Control strategy for seamless transition between grid-connected and islanding modes in microgrid-based PV inverters

One of the main characteristics of microgrids (MGs) is the ability to operate in both grid-connected and islanding modes. In each mode of operation MG inverters may be operated under current source or voltage source control. In grid-connected mode, MG inverters typically operate under a current source control strategy, whereas in islanding mode MG inverters operate under a voltage source control approach. Smooth transfer between the grid-connected mode and the islanding mode is one of the main challenges of MG activity. This paper presents a proposed control strategy that is capable of operating MG-based PV inverters in different operating modes. The proposed control approach is capable, also, of transferring the MG-based PV inverters seamlessly between the different operating modes. This seamless transition can be achieved by mitigating the transient variations in the MG voltage, current, phase, and frequency at the point of common coupling. In addition, the proposed strategy is capable, also, to provide a transient-free transition in the DC-link voltage of the utilized PV inverters. Thereby, the proposed strategy has the capability to enhance the overall MG reliability. The proposed control strategy is validated by software simulation using MATLAB/Simulink. The simulation results indicate the effectiveness of the proposed strategy during MG transitions.