Analysis of Smart Transformer features for electric distribution

The distribution grid is undergoing deep changes created by the integration of new generation resources, such as renewables, and new loads, like electric vehicles. These new actors impact on the distribution grid management, introducing 1) higher variability of the grid power demand and subsequent power unbalance, 2) reverse power flow with increased overvoltage conditions in case of high power production and low power consumption, cables and transformer overload in case of low power production and high power consumption, and 3) decreased system inertia, due to the power electronics-connection of the resources. The Smart Transformer (ST) enables the management of the distribution grid, absolving three main tasks: 1) adapting the voltage level from medium to low voltage grids; 2) managing the distribution grid during the aforementioned issues; and 3) offering higher controllability of distribution and transmission grid. This work describes in details the ST controllers and their tuning, taking into account the services to be provided. The ST enables the direct control of the voltage waveform in the ST-fed grid, varying the voltage amplitude and frequency. This allows to interact with the voltage-sensitive loads power consumption and droop controlled-generators in order to shape the power consumption of the ST-fed grid. Applying this control the ST can offer services to the grid, like limiting the reverse power flow in the medium voltage grid, or managing its overload conditions. The accuracy of these services can be increased if the identification of the grid power sensitivity to voltage and frequency is carried out. The ST, applying a controlled voltage amplitude and frequency variation, performs the on-line load sensitivity identification and evaluates in real time the grid sensitivity. This identification enables the offer of new ancillary services to the distribution and transmission grids.


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