Robustness Study of a Modular Smart Transformer Based on a Combined Control Strategy under Disturbed Operating Conditions in the Smart Distribution Grid

With the large-scale integration of renewable energy sources (RES) and electric vehicles, the smart distribution grid (SDG) represents a promising alternative to power distribution systems. However, the conventional transformer (CT) is a passive device that cannot meet SDG requirements. In this context, the smart transformer (ST) based on modular architecture is considered an attractive alternative to CT since it provides multiple DC buses in medium voltage (MV) and low voltage (LV) grids. This article proposes a modular ST model including a cascaded H-bridge rectifier in the MV AC-DC stage, dual active bridge converters in the high-frequency DC-DC stage, and a four-leg inverter in the LV DC-AC stage for SDG applications. To improve its dynamic performance, an adaptive backstepping-sliding mode control is introduced. The proposed controller enables the automatic estimation of unknown parameters, especially in the presence of intermittent RESs, by the adaptive laws of the adaptive backstepping controller (ABC) and the improvement of the ST robustness under grid disturbances by introducing the discontinuous control of the sliding mode controller (SMC). The obtained simulation results prove the effectiveness of the selected ST model and the higher robustness of the proposed controller against grid disturbances, compared to the ABC and SMC.