International Journal of Trend in Research and Development, Volume 3(6), ISSN 2394-9333 www.ijtrd.com Multi-Objective Optimal Power Flow using Fuzzy Supported Ant Lion Algorithm 1 J. Radha, 2S. Subramanian, 3S. Ganesan and 4M. Abirami 1,3,4 Assistant Professor, 2Professor 1,2,3,4 Department of Electrical Engineering, Annamalai University, Annamalai Nagar, Tamil Nadu, India Abstract— The purpose of this paper is to solve a multiobjective electric power dispatch problem, which is a multiple non-commensurable objective problem, minimizes operating cost, adhering pollution norms, low transmission loss and no violations on voltage levels subject to various constraints. Improved control settings such as generator powers, bus voltage magnitudes, transformer taps and shunt capacitor settings for individual and simultaneous minimization of objectives are obtained by as new algorithm called Ant Lion Optimization (ALO). Fuzzy based approach is used to extract the best compromise solution from the trade off front. The best solution records of IEEE-30 bus, IEEE-118 bus and New England power systems are updated in this work. To further demonstrate the efficiency and effectiveness of the ALO based OPF, it has been compared with other state of the art evolutionary algorithms on this domain. Comprehensive simulation results with various case studies show a great potential for application of ALO in multi-objective OPF problems. Various heuristic and bio inspired algorithms such as Differential Evolution (DE) [1], Evolving Ant Direction Differential Evolution (EADDE) [2], Gravitational Search Algorithm (GSA) [3], improved harmony search [4], fuzzy evolutionary and swarm optimization [5], mixed-binary evolutionary Particle Swarm Optimization (PSO) [6], improved Teaching Learning Based Optimization (TLBO) using Levy mutation strategy (LTLBO) [7], PSO with an aging leader and challengers [8], Artificial Bee Colony (ABC) with quantum theory [9], improved Group Search Optimization (GSO) [10], chaotic Krill Herd Algorithm (KHA) [11], Adaptive Genetic Algorithm (AGA) with adjusting population size [12], Black-Hole-Based Optimization (BHBO) [13], Improved Electromagnetism-like Mechanism (IEM) [14], Gbest guided ABC (GABC) [15], hybrid Modified Imperialist Competitive Algorithm–Teaching Learning Algorithm (MICA-TLA) [16], hybrid Shuffle Frog Leaping AlgorithmSimulated Annealing (SFLA-SA) [17] and Artificial Bee Colony (ABC) [18] have been applied to solve the multi objective OPF problem. Keywords—Ant Lion Optimizer; Emission; Multi-Objective Optimal Power Flow; Voltage Stability; Quadratic Cost The above methods solve the OPF problem by taking into consideration of minimization of objectives individually i.e., one objective is minimized at a time and the values of other objectives at that instant is noted. Nevertheless, it is not worthwhile in many cases to optimize a single objective function, since a power planning designer needs to arrive to a grit handling contrasting and, in some circumstances, conflicting design objectives. At this juncture, the application of a multi-objective optimization algorithm stands out as the only appropriate way to optimally set the control variables at the same time, to consider a wide range of objective functions. Compared with single objective optimization techniques, the multi-objective ones are advantageous, because they are able to generate a solution including various trade-offs among different individual objectives and this facilitates the operators to select the best final solution. This motivates the researchers to handle the objectives individually and simultaneously to reach the exact solution. In this regard, the optimization techniques, Biogeography Based Optimization (BBO) [19], GSA [20], KHA [21], hybrid PSOGSA [22], Adaptive GSO (AGSO) [23], Adaptive Biogeography based Predator-Prey Optimization (ABPPO) [24], TLBO [25], Improved Colliding Bodies Optimization (ICBO) [26], Backtracking Search Algorithm (BSA) [27], Differential Search Algorithm (DSA) [28] and MICA-TLA [16] have been used and Pareto set have been developed by means of weighing factors. Unfortunately, the weighted sum method requires multiple runs to reach the solution and this method cannot be employed in problems having a non-convex Pareto-optimal front. I. INTRODUCTION Optimal Power Flow (OPF) is one of the special tools to optimally analyze, monitor and control different aspects of power system. Since 1962, OPF has attracted worldwide attention for its significant influence on secure and economic operations of power systems. The goal of OPF is to find the optimal settings of a given power system network that optimize a certain objective function while satisfying its power flow equations, system security and equipment operating limits. Different control variables (continuous and discrete) are manipulated to achieve an optimal setting based on problem formulation. The traditional objectives of OPF are minimization of fuel cost, active power losses, bus voltage deviation, emission of generating units, number of control actions and load shedding. Previous