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AC to DC Power ConversionNow and in the Future
PCIC-2001-14
Tony Siebert Anders Troedson Stephan EbnerMember, IEEE Member, IEEE Member, IEEEABB Automation, Inc ABB Automation, Inc ABB Industrie AGP.O. Box 372P.O. Box 372 CH- 5300 TurgiMilwaukee, WI 53201 Milwaukee, WI 53201 SwitzerlandUSA USA
- 2 -
Agenda
• Introduction
• System Design Factors
• Technology Assessment–
• Technology Comparison
• Innovative Information Technology (IT) support
• Conclusions
- 3 -
Rectifier History
1913 Fist Mercury-Arc rectifier
1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000
1925 Mercury-Arc rectifier for grid control1939 First 50 kV HVDC transmission
1950 Development of Contact Rectifier
1947 Invention of Transistor
1902 Invention of Semiconductor Diode (Crystal type)
Mercury Arc Rectifier Contact Rectifier
- 4 -
Rectifier History
1958 First semicond. Diode rectifier
1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000
1960 First diode plant > 100 kA1968 First thyristor rectifier
1970 First diode rectifier unit > 100 kA
Introduction of Thyristor TechnologyIntroduction of Diode Technology
Thyristor Rectifier Diode Rectifier
- 5 -
Rectifier History
1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000
1990 First thyristor rectifier for DC-Arc Furnace
1985 First thyristor rectifier for Aluminium Smelter
Ongoing Development of Diode Rectifier TechnologyOngoing Development of Thyristor Rectifier Technology
3” Thyristor Rectifier 4” Thyristor Rectifier2” Thyristor Rectifier
- 6 -
Rectifier History
1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000
Mid-1990’s first Chopper rectifier in Eletrolysis
Introduction of GTO TechnologyIntroduction of IGBT Technology
Introduction of IGCT Technology
IGBT Chopper Module PowerPac3 IGCT Chopper Module
- 7 -
System design and decision factors
AC-Network Design ParameterÄ Voltage level / voltage variationÄ Frequency / frequency variationÄ Available short circuit capabilityÄ Allowed power factorÄ Allowed harmonic distortion
DC-Process Design ParameterÄ Voltage / current operating range Ä Voltage / current ripple Ä Voltage / current regulation accuracy Ä Voltage / current regulation speed Ä Overload capabilities
Further Decision FactorsÄ System reliabilityÄ System efficiency Ä Reparability and diagnosticsÄ Footprint and mechanical dimension
Ä Investment- / install- / life-cycle cost Ä Production load schedule criteriaÄ Energy day-time tariffs criteria Ä Plant start-up / lay-off criteria
- 8 -
Process Ratings
Rectifier Application Current (Amps) Voltage (DC)Chemical electrolysis 5,000 - 150,000 40 - 1,000 VoltsAluminum potline 10,000 - 300,000 < 1,300 VoltsDC Arc Furnace 50,000 - 130,000 600 - 1,150 VoltsGraphitizing Furnaces 20,000 - 120,000 50 - 250 VoltsZinc/Lead, etc electrolysis 5,000 - 100,000 100 - 1,000 VoltsCopper refining 10,000 - 50,000 40 - 350 VoltsTraction substations 1,000 - 5,000 500 - 1,500 VoltsLV AC Drive (DC bus) 0 - 10,000 250 - 1,000 VoltsMV Drive (DC bus) 0 - 5,000 3,400 - 6,000 Volts
Typical Rectifier Rating
- 9 -
Technology Assessment
• Diode
• Thyristor
• Diode and DC/DC Converter (Chopper)
• Active Rectifier
- 10 -
Diode Rectifier Topology
Double wye connection with interphase transformer
LOAD
6 puls circuit
3 - phase bridge connection
LOAD
6 puls circuit
- 11 -
Diode System Regulation Principle
Step of current setpoint
Step of OLTC
current without saturable reactor ramp control ( load impedance related )
