power electronics for the enhancement of grid efficience

8/12/2019 Power Electronics for the Enhancement of Grid Efficience

1/8

Answers for energy.

Special reprint from BWK Das Energie-Fachmagazin Volume 60 (2008), No. 11, pages 6 13

Authors: Matthias Claus, Karl Uecker, Dietmar Retzmann

Power Electronics for Enhancementof Grid Efficiency


2/8

Authors

Power Electronics for

Enhancement of Grid EfficiencyThe security of power supply in terms of reliability and blackout prevention has the utmost priority whenplanning and extending power grids. The availability of electric power is the crucial prerequisite for thesurvivability of a modern society and power grids are virtually its lifelines. The aspect of sustainability isgradually gaining in importance in view of such challenges as the global climate protection and economi-cal use of power resources running short. It is, however, not a means to an end to do without electricpower in order to reduce CO2 emissions. A more appropriate way is to integrate renewable energy resour-ces to a greater extent in the future (energy mix) and, in addition to this, to increase the efficiency of con-ventional power generation as well as power transmission and distribution without loss of system security.

future for both security and sustainabi-lity of power supply [1 to 4]. With thehelp of power electronics the power sys-tem can be given dynamic support, butnot only; the efficiency of power trans-mission at various voltage levels can al-so be increased. Power electronics is ea-sily controllable which makes the gridmore flexible and, due to this, it can rea-dily include availability-dependent rege-nerative and distributed energy sources.

Regenerative power generation onthe basis of availability-depen-dent energy resources particu-

larly wind power can hardly follow theload profile which leads to significantcongestions in the grid. That is, the re-quirements of wind power to flexibilityand loading capacity of the grids are ex-tremely high. In view of these require-ments, power electronics will play an in-creasingly more important role in the

Matthias Claus,Graduate Engineer, bornin 1968; studied Electrical Engineering atthe University of Erlangen-Nuremberg,since 1996 Consultant in the field of PowerSystem Planning (real-time simulation ofHVDC/FACTS and system protection); sin-ce 2001 in the field of Basic Design forFACTS/Reactive Power Compensation; sin-ce 2005 Senior Sales and Marketing Mana-ger at Siemens Energy, Power TransmissionSolutions, Erlangen.

Karl Uecker, born in 1962, since 1982Specialist in the field of Commissioning ofPower Plants and High-Voltage Installati-

The figure gives a brief insight into the

transmission of electric power based

on hydro resources by means of HVDC.

ons at Siemens; since 1991 Sales Managerfor Power Quality in the region of Asia, lo-cation Singapore and Kuala Lumpur; since2000 Senior Sales Manager for HVDC andFACTS; since 2006 Vice President HVDC/FACTS Sales & Marketing, Siemens Energy,Power Transmission Solutions, Erlangen.

Dietmar Retzmann,Prof. Dr.-Ing., born in1947, studied Electrical Engineering at theTechnical University of Darmstadt, recei-ved a Doctorate at the University of Erlan-gen-Nuremberg; from 1974 till 1975Commissioning Engineer at former BrownBoveri & Cie AG, Mannheim; since 1976

Scientific Assistant at the chair of ElectricPower Supply at the University of Erlan-gen-Nuremberg and since 1982 at Sie-mens AG, Erlangen. 1998 he was ap-pointed Visiting Professor at the Univer-sity of Tsinghua, Beijing, China, and2002 at the University of Zhejiang,Hangzhou, China; since 2004 Lectureron HVDC and FACTS at the University ofKarlsruhe. Siemens Top Innovator, Tech-nical Director Sales & Marketing and In-novations HVDC/FACTS, Siemens Ener-gy Sector, Power Transmission Solutions,Erlangen.

i [email protected]

A flexible grid of this kind is also termedSmart Grid [3].

Power electronics is used in high-vol-tage systems for flexible AC transmis-sion FACTS 1) as well as for high-volta-ge direct-current transmission systems(HVDC). HVDC helps prevent bottlen-ecks and overloads in power grids bymeans of systematic power-flow control.

1) FACTS: Flexible AC Transmission Systems

2


3/8

ITC: International Transmission Company PTDF: Power Transfer Distribution Factor

25 %

Max % PTDF

5 %2 %

An Outlook National Transmission Grid Study, U.S. DOE, May 2002

Grid enhancementis essential!

