Keywords Distributed Generation, Loss Minimization, Distribution Network, Iterative Approach.

Transcription

1 International Jornal of Indstrial Electronics and Electrical Engineering, IN: Volme-5, Isse-1, Jan.-017 A NOVEL ITERATIVE APPROACH FOR OPTIMAL IZING OF DITRIBUTED GENERATION UNIT FOR LO MINIMIZATION IN DITRIBUTION NETWORK 1 BARNALI MOTLING, UBRATA PAUL, 3 UNITA HALDER NEE DEY 1,,3 Electrical Engineering Department, Jadavpr University, India 1 bsmotling@gmail.com, speejpow@yahoo.co.in, 3 snitaj@yahoo.com Abstract This paper presents a novel iterative approach for determination of the optimal size of distribted generation sorce located at any given bs of a distribtion network to minimize the active power loss in the network in the absence of ineqality constraints that can be imposed by varios operational limits. The proposed approach is capable of finding the optimal size with significantly less comptation than is reqired by the evoltionary poplation based iterative approaches reported earlier for the soltion of this type of problems. The method is a generalized one as it is capable of finding the optimal size irrespective of absence or presence of harmonic sorce in the network. However, it is particlarly sefl when harmonic sorces are present in the network as no analytical soltion is available in sch sitation. Analytical soltion reqires the least amont of comptation, bt sch soltion is available for finding optimal size of DG nits only when no harmonic sorce is present. The proposed approach has been tested on two benchmark distribtion test networks, and the reslts are presented to show its efficacy. Keywords Distribted Generation, Loss imization, Distribtion Network, Iterative Approach. I. INTRODUCTION Penetration of distribted generators (DG) into electric power distribtion system has been increasing rapidly over the last few years owing to increased emergence of renewable energy sorces. The primary prpose of a DG nit is to inject real power to a distribtion network. Insertion of DG s in the distribtion network can provide varios technical, economical and environmental benefits [1]. However, installation of non optimized sizes of DG s at arbitrary locations can reslt in degraded voltage profile and increased system losses. This wold conseqently drive cost escalation, and varios other ndesirable effects [-3]. It is therefore necessary that the sizing and location of DG nits shold be sensibly planned. The two major benefits achieved throgh optimal siting and sizing of DG s and are mostly considered for stdies by varios researchers are redctions in network power loss and voltage profile improvement. The problem of loss minimization and voltage profile improvement by optimal DG placement has been addressed by many researchers [4-14].Varios approaches sch as sensitivity based methods [4-5], evoltionary search based optimization [6-13], and load flow based approaches[14]have been reported with both single objective and mlti-objective optimization approaches. All the aforementioned approaches are comptationally intensive. Analytical approaches have been sggested by athors [15-17] for determining the optimal size for minimizing the network loss. These methods reqire mch less comptation bt are capable of finding nconstrained soltion only. However, none of the above methods have considered the presence of harmonic sorces in their stdies. It has been observed that increased se of power electronic devices has reslted in either or both crrent and voltage distortions, leading to harmonic polltion in a distribtion network. Combination of electronic loads and power electronics based DG nits sing voltage sorce inverters can inject harmonic crrents into the network leading to distortions in bs voltages. These distortions in crrents and voltages may have detrimental effects on system operation, protection, stability and reliability isses, and also cases an increase in power loss in the network[18-0]. Optimal DG planning for loss minimization in these sitations shold consider minimization of the total active power loss inclding the harmonic losses while varios operational limits can appear as different ineqality constraints according to the planning reqirements [1-4]. Considerations of the effects of harmonics in optimal siting and sizing of DG have been reported by some athors [5-8]. Few stdies have considered loss minimization along with minimization of total harmonic distortions in bs voltages with constraint on maximm and minimm limits on bs voltages [5]. Others have considered loss minimization with constraints imposed on limits on both bs voltages and total harmonic distortions [6]. All these stdies have sed comptationally intensive methods sch as Evoltionary Programming [5], Genetic Algorithm [6], Particle warm Optimization [7], and Particle warm Optimization in combination with Mixed integer non-linear programming and sensitivity analysis [8]. In the present stdy, a novel iterative method is proposed to determine optimal size of DG nit located at any arbitrarily selected bs for loss minimization in distribtion network. The proposed method is eqally applicable for networks withot A Novel Iterative Approach For Optimal izing of Distribted Generation Units For Loss imization in Distribtion Network 63