research primarily pertained to the single objective optimization of OPF objectives. It is also realistic to use multi-objective functions model as the goal of OPF formulation. A. Classical and Evolutionary Methods for OPF Earlier OPF solution methods are based on optimization methods such as non-linear programming, quadratic programming, Newton‘s method based solution of optimality, linear programming, interior point methods and linear programming. It should be emphasized that all these approaches, are based on gradients and derivatives that are not able to determine the global optimum. In the recent years, many intelligent optimization methods have been developed to overcome the issues and limitations of the classical methods. These methods are population based and are developed by inspiring evolutionary process, nature and biological behaviours of species. IJTRD | Nov-Dec 2016 Available [email protected] Due to the hassle involved in weighting method, fuzzy based approach has been developed to solve multi-objective optimization problem. Enhanced Genetic AlgorithmDecoupled Quadratic Load Flow (EGA-DQLF) [29], MultiObjective Harmony Search (MOHS) [30], multi-objective variants of ABC and TLBO algorithm [31], Grey Wolf Optimizer (GWO) [32], DE [32], Improved PSO (IPSO) [33], Forced Initialised DE (FIDE) [34], Improved Strength Pareto Evolutionary Algorithm (SPEA2) [35], Quasi-Oppositional 86 International Journal of Trend in Research and Development, Volume 3(6), ISSN 2394-9333 www.ijtrd.com TLBO (QOTLBO) [36], hybrid Modified PSO-SFLA (MPSOSFLA) [37], Modified SFLA (MSFLA) [38], glowworm swarm optimization [39], Modified TLBO (MTLBO) [40], and Modified ABC (MABC) [41] have been applied to solve the issue that has both discrete and continuous variables. B. Why ALO? From a problem solving perspective, it is difficult to formulate a universal optimization algorithm that could solve all the problems. According to this, Seyedali Mirjalili et al., developed a new meta-heuristic algorithm, namely, the Ant Lion Optimization (ALO) algorithm [42] and it has been successfully applied to power system optimization problems (short-term wind integrated hydrothermal power generation scheduling). The ALO algorithm mimics hunting mechanism of ant lions in nature [42]. The advantages of ALO such as high rate of local optima avoidance, guarantee of exploration of search space, requiring few parameters to adjust and gradient-free attracts the authors to implement it to solve OPF problem. In this work, it is intend to cover the objectives such as cost, emission, transmission losses and L-index with equality and inequality constraints and ALO has been implemented to solve the issue. Having formulated as multiobjective optimization problem, Pareto solution has been obtained through fuzzy mechanism. Concisely, the main contributions of this article are summarized as follows: i. We proposed an OPF model that consists of four important operational objectives such as fuel cost, pollutant emission, transmission loss and voltage stability index. ii. Fuzzy decision making mechanism is incorporated in ALO and is used to solve MO-OPF problem for the first time in literature. iii. The Best Compromise Solution (BCS) is obtained for the proposed OPF model over the recent report.and not as an independent document. Please do not revise any of the current designations. D. Paper Organisation The rest of the paper is organized as follows. The framework of the proposed multi-objective OPF model is given in section II. Section III gives a brief introduction about ALO algorithm and the implementation of the proposed technique to the MO-OPF problem. Simulation results are presented in Section IV, and these results are compared to other methods, that were used for solving the OPF problem. Finally, the conclusion is presented in Section V. II. OPF MODEL The OPF problem is a non-linear, non-convex optimization problem which determines the optimal control variables for minimizing certain objectives subject to several equality and inequality constraints. Minimize, Fi(x,u) OPF The control variable u can be expressed as (uT): [ PG 2 ,...,PGNG, VG1,...,VGNG, T1,...,TNT , Qc1,...,QcNC ] (5) A. Cost Effective Objective This objective is to minimize the total fuel cost of the system that is represented as follows: NG FT (ai PGi 2 bi PGi ci ) (6) i 1 B. Environmental Objective The representation of emission function of SO2 and NOx which is expressed in ton/h is: NG E i i PGi i PGi 2 i exp( i PGi ) (7) i 1 C. Transmission Loss The objective function to minimize the real power transmission line losses (PL) in the system can be stated as: NL PL g k (Vi 2 V j 2 2ViV j cos( i j )) (8) k 1 C. Contributions of the Paper The Multi-Objective formulated as follows: xT [ PG1, VL1,...,VLNPQ, QG1,...,QGNG, S L1,...,S LNL ] (4) (MO-OPF) i=1,2……….Nobj problem is (1) The formulation of objective function with four objectives can be represented as, Fi(x) = Min [F, E, PL, Lindex] Subject to, g(x,u)=0; h(x,u) ≤ 0 The state variable x is expressed as: IJTRD | Nov-Dec 2016 Available [email protected] (2) (3) D. L-index