Centre JournalWinter 2002

Frequency Response of a Unified Power Flow ControllerInside this issue:

We invite you to visit the new Manitoba HVDC Research Centre website atwww.hvdc.ca. This site will be an important information link for all of our cus-tomers and research partners. Also stay tuned for www.pscad.com, which willbe a valuable information source for all PSCAD simulation users.

Frequency Response of a UnifiedPower Flow Controller

New HVDC Research CentreWebsite

PSCAD Version 4

Centre Receives Historic PowerEngineering Books

PSCAD/Relay Released

Upcoming Conferences

Visit the New HVDC Research Centre Website

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FACTS devices, like the UnifiedPower Flow Controller (UPFC), arelikely to find increasing applications inmodern power transmission networks.The UPFC, shown in Figure 1, consistsof a shunt and series Voltage SourcedConverter (VSC) sharing a common dcbusbar. The series converter allows forthe injection, within certain limits, of anarbitrary ac voltage in series with thetransmission line, thereby allowingprecise control of the real and reactivepower flows (p and q) on the line. Theshunt converter supplies the necessary

real power to the series converter andis also capable of independentlygenerating reactive power at the acposed on the balanced three phase acwaveforms. The resulting currents inthe UPFC are at frequencies ω, as wellas at a frequency ω-2ωo, ωo, being thefundamental frequency. The compo-nent at frequency ω is of the samephase sequence as the exciting volt-age, whereas the ω-2ωo component isof opposite phase sequence. Similarly,a harmonic of frequency ω-ωo is alsointroduced onto the capacitor dcvoltage. An expression of the formXω=TωUω, where Xω is a vector contain-ing the various direct and quadraturecomponents of the shunt and seriescurrents at angular frequencies ω, ω-2ωo; and the capacitor voltage atangular frequency ω-ωo. The vectorUω consists of the direct andquadrature components of the seriesand shunt exciting voltages. Themathematical equation for Tω isderived in the reference, and is afunction of the UPFC’s componentvalues, as well as its operating point.From this equation, the response ofany of the entries in Xω to the excita-tion Uω can be plotted as a function offrequency.

Figure 2 shows the frequencyresponse for a negative sequenceContinued on page 3...

Figure 1: UPFC Schematic Diagram

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ParallelConverter

SeriesConverter

UDC

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The Manitoba HVDC ResearchCentre would like to thank ProfessorM.Z. Tarnawecky, distinguished facultymember of the University of Manitoba,for his thoughtful donation of historicHVDC references and books. Oneparticularly interesting document wasthe Final Report on High VoltageDirect Current Transmission compiledby the Technical Industrial IntelligenceDivision of the Office of MilitaryGovernment of the United States inoccupied Germany of 1947. Thecollection contained many other usefulbooks including one of local interest –a report entitled “The Future of theManitoba Electric Utility Industry,”August 1959. This report by theManitoba Hydro-Electric Board (Mani-toba Hydro) discusses emergingenergy sources of the day. ⌧

Editor’s note: it should be noted that Britain andSweden also contributed to the development ofHVDC technology prior to the Second World War.It was the Swedes (ASEA, now ABB) thatdeveloped the first mercury arc dc valve, whichthey licensed to English Electric in the 1960’s.Several of these vintage mercury arc dc valves(the largest ever built) are still operational atManitoba Hydro’s Dorsey HVDC ConverterStation. (source: “High Voltage Direct CurrentTransmission,” by Adamson and Hingorani, andalso from Dennis Woodford, Electranix Corpora-tion).

Centre Receives Gift

Significant progress has beenmade here at the Centre towards theupcoming release of PSCAD V4.PSCAD V4 will be an integrated set ofpower systems simulation and analysistools all benefiting from the corePSCAD graphical design environmentand advanced plotting technology.

PSCAD V4.0 incorporates a newMicrosoft Foundation Class (MFC)based graphical programming archi-tecture, which provides a commonlook and feel to PSCAD V4 applicationmodules. An intuitive navigationstructure, new plotting and controls -including X-Y plots, and additionalcomponents and libraries will makeVersion 4 of interest to both new andexperienced users of PSCAD. PSCADV4.0 will include an optional single-linediagram representation of 3-phaseelectrical networks and will supportmultiple control settings for users whoneed to run a large series of simula-tions in batch mode.

We are particularly encouraged byour new Power Flow application, whichwill be the first modular addition to thePSCAD power system simulationfamily planned for release as V4.1 in

PSCAD V4 Power System Simulation Suite Development

New PSCAD V4 graphical environment (under development)

November. Initially, the input dataformat will be the widely used PTIPSS/E data format. PSS/E’s load flowdata files can be directly accommo-dated and solved by PSCAD/PowerFlow and/or EMTDC. The result will bea very powerful and fully functionalload flow application integrated intoPSCAD’s graphical design environ-ment.

New Manuals and On-line Help

In the V4 development, we areworking to provide comprehensivedocumentation to our end-users. Youcan look forward to new PSCAD V4and EMTDC printed manuals, a newon-line Help system, and a newpscad.com website with the latestFAQs and help materials.

The new manuals includes topicson program structure, writing models,and theory for transformers, machinesand transmission lines. The PSCADV4 User’s Guide will include “how to”instructions, License Manager informa-tion, Component Workshop help, anddetailed information on the use of theMaster Library components. ⌧

By Paul Buchanan, P. Eng.

voltage of 50 Hz (base frequency) onthe sending end bus UI. Here, negativefrequencies indicate negative se-quence. The three curves in eachgraph correspond to different operatingpoints as in Table 1.

