Assessing the applicability of low voltage direct current in electricity distribution : key factors and design aspects

Abstract

In many countries, the electricity distribution companies are facing the challenge of how to develop the networks effectively and respond to the future needs of societies. Changes in the electricity end use, aging network assets, integration of distributed energy resources, and renewable energy together with the increasing dependence on electricity supply are topical issues. From societies’ point of view, an important question is: What are the socio-economically feasible approaches and solutions that enable the transformation towards a more flexible energy system? One recognized technological alternative for the latter part of the electricity distribution is the application of power electronics and direct current. In this work, the main emphasis is on the public electricity distribution, especially in rural areas.

Low voltage direct current (LVDC) distribution can be used in various application targets having different properties. Its feasibility is highly dependent on the operating environment and its special characteristics including regulation, business environment, energy policy, technical and safety perspectives, existing installations, cost structures, and national and even regional development needs. Concurrently, there are many properties within the LVDC distribution that can be selected and designed in multiple ways. Such are for instance voltage levels, earthing system, converter characteristics, network structures and topologies, and location of converters. The overall feasibility of LVDC is dependent on the selection of suitable system properties for a particular operating environment. For now, as LVDC is a novel solution in public electricity distribution, it is challenging for the distribution system operators to estimate the potential and feasibility of the LVDC as there are no practices of how the LVDC networks and systems could and should be designed.

In this work, a process was developed to support the strategic decision-making and assessment of the role of LVDC in the long-term network development. The work provides answers to the two principal questions of how to determine the potential LVDC targets and which kinds of technical solutions are suitable and advantageous, depending on the characteristics of the operating environment. To be able to answer these questions, the value and impact of various factors have to be understood. These include aspects ranging from the operating environment to the LVDC network itself and technical specifications in the system design. In the work, theoretical analyses, practical experiences, and case examples of different explanatory environments were used. The contributions can be used in assessing the viability of LVDC in different environments.