A Transformerless D-STATCOM Based on a Multi-Voltage Cascade Converter Requiring No DC Sources

This paper deals with a cascaded multilevel converter which has multiple dc voltage values (multi-voltage cascade converter) for a 6.6-kV transformerless distribution static synchronous compensator (D-STATCOM). A control method is proposed to realize dc voltage regulation of series-connected three cells in the STATCOM operation, making it possible to remove dc sources from all H-bridge cells. The simplified configuration without the dc sources makes the STATCOM small and lightweight. A downscaled STATCOM model rated at 220 V and 10 kVA is built and a series of verification tests is executed. Theoretical analysis and experimental results prove the stable operating performance of the proposed method.