Control of inverter-connected sources in autonomous microgrids

The use of distributed generation is growing steadily, motivating a need for flexible interconnection strategies. The resulting microgrid concept allows sub-networks of sources and loads to maintain reliable operation when disconnected from the main grid. The paper presents a control strategy for inverter-based sources that supports transitioning between grid connection and autonomous operation. The controller regulates the inverter terminal voltage and the active power delivered to the AC system, and takes into account the phase-locked loop (PLL) dynamics. An example, in which two SOFC plants provide power to a microgrid, explores controller behaviour. The investigation considers disconnection from the main grid, autonomous operation, and re-synchronization with the main grid.