Improved Power Sharing and Circulating Current Suppression amongst Modular Converter based Distributed Energy Resources in DC Microgrids

Abstract

Direct current (DC) power systems are gaining increased interest DC microgrid systems are attractive from the viewpoint of efficiency, clean energy and ease of renewable energy integration. Typically, parallel connections of smaller power rated converter sub-modules is done to supply high power loads. Such modular DC-DC converters reduce the costs and single point failure issues, caused by employing a single higher power rated converter and therefore enhance supply reliability. The mis-matches in the load powers shared between the parallel connected sub-modules and circulating currents are challenges which have to be addressed for these topologies. This work proposes two de-centralized strategies (without communication) in addition to an adaptive virtual resistance (VR) based strategy to overcome the above mentioned challenges. The control schemes are validated extensively through off-line simulations considering solar photovoltaic (PV) power output fluctuations, which is often neglected in the available literature. Further, simulations have been carried out with various types of DC loads. The proposed schemes have also been tested for their effectiveness in the presence of symmetric and asymmetric AC voltage (noise) shifts in the source output voltages.