Using seven-level cascade H-bridge inverter with HVDC system to improve power quality

In order to improve the power quality of both AC sides of the 6-pulse line commutated converter HVDC link, a proposed technique is used to reduce the THD and improve the effective input power factor. The technique is based on implementing seven-level cascade H-bridge inverter at each side of HVDC system. Each inverter is operating instantaneously as STATCOM and active power filter. In order to drive this inverter, a modified harmonic pulse width modulation method is suggested in order to force the AC source current to be in-phase with its AC voltage in addition to minimize the ac source harmonics. The suggested method is applicable for transient and steady state operating conditions. The obtained results show that the power factor is almost unity and the value of THD is reduced significantly, at AC sides, for different levels of DC link power flow.