A control scheme for islanded and grid-connected DC microgrids

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.