Problems in synchronouslyinterconnected systems only

The Blackout ITC, August 2003

Congestion, overloads and loop-flows

0

0

00

X XX

X

XXX

4.8 GW

3.7 GW

2.2 GW

0.2 GW

Generator DownTransmission Line DownDirection of Power Flow

0X

The function of the HVDC which is deci-sive for system security is that of an au-tomatic firewall. This firewall functioncan prevent the spread of a disturbance,which occurs in the system, at all times;as soon as the disturbance has beencleared, power transmission can imme-diately be resumed. Moreover, the HVDC

technology allows for grid access of ge-neration facilities on the basis of availa-bility-dependent regenerative energysources, including large offshore windfarms, and, compared with the conven-tional AC transmission, it boasts a sig-nificantly lower level of transmissionlosses on the way to the loads.

FACTS technology was originally crea-ted to support weak AC grids and to sta-bilize AC transmission over very longdistances. FACTS technology encompas-ses systems for both parallel and seriescompensation. It rests upon the princi-

ple of reactive power elements, control-led by means of power electronics,which can reduce the transmission an-gle of long AC lines or stabilize the volta-ge of selected grid nodes. Due to a highutilization degree of AC power grids, theapplication of FACTS technology will be-come an increasingly more interestingissue also in the case of meshed powersystems, e.g. in Europe. FACTS andHVDC applications will consequentlyplay an important role in the future de-velopment of power systems. This willresult in efficient, low-loss AC/DC hybrid

grids which will ensure better controlla-bility of power flow and, in doing so, dotheir part in preventing domino effectsin case of disturbances and blackouts.

More Security and Flexibilitydue to Power Electronics

From the point of view of the designconcept, AC grids are seldom configuredas wide-area bulk power transmissionsystems. By way of example, the Wes-tern European Power Union (UCTE) at atransmission voltage of 400 kV was ori-

ginally based on the concept of a systemwhich provides power generation nearthe loads and has additional links tosupport the adjacent grids in the case ofdisturbances or planned outages of indi-vidual generation units. In the course ofderegulation and privatization of Euro-pean power markets the idea of an All-European interconnected system cameup, and in view of climate change, the is-sue of bulk power transmission of envi-ronmentally compatible energy comple-ted the picture [1 to 4]. However, prior toimplementing this vision to the full ex-

tent, the grid concept must be adaptedto these modified conditions. To describethis, Fig. 1 shows a very clear picturefrom the USA, where a large-scale studyon the transmission grid in the year2002 detected a number of bottlenecks

related to local overloads and loop-flows, which indeed lead to an enor-mous blackout in that particular area

one year later [5]. The figure depicts se-parate lines in load-dependent colours;the red colour marks a significant over-load, and the green one reflects a situa-tion in which even more current can ea-sily flow through. For the sake of a con-sistent load flow, the ideal solutionwould be to furnish the grid, which isentirely open for power trading, withyellow lines, which helps do away withthe less loaded grey ones. It is needlessto say that in the context of a complex,largely meshed grid without any additio-nal measures to boost its efficiency, an

optimal load-flow control such as this isnot possible. The rough idea is given inFig. 1: the fact is that in 2003, the gridproblems affected only the synchro-nously interconnected eastern areas ofthe US and Canada, whereas the Hydro-Qubec grid in the East of Canada whichis connected by means of HVDC remai-ned unaffected. The HVDC systems in-stalled there prevented further spread ofthe blackout fully automatically withoutany human interference thanks to theirFirewall function. Moreover, Qubec wasin a position to help restore the affected

adjacent grids in a very effective man-ner by means of power injection from itsHVDC systems [5].

This example proves that even largeAC grids can be enhanced by means ofpower electronics. Electronically con-trolled converter systems can namelycontrol active and reactive power and,subsequently, the grid voltage at a requi-red response time in a far more flexibleand effective way compared with powerplants or phase-shifting transformers 2)distributed in the grid.

