New transformerless medium-voltage STATCOM based on half-bridge cascaded converters

To achieve higher performance in a distorted and unbalanced medium-voltage large-current system, a new shunt compensator is presented based on half-bridge cascaded converters (HBCC). Then, the transformerless HBCC based STATCOM can be controlled for various purposes such as reactive power of STATCOM, simultaneous harmonic cancellation and load balancing procedure. Compared to the conventional modular multilevel converters, the HBCC based STATCOM introduces lower ratings both for active and passive elements, improving the overall efficiency of the converter. A control strategy is proposed to ensure the source-end three phase currents are sinusoidal and balanced. At the same time, the DC capacitors voltages are controlled to operate under balanced condition. One interesting application for the HBCC based STATCOM could be electric traction system. Both power circuit and the proposed control strategy are simulated with PSIM and MATLAB, confirming the pre-defined objectives.