abb hvdc mars larsson 020409

© ABB Group April 14, 2009 | Slide 1

HVDC and HVDC LightAn alternative power transmission system

Mats Larsson, Corporate Research, ABB Switzerland Ltd

Symposium on Control & Modeling of Alternative Energy Systems, April 2, 2009.


Outline

� What is HVDC ?

� Technical Aspects of HVDC Transmission

� HVDC Technologies – Classic and Light

� Control of HVDC Links

� Grid Applications of HVDC

� Some control problems related to HVDC

� Conclusion


What is HVDC ?High-Voltage Direct Current Transmission

AC

Gri

d

HVDC converter station> 1000 MW, classic

HVDC converter station< 1200 MW, Light

Overhead linesTwo conductors

Alternative:submarine cables

Land or submarine,cables or overhead line

HVDC converter station> 1000 MW, classic

HVDC converter station< 1200 MW, Light

Power / energy direction

AC

Gri

dA

C G

ridA

C G

rid


Why is HVDC Alternative ?Battle of the Currents (~1880s-90s)

AC

� 3 phase system

� Power transformer

DC

� No reliable technology for voltage conversion

� Difficult to interrupt

AC

DC

� The early isolated grids were a mix of AC and DC

� In the end all nationwide power grids were based on AC technology

� Most DC grids were eventually phased out


The Early Days of HVDCMilestone – The first Commercial HVDC Link

� Island Gotland to Swedish Mainland

� 100 kV / 20 MW

� ~100 kM distance

� AC cable difficult

� Commissioned in 1954

� Mercury-arc valves

� Refurbished in 1970

� Uprated to 150kV/130MW

� Thyristor valves

� Second pole built in 1986


AC vs DC CablesReactive Power Charging

� Lines and cables act as capacitors

� When energized a charging current is generated

� For DC only only once

� For AC charged and discharged each half-period

� Reactive Power charging is proportional to:

� voltage squared

� length of cable

� frequency

� In practice AC cables longer than 100km not practical

� Problem does not exist for DC cables

2 2

2 2max max

ch

ch

Q CV LcV

P S Q

ω ω= =

= −


AC versus DC TransmissionUnderground/Underwater Cables

Cable Transfer Capability v Distance (1200 A Rating)

0

1200

0 50 100 150

Distance (km)

Tra

nsf

er C

apab

ility

(M

W) 230 kV

345 kV

500 kV

± 320 kV DC

� AC and DC capacity increases with square of voltage

� AC transfer capacity diminishes dramatically with distance, due to reactive power charging

� DC transfer capacity almost unaffected by distance


AC versus DC TransmissionOverhead Transmission Lines

Max Line Capability v Distance

0

1000

2000

3000

4000

5000

6000

0 100 200 300 400 500 600Transmission Distance (mi)

Max

Lin

e Lo

adin

g (M

W)

345 kV AC 500 kV AC 765 kV AC ± 500 kV DC± 660 kV DC± 800 kV DC

� AC and DC capacity increases with square of voltage

� AC transfer capacity diminishes with distance, due to voltage and angle stability limit

� For AC – Switching stations are required every ~400kms

� DC transfer capacity almost unaffected by distance


AC Versus DC TransmissionLosses

� Example

� 1200 MW rated capacity

� HVDC Classic

� Additional converter losses (~ 0.6 %)

� Lower line losses


Conventional alternatingcurrent linesHVDC Classic

HVDC Light (underground)

Mitigating the environmental impacts of power while dramaticallyimproving grid efficiency and reliability

Visual Impact of AC/DC Transmission


3 Generations of HVDC

Year1954 1970 20001980

Mercury Arc

ThyristorGen 1

Thyristor Gen 2

Transistor (IGBT)

HVDC Light

HVDC Classic


Core HVDC TechnologiesHVDC Classic

� Current source converters� Line-commutated thyristor valves� Requires 50% reactive compensation

(35% harmonic filter)� Minimum short circuit capacity > 2x

converter rating� Fast active power control� Conv. Losses ~0.6 %

HVDC Light� Voltage source converters� Self-commutated IGBT valves� Requires no reactive power

compensation (~15% HF)� Weak system, black start� Compact� Fast active and reactive power control� Conv. Losses ~ 1.6%


