The Security Correction of Large Consumers Long-Term Direct Power Trading Based on DC Power Transfer Distribution Factor

Transcription

1 Energy and Power Engneerng, 07, 9, ISSN Onlne: ISSN Prnt: X The Securty Correcton of Large Consumers Long-Term Drect Power Tradng Based on DC Power Transfer Dstrbuton Factor Ouyang Xu, Zhenggang Wang, Bfeng Lv, Jnguo Zhang 3, Jangang Yao, Bn Wang College of Electrcal and Informaton Engneerng, Hunan Unversty, Changsha, Chna State rd Hunan Electrc Power Company, Changsha, Chna 3 State rd Yueyang Power Supply Company, Yueyang, Chna How to cte ths paper: Xu, O.Y., Wang, Z.., Lv, B.F., Zhang, J.., Yao, J.. and Wang, B. (07) The Securty Correcton of Large Consumers Long-Term Drect Power Tradng Based on DC Power Transfer Dstrbuton Factor. Energy and Power Engneerng, 9, Receved: February 0, 07 Accepted: March 30, 07 Publshed: Aprl 6, 07 Abstract The experments of large consumers drect power tradng s conductng n chna natonwde, and t s mportant to the reform of electrcty market. To compensated effcences n securty correcton of large consumers drect power tradng, a novel securty correcton method based on DC power transfer dstrbuton factor was proposed. Usng the presented method to comply securty correcton, all the transactons that satsfy the specfc requrements of maxmzng socal welfare are able to enter securty correcton process, and when the power of transmsson lne s out of lmt, ths method avod the transacton whch causes ths problem s abandoned drectly by ntroducng supplement transactons. The smulaton has shown that the proposed securty correcton method of large consumers drect power tradng based on DC power transfer dstrbuton factor s effectve. Keywords Large Consumers, Drect Power Tradng, DC Power Transfer Dstrbuton Factor, Securty Correcton, Electrcty Markets. Introducton The drect power tradng between power users and power generaton enterprses refers to electrcty users and generaton enterprses who meet the condtons for access to carry out power purchasng and sellng transactons drectly base on the prncple of voluntary partcpaton and ndependent negotaton []. Large consumers drect power tradng s one of the drect power tradng between power users and power generaton enterprses, as ts name mples, requres the power users have a hgher voltage level and a larger electrcty consumpton, for DOI: 0.436/epe.07.94B04 Aprl 6, 07

2 nstance, large consumers drect power tradng n Hunan provnce requres the electrcty users recevng end voltage s above or equal to 0 kv, and last annual electrcty consumpton s more than 00 mllon kwh. For the purposes of electrcty market change from government regulaton to openness, and then establsh a market-orented mechansm, large consumers drect power tradng s an nevtable part. In the market-orented reform of electrc power ndustry n Amerca, Brtan and Japan, large consumers drect power tradng has been mplemented n all these country [] [3]. Large consumers drect power tradng n Chna started n 00, n the electrcty system reform programme ssued by The State Councl, ths concept was frst proposed. In 004, the Natonal Development and Reform Commsson and the State Electrcty Regulatory Commsson ontly ssued Interm Measures about Power Users Purchase Electrcty from eneraton Enterprses Drectly, clarfed the purposes and prncples. Snce 03, especally after the release of government documents, because of ts transton n the resource allocaton model, ntroducng competton mechansms n the sales sde market and other advantages [4], large consumers drect power tradng has been conducted n many provnces. Securty correcton s essental to large consumers drect power tradng. Out of the power system securty consderatons, the transacton result needs to go through securty correcton to determne whether t meets the constrants on power system securty before t wll be truly mplemented. On ths ssue, there have been some research works at ths present. The content and process of monthly securty correcton n provncal power company s ntroduced n [5]. A case study of northeast regonal electrcty market s presented n [6], n ths paper, the problem of monthly securty constraned dspatchng s studed. A congeston management algorthm to mnmze the cost of purchasng electrcty from generaton plants n generaton-sde electrc power market s developed n [7]. Securty correcton system of power generaton plant n east Chna power grd s ndcated n [8]. These studes made some achevements n securty correcton of large consumers drect power tradng, nevertheless, these research smply abandon tradng outcome whch doesn t meet the securty constrant. Such an approach wll hurt enthusasm of consumers and power generaton, s not conducve to large consumers drect power tradng. Regardng the ssue above, based on DC Power Transfer Dstrbuton Factor (PTDF), a new securty correcton method of large consumers drect power tradng s developed n ths paper. Through the ntroducton of supplemental transactons, ths method s able to encourage large users to carry out drect electrcty purchase. In ths artcle, a mathematcal model s establshed, and the effectveness of the proposed method s verfed by an example system.. Drect Power Tradng Mode.. Transacton Model At present, there are prmarly two types of large consumers drect power trad- 366

