# Sustainable Operation of Active Distribution Networks
## 1 Introduction
A hierarchical multi-agent system (MAS) was developed in [22] for the efficient real-time control of large electric ports with a high integration of PEVs, while in [23], the optimal operation of distribution networks comprising PEVs was achieved with the implementation of demand response strategies. To optimally dispatch the total active power of a population of PEVs to each PEV, an effective definition of a PEV's flexibility to adjust its exchanged power was developed in [24]. The power management method suggested in [25] is suitable for real-time application to distribution networks hosting large clusters of PEVs. In this work, simple flexibility indicators were proposed for both PEVs and clusters of PEVs. Additionally, the optimal reactive power dispatch to each PEV was accomplished in real-time. Moreover, a strategy for incorporating energy storage units into ADNs was developed in [26; 27]. The ESSs were suitably designed to take into account their potential to support the ADN by exploiting both active and reactive power. In [28], the batteries used in the examined ADN were optimally designed and scheduled in order to maximize the penetration of the distributed generation units. A brief description of this work and its novel aspects are presented in the following. * The work presented in this paper examines the optimization of distributed small residential prosumers of a distribution network. A large number of operation and technical limitations of the ADN and its components was ensured and the proposed algorithm achieved the highest possible reduction in the daily operation cost of the ADN. * The implementation of the proposed method was based on the exploitation of a hierarchical MAS that allows for the optimization of the complex examined power system in a single optimization level. The goals of each type of agent (smart residential building prosumers, PEV aggregators, and RES) and how they cooperated to accomplish them were fully outlined. The coordinated optimal operation of all types of agents was achieved and the suggested approach for ADN's optimal operation aligns with the growing need for sustainable development. * The thermal and electrical loads of residential buildings and an aggregate battery of numerous plug-in electric vehicles were modeled in detail. * A simple and effective definition of the buildings' cluster flexibility to adjust their power by exploiting fuzzy logic was first proposed in this article. * Smart power dispatch techniques were applied to buildings and PEV clusters as well as to single residential buildings and PEVs. This kept the needed computation time very low, as the minimum possible number of decision variables was achieved. The proposed method for the optimal operation of the ADN was aligned with the increasing need for sustainable development. The examined system included RES that generate clean energy. Moreover, the autonomous operation of the ADN was ensured, mainly through the hosted PEVs and RES, and there was no need for extra investment to conventional polluting auxiliary power generation units. This contributes to a reduction in greenhouse gas emissions and enhances the environmental friendliness of the proposed system. Another significant aspect of the suggested method is the minimization of the daily operation costs of the examined ADN, ensuring its sustainability in this way. Another sustainable feature of the method is the qualitative operation of the ADN as it can ensure the maintenance of the ADN voltages within their permissible bounds. The remainder of the article is structured as follows. Section 2 provides the description of the suggested hierarchical MAS. Section 3 includes the models of the agents and the connection among them. Finally, Section 4 presents the results received by the simulation of the examined active distribution network and evaluates them; while Section 5 draws the general conclusions.