Control schemes of the front-to-front (FTF) power electronic topologies for future HVDC interconnections

In recent years, significant progress has been made in HVDC transmission by the advent of voltage-source-converter (VSC) technology using modular multilevel converters. There is increasing demand to interconnect the existing HVDC lines into meshed HVDC grids for better renewable energy penetration. In this paper, a series of power electronic topologies, all based on the front-to-front VSC structure, are introduced as devices for future HVDC interconnections. The topologies include DC/DC converter, DC/DC auto-transformer, DC power flow controller, and HVDC power tap. Particularly, from the energy balance point of view, the control schemes for stable operation of these topologies are discussed. Simulation results validate these topologies and the proposed control schemes.