Sizing and Allocation of Distributed Energy Resources for Loss Reduction using Heuristic Algorithms Ali Parsa Sirat, Hossein Mehdipourpicha, Niloofar Zendehdel, and Hamid Mozafari Missouri University of Science and Technology Abstract—Loss minimization in distribution networks (DN) is of great significance since the trend to the distributed generation (DG) requires the most efficient operating scenario possible for economic viability variations. Moreover, voltage instability in DNs is a critical phenomenon and can lead to a major blackout in the system. The decreasing voltage stability level restricts the increase of load served by distribution companies. DG can be used to improve DN capabilities and brings new opportunities to traditional DNs. However, installation of DG in non-optimal places can result in an increase in system losses, voltage problems, etc. In this paper, genetic algorithm (GA), harmony search algorithm (HSA) and improved HSA have been applied to determine the optimal location of DGs. Simulation results for an IEEE 33 bus network are compared for different algorithms, and the best algorithm is stated for minimum losses. Index Terms—Distributed Energy Resources, Genetic Algorithm, Harmony Search Algorithm, Loss Reduction, Radial Distribution System. NOMENCLATURE Pi , Qi The injected active/reactive powers to i th bus Vi , i The voltage magnitude/phase angle at bus i Yij , ij The magnitude/argument of the ij th element of Ybus matrix N Number of Buses [P] abc , [Q]abc Three phase real/reactive powers vectors [V] abc Three-phase voltage Magnitude vector [δ]abc Three-phase voltage phase angle vector YBabc The elementary three-phase YBUS matrix [P] abc , [Q]abc Three phase real/reactive power vectors PL , Total power losses of DN m Number of lines in the DN Rj Resistance of j th line |Ij| Magnitude of j th line current PGi Generated power at i th bus including DER units PDi Power demand at i th bus including DER units Vi , wiV Voltage amplitude and associated weighting factor for the i th bus, respectively Vref,j Nominal voltage magnitude which is assumed to be 1 for all load buses (i.e., PQ buses) and to be equal to the specified value for generation buses (i.e., PV buses) NB, NL Number of system buses and lines, respectively HMS Harmony memory size or the number of solution vectors in the harmony memory HMCR Harmony memory considering rate PAR Pitch adjusting rate NI Number of improvisations N Number of decision variables bw An arbitrary distance bandwidth for the continuous design variable U(–1,1) uniform distribution from –1 to 1 PAR(gn) Pitch adjusting rate for each generation PARmin , PARmax Minimum and maximum pitch adjusting rate, respectively NI Number of solution vector generations gn Generation number bw(gn) Bandwidth for each generation c Constant parameter I. INTRODUCTION Distributed/dispersed generation (DG) is an electrical power generation resource that is placed close to the load being served, usually at the customer site. DG may range from a few kilowatts to over 100 Megawatts and can be renewable-based micro-hydro, wind turbines, photovoltaic, etc. or fuel-based fuel cells, reciprocating engines, micro-turbines, etc. [1]-[2]. On one hand, the installation of distributed/renewable energy resources (DERs/RERs) in low-voltage (LV) and medium voltage (MV) grids can provide some advantages such as loss reduction, voltage control, power stress reduction in distribution lines, power quality enhancement, and the reduction of costs and pollution caused by conventional fossil fuel power [3]-[8]. On the other hand, these resources may lead to some undesirable issues such as voltage profile fluctuations, increased short-circuit (SC) current, inversion in the power- flow direction, readjustment of control and protection systems, etc. [9] -[16]. Before installing DG, its effects on voltage profile, line losses, short circuit current, and the amounts of injected harmonic and reliability must be evaluated separately [2], [4]-[5]. Different factors such as choosing the best technology, size, location of DGs, type of network (radial, meshed), and other factors. are considered in the planning of DNs. Based on this issue, the effects of DERs in DN, including the voltage profile, stability, cost, total harmonic distortion and reliability should be taken into account [2], [4]. The problem of allocation and sizing of DER units is of great importance. The inappropriate selection of location and capacity of DERs may lead to more system losses comparing to the normal system without DER units. Thus, the use of an