: This thesis deals with the design consideration of dc microgrids with emphasis on the selection of medium voltage level based on a techno-economical analysis. Conventional ac microgrids use electronically-interfaced distributed generation units which often include renewable energy resources such wind and photovoltaic power plants. Many renewable resources and energy storages primarily use dc-links in their power converter units. On the other hand, the end-user consumers of the energy often need to receive electric power in dc form. Hence, in a microgrid with renewable resources, the generated power can be more effectively transferred to the loads if a dc transmission system is used instead of an ac one. The idea of using dc microgrid is now among the promising solutions for the expansion of future microgrids due to the vast amount of incentives in proliferations of renewable resources. The main challenges in developing dc power systems are dc/dc high-power conversion and dc circuit breakers. Recent advances in high-power converter topologies and especially developing topologies for dc circuit breakers enable realization of dc power systems as an emerging solution for more efficient microgrids in near future. The thesis mainly investigates the design considerations and control issues of dc microgrids, specifically with focus on the design of medium voltage levels for an optimal operation based on a trade-off between initial cost and power losses. The suggested design algorithm is then used for the design of a virtual dc-microgrid for Isfahan University of Technology (IUT) as a case study. In this case study, the loads estimated based on status of the campuses and residential areas at IUT. Two photovoltaic power plants in kW and MW-scales are also considered in the suggested dc microgrids. The thesis also presents a power flow method for dc power systems including high-power dc/dc converters. Such an algorithm for power flow analysis has not been systematically discussed in existing literatures for the dc power systems. In the last part of the thesis, the controller design issue for a dc-microgrid is investigated which is mainly established based on extension of the concepts of primary, secondary, and tertiary control loops in conventional ac microgrids. Finally, the performance of the designed controllers is investigated based on time-domain simulation of a study system in PSCAD/EMTDC simulation software tool. The simulation results show that the suggested control provision for the dc microgrid can maintain the stability of the voltages at dc buses following various disturbances and fault scenarios within the system. Keywords: DC power systems, dc microgrids, renewable energy resources, photovoltaic power plants, distributed generations, dc power system design.
