulse AC-DC converter at light load
Input current waveform of 36-pulse AC-DC converters at light load and its harmonic spectrum
119119
Input and output voltage and current waveforms of 36-pulse AC-DC converter at full load.
Input current waveforms of 36 pulse AC-DC converter at full load and its harmonic spectrum.
120120
Test result showing input power, voltage along with current waveforms and input current harmonic spectrum at (a) light load and (b) full-load.
121121
Sr.Sr.No.No.
TopologyTopology Main Transformer Main Transformer ratingrating
(% of load)(% of load)
IPTIPT ratingrating(% of (% of load)load)
Total Total rating of rating of magneticsmagnetics
,,(% of load)(% of load)
11 6-pulse6-pulse 108.0108.0 -- 108.0108.0
22 36-36-pulsepulse
124.2124.2 0.850.85 125.0125.0
Comparison of magnetic ratings in different AC-DC converters
122122
LoadLoad(kW)(kW)
THD VTHD Vacac
(%)(%)AC Mains AC Mains
Current Current IIacac (A) (A)
THD of THD of I Iacac
(%)(%)
DPFDPF PFPF VVdcdc
(V)(V)IIdcdc
(A)(A)
1.211.21 1.301.30 3.053.05 2.32.3 1.01.0 0.9990.999 168.6168.6 7.2567.256
2.162.16 1.401.40 5.385.38 2.52.5 1.01.0 0.9990.999 160.9160.9 12.8612.86
3.083.08 1.301.30 7.797.79 2.22.2 1.01.0 0.9990.999 151.4151.4 18.4018.40
4.094.09 1.301.30 10.2810.28 2.12.1 1.01.0 0.9980.998 143.7143.7 24.2124.21
5.295.29 1.301.30 13.2913.29 2.12.1 1.01.0 0.9960.996 133.7133.7 31.0931.09
6.026.02 1.201.20 15.2715.27 2.02.0 1.01.0 0.9960.996 127.8127.8 35.3735.37
Test results showing power quality parameters of 36-pulse AC-DC converter
123123
The propose 36-pulse AC-DC converter is realized by three 2.2kVA, single-phase transformers and the design details are as follows:
Flux Density: 0.8Tesla, Current Density: 2.3A/mm2, Turns per volt: 0.88E-Laminations: Length=23.5cm, Width=16cmI-Laminations: Length=23.5cm, Width= 4cmEffective Area of cross-section of core=58cm2 (7.6 cm X 8.6cm)
124124
Transformer winding details WindingNumber of turns Gauge of wire (SWG)
Winding voltageWinding voltage No. of No. of TurnsTurns
Gauge of Wire Gauge of Wire (SWG)(SWG)
VVACAC 365365 1717
KK11*V*VRR 3131 1515
KK22 *V *VRR 6868 1717
KK33* V* VRR 2020 1717
KK44 *V *VRR 69.569.5 1717
KK55* V* VRR 1616 1717
KK66* V* VRR 10.510.5 1717
125125
T-Connected Isolated TransformerT-Connected Isolated TransformerBased AC-DC ConverterBased AC-DC Converter
126126
A Six-Pulse A Six-Pulse T-ConnectedT-Connected AC-DC Converter AC-DC Converter
LOAD
Six-Pulse Diode Bridge
1:a13-phase AC
Mains
~~~
VA
VBVC
iA
iB
iDC
VDC
+
-iC
TSTP
MS2MP1MP2 MS1
127127
Waveforms of 6-pulse AC-DC converter at full-load.
128128
Input current waveform and harmonic spectrum of 6-pulse AC-DC converter at full-load.
0.05 0.06 0.07 0.08
-45
0
45
I A (
A)
time (s)
0 12 24 36 48 0
20
40
60
80
100
THD = 23.89%
% M
agni
tude
Harmonic Order
129129
Twelve-pulse AC-DC converter based on T-transformer configuration.
