Optimized design of a back-to-back NPC converter to be used as interface for renewable energies

As the number of wind power with power electronics interfaces in the grid increases, it becomes unacceptable to disconnect the generating units every time a disturbance occurs, as was a common practice in the past. Keeping the converter online during unbalanced voltage and guaranteeing the actual standards of the converter connected to the grid becomes a very critical issue. From these goals, the design of a robust back-to-back NPC (three levels) converter of 100 KVA is researched in this work. The converter is divided into two main parts: the power electronics system and the control electronics system. In both designs, some important contributions are shown. Concerning the first part, the paper presents primarily the converter limitations to compensate unbalanced dips, the grid filter design and the DC-bus capacitor design. Concerning the control electronics system, the chosen electronic structure and the tasks distribution between the chosen processors are shown.