CONGESTION MANAGEMENT USING COORDINATED CONTROL OF FACTS DEVICES AND LOAD SHEDDING

Transcription

1 COGESTIO MAAGEMET USIG COORDIATED COTROL OF FACTS DEVICES AD LOAD SHEDDIG avel Etngov, ola Voropa Energy Systems Insttute Iruts, Russa Aleandre Oudalov ABB Corporate Research Centre Dättwl, Swtzerland Alan Germond, Rachd Cheraou EFL Lausanne, Swtzerland Abstract The development of a control system and control strateges capable of governng multple fleble AC transmsson system (FACTS) devces n coordnaton wth a sheddng s descrbed here. The man purpose of the presented coordnated control system s to remove overs caused by unplanned lne outages n transmsson networ. A senstvty analyss was used to fnd out an ntercouplng between a varaton of set ponts of dfferent FACTS devces and a volume of sheddng wth a varaton of actve power flow n transmsson lnes. The proposed control system s based on lnearzed epressons n steady state. Therefore, a coordnated control process does not requre ntensve computatons. A prototype of the coordnated control system s sutable for a real tme mplementaton. It constantly montors power flows n a test transmsson networ and generates approprate control sgnals to each and FACTS devce n order to mantan an admssble power flow level. It has been nterfaced wth flow software to test ts effectveness through non-lnear smulatons usng the IEEE 3 bus test power system as the study case. The results obtaned are dscussed. Keywords: ower system automaton, FACTS devces, sheddng, Congeston management, ower flow control, Senstvty analyss. ITRODUCTIO At present there s no doubt about the economcal ustfcaton of the parallel operaton of power plants as component parts of electrc power systems and the parallel operaton of power systems as component parts of power nterconnectons. However, the growng sze and the electrc ndustry deregulaton complcate an operaton of power systems. At the same tme the rs of occurrence and avalanche-le development of emergences also ncreases. That s why the congeston management plays a more and more mportant part n power system control [][4]. Tang nto account the hgh speed of emergency processes, such a control must be largely automatc. Recently, a suppleness n power system control appeared wth the advent of fleble ac transmsson systems (FACTS) technology. FACTS technology allows practcally complete utlzaton of the capacty of transmsson elements up to ther lmts and provdes dfferent nds of devces permttng to redrect power n real-tme and provdng vrtually nstantaneous responses to transmsson system dsturbances []. There are many publcatons consderng applcatons of FACTS devces n power systems, and partcularly the applcaton of FACTS devces to congeston management problem [4], [6][]. However, a coordnaton and combned applcaton of conventonal emergency control actons (e. sheddng) and FACTS devces has not been fully nvestgated. In ths paper, a power flow control method based on a coordnaton of sheddng and FACTS devces s presented. Two types of FACTS devces, a Thyrstor Controlled Seres Capactor () [7] and a Thyrstor Controlled hase Shftng Transformer () [], are consdered n ths study. METODOLOGY. The concept of senstvty analyss The methodology based on the senstvty analyss for FACTS devces [6] was etended here to fnd out an ntercouplng between a varaton of sheddng volume and a varaton of actve power flow n transmsson lnes. A smple (lnearzed) but suffcently accurate relatonshp could be derved for a computaton of control actons (volume of sheddng and set ponts of FACTS devces) n order to meet the requrements for power flow n a post-emergency state of power system. The control varables are the volume of sheddng and the setponts of FACTS devces. The controlled quanttes are the actve power flows n transmsson lnes. For each par FACTSlne or lne a drect effect of control acton on power flow can be epressed as followng: lne f ( Settng FACTS ) and lne f ( ) where Settng FACTS s a drect control varable of FACTS devce (e.g. lne reactance, phase shft angle, etc.) and s a volume of sheddng. Below, the applcaton of senstvty analyss s llustrated wth an eample of FACTS devces. For any par FACTS-lne the above mentoned nonlnear relatonshps can be decomposed n two parts. The frst part s the lnear coeffcent of nfluence nf and the second part s the non-lnear regulaton characterstc of FACTS devce [6]. It means that at frst, the level of volaton of the controlled quantty (power flow) s ntalzed and requred changng of the ndrect control varable of the FACTS th SCC, Lege, -6 August Sesson, aper, age

