الفهرس 
Literature ReviewOnly 14 pages are availabe for public view
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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.
Also, this thesis presents adaptive droop scheme for dc microgrids to overcome the non-linearity of the system. The droop resistance is adjusted using adaptive PI controller to exclude the current sharing error of each unit in the microgrid. In addition, another adaptive PI controller is dedicated for a secondary loop to regulate the dc bus voltage of the microgrid by shifting the droop lines. Moreover, the Sliding Mode Control (SMC), which is distinguished by robustness and fast dynamic response, is utilized to manipulate the input current and output voltage of each converter, instantaneously. The dynamic performance of the droop controller using the proposed current sharing loop, the proposed optimal droop parameters, and the proposed adaptive droop scheme are evaluated using the PSCAD/EMTDC.