Communication-free control concept for operating a low voltage island grid

To ensure a communication-free island grid operation, a control concept has already been proposed in the literature. This control concept uses state machines implemented within smart meters at each household and makes use of grid-forming inverters having batteries and secondary control in grid-forming inverters. During an island grid operation, it is necessary to keep the state of charge of the batteries of the grid-forming inverters within a permitted band, otherwise, the grid-forming inverters will lose its primary energy source and can not form anymore the grid by a reference voltage. Besides that, it is also important to consider the rated power respectively the maximum current of the grid-forming inverters to prevent the semiconductors from damage. Measures have to be taken in cases of an overcurrent. It is a problem to limit the current of a grid-forming inverter when at the same time the grid power balance has to be fulfilled and other inverters are not able to support the overloaded grid-forming inverter due to their limited battery capacities. This publication gives a solution in the form of an extension of the already presented control concept of how to overcome this problem and validates that through an RMS simulation, carried out in PowerFactory.