3 ng modes, namely drect negotaton transacton and centralzed matchng transacton. Drect negotaton transacton means consumers and generator companes conclude the transacton through blateral and ndependent negotaton, and transacton result wll be submtted to the Independent System Operator (ISO). Drect negotaton transacton s flexble and easy to mplement, so t s the man way to carry out large consumers drect power tradng at an ntal stage. However, t also has characterstcs such as small competton ntensty and opaque prce sgnal [9]. In the background of the market-orented reform of generaton-sde electrc power market has been carred out for many years and the power market techncal support system has been perfected, compared wth drect negotaton transacton, centralzed matchng transacton s more sutable for large consumers drect power tradng, and s benefcal to the constructon of the market n the future []. To maxmze socal welfare, centralzed matchng transacton obtans transacton result accordng to generators and large users of ther declared transfer quantty and prce. The exact process s as follows. Frst of all, sort declared prce of buyer from hgh to low and declared prce from seller low to hgh, then match these prce one by one, the dfference between buyer s prce and seller s prce s greater than or equal to zero s effectve transacton. Effectve transacton determnes transacton volume, f there s surplus, then enter the top of the queue to contnue untl the transacton s complete. The mathematcal model s: F = max [( p p ) Q ] () U where F s socal welfare, U s set of large users, s set of power generaton enterprses, p and p s declared prce of buyer and seller respectvely, Q s transacton volume whch s gven by: Q = mn( Q, Q ) () where Q s declared transfer quantty of large users, Q s declared transfer quantty of large users. The constrants of the model are as follows: ) Power quantty balance Q Q = 0 (3) U ) Actve power flow constrant of transmsson lne P l P (4) max l 3) Total transacton amount Q Qmax (5) max where P l s actve power of transmsson lne l, P l s maxmum actve power flow of transmsson lne l, Q max s maxmum amount of large consumers drect power tradng determned by ISO. 367

4 .. Securty Correcton In the actual tradng, based on the above-mentoned centralzed matchng transacton model, securty correcton process s outlned n the followng. Frst, for the model that does not consder the actve power flow constrant of transmsson lne, solve the ntal transacton result by the conventonal optmzaton method or the fast algorthm [0]. And then, for each specfc transacton n the ntal transacton result, execute securty correcton n accordance wth the prce dfferental spread from hgh to low. Fnally, determne whether the transmsson lne securty constrants are fulflled. When a specfc transacton leads to the lne out of ts constrants, then gve up ths transacton drectly. Repeat ths process untl all transactons have been checked. Ths method s easy and fast, whch embodes the prncple of marketzaton. However, there are some problems wth ths method. For example, the mpact of dfferent transactons on the same lne may be opposte. So, when a specfc transacton executes securty correcton prorty, t may fal and be dscarded, but when the subsequent transacton onng, ths specfc transacton can pass the correcton somehow []. The exstence of ths stuaton wll result n the abandonment of some transacton whch could have been carred out. Moreover, there are also dsadvantages to set constrant of total transacton amount n Equaton (5). Although t can guarantee the securty and stablty of the electrcty market, but also may lead to some transacton whch could have been to maxmze socal welfare cannot be mplemented. The above-mentoned problems, n a manner, s a blow for large consumers drect power tradng. 3. DC Power Transfer Dstrbuton Factor 3.. DC Power Flow For the branches wth node and node at both ends, the actve power flow equaton can be wrtten as: P = V VV θ g VV θ b (6) ( cos ) sn where P s power flow of branch, V and V s voltage of node and node, θ s angular phase dfference of branch, g s branch conductance, b s branch susceptance []. For normal transmsson network, the node voltage s equal to rated voltage, angular phase dfference of branch s small, and the lne resstance s much smaller than the reactance, that s, V = V =, θ 0, r = 0, so Equaton (6) can be smplfed nto: θ θ P = b ( θ θ ) = (7) x where b = / x, x s branch reactance. Because power of node s balance, consequently, θ θ P = P = x =,,, n (8),, 368

