Control of three-level four-leg flying capacitor converter with active filtering function for RES

This paper presents operation of the four-leg three-level flying capacitor converter with active filtering function interfacing renewable energy source with the grid. Such solution in contrast to three-leg converter gives possibility to eliminate dy transformer mandatory for proper stand-alone mode of operation. The four-leg converter with proposed control method enables work at different electrical grid disturbances by switching all legs separately to stand-alone or grid connected mode, what makes possible to treat each leg as independent single-phase converter. The described control method is modification of well-known voltage oriented control (VOC) based on the proportional multiresonant controllers. Moreover active filtering function added to control reduce total harmonic distortion of grid current to acceptable level. Simulation study presents good performance and verified validity of the proposed solution. In this paper all possible operation modes are discussed and shown.