facts: a modern tool for flexible power systems ... a modern tool for flexible power systems...

FACTS: FACTS: A Modern Tool For Flexible Power A Modern Tool For Flexible Power Systems InterconnectionsSystems Interconnections

Prof. Dr. Enrique Prof. Dr. Enrique AchaAchaThe University of GlasgowThe University of Glasgow

Glasgow, Scotland, UKGlasgow, Scotland, UK

9 CHLIE, 9 CHLIE, MarbellaMarbella, , EspaEspañña a 30 June 200530 June 2005

CONTENTCONTENT

What Is FACTSWhat Is FACTS

FACTS EquipmentFACTS Equipment

FACTS Equipment RepresentationFACTS Equipment Representation

FACTS Network PerformanceFACTS Network Performance

FACTS Equipment for InterconnectionsFACTS Equipment for Interconnections

FACTS: FACTS: A Modern Tool For Flexible Power A Modern Tool For Flexible Power Systems InterconnectionsSystems Interconnections

What is FACTS?What is FACTS?

The term FACTS is an acronym for Flexible Alternating The term FACTS is an acronym for Flexible Alternating Current Transmission SystemsCurrent Transmission Systems

In its most general expression, the FACTS concept is In its most general expression, the FACTS concept is based on the incorporation of power electronic devices based on the incorporation of power electronic devices and methods into the highand methods into the high--voltage side of the network, to voltage side of the network, to make it electronically controllablemake it electronically controllable

FACTS looks at ways of capitalising on the many FACTS looks at ways of capitalising on the many breakthroughs taking place in the area of highbreakthroughs taking place in the area of high--voltage and voltage and highhigh--current power electronics, aiming at increasing the current power electronics, aiming at increasing the control of power flows in the highcontrol of power flows in the high--voltage side of the voltage side of the network during both steadynetwork during both steady--state and transient conditionsstate and transient conditions


Many of the ideas upon which the foundation of FACTS Many of the ideas upon which the foundation of FACTS rests, evolved over a period of many decades. Among rests, evolved over a period of many decades. Among these are the experience gained with HVDC transmission these are the experience gained with HVDC transmission and electronic reactive power compensationand electronic reactive power compensation

Nevertheless, FACTS, as an integrated philosophy, is a Nevertheless, FACTS, as an integrated philosophy, is a concept that was brought to fruition during the eighties at concept that was brought to fruition during the eighties at EPRI by N.G. EPRI by N.G. HingoraniHingorani and his associatesand his associates

The new reality of making the power network The new reality of making the power network electronically controllable, has began to alter the thinking electronically controllable, has began to alter the thinking and procedures that go into the planning and operation of and procedures that go into the planning and operation of transmission and distribution networks in many parts of transmission and distribution networks in many parts of the worldthe world


The ability of the transmission The ability of the transmission system to transmit power system to transmit power becomes impaired by one or becomes impaired by one or more of the following steadymore of the following steady--state and dynamic limitations:state and dynamic limitations:

sins r

eq

V VPX

δ= ⋅

-- Angular stabilityAngular stability-- Voltage magnitudeVoltage magnitude-- Thermal limitsThermal limits-- Transient stabilityTransient stability-- Dynamic stabilityDynamic stability

Act

ive

pow

er (p

.u.)

With 50% of series capacitive compensation

1

2

With no compensation

With shunt compensation

With phase-shifter compensation

Phase angles (rad)0 2

π π π σ+ 2π


Two kinds of power electronics applications in power systems areTwo kinds of power electronics applications in power systems are already already well defined:well defined:-- Bulk active and reactive power controlBulk active and reactive power control-- Power quality improvementPower quality improvement

Transmissionsubstation

Power plant

Transformer

Distributiontransformers

400 V

3 – 34 kV120 – 765 kV

Distributionfeeder

Distributionsubstation

Transmission(FACTS)

Distribution(Custom power)

High Voltage High Voltage transmission benefits transmission benefits from the installation from the installation of FACTS equipmentof FACTS equipment