Modular DesignHVDC Classic

� Thyristor valves

� Thyristor modules

� Thyristors

HVDC Light

� IGBT valves

� IGBT valve stacks

� StakPaks

� Submodules

� Chips

Thyristor Module

Thyristors

IGBT Valve Stacks

StakPak

Submodule

Chip

Cable Pair


Evolution of HVDCLink Capacity

� HVDC Classic

� 6400 MW

� +/- 800 kV

� HVDC Light

� 1200 MW

� +/- 320 kV


Control of HVDCThe Thyristor Power Converter

� 6-pulse converter

� Commutation controlled by firing angle – alpha (α)

� 0 < α < 90° Rectifier mode

� 90 < α < 180 ° Inverter mode

� DC voltage ~ cos(α)

� Current ripple on DC side

� Non-sinusoidal currents AC side

Udc


Control of HVDC ClassicLink Control

( )

dR dIdc

dR dR dIdcr dR dc

U UI

RU U U

P U IR

−=

−= =

uR

uS

uT

1 3 5

4 6 2

Id

Ud

IR

IS

IT

IR

IS

αu

IT

UdR and UdI voltage controllable through:

� firing angle (fast)

� tap changer (slow)


Control of HVDC LightThe VSC Converter

� PWM Icc: Controller has 2 outputs

� Modulation index -> controls Udc

� Phase angle -> controls AC phase angle on AC Side

� Can implement:

� DC Voltage Control

� AC Voltage Control

� AC Power Control

� Frequency control

DCvoltagecontrol

uDC-ref1

uDC1

+

-

uAC1uAC-ref1

pref1

PWMinternalcurrentcontrol

qref1

ACvoltagecontrol

+

-i

80.000m 90.000m 100.000m-200.000K

0.000K

200.000K

300.000K


Control of HVDC LightLink Control

Principle control of HVDC-Light

DCvoltagecontrol

uDC-ref1

uDC1

+

-

uAC1uAC-ref1

pref1

DCvoltagecontrol

uDC-ref2

uDC2

+

-

uAC2 uAC-ref2

pref2 q ref2

ACvoltagecontrol



qref1

ACvoltagecontrol

+

-i i

� One side control Udc

� One side controls power flow

� Both can control AC Voltage/Reactive power


Comparison of Reactive Power Characteristics

� HVDC Classic (~ SVC with TCR+FC, -0.5Pd / +0 MVAr)

� HVDC Light (~ STATCOM, -0.5Pd/+0.5Pd MVar)

� HVDC Light terminals can act as virtual generators

Reactive Power (p.u.)

Act

ive

Pow

er (p

.u.)

Operating Area

P-Q Diagram

HVDC Light Operating Range

HVDC Classic Operating Range


Control SystemStructure



Grid Applications of HVDCAsynchronous Connection

� AC connection between grids may be difficult

� Stability issues

� Undersea cables

� Frequencies 50/60 Hz

HVDC interconnections

Scandinavia-Continental Europe

NORDEL grid – UCTE Grid

Benefits:

� Controllability - Cross border trading

� The networks can retain their independence

� An HVDC link can never be overloaded

� HVDC transmission will act as a firewall against cascading disturbances.


Grid Applications of HVDCBulk Power Transport

� DC Lines cheaper than AC for same rating

� DC terminals more expensive than AC

� Most line project breaks even at > 700km, in favour of DC

Benefits

� Smaller right of way

� Lower losses

� No increase in Short-circuit current

� No intermediate switching stations


Grid Applications of HVDCGrid Bottlenecks – Embedded HVDC

Benefits:

� Increased Power Transfer Capability

� Damping of InterareaOscillations

� Rapid Power Flow Control

� Dynamic Voltage Support (HVDC Light)


Grid Applications of HVDCOffshore Wind Connection – e.g. Borkum 2 Germany

Scope� 400 MW HVDC Light

Offshore Wind� ±150 kV HVDC Light

Cables (route = 130 km by sea + 75 km by land)

� Serves 80 x 5 MW offshorewind turbine generators

� Controls collector systemac voltage and frequency

Project Basis� Customer: E.ON Netz

GmbH� Germany gets gets access

to clean wind power with higher capacity factor than land based wind generation

� Enhances main grid stability


Grid Applications of HVDC Multi-terminal HVDC Light

Benefits

� Excellent Characteristics for Multiterminal Applications

� Flexible DC grid power flow control

� Independent P and Q control at each converter station.

� DC grid configuration can be radial, ring or meshed; can be easily reconfigured and expanded.