5 where P s nected actve power of node. For each node n the network except balance node, wrte the above equaton, the matrx expresson of DC power flow can be obtaned: P = Bθ (9) where B s n n order node admttance matrx, matrx element s: B0 (, ) =, x B0 (, ) = x 3.. Transfer Dstrbuton Factor When actve power of node change P, from Equaton (9), the correspondng varaton of node voltage phase angle s: θ = X( e P) = X P () where e s unt column vector, the value n the correspondng poston of node s, X s nverse matrx of node admttance matrx B, X s the th column vector of X. Assume M k s node-branch ncdent matrx of branch k, and nflow s +, outflow s, when actve power of node change, the homologous varaton of actve power flow of branch k s: where T k MkX xk (0) T M k θ T Pk = = Mk X P = k P () x x k k = s transfer dstrbuton factor between branch k and node. Specfc to large consumers drect power tradng, let the nodes of branch k s node m and node n, when power generaton enterprses (node ) and large consumers (node ) make a transacton wth amount of P, sncetransacton between power generaton enterprses and large consumers subect to Equaton (3), the actve power of node and node change P and P respectvely, substtute ths nto Equaton (), transfer dstrbuton factor n ths stuaton s: T k = Mk X e e x k (3) xm xm xn + xn = x From Equaton (3) we conclude that PTDF s only correlatve wth topology of transmsson network, hence t s easy to calculate and use. 4. Securty Correcton Based on DC PTDF Suppose C = ( c,, c,, cn) s a set of large consumers drect power tradng prelmnary result whch haven t executed securty correcton yet, and c s one k 369

6 specfcally transacton one of the result, subscrpt ndcates the prce dfferental spread from hgh to low, so the securty correcton process descrbed n. s shown n Fgure. To solve the problems of securty correcton n ths process, calculate DC PTDF δ k between branch k and transacton c by usng Equaton (3), and modfy securty correcton process as shown n Fgure, where M s mark vector, n the securty correcton process, transacton resultng n transmsson lne out of ts constran and number of lne wll be remarked. After all the specfc transacton have been checked, execute securty correcton agan to determne whether there s transacton whch s unable to meet the constrant of securty, f there s no transmsson lne out of power lmtaton, then the process s end, otherwse, supplemental transacton s performed. Let C = ( C C ) = ( c,, c c +, c m) s set of avalable supplemental transacton, δ k s DC PTDF between branch k and transacton c, hence supplemental transacton should satsfy Equaton (4): δ k δ k< 0 after P (4) < ξ max P where P after s actve power of normal transmsson lne, the adusted power s taken nto account, t can be calculated from the orgnal transmsson power, max supplemental transacton value and Equaton (3), P s the maxmum transmsson power of ths lne, ξ s power margn percentage. Fgure. Flow chart of orgnal securty correcton. 370