3-phase AC
Mains
iDC
1:a2
~~~
iA
iB
iC
VA
VBVC
LOAD
+
-
VDC
IPR
130130
Connection diagram of T-connected transformer for isolated Connection diagram of T-connected transformer for isolated 24-pulse AC-DC converter. 24-pulse AC-DC converter.
iDC
1:a2
3-phase AC
Mains
~~~
iA
iB
iC
VA
VBVC
LOAD
+
-
VDC
IPR
ZSBT
D1 D2
NA
NBVm
131131
Winding arrangement and phasor representation of transformer for 12 and 24-pulse AC-DC converter having T-connected windings.
TP1
MP1MP2
A
N
BC
Primary
TS1
TS2
TS3
TS5
TS4
TS6
MS1MS2
MS3
MS4MS7
MS6 MS5
MS8
15° 15°
15°
15°
15°15°
a
bc
n
a’ a”
b”
b’c”
c’
Secondary
132132
Design of Transformer for 12-Pulse and 24-Pulse AC-DC ConvertersThe voltages across primary winding of the T-connected transformers VTP1= 0.866 VLP VMP1= VMP2=0.5 VLPThe secondary voltage produced is related to primary voltage by the transformation ratio. a3 = VLP / VLSThe secondary produces two sets of three-phase voltages that are displaced from respective primary voltages by +15° and -15°. The various winding voltages in terms of secondary voltage VLS can be determined from Fig. 3 by following relations.VTS1= K1*VLSVTS2= K2*VLSVTS3= VTS3= K3*VLSVTS5= VTS6= K4*VLSVMS1= VMS2= K5*VLSVMS3= VMS8= K6*VLSVMS4= VMS7= K7*VLSVMS5= VMS6= K8*VLS
133133
The values of constants K1 to K8 are:K1=0.5577, K2=0.2887, K3=0.1392, K4=0.1196,K5=0.1494, K6=0.0577, K7=0.0917, K8=0.4082
134134
MATLAB model of T-transformer based 24-pulse AC-DC converter
135135
Matlab model of T-transformer for the 24-pulse AC-DC converter system simulation.
136136
Waveforms of 12-pulse T-connected AC-DC converter at full-load - supply phase voltage VA, supply line currents IA, IB and IC , output DC link current (IDC) and voltage (VDC).
137137
Input current waveform and harmonic spectrum of 12-pulse T-connected AC-DC converter at full-load.
0.04 0.05 0.06 0.07 0.08
-50
0
50
I A (
A)
time (s)
0 12 24 36 480
20
40
60
80
100
THD = 6.142%
% M
agni
tude
Harmonic Order
138138
Waveforms of 24-pulse T-connected AC-DC converter at full-load - supply phase voltage VA, supply line currents IA, IB and IC , output DC link current (IDC) and voltage (VDC)
139139
0.05 0.06 0.07
-50
0
50
I A (
A)
time (s)
0 12 24 36 48 0
20
40
60
80
100
THD = 3.507%
% M
agni
tude
Harmonic Order
Input current waveform and harmonic spectrum of 24-pulse T-connected AC-DC converter at full-load.
140140
Comparison of Power Quality Parameters of 12-Pulse and 24-Pulse AC-DC Converters.
