DC microgrids can be operated either in the islanded
mode or the grid-connected mode. The droop technique is
widely used to control dc microgrids in both modes. The voltage
deviation and the current sharing error are the main problems
associated with the droop technique. This paper presents a
control system for both islanded and grid-connected dc
microgrids. The droop method is used to control each converter
in dc microgrid to share the required power depending on its
rating. The secondary loop is used to solve the problems
associated with the voltage deviation in islanded mode, while in
grid-connected mode, the tertiary controller is used to control
the supplied power from dc microgrid to the main grid. The
current sharing loop is used to improve the accuracy of power
sharing between all converters in both modes, where the droop
resistance of each converter in dc microgrid is updated
continuously based on the current sharing error. The dynamic
performance of the proposed control system for dc microgrid is
numerically evaluated under different modes of operations.