Control and operation of a DC microgrid

Abstract

Abstract DC microgrid becomes more attractive than ac microgrid. DC microgrids can be operated either in the islanded or the grid-connected mode. The droop control is the most effectively used technique for load current sharing in DC microgrid. The disadvantages of the conventional droop controllers are the increased voltage deviation and current sharing errors when the load current is increased. The secondary controller is utilized to fix 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. This thesis presents two improved techniques for current sharing in dc microgrids. In the first technique, the droop resistance is updated for each converter in the microgrid to exclude the current sharing error. The current sharing reference for each converter is calculated based on the ratio of its rating to the load current. Hence, the load current is the only parameter that needs to be communicated to the current sharing loops. The second proposed technique is based on utilizing optimal droop resistances to eliminate the need for current sharing loops and their associated communications. The Harmony Search (HS) technique is utilized to attain the optimal droop resistances which results in minimizing the error in the current sharing. A comparison is made between the results acquired using the HS technique and the Particle Swarm Optimization (PSO) technique.