Selective harmonic elimination technique with control of capacitive DC-link voltages in an asymmetric cascaded H-Bridge Inverter for STATCOM Application

In this paper, the selective harmonic elimination (SHE) technique is introduced for a cascaded H-bridge-based static VAR compensator (CHB-STATCOM) with unequal capacitive dc-link voltages. The asymmetric topology allows increasing the number of voltage levels while keeping the converter losses low. Moreover, reactive power control is realized by using the decoupled current control, and the voltage of individual capacitors is controlled by the help of SHE modulation. Mathematical equations are derived for synthesizing the multilevel ac waveform and regulation of dc-link voltages for a CHB inverter with an arbitrary number of H-bridge cells. Then, to verify the theoretical claims, simulation and experimental results are provided for a three-phase CHB inverter with two H-bridge cells in each phase.