current with saturable reactor ramp control
Range of saturable reactor control
T *) typ. 3 .. 5 s depending on OLTC drive(saturable reactor control up to 5 ms depending on the load)
t [seconds]
Idc[kA]
T *)
- 12 -
Diode Rectifiers
• Simplest Technology• Longest use• Used with On-Load-Tap-Changers• Used with saturable core reactors
(amplistats, voltage controlled reactors)
2 4 - P u l s e D i o d e R e c t i f i e r
+ 7 . 5 °
- 7 . 5 °
L o a d
- 13 -
Thyristor Rectifier Topology
Double wye connection with interphase transformer
LOAD
6 puls circuit
3 - phase bridge connection
LOAD
6 puls circuit
- 14 -
Thyristor System Regulation Principle
Step of current setpoint
theor.current without phase angle ramp control () ( load impedance related )
current with phase angle ramp control in operation
Range of phase angle control
T *) typ. 100 ms .. 300 mspossible up to 5 ms depending on the load
T *) t [milliseconds]
Idc[kA]
Steps only with OLTC
- 15 -
Thyristor Rectifiers
• Simple Technology• Widely Used• Can be used with On-Load-Tap-
Changers• Relatively fast control of current
2 4 - P u l s e T h y r i s t o r R e c t i f i e r
+ 7 . 5 °
- 7 . 5 °
L o a d
- 16 -
Diode Rectifier + DC-Chopper Topology
3 - phase bridge connection
LOAD
6 puls circuit
- 17 -
DC-Chopper Regulation Principle
Step of current setpoint
theor.current without PWM ramp control ( load impedance related )
current with PWM ramp control
Range of modulation control
T 1) typ. 100 ms .. 300 ms with electrolyis process loadpossible up to 1 .. 5 ms depending on the load
t [milliseconds]
Idc
[kA]
T 1)
Tmod 2) typ. 0.2 ms .. 1 ms
Tmod2)
Ton Toff
- 18 -
Diode Rectifier with Chopper Converter
• Newer Technology• Relatively entering into Market• Merging of older (diode) and new
technology• Fast control of current
+7.5°
-7.5°
- 19 -
Active Rectifier Topology (AC-Chopper)3 - phase bridge connection
LOAD
6 puls circuit
Active Current Source Inverter
- 20 -
AC-Chopper Regulation Principle
T 1) typ. 100 ms .. 300 ms with electrolyis process loadpossible up to 1 .. 5 ms depending on the load
Step of current setpoint
theor.current without ramp control ( load impedance related )
current with ramp control
Range of modulation control
t [milliseconds]
Idc
[kA]
T 1)
Tmod 2) typ. 0.2 ms .. 1 ms
Tmod2)
Ton Toff
- 21 -
Active Rectifier (AC-Chopper)
• Newest Application of Technology• Limited Market entry• Based upon proven technology• Fast control of current
Active Current Source Inverter
Load
- 22 -
Technology use by Process
Application Diode Thyristor Chopper Active Rectifier
Chemical Electrolysis Seldom Standard Seldom Future
Aluminum Potline Standard Seldom Not Acceptable Distant Future
DC Arc Furnace Not Acceptable Standard Seldom Future
Graphitizing Furnace Standard Seldom Future Future
Zinc Electrolysis Standard Seldom Future Future
Copper Refining Seldom Standard Seldom Future
Traction Substation Standard Seldom Future Distant Future
LV AC Drive (DC Link) Standard Seldom Not Applicable Seldom
MV Drive (DC Link) Standard Seldom Not Applicable Seldom
- 23 -
Technology Share of Units > 10 kA
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
1972
1974
1976
1978
1980
1982
1984
1986
1988
1990
1992
1994
1996
1998
2000
ChopperThyristorDiode
Technology Share
- 24 -
Technology Comparison
• Power Factor• Efficiency• Harmonic Distortion• Reliability / Availability / Service Support• Space Requirements• System Cost
- 25 -
The Process Load Characteristic
U d o
I d
