AC to DC Now and Future

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

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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

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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

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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

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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

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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

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Technology Assessment

• Diode

• Thyristor

• Diode and DC/DC Converter (Chopper)

• Active Rectifier

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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 *)

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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

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Thyristor Rectifier Topology

Double wye connection with interphase transformer

LOAD

6 puls circuit

3 - phase bridge connection

LOAD

6 puls circuit

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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

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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

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Diode Rectifier + DC-Chopper Topology

3 - phase bridge connection

LOAD

6 puls circuit

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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

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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°

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Active Rectifier Topology (AC-Chopper)3 - phase bridge connection

LOAD

6 puls circuit

Active Current Source Inverter

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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

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Active Rectifier (AC-Chopper)

• Newest Application of Technology• Limited Market entry• Based upon proven technology• Fast control of current

Active Current Source Inverter

Load

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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

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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

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Technology Comparison

• Power Factor• Efficiency• Harmonic Distortion• Reliability / Availability / Service Support• Space Requirements• System Cost

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The Process Load Characteristic

U d o

I d

Aluminium

Zinc

Chlorine

Copper

I Range

U Range

100 %

100 %

50 %

25 %

75 %

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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

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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

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Power Factor Comparison

• Diode Good• Thyristor Low• Diode and Chopper Good• Active Rectifier Best

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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

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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

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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

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Efficiency Comparison

• Diode High• Thyristor Medium - High• Diode and Chopper Low• Active Rectifier Medium - Low

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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

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Harmonic Comparison

• Diode Good• Thyristor Lower• Diode and Chopper Good• Active Rectifier Best

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Reliability Comparison

Based Upon Component Count of Rectifier Devices

• Diode High• Thyristor High• Diode and Chopper Low• Active Rectifier Medium

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Service Skill Comparison

• Diode Low• Thyristor Medium• Diode and Chopper High• Active Rectifier High

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System Cost Comparison

Diode Rectifier 105%Thyristor Rectifier 100%Diode & Chopper 124%Active Rectifier 115%

Based upon past projects, component count and further developments.

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Space Comparison

• Diode Average• Thyristor Larger

– (with power factor included)

• Diode and Chopper Larger• Active Rectifier Average

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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 -