Optimal placement of distributed generation in distribution networks

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1 MultCraft Internatonal Journal of Engneerng, Scence and Technology Vol. 3, o. 3, 20, pp ITERATIOAL JOURAL OF EGIEERIG, SCIECE AD TECHOLOGY 20 MultCraft Lmted. All rghts reserved Optmal placement of dstrbuted generaton n dstrbuton networks Satsh Kansal *, B.B.R. Sa 2, Bareev Tyag 3, Vshal Kumar 4 Department of Electrcal Engneerng, Indan Insttute of Technology, Roorkee, IDIA *Correspondng Author: e-mal:kansal.bhsb@gmal.com, Tel , Fax Abstract Ths paper proposes the applcaton of Partcle Swarm Optmzaton (PSO) technque to fnd the optmal sze and optmum locaton for the placement of DG n the radal dstrbuton networks for actve power compensaton by reducton n real power losses and enhancement n voltage profle. In the frst segment, the optmal sze of DG s calculated at each bus usng the exact loss formula and n the second segment the optmal locaton of DG s found by usng the loss senstvty factor. The analytcal expresson s based on exact loss formula. The optmal sze of DG s calculated at each bus usng the exact loss formula and the optmal locaton of DG s found by usng the loss senstvty factor. The proposed technque s tested on standard 33-bus test system and the obtaned results are compared wth the exhaustve load flows. Keywords: dstrbuted generaton, Partcle Swarm Optmzaton (PSO), optmal sze, optmal locaton, power loss.. Introducton The obectve of power system operaton s to meet the demand at all the locatons wthn power network as economcally and relably as possble. The tradtonal electrc power generaton systems utlze the conventonal energy resources, such as fossl fuels, hydro, nuclear etc. for electrcty generaton. The operaton of such tradtonal generaton systems s based on centralzed control utlty generators, delverng power through an extensve transmsson and dstrbuton system, to meet the gven demands of wdely dspersed users. owadays, the ustfcaton for the large central-staton plants s weakenng due to depletng conventonal resources, ncreased transmsson and dstrbuton costs, deregulaton trends, heghtened envronmental concerns, and technologcal advancements. Dstrbuted Generatons (DGs), a term commonly used for small-scale generatons, offer soluton to many of these new challenges. CIGRE defne DG as the generaton, whch has the characterstcs (CIGRE, 999): t s not centrally planned; t s not centrally dspatched at present; t s usually connected to the dstrbuton networks; t s smaller then 50-00MW. Other organzaton lke, Electrc Power Research Insttute defne dstrbuted generaton as generaton from few klowatts up to 50MW. Ackermann et al. have gven the most recent defnton of DG as: DG s an electrc power generaton source connected drectly to the dstrbuton network or on the customer sde of the meter. Usng DG can enhance the performance of a power system n many aspects. Employng DG n a dstrbuton network has several advantages as (Khoa et al, 2006), reducton n lne losses, emsson pollutants, overall costs due to mproved effcency & peak savng. Improvement of voltage profle, power qualty, system relablty and securty and the dsadvantages are (Illerhsus et al, 2000), reverse power flow, nected harmoncs, Increased fault currents dependng on the locaton of DG unts. DG also has several benefts lke energy costs through combned heat and power generaton, avodng electrcty transmsson costs and less exposure to prce volatlty (Ghosh et al, 200). 2. Locaton and Szng ssues Fg. shows a 3D plot of typcal power loss versus sze of DG at each bus n a standard 69-bus dstrbuton test system. From the fgure, t s obvous that for a partcular bus, as the sze of DG s ncreased, the losses are reduced to a mnmum value and ncreased beyond a sze of DG (.e. the optmal DG sze) at that locaton. If the sze of DG s further ncreased, the losses starts to ncrease and t s lkely that t may overshoot the losses of the base case. Also notce that locaton of DG plays an mportant role n mnmzng the losses. The mportant concluson that can be drawn from Fg. s that, gven the characterstcs of the dstrbuton