Low voltage Low voltage distribution benefits distribution benefits from the installation from the installation of custom power of custom power equipmentequipment


Tap changer

Phase angle regulator

Static Var Compensator (SVC)

Thyristor Controlled Series Compensator (TCSC)

Static Compensator (STATCOM)

Unified Power Flow Controller (UPFC)

Static Compensator (STATCOM)

HVDC Using Voltage Source Converters (HVDC-VSC)

Thyristorbased

IGBT based

GTO basedFACTSEquipment

FACTS Equipment FACTS Equipment –– SVCSVC

Static VAR Compensator (SVC)Static VAR Compensator (SVC)

Bank of capacitorsThyristor-Controlled

Reactor (TCR)

VaVbVc

ITCRc ITCRb ITCRa

ITCR1 ITCR2 ITCR3

Branch 1 Branch 2 Branch 3

C1 C2 C3

ICc ICb ICa

n

IaIbIc

FACTS Equipment FACTS Equipment -- TCRTCR

iTCR(t)

v(t)Th2(α2)

L

Basic TCR CircuitBasic TCR Circuit

Th1(α1) 90 180 270 360(a) α = 90° σ = 180°

Vi

0 90 180 270 360(b) α = 100° σ = 160°

0

i

90 180 270 360(c) α = 130° σ = 100°

i

0 90 180 270 360(d) α = 150° σ = 60°

i

0

( )2σ π α= −

2π α π< <Voltage and current waveforms in the basic TCRVoltage and current waveforms in the basic TCR0 σ π< <

FACTS Equipment FACTS Equipment -- TCRTCR

Increasing Increasing αα above above ππ//2 causes the TCR current waveform 2 causes the TCR current waveform to become nonto become non--sinusoidal, with its fundamental frequency sinusoidal, with its fundamental frequency component reducing in magnitudecomponent reducing in magnitude

The TCR instantaneous current isThe TCR instantaneous current is

( )TCR

1 22 sin d cos cos if( )

0 otherwise

tVV t t t t

i t L L

ω

α

ω α ω α ω α σω

⎧⎪ = − ≤ ≤ +⎪= ⎨⎪⎪⎩

∫Using Fourier analysis yieldsUsing Fourier analysis yields

( )TCR 1 2 sin 2jf

VIL

π α αω π

= − +⎡ ⎤⎣ ⎦

( )( )

( )( )TCR

4 sin 1 sin 1 sincos where 3,5,7,9,11,13...j 2 1 2 1h

V h h hI hL h h h

α α ααω π

⎡ + − ⎤= + − =⎢ ⎥+ −⎣ ⎦

FACTS Equipment FACTS Equipment -- VSCVSC

There are several Voltage Source Converter (VSC) There are several Voltage Source Converter (VSC) topologies currently in use in actual power systems topologies currently in use in actual power systems operation. Common aims of these topologies are:operation. Common aims of these topologies are:

(i) to minimise the switching losses of the semiconductors (i) to minimise the switching losses of the semiconductors inside the VSCinside the VSC

(ii) to produce a high(ii) to produce a high--quality sinusoidal voltage waveform quality sinusoidal voltage waveform with minimum or no filtering requirementswith minimum or no filtering requirements

FACTS Equipment FACTS Equipment -- VSCVSC

By way of example, the topology of a conventional twoBy way of example, the topology of a conventional two--level VSC using IGBT switches is illustrated belowlevel VSC using IGBT switches is illustrated below

+

VDC/2

-

cb

a

Dc-Db-Da-

Dc

+

Db

+

Da

+

Tb-

Tc+

Ta-

Tb+

Tc-

Ta+

Vbc

Vab

Vc

Vb

Vao

+

VDC

-

+

VDC/2

-

Voltage Source Converter (VSC)Voltage Source Converter (VSC)

