Keywords: Distributed generation, microgrid, grid-connected operation, islanded operation, utility-interactive inverter.
The paper presents a general control technique for utility interactive
inverters in low-voltage microgrids. The Utility Interface (UI) is a
three-phase power conversion unit, equipped with energy storage, that
governs the interaction between the utility grid and the microgrid.
The UI is in charge of several functions: in grid-connected operation,
it performs as a voltage-supporting unit and compensates the reactive
power, unbalance, and distortion caused by loads, whereas in islanded
operation, it performs as a voltage-forming unit and sets the voltage
and frequency for the entire microgrid. Moreover, the UI ensures
seamless transitions from grid-connected to islanded operation and
actively decouples the microgrid and the mains. Finally, the UI can
perform as a centralized microgrid controller for distributed energy
resources. The UI is therefore a crucial component, which needs to be
analyzed carefully to ensure safe and reliable operation for the
microgrid. This paper discusses a control approach that provides all
required functionalities and ensures proper microgrid operation even
in case of non-intentional islanding or severe load transients. The
experimental results show the behavior of the system in different
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