Transient mode of parallel inverters connected to a hybrid microgrid: evaluation of dynamic performance considering a virtual impedance droop controller

This paper investigates the effect of unintended island mode and load change on parallel inverters in a hybrid microgrid system. The power system consists of three voltage source inverters with different power ratings connected in parallel to the AC bus. Moreover, two DC/DC converters are connected to the DC bus. An interlinking converter (ILC) is used to achieve bidirectional power flow between the AC and DC buses. A virtual impedance-based droop controller is implemented achieve an accurate power-sharing between the inverters connected to the AC bus and a smooth transition between grid-connected and island modes. The main motivation behind the use of the virtual impedance is to overcome the problem caused by the mismatch of inverters’ impedances. In this regard, the performance of parallel inverters are evaluated under transient operation from grid-connected to island mode and considering load change. The results of numerical simulations confirm the effectiveness of the method and the capability of the virtual impedance controller to avoid the problem of impedance mismatch.