In cases 1 and 2, the transmissionline transmits 5.0 pu real power (note:Pbase equals the UPFC’s rating which ismuch smaller than the transmittedpower), with different amounts ofreactive powers (+0.9 or -0.9) deliv-ered by the series branch. Case 3corresponds to a transmittal of 1.0 puin the line. From Figure 3, it is clearthat operating points 2 and 3 havevery similar responses, indicating thatthe frequency response is not signifi-cantly affected by the transmission line

Figure 2: UPFC Frequency ResponseCharacteristic

gnitarepOtnioP

i qp ' /up

i ds ' /up

i qs ' /up

u cd ' /up

1 9.0- 0.5 0.0 75.1

2 9.0 0.5 0.0 75.1

3 9.0 0.1 0.0 75.1

Table 1: Different UPFC Operating Points

Figure 3: Quasi 24-pulse VSC building block ofUPFC

Figure 4: Shunt Converter currents with 0.02 punegative sequence on UI

(UPFC Continued from page 1)

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power. On the other hand, if thereactive power of the shunt branch ischanged, the characteristic changessignificantly. In our particular case,there is a negative sequence reso-nance (-50 Hz) for leading reactivepower (+0.9 pu). For this operatingcondition, there will be a large nega-tive sequence component in theseries and shunt currents; as well as acomplementary current of positivesequence at the frequency

We carried out a detailed simula-tion using a quasi 24 – pulse voltagesourced converter based UPFC(Figure 3) to obtain the currentwaveforms shown in Figure 4. As canbe seen, the fundamental frequencynegative sequence component andthe 3rd harmonic positive sequencecomponent are clearly evident. Theirmagnitudes were also shown to agreevery well with the derived characteris-tics of Figure 4. The resonancedisappears when the shunt reactivepower order is changed to -0.9 pu(lagging).

The simulation shown here onlyverified one point on the characteris-tic. By using the method discussed in[2] where we inject a suitable “whitenoise” signal into the PSCAD/EMTDCmodel and plot the spectrum of theobserved response, we also obtainedthe entire characteristic. This studytherefore confirms the validity of themathematically obtained frequencyresponse, as the PSCAD model isdetailed and contains all the inherentnon-linearities of the actual UPFC.

by Dr. A. Gole (University ofManitoba, CANADA),

and Dr. Igor Papic (University ofLjubljana, SLOVENIA)

References:

[1] I. Papic and A.M. Gole, “Steady StateResponse of the Unified Power Flow Controller,”IEEE PES Winter Meeting, New York, NY,January 27- Feb 1, 2002.

[2] X. Jiang and A.M. Gole, “A Frequency ScanningMethod for the Identification of Harmonic Instabili-ties in HVDC Systems,” IEEE Trans. PowerDelivery, Vol 10, No. 4., October 1995, pp 1875-1881.

)]50250[(150 HzHz •−−=

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The Centre Journal is distributed free of chargeand is posted electronically at http://www.hvdc.ca.

If you would like to receive email notification of anew Journal in the future and not receive a copy inthe mail, please send us your request by email tojournal@hvdc.ca

The Manitoba HVDC Research Centre will be participating in thefollowing technical conferences:

• IEEE Advanced Power Electronics Conference, March 10 – 14, Dallas,Texas, Booth 301

• T&D World Conference, May 7 – 10, Indianapolis, Indiana, Booth 707

• WindPower 2002, June 14 – 16, Portland, Oregon

• Electimacs 2002, Official Sponsor, August 10 – 14, 2002, Montreal,Canada

• IEEE-PES International Conference on Power System Technology,October 13-17, 2002, Kuming, China

We look forward to seeing you!

PSCAD/Relay Protection for transient testing. Highlights the new single line diagram interface.

PSCAD/Relay Released!PSCAD/Relay is a power system

simulation program ideally suited forprotection engineers and technologists.PSCAD/Relay is used to create accu-rate full time domain transient(COMTRADE) test waveforms. Thetransient waveforms are then playedinto the relay system under test, thusverifying the operation of the protec-tion system under conditions matchingreal system faults. Transient testing of

protection greatly increases the confi-dence that the protection system willperform as designed.

PSCAD/Relay provides a tool thatis fast and easy to use and yet simu-lates complex features, such asreverse current, point of fault switch-ing, mutual coupling, effects of breakeroperation, sequence of fault events,multiple fault resistances, all of whichare unavailable with traditional phasor

based testing methods. End-to-endGPS based testing is also supported,since both ends of the transmissionline are recorded. In short, PSCAD/Relay, with dynamic transient testing,allows the performance of the relay tobe tested and validated at the point inthe system where it is installed. As atestament to the validity of thePSCAD/Relay technology, we areextremely pleased to announce thatDoble Engineering Company of

Massachusetts, USA has recentlysigned an agreement with the Mani-toba HVDC Research Centre topromote and distribute PSCAD/Relayto the Protection Engineering commu-nity. Doble Engineering Company(www.doble.com) manufactures anddistributes relay test equipment andother power apparatus test instru-ments worldwide. Please contact usor Doble Engineering to find out moreabout this new product. ⌧

By Randy Wachal, P. Eng.Paul Buchanan, P. Eng.

E L A Y

Download PSCAD 3.0.8 at

http://www.pscad.com