FACTS Equipment FACTS Equipment –– PWM ControlPWM Control

In the basic PWM In the basic PWM method a sinusoidal, method a sinusoidal, fundamental fundamental frequency signal is frequency signal is compared against a compared against a highhigh--frequency frequency triangular signal; triangular signal; producing a squareproducing a square--wave signal, which wave signal, which controls the firing of controls the firing of the converter valves

vcontrol < vtrivcontrol > vtri

vAo

(1/fs)

vtrivcontrol

+VDC/2

-VDC/2the converter valves

Operation of a PWM Operation of a PWM –– ffss is nine times fis nine times f11

FACTS Equipment FACTS Equipment –– PWM ControlPWM Control

The corresponding harmonic voltage spectrum, for the The corresponding harmonic voltage spectrum, for the case of mcase of mff=9 and m=9 and maa=0.8, in normalised form, is shown in =0.8, in normalised form, is shown in the figure belowthe figure below

Harmonics h of f1

1.2

1.0

0.8

0.6

0.4

0.2

0.0

ma = 0.8, mf = 9

1 mf

(mf +2)

2mf

(2mf +1)3mf

(3mf +2)

( ) ( )DC 2Aoh

V V

Variable Frequency Transformer (VFT)Variable Frequency Transformer (VFT)

The VFT is a new equipment for active power flow control The VFT is a new equipment for active power flow control which is based on a combination of hydrowhich is based on a combination of hydro--generator, generator, transformer and drives technologiestransformer and drives technologies

The VFT may be seen as a threeThe VFT may be seen as a three--phase, twophase, two--winding winding transformer with a rotary secondary, for continuously transformer with a rotary secondary, for continuously controllable phase shift. A drive system and control adjust controllable phase shift. A drive system and control adjust precisely the phase angle and speed of the rotor to precisely the phase angle and speed of the rotor to regulate the power flow through the VFTregulate the power flow through the VFT

The vendors of the VFT technology argue that the The vendors of the VFT technology argue that the equipment has low complexity and low maintenance costsequipment has low complexity and low maintenance costs

Variable Frequency TransformerVariable Frequency Transformer

The figure shows a cutThe figure shows a cut--away drawing of a 100 away drawing of a 100 MW VFT installed at MW VFT installed at LangloisLanglois, Canada. The , Canada. The main components are:main components are:-- The rotary transformerThe rotary transformer-- The drive motorThe drive motor-- The collectorThe collectorOne power grid is linked to One power grid is linked to the the VFT’sVFT’s rotor and the rotor and the other grid is connected to other grid is connected to the the VFT’sVFT’s statorstator

Representation of FACTS Controllers Representation of FACTS Controllers Based on Conventional Based on Conventional ThyristorsThyristors

The The thyristorthyristor--controlled reactor (TCR)controlled reactor (TCR)

The static VAR compensator (SVC)The static VAR compensator (SVC)

The The thyristorthyristor--controlled series compensator (TCSC)controlled series compensator (TCSC)

ITCR

LVTCR

Q QLC

VSVC

C

LVTCSC

Iloopp

Representation of SVCRepresentation of SVC

The static VAR compensator (SVC)The static VAR compensator (SVC)

Q Q

VSVC BTSC(αC) BTCR(αL)

Q

VSVC BTSC(α)

Q QLC

VSVC

( )CL

SVC TSC TCRC L

L

C

2 sin 2

1

XXB B B

X XX L

XC

π α απ

ω

ω

− − +⎡ ⎤⎣ ⎦= − =

=

=

SVC SVCjI B V= where

Representation of SVC Representation of SVC –– VV--II characteristiccharacteristic

Vmax

Vmin

VSVC

ISVC

Capacitive rating Inductive rating

System reactive

Load characteristic

SVC voltage/current characteristic with system loadSVC voltage/current characteristic with system load


bus mbus k

+VDC

-

IcR

Vk Vm

ma

k kI γ∠cR cRE δ∠

k kV θ∠ m mV θ∠

m mI γ∠

bus k

+VDC

- IvR

EvR

Vkma

bus kYvRvR vRE δ∠

k kV θ∠

k kI γ∠

VSC connected to the AC network via a VSC connected to the AC network via a shuntshunt--connected transformer