7 Fgure. Flow chart of mproved securty correcton. The above condtons reflect two prncples of choosng a supplemental transacton. Frst, t s able to reduce the load of the transmsson lne whch s out of power lmtaton. Secondly, t wll not exacerbate load on other lnes. If there s no supplemental transacton to meet the condtons, accordng to the mark vector M, forward exclude transacton whch wll lead to the lne exceed ts lmtaton, repeat the above procedure untl securty correcton s ended. The exact composton of the supplemental transacton set s as follows. C s set of transacton whose socal welfare s greater than 0 but s unable to carry out because of total transacton amount constrant, C s set of transactons whose socal welfare s less than 0. For set C, these transactons cannot be mplemented n orgnal securty correcton due to total transacton amount constrant. However, n the new securty correcton, there may be a transacton that s benefcal to the securty of the system, so t s reasonable to provde a separate 37

8 tradng amount for such transacton as a reward. For set C, these transactons are unable to meet the requrement of maxmum socal welfare, so t s mpossble for them to wn the bd n the orgnal securty correcton. Nevertheless, n the electrcty market, the successful bdder may negotate wth power generaton and users n set C n order to successfully pass securty correcton, and make the transacton of set C nto a transacton of set C. Set C s desgned separately s to ensure that mproved securty correcton n the more open market s stll vald. 5. Smulaton In order to verfy the feasblty and effect of the method, a verfcaton smulaton s mplemented n the IEEE New England test system, the system wrng dagram s shown n Fgure 3. There are three assumptons n the smulaton calculaton: ) Large consumers drect power tradng s manly quarterly and monthly transactons, n ths smulaton, choose the monthly transacton as the type and electrcty of every transacton dstrbute to one month (30 days) equally. ) To smplfy the calculaton, only the load of large consumers drect power tradng s taken nto account, other load s not ncluded. 3) Supplemental transacton s formed by set C only. Let the total transacton amount s 600 W h, ξ s 0.9, take branch TL34 between node 3 and node 4 as the analyss obect, ts actve power lmtaton s 60 MW, power flow from node 4 to node 3 s postve. Examne the varety of actve power of TL34 n the smulaton process to verfy the effectveness of the new method Fgure 3. IEEE New England test system

9 Specfc nformaton of the transactons s shown n Table. Socal welfare of each transacton n the table s greater than 0 and permutaton of each transacton spread from hgh to low based on the prce dfferental between declared buyer s prce and seller s prce. So we can easly conclude that No.5 and No.6 transacton are unable to enter securty correcton process due to total transacton amount constrant. On the bass of these data, execute securty correcton process for each transacton, the actve power varaton of TL34 s llustrated as below. Fgure 4 shows that the frst three transactons wll not lead to TL34 actve power out of lmt, but when the fourth transacton s taken nto consderaton, power of TL34 s out of ts lmtaton. Hence the No. 4 transacton wll be dscarded drectly n orgnal securty correcton. Now calculate DC PTDF between TL34 and transacton whch leads to power out of lmt (.e. No. 4 transacton), and calculate DC PTDF between TL34 and transacton n the supplemental transacton set (.e. No. 5 and No. 6 transacton). The results are n Table. Accordng to Equaton (4), No. 5 transacton s chosen as supplemental transacton, and actve power of TL34 declne to MW, ths mples that securty correcton result s satsfactory. In ths stuaton, No. to No. 4 transactons s normal transactons, No. 5 transacton s supplemental transacton, compared wth the orgnal method, No. 4 transacton s not abandoned and solves the problem that No. 5 transacton s unable to enter securty correcton process due to total transacton amount constrant. In summary, new method s more flexble and effectve. 6. Conclusons Ths paper proposes a new securty correcton method whch s ntended to solve the problem that the total transacton quantty of large consumers drect power tradng s lmted and the transacton result may be drectly dscarded durng Table. Informaton of drect tradng. Transacton No. enerator No. User Node No. Tradng volume ( W h) Table. The value of DC power transfer dstrbuton factor. Transacton No DC PTDF