2 (the power flow through a FACTS devce) s found to remove that volaton. Then, for a nown level of power flow through the FACTS devce the value of drect control varable of FACTS devce (lne reactance for and phase shft angle for devces) s computed to provde a requred ndrect control varable.. Coeffcents of nfluence of FACTS The coeffcent of nfluence of FACTS FACTS estmates a relatonshp between the varaton of actve power flow n the controlled transmsson lne lne and the varaton of actve power flow through the FACTS devce FACTS [6]. lne lne FACTS FACTS FACTS lne lne FACTS, () where s the value of actve power flow n the controlled lne before changng the setpont of FACTS, lne s the value of actve power flow n the same lne after changng the setpont of FACTS, FACTS s the value of actve power flow n the lne wth FACTS before changng ts setpont, and s the value of FACTS actve power flow n the lne wth FACTS after changng ts setpont..3 Regulaton characterstcs of FACTS The regulaton characterstc numercally lns together the effect of FACTS control varable on the controlled parameters (power flows) n the transmsson lnes where the FACTS s located. Thus, t helps to transform the requred amount of power flow through the FACTS devce, for a modfcaton of power flow n the controlled lne, nto a real setpont of the FACTS devce such as a reactance or a phase shft angle..3. The regulaton characterstc of the for actve power flow represents the effect of the varaton of the control varable of the on the actve power n the lne wth that. Fg. shows an eample of the typcal regulaton characterstcs of the. The best appromaton of ths characterstc s provded by a quadratc functon [7], but as we could see n the most analyzed cases the quadratc term was relatvely small. Therefore, t s possble to lnearze the regulaton characterstc of the. Fg. presents the regulaton characterstc of the for dfferent power system operaton condtons (dfferent power flow patterns). The gradent of regulaton characterstc of depends on operaton condtons of power system (Fg. ) and t could be calculated as: (), MW , % However, there s a lnear relatonshp between the gradent of the regulaton characterstc and the ntal actve power flow n the (Fg. 3). Therefore we can formulate the followng relatonshp: γ where Quadratc appromaton -4,9 -, γ. Lnear appromaton -33,3 -. Fgure : Regulaton characterstc of the for actve power flow. Delta FACTS, MW DeltaX, % Fgure : Regulaton characterstc of the for dfferent operaton condtons. - γ , MW Fgure 3: Relatonshp between the gradent of regulaton characterstc and ntal actve power flow n the., (3).3. The regulaton characterstc of the for actve power flow s a relatonshp between the varaton of actve power flow n that and the vara- th SCC, Lege, -6 August Sesson, aper, age

3 ton of ts control varable α (Fg. 4). The gradent of the regulaton characterstc of for actve power flow unle does not depend on operaton condtons of power system (ntal power flow through a devce) and t can be calculated as: (4) α.4 Coeffcents of nfluence of By analogy wth coeffcents of nfluence of the FACTS devces we can formulate the followng equaton for coeffcents of nfluence of the sheddng at bus on the power flow n the lne : lne lne lne, () where s the ntal value of actve power flow n lne lne the controlled lne ; s the value of actve power flow n the controlled lne after sheddng (changng); s the ntal value of actve power of the ; s the value of actve power of the after ts changng. 