Short Communication Discussion of ‘‘Reserve constrained multi-area economic dispatch employing differential evolution with time-varying mutation’’ by Manisha Sharma et al. ‘‘International Journal of Electrical Power and Energy Systems’’, 33 March (2011) 753–766 Kalpana Jain, Manjaree Pandit ⇑ Department of Electrical Engineering, M.I.T.S., Gwalior, India article info Article history: Received 11 March 2011 Received in revised form 1 December 2011 Accepted 12 January 2012 Available online 21 February 2012 Keywords: Prohibited operating zones Ramp rate limits Multi-area economic dispatch abstract This short communication presents a discussion of ‘‘Reserve constrained multi-area economic dispatch employing differential evolution with time-varying mutation’’ by Manisha Sharma et al. ‘‘International Journal of Electrical Power and Energy Systems’’, 33 March (2011) 753–766. The discussed paper pre- sented a multi-area economic dispatch solution for a large 40-unit system having complexities like valve point loading effects, ramp rate constraints, prohibited operating zones and transmission constraints for a large 40-unit system. Multi-area economic dispatch for such a large and complex system was not reported before in available literature. However in the reported results one unit is violating the con- straints. In this communication, corrected results with lesser costs than reported in the discussed paper are presented. Ó 2012 Elsevier Ltd. All rights reserved. The discussed paper [1] presented a multi-area economic dis- patch solution for a large 40-unit system having complexities like valve point loading effects, ramp rate constraints, prohibited oper- ating zones and transmission constraints for a large 40-unit system [2] which is test system III in [1]. Economic dispatch (ED) is a very important function in power system and it presents a large and complex constrained optimization problem. Many new nature inspired optimization methods such as differential evolution (DE) [1–3], particle swarm optimization (PSO) [4], evolutionary algorithm [5], bacterial foraging [6], hybrid PSO–DE [7] have been proposed in recent years for ED with different constraints. Multi-area economic dispatch for such a large and complex sys- tem was not reported before. The performance of different meth- ods was compared in Table 9 [1] of the paper. The best results for tie-line capacity (i) 1500 MW (ii) 2000 MW were reported in Table 10 [1]. The output of unit 11 in Table 10 [1] is 311.5121 MW (for tie-line capacity 2000 MW) which is violating the prohibited zone constraints, (300,350) in [2]. The optimal out- put of unit 11 is reported 375 MW (for tie-line capacity 1500 MW) which is violating the ramp rate limits (P o = 210; up rate 150 MW/ h, down rate 185 MW/h [2], which restrict the P 11 maximum limit to 360 MW in place of 375 MW). With correct formulation of ramp rate limits and prohibited zones the correct comparison of different methods in [1] is given in Table 1. The best dispatch obtained by DEC2 approach is presented in Table 2. The global minimum for this complex system is not yet known but the cost has significantly reduced from $1277 45.5241/h [1] to $123196.2498/h for tie-line limit 2000 MW and from $131549.6080/h [1] to $127344.8528/h for tie-line limit 1500 MW. References [1] Sharma Manisha, Pandit Manjaree, Srivastava Laxmi. Reserve constrained multi-area economic dispatch employing differential evolution with time- varying mutation. Int J Electr Power Energy Syst March 2011;33(3): 753–66. [2] Wang SK, Chiou J-P, Liu CW. Non-smooth/non-convex economic dispatch by a novel hybrid differential evolution algorithm. IET Gener Trans Distrib 2007;1(5):793–803. [3] Amjady Nima, Sharifzadeh Hossein. Solution of non-convex economic dispatch problem considering valve loading effect by a new modified differential evolution algorithm. Int J Electr Power Energy Syst 32(8);2010: 893-903. [4] Azadani E, Hosseinian SH, Moradzadeh B. Generation and reserve dispatch in a competitive market using constrained particle swarm optimization. Electr Power Energy Syst 32;2010:79–86. [5] Manoharan PS, Kannan PS, Baskar S, Willjuice Iruthayarajan M. Evolutionary algorithm solution and KKT based optimality verification to multi-area economic dispatch. Electr Power Energy Syst 2009;31:365–73. [6] Hota PK, Barisal AK, Chakrabarti R. Economic emission load dispatch through fuzzy based bacterial foraging algorithm. Electr Power Energy Syst 2010;32:794–803. [7] Gong Dun-Wei, Zhang Yong, Qi Cheng-Liang. Environmental/economic power dispatch using a hybrid multi-objective optimization algorithm. Electr Power Energy Syst 2010;32:607–14. 0142-0615/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. doi:10.1016/j.ijepes.2012.01.003 ⇑ Corresponding author. Tel.: +91 0751 2665962/2409380. E-mail address: manjaree_p@hotmail.com (M. Pandit). Electrical Power and Energy Systems 39 (2012) 68–69 Contents lists available at SciVerse ScienceDirect Electrical Power and Energy Systems journal homepage: www.elsevier.com/locate/ijepes