Modeling and analysis of droop based hybrid control strategy for parallel inverters in islanded microgrids

Abstract

The well-known active power-frequency and reactive power-voltage amplitude droop scheme is widely used in islanded microgrids to automatically share load power and regulate output voltage of parallel voltage-controlled inverters (VCIs) in microgrids. However, droop controlled VCIs tend to lose stability as droop slopes increasing. Meanwhile, parameter discrepancies extend synchronization time between VCIs which degrade system dynamic performance. In order to compensating above limitations of traditional method, this paper proposed a droop based hybrid control strategy by exploiting advantages from both voltage-controlled and current-controlled inverters. Capturing the detail of inner control loops, a small-signal state-space model is derived to analyze characteristics of the overall parallel system. Comparing to traditional method, eigenvalues of the hybrid control strategy indicate better stability and dynamic performance. In agreement with theoretical analysis, both simulation and experimental results are presented to validate the advantages of this proposed strategy.