3 COTROL STRATEGY 3. Control strategy for the In case of the over of the lne ( lne lne ), the control acton for the lne ma devce can be calculated as: lne lne lne ma α (6) Ths equaton does not observe the appearance of congestons n other transmsson lnes after the control acton. Therefore we wrote the followng system of nequaltes on the bass of (6):, MW lne lne ma α, grad Fgure 4: Regulaton characterstc of the for actve power flow. KM α, (7) where M s a number of controlled lnes, lne ma s the mamal admssble value of actve power flow n the controlled lne. Usng the prncple of superposton of control actons of several controllers we can deduce an equaton (7) for a more general case wth several devces: lne lnema α, () KM Moreover, there are as well the followng regulaton constrants: α α + α α, (9) mn ma K where s a number of devces, α and α mn are the mnmal and mamal values of phase shft angle of th. ma 3. Control strategy for the We can formulate the system of nequaltes for devces by analogy wth () and (9). lne lne ma γ, () KM +, () mn ma K where s a number of devces, mn and are the mamal and mnmal values of ma reactance compensaton of th. 3.3 Control strategy for the sheddng If we have over lne on the lne, the volume of that must be shed can be calculated as: lne lnema lne () A mnmzaton of the total outage cost caused by the Sheddng s chosen as obectve functon: ( ) Cost mn Cost, (3) where Cost s the outage cost of the, $/MW, s a number of the s avalable to shed. The optmzng varables are subected to the followng nequaltes constrants:, KM (4) lne lne ma, ma K () where M s a number of controlled lnes; ma s the mamal volume of the sheddng. th SCC, Lege, -6 August Sesson, aper, age 3

4 3.4 Coordnated control strategy for the sheddng and FACTS devses. Fnally we can formulate the optmzaton problem to fndng coordnated control actons on the bass of equatons (). mn Cost ( ) Cost subect to lne where lnema sheddng sheddng m KM + + l n n m l γ n α m n l m subect to followng engneerng constrants: α α + α l mal α, (6) n mmn m m mma + nmn n n nma l K, m K, n K Obvously the cost of control actons of FACTS devces equals to zero. Therefore, the algorthm frst tres to remove the overs by coordnated actons of FACTS devces. In the case of nsuffcency of FACTS devces the algorthm nvolves the sheddng. The proposed technque allows fndng the optmal volume of sheddng (wth mnmal total outage cost) tang nto account the effect of FACTS devces. 4 TEST RESULTS (7) Fgure : IEEE 3 bus test power system. 4. Descrpton of the test power system The Matpower pacage for Matlab has been used for flow computatons [9]. A specal procedure was created to calculate the values of coeffcents of nfluence and parameters of regulaton characterstcs. Also, a calculaton program for the coordnated emergency control actons was developed on the bass of the proposed technque by usng Matlab Optmzaton Toolbo. The studes were carred out on the IEEE 3 bus test power system (Fg. ). It contans two dstnct areas: the frst one wth a lac of producton s n vcnty of the buses 37 and the second one wth a surplus producton s n vcnty of the buses and. The transmsson lnes, whch connect these areas, are ntensvely ed n the pea perod. Therefore, trppng one of these lnes s a strong dsturbance, whch can result n a large over n the networ and even leads to the system nstablty. Dfferent power system operaton condtons (scenaros) were consdered n ths study. arameters of some of them are presented n Table I. We supposed that FACTS devces ( or ) are nstalled n the lnes 4 and 6 and the at buses,, 7, and s avalable for sheddng. Frst, we calculated the coeffcents of nfluence of s and FACTSs and parameters of regulaton characterstcs for each FACTS devce. Eamples of relatonshps f ( αtsst ) and ( ) f are represented n Fgs. 6 and 7 respectvely. These relatonshps are lnear and do not depend on the value of setponts of FACTS devces. ode Generators 3 s Scenaro (base) Scenaro Scenaro 3 Q Q Q Table : arameters of consdered power system operaton scenarous. th SCC, Lege, -6 August Sesson, aper, age 4

