Grid-Connected Voltage Source Converters with integrated Multilevel-Based Active Filters

Low- and medium voltage power converters for grid applications require bulky and expensive LCL-filters in order to meet the harmonic limits defined by the grid code. This paper presents a novel hybrid converter topology with smaller passive components, composed of a high power main converter with an integrated low power active filter. The presented coupled control strategies for a current-source and a voltage-source topology enable the immediate mitigation of the switching frequency current ripple, significantly decreasing the total harmonic distortion (THD) of the output current to below 5 % and thereby eliminating the need for a passive LCL-filter. Compared to LCL-filter based converter systems, a reduction of the inductive component expenditure of up to 50 % is achievable even for a very low active filter to main converter power rating ratio of 10 %. The outstanding harmonic performance and reduced passive component demand of the hybrid converter allow increased power density and efficiency as well as lower costs of low- and medium voltage power converters.