10 Fgure 4. Actve power varaton of TL34. securty correcton. The new approach based on DC power transfer dstrbuton factor that s only correlatve wth the network structure and parameter. Moreover, supplemental transactons are ntroduced to the transactons that do not meet the requrement of securty correcton, so that all the transactons whch can maxmum socal welfare s able to enter securty correcton progress and avod beng dscarded drectly. The valdty of the proposed method s demonstrated by a smulaton. The result mples that n the case of the ntroducton of supplemental transactons, large consumer drect purchase transactons that wll be dscarded n the exstng securty correcton process have been retaned. Ths s sgnfcant for encouragng large users and power plants partcpate n transactons actvely and benefcal to promoton of large consumers drect power tradng. References [] Wang, P., Wu, S.H., Da, J.L., et al. (009) Research on Model and Mechansm of Large Consumers Drect-purchasng Based on Incentve Compatblty Prncple. Proceedngs of the CSEE, 0, [] Zhang, X., Lu F.B., Peng T., et al. (04) A Dscusson on Key Issues for Drect Tradng Between Power Users and Plant. Automaton of Electrc Power Systems, 3, [3] Lu, F.B., Peng, T., Zhang, X., Pang, B. and Han, Y.(03) Plot and Promoton Recommendatons for Drect Tradng between Power Users and Plants. East Chna Electrc Power, 9, [4] Xa, Q., Ba, Y., Zhong, H.W. and Chen, Q.X. (03) Insttutonal Desgn and Suggestons for Promoton of Drect Electrcty Purchas by Large Consumers n Chna. 374

11 Automaton of Electrc Power Systems, 0, [5] L, J., Lu, D.N., Chen, Z.Y., Wang, H.C. and Zeng, M.(0) Research of Securty Constraned Dspatchng for Monthly eneraton Plan. Proceedngs of 0 AASRI Conference on Appled Informaton Technology, [6] Wang,.T., Dng, P., Lu, X., et al. (004) Sectonal Securty Constraned Dspatchng n Northeast Regonal Power Market. Power System Technology,0, [7] Wu Y.., Deng Y.M., Zheng R., Le J.S. andjn, Z.H.(00) A Securty Correcton Algorthm for the eneraton Market. Proceedngs of the CSEE, 6, [8] e, C.J., Wang, D.X., e, M.H., et al. (008) Securty Checkng System for Daly eneraton Schedulng of East Chna Power rd and Its Expanson. Automaton of Electrc Power Systems, 0, [9] Chen, H.Y., Zhang, S.L. and Zhang, Y.(008) Research on Transacton Mode of Drect Power Purchase by Large Consumers n Electrcty Market. Power System Technology,, [0] Chen, X.Y. and Hu, J.Y.(008) Prelmnary Dscusson on the Straght Power Transactons Between LargePower Users and eneraton Enterprses. Automaton of Electrc Power Systems, 4, [] Xao, J. and Wen, F.S. (008) Congeston Dspatch for eneraton Rghts Trade. Automaton of Electrc Power Systems, 8, [] Zhang, B.M., Chen, S.S. and Yan, Z. (007) Advanced Electrc Power Network Analyss. nd Edton.Tsnghua Unversty Press, Beng. Submt or recommend next manuscrpt to SCIRP and we wll provde best servce for you: Acceptng pre-submsson nqures through Emal, Facebook, LnkedIn, Twtter, etc. A wde selecton of ournals (nclusve of 9 subects, more than 00 ournals) Provdng 4-hour hgh-qualty servce User-frendly onlne submsson system Far and swft peer-revew system Effcent typesettng and proofreadng procedure Dsplay of the result of downloads and vsts, as well as the number of cted artcles Maxmum dssemnaton of your research work Submt your manuscrpt at: Or contact epe@scrp.org 375