Renewable Energy Sources:Challenges to the Grids

Sustainability of power supply standsfor a number of measures for efficiencyenhancement with regard to power ge-

neration, it means the increase in effi-ciency ratio during energy conversion ata power plant, the reduction in trans-mission losses in the grid and, last butnot least, efficiency enhancement at theload. The decisive role in terms of sus-tainability is played by the renewableenergy sources, particularly those capa-ble of producing entirely CO2-free power,such as hydro, solar and wind energy. As

far as Europe is concerned, wind powerconstitutes a cornerstone of its futureenergy supply; hydro power resourcesare relatively small with the exceptionof Nordel grid and solar energy is availa-ble virtually only in the South of Europe.In the course of the last years, Germanycould boast extremely high increase inthe amount of wind power plants. Theaggregated installed rated power of on-shore installations increased fromaround 12 GW in the year 2003 to over22 GW in the year 2007. In terms of futu-re use of offshore wind energy in the

German parts of the North and the Bal-tic Sea, a long-term feasibility of 30 to50 GW of installed capacity was deter-mined in numerous studies. This is animpressive value when compared withtoday's national German installed gene-ration capacity of around 120 GW.

Fig. 2 depicts power infeed from agroup of onshore power plants as well asthe load pattern of this control area. Ac-cording to it, the balance between gene-ration and consumption does not matchat all in this case; the unbalance requi-res large amounts of reserve capacity

from the rest of the grid which must beat hand. In the case of thermal powerplants, this kind of reserve capacity iscomparatively expensive (peak power).

Fig. 1

Extreme increase in

the load flow results

in a blackout.

2) PST: Phase-Shifting Transformer

3


4/8

Loa

dinGW

PowerinfeedinGW

2

10

12

14

18

0

Mo Tu We Th Fr Sa Mo Tu We Th Fr SaSu Su

8

16

6

4

Time period between November, 17 and 30, 2003

0.5

2.5

3.0

3.5

4.5

0.0

2.0

4.0

1.5

1.0

Source: E.ON Netz

Maximal load

Wind power plants

Problems with wind power generation in Germany and in most other countries:

Due to severe fluctuations, wind power can hardly follow load patterns. Additional reserve capacity is required.

Fig. 3 depicts how this problem wassolved in Australia, namely by means ofenergy mix. A combination of flexibly

applied hydro power plants and availa-bility-dependent that is not permanent-ly available (fuzzy) wind power plantsplus the HVDC technology as a highwayfor power trade and back-up reserve inboth directions is a glorious example ofhow feasible environmentally compati-ble power supply can be. For the sake ofgrid security, a thermal power plant bothin Tasmania and on the Australian con-tinent would have had to be constructedat higher cost alternatively to an HVDCsystem.

Security and Sustainabilitydue to Power Electronics

Europe carries a high potential for im-plementation of renewables as well. In[4], an example from Denmark is given,where a Static Var Compensator 3) isused to stabilize the voltage of offshorewind farms in the weak grid of the Lol-

land island. Moreover, the combinationof wind and hydro power has alreadybeen intensively used in different coun-

tries; the electric power provided by hy-dro power plants situated in the Nordelarea is basically delivered to the UCTEsystem through the sea by means ofHVDC systems. Item [2] gives an exam-ple of how significantly the capacity andstability of the Baltic CableHVDC systemcould be boosted by means of the StaticVar Compensator Siems on the side ofthe weak 110 kV grid in the North of Ger-many. The initial objective at the plan-ning stage was to connect the HVDC sys-tem directly to the stronger 400 kV gridwhich, however, could not be implemen-

ted due to the right-of-way problems inthat region.

Now, the question is how renewableenergies, wind power in particular, influ-ence the grid in the event of an outage.The prime example here is the massiveoutage experienced in the European gridon November, 4, 2006. The events startedin the evening around 9:30 pm, and weretriggered by the deliberate disconnecti-on of two 400 kV lines over the Ems riverin order to let a large vessel pass. Due tothis, a number of lines were overloadedwhich resulted in a domino effect typi-

cal of massive outages of this kind andended up in the splitting of the UCTE

system into three areas at different fre-quencies. It was the over-frequency area

which, in addition to the congestion pro-voked by the failed lines, suffered froman excessive electric power infeed fromwind farms, which was exactly what anover-frequency area required the least atthat period of time. This scenario is de-picted in Fig. 4.

