# Experimental Validation of Peer-to-Peer Distributed Voltage Control System
## 1 Introduction  
Over the last decade, there has been a clear focus in the European Union (EU) on promoting low-carbon generation technologies and renewables. To ensure the EU meets its climate and energy goals, the 20-20-20 targets aim to cut the emission of greenhouse gasses by 20% compared to the 1990 level, achieve a 20% share of renewables in the total energy consumption, and improve the energy efficiency by 20%. In many countries, feed-in tariffs for eligible technologies have guaranteed returns for investors, and this along with other forms of market support have contributed to a reduction in technology costs and an increasing penetration of renewable energy resources (RESs) into distribution networks across Europe. This growth of renewable energy is expected to maintain since by 2030 the EU aims for 27% of the final energy consumption to come from renewable sources. The progress of the EU and its member states towards 2020 climate and energy targets are summarized in [1]. These trends are impacting the operation of distribution networks, making the Distribution System Operators' (DSOs) mission of providing secure electricity supply and high quality of service increasingly challenging. The historical \"fit-and-forget\" strategy of distribution networks was consistent with the unidirectional power flows from substations to end consumers and their predictable load profiles. When connecting significant amounts of RESs to the network, the assumption of unidirectional power flows is not always valid anymore. The generated power of RESs can reverse the power flows in the grid, what could lead to a rise of the voltage profiles beyond the allowed limits. Moreover, intermittent and unpredictable nature of renewables increases the complexity of controlling the distribution networks. A comprehensive overview of the impacts of the renewable energy and information and communications technology (ICT) driven energy transition on distribution networks is presented in [2]. To maintain a high security of supply and quality of service, DSOs have to find new strategies to control their networks. A transition towards active management strategies would be capable of maintaining the voltage profiles of distribution networks within acceptable limits to comply with the European standard EN 50160 [3] while minimizing, deferring, or even avoiding any capacity upgrades. Additionally, valuable flexibility of prosumers can be embedded in the operational management of the networks, to allow the prosumers to participate in supporting the grid as kind of ancillary service. Details of the most effective and efficient ways for managing the future active distribution networks, to address the 21 st century challenges of transitioning to low-carbon electricity, are discussed in [4]. The need for managing distribution networks actively by employing smart grid solutions and creating innovative investments and business models are the reasons for launching the EU funded Peer-to-Peer Smart Energy Distribution Networks (P2P-SmarTest) project. The project was launched in 2015 and continued until the end of 2017. The idea of the project consists in developing intelligent control, trading, and communication algorithms through a \"Peer-to-Peer\" concept; to facilitate the integration of demand side flexibility and to ensure optimal operation of RESs within the network while maintaining quality and security of supply. The deliverables of the project can be found on the website of the project [5]. In [6], the view to Peer-to-Peer (P2P) approach for smart grid operation adopted in P2P-SmarTest project is presented. The P2P control paradigm used in the project is presented in [7]. The approach adopted in P2P-SmarTest project to regulate voltage profiles of active distribution networks is based on distributed optimization techniques and P2P communication. Distributed optimization, as an alternative approach to solve challenges of the centralized optimization mechanism, has attracted increasing attention recently [8].