5 Table shows the values of coeffcents of nfluence and gradent of regulaton characterstc of 6, 6 and on the transmsson lnes dependng on the operaton condtons of power system. The values of the coeffcents of nfluence are practcally constant and ndependent of the operaton condtons. Therefore t s possble to use constant coeffcents of nfluence of FACTS n most cases. Though obvously that f there are avalable measurements we can update all parameters on-lne. Table 3 shows the calculated average values of coeffcents of nfluence to the transmsson networ. Then, the lst of man dsturbances (lne outages) was formed on the bass of the analyss of the test power system. The coeffcents of nfluence of s and FACTS devces and the gradents of the regulaton characterstcs of FACTS devces were calculated for each emergency stuaton n the same way as for normal K -6 K α -6, grad , MW 3 _4 3_4 6 4_6 _7 6_7 Fgure 6: Influence of the -6 on the lnes -, -3, -4, 3-4, -, -6, 4-6, -7, _4 3_4 6 4_6 _7 6_7 Fgure 7: Influence of at bus 7 on the lnes -, -3, -4, 3-4, -, -6, 4-6, -7, 6-7. Mode Table : The values of nf and dependng on operaton condtons. Lne Table 3: The values of coeffcents of nfluence (no lne outages). power system state. Table 4 presents the values of nf and of the 6 for dfferent lne outages. After we have found all requred numercal data a number of dfferent smulatons were carred out to evaluate the proposed emergency control algorthm. Coordnated control actons for dfferent lne outages n dfferent power system operaton condtons were calculated and analyzed. These studes have shown the proper operaton of the proposed technque. Let us present n detal an eample of emergency control algorthm s operaton. 4. Eample of emergency control algorthm s operaton (outage of the lne 46, operaton scenaro (Table )) In the case of the emergency outage of lne 46 we have three heavy overed lnes, 6 and (Fg. ). The values of coeffcents of nfluence for ths emergency state are presented n Table. Several possble cases are consdered.. There are no FACTS devces, only sheddng s avalable... All s have the same sheddng cost,.e. Cost Cost Cost 7 Cost Cost $/MW; We used $ as a symbol of some conventonal unts... Cost $/MW; Cost Cost 7 Cost Cost,33 $/MW..3. Cost $/MW; Cost Cost 7 Cost Cost,66 $/MW..4. Cost $/MW; Cost Cost 7 Cost Cost $/MW... Cost $/MW; Cost Cost 7 4 $/MW; Cost 3 $/MW; Cost $/MW..6. Cost Cost Cost 7 $/MW; Cost Cost 3 $/MW.. devce s nstalled n the lne 6. Cost 3 Cost 4 Cost 9 Cost 3 $/MW. 3. devce s nstalled n the lne 4. Cost 3 Cost 4 Cost 9 Cost 3 $/MW. 4. devce s nstalled n the lne 4. Cost 3 Cost 4 Cost 9 Cost 3 $/MW.. devces are nstalled n the lnes 4 and 6. Cost 3 Cost 4 Cost 9 Cost 3 $/MW. The followng volumes of mamum sheddng were specfed: ma MW, ma MW, ma7 3 MW, ma MW, ma MW. And FACTS devces have the followng worng th SCC, Lege, -6 August Sesson, aper, age

6 Outage Lne of lne ( crcut) Table 4: Values of nf outages. Lne and of 6 for dfferent Table : Values of coeffcents of nfluence (outage of lne 4 6). Fgure : Fragment of test power system. Outage of the lne 46. range: <α <+ ; <α 34 <+ ; %< < % The calculated optmal solutons for all cases are shown n Table 6. Below, an analyss of the results s presented. In the case. the followng optmal soluton was obtaned: n order to un lnes, and 6 t s necessary to shed the s number, 7, and ( 43 MW, 7 3 MW, MW, MW). The cost of sheddng s 43 $ and the total amount s 43 MW. Ths soluton corresponds to a soluton wth a mnmum total amount of sheddng. The s not nvolved n control acton because t practcally does not have nfluence on the overed lnes 6 and. In the case. we have the same soluton as n the prevous case. It could be eplaned by the fact that the has a small nfluence on the overed lnes and ths soluton s economcally feasble regardless the sheddng cost of the s cheaper by a factor of.33. In the case.3 the optmal soluton s 9 MW, 7 7 MW, MW, 3 MW. The total cost of sheddng s $ and the Scenaro Cost % Table 6: Lst of calculated control actons. total amount s 49 MW. As may be seen, the total amount of sheddng s hgher than n the frst case. Ths effect has the followng eplanaton: the sheddng of the (the wth a small nfluence on the overed lnes) s cheaper by a factor of.66. Therefore, t s economcally feasble to shed the wth smaller nfluence on the overed lnes, but wth lower cost. In the case.4 the optmal soluton s MW, 7 MW, MW, 6 MW. Total cost of sheddng s 34 $ and the total amount s 7 MW. Hence, the volume of the sheddng reached the mamum value snce the sheddng of the s two tmes cheaper. lots n Fg. 9 llustrate the effcency of control actons. Fg. 9(а) shows a comparson of dfferent control