Should even far higher input from off-shore wind farms into the northern Ger-man grid come into play in the future, asthe figure suggests, the HVDC technolo-gy provides the best possibility to for-ward the power surplus from the low-lo-ad North directly to the southern load

centres of Germany or to the adjacentcountries with higher power demand.This idea rests upon a well-known expe-rience with hybrid grids in other coun-tries, according to which the DC point-to-point connection carries out an easypower transfer over large distances andthe adjacent AC grid is additionally sup-ported by means of FACTS [5]. The mostdevoted user of this hybrid concept isChina. In the South of China, Siemenstogether with its Chinese partners is cur-rently implementing an 800 kV HVDCproject Yunnan-Guangat a transfer capa-

city of 5 GW (Fig. 5). Further 800 kV pro-jects at a transmission capacity of up to7.2 GW are being currently planned. Atotal of 20 Bulk Power HVDC projectsare planned in China for the time periodbetween 2008 and 2019. The total ratingamounts to 104 GW or higher (as cur-rently planned).

At a DC voltage of 800 kV the line los-ses drop by approx. 60 % compared withthe present standard of 500 kV at the sa-me power rating. A great number of the-se projects in China is meant for powertransmission from hydro power plants

situated in the middle of the country tothe distant load centres.

The project Yunnan-Guang helps savearound 33 Mt CO2 in comparison withlocal power generation, which, in view ofthe current energy mix in China, wouldbe connected with a relatively high car-bon amount.

The 2nd800 kV HVDC project Xiangjia-ba-Shanghai, which also involves Sie-mens as well as ABB and Chinese part-ners, boasts significantly higher yearlyCO2savings of over 40 Mt thanks to evenhigher hydro power transmission capa-

city of 6.4 GW. When comparing trans-mission losses of AC and DC, it becomesapparent that the latter typically has 30to 40 % less losses. For instance, in the

Fig. 2

Example of actual power generated

by an onshore wind farm during a

week of maximum load.

Benefits of HVDC

Clean power CO2reduction Cost reduction

Flexible

Fuzzy

Hydro power for baseload and energy storage

Plus wind power

For base load and peak-load demand 2005

Fig. 3

The Basslink HVDC project in Australia

enables the utilization of renewable

energy sources from Tasmania.

3) SVC: Static Var Compensator

4


5/8

case of the 500 kV HVDC project Ballia-Bhiwadiin India, the transmission rating

of 2.5 GW helps saving approximately0.7 Mt CO2due to the transmission los-ses which are 37 % lower than those ofthe 400 kV AC double-circuit system, ty-pical of this country. The converter los-ses (i.e. those of both converter stations,incl. transformers, valve cooling and ot-her equipment) amount to 1.4 % of therated power only.

HVDC and FACTS an Insightinto Converter Technology andStation Equipment

HVDC: Bulk Powerexample at 800 kV

The HVDC systems at 800 kV requirethe most state-of-the-art convertertechnology. The separate components ofthis kind of installations boast impressi-ve design and dimensions owing to therequired insulation clearance distances.Fig. 6 depicts one of the all in all 48transformers of the 5 GW HVDC systemYunnan-Guang. All the type tests of thisworld-wide first 800 kV HVDC were suc-cessfully completed in September 2008,which constitutes a milestone in the

field of the ultra-high voltage DC powertransmission. Additionally, the figureshows huge DC-disconnectors, DC-vol-tage dividers and one of the convertervalve towers. For reasons of transporta-tion, the 800 kV DC voltage is generatedby two converter halls at 400 kV eachwhich allows for smaller dimensions ofthe transformers, i.e. critical elementsfrom the point of view of transportation,for, with the exception of wall bushings,they cannot be taken apart.

China requires this HVDC technologyto construct a high-power DC system,superimposed to the AC grid, in order totransmit electric power from huge hydropower plants in the centre of the coun-try to the load centres located as far as2,000 to 3,000 km away with as little los-ses as possible. An HVDC system at a DCvoltage of 500 kV is depicted at the frontpage of this issue.

FACTS: Precise use of reactive power in ACgrids

In the case of AC grids, the control ofreactive power by means of FACTS is thesame as a compressor for an engine

when applied to a correct degree and atthe correct point it makes the AC grid toan energy highway similar to an HVDCroute, but without the Firewall protecti-on function mentioned above. FACTSparallel compensation provides voltagesupport of weak grids and helps avoidcritical voltage collapse in case of largesystem outages. When it comes to sub-stantial line length, FACTS series com-pensation can also reduce the inductivecomponent to such an extent that the li-ne length becomes virtually much shor-ter. This means that even long lines re-

main within the stable range, for theyare virtually cut by 50 to 70 per cent.Due to this, the 1,000 kV AC lines, plan-ned in China, can bridge the distances of2,000 km and above in a stable way.