Topology
Topology
LoadLoad THD THD of Vof VACAC
(%)(%)
AC AC CurrenCurrent It IAA
(A)(A)
THD of THD of I IAA(%)(%)
DistortioDistortion Factor,n Factor,
DFDF
Displace-Displace-ment ment
Factor, Factor, DPFDPF
Power Power Factor Factor
PFPF
DC DC VoltagVoltage (V)e (V)
Load Load Current Current IIdcdc (A) (A)
RippleRippleFactor Factor
%%
12-Pulse
12-Pulse
2020 0.8140.814 8.8208.820 9.6339.633 0.99530.9953 0.98530.9853 0.98070.9807 300.2300.2 20.0920.09 1.9551.955
4040 1.2811.281 17.0317.03 7.6127.612 0.99710.9971 0.97290.9729 0.97010.9701 298.4298.4 40.1640.16 1.8231.823
5050 1.6811.681 21.1921.19 7.4007.400 0.99710.9971 0.96820.9682 0.96540.9654 297.0297.0 49.8849.88 1.7591.759
6060 1.9131.913 25.4725.47 6.9396.939 0.99740.9974 0.97040.9704 0.96790.9679 296.7296.7 59.7459.74 1.6961.696
8080 2.3072.307 33.8733.87 6.3486.348 0.99770.9977 0.97310.9731 0.97090.9709 296.2296.2 79.4779.47 1.7251.725
100100 2.8042.804 41.8541.85 6.1426.142 0.99770.9977 0.97380.9738 0.97160.9716 295.8295.8 98.7898.78 1.7571.757
24-Pulse
24-Pulse
2020 1.0321.032 8.5838.583 5.4695.469 0.99850.9985 0.99800.9980 0.99650.9965 301.5301.5 20.1020.10 0.50620.5062
4040 1.6041.604 16.9916.99 4.7594.759 0.99880.9988 0.99690.9969 0.99570.9957 300.4300.4 40.0440.04 0.32730.3273
5050 1.8341.834 21.1721.17 4.4524.452 0.99890.9989 0.99650.9965 0.99540.9954 299.9299.9 49.9849.98 0.73680.7368
6060 2.0222.022 25.3325.33 4.2184.218 0.99890.9989 0.99610.9961 0.99500.9950 299.3299.3 59.8559.85 0.80250.8025
8080 2.3372.337 33.5733.57 3.8143.814 0.99900.9990 0.99520.9952 0.99420.9942 298.2298.2 79.5379.53 0.95860.9586
100100 2.5822.582 41.7741.77 3.5073.507 0.99910.9991 0.99450.9945 0.99360.9936 297.2297.2 99.0999.09 1.13901.1390
141141
Comparison of power quality parameters of12-pulse and 24-pulse AC-DC converters with varying load
Topology
Topology
% % THDTHD
ofofVVacac
AC MainsAC MainsCurrent ICurrent I
aa
(A)(A)
% THD of% THD ofIIaa
DistortionDistortionFactorFactor
DisplacementDisplacementFactorFactor
PowerPowerFactorFactor
DC VoltageDC Voltage(V)(V)
LightLightLoadLoad
FullFullLoadLoad
LightLightLoadLoad
FullFullLoadLoad
LightLightLoadLoad
FullFullLoadLoad
LightLightLoadLoad
FullFullLoadLoad
LightLightLoadLoad
FullFullLoadLoad
LightLightLoadLoad
FullFullLoadLoad
6-6-pulsepulse 4.8484.848 8.8998.899 42.3742.37 27.5627.56 23.8923.89 0.96400.9640 0.97160.9716 0.99450.9945 0.97770.9777 0.95870.9587 0.94990.9499 300.7300.7 292.7292.7
12-12-
pulsepulse 2.8042.804 8.8208.820 41.8541.85 9.6339.633 6.1426.142 0.99530.9953 0.99770.9977 0.98530.9853 0.97380.9738 0.98070.9807 0.97160.9716 300.2300.2 295.8295.8
24-24-
pulsepulse 2.5822.582 8.5838.583 41.7741.77 5.4695.469 3.5073.507 0.99850.9985 0.99910.9991 0.99800.9980 0.99450.9945 0.99650.9965 0.99360.9936 301.5301.5 297.2297.2
142142
Converter Specifications
AC Supply: 415V, 50Hz.Source impedance: Zs= j0.172 ohms (=3%)DC Load: 300V, 30kW, Ldc =1mHTransformation ratio of transformers:
6-pulse AC-DC Converter: 1: 0.5112-pulse AC-DC Converter: 1: 0.5324-pulse AC-DC Converter: 1:0.53
143143
1. Power quality is improved significantly by employing the proposed T-connected isolation transformer based 24-pulse AC-DC converter.
