Decentralized Current Sharing in Islanded DC Microgrids Based on AC Frequency Droop

In islanded dc microgrids, multiple parallel-connected distributed generation units (DGUs) are involved, and current sharing is an essential issue. However, it is always degraded by mismatched feeder impedances. To address this issue, a decentralized current sharing approach is proposed in this paper. In this method, a small ac signal is injected into the output voltage of each DGU. On this basis, the current sharing process is divided into two sequential stages: in Stage 1, Q − f droop is implemented to generate reactive power references, and in Stage 2 the virtual resistance is adaptively regulated. By following this process, both dc and the injected ac current components are shared accurately among DGUs with small virtual resistances. Additionally, as the frequency of the injected ac signal is a global variable and reactive power sharing is accomplished with Q−f droop, no dedicated communication network is required. The effectiveness of the proposed current sharing strategy is then confirmed by simulation results.