The n1 redundancy criterion, howe-ver, requires a double-circuit systemthat is, in the case of 1,000 kV, it is an ex-tremely complex matter owing to thesubstantial route width. When it comesto a DC system, the n1 redundancy isalready fulfilled, for there are two linesof one bipolar system.

As far as 800 kV AC systems are con-

cerned, the transmission length of ap-proximately 1,500 km is feasible in com-bination with series compensation, whe-reas the 500 kV AC can manage appro-ximately 1,000 km only. A project of thiskind with the line length of 1,000 km is,e.g. the North-South Interconnector inBrazil. In the case in this interconnecti-on, in addition to fixed series compensa-tion, a controlled series compensation 4)is installed at both the beginning andthe end of the line in order to stabilizepower oscillations. Further examples ofFACTS projects are depicted in Fig. 7:

> SVC Radsted, Denmark, a Static VarCompensator installation with noise-ab-sorbing indoor construction [4].

Area 1Under-frequency

Area 2Over-frequency


An idea for Europe: wind power transmission from the North to the South by means of HVDC


Area 2ver-frequen

The Problem

eRe to rea 2A ansupportquencyr or

ea 1Ar an rea 3HVDC

Fig. 4

The European grid outage

on November, 4, 2008 andan HVDC solution concept.

Fig. 5

Large HVDC projects in southern China

enable low-loss west-to-east transmission

of as much as 5 GW of hydropower-based

electrical energy produced in the countrys

interior to coastal load centers.

4) TCSC: Thyristor Controlled Series Compensation

5


6/8

Bulk Power HVDC800 kV DC

>SVC Bom Jesus da Lapa, Brazil, is a StaticVar Compensator installation with val-ves and controls in a container; transfor-

mers, voltage-limiting reactors as wellas voltage-increasing capacitors are pro-vided in form of an outdoor installation.> SVC Pelham, UK, is a Static Var Com-pensator installation with a classic buil-ding solution for valves and controls;the rest of the components are installedoutdoor as well.>The thyristor of the TPSC installation 5)in the West of the USA provides only fastovervoltage protection of the series ca-pacitor in case of faults; these sevenprojects require no closed-loop controlat all.

Power electronics what is it all about?

The core or the workhorse of HVDCand FACTS installations are high-powerthyristors, triggered optically by meansof laser technology or electrically depen-ding on application. Thyristors can onlyswitch on the current. The switching-offis carried out by the next current zerocrossing itself. This is the reason why athyristor converter is referred to as a li-ne-commutated system. Should no line

voltage be available on one side of anHVDC system or in a FACTS application,the system is no longer functioning. An

advantage of thyristor converters is theirhigh loading capacity both during nomi-nal and overload operation as well as inthe event of contingency. Consequently,bulk-power systems at high transmis-sion capacities of 5 to 7 GW can be im-plemented with thyristors only. A furt-her benefit consists in comparativelylow station losses. The TPSC projectsdescribed above use special-purposethyristors capable of withstanding tran-sient overloading of up to approximately110 kA.

The strength, i.e. short-circuit power

of the grid is an important design criteri-on for the application of line-commuta-ted HVDC systems. If the grid is too we-ak, a thyristor-based HVDC system mustreduce its power or, under certain condi-tions, shut down completely in order toavoid system collapse resulting from re-petitive commutation failures. In the ca-

se of weak grids, remedy is provided byFACTS for grid support, i.e. a combinati-on of the HVDC and FACTS as in theexample of the SVC Siemsfor the HVDC

project Baltic Cable. Additionally, the pro-blem can be tackled by means of self-commutated converters. Self-commu-tated converters make use of elementswhich can be switched off, mostly mo-dular of press-pack high-power transis-tors, all of which, in their turn, consist ofa number of separate elements, con-nected in parallel. In this way, a conver-ter turns into an electronic generator.Self-commutated converters are nor-mally furnished with a voltage source.With its help a separate capacitor or anumber of them keep the voltage con-

stant 6), whereas a conventional thyris-tor-based HVDC system keeps the sour-ce current constant 7) by means of re-actors.