2. The input line current has 23rd and 25th harmonics as the dominant harmonics in 24-pulse AC-DC converter.
3. Total harmonic distortion of input current remains below 8% and power factor remains above 0.99 at varying loads.
4. It meets the requirements of IEEE-519 standard.5. Only two single-phase transformers are used.
144144
Multipulse Full Wave AC-DC Multipulse Full Wave AC-DC ConvertersConvertersIsolated Full-Wave
Multipulse AC-DC Converters
Star-connection Zigzag-connection T-connection
6-Pulse
12-Pulse
18-Pulse
24-Pulse
6-Pulse
12-Pulse
18-Pulse
24-Pulse
6-Pulse
12-Pulse
18-Pulse
24-Pulse
145145
Star Connected Multipulse Star Connected Multipulse Full Wave 6-Pulse AC-DC Full Wave 6-Pulse AC-DC
ConverterConverter
Idc
Load~~~3-phase
AC mains
ANSI 45 transformer
146146
Star Connected Multipulse Star Connected Multipulse Full Wave 12-Pulse AC-DC Full Wave 12-Pulse AC-DC
ConverterConverter3-phase AC mains
Idc/2 Idc/2
+
-
Load
ANSI 46 transformer
147147
Star Connected Multipulse Star Connected Multipulse Full Wave 18-Pulse AC-DC Full Wave 18-Pulse AC-DC
ConverterConverter
+
-
Load
idc
vdc
va
vb
vc
ib
ic
ia
148148
Star Connected Multipulse Star Connected Multipulse Full Wave 24-Pulse AC-DC Full Wave 24-Pulse AC-DC
ConvertersConverters
+
-
Load
idc
vdcva
vb
vc
ib
ic
ia30°
45°
60°
15°
149149
Multipulse Controlled AC-DC Multipulse Controlled AC-DC ConvertersConverters
150150
A 48-pulse controlled AC-DC converter derived A 48-pulse controlled AC-DC converter derived from six-pulse converter by pulse multiplicationfrom six-pulse converter by pulse multiplication
Three-Phase 24-Pulse Bidirectional Mid Point Reactor Converter.
va
vb
vc
ia
ib
ic
vdc
Load
idcCp
Cq
Transformer
Transformer
151151
Pulse multiplication in series connected isolated Pulse multiplication in series connected isolated AC-DC converter using auxiliary circuitAC-DC converter using auxiliary circuit
Three-Phase Unidirectional 24-Pulse Converter
Tr3 vdc
Load
idc
va
vb
vc
ia
ib
ic
La
Lb
Lc
Transformer
Tr2
Cp
Cq
152152
Pulse Multiplication in parallel connected bridges using Pulse Multiplication in parallel connected bridges using DC ripple reinjection TechniqueDC ripple reinjection Technique
Three-Phase 48-Pulse Bidirectional Converter
vdc
Load
va
vb
vc
ia
ib
ic
Transformer
Ld
o0
o30idc
153153
Y
LOA
D
YY L
v1
v2
I0
3-phasesupply
Pulse multiplication in 12-pulse controlled rectifier using multi-tap interphase reactor
154154
N o
N K
v SK
v YK
T K
T m
a
V M
N o
N m
v SK
v Ym
T K T m
a
V M
V y1
.
V y2
.
V y1
.
V x
.
V 2
.
V 1
.
V z2
.
V z1
.
V zn
.
q
q-
0 0
/2n
/n
/2n
V M
.
q-
V yn
.V y(n-1)
.
V yn
.V y1
.
V x
. V 2
.V 1
.
V z1
.V zn
.
qq-
0 0
/2n
/n
/2n
V y(n-1)
.
V z(n-1)
.V M
.
