MULTIOBJECTIVE APPROACH FOR POWER FLOW AND UNBALANCE CONTROL IN LOW-VOLTAGE NETWORKS CONSIDERING DISTRIBUTED ENERGY RESOURCES W. M. Ferreira 1,2 , D. I. Brandao 1 , F. G. Guimarães 1 , E. Tedeschi 3 , F. P. Marafão 4 1 Graduate Program in Electrical Engineering, Federal University of Minas Gerais, Belo Horizonte – MG, Brazil 2 Federal Institute of Education Science and Technology of Minas Gerais, Ipatinga – MG, Brazil 3 Department of Electric Power Engineering, Norwegian University of Science and Technology, Trondheim, Norway 4 Group of Automation and Integrated Systems, Universidade Estadual Paulista, Sorocaba – SP, Brazil e-mail: willian.ferreira@ifmg.edu.br, dibrandao@ufmg.br, fredericoguimaraes@ufmg.br, elisabetta.tedeschi@ntnu.no, fmarafao@sorocaba.unesp.br Abstract – This paper proposes a multiobjective optimization technique that maximizes the active power generation from single-phase distributed generators, and minimizes the unbalance factor at the point of common coupling of the network. Such technique is incorporated into a centralized control strategy for optimal power flow control purpose. The centralized control strategy used herein is the Power-Based Control that coordinates the distributed units to contribute to the network´s active and reactive power needs, per phase, in proportion of their power capacity. The simulation results of a simplified network with three single-phase distributed generators validate the proposal in terms of power flow control, voltage regulation and power quality. Keywords – Distributed generation, Genetic algorithm, Microgrid, Multiobjective power flow, Unbalance. I. INTRODUCTION With the steady growing of energy demand and society concerns about the environment, alternative methods for energy generation have been studied by many research groups. Distributed generation has emerged as a feasible and smart solution to bring the conventional and centralized grid towards a modern paradigm of generation in a distributed fashion [1]. Although, new technological developments carry new challenges, such as reliable and efficient operation of parallel small distributed units, how to incorporate new devices into the already existed grid, and optimal and high quality of power supplying are typical examples of obstacles that must be overcome. An apparent and efficient model to deal with the distributed generation and energy storage systems is gathering them in microgrid structures, where the distributed energy resources (DERs) and loads are interconnected to the distribution systems. These DERs are fully controlled as dispatch units. DERs commonly consist of renewable energy sources (e.g., photovoltaic, wind, full-cell, etc.), energy storage, and a single- or three-phase inverter (e.g., DC-AC converter) that performs the interconnection between the primary energy source (PES) and the distribution network. Besides injecting active power into the network, DERs can perform ancillary services in order to enhance the system power quality and reliability [2], [3], [4]. Some of these ancillary services are: voltage support under low-voltage ride-through, reactive compensation, harmonic mitigation, and power unbalance reduction, mainly due to load unbalance and intermittent power generation from single-phase converters. When those DERs are incorporated into a network and they are coordinately controlled through a central agent-based unit, they may cooperate to achieve a common goal at the point of common coupling (PCC) of the network [5]. One of the major advantages of such structure is the accurate power flow and power factor control at the PCC allowing the utility to exchange power with the microgrid, within high quality and respecting their limited power/current capability. However, when the network is full of heavy single-phase power generation, there exist a trade-off between power generation from single-phase DERs and power unbalance at the PCC of the network. It occurs because the distributed units are arbitrarily connected to the grid worsening the power unbalance. In [3] it was shown how to distributedly compensate load unbalance through coordinating single-phase DERs arbitrarily connected to a three-phase network. To optimize the use of energy, a generation energy cost dispatch system was proposed in [6] and [7], but no energy quality issues were explored. In [5] an association of central and local controller to regulate active and reactive power of DERs was proposed in order to enhance the voltage profile. The optimization algorithm manipulates ten neighboring nodes to guarantee that the voltage value stays within acceptable limits, but it is needed to know the power line impedances and the location of each DER. These conditions are tough to comply with in distributed networks. A methodology to reduce the power line losses, voltage deviation and inverter losses was proposed in [8], which is based on injection of reactive power under voltage deviation control. However, it is also needed to know the system parameters, and the optimization processing time is critical. Then, due to the trade-off abovementioned, this paper proposes the application of a multiobjective optimization technique to set the power flow at the PCC maximizing the active power generation from single-phase distributed units and minimizing the power unbalance. The optimization technique is incorporated into a centralized control strategy called Power-Based Control (PBC) [9]. This control strategy drives the DERs to contribute to the active and reactive power needs of the network in proportion to their capability. As a result, the utility may choose from prioritizing active power generation extracting maximum power from DERs, reducing the power unbalance at the PCC for enhancing power quality, or an intermediate action between these goals.