VSC connected to the AC network via a VSC connected to the AC network via a seriesseries--connected transformerconnected transformer connected transformer


0.10.20.30.40.50.60.70.80.91.0

VT

ILIC 0

Transient

Inductive

Rating

Transient

Capacitive

Rating

STATCOM STATCOM VV--II CharacteristicCharacteristic

FACTS Network PerformanceFACTS Network Performance

Newton’s Method Newton’s Method –– Numerical ExampleNumerical Example

A fiveA five--bus test network is employed to illustrate the use of bus test network is employed to illustrate the use of the UPFC power flow model within a OPF computer the UPFC power flow model within a OPF computer programprogram

The maximum and minimum voltage magnitude limits at all The maximum and minimum voltage magnitude limits at all buses are taken to be buses are taken to be 0.9 0.9 p.up.u.. and and 1.1 1.1 p.up.u.., respectively, , respectively, except at North where the maximum limit is set at except at North where the maximum limit is set at 1.5 1.5 p.up.u..

The cost coefficients of the two generating units are taken The cost coefficients of the two generating units are taken to be:to be:

a=a=60 $/hr ; 60 $/hr ; b=b=3.4 $/MW3.4 $/MW--hr ; hr ; c=c=0.004 $/MW0.004 $/MW22--hrhr


5.01

5.00

60+j10

North Lake Main

South Elm

14.8714.8932.2332.94

1.08

5.15

27.66

1.53

20+j10

87.89

0.2945+j15 40+j5

56.06 55.00

5.201.3747.20

46.84

2.024.29

6.07 6.44

2.16

3.56

5.50

1.96

30.61

4.85

14.41

80.15

30.14

28.06


The table below summarises the key parameters The table below summarises the key parameters generated by the OPF solution, such as active power generated by the OPF solution, such as active power generation cost and active power lossgeneration cost and active power loss

Results OPF

Active power generation cost ($/hr) 747.98

Active power loss (MW) 3.02Active power generation (MW) 168.05Reactive power generation (MVAR) 14.71

UPFC OPF UPFC OPF –– Regulated CaseRegulated Case

8.37

8.31

60+j10

North Lake Main

South Elm

24.932535.9236.95

4.19

1.16

20+j10

88.47

1.8745+j15 40+j5

52.76 51.68

4.402.3243.20

42.85

4.166

24.15

7.59

2.45

2.40

80.15

3.57

23.77

6.70

23.4334.075.98

3.98

34.78

7.75

UPFC OPF UPFC OPF –– Unregulated CaseUnregulated Case

In order to illustrate the behaviour of the various UPFC operatiIn order to illustrate the behaviour of the various UPFC operating ng modes, its functional constraints are freed in sequence:modes, its functional constraints are freed in sequence:

(i) The normal UPFC operating mode (all constraints activated) i(i) The normal UPFC operating mode (all constraints activated) is s compared against cases where active and reactive power flows arecompared against cases where active and reactive power flows arefreed and the voltage magnitude remains fixedfreed and the voltage magnitude remains fixed

(ii) Compared against the case when the voltage magnitude is fre(ii) Compared against the case when the voltage magnitude is freed ed and active and reactive power flows are fixedand active and reactive power flows are fixed

(iii) and compared against the case when all three constraints a(iii) and compared against the case when all three constraints are re freedfreed

UPFC OPF UPFC OPF –– Unregulated CaseUnregulated Case

Operating mode Number of iterations

Generation cost($/hr)

Power loss(MW)

Normal UPFC operation 2 750.357 3.631

Fix Voltage (at bus Lake) 2 749.928 3.519Fix P and Q 3 748.236 3.119

All constraints de-activated 3 747.982 3.015

FACTS Equipment for InterconnectionsFACTS Equipment for Interconnections

Requirements of Selected Equipment in Requirements of Selected Equipment in Asynchronous InterconnectionsAsynchronous Interconnections