2 International Jornal of Indstrial Electronics and Electrical Engineering, IN: any harmonic sorce or with harmonic sorces (sch as non linear loads and non sinsoidal DG nits) present. The method is capable of finding the nconstrained optimal size, and reqires significantly less comptation than is reqired by the evoltionary poplation based iterative approaches. When no harmonic sorce is present, the method reqires only few distribtion load flow (DLF) to reach the desired soltion. In the presence of harmonic sorces, only few harmonic load flow (HLF) will be reqired to arrive at the soltion. Both the DLF and HLF programs are developed sing Mat lab platform and is based on the principle of Backward Forward load flow[9-33]. Thogh the analytical approaches [15-17]are comptationally less demanding than the proposed method, they are not applicable in the presence of harmonic sorces in the network. This paper is organized in the following manner. ection explains the proposed methodology. The problem formlation and the comptational steps are presented in ection 3. ection 4 presents the reslts of stdy performed on benchmark IEEE-33 and IEEE-69 network. ection 5 presents the conclsions drawn from the stdy ndertaken. II. BAI OF THE PROPOED APPROACH The proposed approach is based on the following observations: Power loss Volme-5, Isse-1, Jan.-017 h the total nmber of branches in the network, I m is the rms vale of the h th harmonic component of crrent throgh the m th branch, and R m is h the resistance of the m th branch. I m is obtained from harmonic load flow (HLF) as presented in [31-3] loss withot Harmonics loss with Harmonics Bs 9 Bs 1 Bs DG size Fig.1(a). Loss crves for different bses of IEEE- 33 bs network When no harmonic sorces are present in the network the power loss is given as: B loss m m m1 P I R () a. It has been shown by earlier athors [16], that when no harmonic sorce is present in the network, the network power loss varies parabolically with the DG size at any given bs. That means the loss contines to decrease p to a certain size of DG, till it reaches minimm, and then goes on increasing for frther increase in DG size. A rigoros stdy has been done by the present athors with repeated HLF, by placing non sinsoidal DG at different arbitrarily selected bses taken one at a time, and by varying the DG size in small steps. This stdy has revealed that the variation of network power loss with the size of a non sinsoidal DG sorce placed at any given bs has almost same natre as that with a sinsoidal DG placed at the same bs. Fig. 1(a) and Fig. 1 (b) show these variations (henceforth will be termed as Loss crve) for some of the bses of IEEE-33 bs network [35] and IEEE-69 bs network [36] respectively. As these two network data do not incorporate any non linear loads, non sinsoidal DG has been sed as the harmonic sorce to introdce the effect of harmonics. To maintain clarity of the figres within the limited availability of space, the loss crves are shown for a few arbitrarily selected bses only. The total active power loss in the network inclding the losses de to harmonics is calclated as: H B ( h) Ploss Im Rm h1 m1 where, H is the total nmber of harmonics, B is Fig.1(b). Loss crves for different bses of IEEE- 69 bs network b. Fig. shows a typical loss crve where and are the minimm and maximm DG size to be considered, and is the optimal size for which the network power loss becomes minimm in the absence of any constraint. At a size with, a small increment s in size will reslt in decrement of loss while a decrement s will increase the loss. On the other hand, if, an increment s will increase the loss whereas a decrement of same amont in size will reslt in redction in loss. For, a small A Novel Iterative Approach For Optimal izing of Distribted Generation Units For Loss imization in Distribtion Network 64

