Extension of low voltage distribution by pure DC or mixed AC/DC parts for integration of solar PV and EV charging

Abstract: This work examines the local distribution system in two residential areas in two Swedish towns, Oxelösund and Karlskrona, and studies how integration of PV systems and electric vehicle (EV) charging stations (CS) will affect the present distribution system. The research questions focus on the economic feasibility of a LVDC system, how it compares to a traditional LVAC (low voltage alternating current) system from an economic and technical perspective, and the possibilities a LVDC system brings to other DC component applications. The Swedish government aims to have a fossil-free vehicle fleet by 2030 and one of the measures is no fossil-fuel burning vehicle will be produced and sold in Sweden. This means the number of CS, and the charging infrastructure around these, need to be developed, to contribute to this goal and sustain this transformation. A connected issue is that updates on the regulations for non concession-regulated networks (IKN) in January 2022 extended the basic preconditions and allows possibilities for energy sharing between buildings. The new regulations are also in favor of micro-production and contribute to more decentralised systems. Connections of Renewable Energy Sources (RES) to the distribution system are expected to increase in the coming years. Grid-connected solar PV systems in Sweden have increased by 56% between 2019 and 2020, and at the same time EVs are becoming more apparent on the roads. These DC-(direct current) based technologies, and the possible need to strengthen local networks to accommodate new sources and loads, are bringing new opportunities for low voltage direct current (LVDC) based distribution systems. To answer the research questions, two different models with different concepts, parallel pure DC and parallel AC/DC, were built in simulation software. The conclusion of this study is that a traditional LVAC system is preferable over pure DC system from both economic and technical perspective for already connected areas, such as the two areas in this project. A parallel pure DC system might be preferable in newly built areas with substantial PV and EV, where exchange is wanted between buildings with separate AC grid connections.