Aluminium
Zinc
Chlorine
Copper
I Range
U Range
100 %
100 %
50 %
25 %
75 %
- 26 -
Power Factor Comparison
Power Factor vs Transformer Impedance
0.88000.89000.90000.91000.92000.93000.94000.95000.9600
6 7 8 9 10 11 12
Transformer Impedance
Po
wer
Fac
tor
Diode / DB
Thyristor / DB
Note: Low Transformer Impedance = High Voltage Harmonics
- 27 -
Power Factor Comparison
0.40
0.45
0.50
0.55
0.60
0.65
0.70
0.75
0.80
0.85
0.90
0.95
1.00
250.00 300.00 350.00 400.00 450.00Ud [V]
PF
[-]
Diode OLTC Thyristor OLTC Thyristor Uncompensated Thyristor Compensated
Diode vs Thyristor with Electrolysis Process Load
Ud
Id
- 28 -
Power Factor Comparison
• Diode Good• Thyristor Low• Diode and Chopper Good• Active Rectifier Best
- 29 -
Efficiency vs. Voltage
0.9
0.91
0.92
0.93
0.94
0.95
0.96
0.97
0.98
0.99
1
0 200 400 600 800 1000 1200 1400 1600Voltage
Effic
ienc
y
Typ Dio/Thy Bridge Typ Dio/Thy Single WayTyp Chopper Dio/Thy Projects
- 30 -
Comparison at Nominal load OperationNominal Load Operation DC-Voltage: 500 V
DC-Current: 70 kA DC-Power: 35 MW
DiodeSystem
ThyristorSystem
ChopperSystem
AC-Power (12p-Transformer) 39 MVA 41 MVA 38 MVAPower Factor without correction 0.91 0.86 0.93Compensation up to PF=0.93 3 MVAR 8 MVAR -Compensation up to PF=0.98 10 MVAR 15 MVAR 7 MVARLossesTransformer (including harmonics) 430 kW 450 kW 400 kWRectifier 183 kW 192 kW 170 kWChopper 250 kWLine Filter (for PF=0.93) 56 kW 84 kWTotal 669 kW 726 kW 820 kWRelative Difference -151 kW -94 kW 0 kWEfficiency (for Components considered) 0.981 0.980 0.977
- 31 -
Comparison at Reduced load OperationReduced Load Operation DC-Voltage: 440 V
DC-Current: 50 kA DC-Power: 22 MW
DiodeSystem
ThyristorSystem
ChopperSystem
AC-Power (12p-Transformer) 25 MVA 34 MVA 24 MVAPower Factor without correction 0.90 0.65 0.93Compensation up to PF=0.93 3 MVAR 8 MVAR -Compensation up to PF=0.98 10 MVAR 15 MVAR 7 MVARLossesTransformer (including harmonics) 240 kW 260 kW 170 kWRectifier 105 kW 120 kW 100 kWChopper 250 kWLine Filter (for PF=0.93) 56 kW 84 kWTotal 401 kW 464 kW 520 kWRelative Difference -119 kW -56 kWEfficiency (for Components considered) 0.982 0.979 0.977
- 32 -
Efficiency Comparison
• Diode High• Thyristor Medium - High• Diode and Chopper Low• Active Rectifier Medium - Low
- 33 -
Harmonic Comparison
1 5 7 11 13 17 19 23 2529 31 35 37 41 43 47
0o20o
40o
6 0 o
0
2
4
6
8
10
12
14
16
AC Current in [kA]
Harmonic Number
20 kA, 200 V DC, 6 Pulse Rectif ierDiode and Chopper ( 0 degrees) and Thyristor(variable depending on output DC voltage)
0o10o20o30o40o50o60o
- 34 -
Harmonic Comparison
• Diode Good• Thyristor Lower• Diode and Chopper Good• Active Rectifier Best
- 35 -
Reliability Comparison
Based Upon Component Count of Rectifier Devices
• Diode High• Thyristor High• Diode and Chopper Low• Active Rectifier Medium
- 36 -
Service Skill Comparison
• Diode Low• Thyristor Medium• Diode and Chopper High• Active Rectifier High
- 37 -
System Cost Comparison
Diode Rectifier 105%Thyristor Rectifier 100%Diode & Chopper 124%Active Rectifier 115%
Based upon past projects, component count and further developments.
- 38 -
Space Comparison
• Diode Average• Thyristor Larger
– (with power factor included)
• Diode and Chopper Larger• Active Rectifier Average
- 39 -
Conclusions
Considerations• Total System Requirements • Future Provision of System
Requirements• Customer’s Experience / Background• Technology comparison for exact
project
– All Technologies Will continue for near future
- Thank You -