The selected equipment must have the ability to enable The selected equipment must have the ability to enable one interconnecting system to receive “black start” one interconnecting system to receive “black start” support from the other interconnecting systemsupport from the other interconnecting system

The equipment must be able to operate with no demand The equipment must be able to operate with no demand of reactive power from the interconnecting systems. This of reactive power from the interconnecting systems. This applies to both cases, when there is and when there is applies to both cases, when there is and when there is not exchange of active power between the two systemsnot exchange of active power between the two systems

The equipment must have the ability to prevent voltage The equipment must have the ability to prevent voltage perturbations from propagating to the neighbouring perturbations from propagating to the neighbouring system in order to prevent conditions of voltage collapse system in order to prevent conditions of voltage collapse in that systemin that system

HVDCHVDC--VSCVSC

BackBack--toto--back, 36 MW, back, 36 MW, ±±138 kV HVDC138 kV HVDC--VSC tie located at VSC tie located at Eagle Pass substation. Used for export/import of Eagle Pass substation. Used for export/import of electrical energy between AEPelectrical energy between AEP--TCC in Texas and CFE, TCC in Texas and CFE, Mexico Mexico

HVDCHVDC--VSCVSC

The HVDCThe HVDC--VSC at VSC at PiedrasPiedras NegrasNegras –– Eagle Pass uses IGBTEagle Pass uses IGBT--based based converters, which switch at converters, which switch at 12601260 Hz (Hz (mmf f = 1260/60 = 21)= 1260/60 = 21)It connects the 138 kV grids of CFE and AEPIt connects the 138 kV grids of CFE and AEP--TCC. It consists of two 36 TCC. It consists of two 36 MVA MVA VSCsVSCsPWM harmonics are generated at:PWM harmonics are generated at: ( ) 1h ff m fβ κ= ±

ββ Harmonic orderHarmonic order

11 19, 19, 2121, 23, 23

22 39, 41, 43, 4539, 41, 43, 45

33 59, 61, 59, 61, 6363, 65, 67, 65, 67

44 81, 83, 85, 8781, 83, 85, 87

…… ……

1010 207207, 209, 211, 213, 209, 211, 213

…… ……

The The 33rdrd harmonic is also harmonic is also significantsignificant

The 207The 207thth harmonic varied harmonic varied between 13% and 40% of the between 13% and 40% of the power frequency voltage, power frequency voltage, depending on the operation of depending on the operation of the the BtBBtB and phase angle and phase angle between the two invertersbetween the two inverters

Layout of a VFT SubstationLayout of a VFT Substation

The figure shows the The figure shows the layout of a 200 MW VFT layout of a 200 MW VFT substation. The following substation. The following items are highlighted:items are highlighted:(1) Rotary system(1) Rotary system(2) Main transformers(2) Main transformers(3) Drive transformer(3) Drive transformer(4) VARs banks to yield (4) VARs banks to yield unity pfunity pf(5) Control room(5) Control room(6) High(6) High--voltage linesvoltage lines

VFT Dynamic ResponseVFT Dynamic Response

The figure opposite illustrates the The figure opposite illustrates the VFT’sVFT’sresponse to steps in power orderresponse to steps in power order

The red line is the torque command The red line is the torque command stepping from 0 to 1 stepping from 0 to 1 pupu, to , to --1, and back 1, and back to 0to 0

The blue line in the same plot shows the The blue line in the same plot shows the actual VFT power transfer. The actual VFT power transfer. The corresponding phase angle is shown in corresponding phase angle is shown in the lower plotthe lower plot

These results were obtained using a These results were obtained using a realreal--time VFT simulatortime VFT simulator

