TopicsHVDC Fundamentals

Conventional ConvertersCapacitor Commutated ConvertersVoltage Source ConvertersReactive Power RequirementsSystem ConfigurationsTappingControl basicsHigh Power Transmission

Evolution . . .

Core HVDC Technologies

AC DC

HVDCHVDC--CSCCSC

Indoor

Outdoor

AC FiltersAC Filters

DC FiltersDC Filters

Thyristor ValvesThyristor Valves

Converter Converter TransformersTransformers

AC DC

HVDCHVDC--CSCCSC

Indoor

Outdoor

AC FiltersAC Filters

DC FiltersDC Filters

Thyristor ValvesThyristor Valves

Converter Converter TransformersTransformers

AC DC

HVDCHVDC--VSCVSC

Indoor

Outdoor

IGBT ValvesIGBT Valves

AC DC

HVDCHVDC--VSCVSC

Indoor

Outdoor

IGBT ValvesIGBT Valves

HVDC ClassicCurrent source convertersLine-commutated thyristorvalvesRequires 50% reactive compensation (35% HF)Converter transformersMinimum short circuit capacity > 2x converter rating

HVDC LightVoltage source convertersSelf-commutated IGBT valvesRequires no reactive power compensation (15% HF)Standard transformersNo minimum short circuit capacity, black start

The HVDC Classic Converter Station

Converter station Transmissionline or cable

Converter

Smoothingreactor

DC filter

Telecommunication

Controlsystem

AC filtersShunt

capacitorsor otherreactive

equipment

AC bus

~~

The CCC* Station*Capacitively-commutated converter

TransmissionLine, Cable or Back-Back

Converter

Controlsystem

Contune AC filters

AC bus

Smoothingreactor

DC filter

Telecommunication~~

Commutation capacitors

Modular Back-toBack CCC Asynchronous Tie

Improved Stability and Higher Power Transfer

HVDC Classic HVDC CCC

The HVDC Light Converter Station

Converter station

Transmission Cable

Voltage Source Converter - VSC

AC filters

AC bus

Controlsystem

PhaseReactor

DC Capacitor

IGBT Valves

Dry DC Capacitor

Indoor

Comparison of Reactive Power Characteristics

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

VSC Based HVDC – HVDC Light (~ STATCOM, -0.5Pd/+0.5Pd MVar)

Reactive Power (p.u.)

Act

ive

Pow

er (p

.u.)

Operating Area

P-Q Diagram

HVDC VSC Operating Range

HVDC Converter Arrangements

HVDC ClassicThyristor valves

Thyristor modules

Thyristors

Line commutated

HVDC LightIGBT valves

IGBT valve stacks

StakPaks

Submodules

Self commutated

SingleValve

DoubleValve

QuadrupleValve

Thyristor Module

Thyristors

IGBT Valve Stacks

StakPak

Submodule

Chip

Cable Pair

HVDC Operating Configurations and Modes

Tapping OVHD HVDC with Large VSC ConvertersHVDC Tap

Reverse power by polarity reversalElectronic clearing of dc line faultsFast isolation of faulty convertersReactive power constraintsMomentary interruption due to CF at tapLimitations on tap rating, location and recovery rate due to stability

HVDC Light TapPolarity reversal if main link is bidirectionalCannot extinguish dc line fault current contribution without special provision, e.g., diode coupling for inverterNo interruption to main power transfer due to CF at tapLess limitations on tap rating and locationCascade VSC connection for lower tap ratingNo reactive power constraintsImproved voltage stability

HVDC Classic Control

uR

uS

uT

1 3 5

4 6 2

Id

Ud

IR

IS

IT

IR

IS

αu

IT

Control of VSC Based HVDC Transmission

Principle control of HVDC-Light

DCvoltagecontrol

uDC-ref1

uDC1

+

-

uAC1uAC-ref1

pref1

DCvoltagecontrol

uDC-ref2

uDC2

+

-

uAC2 uAC-ref2

pref2 q ref2

ACvoltagecontrol

PWMinternalcurrentcontrol

PWMinternalcurrentcontrol

qref1

ACvoltagecontrol

+

-i i

K

K

K

K

AC Line Voltages OPWM

Comparison - AC, HVDC, HVDC CCC and HVDC Light

None – black start, passive load, induction generators OK

Min SCC>1.3x converter rating

Min SCC>2x converter rating

Cable derated with distance by charging current

AC system limitation

Superior, no CFImproved, CF lower probability

Degraded, special control

Dependent on P, Q and Z

Voltage stability

Dynamic –virtual generator

Slow - switched filters, capacitors & reactors + LTC

Slow - switched filters, capacitors & reactors + LTC

StaticAC voltage control

STATCOM + 15% in fixed filters

Filters + series compensation of 3 I^2 Xcc

Switched shunt banks 35% in filters + 15% in capacitors

Shunt reactorsReactive power compensation & control

No reactive power demand

Reactive power demand reduced by series cap

Reactive power demand = 50% power transfer

3 I^2 X

- 3 V^2 B

Reactive power demand

Continuous 0 to ±Pr

Continuous

±0.1Pr to ±Pr

Continuous

±0.1Pr to ±Pr

None unless PST or series reactor

Power flow control

HVDC Light HVDC –Capacitor

Commutated

HVDC -Conventional

AC CableAttributes

Running Underground

500 kV EHV1500 MW

± 500 kV HVDC3000 MW

± 320 kV HVDC Light1000 MW

10

100

1000

10000

20 60 80 150 300 500 800Voltage in kV

Pow

er in

MW

Power Ranges HVDC-Classic and HVDC-Light

Back to back

HVDC Light

HVDC

Comparison of overall line design800 kV

1000 kV

±600 kV

±800 kV

Itaipu 765 kV AC Line Performance

Note: “,” = “.”800 kV AC ± 600 kV DC

Itaipu 600 kV HVDC Line Performance

Note: “,” = “.”800 kV AC ± 600 kV DC