Overview of Electric Energy Distribution Networks Expansion Planning <s> II. DISTRIBUTION EXPANSION PLANNING MODEL A. VARIABLES <s> This paper presents a model for use in the problem of multistage planning of energy distribution systems including distributed generation. The expansion model allows alternatives to be considered for increasing the capacity of existing substations, for installing new ones, for using distributed generation, and for the possible change to feeders in terms of addition and removing feeders sections; combining, subdividing, and load transfer between feeders; and replacement of conductors. The objective function to be minimized is the present value of total installation costs (feeders and substations), of operating and maintaining the network, and of distributed generation. The model takes operational constraints on equipment capacities and voltage limits together into account with logical constraints, aimed at reducing the search space. This paper presents: (1) an extension to the linear disjunctive formulation to represent the inclusion, exclusion, and replacement of branches and (2) a generalization of constraints related to the creation of new paths which can be applied in more complex topologies. The resulting mixed integer linear model allows the optimal solution to be found using mathematical programming methods, such as the branch-and-bound algorithm. The validity and efficiency of the model are demonstrated in Part II of this paper. <s> BIB001 </s> Overview of Electric Energy Distribution Networks Expansion Planning <s> II. DISTRIBUTION EXPANSION PLANNING MODEL A. VARIABLES <s> This paper proposes a methodology to achieve integrated planning and projects for secondary distribution circuits. The planning model is formulated as a mixed integer nonlinear programming problem (MINLP). In order to resolve this problem, a tabu search (TS) algorithm is used, with a neighborhood structure developed to explore the physical characteristics of specific geographies included in the planning and expansion of secondary networks, thus obtaining effective solutions as well as low operating costs and investments. The project stage of secondary circuits consists of calculating the mechanical efforts to determine the support structures of the primary and secondary distribution systems and determining the types of structures that should be used in the system according to topological and electrical parameters of the network and, therefore, accurately assessing the costs involved in the construction and/or reform of secondary systems. A constructive heuristic based on information of the electrical and topological conditions between the medium voltage and low voltage systems is used to connect the primary systems and secondary circuits. The results obtained from planning and design simulations of a real secondary system of electric energy distribution are presented. <s> BIB002 </s> Overview of Electric Energy Distribution Networks Expansion Planning <s> II. DISTRIBUTION EXPANSION PLANNING MODEL A. VARIABLES <s> The integration of distributed generation (DG) units in power distribution networks has become increasingly important in recent years. The aim of the optimal DG placement (ODGP) is to provide the best locations and sizes of DGs to optimize electrical distribution network operation and planning taking into account DG capacity constraints. Several models and methods have been suggested for the solution of the ODGP problem. This paper presents an overview of the state of the art models and methods applied to the ODGP problem, analyzing and classifying current and future research trends in this field. <s> BIB003
The decision variables of a DEP problem are generally, the place, size, and investment scheduling to install new equipment or upgrade the pre-existed facilities, as well as the number, state (open/close), and location of switches. DG owners make decisions on the location, size and the VOLUME 8, 2020 type of DGs to install based on geographical conditions, fuel resources, and feasibility of using RERs like wind turbines, photovoltaic panels, biomass, etc. BIB003 . In a design problem, we must determine the suitable diameters of lines and conductor options (e.g. underground cables, overhead line conductors) based on the required voltage levels. Here, lines' reinforcement is aimed to increase the capacity of pre-existed substations and distribution feeders or to install new ones if required BIB001 . A generic DEP is inherently a complex mixed-integer non-linear programming problem with continuous and discrete (binary) variables BIB002 . Binary variables represent installing new feeders and distribution substations, changing the type of conductors, and upgrading the capacity of distribution substations. Continues variables represent the amount of voltage level in each bus, power flow from the feeders, generated power with DGs, injected power from the substations, and curtailed load (see Fig. 2 ).