Proportional reactive power sharing for islanded microgrids

In this paper, droop-based automatic control schemes are presented to control parallel inverter-interfaced distributed generators (DG) in a way that proportional reactive power sharing is possible in islanded microgrids under different structures. This paper modifies the conventional reactive power-voltage (Q-V) droop control strategy used in inductive (L-type) islanded microgrids by implementing voltage control law in overall control operation such that reactive power becomes inversely proportional to the reactive droop gain if the initial values of inverter-interfaced voltage-sources are the same. Reactive power sharing approach for resistive (R-type) islanded microgrids is also included in this paper; in which it is shared depending on rate-of-angle of voltage-sources, i.e., reactive power-frequency (Q-f) droop. The proposed control methods utilize linear modal analysis to design both types of droop-based controllers. A 5-bus microgrid with 4-parallel inverter-connected DG units is considered for simulations under load changing phenomenon where results show the excellency of the designed control schemes.