3SC Control for high efficiency grid connected photovoltaic converters

Abstract

Nowadays there are several grid connected converters in the grid system. These grid connected converters are generally the converters of renewable energy sources, industrial four quadrant drives and other converters with DC link. These converters are connected to the grid typically through a three phase IGBT bridge. The standards prescribe the permissible maximal harmonic emission and the maximal reactive current for the grid connected converters. For a converter working at nominal power these two prescriptions together mean almost unity power factor. The harmonic emission could be easily limited with high switching frequency and/or with large harmonic filters. Further financial viewpoints are the efficiency, the small size and weight. Comparing to traditional control these requirements can be simultaneously satisfied much better with the 3SC (three state control) method. At 3SC we utilize all the three allowed state of one arm of the IGBT bridge, i.e. upper part conducting, lower part conducting, none of the m conducting.