3 International Jornal of Indstrial Electronics and Electrical Engineering, IN: change s in size will not case any perceptible change in the amont of loss, i.e., the loss changes only by a very small amont less than some small tolerance. The above facts can be sed a criteria to check whether or or, where, is any arbitrary size of the DG. h h h Volme-5, Isse-1, Jan.-017 Fig.3 (a): Demonstration of the proposed Fig.. A typical loss crve III. PROPOED METHODOLOGY 3.1 The iterative process: The proposed iterative method is demonstrated with the help of Fig. to Fig.(3), where, is the initial estimate of with which the iteration starts, and, is given by () and and,respectively, are the first and the second estimates obtained iteratively (sing r=0 and r=1) from the following eqation: ( r) ( old) ( r 1) ( old) ( r) for r = 0, if () where r=0,1, ( r) if and, for r > 0, ( r 1) ( r) ( r 1) if and are on the two sides of (as shown in Fig.3(a) and Fig.3(b)). ( r) remains nchanged when ( r 1) and are on the same side of (as shown in Fig. 3(c)). As example, in Fig. 3(a), is obtained by ptting r=0, and Ths ( old) in eqation () as is given as follows: where as in Fig. 3(b), and a reslt. is obtained by ptting r=0, in eqation() as in Fig. 3(b) is given as, and, as The second estimate () in Fig. 3(a) is obtained from eqation() by ptting r=1, and remains same as the previos vale (i.e. ) as and are on the same side of. Ths, () whereas, in Fig. 3(a ) and Fig.3 (b), and ( old), as are on the two sides of. In this case, () The iteration contines ntil convergence is obtained i.e., the condition ( r) is reached. The convergence is checked with the help of the criteria mentioned nder observation () in section. Fig.3(b): Demonstration of the proposed iterative process Fig.3(c): Demonstration of the proposed iterative process A Novel Iterative Approach For Optimal izing of Distribted Generation Units For Loss imization in Distribtion Network 65

4 International Jornal of Indstrial Electronics and Electrical Engineering, IN: Comptational teps: The following comptational steps are developed for determining the optimal size of DG nit for a given bs: 1. elect a bs and set,, THD, s, and r. L. If 0, then sing the criteria (as set in observation ()), check if. If yes, then and go to step 13, else go to next set opt step. 3. Using the criteria (as set in observation ()), check if. If yes, then set opt and go to step 13, else, go to next step. 4. et r=0. ( r) 5. Calclate. ( r) 6. If, then set opt and go to step 13, else, go to next step. 7. et ( old) ( r) if ( r) if ( r) r ( 1) 8. Calclate ( r1) 9. If, then set opt step 13, else, go to next step. 10. et ( r 1) ( r1) ( r) ( r 1) if and, and go to are on the two sides of, or, ( r) ( r 1) keep nchanged if and are on the same side of. 11. et r r 1 1. If r r, then go to step 14, else, go to step Print/Display the vale of opt and go to step Print/Display No convergence. 15. top. IV. REULT AND DICUION The proposed method was applied on two benchmark radial distribtion test networks, namely, IEEE-33 bs network and IEEE-69 bs network, to demonstrate its efficacy. For the 33 bs network, bs nos. 6 to 15 are chosen as candidate bses, while bs nos. 6 to 7 are chosen for the 69 bs network. A sixplse inverter based DG is considered, which also acts as the harmonic sorce in the network. The harmonic order of the 6 plse converter sed for harmonic modeling of the DG is in accordance to [37-38], and is given in Table A1 in the appendix. For stdy withot harmonics only the fndamental reslts are considered. Unity power factor DG has been considered. The reslts are smmarized in Table 1(a) to Table (b), which enlist the optimal DG size for each candidate bs. The minimm and maximm Volme-5, Isse-1, Jan.-017 A Novel Iterative Approach For Optimal izing of Distribted Generation Units For Loss imization in Distribtion Network 66 limit on the size of DG nit to be installed has been assmed to be 500 kw and 3000kW respectively. The sbstation bs voltage for this stdy is assmed to be 1.0 p.. The soltions are obtained with s 5kW, r 0 and (which is eqivalent to 0.1 kw). The reslts obtained by the proposed method are compared with those obtained by Particle warm Optimization (PO) techniqes [33-34]. Two case stdies have been carried ot to stdy the effect of DG placement in the presence and absence of harmonic sorces in the network on active power losses in the system. Case-1: Optimal DG size for minimm loss in the absence of harmonics. Case- : Optimal DG size for minimm loss in the presence of harmonics. Table 1(a): Optimm DG sizes for IEEE-33 bs network in absence of harmonics Bs No Table 1(b): Optimm DG sizes for IEEE-69 bs network in absence of harmonics Bs No Optimm DG size sing New Iterative Approach ize P LO No. of DLF Optimm DG size sing New Iterative Approach ize P LO No. of DLF Optimm DG size sing PO ize P LO Optimm DG size sing PO ize P LO Table 1(a) and 1(b) shows the reslts obtained for IEEE-33 and IEEE-69 bs system when harmonic

