Improved Current Sharing Techniques for DC Microgrids

Abstract

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. This paper 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 eliminate 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 obtained using the HS technique and the particle swarm optimization technique. The dynamic performance of the droop controller using the proposed current sharing loop and the proposed optimal droop parameters is evaluated using the PSCAD/EMTDC simulation package.