An Improved Virtual Capacitor Algorithm for Reactive Power Sharing in Multi-Paralleled Distributed Generators

Distributed power generators in islanded microgrid usually adopt droop control strategy or virtual synchronous generator (VSG) control strategy to simulate Q-U droop characteristic of synchronous generators for voltage support ability enhancement and reliability improvement. However, because the distributed power generators' capacities and locations are random, they cannot share reactive load proportional to their rated capacity, resulting in overload protection, and even system instability. In order to improve reactive power sharing precision, voltage control precision, and system stability simultaneously, an improved reactive power sharing algorithm combining virtual impedance and virtual capacitor is proposed in this paper. First, the three existing open-loop reactive power sharing strategies are summarized and the effect of their parameters on reactive power sharing error, steady-state voltage deviation, and system stability are analyzed. Afterwards, based on the analysis results, a reasonable configuration of virtual impedance and virtual capacitor values are put forward to realize the control targets of reducing steady-state reactive power sharing error, improving voltage control precision and system stability meanwhile. Finally, simulation and experimental platforms are built to verify the effectiveness of the proposed strategy.