Transients during Mode Transition in Microgrids: Performance evaluation for various Droop controllers

The distributed generators (DGs) operate in current control (CC) for the grid connected mode and droop control (DC) for islanded mode. A large transient is observed when there is an operational shift form grid connected mode to droop control mode and vice-versa. A proper control scheme has to be designed for reducing these transients. Among the variety of droop controllers employed, four commonly used controller configurations include the conventional droop, generalised droop, conventional droop with virtual impedance (VI) based control, and the transient droop. This paper deals with a state machine based mode transition strategy and compares the transient power sharing performances on a two inverter based DG microgrid, under the various combinations of these droop controller structures. The investigation is cvarried out through simulations and the results for various possible combinations and sub-cases involving power import and export from/to the grid are presented.