Minimization In order to enhance the voltage stability of the system, the voltage stability indicator (Lindex) should be minimized. NG L j 1 F ji i 1 Vi Vj (9) Lindex =Lmax= max {Lj, j=1,2,....,NL} (10) E. Constraints The equality constraints are distinctive load flow equations which can be stated using (11)-(12). PGi PDi Vi NB V j (Gij cos ij Bij sin ij ) 0, iN PQ (11) j 1 QGi QDi Vi NB V j (Gij cos ij Bij sin ij ) 0, iNB (12) j 1 The inequality constraints characterize the system operating limits which are mentioned using (13)-(19). (13) VGimin VGi VGimax , i 1, ........,NG PGimin PGi PGimax , min max QGi QGi QGi , min max Ti Ti Ti , Qcimin Qci Qcimax , VLimin VLi VLimax , S Li max S Li , i 1, ........,NG (14) i 1, ........,NG (15) i 1, ........,NT (16) i 1, ........,NC (17) i 1, ........,NPQ (18) i 1, ........,NL (19) (13)-(15) represents generator constraints and the transformer, Shunt VAR settings are restricted by their upper and lower limits as in (16)-(17) respectively. The security constraints are included in (18)-(19). III. FUZZY SUPPORTED ALO A. ALO in Brief Inspired by the foraging behavior of ant lion‘s larvae, Seyedali Mirjalili has proposed a mathematical model to design an optimization algorithm known as Ant Lion Optimization (ALO). The ALO algorithm impersonates 87 International Journal of Trend in Research and Development, Volume 3(6), ISSN 2394-9333 www.ijtrd.com interface between ant lions and ants in the trap. Five main steps of hunting prey in ALO [42] are the random walk of ants, building traps, entrapment of ants in traps, catching preys and rebuilding traps. In the first step of ALO, to model the interactions between ant lions and ants in the trap, ants are necessitated to move over the search space and ant lions are consented to hunt them and become fitter using traps. A random walk is chosen for modeling ants‘ movement, since, during the search for food, the ants move stochastically in nature. The assumption considered in ALO is that ―The random walks of ants are affected by ant lion‘s traps‖ [42]. In building traps phase, a roulette wheel operator is used to select the ant lions based on their fitness during optimization. This mechanism offers high possibilities to the fitter ant lions for grasping ants. To prevent the trapped ants from escaping the radius of ants‘s random walks, hyper-sphere is reduced adaptively. In the final stage of hunting behavior, when an ant reaches the bottom of the pit it is caught in the ant lion‘s jaw. Then, the ant lion pulls the ant inside the sand and consumes its body. In ALO, it is assumed that every ant randomly walks around a selected ant lion and the elite. B. Decision Making with Multi-Objective Solution The OPF problem is formulated as a multi-objective search, aiming at searching for a set of control variable settings that are comparatively ‗equally good‘ for multiple objectives. In order to select a suitable representative solution for the multiple objectives, Pareto-optimality concept is used. To evaluate the solutions on the Pareto front, a membership function [42] is utilized. Therefore, the ith objective value of solution p is normalized using: ip 1 if Fi F imin F max -F i i max if F imin Fi -Fi min Fi if Fi F imax 0 F imax (20) Nobj M Nobj i 1 p 1 i 1 (22) ALi, j x min rand * ( x max - x min j j j ) (23) Step 4: Run Newton-Raphson load flow and calculate the objective functions for all ants and ant lions subject to constraints. Step 5: Frame J(x) using the computed objective function values as: (24) J ( x) [ F1 ( x) F2 ( x) F3 ( x) F4 ( x)] Step 6: Formulate fuzzy membership function using (20) for all objective function values. Step 7: Compute the values of p for each search agent using (21), the value having maximum value of p is the BCS (elite). Step 8: For every ant select an ant lion using Roulette wheel. Step 9: Update the minimum (rk) and maximum (mk) bounds of variables using, r (25) rk k C m (26) mk k C Step 10: Generate a random walk and normalize it. Step 11: Update the position of ant and compute the objective functions for all ants. Step 12: Calculate membership function for all ants and find the BCS. Step 13: Update elite, if an ant lion becomes fitter than the elite. Step 14: Termination criterion: If the iteration value exceeds the maximum number of iterations, print the optimal results, otherwise goto Step 8. “Fig. 1,” depicts the flowchart for the implementation of FSALO algorithm for solving MO-OPF problem. IV. SIMULATION RESULTS AND ANALYSIS The normalized membership function is computed by, p ( ip) /( ip) Ai, j x min rand * ( x max - x min j j j ) (21) The solution p with the largest membership function p is considered as the best representative solution. C. Implementation of FSALO to MO-OPF The fuzzy set theory is introduced for multi-objective optimization using ALO and is made possible with simple modifications in Steps 5-7 and 12. The implemented procedure of the Fuzzy Supported ALO (FSALO) algorithm for solving MO-OPF problem can be summarized as follows: In order to illustrate the effectiveness of the proposed methodology, four benchmark systems