q
0 0
Tapped IPT
155155
Simulation for isolated 12x3-PulseControlled operationContinuous
v+-
Vin3
v+-
Vin2
v+-
Vin1
v+-
Ving
A
B
C
+
-
Univ2
g
A
B
C
+
-
Univ1
Conn1
Conn3
Conn2
Subsystem1
Step2
A
B
C
a2
b2
c2
a3
b3
c3
StarDelTr
Conn3
Conn1
Conn2
Conn4
Src&SrcX
Scope2
Scope1
RL3
RL!3
RL!2
i+-
Iin1i+ -
Iin
-K-
Gain
alpha
FiringAngle
0
Constant
c 12
Breaker
alpha_deg
A
B
C
Block
PY
PD
12plsGen
Matlab model for pulse multiplication in 12-pulse controlled rectifier using multi-tap interphase reactor
156156
0 0.05 0.1 0.15 0.2-20
-10
0
10
20
Time (s)
Cur
rent
(A),
Vol
tage
/25(
volts
)
0.15 0.16 0.17 0.18-10
-5
0
5
10
Time (s)
FFT window: 2 of 9.209 cycles of selected signal
0 20 40 600
0.05
0.1
0.15
0.2
0.25
Harmonic order
Fundamental (50Hz) = 9.214 , THD= 3.97%
Mag
Simulation resultsfor pulse multiplication in 12-pulse controlled rectifier using multi-tap interphase reactor
157157
Y
LOAD
T m
T pq
C p
C q
I0
Pulse multiplication in 12-pulse rectifier with series connected bridges for high voltage
applications
158158
Controlled Multi-pulse (12 pulse)Controlled Multi-pulse (12 pulse)
159159
Controlled Multi-pulse (12 pulse)Controlled Multi-pulse (12 pulse)
160160
Controlled Multi-pulse (12 pulse)Controlled Multi-pulse (12 pulse)
161161
Controlled Multi-pulse (12 pulse)Controlled Multi-pulse (12 pulse)Control CircuitControl Circuit
162162
Controlled Multi-pulse (12 pulse)Controlled Multi-pulse (12 pulse)AnalysisAnalysis
163163
Controlled Multi-pulse (12 pulse)Controlled Multi-pulse (12 pulse) Simulated Waveforms Simulated Waveforms
164164
Controlled Multi-pulse (12 pulse)Controlled Multi-pulse (12 pulse)Simulated WaveformsSimulated Waveforms
165165
Controlled Multi-pulse (12 pulse)Controlled Multi-pulse (12 pulse)Experimental waveformsExperimental waveforms
166166
Controlled Multi-pulse Controlled Multi-pulse HVDC ApplicationHVDC Application
167167
Controlled Multi-pulse Controlled Multi-pulse HVDC ApplicationHVDC Application
168168
Controlled Multi-pulse Controlled Multi-pulse HVDC ApplicationHVDC Application
169169
Controlled Multi-pulse Controlled Multi-pulse HVDC ApplicationHVDC Applicationinverter mode of inverter mode of
opeartionopeartion
170170
Controlled Multi-pulse HVDC ApplicationControlled Multi-pulse HVDC Application
ControlControl
171171
Controlled Multi-pulse (36 pulse)Controlled Multi-pulse (36 pulse)
172172
Controlled Multi-pulse (36 pulse)Controlled Multi-pulse (36 pulse)
173173
Controlled Controlled Multi-pulse Multi-pulse (36 pulse)(36 pulse)
174174
Controlled Multi-pulse (36 pulse) Controlled Multi-pulse (36 pulse) conventional methodconventional method
175175
Controlled Multi-pulse (36 pulse)Controlled Multi-pulse (36 pulse)modified methodmodified method
176176
Selection Criterion of Multipulse AC-DC Selection Criterion of Multipulse AC-DC ConvertersConverters
Number of phases in AC mains Number of phases in AC mains Required level of power quality in input (permitted PF, CF, Required level of power quality in input (permitted PF, CF,
THD)THD) Type of output DC voltage (constant, variable, etc.)Type of output DC voltage (constant, variable, etc.) Power-flow (unidirectional and bi-directional)Power-flow (unidirectional and bi-directional) Number of quadrants (one, two or four)Number of quadrants (one, two or four) Nature of DC output (isolated, non-isolated)Nature of DC output (isolated, non-isolated) Requirement of DC output (Controlled and Uncontrolled)Requirement of DC output (Controlled and Uncontrolled) Required level of power quality in DC output (voltage ripple, Required level of power quality in DC output (voltage ripple,
voltage regulation)voltage regulation) Type of DC loads (linear, nonlinear, etc.)Type of DC loads (linear, nonlinear, etc.)
177177
Selection Criterion of Multipulse AC-DC Selection Criterion of Multipulse AC-DC ConvertersConverters
CostCost SizeSize WeightWeight EfficiencyEfficiency Noise level (EMI, RFI, etc.)Noise level (EMI, RFI, etc.) Rating (W, kW, MW, etc.)Rating (W, kW, MW, etc.) ReliabilityReliability Number of DC outputsNumber of DC outputs Environment (ambient temperature, altitude, pollution Environment (ambient temperature, altitude, pollution
level, humidity, types of cooling, etc.)level, humidity, types of cooling, etc.)
178178
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