Energy Diverting Converter Topology Using Unidirectional Current H-Bridge Submodules for VSC-HVDC Transmission System

The voltage source converter-based high-voltage direct current transmission has been the preferred choice for integrating long-distance, bulky offshore wind farms. The fault ride-through capability during onshore ac network faults is one of the greatest challenges, and the dynamic braking resistor (DBR) circuit for diverting the excess energy is essential. In this article, a novel modular multilevel converter (MMC) DBR circuit based on unidirectional current H-bridge submodules (UCH-SMs) and a two-state transition control strategy are proposed. The UCH-SM-based MMC-DBR (UCH-MMC-DBR) has advantages, such as a simple lumped cooling system and a modular design. The semiconductor usage is very low compared with the existing topologies. The two-state transition control strategy can maintain the charging–discharging balance on the SM capacitors while enabling the braking power to track the reference. The feasibility of the proposed UCH-MMC-DBR and the two-state transition control strategy is verified using the simulation and experimental results.