such as IEEE-30 bus, New England 39 bus and IEEE-118 bus systems are considered. The proposed methodology has been implemented in Matlab7.9 programming language and executed on Intel(R) core(TM) i3 CPU 3 GHz with 3 GB RAM. The following control parameters have been chosen for the ALO to obtain the optimal results: PS=50 and Itermax=500. The following four cases are studied to analyze the efficacy of the proposed approach: Case 1: All the objectives are optimized individually (FT, E, PL, Lindex) Case 2: Bi-objective optimization (FT and PL, FT and Lindex, PL and Lindex, FT and E, PL and E, Lindex and E) Step 1: Initialize the system data including maximum and minimum values of control variables such as power outputs of generating units, voltages, transformer taps and shunt capacitors. Case 3: Tri-objective optimization (FT, PL and Lindex, FT, PL and E, FT, E and Lindex, E, PL and Lindex) Step 2: Initialize ALO variables such as number of search agents (ants and ant lions) (Ps) and maximum number of iterations (Itermax). To demonstrate the proposed OPF model in ALO algorithm, the objectives such as total fuel cost, total emission, transmission loss and L-index are minimized individually in Case 1. Table I shows the optimal settings of control variables obtained after single objective optimization. Further two, three and four objectives optimizations are carried out by the FSALO algorithm in cases 2, 3 and 4 respectively. Step 3: Generate the initial population: Obtain the initial population matrix of ants (Ai,j), ant lions (ALi,j) according to the number of ants, ant lions and dimension of the OPF problem (number of control variables) (Nd) using (22) - (23) as, IJTRD | Nov-Dec 2016 Available [email protected] Case 4: Tetra-objective optimization (FT, PL, Lindex, E) 88 International Journal of Trend in Research and Development, Volume 3(6), ISSN 2394-9333 www.ijtrd.com PG11 PG13 V1 V2 V5 V8 V11 V13 T11 T12 T15 T36 Qc10 Qc12 Qc15 Qc17 Qc20 Qc21 Qc23 Qc24 Qc29 START Initialize system data, number of ants, ant lions and maximum number of iterations sesearchagents Initialize the population of ants and ant lions according to (22) - (23) Compute the value of objective function for each ant & ant lion subject to constraints Form J(x) for each ant and ant lion Formulate fuzzy membership function for all fitness values and determine elite k=1 Select an ant lion for every ant using Roulette wheel Case 1: In this case, all the objective functions are optimized individually using ALO and the best value of FT, obtained using ALO is found to be 798.6718 $/h and the corresponding control variables settings are shown in Table I. Obtained result from the proposed ALO for this test system are shown in Table II and compared with the results of 40 other solution methods. It is seen that the ALO outperforms other methods reported in the literature. Update minimum and maximum bounds of variables Create a random walk, normalize it and update the position of ant Calculate the objective function values, Form J(x) and Formulate fuzzy membership values for all objectives k= k+1 In the view of economy and security operation of power plant, Emission (E), transmission losses (PL) and Lindex should also be regard as objectives in the OPF problem. Therefore, the three objectives E, PL and Lindex are added in our proposed model. The best values of E, PL and Lindex found using ALO are 0.20479 ton/h, 2.795 MW and 0.0953 respectively which are lesser than the results obtained using different techniques reported in the literature. Table III shows the capability of ALO for getting best values of E, PL and Lindex when compared with various algorithms applied to solve the OPF problem and the optimal control settings for the variables acquired using ALO are given in Table I. YES Is Ant lion fitter than elite? Update the position of elite NO Retain the position of elite NO Is k≧Itermax? YES Print the results STOP a. Fig. 1. Flowchart for implementation of ALO to OPF problem. A. Test System 1: IEEE-30 Bus System To authenticate the performance of the proposed algorithm, a standard IEEE 30 bus system comprising of 6 generating units at buses 1, 2, 5, 8, 11 and 13, 4 transformers with offnominal tap ratio in the lines 6–9, 6–10, 4–12 and 27–28 and reactive power injection at the buses 10, 12, 15, 17, 20, 21, 23, 24 and 29 is considered. The test system data are adopted from [3, 40]. Table 1: Optimal Control Settings Obtained Using Alo – Ieee30 Bus System – Case 1 Control variables PG1 PG2 PG5 PG8 13.0663 30 22.5758 29.8510 13.2438 40 13.9669 39.9213 1.1 1.1000 1.1000 1.1 1.09 1.0973 1.0900 1.1 1.06 1.0900 1.0352 1.1 1.0584 1.0992 1.0800 1.1 1.07 1.0431 0.9765 1.1 1.07 1.0800 1.0396 1.1 1.1 1.0020 1.1000 0.9909 0.9208 1.0791 0.9392 0.9740 1.0765 1.0962 1.1000 0.9682 1.0173 1.0334 1.0574 0.9808 3.5873 5.0000 1.1770 5.0000 3.0691 5.0000 5.0000 5.0000 4.6059 4.3601 1.9008 4.5499 3.0701 5.0000 2.2973 5.0000 5 4.4947 3.4300 5.0000 5 5.0000 2.4233 5.0000 2.2871 4.5101 4.6311 5.0000 3.1504 5.0000 1.2573 5.0000 3.2 3.1509 1.5064 3.7288 PGi in MW; Vi in p.u; T in p.u.; Qc in p.u. Case 2: This case presents