Fault Current Capability Assessment of Low-Voltage side Inverters in Smart-Transformers

The Smart Transformer (ST) arises as one promising solution for the modern electric grid by providing ancillary services to support AC and DC distribution grid. In this context, as the classical low-frequency transformer (LFT), the ST is prone to experience overload conditions caused by faults and peak loads. However, unlike the LFT, the overcurrent capability of the ST is further limited by the thermal time constant of the power semiconductors. Thus, since the overload operation has been only partially investigated, this paper proposes and presents a comprehensive analysis of the LV-side power converter under normal and overload conditions to estimate its overcurrent capability. For this purpose, the LV-side inverter is assessed in terms of power losses considering continuous and discontinuous modulation strategies and different power semiconductor technologies along with multiple types of cooling systems.