A detailed description of different VSCsolutions is given in, e.g. [6]. A generaladvantage of the VSC-based HVDC sys-tems consists in the fact that one of thepower grids subject to coupling can becompletely voltage-free or passive, for,with the help of the intact grid, the otherone can be started again similar to apower plant. This black-start capabilityis particularly interesting for connecting

large offshore wind farms off the coastof Germany.

In item [6] an innovative developmentwith what is known as the MMC tech-nology8) is described, which is appliedby Siemens as an HVDC PLUS for theHVDC projects and as an SVC PLUS forFACTS. This technology stands out dueto its compact modular design and anew multilevel converter, which allowsto generate an AC system of a virtuallyideal sinus waveform from DC voltage inthe voltage source by means of a greatnumber of fine steps without any addi-

tional filters. The reactive power ele-ments and filters of normally 50% of theactive power, required in HVDC Classicapplications, can be done completelyaway with in this case, which helps re-duce the footprint of an HVDC stationby approx. 40 %. An overview of the firstMMC project with a 200 kV XLPE DC ca-ble is given in Fig. 8. The goal of this pro-

ject is to eliminate bottlenecks in theoverloaded Californian grid: new powerplants cannot be constructed in thisdensely populated area and there is noright-of-way for new lines or land ca-

bles. This is the reason why a DC cable

Fig. 6

HVDC components for

the energy highway.

SVC Radsted, Denmark SVC Bom Jesus da Lapa, Brazil

TPSC Installation, West of the USASVC Pelham, UK

Fig. 7

Examples of FACTS projects.

6) VSC: Voltage-Sourced Converter7) CSC: Current-Sourced Converter8) MMC: Modular Multilevel Converter

5) TPSC: Thyristor Protected Series Compensation

6


7/8

Transmission constraintsbeforeTBC project

Power exchange by means of sea cable No increase in short-circuit power

400 MW88 km

2010

P = 400 MWQ = 170 to 300 MVAr

Dynamic voltagesupport

Eliminiation ofbottlenecks

Transmission constraintsafterTBC project

will be laid through the bay, and thepower will flow through it by means ofthe HVDC technology in an environmen-tally compatible way.

HVDC and FACTS: Comparison

of Stability and TransmissionFunctions

In addition to the abovementioned Fi-rewall function, the HVDC systems pri-marily boast capability of directedpower control in terms of sign and mag-nitude. When the operator of an HVDCsystem gives a value of 1,000 MW, thereare exactly these 1,000 MW flowingthrough the line or link.

In the case of FACTS installations, it isquite different; they operate rather indi-rectly with variable impedances for re-

active power control: while supportingthe grid, they, however, cannot force thepolarity of the load flow. The best way todescribe FACTS applications is to com-pare them with traffic lights in a big-citytraffic: when the traffic lights are usedin the right place at the right time, thetraffic runs smoothly. If there are notraffic lights, a traffic jam can developquickly, which can then be bridged onlyby means of an HVDC power highway.This is pictured in Fig. 9. In order to pro-vide stable power flow from the left tothe right grid with the help of a FACTS

application, the voltage on the load sideis to be stabilized and, in addition tothis, the line must be made virtuallyshorter by means of series compensati-on both steady-state and dynamicallyfor the case if power oscillations occur.In doing so, the volume of power trans-mission can be changed, whereas the di-rection of power flow is determined byphasing of both grids to each other only.That is, compared with HVDC systems,FACTS installations as they are cannotchange the direction of the power flow.

In the case of an HVDC system, the

magnitude as well as the sign of thepower P can be changed, whereas thegrids can be quite different in phase andfrequency; the HVDC system forces thepower flow in any case. Along with theactive power control, the reactive power

control on both sides of the HVDC routecan be of advantage to the grids. In thecase of classic line-commutated HVDCtechnology, the reactive power variablerange of the system can be extendedwith additional elements. This, however,requires corresponding space.

In a VSC-based HVDC system, an ad-ditional reactive power control systemhas already been integrated into theconverter design (see Fig. 8); in this case,external reactive power elements are nolonger required. In the case of an MMC-

based HVDC system, even filters can bedispensed with.