the results obtained after biobjective optimization of objectives such as FT and PL, FT and Lindex, PL and Lindex, FT and E, PL and E, Lindex and E. Obtained control settings from the ALO for this test case are presented in Table IV and the results are compared with earlier reports. The values of FT and PL obtained using ALO are 822.3986 $/h and 5.2449 MW respectively. Table 2: Comparison Of Results For Total Fuel Cost Minimization – IEEE-30 Bus System – Case 1 Methods Gradient method [13] SFLA [38] Modified DE [38] MSFLA [39] PSO-Fuzzy [29] GSO [23] Stochastic GA [23] EGA [13] MTLBO [40] Cost ($/h) 804.853 802.509 802.376 802.287 802.19 802.188 803.7 802.06 801.892 E(ton/h) NR 0.3720 NR 0.3723 NR NR NR NR 0.3665 PL(MW) NR NR 9.459 9.6991 10.083 NR NR L-index NR NR NR NR 0.12256 NR NR NR NR NR NR Hybrid SFLA-SA [17] 801.79 NR NR NR FT E Lindex PL AGSO [23] 801.75 NR NR NR 179.189 3 49.1102 18.0293 19.2931 64.053 3 67.500 6 50 35 165.478 293 29.8831 28.8279 27.4782 51.5040 79.9299 49.9888 35.0000 HMPSO-SFLA [37] 801.75 NR 9.54 NR PSO [28] GWO [32] 800.41 801.41 NR NR NR 9.3 NR NR IJTRD | Nov-Dec 2016 Available [email protected] 89 International Journal of Trend in Research and Development, Volume 3(6), ISSN 2394-9333 www.ijtrd.com NR NR DE [32] MICA [16] MICA-TLA [16] ABC [18] GABC [15] DSA [28] BHBO [13] 801.23 801.079 801.048 800.66 800.440 800.388 799.921 NR NR 0.20482 NR 0.36672 NR 9.22 9.1923 9.1895 9.0328 NR 8.9819 8.6793 AGA [12] 799.844 NR 8.9166 NR EGA-DQLF [29] 799.56 NR 8.697 0.111 8.7558 8.615 NR 8.6591 8.63 8.63 8.6543 8.6260 8.62457 8.48 8.615 8.61 8.6132 NR NR 8.94 8.38604 8.532 NR 0.1226 NR 0.1176 NR 0.1277 0.1273 0.1159 0.1164 NR 0.11796 0.1197 0.1261 NR 0.1265 NR 0.1307 0.1076 LTLBO [7] DE [1] LCA [14] IEM [14] BBO [19] FIDE [34] BSA [27] TLBO [25] Hybrid PSOGSA [22] GSO [39] ABPPO [24] EADDE [2] ICBO [26] IGA [21] KHA [21] MADE [40] GSA [3] ALO 799.436 0.3672 799.289 NR 799.197 NR 799.182 NR 799.111 NR 799.082 NR 799.076 0.3671 799.071 NR 799.070 NR 799.06 NR 799.056 NR 799.054 NR 799.035 NR 800.805 NR 799.031 NR 798.73 NR 798.675 NR 0.3722 798.672 NR - Not Reported NR NR 0.1381 NR 0.12624 0.1302 The percentage increase in values of cost and loss with respect to case 1 are 2.89% and 46.71% respectively. When FT, Lindex and PL, Lindex are considered to optimize simultaneously, BCS obtained using ALO are 0.05%, 2.66% and 6.4% and 8.89% respectively higher than the single objective optimized values. It is evident from Table VI that the result obtained by the proposed approach is least against other approaches which shows the capability of FSALO for getting the best BCS when compared with other techniques that are reported in the literature. Table 3: Comparison of Results – IEEE-30 Bus System Cost E (ton/h) ($/h) Emission minimization BSA [27] 835.0199 0.2425 SFLA [38] 960.1911 0.2063 GSO [23] NR 0.206 AGSO [23] NR 0.2059 DSA [28] 944.4086 0.2058 IPSO [33] 954.248 0.2058 MSFLA [38] 951.5106 0.2056 HMPSO-SFLA [38] NR 0.2052 TLBO [40] 947.4392 0.20503 MTLBO [40] 945.1965 0.20493 ABC [18] 944.4391 0.20483 944.0706 ALO 0.20479 Transmission loss minimization IPSO [33] 941.672 0.20807 BHBO [13] 924.1365 NR PSO-Fuzzy [29] 956.45 NR GWO [32] 968.38 NR DE [32] 968.23 NR EGA-DQLF [29] 967.86 NR ABC [18] 967.6810 0.20727 DSA [28] 967.6493 0.20826 MOHS [36] 964.5121 NR TLBO [36] 967.0371 NR QOTLBO [36] 967.0371 NR IEM [14] 967.1147 NR ABPPO [24] 966.4081 NR Methods IJTRD | Nov-Dec 2016 Available [email protected] PL (MW) Lindex 5.0526 NR NR NR 3.24373 5.362 NR NR NR NR 3.247 3.164 0.1266 NR NR NR 0.12734 0.1131 NR NR NR NR 0.1402 0.1425 5.0732 3.7545 3.6294 3.41 3.38 3.2008 3.1078 3.0945 2.9678 2.8834 2.8834 2.8699 2.867 0.1294 0.1371 0.1286 NR NR 0.12178 0.1386 0.12604 0.1154 0.1262 0.1262 0.1156 0.11611 FIDE [34] ALO ABC [18] DSA [28] FIDE [34] Hybrid PSOGSA [22] DE [1] TLBO [25] IEM [14] ABPPO [24] TLBO [36] PSO-Fuzzy [29] EGA-DQLF [29] IPSO [33] MOHS [36] QOTLBO [36] KHA [21] ALO 967.0002 NR 966.2086 0.2073 L-index minimization 801.6650 0.3643 967.4718 NR 915.2172 NR 801.22928 NR 807.5272 NR 805.0087 NR 799.8349 NR 877.3579 NR 912.5914 NR 837.06 NR 898.817 NR 866.11393 0.24709 895.6223 NR 844.1237 NR 919.6706 NR 806.639 0.3333 NR - Not Reported 2.8535 2.795 0.1262 0.1346 9.2954 3.4217 3.626 9.26567 10.3142 8.42603 8.9477 4.679 3.7474 8.8209 6.092 14.001 4.3244 7.2826 NR 5.2622 0.1379 0.1244 0.1243 0.12393 0.1219 0.11671 0.1144 0.11388 0.1003 0.11055 0.10402 0.1037 0.1006 0.0994 0.09754 0.0953 Along with these combinations of bi-objectives, the stated approach deliberates on concurrent optimization of FT and E, PL and E, Lindex and E. The FSALO attains BCS values of 867.5875 $/h and 0.2247 ton/h, 2.9804 MW and 0.2054 ton/h, 0.1049 and 0.2269 ton/h while considering simultaneous minimization of FT and E, PL and E, Lindex and E respectively. It is worthwhile to note that the bi-objective optimization of PL and E, Lindex and E using FSALO yields better results as compared to IPSO [33]. Table 4: Optimal Control Settings Obtained Using ALO – IEEE-30 Bus System – Case 2 Control variable PG1 PG2 PG5 PG8 PG11 PG13 V1 V2 V5 V8 V11 V13 T11 T12 