Integration of Large Photovoltaic and Wind System by Means of Smart Transformer

Large renewable energy systems, e.g., photovoltaic and wind turbine, are connected to grid, which is usually weak, with long lines. This degrades power system stability and reliability. Additionally, the magnetic characteristic of a conventional power transformer (CPT) implies a slow dynamic and leads to grid current harmonic too high when wind speed is low and irradiance is weak. This paper proposes a parallel connection of a solid-state transformer-based smart transformer and a CPT to not only reduce the power rating, but also to support the voltage amplitude and improve the grid current quality. The simulation and experimental results clearly verify the correctness and feasibility of the proposed strategy.