A microgrid (MG) is a stand-alone or grid-connected hybrid renewable system that uses distributed renewable and nonrenewable energy sources and energy storage systems (ESSs) to supply power to local loads. The system is ordinarily based on power electronics, with interface converters allowing the sources to supply power to the system and the loads to draw power from the common bus in a controllable fashion. A MG is normally designed such that renewable energy sources (RESs) supply the average load demand, while ESSs, nonrenewable generation, and the grid are used to ensure that the loads enjoy a continuous supply of power in the presence of variable RES production. This chapter describes some specific features of DC MGs in terms of power architecture, control, and protection. It also reviews several uncommon power electronic interfaces. Regarding control, operation without critical communication links between units is an attractive solution from the point of view of both reliability and wiring hardware savings. Therefore, the conventional droop control concept from the bulk AC power systems was used at the primary control level because it requires only locally obtainable measurements. However, the higher control level becomes a challenging task with an increase in the number of units with different characteristics and topology complexity. It has to deal with RESs, which are controllable only within the limits imposed by natural phenomenon, while the battery recharging usually has to be done in a specific way. Moreover, the technical constraints such as stability margins and maintenance of acceptable voltage deviation within the system must also be respected while the aforementioned issues are considered. While a centralized control is commonly deployed for this purpose, distributed techniques are explained in this chapter. The chapter concludes with a review of power electronic intensive protection solutions for DC MGs.
Microgrid: Advanced Control Methods and Renewable Energy System Integration, 2016
DC microgrids; Hierarchical power sharing; Droop control; Primary control; Secondary control; Tertiary control