A Control Technique to Eliminate dc Harmonics in Series-Connected Hybrid VSCs for HVDC Applications

The series connected converters (SCCs) are popular for high voltage direct current (HVDC) applications like off-shore, city infeed and current taping. However, most of the SCCs suffer from dc voltage and current harmonics, which necessitates bulky filters. A new control technique is proposed in this paper to eliminate the dc side harmonics in the SCCs. The proposed method can be used in any SCC containing two chain links (CLs) per phase such as series bridge converter (SBC) and hybrid cascaded converter (HCC). Also, a new parallel series hybrid converter (PSHC) is proposed, which does not suffer from any dc side harmonics and is tolerant to dc side faults. To control the energy exchanged amongst the CLs in PSHC, a modified control technique is proposed. The ability of the proposed control technique to eliminate the dc side harmonics in PSHC are verified using various three-phase simulation and experimental models.