Abstract

An H-bridge hybrid modular converter (HBHMC) is proposed for high-voltage direct current (HVDC) applications. At the output of the main H-bridge converter, it has a wave-shaping circuit made up of full-bridge submodules (FBSMs) that are connected in series. For a three-phase system, three HBHMCs are connected either in series (series-HBHMC) or in parallel (parallel-HBHMC) across the dc-link. The operating modes of HBHMC, novel modulation strategies for voltage balancing of FBSMs, and control of HBHMC-based HVDC systems are presented in this paper. A detailed comparison between HBHMC and other hybrid topologies is performed on the basis of the required number of switches and capacitors. The HBHMC has the features of dc fault blocking capability, a lower footprint structure, and an extra degree of freedom for submodule capacitor voltage balancing. The HBHMC-based HVDC system works well for both balanced and unbalanced three-phase grids, and it can handle faults, as shown by PSCAD simulation studies. Also, the proposed converter's ability to work in normal and dc fault situations is tested, along with the proposed capacitor voltage control scheme. This is done by using a three-phase grid-connected HBHMC laboratory prototype.

Description