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In this paper, an adaptive control system for a dc microgrid for data centers is proposed. Data centers call for electric power with high availability, and a possibility to reduce the electric losses and, consequently, the need for cooling. High reliability can be achieved by using local energy sources, and by using a dc power system, the number of conversion steps, and therefore also the losses, can be reduced. The dc microgrid can also supply closely located sensitive ac loads during outages in the ac grid. The proposed dc microgrid can be operated in eight different operation modes described here, resulting in 23 transitions. The control system coordinates the operation of converters, sources, and switches used in the dc microgrid. The control system is tested in the simulation software package PSCAD/EMTDC, and the results of the most interesting transitions are presented. The results show that it is possible to use the proposed dc microgrid to supply sensitive electronic loads and also, during ac-grid outages, supply closely located sensitive ac loads. To reduce the current transients experienced by grid-connected ac/dc converters, fast grid-outage detection and fast switches are required.
Date of Publication: Nov.-dec. 2008