Voltage and current balancing in Low and Medium Voltage grid by means of Smart Transformer

The Smart Transformer (ST), which is a power electronics-based transformer, represents an enabling technology for providing new services to the Low Voltage (LV) and Medium Voltage (MV) grid. The 3-stage configuration, with a high frequency transformer and 2 DC links, allows the electrical separation of the LV and MV grids. This leads to the independence of the two grids: any disturbance downstream and upstream can be compensated and mitigated by the ST action, which is the case of the unbalanced load condition of the LV grids. The unbalanced currents demanded by the loads could create unbalanced voltages at the LV side and also unbalanced currents at the MV side of a traditional transformer. This paper presents the improvements achieved by ST implementation in terms of voltage and current balancing: with a proper control of the ST, it provides balanced voltage in the LV grid, demanding a balanced current from the MV grid. This feature increases the power quality in both grids and provides an improved service to the customers