2 48 Kansal et al. / Internatonal Journal of Engneerng, Scence and Technology, Vol. 3, o. 3, 20, pp system, t s not advsable to construct suffcently hgh DG n the network. The sze at most should be such that t s consumable wthn the dstrbuton substaton boundary. Any attempt to nstall hgh capacty DG wth the purpose of exportng power beyond the substaton (reverse flow of power though dstrbuton substaton), wll lead to very hgh losses (Laksham et al, 2008). So, the sze of dstrbuton system n term of load (MW) wll play mportant role s selectng the sze of DG. The reason for hgher losses and hgh capacty of DG can be explaned by the fact that the dstrbuton system was ntally desgned such that power flows from the sendng end (source substaton) to the load and conductor szes are gradually decreased from the substaton to consumer pont. Thus wthout renforcement of the system, the use of hgh capacty DG wll lead to excessve power flow through smallszed conductors and hence results n hgher losses Loss %DG Sze Bus no Fgure. Effect of sze and locaton of DG on system loss. 2. Loss senstvty factor: The loss senstvty factor s used for the placement of DG s explaned as, the real power loss n the system s gven by ().Ths formula s popularly referred as Exact Loss formula (Elgerd, 97; Kazem et al, 2009). P L = = = [ α ( P P + Q Q ) + β ( Q P + P Q )] () Where, α β r = v v r = v v Cos( δ δ ) Sn( δ δ ) and z = r + x are the th element of [Zbus] matrx P = P G P D and Q = Q G - Q D P G & Q G are power necton of generators to the bus. P D & Q D are the loads.

3 49 Kansal et al. / Internatonal Journal of Engneerng, Scence and Technology, Vol. 3, o. 3, 20, pp P & Q are actve and reactve power of the buses. The senstvty factor of real power loss wth respect to real power necton from the DG s gven by PL α = = 2α P + 2 ( α P - βq ) (2) P = Senstvty factor are evaluated at each bus by usng the values obtaned from the base case load flow. The bus havng lowest loss senstvty factor wll be best locaton for the placement of DG (Acharya et al, 2006). Conventonal load flow studes lke Gausssedal, ewton raphson and fast decoupled load flow methods are not sutable for dstrbuton load flows because of hgh R/X rato. A load flow method for dstrbuton systems.e backward sweep and forward sweep method for load flow that offers better soluton was proposed (Haque 996). 2.2 Optmal Szng of DG: The total power loss aganst nected power s a parabolc functon and at mnmum losses, the rate of change of losses wth respect to nected power becomes zero [9]. PL P = 2α P + 2 ( α P - β Q ) = 0 (3) = It follows that P = ( α P α = - βq ) (4) Where P s the real power necton at node, whch s the dfference between real power generaton and the real power demand at that node: P = ( PDC - PD ) Where P DG s the real power necton from DG placed at node, and P D s the load demand at node. By combnng the above we get. P DG = PD ( α P α = - β Q ) (5) The equaton (5) gves the optmum sze of DG for each bus, for the loss to be mnmum. Any sze of DG other than P DG placed at bus, wll lead to hgher loss.

4 50 Kansal et al. / Internatonal Journal of Engneerng, Scence and Technology, Vol. 3, o. 3, 20, pp Optmal Locaton of DG: The optmal locaton can be fnd for the placement of optmal szes of DG as shown n fg.(2) as obtaned from eq. (5) whch wll gve the lowest possble total loss due to placement of DG at the respectve bus s as shown n fg. (3). The bus havng least power loss wll be optmal locaton for the placement of DG (Acharya et al, 2006) Optmum DG Sze (MW) Bus o. Fgure 2. Optmum sze of DG at varous locatons for 33 bus dstrbuton system Total Power Loss (MW) DG Locaton Fgure 3. Accurate Total Power Loss of 33 bus dstrbuton system.

5 5 Kansal et al. / Internatonal Journal of Engneerng, Scence and Technology, Vol. 3, o. 3, 20, pp Partcle Swarm Optmzaton 3. Introducton Partcle swarm optmzaton (PSO) s a populaton-based optmzaton method frst proposed by Kennedy and Eberhart n 995, nspred by socal behavor of brd flockng or fsh schoolng (Kennedy et al, 995). The PSO as an optmzaton tool provdes a populaton-based search procedure n whch ndvduals called partcles change ther poston (state) wth tme. In a PSO system, partcles fly around n a multdmensonal search space. Durng flght, each partcle adusts ts poston accordng to ts own experence (Ths value s called Pbest), and accordng to the experence of a neghborng partcle (Ths value s called Gbest), made use of the best poston encountered by tself and ts neghbor (Fg 4). Y s k+ V k V k+ sk V Pbest V Gbest Fgure 4. Concept of a searchng pont by PSO Ths modfcaton can be represented by the concept of velocty. Velocty of each agent can be modfed by the followng equaton: v k + k k ( k d d d d 2 d d = ω v + c rand pbest s ) + c rand ( gbest s ) (6) Usng the above equaton, a certan velocty, whch gradually gets close to pbest and gbest can be calculated. The current poston (searchng pont n the soluton space) can be modfed by the followng equaton: Where, k + k k + sd = sd + vd, =, 2,...,n. (7) d =, 2,, m s k s current searchng pont, s k+ s modfed searchng pont, v k s current velocty, v k+ s modfed velocty of agent, v pbest s velocty based on pbest,, v gbest s velocty based on gbest, n s number of partcles n a group, m s number of members n a partcle, pbest s pbest of agent, gbest s gbest of the group, ω s weght functon for velocty of agent, c s weght coeffcents for each term. The followng weght functon s used: ωmax ω ω = ω.k (8) max k max mn X

