Distribution power quality improvements using DC links with battery storage in existing networks

The use of DC links with battery storage in LV distribution networks provides several advantages for both the final user and the electric utility. In particular, with the use of DC links between the LV windings of the distribution transformers and the load, the following advantages can be obtained: improvement of the power quality of the energy supplied to the user, in particular because the DC link with battery storage can eliminate short voltage interruptions and dips of up to a few minutes; and possibility of using a higher voltage level for the DC line than those presently used for AC lines, thus increasing the link power carrying capability. These features are very important in urban areas, where the installation of new power cables is costly (and sometimes very difficult to realise) and the request for power quality is ever increasing due to the growth in the number of electronic appliances. In this paper, several possible alternatives for realising such a DC link are presented and their feasibility is shown, both in terms of normal and faulty operation and of reliability. Some economic considerations are also dealt with, with particular attention given to a case study.