A control system for battery current sharing in DC microgrids with DC bus voltage restoration

This work aims at studying and simulating a strategy for controlling the charge and discharge of a battery bank in parallel with a DC (direct current) microgrid fed by alternative energy sources in a distributed generation system. The main goal of this control strategy is to ensure load division among the batteries according to their individual capacities, besides of equalizing their loads and restoring the DC bus voltage level to acceptable values. Also, it ensures that the batteries can be charged and discharged efficiently, which avoid overloads and depth of discharge. The control also provides a safe and limited terminal voltage for the battery bank and a controlled state of charge. In order to establish the charge and discharge control and a current stabilization, a bidirectional DC-DC converter (Buck-Boost) is implemented. In addition, a droop control method is used to perform the load division, which inserts a virtual resistance — a gain controlled by the battery state of charge — into the output of each converter — there is no communication among them. Classical PI controllers are used to controlling the DC-DC converters through block diagrams and analog circuits.