T15 T36 Qc10 Qc12 Qc15 Qc17 Qc20 Qc21 Qc23 Qc24 Qc29 PL , E Lindex, E 130.25 168.39 91.34 97.575 65.12 46 81 2 96 11 50.459 49.347 60.433 68.03 66 4 6 79 57 18.261 21.183 31.233 49.10 50 5 7 2 25 33.405 19.145 34.12 35 35 8 0 11 29.209 15.650 23.01 30 30 6 8 67 17.290 21.02 35.580 27.058 40 9 75 101 1.1 1.1 1.1 1.1 1.07 1.053 1.0882 1.1 1.07 1.0662 8 1.020 1.027 1.07 1.0651 1.05 4 5 1.018 1.044 1.09 1.1 1.0607 1 2 1.038 1.0744 1.07 1.05 1.07 2 1.030 1.028 1.0946 1.07 1.0554 8 6 1.084 1.079 1.0217 1.1 1.1 2 2 0.931 1.056 1.0271 1.1 0.9239 3 2 0.997 1.078 1.0214 1.0867 1.0283 8 7 1.061 0.9764 1.0472 1.0436 0.9 6 2.482 4.6358 1.1834 5.0 5.0000 6 0.140 3.501 2.8891 4.7607 2.6750 1 2 1.941 3.290 4.4853 3.956 1.0000 9 8 2.652 3.5895 2.368 5.0 4.7870 2 4.525 2.193 5 5 5.0000 0 3 2.468 2.703 5 5 5.0000 1 8 1.639 2.285 4.4293 4.0953 2.0000 1 2 4.784 0.029 2.5373 5 2.6240 4 5 2.790 4.753 1.9212 5 4.0000 PGi in MW; Vi in p.u; 6T in p.u.; Qc in p.u. 6 101.3 294 52.68 67 50.00 00 28.79 92 28.66 43 26.96 91 1.1 1.1 1.078 3 1.056 9 1.05 0.991 4 1.1 1.1 1.046 5 0.923 3 1.292 4 2.000 0 2.416 7 0.754 8 0.101 3 4.161 1 3.311 1 2.277 5 1.737 1 FT, PL FT , Lindex PL , Lindex FT, E Table 5: Optimal Control Settings obtained using ALO – IEEE-30 Bus System Control variable PG1 PG2 PG5 PG8 PG11 PG13 V1 Tri-objective optimization FT, PL, FT, PL, FT, E, E, PL, Lindex E Lindex Lindex 159.950 94.629 115.04 91.846 28.5401 79.249 44.002 72.610 3 3 76 8 37.4583 29.169 38.227 48.103 7 17.0711 34.956 32 34.638 6 9 9 19.1151 27.787 21.337 21.231 4 3 26.8822 24.777 39.998 22.127 7 3 8 1.1 1.1 1.1 1.1 5 6 6 Tetraobjective optimization 109.1106 79.2819 44.2315 30.5712 15.5443 12.1947 1.1 90 International Journal of Trend in Research and Development, Volume 3(6), ISSN 2394-9333 www.ijtrd.com V2 V5 V8 V11 V13 T11 T12 T15 T36 Qc10 Qc12 Qc15 Qc17 Qc20 Qc21 Qc23 Qc24 Qc29 1.086 1.0771 1.0083 1.0794 1.06 1.05 1.1 1.06 1.0497 1.0389 0.9666 1.0723 1.0769 1.09 1.1 1.0188 1.0585 1.0692 1.08 1.0244 1.0399 0.9986 1.0229 1.0023 0.9218 1.0483 1.0337 1.0142 1.0091 0.9 1.0050 1.0104 1.0842 1.1 1.0305 1.0758 0.7696 5.0 3.1491 4.3422 1.4911 3.9231 1.9716 3.4159 2.4902 4.9495 5.0 4.9607 0.8842 0.5740 0.8312 4.0087 0.5773 5.0 5.0 5.0000 4.1422 4.0948 5.0 2.9583 3.5606 0.7832 5.0 2.3273 3.7278 0.9801 5.0 3.0504 2.5456 1.0531 3.4632 1.7635 PGi in MW; Vi in p.u; T in p.u.; Qc in p.u. 869.9272 $/h, 7.1695 MW, 0.2328 ton/h and 868.1073 $/h, 0.2404 ton/h, 0.1175 respectively. The corresponding optimal control settings are provided in Table V. The three dimensional Pareto solutions with projection views of threeobjective optimization problem are depicted in Fig. 2. When E, PL and Lindex are considered as tri-objectives, the increase in E, PL and Lindex level with respect to case 1 are found to be 9.94%, 60.96% and 19.17% respectively. 1.09 1.06 1.0548 1.05 1.05 1.1 1.0412 1.1 1.0959 3.471 2.6054 4.176 5.0 5.0 5.0 4.0 5.0 2.0304 Table 6: Comparison of Results for Multi-Objective Optimization – IEEE-30 Bus System Objectives Methods FT E PL Bi-objective optimization NR 822.87 5.61 EGA-DQLF [29] 3 NR 847.011 5.66 PSO-Fuzzy [29] 58 MOEAD/DRA NR 827.717 5.26 [31] MOTLA/D [31] NR 826.446 5.30 FT, PL 74 MOABC/D( [31] NR 827.636 5.24 ABPPO [24] NR 51 822.769 5.45 PSOGSA [22] 3 NR 2 822.406 5.46 FIDE [34] 820.880 31 NR 826 5.59 2 0.2645 49 FSALO 822.398 5.24 6 49 NR NR 802.06 EGA-DQLF [29] NR NR 809.79 PSO-Fuzzy [29] MOEAD/DRA NR NR 799.111 [31] MOTLA/D [31] NR NR 799.116 MOABC/D [31] NR NR 799.064 FT, Lindex KHA [21] NR 3.40 801.863 62 ABPPO [24] 3 NR 8.61 799.069 9 PSOGSA [22] 6 NR 9.27 801.229 FIDE [34] NR 8.60 799.691 2 2 ICBO [26] NR 8.64 799.327 65 7 BSA [27] NR 8.49 800.334 04 0 0.3414 7.61 FSALO 799.044 61 3 NR NR 3.15 EGA-DQLF [29] 81 NR NR 5.57 PSO-Fuzzy [29] 79 NR NR PL, Lindex IPSO [33] 7.91 3 960.321 NR ABPPO [24] 2.98 9 9 892.348 0.2245 FSALO 2.98 8 62 872.853 0.2249 NR SFLA [38] 3 0.2247 NR FT, E MSFLA [38] 867.713 6.42 FSALO 867.587 0.2247 31 5 0.2066 5.16 IPSO [33] NR PL, E 2 939.109 FSALO 0.2054 2.98 4 04 NR 0.2286 IPSO [33] NR Lindex, E 894.331 8.01 FSALO 0.2269 7 31 Tri-Objective optimization NR 5.69 EGA-DQLF [29] 844.5 FT, PL, NR 7.22 PSO-Fuzzy [29] 836.96 Lindex 07 0.3171 FSALO 828.298 5.61 5 71 FT, PL, E 869.927 0.2328 7.16 2 95 FT, E, Lindex 7.21 868.107 0.2404 FSALO 34 3 E, PL, Lindex 903.559 0.2274 7.15 8 NR - Not Reported 91 FT in ($/h); E in (ton/h); PLin MW; Lindex NR NR NR NR NR NR NR NR 0.1158 0.1056 0.1146 (a) (b) 0.1287 0.1287 0.1288 0.1092 0.1148 1 0.12 0.1249 39 0.1252 0.1259 0.0979 0.1049 0.1140 0.1073 0.1140 8 0.1046 NR NR 0.1174 NR 0.1332 0.1051 0.1049 0.1084 0.1091 0 0.1067 0.1391 0.1175 0.1179 Case 3: During tri-objective minimization of FT, PL and Lindex, the BCS value acquired using FSALO algorithm is 828.2985 $/h, 5.6171 MW and 0.1067 respectively. The BCS values reported so far in the literature are given in Table VI. It can be deduced from the results that the FSALO performs better in finding the FT, PL and Lindex optimally. The tri-objective optimization of FT, PL, E and FT, E, Lindex yields BCS values of IJTRD | Nov-Dec 2016 Available [email protected] Case 4: In the