A 1.5-MW Seven-Cell Series-Stacked Converter as an Active Power Filter and Regeneration Converter for a DC Traction Substation

A prototype 1.5 MW series-stacked converter system was built and installed at a dc traction substation. The converter inverts energy generated by slowing an electric train using regenerative braking. The regenerated energy is fed into the local ac network at the dc substation. A secondary function of the converter is to perform active power filtering (APF) while a train is drawing power from the substation. The system´s control is based on the instantaneous reactive power theory. An interleaved switching scheme was used to switch the seven-cell series-stacked converter, thus exploiting the natural balancing properties of the series-stacked converter. Results obtained from tests done show that both the APF and regeneration functions of the system were successfully implemented.