6 52 Kansal et al. / Internatonal Journal of Engneerng, Scence and Technology, Vol. 3, o. 3, 20, pp Where, ω mn and ω max are the mnmum and maxmum weghts respectvely. k and k max are the current and maxmum teraton. Approprate value ranges for C and C 2 are to 2, but 2 s the most approprate n many cases. Approprate values for ω mn and ω max are 0.4 and 0.9 (Eberhart et al, 2000) respectvely 3.2 Obectve Functon: The man obectve s to mnmze the total power loss as gven n eq. () whle meetng the followng constrants. The network power flow equaton must be satsfed. The voltage at every bus n the network should be wthn the acceptable range (Utlty s standard ASI Std. C ).e., wthn permssble lmt (±5%) (Wlls, 2004), V mn V V max {buses of the network} 3.3 PSO Procedure: The PSO-based approach for solvng the optmal placement of DG problem to mnmze the loss takes the followng steps: Step : Input lne and bus data, and bus voltage lmts. Step 2: Calculate the loss usng dstrbuton load flow based on backward sweep-forward sweep method. Step 3: Randomly generates an ntal populaton (array) of partcles wth random postons and veloctes on dmensons (Sze of DGs and Locaton of DGs) n the soluton space. Set the teraton counter k = 0. Step 4: For each partcle f the bus voltage s wthn the lmts as gven above, evaluate the total loss n equaton (). Otherwse, that partcle s nfeasble. Step 5: For each partcle, compare ts obectve value wth the ndvdual best. If the obectve value s lower than Pbest, set ths value as the current Pbest, and record the correspondng partcle poston. Step 6: Choose the partcle assocated wth the mnmum ndvdual best Pbest of all partcles, and set the value of ths Pbest as the current overall best Gbest. Step 7: Update the velocty and poston of partcle usng (6) and (7) respectvely. Step 8: If the teraton number reaches the maxmum lmt, go to Step 9. Otherwse, set teraton ndex k = k +, and go back to Step 4. Step 9: Prnt out the optmal soluton to the target problem. The best poston ncludes the optmal locatons and sze of DG and the correspondng ftness value representng the mnmum total real power loss. Test system Ths methodology s tested on test system contans 33 buses and 32 branches as shown n fg.5. It s a radal system wth a total load of 3.72 MW and 2.3 MVAR (Kashem et al, 2000). A computer program s wrtten n MATLAB 7 to fnd the optmal sze of DG at varous buses and approxmate total loss wth DG at varous locatons to fnd out the best locaton by analytcal method, repeated load flow (Acharya et al, 2006) and PSO.

7 53 Kansal et al. / Internatonal Journal of Engneerng, Scence and Technology, Vol. 3, o. 3, 20, pp S/S Results and Dscussons Fgure 5. Sngle lne dagram of 33 bus dstrbuton test system. Based on the analytcal expresson, the optmum sze of DG s calculated at each bus for the test system and bus havng least total power loss wll be the optmal locaton for the placement of DG; the best locaton s bus 6 wth a total power loss of.2 kw, but ths approach volates the voltage lmts as shown n fg.(6).the optmal placement of DG by loss senstvty approach s not able to dentfy the best locaton. The optmal placement of DG by repeated load flow wth loss of.02kw as shown n Table I volate the voltage lmts, If voltage lmts are taken nto consderaton then sze of DG wll ncrease but f the same s done by PSO technque by takng the voltage lmt constrants nto consderaton the sze of DG wll decrease drastcally.e. 240kW, wth approxmately same power loss as shown n table II, and voltage profle s as shown n fg.(7). wthout DG wth DG Voltage Profle n p.u Bus umber Fgure 6. Varaton of voltage profle by analytcal method.

