An improved droop control based on complex virtual impedance in medium voltage micro-grid

Due to not consider the impact of feeder impedance, conventional droop control may result in instability and errors in proportional load sharing when implemented in medium micro-grid. In this paper, inherent limitations of conventional droop control are analyzed, then an improved droop control based on complex virtual impedance is proposed to achieve accurate proportional load sharing, in which complex virtual impedance is introduced to reduce power coupling due to uncertain impedance model and additional improved voltage/reactive power control is proposed to eliminate reactive power sharing errors due to imbalanced line impedance. Accurate power sharing can be achieved and the load voltage can be maintained within desired range by the proposed control strategy. Simulation results are provided to verify the analysis and design.