Analysis, Requirements and Boundary Condition of Droop Control in Multiple Parallel Connected Converters in DC Microgrid

Distributed energy resources (DERs) connected in parallel using AC/DC, DC/DC converters to form a DC or AC Microgrid. DC Microgrid is essentially important for community building for future smart cities. For the limited space multiple sources i.e., PV and small wind farms are connected through multiple parallel DC/DC converters to form a DC Microgrid. The control of multiple parallel connected DC/DC converters are challenging due to different operational environmental conditions such as mismatch in converter parameters and cable resistance. For a different output voltage from separate parallel converter leads to local circulating current within the PV modules and creates difficulties in maintaining common DC link voltage as well as proportional current sharing. This also increase series power loss from each converter. Traditionally droop control is adopted to control these problems in DC Microgrid. However, the applicability, operating regions as well as working boundary conditions of droop control is critical. This paper discusses mainly on the problems of parallel connected DC/DC converter system and provides the guidelines of operational boundaries without any control and with only MPPT control. Analysis of MPPT with droop control is also performed. Finally, the theoretical findings are verified by simulation study performed in PSIM 9.1.1.