� Well suited for cable connection

Applications

� In-city networks

� Offshore wind collector system

c)


Grid Applications of HVDC LightBlackstart

� EstLink - Finland-Estonia

� 350 MW/330kV HVDC Light

� 100 kM

� Capable of blackstart on Estonian side


� “The European Supergrid”

� Paralell DC Backbone Grid

� A Perfect Application of HVDC

Open Research topics

� DC grid protection systems

� Coordinated control of DC Converters

� Multiterminal HVDC Classic challenging

Grid Applications of HVDCVision 20xx -The 100 % Renewable Scenario


A Control Engineer‘s View of Power Systems

� Large-scale

� Substantial nonlinearity

� Uncertainty

� Changing operating point

� Mix of continuous and discrete controlvariables

� System model has differential-algebraicstructure

� A good example of a ”complex” system !


Open Control Issues Related to HVDCTransient Stability

� A fault will cause nearbygenerators to slow down oraccelerate

� Fast fault clearance and strong network critical

Objective

� Use fast controllability of HVDC

� Non-linear control problem

� Response time ~ 0.1 s

0 5 10 15 2045

50

55

Time (s)

Spe

ed (H

z)

Clearing time

170 ms

100 ms


Open Control Issues Related to HVDCSmall-signal Stability

� Poor or negative damping of pulsating power flows

� Use fast modulation of HVDC active and reactive power

� Multi-modal control

� Response time ~ 0.1-0.2s

� Adaptive and learning control ?

0 5 10 15 2048

49

50

51

52

Time (s)

Spe

ed (H

z)


ABB Track RecordHVDC Projects 1954-2010

TrollNelson River 2

CU-projectVancouver Island

Pole 1

Pacific IntertiePacific IntertieUpgrading

Pacific IntertieExpansion

IntermountainBlackwater

ItaipuInga-Shaba

Cahora Bassa

Brazil-ArgentinaInterconnection I&II

English

DürnrohrSardinia-Italy

HighgateChateauguay

Quebec-Skagerrak 1&2Skagerrak 3Konti-Skan 1Konti-Skan 2Baltic Cable

Fenno-SkanGotland 1Gotland 2Gotland 3

KontekSwePol

Chandrapur-Padghe

Rihand-DelhiVindhyachal

SakumaGezhouba-Shanghai

Three Gorges-ShanghaiLeyte-LuzonBroken HillNew Zealand 1New Zealand 2

Gotland

Murray link

Eagle Pass

Tjæreborg

HällsjönHagfors

52 HVDC Classic Projects since 195411 HVDC Light® Projects since 1997

Directlink

Cross Sound

Greece - ItalyRapid City

Vizag II

Three Gorges-Guandong

Estlink

NorNed

Valhall

Cahora Bassa Upgrade

SapeiSquare Butte

SharylandThree Gorges-Changzhou

Channel

New

Outaouais

England


Conclusion

� AC transmission is standard but has limitations

� HVDC not a new technology

� Bulk power transfer over large distances

� Controllability of Active Power

� Undersea or asynchronous connections

� Ratings up to 6400 MW

� HVDC Light

� Controllability of Active and Reactive Power

� Inexpensive cable technology

� Offshore as well as underground cable applications

� Ratings up to 1200 MW

� Multiterminal: off-shore collector grid, DC Supergrid(?), city DC distribution


800kV HVDC Video

� 800 kV HVDC


Summary: Transmission SolutionsTechnical Characteristics

None, also suited for underground cablenone

~ 400 km OH

~50-100 km Cable

Practical

Distance

Limit

Dynamic – virtual generator

Slow - switched filters, capacitors & reactors + LTC

NoneAC voltage

control

STATCOM +

15% in fixed filters

Switched shunt banks

35% in filters + 15% in capacitors

Shunt reactors /

Capacitors

Reactive power compensation & control

No reactive power

demand

Reactive power demand

0.5Pr

3 I^2 X

- 3 V^2 BReactive power demand

Continuous 0 to ±Pr

Continuous

±0.1Pr to ±Pr None unless PST or series reactor

Power flow

control

HVDC Light HVDC ClassicHVACAttributes


Contract signed: April 2005

In service: November 2006

Project duration: 19 months

Capacity: 350 MW

AC voltage: 330 kV at Harku

400 kV at Espoo

DC voltage: ±150 kV

DC cable length: 2 x 105 km (31 km land)

