Symmetrical Monopole Three-Wire HVDC Transmission System based on Hybrid Modular Multilevel and Alternate Arm Converters

Conversion of existing alternating current (ac) systems into direct current (dc) is a possible option to avoid wholescale construction of new corridors for future medium-voltage (MV) and high-voltage (HV) projects. This paper explores a symmetrical monopole three-wire HVDC transmission system based on an modular multilevel converter (MMC) and an alternate arm converter (AAC). It is shown that the power carrying capability can be further enhanced by 11% with the proposed novel method that two sets of resistors are inserted in positive and negative poles. However, technical complexities and financial feasibility of such implementations should be further overcome for practical project execution.