actons accordng to the total amount of sheddng. Fg. 9(b) presents a comparson of the economc feasblty of the calculated optmal control actons and the control acton wth the mnmum amount of sheddng (obtaned n the case.). In the case the followng soluton was acheved: 9 MW, 7 MW, 6 MW, 7 MW, α -6. The cost of the sheddng s 6 $ and the total amount s 6 MW. Thus, the amount of requred sheddng s decreased by % n comparson wth the frst scenaro n the case of the applcaton of the 6 (case.). In the thrd and the fourth cases the applcaton of the 4 and 4 demonstrates smaller eff- Total amount of sheddng, MW Total cost of sheddng, $ Scenaro b) Scenaro m n tota l a mount of sheddng optmal soluton Fgure 9: Comparson of dfferent sheddng scenaros: accordng to a total amount (a) and a total cost (b). a) th SCC, Lege, -6 August Sesson, aper, age 6

7 cency because they have a smaller nfluence on the overed lnes. Moreover, the 4 has shown a worse performance compared to the 4 because of the low ntal current through devce. In the ffth case the followng soluton was acheved: 3 MW, 7 3 MW, MW, α -6.; α The cost of the sheddng s $ and the total amount s MW. Thus n the case of the applcaton of the coordnated multple FACTS devces the amount of requred sheddng s reduced by 64 % n comparson wth the frst case. The llustraton of the effcency of FACTS devces as congeston management means s shown n Fg.. The combned applcaton of the sheddng and FACTS devces allows to curtal a fnancal damage to consumers. Total cost of sheddng, $ Wthout FACTS & -6 Fgure : Economc benefts of FACTS applcatons. COCLUSIOS Ths paper presents a coordnated control system for over lmtatons n a transmsson system usng sheddng combned wth multple FACTS. The coordnaton algorthm s based on a senstvty analyss and a lnear optmzaton technque. The conclusons of the paper can be summarzed as follows: The proposed coordnated control system and ts control strateges can be successfully used for the coordnaton of the sheddng as well as for the sheddng combned wth the control of multple FACTS devces to lmt lne overs and prevent power system nstablty caused by the outages of transmsson lnes. The proposed control strategy allows choosng optmal selecton of sheddng to lmt lne overs tang nto account the cost of consumers dsconnecton. Smulatons have shown that FACTS devces are an effectve tool for congeston management. The applcaton of FACTS devces combned wth a sheddng decreases the amount of requred sheddng and so allows reducng a fnancal damage to customers. A performance of a devce s usually hgher than a performance of a devce n a meshed networ topology (presence of many parallel paths). ACKOWLEDGMET The study was supported by the Grant of Russan Leadng Scentfc School # REFERECES [] E. Bompard,. Correa, G. Gross et al, Congeston-management Schemes: a Comparatve Analyss under a Unfed Framewor, IEEE Trans. on ower Systems, Vol., Feb, 3 pp [] G. Trudel, S. Bernard, G. Scott, Hydro-Quebec's Defence lan Aganst Etreme Contngences, IEEE Trans. on ower Systems, Vol. 4, o. 3, 999, pp [3].I. Voropa, Emergency Operaton Control and Congeston Management roblems n Russa s Electrc ower Systems: a Conceptual Vew, roc. Of the Int. Worshop Lberalzaton and Modernzaton of ower Systems: Congeston Management roblems, Iruts, Russa, August -4, 3, pp. - 9 [4] J. Brosda, E. Handschn, A. L'Abbate et al, Vsualzaton for a Correctve Congeston Management based on FACTS Devces, roc. of the IEEE ower Tech 3 Conference, Bologna, Italy, June 3-6 [].H. Hngorany, Fleble AC Transmsson System, IEEE Spectrum, Aprl 993, pp.4-4 [6] A. Oudalov, R. Cheraou, A.J. Germond, M. Emery, Coordnated ower Flow Control by Multple FACTS Devces, roc. of the IEEE ower Tech 3 Conference, Bologna, Italy, June 3-6, pp. 4- [7] M. oroozan, G. Anderson, ower Flow Control by Use of Controllable Seres Components, IEEE Trans. ower Delvery, Vol., o.3, pp.4-49, July 993 [] M. Iravan, Applcaton of Statc hase Shfters n ower Systems, IEEE Trans. ower Delvery, Vol.9, o.3, pp.6-6, July 994 [9] MATOWER. User s Manual, ower Systems Engneerng Research Center (SERC), School of Electrcal Engneerng, Cornell Unversty, Ithaca, Y 43, th SCC, Lege, -6 August Sesson, aper, age 7