Converters: 2 level, OPWM

Special features: Black start Estonia, no diesel

Rationale: Electricity trade

Asynchronous Tie

Long cable crossing

Dynamic voltage support

Black start

Example Asynchronous Connection EstLink – HVDC Light between Finland and Estonia


EstLinkTest of Black Start Capabilities

� Estonian part of the network deenergized

� Network reenergized using the HVDC terminal in Estonia


Bulk Power Transport ExampleXiangjiaba - Shanghai ± 800 kV UHVDC Project

Scope� Power: 6400 MW (4 x 1600 MW converters)� ± 800 kV DC transmission voltage� System and design engineering� Supply and installation of two ± 800 kV converter

stations including 800 kV HVDC power transformers and switchgear

Project Basis� Customer: State Grid Corporation of China� Project delivers 6400 MW of Hydro Power from

Xiangjiaba Power Plant in SW China � Length: 2071 km (1286 mi), surpasses 1700 km

Inga-Shaba as world’s longest � Pole 1 commissioned in 2010, pole 2 in 2011� AC voltage: 525 kV at both ends


Caprivi Link, NamPower+ 350 kV

- 350 kV

300 MW

300 MW

� 300 MW, 350 kV HVDC Light Monopole with groundelectrodes

� Expandable to 600 MW, ± 350 kV Bipole� ± 350 kV HVDC Overhead Line� Links Caprivi region of NE Namibia with power

network of central Namibia and interconnects withZambia, Zimbabwe, DR Congo, Mozambique

� Improves voltage stability and reliability� Length of 970 km DC and 280 km (400kV) AC


Caprivi Link - Salient features� + 300/600 MW import to – 280/560 MW export without filter switching or stop at

0 MW

� ± 200 MVAr for continuous voltage stabilizatiion of 400 kV/320 kV AC networks at Gerus/Zambezi

� Stable and robust power transmission verified for low short-circuit powert down to 300 MVA

� Black start of Caprivi AC system

� Restart after DC line faults due to lightning and bushfires, 500 ms after fault clearing including deionization time


Xiangjiaba - Shanghai ± 800 kV UHVDC ProjectScope

� Power: 6400 MW (4 x 1600 MW converters)� ± 800 kV DC transmission voltage� System and design engineering� Supply and installation of two ± 800 kV converter

stations including 800 kV HVDC power transformers and switchgear

� Valves use 6 inch thyristors and advanced controlequipment

Project Basis� Customer: State Grid Corporation of China� Project delivers 6400 MW of Hydro Power from

Xiangjiaba Power Plant in SW China � Length: 2071 km (1286 mi), surpasses 1700 km Inga-

Shaba as world’s longest � Pole 1 commissioned in 2010, pole 2 in 2011� AC voltage: 525 kV at both ends


SouthWestlink, SVK and Statnett

Stage 2, 2010

� 1 x 1200 MW converter

� About 350 km underground cable

Stage 1, 2008

� 2 x 1200 MW converters

� 200 km underground cable

� 200 km a.c. OHL upgrade 220 – 400 kV


SouthWestlink, breakthrough in UG transmission� Jan 17 2008, two major TSO, Svenska Kraftnät (SVK) and Statnett, decided to

build the worlds largest underground system.

� Three terminals rated 1200 MW

� Total distance 500 – 550 km

� Accelerated interest in applying the new technology for underground transmission by other TSO


Transfer Capacity OHL HVDC Light

0

200

400

600

800

1000

1200

1400

0 km 100 km 200 km 300 km 400 km

MW

HVDC Light

380 kV OHL


Cross Sound Cable, TransÉnergie, USA

Customer’s need

� Enable power exchange between Connecticut and Long Island, USA.

� Improve security of power supply in this area

ABB’s response� Turnkey 330 MW ±150 kV HVDC

Light® transmission system including 40 km subsea cable, delivered in 21 months

Customer’s benefits� The Cross Sound link improves the

reliability of power supply in the Connecticut and New England power grids, while providing urgently needed electricity to Long Island.


Troll A Precompression project, Statoil

Customer’s need

� Enable power supply from mainland to platform to minimise emission of large amounts of CO2 and unnecessarily high fuel consumption.

ABB’s response

� Turnkey 2x40 MW ±60 kV HVDC Light® offshore transmission system

Customer’s benefits

� With electric power supplied from shore, for power supply as well as compressor drivers, CO2 emissions from offshore installations are eliminated.

abb hvdc mars larsson 020409

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