Control Schemes for Seamless Transition in Dual-Mode Microgrids

Microgrids (MGs) have gained popularity due to their many advantages in the integration of renewable energy sources to the power grid. With its capability to change its mode of operation, a microgrid can provide effective operation to supply electricity continuously to the customers. When the microgrid gets disconnected from the utility power system (islanding), it can exist as an independent entity by supplying the load with a sinusoidal voltage keeping its amplitude and frequency in the acceptable band by incorporating proper control. The islanding of microgrids may occur due to unpredicted natural calamities (unintentional) or by an intentional event. One of the key desired characteristics of a microgrid is its capability of achieving seamless transition from grid-connected mode (GCM) to islanded mode (ISM), and vice versa. It is necessary to supply power to the loads during the transition phase without losing its quality. Thus, it is mandatory to implement efficient control strategies to reduce the transients due to frequency and phase mismatches, which can lead to voltage and current variations during the transition phase. This paper presents a review on the literature related to the control schemes for seamless mode transition and how resynchronization to the utility can be established.