A New Delta Hybrid Series STATCOM and DC Capacitor Voltage Balance Using Zero-Sequence Current

A new delta hybrid series converter-(DHSC) is proposed to compensate reactive power in the transmission lines operating at medium and high voltage ranges. The proposed DHSC converter has unique advantages over the existing modular-multilevel-converters-(MMCs) based static-compensators(STATCOMs) such as DSCC and DSBC in terms of number of capacitors and energy storage requirements. The series chain-links(SCLs) of the proposed DHSC contributes in increasing the output voltage levels unlike the hybrid-series-converter-(HSC) and hence has less number of switches and capacitors. The DHSC converter has zero-voltage-switching-(ZVS) nature and has reduced switching losses than the HSC. The proposed DHSC accommodates zero-sequence currents in its individual phases and hence has an extra degree of freedom to regulate its capacitor voltages even during unbalanced grid conditions. A capacitor voltage control technique is also proposed using the zero-sequence current. The working of the proposed DHSC STATCOM and proposed capacitor voltage control is verified using simulation results.