literature, few attempts have been made at simultaneous optimization of four objectives which always exist in real-time power system operations. Herein, the proposed algorithm has been employed to optimize simultaneously all the considered objectives (FT, E, PL and Lindex) and the BCS obtained is 878.2416 $/h, 0.2514 ton/h, 7.5342 MW and 0.1204. The corresponding control settings are given in Table V and the percentage increase level in the values of objectives with respect to case 1 are 9.06, 18.54, 62.9 and 20.85 respectively. (c) (d) Fig. 2. Pareto optimal front for three objectives – IEEE 30 bus system: (a) Cost, Loss and L-index, (b) Cost, Loss and Emission, (c) Cost, emission and L-index (d) Emission, Loss and L-index B. Test System 2: New England 39 Bus System To demonstrate the practical application of the proposed approach, New England 39 bus system consisting of 10 generating units interconnected with 46 branches of a transmission network is considered. The bus data and the branch data are taken from [35]. Case 1: During individual optimization of objectives, the best value of cost obtained using ALO is 350660 $/h which is comparatively less by 0.04% than SPEA2 [35]. The settings of the control variables for the results obtained using ALO is given in Table VII. The best values of E and Lindex are found to be 317.9566 ton/h and 0.1593 respectively (Table VIII) and when compared to SPEA2, the percentage of reduction in E is 0.09. Case 2: In the bi-objective optimization process, the trade off values between FT and E, FT and Lindex, E and Lindex are found to be 351700 $ /h and 9983.1 ton/h, 358700 $ /h and 0.1739, 8842 ton/h and 0.1729 respectively. 91 International Journal of Trend in Research and Development, Volume 3(6), ISSN 2394-9333 www.ijtrd.com Table 7: Optimal Control Settings obtained using ALO – New England 39 System Control variables PG30 PG31 PG32 PG33 PG34 PG35 PG36 PG37 PG38 PG39 V30 V31 V32 V33 V34 V35 V36 V37 V38 V39 T12-11 T12-13 T6-31 T10-32 T19-33 T20-34 T22-35 T23-36 T25-37 T2-30 T29-38 T19-20 Single objective optimization FT 168.32 16 311.62 16 455.05 67 307.47 42 742.39 15 773.65 09 900.03 10 857.25 05 485.10 00 499.10 20 1.0016 0.94 1.006 0.9818 0.94 1.06 0.9671 1.0225 0.9683 0.9471 0.907 0.9 0.9024 0.9293 0.9466 1.0156 1.0984 0.9 0.9629 1.0923 1.0912 1.1 E 472.04 48 547.03 22 584.11 00 591.20 00 591.01 00 600.30 10 557.00 10 560.00 00 494.00 10 503.30 00 1.0185 1.0087 0.9737 0.9612 1.0131 0.9746 0.94 1.0121 1.0195 1.06 1.1 1.0709 0.9881 1.1 1.0496 1.0433 0.9021 1.0679 1.0424 1.1 0.9294 0.9659 Bi-objective optimization Lindex FT , E FT, Lindex 137.000 49.9083 250.1800 0 300.000 300.801 435.0100 0 3 404.524 551.089 444.2000 4 0 300.000 598.968 681.5400 0 1 700.000 570.168 686.9300 0 2 781.153 605.435 510.0800 2 4 889.242 718.148 684.7200 9 5 893.881 814.811 514.0900 0 0 583.721 551.300 540.4000 7 4 597.568 508.344 498.1000 6 3 0.9677 1.0078 0.9677 1.0225 0.96 1.0497 1.0057 0.968 1.0058 0.94 1.0443 0.94 1.0044 0.9797 1.0044 0.94 1.0448 0.94 1.0165 1.0453 1.05 1.06 1.0464 1.06 0.9727 0.9560 0.9551 0.9743 0.9808 0.9586 0.98 0.9322 0.98 0.9 1.0580 0.9 0.9 1.0669 0.9 0.9 1.0163 0.9 0.9 0.9000 0.9 1.0628 0.9605 1.0606 0.98 1.0899 0.98 0.9668 0.9380 0.9664 0.9499 1.0684 0.9487 0.9598 1.0775 0.9597 0.97 0.9245 0.9698 0.9292 0.9000 0.9266 PGi in MW; Vi in p.u; T in p.u. It is clear from the BCS values, that the proposed approach is superior and preserves the diversity of the non-dominated solutions over the trade-off front. Case 3: The tradeoff curve in three facet for the 20 generated Pareto optimal solutions of the FSALO algorithm is depicted in Fig. 3 which clearly shows the relationships among FT, E and Lindex. The increase in FT, E and Lindex are 2.75%, 97.52% and 11.01% respectively with respect to case 1. E, Lindex 109.5579 326.4515 445.6551 460.3871 761.6523 733.1450 800.0000 700.0000 600.0000 563.1512 0.9665 1.0225 1.0059 0.94 1.0052 0.94 1.05 1.06 0.9552 0.9587 0.9792 0.9 0.9 0.9 0.9 1.0791 0.9794 0.9676 0.9479 0.96 0.9697 0.9286 Tri-objective optimization FT, E, Lindex 303.2200 300.0000 405.2526 395.7044 703.0631 653.5961 798.0000 800.0000 548.9265 523.6173 0.9572 1.05 1.0057 0.94 1.0055 0.94 1.0362 1.06 0.99 0.9542 0.9743 0.9 0.9 0.9 0.9 1.0648 0.9765 0.9666 0.9441 0.9599 0.9698 0.9286 C. Test System 3: IEEE-118 Bus System The aim of this example is to demonstrate the effectiveness of the proposed method for the large scale IEEE-118 [42] bus system which consist of 54 thermal units, 64 loads, 9 transformer settings and 12 shunt capacitor var injections. The total system demand is 4242 MW and base MVA is assumed as 100. The chosen objectives such as FT, E, PL and Lindex are minimized in the multi-objective frame and the obtained values are 47768 $ /h, 3465.2 ton//h, 103.77 MW and 0.1176 respectively. It can be inferred from Table IX, that the results obtained using FSALO outperforms the results by MABC [42]. The proposed ALO takes execution time of about 280 s for the chosen complex large scale system. Table 9: Comparison of Results for Tetra Objective Optimization – IEEE-118 Bus System Methods MABC [45] ALO Fig. 