8 54 Kansal et al. / Internatonal Journal of Engneerng, Scence and Technology, Vol. 3, o. 3, 20, pp Table I Power loss wth and wthout DG for 33 bus system wthout lmts Method Optmum locaton Optmum DG sze (MW) Power loss (KW) Wthout DG Wth DG Analytcal approach Bus Loss senstvty factor Bus Repeated load flow Bus Table II Power loss wth and wthout DG for 33 bus system wth lmts Method Optmum locaton Optmum DG sze (MW) Power loss (KW) Wthout DG Wth DG Repeated load flow Bus PSO Bus wthout DG wth DG Voltage Profle n p.u Bus umber Fgure 7. Varaton of voltage profle by PSO. 5. Concluson Optmal placement of DG plays an mportant role for maxmzng the total real power loss reducton n the dstrbuton system wth actve power compensaton. The optmal placement by analytcal method volates the lne voltage lmts, f voltage s wthn lmts then the sze and lne losses ncreases. The optmal placement of DG by PSO technque takng the voltage lmts of the system nto consderaton to mnmzng the real power loss mproves the results drastcally. But n practce the best locaton or sze may not always be possble due to many constrants.e. such sze may not be avalable n the market. References Acharya., Mahat P., Mthulananthan., An analytcal approach for DG allocaton n prmary dstrbuton network, Electrc Power & Energy Systems, Vol.28, o.0, pp , December. Ackermann T., Andersson G., and Solder L., 200. Dstrbuted generaton: a defnton, Electrc Power system Research, Vol.57, o.3, pp , Aprl. CIGRE, 999. Impact of ncreasng contrbuton of dspersed generaton on the power system, Workng Group Eberhart R.C.and Sh Y., Comparng nertal weghts and constrcton factor n partcle swarm optmzaton, Proceedngs of the Internatonal Congress on Evaluatng Computaton, San Dego,Calforna, IEEE servce center, Pscataway, J, pp

9 55 Kansal et al. / Internatonal Journal of Engneerng, Scence and Technology, Vol. 3, o. 3, 20, pp Elgerd I.O. 97. Electrc energy system theory: an ntroducton, McGraw-Hll. Ghosh S., Ghoshal S.P., Ghosh S., 200. Optmal szng and placement of dstrbuted generaton n a network system, Electrc Power and Energy Systems, Vol.32, pp , January. Haque M.H., 996. Effcent load flow method for dstrbuton systems wth radal or mesh confguraton, IEE Proceedngs Generaton, Transmsson and Dstrbuton, Vol. 43, o., pp.33-38, January. Illerhaus S.W., Versteg J.S., Optmal operaton of ndustral CHP-based power systems n lberalzed energy markets, IEEE Industry Applcatons Conference, Vol. 2, pp Kashem M.A., Ganapathy V., Jasmon G.B., Buhar M.I., A novel method for loss mnmzaton n dstrbuton networks, Int.Conference on Electrc Utlty Deregulaton and Restructurng and Power Technology, London, Aprl. Kazem A., Sadegh M., Sttng and szng of dstrbuted generaton for loss reducton, Power and Energy Conference, APPEEC, pp.-4, Asa-Pacfc, Wuhan. Kennedy J., Eberhart R., 995. Partcle Swarm Optmzer, IEEE Internatonal Conference on eural etworks, Perth(Australa), IEEE Servce Centre Pscataway, J, IV, pp Khoa T.Q.D., Bnh P.T.T., Tran H.B., Optmzng locaton and szng of dstrbuted generaton n dstrbuton systems Proceedngs of IEEE PES Power Systems Conference and Exposton-PSCE 2006, pp , October/ovember. Laksham Dev A., Subramanyam B., Sttng of DG unt operated at optmal power factor to reduce losses n radal dstrbuton system. A case study, Theoretcal and Appled Informaton Technology. Wlls H.L., Power Dstrbuton Plannng Reference Book. ew York: Marcel Deckker. Bographcal notes Satsh Kansal receved the M.E. degree n Power System Engneerng from the Punab Engneerng College (PEC), Chandgarh, n 998.Currently, he s pursung Ph.D. at IIT Roorkee (U.K.) and s a Assocate Professor n the Electrcal Engneerng Department at BHSBIET Lehragaga (Pb.). Hs research nterest ncludes power dstrbuton system, power system optmzaton, dstrbuted generaton and renewable energy. B.Bhaskara Rama Sa receved the B.Tech. degree n Electrcal and Electroncs Engg. From MVGR college of Engg., Vzanagaram (A.P.). Currently he s pursung M-Tech at IIT Roorkee n System Engneerng and Operaton Research. Bareev Tyag receved the PhD n Electrcal Engneerng, IIT-Kanpur, 2005 and M. Tech Electrcal Engneerng (Control System) from IIT-Kharagpur n the year Pror to these he completed hs B. E. Electrcal Engneerng from IIT-Roorkee (Formally Unv. of Roorkee) n 987. Presently he s servng as Assstant Professor n EED, IIT-Roorkee snce Hs research nterests nclude power system deregulaton, power system optmzaton, dstrbuted generaton and control. Vshal kumar receved the Ph.D.degree n power system engneerng from Indan Insttute of Technology, Roorkee (IITR), Inda, n Currently he s faculty member n the Department of Electrcal Engneerng, Indan Insttute of Technology, Roorkee. Hs research nterest ncludes power dstrbuton system, operaton and control, dgtal desgn and verfcaton. Receved January 20 Accepted March 20 Fnal acceptance n revsed form Aprl 20