Frequency-Based Overload Control of Smart Transformers

A Smart Transformers (ST) is an automated transformer based on the latest power electronics and communication technologies. It aims not only at replacing the traditional transformer, but at providing also ancillary services to the grid, thanks to the greater flexibility offered by power electronics. However, in the case of grid overload caused by high load demand or high production from renewable energy sources, the power electronics have no extra capability. The power semiconductors can be overloaded only for few microseconds, in contrast with the grid components requirement of bearing currents higher than the rated values for several seconds. Thus the ST needs new procedures for dealing with the transients/conditions of the high current requests by the load. This paper presents the Frequency-Based Overload Control (FBOC), an innovative procedure for the overload management that acts in coordination with the droop controller of Distributed Generation (DG) systems, enabling the limitation of the transformer current.