SSSCSSSC

Vdc 370 V

VLoad_1

ILoad_1

45.3+j71.1Ω

Load 1

VS 11 kV

ZS 11.75Ω

Brk

VVSC

45.3+j71.1Ω

Load 2

14.5+j45.4Ω

Load 3

11kV/220V

T2

11kV/220V

T1Fault 50 Hz, 190.73 V

50 Hz, 190.73

150 Hz, 8.36 V

2250 Hz,

27.3 V

2-ph fault

Voltages at load 1 - with no SSSC

Test circuit with a three-phase SSSC to restore voltage balance at point load 1

Voltages at load 1 - with SSSC

Comparison of Two FACTS TechnologiesComparison of Two FACTS Technologies

FunctionFunction HVDC LightHVDC Light VFTVFT

Core technologyCore technology IGBT valvesIGBT valves Induction machine plus Induction machine plus variable speed drivevariable speed drive

Network connectionNetwork connection Transformers plus series inductorsTransformers plus series inductors TransformersTransformers

Filtering and reactiveFiltering and reactivecompensationcompensation

Quite considerable filter Quite considerable filter requirementsrequirements

Switched capacitorsSwitched capacitors

Power controlPower control 0 to 0 to ±±150 MW150 MW 0 to 0 to ±±100 MW100 MW

Speed of responseSpeed of response Very fastVery fast Quite slowQuite slow

Modulation/controlModulation/control Active and reactive powersActive and reactive powers Active powerActive power

Voltage controlVoltage control Continuous, fast and independentContinuous, fast and independent Not possibleNot possible

Black startBlack start YesYes YesYes

MaturityMaturity Rapidly maturing Rapidly maturing –– several sitesseveral sites One installationOne installation

Full load lossesFull load losses 3.46%3.46% 1.78%1.78%

FACTS Equipment FACTS Equipment –– STATCOM and UPFC STATCOM and UPFC InstallationsInstallations

Installations:

- Orange and Rockland STATCOM ±1 MVA 1986

- WAPA UPFC Model 1993

- TVA, Sullivan STATCOM ±100 MVA 1995

- AEP, St Inez STATCOM ±160 MVA 1997

(UPFC)

- SMI Arc Furnace STATCOM ±80 MVA 1998

- Pacific Gas & Electric STATCOM -20/+60MVA 1998

- AEP, St Inez UPFC ±320 MVA 1998

(2 × ±160)

FACTS Equipment FACTS Equipment –– SSSC InstallationsSSSC Installations

Installations:

- Duke Power SSSC 2 MVA 1996

- Powercor (Australia) SSSC 2 MVA 1996

- Florida Power Corp SSSC 2 MVA 1997

- Scottish Power SSSC 4 MVA 1997

- Asian Electronics SSSC 2 MVA 1998

Manufacturer

- Salt River Project SSSC 2×6MVA 1998

FACTS Equipment FACTS Equipment -- HVDCHVDC--VSC InstallationsVSC Installations

Installation:Installation:

-- HellsjHellsjöönn--GrGräängergngerg 3 MW ; 3 MW ; ±±10 kV10 kV March 1977March 1977-- GotlandGotland--VisbyVisby CityCity 50 MW ; 50 MW ; ±±80 kV80 kV midmid--20002000-- DirectlinkDirectlink in Australiain Australia 180 MW ; 180 MW ; ±±80 kV80 kV midmid--20002000-- Eagle PassEagle Pass--PiedrasPiedras NegrasNegras 36 MW ; 138 kV36 MW ; 138 kV midmid--20002000-- Cross Sound link in NYCross Sound link in NY 330 MW ; 330 MW ; ±±150 kV150 kV Sep. 2002Sep. 2002-- MurraylinkMurraylink in Australiain Australia 200 MW ; 200 MW ; ±±150 kV150 kV Oct. 2002Oct. 2002

All in all, thirteen Light installations (HVDCAll in all, thirteen Light installations (HVDC--VSC and STATCOM) are known VSC and STATCOM) are known to be in operation or in the construction stageto be in operation or in the construction stage

facts: a modern tool for flexible power systems ... a modern tool for flexible power systems...

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