Conclusion

The future power grids will have towithstand increasingly more stressescaused by large-scale energy tradingand a growing share of fluctuating rege-nerative energy sources, such as windand solar power. In order to keep genera-tion, transmission and consumption inbalance, the grids must become moreflexible, i.e. they must be controlled in a

better way. State-of-the-art power elect-ronics with HVDC and FACTS technolo-gies provides a wide range of applicati-ons with different solutions, which canbe adapted to the respective grid in thebest possible manner. DC current trans-

combination of FACTS and classic line-commutated HVDC technology is feasi-ble as well. In the case of state-of-the-art VSC-based HVDC technologies, theFACTS function of reactive power con-

trol is already integrated that is, additio-nal FACTS can be done without. Howe-ver, Bulk Power transmission up to theGW range remains reserved to classic, li-ne-commutated thyristor-based HVDCsystems.

Fig. 8

The Trans Bay Cable project

in the U.S., worlds first HVDC

VSC system with the MMC

technology.

Literature

[1] Luther, M.; Radtke, U.: Betrieb und Planung

von Netzen mit hoher Windenergieeinspeisung.

ETG-Congress, October 23-24, 2001, Nurem-

berg, Germany.

[2] Waldhauer, H.: Grid Reinforcement and SVC for

Full Power Operation of Baltic Cable HVDC Link.

38th Meeting and Colloqium of Cigr Study

Committee B4 on HVDC and Power Electronics,

Technisches Kolloqium, September 25, 2003,

Nuremberg, Germany.

[3] Retzmann, D.; Srangr, D.; Uecker, K.: Flexibler

und sicherer. Smart Grids fr den Strommarkt von

morgen. BWK 58 (2006) No. 11, pp. 1013.

[4] Andersen, N.; Megos, J.; Retzmann, D.: Stati-

scher Kompensator fr den Offshore-Einsatz. Dyna-

mische Spannungsregelung von Offshore-Windturbi-

nen. BWK 59 (2007) No. 9, pp. 4853.

[5] Beck, G.; Povh, D.; Retzmann, D.; Teltsch, E.:

Global Blackouts Lessons Learned. Power-Gen

Europe, June 28-30, 2005, Milan, Italy.

[6] Dorn, J.; Retzmann, D.; Uecker, K.: Vorteile von

Multilevel-VSC-Technik in Energiebertragungs-

anwendungen. VDE Congress 2008, November 3-5,

2008, Munich, Germany.

FACTS

HVDC

~

~

P G ~

G ~

G ~

G ~

P

G ~

Loads

Loads

Loads

Loads

Fig. 9

Comparison of stability and transmission

functions of FACTS and HVDC systems.

mission constitutes the best solutionwhen it comes to loss reduction when

transmitting power over long distances.The HVDC technology also helps controlthe load flow in an optimal way. This isthe reason why, along with system inter-connections, the HVDC systems becomepart of synchronous grids increasinglymore often either in form of a B2B for

load flow control andgrid support, or as aDC power highway torelieve heavily-loadedgrids. FACTS technolo-gy was originally de-veloped to support

systems with long ACtransmission lines.FACTS installationsare increasingly moreoften used in meshedgrids to eliminatecongestion and bott-lenecks. It goes wit-hout saying that a

7

Springer-VDI-V

erlagGmbH&Co.KG,Dsseldorf2009


8/8

www.siemens.com/energy

Published by and copyright 2009:

Siemens AG

Energy Sector

Freyeslebenstrasse 1

91058 Erlangen, Germany

Siemens AG

Energy Sector

Power Transmission Division

Power Transmission Solutions

Freyeslebenstrasse 1

91058 Erlangen, Germany

www.siemens.com/hvdc-facts

For more information, please contact

our Customer Support Center.

Phone: +49 180/524 70 00

Fax: +49 180/524 24 71

(Charges depending on provider)

E-mail: [email protected]

Power Transmission Division

Order No. E50001-G610-A106-X-4A00

Printed in Germany

Dispo 30000

TH 263-090034 470224 SD 03090.5

Printed on elementary chlorine-free bleached paper.

All rights reserved.

Trademarks mentioned in this document

are the property of Siemens AG, its affiliates,

or their respective owners.

Subject to change without prior notice.

The information in this document contains general

descriptions of the technical options available, whichmay not apply in all cases. The required technical

options should therefore be specified in the contract.

power electronics for the enhancement of grid efficience

Documents