DC distribution systems and microgrids

The idea of merging variable sources with energy storage and controllable loads into flexible systems called microgrids (MGs) has been presented more than a decade ago [1]. MGs can operate autonomously or be grid-connected, and depending on the type of voltage in the point of common coupling (PCC), AC and DC MGs can be distinguished. While remarkable progress has been made in improving the performance of AC MGs during the past decade [2-5], DC MGs have been recognized as more attractive for numerous uses due to their higher efficiency, more natural interface to many types of renewable energy sources (RESs) and energy storage systems (ESSs), and better compliance with consumer electronics [6]. Besides, when components are coupled around a DC bus, there are no issues with reactive power flows, power quality, and frequency regulation, resulting in a notably less complex control system [7-10]. Therefore, DC MGs have gained a high momentum over the past couple of years both in academia and industry. A broad class of traditional DC distribution applications, such as traction, telecom, vehicular, and distributed power systems can be classified under DC MG framework and on-going development, and expansion of the field is largely influenced by concepts used over there. This chapter aims to present a technology overview of DC microgrids both from the aspects of hardware design and control.