3. Pareto optimal front – New England 39 bus system : Case 3 Table 8: Comparison of Results – New ENgland 39 Bus System Objective FT E Lindex Cost E ($/h) (ton/h) Single objective optimization SPEA2 [35] 350810 76814 76638 ALO 350660 SPEA2 [35] 396590 318.083 396220 ALO 317.9566 372310 91132 ALO Methods IJTRD | Nov-Dec 2016 Available [email protected] L-index NR 0.1867 NR 0.1926 0.1593 FT ($/h) 47823 47768 E (ton/h) 3502.2 3465.2 PL(MW) 120.31 103.77 Lindex NR 0.1176 D. Solution Quality From Tables II, III, IV and VIII it is clear that the minimum values of FT, E, PL and Lindex for all the considered test systems are best and less compared to that reported in literature emphasizing its better solution quality. Further, for IEEE-118 and New England test systems, ALO exhibited better performance when compared with other algorithms. As the best values in ALO are better as compared to other approaches, it only indicates its ability to reach global minima in a consistent manner and its better convergence characteristics. Due to limitations of space, the convergence and robustness characteristics are not provided in the article. The computational time taken for all the test systems is less 92 International Journal of Trend in Research and Development, Volume 3(6), ISSN 2394-9333 www.ijtrd.com which indicates that the time taken by the proposed approach does not increase greatly as the system size increases. Generally, the test on a large scale system requires long computation time to converge and large memory requirement. These two major obstacles are overcome by ALO in solving OPF problems. Succinctly, considering all the results for study with different dimensions and constraints it can be concluded that ALO yields better optimal solutions with less computational effort in terms of cost, emission, transmission loss and L-index than the previously reported results. CONCLUSIONS The major focus of this paper is to present the application of ALO to optimal P-Q dispatch in power system. The realistic OPF is complicated because of multiple objectives and hardly, very few reports in the literature have been made with four objectives. The algorithm has been tested and examined with different objectives such as fuel cost, emission, loss and L-index for standard IEEE-30, IEEE-118 and New England power systems. Detailed case studies are presented to demonstrate the application of the proposed scheme. The Pareto based approach have the advantage of including multiple criteria without the need of introducing weights. Case studies with single objective, bi-objective, tri-objective and four objectives are performed to check the performance, accuracy, robustness in comparison with the other reports in the literature. The advantages of the exploitation of ALO for MO-OPF are as follows: The search mechanism of ALO works well for unknown, challenging search space that helps to identify the optimal real/reactive power settings. As there is no relation between search agents and the fitness functions in the updating process of ALO, this facility avoids trapping in local optima and explores the best solution for MO-OPF problems. Following the results of the proposed approach many interesting topics such as incorporation of multi-objective framework in reserve constrained dynamic OPF problem are worth investigating in future research work. List Of Abbreviations And Acronyms Fi ith objective function g,h Equality and inequality constraints x, u Vector of dependent and control variables VG, VL Generator and load voltages PG, QG Real and reactive power of generators Qc Reactive power injections T Transformer tap settings SL Transmission line loading NG Number of generator buses NL Number of transmission lines NB Number of buses NPQ Number of load buses NT Number of regulating transformers NC Number of VAR compensators ai,bi,ci Cost coefficients of ith generator αi,βi,γi,εi,λi Emission coefficients of ith unit gk Conductance of transmission line k V, δ Voltage magnitudes, phase angles of buses Fji Partial inversion of Ybus matrix PDi, QDi Real and reactive power demand at ith bus Gij Transfer conductance between i and jth bus Bij Susceptance of the line between i and j bus rand Random values in the range (0,1) ximax, ximin Upper and lower bounds of control variables IJTRD | Nov-Dec 2016 Available [email protected] Fimin, Fimax Minimum and maximum value of ith objective function among all non-dominated solutions M Total number of non-dominated solutions Nobj Number of objective functions Itermax Maximum number of iterations C Ratio that relates current iteration, Itermax BBO Biogeography Based Optimization MOEAD Multi-Objective Evolutionary Algorithm /DRA based on Decomposition with Dynamical Resource Allocation MOTLA/D Multi-Objective Teaching-Learning Algorithm based on Decomposition MOABC/D Multi-Objective ABC Algorithm based on Decomposition Acknowledgment The authors gratefully acknowledge the authorities of Annamalai University, Annamalai Nagar, Tamilnadu, India, for providing facilities to carry out this research work. 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