Optimization of Fundamental Frequency Modulation for Cascaded Multilevel Inverter Based Transformer-less UPFC

This paper proposes an optimized fundamental frequency modulation (FFM) for cascaded multilevel inverter (CMI) based transformer-less unified power flow controller (UPFC). Compared to traditional FFM techniques, the proposed method features superior power sharing between H-bridge modules, thereby leading to better equalization of dc capacitor currents and voltage ripples. It also retains all the advantages of the traditional FFM such as low total harmonic distortion (THD) of output voltage and high efficiency. The proposed method is developed for a 2 MVA transformer-less UPFC system, nevertheless, it also can be applied to other applications such as CMI based static synchronous compensators (STATCOM), static synchronous series compensator (SSSC) and motor drives.