5 International Jornal of Indstrial Electronics and Electrical Engineering, IN: sorces are not present. From the tables it is obvios, that the reslt obtained by the proposed method is very close to that obtained by PO, bt the nmber of DLF reqired by the proposed method for each bs is qite small. The maximm nmber of DLF reqired is 1 whereas, PO reqires large nmber of DLF (may be few hndreds) for each bs. Table (a): Optimm DG sizes for IEEE-33 bs network in presence of harmonic sorces Bs No. Table (b): Optimm DG sizes for IEEE-69 bs network in presence of harmonic sorces Bs No. ize Table (a) and (b) show the reslts when harmonic sorces are present. The maximm nmber of HLF reqired is 1, whereas, PO reqires large nmber of HLF for each bs. It is obvios that comparable reslts are obtained by the proposed method at the cost of significantly less comptation. CONCLUION Optimal DG size With Proposed method P LO No. of HLF Optimal DG size With Proposed method ize With PO P LO With PO ize P LO No. of HLF ize P LO This paper proposes a novel iterative method for calclating the optimal DG size located at any Volme-5, Isse-1, Jan.-017 A Novel Iterative Approach For Optimal izing of Distribted Generation Units For Loss imization in Distribtion Network 67 arbitrarily selected bs. The method reqires significantly less comptation than is reqired by the evoltionary methods. The method is generalized as it is eqally applicable in both cases when harmonic sorces are present in the network or not. The reslts shown corroborate with the above statements. Thogh the proposed method can find nconstrained optimal size of DG nits, it is expected that it s capability of fast detection of the same can contribte significantly in redcing the amont of comptation for finding the constrained optimal size. An investigation in that direction is being carried ot by the present athors, and the reslts will be reported shortly. REFERENCE [1] Thomas Ackermann, Goran Anderson, Lennart oder, Distribted generation: a definition, Electric Power systems Research, volme, 57, pp , 001. [] G. Pepermans, J. Driesen, D. Haeseldonckx, R. Belmans, W. D haeseleer. ( K. U. Leven - Energy Institte) working paper series n 003-8, Distribted Generation: Definition, Benefits and Isses, faclty of economics and applied economic sciences center or economic stdies energy, transport &environment, Agst 003. [3] Y. M. Atwa, E. F. El-aadany, M. M. A. alama, and R. eethapathy," Optimal renewable resorces mix for distribtion system energy loss minimization," IEEE Trans. Power yst., vol. 5, pp , Feb.010. [4] HasanHedayati,. A. Nabaviniaki, and Adel Akbarimajd, A Method for Placement of DG Units in Distribtion Networks, IEEE transactions on power delivery, volme. 3, 008. [5] Kashem M A, Ganapathy V, Jasmon G B, Bhari M I, A novel method for loss minimization in distribtion networks, In Proceedings of international conference on electric tility dereglation and restrctring and power technologies, pp , 000. [6] Deependra ingh, Devender ingh, and K.. Verma, GA based Optimal izing & Placement of Distribted Generation for Loss imization, World Academy ofcience, Engineering and Technology, International Jornal of Electrical, Compter, Energy, Electronic and Commnication Engineering, volme.1, 007. [7] Talaat, H. E. A., Al-Ammar, E., Optimal allocation and sizing of distribted generation in distribtion networks sing Genetic Algorithms, 11th International Conference on Electrical Power Qality and Utilization (EPQU), pp. 1 6, October,011. [8] ingh, R. K., and Goswami,. K., Optimm siting and sizing of distribted generations in radial and networked systems, Electr. Power Compon. yst., Vol. 37, No., pp , 009. [9] oma Biswas,. K. Goswami, and A. Chatterjee, A tdy of the Factors Inflencing the Optimal ize and ite of Distribted Generations, Jornal of Clean Energy Technologies, volme., 014. [10] atishkansal, B.B.R. ai, BarjeevTyagi, Vishal Kmar, Optimal placement of distribted generation in distribtion networks, International Jornal of Engineering, cience and Technology,volme. 483, pp , 011. [11] A.Apparao, K. Bhashna, Optimal Allocation of DG Considering Loss imization and Voltage Profile Using PO, International Jornal of cience and Research (IJR)IN (Online): , volme. 4, pp , 015. [1] nigdha Rani Behera, omyaprakash Dash, B. K. Panigrahi, Optimal Placement and izing of DGs in

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